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ORGANIZATION OF THE CENTRAL NERVOUS SYSTEM
In the brain, the gray matter forms cortex; the white matter forms medulla.
The cortex of gray matter in the brain contains nerve cell, bodies, axons, dendrites,
and glial cells.
The white matter contains only axons of nerve cell plus the associated glial cells
and blood vessels.
Whereas many of the axons going to or coming from a specific location are
grouped into bundles called tracts.
CEREBRAL CORTEX LAYERS
The cerebral cortex is described as containing six different layers.
I.
II.
III.
IV.
V.
VI.
The molecular layer consists largely of fibers, most of which travel
parallel to the surface and few cells.
The external granular layer contains small pyramidal and numerous
stellate neurons.
The external pyramidal layer contains small and medium-size pyramidal
neurons, as well as non-pyramidal neurons.
The internal granular layer contains different types of granule and
pyramidal neurons.
The internal pyramidal layer contains large pyramidal neurons (the Betz
cells).
The layer of polymorphic cells contains cells with diverse shapes, many
of which have a spindle or fusiform shape.
The basic functional and structural unit of cortex is called cortical column or
cortical module.
Cortical areas that lack a layer IV are called agranular.
Cortical areas that have only a rudimentary layer IV are called dysgranular.
CEREBELLUM
There are three layers to the cerebellar cortex.
I.
Molecular layer
1. This outermost layer of the cerebellar cortex contains two types of inhibitory
interneurons: the stellate and basket cells.
II.
Purkinje layer
1. The middle layer contains only cell body of Purkinje cells. It is extremely
large flask-shaped cell bodies.
2. Purkinje cell dendrites with hundreds of branches go into the molecular
layer.
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3. Purkinje axons have inhibitory synapses with the neurons of the deep
cerebellar and vestibular nuclei in the brainstem.
4. Purkinje cells also receive input from the inferior olivary nucleus via
climbing fibers.
III. Granular layer
1. The innermost layer contains the cell bodies of two types of cells: the
numerous and tiny granule cells, and the larger Golgi cells.
2. Incoming (mossy) fibers enter the granular layer and form excitatory
synapses with the granule cells and the cells of the deep cerebellar nuclei.
3. The granule cells send their T-shaped axons into the molecular layer.
4. Golgi cells provide inhibitory feedback to granule cells, forming a synapse
with them and projecting an axon into the molecular layer.
5. Mossy and climbing fibers carry sensorimotor information into the deep
nuclei, which in turn pass it on to various premotor areas.
6. The function of the cerebellar cortex is essentially to modulate information
flowing through the deep nuclei.
Deep in the granular layer is the white matter.
BLOOD BRAIN BARRIER
Blood-Brain-Barrier (BBB) prevents materials from the blood to entering the brain.
Structure of the BBB
1. Endothelial lining.
2. Basal membrane of endothelial cells.
3. Glial cells (astrocytes).
Functions of the BBB
1. Protects the brain from "foreign substances" in the blood that may injure the
brain
2. Protects the brain from hormones and neurotransmitters in the rest of the body
3. Maintains a constant environment for the brain
General Properties of the BBB
1. Large molecules do not pass through the BBB easily.
2. Low lipid (fat) soluble molecules do not penetrate into the brain.
3. However, lipid soluble molecules, such as barbiturate drugs, rapidly cross
through into the brain.
4. Molecules that have a high electrical charge are slowed.
The barrier is ineffective or absent in the neurohypophysis, substantia nigra and
locus ceruleus.
SPINAL CORD
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The spinal cord is organized into two discrete parts.
1. The outer part contains ascending and descending nerve fibers. These fibers are
divided into longitudinal columns or funiculi. They constitute the white matter
of the cord.
2. The inner part contains cell bodies of neurons and nerve fibers. This is the gray
matter of the spinal cord. Spinal gray matter is butterfly-shaped or H shaped. It
extends from the ependymal cells lining the central canal to the surrounding
white matter.
Spinal neurons within the gray matter are either
 efferent neurons
 projection neurons
 interneurons
 Functionally related groups of nerve cell bodies in the gray matter are called
nuclei.
 Functionally related bundles of axons in the white matter are called tracts.
The dorsal horn
 marginal nucleus
 substantia gelatinosa
 nucleus proprius
 the nucleus thoracicus is present in thoracolumbar segments
The lateral horn
 intermediolateral nucleus, which is composed of sympathetic preganglionic
neurons
The ventral horn
 somatic efferent motor neurons
 medial motor nuclei innervate muscles of the trunk and are found in all
spinal segments
 lateral collections of motor neurons, which innervate limb muscle, are seen
in segments of the cervical and lumbosacral enlargements
PERIPHERAL NERVOUS SYSTEM
There are two classifications of the PNS: anatomical and physiological.
According to the first one, there are nervous, nerve ganglia and nerve endings
(terminals) in the PNS.
Physiologically, PNS is subdivided into two subsystems: the sensory-somatic
nervous system and the autonomic nervous system.
ANATOMICAL CLASSIFICATION OF PNS
I.
NERVES
 Epineurium is external, dense connective tissue. It contains fibroblast and
histiocytes (inactive macrophage), capillaries and blood vessels.
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 Perineurium is the 2nd layer, covers bundle or nerve fibers. Perineurium
consists of collagen and elastic fibers and connective tissue cells.
 Endoneurium surrounds individual nerve fibers, continuous with
perineurium.
II.
NERVE ENDINGS
The skin is richly innervated, served by a variety of sensory nerve endings which
respond to a variety of modalities (e.g., pressure, vibration, heat, cold, itch, pain)
and by motor nerve endings which control blood flow, sweat secretion, and
piloerection.
 Free nerve endings terminate within the epidermis, penetrating almost to the
stratum corneum.
 Merkel's touch corpuscles are nerve endings associated with Merkel cells at
the base of the epidermis in thick (glabrous) skin of palms and soles.
 Meissner's corpuscles are encapsulated endings in dermal papillae, most
common in palmar and plantar skin, especially in fingertips.
 Pacinian corpuscles, located deeper in dermis, are simple nerve endings but
are each encapsulated by multilamellar, ovoid structures resembling small
onions. Pacinian corpuscles respond to deep pressure.
 Ruffini endings have numerous fine branches from a single axon within the
fluid-filled space of a single thin capsule. They are respond to the permanent
pressure.
 Hair follicle receptors are unencapsulated nerve endings wrapped around
hair follicles.
 Each skeletal muscle fiber is innervated by a single motor axon. The same
axon may also innervate other muscle fibers. All the fibers innervated by
the same axon are called a motor unit.
 Muscle action begins at the motor end plate (or neuromuscular junction),
which is analogous to a synapse.
 Skeletal muscles contain specialized proprioceptive sense organs, called
muscle spindles, which function to detect muscle stretch.
 Each muscle spindle consists of an encapsulated cluster of small striated
muscle fibers ("intrafusal muscle fibers"). Each fiber has a
mechanosensory nerve ending.
 Proprioceptor endings (Golgi tendon organs) are located at the point where
muscle fibers attach to tendon. These sensitively respond to tension (force)
exerted by the muscle; activity in these axons inhibits muscle contraction.
III.
SENSORY GANGLIA
 Sensory ganglia house cell bodies of sensory neurons.
 Sensory neurons in the dorsal root ganglia are pseudounipolar.
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 They have a single process that divides into a peripheral segment that brings
information from the periphery to the cell body
 They have a central segment that carries information from the cell body into
the gray matter of the spinal cord.
 The ganglions are surrounded by a connective tissue capsule composed of
collagen.
PHYSIOLOGICAL CLASSIFICATION OF PNS
I.
SENSORY- SOMATIC NERVOUS SYSTEM
 Somatic nervous system is the portion of the peripheral nervous system
consisting of the motor neuron pathways that innervate skeletal muscles.
 The sensory nervous system comprises 12 pairs of cranial nerves and 31
pairs of spinal nerves.
 All of the spinal neuron pairs are mixed: they contain both sensory and
motor neurons. This allows the spinal neurons to properly function as the
conduit of transmission of the signals of the stimuli and the subsequent
response.
 The somatic nervous system always acts to excite muscle groups.
II.
THE AUTONOMIC NERVOUS SYSTEM
The Autonomic Nervous System is that part of PNS consisting of motor neurons
that control internal organs.
The autonomic nervous system (ANS) consists of three subsystems:
 the sympathetic nervous system
 the parasympathetic nervous system
 the enteric nervous system
The ANS regulates the activities of cardiac muscle, smooth muscle, endocrine
glands, and exocrine glands.
The autonomic nervous systems can act to excite or inhibit innervated tissue.
Most target organs and tissues are innervated by neural fibers from both the
parasympathetic and sympathetic systems. The systems can act to stimulate organs
and tissues in opposite ways (antagonistically).
 THE SYMPATHETIC NERVOUS SYSTEM
 The nerve fibers of the sympathetic system innervate smooth muscle,
cardiac muscle, and glandular tissue.
 In general, stimulation via sympathetic fibers increases activity and
metabolic rate. Accordingly, sympathetic system stimulation is a critical
component of the fight or flight response (release of a chemical called noradrenaline). Examples include the acceleration of the heartbeat, raising of
blood pressure, shrinkage of the pupils of the eyes, and the redirection of
blood away from the skin to muscles, brain, and the heart.
 THE PARASYMPATHETIC NERVOUS SYSTEM
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 Parasympathetic fibers innervate smooth muscle, cardiac muscle, and
glandular tissue.
 In general, stimulation via parasympathetic fibers slows activity and results
in a lowering of metabolic rate and a concordant conservation of energy.
Accordingly, the parasympathetic nervous sub-system operates to return the
body to its normal levels of function the so-called "rest and digest" state.
Examples include the restoration of resting heartbeat, blood pressure, pupil
diameter, and flow of blood to the skin.
 The preganglionic fibers of the parasympathetic system derive from the
neural cell bodies of the motor nuclei of the occulomotor (cranial nerve: III),
facial (VII), glossopharyngeal (IX), and vagal (X) cranial nerves.
 With regard to specific target organs and tissues, parasympathetic
stimulation acts to decrease heart rate and decrease the force of contraction.
 THE ENTERIC NERVOUS SYSTEM
 The enteric nervous system is made up of nerve fibers that supply the
viscera of the body: the gastrointestinal tract, pancreas, and gallbladder.
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EYE
The eyes are complex sensory organs that provide us with the sense of sight. The
wall of the eye consists of three concentric layers or coats.
 Corneoscleral coat, the outer or fibrous layer that includes the sclera and the
cornea.
 Uvea, the middle layer or vascular coat that includes the choroid and the
stroma of the ciliary body and iris.
 Retina, the inner layer that includes an outer pigment epithelium, the inner
neural retina, and the epithelium of the ciliary body and iris.
The cornea
The cornea covers the anterior one-sixth of the eye. The cornea is continuous with
the sclera. The cornea is transparent.
The cornea consists of five layers: three cellular layers and two lamellae.
 The corneal epithelium is nonkeratinized stratified squamous epithelium.
 Bowman’s membrane is a homogenous fibrillar lamina on which the
corneal epithelium rests. Bowman’s membrane is a barrier to the spread of
infections.
 The corneal stroma constitutes 90% of the corneal thickness. It is
composed of about 60 thin lamellae of collagen fibrils between which are
found fibroblasts.
 Descement’s membrane is an unusually thick basal lamina of the corneal
endothelial cells.
 The corneal endothelium is a single layer of flattened cells. It provides
metabolic exchange between cornea and aqueous humor.
The sclera
The sclera is an opaque layer consisting of dense connective tissue. Flat collagen
bundles interspersed with elastic fibers and a moderate amount of ground
substance. Fibroblasts are scattered among these fibers. The sclera is pierced by
blood vessels, nerves, and the optic nerve.
Limbus
The limbus is the transitional zone between cornea and sclera. It is the limbus
region that contains the apparatus for the outflow of aqueous humor..
Iris
The iris forms a contractile diaphragm anterior to the lens surface. The iris arises
from the anterior border of the ciliary body. The pupil is the central aperture of this
thin disc.
The layers of the iris, from anterior to posterior, consist of
 fibroblasts and melanocytes
 the anterior stromal lamella
 a loose connective tissue layer that contains many small blood vessels
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 the posterior membrane (the sphincter pupillae and the dilator pupillae)
 a double layer of pigmented epithelial cells (to absorb light rays and
responsible for variation in eye color)
Ciliary body
The ciliary body is a thickened anterior portion of the tunica vasculosa, located
between iris and choroid. The anterior third of the ciliary body has ciliary
processes. The layers of the ciliary body are similar to those of the iris, consisting
of a stroma and an epithelium.
The stroma is divided into two layers:
-an outer layer of smooth muscle, the ciliary muscle, that makes up the bulk of the
ciliary body
-an inner vascular region that extends into the ciliary processes
Ciliary processes are ridge-like extensions of the ciliary body from which zonulae
fibers emerge and extend to the lens. The ciliary epithelium which covers the
ciliary body has three principal functions:
 secretions of aqueous humor
 serving as the major component of the blood-aqueous barrier
 secretion and anchoring of the zonular fibers
Choroid
The choroid is the portion of the vascular layer that lies between the sclera and the
retina and has two layers
 choriocapillary layer, an inner vascular layer
 Bruch’s membrane, a thin, amorphous, hyaline membrane
Retina
It consists of two basic layers:
-Neural retina or retina proper, an inner layer that contains the photoreceptors
-Retinal pigment epithelium, an outer layer
In the neural retina, two regions are recognized:
 the nonphotosensitive region, located anterior to the ora serrata
 the photosensitive region located posterior to the ora serrata
The fovea centralis is the area of greatest visual acuity. The visual axis of the eye
passes through the fovea.
The macula lutea surrounds the fovea and characterize as a yellow pigmented
zone.
There are four groups of cells, which constitute photosensitive region of retina:
 photoreceptors − the retinal rods and cones
 conducting neurons − bipolar and ganglion cells
 association and other neurons − horizontal, centrifugal and amacrine
 supporting cells − Müllers cells and neuroglial cells
The layers of the retina, from outside inward are:
1. Pigment epithelium − the outer layer which consists of cuboidal cells.
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2.
Functions:
absorption of the light passing through neural retina to prevent reflection
isolation of the retinal cells from blood borne substances
phagocytosis and disposal of membranous discs from the rods and cones
Layer of rods and cones − contains the outer and inner segments of
photoreceptor cells. Each rod and cone photoreceptor consists of outer
segment, connecting stalk and inner segment.
Difference between rods and cones:
 Amount: 120 million of rods and only 7 million of cones
 Sensitivity: the rods are more sensitive to light and used during
periods of low light intensity but cones are less sensitive to low light
 Color perception: black and white picture for rods and the red, green
or blue colors for cones
 The visual pigments: rhodopsin present in rods and iodopsin in cones.
 Outer segment: cylindrical in the rods and conical in the cones.
3. External (outer) limiting membrane − the apical boundary of Müllers
cells.
4. Outer nuclear layer − contains the cell bodies (nuclei) of retinal rods and
cones.
5. Outer plexiform layer −contains the processes of retinal rods and cones
and processes of the horizontal, amacrine and bipolar cells that connect to
them.
6. Inner nuclear layer − contains the cell bodies (nuclei) of horizontal,
amacrine, bipolar and Müllers cells.
7. Inner plexiform layer − contains the processes, amacrine, bipolar and
ganglion cells that connect to each other.
8. Ganglion cell layer − contains the cell bodies (nuclei) of large multipolar
ganglion cells.
9. Layer of optic nerve fibers − contains processes of ganglion cells that lead
from the retina to the brain.
10.Internal (inner) limiting membrane − composed of the basal lamina of
Müllers cells which separating the retina from the vitreous body.
Crystalline lens
The lens is a transparent, avascular, biconvex structure. It is suspended between the
edges of the ciliary body by the suspensory ligament. The lens includes lens
capsule, subcapsular epithelium and lens fibers
Vitreous humor
Vitreous humor is the transparent jelly-like substance that fills the posterior
segment (vitreous space) of the eye. The main body of the vitreous is a
homogenous gel containing about 99% of water, hyaluronic acid, widely dispersed
collagen fibers, and other proteins and glycoproteins.
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Ear
The ear is a three chambered sensory structure that in the auditory system functions
in the perception of sound and in the vestibular system functions in the
maintenance of balance.
The external and middle ear collect and conduct sound energy to the inner ear,
where auditory sensory receptors transducer that energy into the electrical energy
of nerve impulses.
External ear
The external ear is composed of an auricle and an external auditory meatus. Thin
skin with hair follicles, sweat glands and sebaceous glands covers the auricle.
The lateral part of the canal is lined by skin that contains hair follicles, sebaceous
glands, and ceruminous glands.
Middle ear
The tympanic membrane (eardrum) separates the external auditory canal from the
middle ear.
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Structure of the middle ear:
An air-filled space that contains three small bones, the ossicles which cross
the space of the middle ear in series and connect the tympanic membrane to
the oval window.
Presence of the vestibular (oval) window and the cochlear (round) window
in the medial wall of the middle ear.
It contains the auditory tube (Eustachian tube) which connects the middle
ear to the nasopharynx.
Functions:
convert sound waves (air vibrations) arriving from the external auditory
meatus into mechanical vibrations that are transmitted to the inner ear
equilibrate pressure in the middle ear with atmospheric pressure (due to
Eustachian tube)
Inner ear
The inner ear consists of two labyrinthine compartments, one contained within the
other.
The bony (osseous) labyrinth is a complex system of interconnected cavities and
canals.
The membranous labyrinth lies within the bony labyrinth and also form
continuous spaces enclosed within a wall of epithelium and connective tissue.
There are three fluid-filled spaces in the inner ear.
 Endolymphatic space contained within the membranous labyrinth.
 Perilymphatic space lies between the wall of the bony labyrinth and the
wall of the membranous labyrinth.
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 Cortilymphatic space lies within the organ of Corti.
Bony labyrinth
The bony labyrinth consists of semicircular canals, vestibule and cochlea.
Structure of the vestibule:
 It is the central space that contains an elliptical and spherical recess.
 The semicircular canals extend from the vestibule posteriorly, and the
cochlea extends from the vestibule anteriorly.
 The vestibular (oval) window lies in the lateral wall of the vestibule.
Structure of the semicircular canals:
 They are bony walled tubes that lie in superior, posterior and horizontal
planes.
 Each inner ear has three ampullae which are dilation of the lateral end of
semicircular canal.
 The three canals open into the vestibule through five orifices.
Structure of the cochlea:
 It is a conically shaped helix connected to the vestibule on the side opposite
the semicircular canals.
 Between its base and the apex the cochlea makes about 2,5 turns around a
central bony core called the modiolus.
 One opening of the canal, the cochlear (round) window is covered by the
secondary tympanic membrane.
Membranous labyrinth
The membranous labyrinth consists of membranous semicircular ducts, utricle and
saccule, and membranous cochlea (cochlea duct).
Structure:
 Membranous semicircular ducts lie within the bony semicircular canals and
are continuous with the utricle.
 The utricle and saccule are contained in recesses in the vestibule and are
connected by the membranous utriculosaccular duct.
 The membranous cochlear duct is contained within the bony cochlea and is
continuous with the saccule.
The membranous semicircular ducts, utricle and saccule are components of the
vestibular system.
The membranous cochlea is part of the auditory system.
Specialized sensory cells are located in six regions in the wall of the membranous
labyrinth.
 Three cristae ampullaris located in the ampullae of the semicircular ducts.
 Two maculae, one in the utricle (macula utriculi) and the other in the saccule
(macula sacculi).
 The organ of Corti that project into the endolymph of the cochlear duct.
 The three cristae ampullaris are sensitive to angular acceleration of the head
(i.e., turning of the head).
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 The maculae of utricle and saccule sense the position of the head (sensors of
gravity) and linear movement.
 The organ of Corti functions as the sound receptor.
The hair cell, a nonneuronal mechanoreceptor is the common receptor cell of the
vestibulocochlear system.
Several important characteristics are common to hair cells:
 all are epithelial cells
 each possesses numerous stereocilia, modified microvilli, called sensory
“hairs”
 in the vestibular system, each hair cell possesses a single true cilium called a
kinocilium
 in the auditory system, hair cells have only a residual basal body
 they are transducers, i.e., they convert mechanical energy to electrical
energy
 function by the bending or flexing of their stereocilia which generates
transmembrane potential changes in the receptor cell that are conveyed to
the afferent nerve ending(s)
 there are two types of hair cells and associated nerve endings in the
vestibular system
Organ of Corti: sensor of sound vibration
The cochlear duct divides the cochlear canal into three parallel compartments or
scalae:
1. The scala media contains an endolymph and the organ of Corti.
 The upper wall of the scala media is the vestibular membrane.
 The lateral wall is the stria vascularis. It is may be the site of synthesis of
endolymph.
 The lower wall is the basilar membrane.
2. The scala vestibuli and the scala tympani contain perilymph.
The organ of Corti rests on the basilar membrane and is overlain by the tectorial
membrane.
The organ of Corti is a complex epithelial layer on the floor of the scala media.
It is formed by
 inner (close to the spiral lamina) and outer (farther from the spiral lamina)
hair cells
 inner and outer phalangeal (supporting) cells
 pillar cells
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Integumentary system (skin)
The skin and its derivates constitute the integumentary system. The skin consists of
3 layers:
 epidermis, composed of a keratinized stratified squamous epithelium
 dermis, composed of a dense connective tissue
 hypodermis contains variable amounts of adipose tissue
The epidermal derivates of the skin contain:
1. hair follicles and hair
2. sweat (sudoriferous) glands
3. sebaceous glands
4. nails
5. mammary glands
Functions of integumentary system include:
 homeostatic function
 barrier function
 sensory function
 ''secretory'' function
 excretory function
Epidermis
The epidermis is composed of stratified squamous epithelium in which 5 distinct
layers are observed.
Beginning with the deepest layer, these are
I. The stratum basale provides for epidermal cell renewal and contains the
stem cells from which the new cells, the keratinocytes, arise.
II. The stratum spinosum has cells which exhibit numerous spinous processes,
which gives this layer its name.
III. The stratum granulosum has cells that contain numerous keratohyaline
granules.
IV. The stratum lucidum is a translucent, thin layer of extremely flattened
eosinophilic cells. This layer is found only in the skin of the palms of the
hands and of the soles of the feet.
V. The stratum corneum consists of 15-20 layers of flattened nonnucleated
keratinized cells whose cytoplasm is filled with a keratin.
Cells of the epidermis
Keratinocyte
The keratinocyte is predominate cell type of the epidermis. The intermediate
filaments, more commonly called tonofilaments in the keratinocytes, represent the
essential protein in keratin production.
Functions:
 production of keratin
 creation of an extracellular water barrier
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Melanocytes
The epidermal melanocyte is a dendritic cell. The ratio of melanocyte to
keratinocyte in the basal layer ranges from 1:4 to 1:10 in different parts of the
body. Melanocytes have developing and mature melanin granules in the
cytoplasm.
Function:
 produce pigment
Langerhans Cell
The Langerhans cell possesses surface receptors. As an antigen-presenting cell, the
Langerhans cell is involved in the initiation of cutaneous contact hypersensitivity
reactions, i.e., contact allergic dermatitis, and in other cell-mediated immune
responses in the skin.
Function:
 present antigens to T cells
Merkel Cell
Merkel's cells are modified epidermal cells that are located in the stratum basale.
The combination of the neuron and epidermal cell, called a Merkel's corpuscle, is
a very sensitive mechanoreceptor.
Function:
 cutaneous sensation
Dermis
The dermis is composed of two layers.
I. The papillary layer consists of loose connective tissue beneath the
epidermis and includes the dermal papillae and dermal ridges. It contains
blood vessels that serve the epidermis.
II. The reticular layer lies deep to the papillary layer. It is characterized by
presence of collagen and elastic fibers which form regular lines of tension in
the skin.
Hypodermis
It consists of adipose tissue and its associated loose connective tissue.
Functions:
 energy storage site
 an important insulating layer
SKIN APPENDAGES
HAIR
Hairs are composed of keratinized cells that develop from hair follicles.
Structure of the Hair Follicle:
The hair follicle is responsible for the production and growth of a hair.
 The growing follicle expands on its base to form the bulb.
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 The bulb consists of matrix cells.
 The outermost part of the hair follicle is the external (outer) root sheath.
 The dividing cells in the germinative layer of the matrix are the internal
root sheath.
 The hair consists of a medulla, cortex, and cuticle.
 The internal root sheath consists of a cuticle, Huxley's layer, and Henle's
layer.
SEBACEOUS GLANDS
Structure:
 Sebaceous gland is simple, branched and acinar, with holocrine type of
secretion. It produces sebum.
 Sebaceous glands secretes into the pilosebaceous canal.
 The basal cells of the sebaceous gland contain smooth endoplasmic
reticulum for lipid synthesis and secretion and few lipid droplets.
Functions:
 secrete sebum that coats the hair and skin surface
SWEAT GLANDS
Two types of sweat glands are recognized:
I. Eccrine Sweat Glands
Location in the body:
 distributed over the entire body surface except for the lips and part of the
external genitalia
Structure:
 It is arranged as simple coiled tubular glands with merocrine type of
secretion.
 Secretory segment has clear, dark and myoepithelial cells.
 Clear cells produce the watery component of sweat.
 Dark cells secrete glycoprotein.
 Myoepithelial cells are responsible due their contraction for the expression
of sweat from the gland.
 The epithelium of the duct is stratified cuboidal, consisting of a basal cell
layer and luminal cell layer.
Function:
 regulating body temperature
 serves as an excretory organ (for sodium chloride, urea, uric acid, and
ammonia)
II. Apocrine Sweat Glands
Location in the body:
 axilla
 areola
 nipple of the mammary gland
 circumanal region
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 the external genitalia
 the ceruminous glands of the ear canal
 the glands of Moll of the eyelid
Structure:
 Apocrine glands are coiled tubular glands with apocrine type of secretion.
 They are associated with hair follicles.
 The apocrine glands store their secretory product in the lumen, which is
very wide.
 The apical cytoplasm contains numerous small granules, the secretory
component within the cells and also includes lysosomes and lipofuscin
pigment granules.
 The duct epithelium is stratified cuboidal.
 Secretory segment contains secretory and myoepithelial cells
Function:
 secrete protein, carbohydrate, ammonia, lipid, and certain organic
compounds
NAILS
Nails are plates of keratinized cells containing hard keratin.
Structure:
 The nail plate rests on the nail bed.
 The proximal part of the nail is the nail root.
 It covers the cells of the germinative zone, the matrix.
 The crescent-shaped white area near the root of the nail is the lunula.
 The edge of the skin fold covering the root of the nail is the eponychium
or cuticle.
 A thickened epidermal layer, the hyponychium, secures the free edge of the
nail plate at the fingertip.
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Cardiovascular system
The cardiovascular system is a transport system that carries blood and lymph to
and from the tissues of the body.
The cardiovascular system includes:
 the heart
 blood vessels (arteries, arterioles, capillaries, venules and veins)
 lymphatic vessels
Together, the arterioles, associated capillary network, and post capillary venules
form a microvascular bed.
Arteries
Arteries are classified into three types
I. Elastic arteries
Structure:
Tunica intima
 an endothelial lining with its basal lamina
 a subendothelial layer of connective tissue
 not prominent internal elastic membrane
Tunica media
 elastin lamellae between the muscle layers
 smooth muscle cells
 collagen fibers and ground substance
Tunica adventitia
 collagen fibers
 elastic fibers
 fibroblasts and macrophages
 blood vessels (vasa vasorum) and nerves (nervi vascularis)
II. Muscular arteries
Structure:
Tunica intima
 Same structure as in elastic arteries except presence of prominent elastic
membrane
Tunica media
 Same structure as in elastic arteries except less amount of elastic fibers
Tunica adventitia
 Same structure as in elastic arteries except presence of:
 external elastic membrane
 adipose cells
 and absence of vasa vasorum and nervi vascularis
17
III.
Small arteries and arterioles
Small arteries
have up to about eight layers of smooth
muscle in the tunica media
has an internal elastic membrane in the
tunica intima
the tunica adventitia is a thin, sheath of
connective tissue
Arterioles
one or two layers of smooth muscle in
the tunica media
this layer may or may not be present
the tunica adventitia is a thin, sheath of
connective tissue
The arterioles have two important functions:
1). Maintain the blood pressure inside the arterial system
2). Control blood flow to the capillary networks.
The arterio-venous connections
The arterio-venous connections are classified into two main types, namely;
1). Blood capillaries and the vessels regulating their blood flow
2). Arterio-venous anastomosis (A-V shunts)
Capillaries
Capillaries are the smallest diameter blood vessels, often smaller than diameter of
an erythrocyte.
They consist of a single layer of endothelial cells and their basal lamina.
Capillaries are described as:
1). Continuous or somatic capillaries
Location in the body:
 muscle
 lung
 central nervous system (CNS)
 skin
Structure:
 continuous endothelial lining
 continuous basal lamina
 pinocytotic vesicles
2). Fenestrated or visceral capillaries,
Location in the body:
 endocrine glands
 gallbladder
 intestinal tract
Structure:
 fenestrae in the walls of endothelial cells
 continuous basal lamina
18
 pinocytotic vesicles
3). Discontinuous or sinusoidal capillaries
Location in the body:
 liver
 spleen
 bone marrow
Structure:
 presence of unusually wide gaps (fenestrae) between endothelial cells
 partial of total absence of basal lamina
 presence of specialized cells, such as the stellate sinusoidal macrophages
(Kupffer cells) and vitamin A storage cells (of Ito) in the liver, among the
lining endothelial cells
Capillaries have three essential functions:
 selective permeability
 synthetic and metabolic activities
 antithrombogenic function
Arteriovenous shunts
Direct routes between the arteries and veins that can divert blood from the
capillaries are called arteriovenous anastomoses or shunts.
Location in the body:
 in the skin of the fingertips
 nose
 lips
 in the erectile tissue of the penis
 clitoris
Functions:
 serve in thermoregulation at the body surface (closing an AV shunt in the
skin causes increasing heat loss and open it conserving body heat)
 control the amount of blood passing through the capillary bed
How it work:
 contraction of the arteriole smooth muscle of the AV shunt sends blood to a
capillary bed
 relaxation of the smooth muscle sends blood to a venule, bypassing the
capillary bed
Difference between veins and arteries
1. Typically, veins have thinner walls than their accompanying arteries.
2. The lumen of the vein is usually larger than that of the artery.
3. The lumen of the vein is often collapsed, whereas the lumen of the artery is
often patent.
4. Many veins have valves.
5. Adventitia is the thickest tunica in the veins and media in the arteries.
19
6. The veins have more collagen fibers than elastic.
7. Shape of the wall in the vein is irregular and in the artery is regular.
Veins
Traditionally, veins are divided into three types on the basis of size.
Large veins
Structure:
The tunica intima
 an endothelial lining with its basal lamina
 a small amount of subendothelial connective tissue
 some smooth muscle cells
The tunica media
 smooth muscle cells
 collagen fibers
 some fibroblasts
The tunica adventitia
 bundles of longitudinally disposed smooth muscle cells
 collagen fibers
 elastic fibers
 fibroblasts
Medium veins
Structure:
The tunica intima:
 an endothelium with its basal lamina
 a thin subendothelial layer with smooth muscle cells and connective tissue
elements
 a thin internal elastic membrane
The tunica media
 circularly arranged smooth muscle cells
 collagen fibers
The tunica adventitia
 longitudinally oriented bundles of smooth muscle cells
 collagen fibers
 networks of elastic fibers
Venules
Muscular venules are distinguished from postcapillary venules by the presence of
a tunica media.
Postcapillary venules receive blood from capillaries and possess an endothelial
lining with its basal lamina and pericytes.
Muscular venules are located distal to the postcapillary venules in the returning
venous network. Whereas postcapillary venules have no true tunica media, the
20
muscular venules have one or two layers of smooth muscle that constitute a tunica
media and have a thin tunica adventitia.
LYMPHATIC VESSELS
Lymphatic vessels convey fluids from the tissues to the bloodstream.
In addition to blood vessels, there is a set of vessels that circulates fluid, called
lymph, through certain parts of the body. These lymphatic vessels are an adjunct
to the blood vessels.
Difference between lymph and blood capillaries
Lymph capillaries
Blood capillaries
Wider irregular lumen.
Narrower regular lumen.
Blind ended, i.e. it begins by a blind end. Has arterial and venous ends.
The endothelium is not fenestrated.
The endothelium may be fenestrated.
It lacks a well-developed basement It has a well-developed basement
membrane.
membrane.
Lacks pericytes.
Has pericytes.
The outer surface of the endothelium is No anchoring fibers.
attached to the surrounding C.T. by
anchoring fibers
Heart
The heart is a pump with four chambers with valves that maintain a one-way flow
of blood.
General structure:
 The heart contains 4 chambers (two atria and two ventricles) through which
blood is pump.
 Valves guard the exits of chambers, preventing the backflow of blood.
 An interatrial septum and an interventricular septum separate the right and
left sides of the heart.
Structure of the heart wall:
I. Epicardium consists of a layer of mesothelial cells on the outer surface of
the heart and its underlying connective tissue. The blood vessels and nerves
that supply the heart lie in epicardium and are surrounded by adipose tissue.
II. Myocardium, the cardiac muscle, is the principal component of the heart.
Difference between cardiac and skeletal muscle
Cardiac muscle
Skeletal muscle
formed by individual cardiac muscle formed by muscle fiber
cells
mononucleated
multinucleated
location of the nucleus in the center
location of nuclei under the plasma
membrane (sarcolemma)
presence
of
intercalated
disks absence of intercalated disks
21
(attachment between neighboring
muscle cells)
presence of diad (T tubule and terminal
cisternae)
presence of juxtanuclear mitochondria
presence of cardiac conducting cells
(Purkinje cells)
III.
presence of triad (T tubule and two
terminal cisternae)
absence of juxtanuclear mitochondria
absence of cardiac conducting cells
(Purkinje cells)
Endocardium consists of an inner layer of endothelium and subendothelial
connective tissue (which includes impulse-conducting system), a middle
layer of connective tissue and smooth muscle cells, and a deeper layer, also
called the subendocardial layer of connective tissue that is continuous with
the connective tissue of the myocardium.
Intrinsic regulation of heart rate
Cardiac muscle is capable of contracting in a rhythmic manner without any direct
stimulates from the nervous system.
 The base of this beating action is initiated at the sinoatrial (SA) node, a
group of specialized cardiac muscle cells located near the junction of the
superior vena cava and the right atrium. The SA node is referred to as the
pacemaker. The SA node initiates an impulse that spreads along the cardiac
muscle fibers of the atria and along internodal tracts composed of modified
cardiac muscle fibers.
 The impulse is then picked up at the atrioventricular (AV) node and
conducted across the fibrous skeleton to the ventricles by the AV bundle (of
His).
 The bundle divides into smaller right and left bundle branches and then into
Purkinje fibers.
The AV bundle, the bundle branches, and the Purkinje fibers are modified cardiac
muscle cells that are specialized to conduct impulses.
22
Lymphoid system and organs of hematopoiesis and immune
response
Classification of hematopoiesis and immune defense organs
1. Central organs of hematopoiesis and immune defense are thymus and red
bone marrow.
2. Peripheral organs of hematopoiesis and immune defense are spleen, lymph
nodes and solitary lymphatic nodules.
Thymus
Function:
 Site of the programming, differentiation and proliferation of T lymphocytes
Structure:
 Thymic lobule is the structural and functional unit of the thymus.
 Connective tissue capsule surrounds the cortex and extends trabeculae to
the margin of the cortex and medulla.
 Cortex is the outer portion of the parenchyma which consists of dense
population of so-called thymocytes that are T lymphocytes, and scattered
epithelial reticular cells that have multiple processes and partially
compartmentalize thymocytes. The connective tissue here contains variable
number of plasma cells, granulocytes, T lymphoblasts, mast cells, fat cells
and macrophages.
 Medulla is the inner portion of the parenchyma that contains a lesser
number of lymphocytes and T lymphoblasts and more epithelial reticular
cells than the cortex. Thymic or Hassall’s corpuscles are concentrically
arranged epithelioreticular cells.
Blood thymic barrier
The blood thymic barrier present only in the cortex.
Structure:
1. capillary endothelium
2. endothelial basal lamina
3. thin perivascular connective tissue sheath
4. basal lamina of the epithelioreticular cells
5. epithelioreticular cells sheath
Function:
 Prevents the contact between the high concentrations of antigens circulating
in the blood and the developing immature lymphocytes in the thymic cortex.
Red bone marrow
Structure:
 developing blood cells in different stages of development
 network of reticular cells and fibers (supporting framework)
23
 blood vessels
 erythroblastic islands which are clusters of developing erythrocytes
surround and receive iron from macrophages
Yellow bone marrow
 In later stages of growth and in the adult, when the rate of blood cell
formation has diminished, the tissue in the medullary cavity consists mostly
of fat cells; it is then called yellow marrow.
 Under appropriate stimuli; such as extreme blood loss, the yellow marrow
can revert to red marrow. In the adult, red marrow is normally restricted to
the spaces of spongy bone in a few locations such as the sternum and the
iliac crest.
Spleen
The spleen is the largest lymphatic organ.
In addition to large numbers of lymphocytes, it contains specialized vascular
spaces or channels, a meshwork of reticular cells and reticular fibers, and a rich
supply of macrophages.
 Capsule of dense connective tissue from which trabeculae extend into the
substance of the organ
 White pulp is the concentration of lymphatic tissue within the red pulp that
surrounds portions of central arteries forming nodules along their lengths.
 Malpighian corpuscles are enlarged nodules in the white pulp.
 Nodules consist of reticular mesh with spaces in mesh being filled with
lymphocytes, monocytes, plasma cells and macrophages. They have
germinal center and marginal zone (separates white pulp and red pulp)
where located dendritic cells (macrophages).
 T-lymphocytes aggregated around the central artery constitute the
periarterial lymphatic sheath.
 B-lymphocytes located at periphery of white pulp.
 Red pulp consists of splenic sinuses separated by the splenic cords.
 The splenic cords consist of the loose meshwork of reticular cells and
reticular fibers that contain large numbers of erythrocytes, macrophages,
lymphocytes, plasma cells and granulocytes. Many of the macrophages are
engaged i n the phagocytosis of damaged red blood cells.
 Present blood sinusoids are site of cellular exchange between spleen and
circulatory system.
Functions:
Immune system functions of the spleen include:
 proliferation of lymphocytes
 production of humoral antibodies
 removal of macromolecular antigen from the blood
Hematopoietic functions of the spleen include:
 formation of blood cells during fetal life
24
 removal and destruction of senile, damaged and abnormal red blood cells
and platelets
 retrieval of the iron from red cell hemoglobin
 storage of blood, especially red blood cells, in some species
Lymph Nodes
Lymph nodes are small, bean-shaped, encapsulated organs located along the
pathway of lymphatic vessels.
Structure:
Supporting elements (stroma) of lymph node consist of:
 Capsule is composed of dense C.T. that surrounds the node. The capsule is
penetrated at the cortex by the afferent lymphatic vessels and at the hilum by
blood vessels, efferent lymphatic vessels and nerves.
 Trabeculae are composed of dense C.T., which extend from the capsule into
the substance of the node, forming a gross framework
 Reticular C.T., is composed of reticular cells and reticular fibers that form a
supporting meshwork throughout the organ.
The parenchyma of lymph node consists of:
 The cortex is composed of cortical lymph nodules surrounded by lymph
sinuses.
 The cortex is divided into an outer and an inner cortex.
 The outer cortex has lymphatic nodules that mostly contain B-cells. Also
they contain small lymphocytes, macrophages, dendritic cells, and some T
cells.
 The inner cortex contains mostly T-cells.
 There are afferent lymphatic vessels through which lymph enters the
subcapsular sinus from which it runs through cortical sinuses into
medullary sinuses and leaves through the efferent lymphatic vessels. Main
cell type around the sinuses is macrophage.
 The medulla is composed of medullary cords of lymphoid tissue surrounded
by medullary lymph sinuses.
 Medullary cords contain mainly plasma cells and B cells.
Functions:
1)
Filtration of lymph:
As lymph flows through the sinuses, 99% or more of the antigens and other debris
it carries are removed, by the phagocytic activity of macrophages that span the
sinuses.
2)
Antibodies production:
Antigens carried to the lymph nodes, activate its B-lymphocytes to change into
plasma cells which produce the specific antibodies.
The antibodies pass with the lymph to the circulation. Memory cells leave the node
25
with the lymph to the circulation. If they are stimulated again by the same antigen,
they migrate to the surrounding CT. and change to plasma cells and secrete the
antibodies.
3) Site of proliferation of lymphocytes.
Lymphatic tissue and the immune response
The lymphatic system is specialized form of connective tissue that consists of cells,
tissues, and organs that monitor body surfaces and internal fluid compartments and
react to the presence of potentially harmful antigenic substances.
Immune defenses fall into two categories:
I.
II.
Nonspecific defenses that guard against a wide variety of pathogens
Immunity, composed of mechanisms whereby lymphocytes
recognize and destroy specific pathogens
Nonspecific Body Defenses
 Surface membranes (skin and mucous membranes) provide
mechanical barriers to pathogens. Some produce secretions and/or
have structural modifications that enhance their defensive effects. The
skin's acidity, lysozyme, mucus, keratin, and ciliated cells are
examples.
 Phagocytes (monocytes, macrophages and neutrophils) swallow up
and destroy pathogens that penetrate epithelial barriers.
Antigens and antibodies
Antigens (Ag) are large, complex molecules (or parts of them) recognized
as foreign by the body. Foreign proteins are the strongest antigens.
 Complete antigens provoke an immune response and bind with
products of that response (antibodies or sensitized lymphocytes).
 Incomplete antigens, or haptens, are small molecules that are unable
to cause an immune response by themselves but do so when they bind
to body proteins and the complex is recognized as foreign.
An antibody (Ab), or immunoglobulin, is a gamma globulin. An antibody is
composed of four polypeptide chains (two heavy and two lights) that form a
Y-shaped molecule.
Immunoglobulins are highly specialized protein molecules, also known as
antibodies, fit foreign antigens like a lock and key. Their variety is so
extensive that they can be produced to match all possible microorganisms in
our environment.
Cells of the immune system

B-LYMPHOCYTES - These lymphocytes arise in the bone
marrow and differentiate into plasma cells which in turn produce
26
immunoglobulins (antibodies).

MONOCYTES - A type of phagocytic cell found in the
bloodstream which develops into a macrophage when it migrates to
tissues.

PLASMA CELLS - These cells develop from B-lymphocytes and
are the cells that make immunoglobulins.

T-LYMPHOCYTES - These lymphocytes arise in the bone
marrow but migrate to the thymus where they are instructed to mature
into T-lymphocytes.

T-EFFECTOR LYMPHOCYTES - These lymphocytes produce
chemicals that function in a variety of ways to mediate tissue
inflammation and the killing of foreign cells and microorganisms.

T-HELPER LYMPHOCYTES - These specialized lymphocytes
"help" other T-lymphocytes and B-lymphocytes to perform their
functions.

T-SUPPRESSOR LYMPHOCYTES - These specialized
lymphocytes "suppress" T-helper lymphocytes and thereby turn off the
immune response.
Two main cell populations, lymphocytes and macrophages, provide for
immunity. Macrophages are active in nonspecific resistance.
Antibodies
Five classes of antibodies exist: IgA, IgG. IgM, IgD, IgE, They differ
structurally and functionally.
Antibody
Main functions
IgG
Provides resistance against many viruses, bacteria and
bacterial toxins. Can cross placenta and provide passive
immunity to fetus (80% of antibodies)
IgE
Found on the surface of basophils and mast cells.
Release histamine and other chemicals that promote
inflammation reaction. Also active in allergic reaction.
IgD
Found on the surface of B-cell. Help in the activation of
b-cells
IgM
The first to be secreted after antigen invasion.
IgA
Found in glandular secretion (mucus, tears and saliva).
Attack pathogens before they access the internal tissues.
Specific body defenses: the immune system
The two arms of immune response are humoral immunity, mediated by
antibodies, and cellular immunity mediated by living cells (lymphocytes).
27
Humoral (antibody-mediated) immune response
In humoral immunity, the essential stages are recognition, attack, and
memory.
 Primary immune response occurs when antigens bind for the first
time to B-cells receptors, causing them to proliferate. Most clone
members become plasma cells, which secrete antibodies. Other clone
members become memory B cells, capable of mounting a rapid attack
against the same antigen in subsequent meetings (secondary immune
responses). These memory cells provide immunological "memory."
 Active humoral immunity is acquired during an infection or via
vaccination and provides immunoiogical memory.
 Passive immunity is conferred when a donor's antibodies are injected
into the bloodstream, or when the mother's antibodies cross the
placenta. It does not provide immunological memory.
 Cellular (cell-mediated) immune response. In cellular immunity,
lymphocytes directly attack and destroy foreign cells and diseased
host cells.
28
Endocrine organs
The primary function of two major organ systems, the endocrine system and the
nervous system is intercellular communication.
The endocrine system communicates through the release of hormones, secretory
products of endocrine cells and organs that pass into the circulatory system for
transport to target cells that possess receptors for the hormones.
Endocrine hormones include three classes of compounds.
1. Steroids are synthesized and secreted by cells of ovaries, testes and adrenal
cortex.
2. Small peptides, proteins and glycoproteins are synthesized and secreted by
the cells of the hypothalamus, hypophysis (pituitary), thyroid, parathyroid,
pancreas and scattered endocrine cells of the gastrointestinal tract and lungs.
3. Amino acid analogues and derivatives, including the catecholamines are
synthesized and secreted by many neurons as well as cells of the adrenal
medulla.
Hypophysis (pituitary gland)
The hypophysis has two functional components:
I.
The adenohypophysis consists of:
 pars distalis
 pars intermedia
 pars tuberalis
II.
The neurohypophysis consists of:
 pars nervosa
 pars infundibulum
Pars distalis
There are three types of cells according to their staining reaction, such as,
basophiles 10%, acidophils 40%, and chromophobes 50%.
Basophiles is divided into:
 the adrenocorticolipotropes (the most common basophiles) which produce
adrenocorticotropic hormone (ACTH) and lipotropic hormone (LPH)
 the gonadotropes (small basophiles) which produce luteinizing hormone
(LH) and follicle-stimulating hormone (FSH)
 the thyrotropes (large basophiles) which produce thyroid-stimulating
hormone (TSH)
Acidophils is divided into:
 the somatotropes (small acidophils) which produces somatotropin, a growth
hormone (GH)
 the lactotropes (mammotropes) which produce prolactin (PR) or lactogenic
hormone (LTH)
Chromophobes have undifferentiated cells and follicular cells.
29
Pars intermedia
This region made up of cords and follicles of weakly basophilic cells and
chromophobic cells. In the basophilic cells are found small amount of melanocytestimulating hormone.
Pars tuberalis
The endocrine cells are arranged in short clusters or cords in association with the
blood vessels. Some functional gonadotropes are present in this region.
Neurohypophysis
The neurohypophysis is a nerve tract whose terminals store and release secretory
product from the hypothalamus.
Structure:
 The neurohypophysis consists of pars nervosa and infundibulum.
 Pars nervosa contains nonmyelinated axons and nerve endings of
approximately 100.000 neurosecretory neurons whose cell bodies lie in the
supraoptic and paraventricular nuclei of the hypothalamus.
 Dilatations of the axons are called Herring bodies. The Herring bodies
contain either oxytocin or vasopressin (antidiuretic hormone) which
synthesized in the hypothalamus.
 The neurohypophysis contains pituicytes (about 25% of the volume of
organ) associated with the fenestrated capillaries.
Functions of hormones:
Antidiuretic hormone (vasopressin)
 increases blood pressure by promoting the contraction of smooth muscle in
small arteries and arterioles
 decreases urine volume by altering the permeability of kidney collecting
tubules
 decreases the rate of perspiration
Oxytocin
 promotes contraction of smooth muscle of the uterus during copulation and
parturition
 promotes contraction of myoepithelial cells of the breast
The hypothalamus
Structure:
 The hypothalamus has supraoptic and paraventricular nuclei. Antidiuretic
hormone and vasopressin are secreted by these nucleuses.
 The hypothalamus is the site of production of a number of neurosecretory
proteins.
 The hypothalamic neurons secrete proteins that promote and inhibit the
secretion and release of adenohypophyseal hormones. These hormones are
30
called hypothalamic releasing hormones and hypothalamic inhibiting
hormones.
Function:
 The hypothalamus regulates hypophyseal function.
Pineal gland
Structure:
The pineal gland contains two basic types of parenchymal cells
 Pinealocytes are the most common parenchymal secretory cells. They are
arranged in clumps within the lobules. They have large, deeply infolded
nucleus, contain lipid droplets within their cytoplasm and have expanded
club- like endings of their processes. They secrete serotonin and melatonin.
 The interstitial (glial) cells comprise about 5% of the cells in the gland.
They provide support for the pinealocytes.
Functions of hormones:
Melatonin influences
 seasonal sexual activity
 circadian (24 hour) biorhythms
 slows steroid secretion by the ovaries
Serotonin influences
 hormone of happiness
ADRENAL GLANDS
Structure:
 The glands are covered with a thick connective tissue capsule from which
trabeculae extend into the parenchyma.
 The secretory parenchymal tissue is organized in cortical and medullary
regions.
 The cortex is the steroid-secreting portion. It lies beneath the capsule and
constitutes nearly 90% of the gland by weight.
 The medulla is the catecholamine-secreting portion. It lies deep to the
cortex and forms the center of the gland.
 The adrenal cortex is divided into three zones.

Zona glomerulosa, the narrow outer zone

Zona fasciculata, the thick middle zone

Zona reticularis, the inner zone
Zona Glomerulosa
Structure:
 The cells are relatively small columnar or pyramidal shaped.
 They secrete mineralocorticoids mainly aldosterone
Functions of hormones:
 control electrolyte homeostasis (act in distal tubule cells of kidney to
increase sodium resorption and decrease potassium resorption)
31
 maintain the osmotic balance in the urine
 control of blood pressure
 exacerbate inflammatory processes
Zona Fasciculata
Structure:
 The cells of the zona fasciculata are large and polyhedral.
 The cytoplasm contains numerous lipid droplets that are precursors for the
steroid hormones secreted by these cells.
 These cells secrete glucocorticoids mainly hydrocortisone (cortisol),
cortisone and corticosteron.
Functions of hormones:
 regulate glucose and fatty acid metabolism
 depress the immune response
 depress the inflammatory response
 inhibit macrophage recruitment and migration
 stimulate destruction of lymphocytes in lymph nodes
 provide resistance to stress and suppress some allergic reaction
Zona Reticularis
Structure:
 The cells of the zona reticularis are noticeably smaller than those of the
zona fasciculata.
 They are arranged in anastomosing cords, separated by fenestrated
capillaries.
 These cells secrete weak androgens (mostly dehydroepiandrosterone) and
glucocorticoids (principle one is hydrocortisone)
Adrenal Medulla
Structure:
 It contains large, epithelioid cells, called chromaffin cells
 connective tissue
 numerous sinusoidal blood capillaries
 nerves
 These cells secrete catecholamines: epinephrine (80%) and norepinephrine (20%)
Functions of hormones:
Catecholamines increase
 heart rate
 blood pressure
 sweating
 rate of respiration
Catecholamines decreases
 blood flow to viscera and skin
 digestion,
 urine production
32
Thyroid gland
Structure:
 The thyroid is a bilobed endocrine gland located in the neck.
 The lobes are connected by the isthmus.
 A thin connective tissue capsule surrounds the gland.
 It sends trabeculae into the parenchyma to partially outline irregular lobes
and lobules.
 Secretory follicles constitute the functional units of the gland.
 The lumina of the follicles are filled with a gel-like mass called colloid.
 Colloid contains thyroglobulin, the inactive storage form of the thyroid
hormones.
 The thyroid hormones are formed by the coupling of two iodinated tyrosine
residues to produce thyroxine (T4 and T3 ratio of 20: 1) which cross the
basal membrane and enter blood and lymphatic capillaries.
 Two basic cell types are present in the follicles principal or follicular cells
and parafollicular or C cells.
 Follicular cells secrete T4 and T3.
 Parafollicular cells secrete calcitonin.
Functions of hormones:
Thyroxin (tetroidothyronine T4) and triidothyronin T3
 regulate cell and tissue metabolism
 influences body and tissue growth
 influences development of the nervous system in the fetus and young child
 responsible for homeostasis
Calcitonin
 lowers blood calcium level
 suppressing bone resorption
Parathyroid glands
Structure:
 They are ovoid and arranged in two pairs, to comprise the superior and
inferior parathyroid glands.
 Each parathyroid gland is surrounded by a thin connective tissue capsule
that separates it from the thyroid gland.
 Septa extend from the capsule into the gland to divide it into lobules and to
separate the densely packed cords of cells.
 Principal (chief) cells which responsible for the secretion of parathyroid
hormone (parathormone) and oxyphil cells constitute the epithelial cells of
the parathyroid gland.
Functions of hormones:
 increase level of calcium in the blood
 reduce the concentration of phosphate
 stimulate bone resorption
33
DIGESTIVE SYSTEM
The digestive system consists of alimentary canal and its associated organs,
namely, the tongue, teeth, salivary glands, pancreas, liver and gallbladder.
The alimentary mucosa is the surface across which most substances enter the body.
Functions of the alimentary mucosa:
1. Barrier function: The mucosa serves as a barrier to the entry of noxious
substances, antigens, and pathogenic organisms.
2. Immunologic function: Lymphatic tissue in the mucosa serves as a first line of
defense of the body by the immune system.
3. Secretory function: The lining of the alimentary canal secretes, at specific
sites, digestive enzymes, hydrochloric acid, mucin, and antibodies.
4. Absorptive function: The epithelium of the mucosa absorbs metabolic
substrates, i.e., the breakdown products of digestion, as well as vitamins, water,
electrolytes, and other substances.
Oral cavity
The oral cavity consists of the mouth and its contents, i.e., the tongue, teeth,
salivary glands, and tonsils.
Tongue
Structure:
 The tongue is a muscular organ. The striated muscles of the tongue are
arranged in bundles that generally run in three planes and usually separated
by connective tissue.
 The dorsal surface of the tongue is divided into an anterior two-thirds and a
posterior one-third by a V shaped depression, the sulcus terminalis.
 Papillae cover the dorsal surface of the anterior portion of the tongue.
 There are four types: fungiform, circumvallate and foliate papillae have taste
buds but filiform don’t have them.
Lingual tonsils
Structure:
 Lingual tonsils are located in the lamina propria of the root or base of the
tongue.
 They are found posterior to the sulcus terminalis.
 The lingual tonsils contain lymphatic nodules.
 Epithelial crypts usually invaginate into the lingual tonsil.
Gingiva
Structure:
 The gingiva is firmly attached to the teeth and underlying bony tissue.
 It is composed of stratified squamous epithelium and numerous connective
tissue papillae.
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 This epithelium is bound to the tooth enamel by means of a cuticle that
resembles a thick basal lamina and forms the epithelial attachment of
Gottlieb.
 Between the enamel and the epithelium is the gingival crevice a small
deepening surrounding the crown.
Teeth and supporting tissues
Teeth are embedded in and attached to the maxilla and mandible.
Enamel
Structure:
 Enamel covers the crown of the tooth.
 The enamel layer ends at the neck or cervix of the tooth at the
cementoenamel junction.
 Enamel is the hardest substance in the body
 It Consists of 96-98% hydroxyapatite.
 The structural and functional unit of the tooth is rods or prisms.
 Striations observed on enamel rods (contour lines of Retzius) may
represent evidence of rhythmic growth of the enamel in the developing
tooth.
 The enamel in a mature tooth is acellular and nonreplaceable.
Cementum
Structure:
 Cementum covers the root of the tooth.
 Like bone, cementum has a mineral content of 45-50%.
 The lacunae and canaliculi in the cementum contain the cementocytes and
their processes, respectively.
 Cementum is avascular.
 The canaliculi in cementum do not appear to form an interconnecting
network.
 A layer of cementoblasts is seen on the outer surface of the cementum,
adjacent to the periodontal ligament.
 Collagen fibers that project out of the matrix of the cementum and embed
in the bony matrix of the socket wall form the bulk of the periodontal
ligament. These fibers are another example of Sharpey's fibers.
 Oxytalan fibers that resemble developing elastic fibers are also a
component of the periodontal ligament.
Dentin
Structure:
 Dentin lies deep to the enamel and cementum.
 It contains less hydroxyapatite than does enamel, about 70%.
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 Dentin is secreted by odontoblasts that form an epithelial layer over the
inner surface of the dentin, i.e., that surface that is in contact with the pulp.
 Odontoblasts processes embedded in the dentin are narrow channels called
dentinal tubules.
 The rhythmic growth of dentin produces certain "growth lines" in the dentin
(incremental lines of von Ebner and the thicker lines of Owen) that can
identify significant developmental times such as birth (neonatal line).
 Study of growth lines has proved useful in forensic medicine.
 Predentin is newly secreted organic matrix, closest to the cell body of the
odontoblasts that has yet to be mineralized.
Dental Pulp and Pulp Cavity
Structure:
 The pulp cavity is the space within a tooth that is occupied by pulp, a
loose connective tissue that is richly vascularized and supplied by
abundant nerves.
 The pulp cavity has the general shape of the tooth.
 The blood vessels and nerves enter the pulp cavity at the tip (apex) of
the root, at a site called the apical foramen.
 The blood vessels and nerves extend to the crown of the tooth where
they form vascular and neural networks beneath and within the layer
of odontoblasts.
 In teeth with more than one cusp, pulpal horns extend into the cusps
and contain large numbers of nerve fibers.
Alveolar Process and Alveolar Bone
Structure:
 The alveolar bone proper, a thin layer of compact bone, forms the wall
of the alveolus and is the bone to which the periodontal ligament is
attached.
 The rest of the alveolar process is supporting bone.
Periodontal Ligament
Structure:
 The periodontal ligament is the fibrous connective tissue joining the
tooth to its surrounding bone.
Functions:
 Attachment
 Support
 Bone remodeling (during movement of a tooth)
 Nutrition of adjacent structures
 Proprioception
 Tooth eruption
 Attachment and support are the most apparent functions.
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Salivary glands
Exocrine glands in the mouth produce saliva, which has digestive, lubricating and
immunologic functions.
Classification of the salivary glands
labial buccal molar palatine
The minor salivary glands lingual
parotid
submandibular sublingual
The major salivary glands
Cells of salivary glands:
 Serous cells are protein -secreting cells.
 Mucous cells are mucus-secreting cells.
 Myoepithelial cells are instrumental in moving secretory products toward
the excretory duct.
Salivary ducts
The lumen of the salivary acinus is continuous with that of a duct system that may
have as many as three sequential segments.
 intercalated duct
 striated duct
 excretory duct
Parotid gland
Structure:
 The parotid glands are branched acinar and totally serous.
 The parotid duct travels from the gland, which is located below and in front
of the ear, to enter the oral cavity opposite the second upper molar tooth.
 The secretory units in the parotid glands are serous and surround numerous,
long, narrow intercalated ducts.
 Striated ducts are large.
 Large amounts of adipose tissue may be one of its distinguishing features.
Submandibular gland
Structure:
 The submandibular glands are branched tubuloacinar gland.
 Its secretory portion contains mainly serous and some mucous cells.
 The paired, large, mixed submandibular glands are located under either side
of the floor of the mouth, close to the mandible.
 A duct from each of the two glands runs toward and medially to a papilla
located on the floor of the mouth just lateral to the frenulum of the tongue.
 Intercalated ducts are less extensive than in the parotid gland.
Sublingual gland
Structure:
 The small sublingual glands are branched tubuloacinar gland;
 Its secretory portion contains mainly mucous and some serous cells.
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 The sublingual glands are located in the floor of the mouth anterior to the
submandibular glands.
 Their multiple small sublingual ducts empty into the submandibular duct as
well as directly onto the floor of the mouth.
 Intercalated ducts and striated ducts are difficult to locate or may be absent.
Alimentary canal structure
The wall of the tract is formed by four distinctive layers.
1. Mucosa consists of a lining epithelium, an underlying connective tissue
called lamina propria which contains glands, vessels and elements of the
immune system, and also of muscularis mucosae, composed of smooth
muscle cells arranged as an inner circular and an outer longitudinal layer.
2. Submucosa consists of dense irregular connective tissue which contains the
larger blood vessels and the nerve network
3. Muscularis externa consists of the inner layer of circularly oriented smooth
muscle cells and the outer one of a longitudinally oriented smooth muscle
cells.
4. Serosa or adventitia, a serous membrane consists of a simple squamous
epithelium, the mesothelium, and a small amount of underlying connective
tissue, where the wall is directly attached to adjoining structures, the outer
layer is the adventitia and is composed of connective tissue
Esophagus
Structure:
 The esophagus is lined with a nonkeratinized stratified squamous
epithelium.
 The underlying lamina propria and the muscularis mucosae are not unique.
 The submucosa along with the muscularis mucosae forms a number of
longitudinal folds and creates a highly irregular luminal profile.
 Upper one-third of the muscularis externa is striated muscle, the middle third
is striated and smooth muscle and the distal third consists of smooth muscle.
 The outer layer of esophagus in the thoracic cavity is composed of
adventitia.
 After entering the abdominal cavity it is covered by serosa.
 Esophageal glands proper occur in the submucosa. They are small
compound tubuloalveolar mucous secreting glands.
 Esophageal cardiac glands occur in the lamina propria of the mucosa. They
are simple tubular mucous secreting glands.
Functions:
 The esophagus is a muscular tube that delivers food and liquid from the
oropharynx to the stomach.
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Stomach
Structure:
 The stomach is an expanded part of the digestive tube that lies under the
diaphragm.
 The stomach has mucosae, submucosa, muscularis externa and a serosa.
 The inner surface of the empty stomach has a number of longitudinal folds
or ridges called rugae.
 In the mucosal surface is present numerous openings. These are the gastric
pits or foveolae.
 The smaller regions of the mucosa are formed by grooves or shallow
trenches that divide the stomach surface into bulging irregular areas called
mamillated areas.
 The stomach is divided into three distinct into three distinct parts:
 the cardia (cardiac region) contains the cardiac glands
 the pylorus (pyloric region) contains the pyloric glands
 the fundus (fundic region) contains the fundic or gastric glands.
I. Gastric mucosa
 The epithelium that lines the surface and the gastric pits of the stomach is
simple columnar.
 Fundic glands of the gastric mucosa are simple, branched tubular glands.
Fundic glands are composed of
1. Undifferentiated cells that give rise to the mature cells.
2. Mucous neck cells secrete soluble mucus compared with insoluble or
cloudy mucus produced by the surface mucous cells.
3. Chief cells secrete pepsin in an inactive precursor form designated
pepsinogen and a weak lipase
4. Parietal cells secrete HCL and intrinsic factor. Intrinsic factor, a
glycoprotein that is essential for the absorption of vitamin B 12.
5. Enteroendocrine cells secrete gastrin, one of the gastrointestinal
polypeptide hormones, is the principal effective agent for stimulating the
secretion of HCL.
 Cardiac glands of the gastric mucosa are simple tubular, and branched.
They are composed mainly of mucus-secreting cells, with occasional
interspersed enteroendocrine cells.
 Pyloric glands of the gastric mucosa are branched, tubular glands that are
coiled. Enteroendocrine cells are found interspersed within the gland
epithelium along with occasional parietal cells.
 Lamina propria and muscularis mucosae are not unique.
II. Gastric submucosa is composed of a dense connective tissue and
submucosal (Meissner’s) plexus.
III. Gastric muscularis externa consists of an outer longitudinal layer, a
middle circular layer, and an inner oblique layer.
iV. Gastric serosa is not unique.
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Functions:
 Mixing and partial digestion of the food in the stomach by its gastric
secretions produces a pulpy fluid mix called chime.
 The gastric secretions include pepsinogen, hydrochloric acid and intrinsic
factor.
 In addition, the hormone gastrin and other hormones and hormone like
secretions are produced by enteroendocrine glands in the gastric epithelium.
Small intestine
Structure:
I. Mucosa consists of:
 Plicae circulares are permanent transverse folds that contain a core of
submucosa.
 Villi are finger-like and leaf-like projections of the mucosa that extend into
the intestinal lumen.
 Microvilli of the enterocytes give the apical region of the cell a striated
appearance, the so-called striated border.
 The intestinal glands or crypts of Liberkühn are simple tubular structures.
They open on to the luminal surface of the intestine of the base of the villi.
 The lamina propria contains numerous cells of the immune system and
nodules of lymphatic tissue that represent a major component of the Gut
Associated lymphoid tissue
 The muscularis mucosae consist of two thin layers of smooth muscle cells,
an inner circular and an outer longitudinal layer.
Cells of the mucosal epithelium
Enterocytes
Structure:
 They are tall columnar cells with a basally positioned nucleus.
 Microvilli of the enterocytes increase the apical surface area as much as 600
times.
Functions:
 Enterocytes are specialized for the absorption and transport of substances
from the lumen of the intestine to the circulatory system.
 Enterocytes are also secretory cells producing glycoprotein enzymes needed
for terminal digestion and absorption.
Goblet cells
Structure:
 There are a large accumulation of mucinogen granules in the apical
cytoplasm that distends the apex of the cell.
 An extensive array of flattened Golgi saccules forms a wide cup around the
newly formed mucinogen granules near the basal part of the cell.
 Goblet cells have microvilli that are restricted to a thin rim of cytoplasm.
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Function:
 As in other epithelia, goblet cells produce mucus.
Paneth cells
Structure:
 The acidophilic secretory granules contain the antibacterial enzyme
lysozyme, other glycoproteins, an arginine rich protein and zinc.
Functions:
 Lysozyme digests the cell walls of certain groups of bacteria.
 This antibacterial action and the phagocytosis of certain bacteria and
protozoa by Paneth cells suggest that they have a role in regulating the
normal bacterial flora of the small intestine.
Enteroendocrine cells
Functions:
 Cholecystokinin, secretin and gastric inhibitory peptide are the most active
regulators of gastrointestinal physiology that are released in this portion of
the gut.
 These three hormones increase pancreatic and gallbladder activity and
inhibit gastric secretory function and motility.
M cells (microfold cell)
Structure:
 The epithelial cells that overlie Peyer’s patches and other large lymphatic
nodules are nearly squamous.
 They have microfolds rather than microvilli on their apical surface.
Function:
 Take up macromolecules of antigens from the lumen in endocytic vesicles
and discharge them in the vicinity of lymphocytes.
Intermediate cells
Structure:
 . These cells have short, irregular microvilli and small mucin-like secretory
droplets which form a column in the center of the supranuclear cytoplasm.
 Intermediate cells have characteristics of both immature absorptive cells and
goblet cells.
Function:
 These cells are still capable of cell division
II. Submucosa consists of:
 A dense connective tissue and localized sites that contain aggregates of
adipose cells
 Submucosal branched tubuloalveolar glands (of Brunner)
 The secretion of these glands contains neutral and alkaline glycoproteins and
bicarbonate ions.
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Function:
 Secretion of these glands serves to protect the proximal small intestine by
neutralizing the acid-containing chime that is delivered to it
 Secretion of these glands serves to bring the Ph of the intestinal contents
close to the optimal pH for the pancreatic enzymes that are also delivered to
the duodenum.
III.
Muscularis externa consists of:
 an inner layer of circularly arranged smooth muscle cells
 an outer layer of longitudinally arranged smooth muscle cells
IV.
Serosa
 Serosa is not unique.
Large intestine
Structure:
 The mucosa has a smooth surface; neither plicae circulares nor villi are
present.
 The outer longitudinal layer of the muscularis externa exhibits three equally
spaced bands.
I. Mucosa
 The mucosa of the large intestine contains numerous straight tubular glands
that extend through the full thickness of the mucosa.
 The glands consist of simple columnar epithelium.
 The mucosal epithelium of the large intestine contains the same cell types as
the small intestine except Paneth cells which are normally absent in the adult
human.
 Absorptive cells of the mucosa are columnar cells with morphology identical
to the enterocytes of small intestine.
 Goblet cells are more numerous in the large intestine than in the small
intestine.
 The lamina propria has:
 a thick layer of collagen and ground substance just below the free surface
 elaborate development of GALT
 absence of lymphatic vessels in the lamina propria
Functions of the mucosa:
 reabsorption of electrolytes and water and elimination of undigested food
and waste
 production of mucin by Goblet cells to lubricate the bowel, facilitating the
passage of the increasingly more solid colonic contents
 epithelial cell renewal from the stem cells
II. The submucosa is not unique.
III. Muscularis externa
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 In the colon, the outer layer of the muscularis externa is, in the part,
condensed into prominent longitudinal bands of muscle that are called the
teniae coli.
 In the rectum, the outer longitudinal layer of smooth muscle is a uniformly
thick layer, as in the small intestine.
 Bundles of muscle from the teniae coli penetrate the inner, circular layer of
muscle at intervals along the length and circumference of the colon.
 These apparent discontinuities in the muscularis externa allow segments of
the colon to contract independently, leading to the formation of saccules
(haustra) in the colon wall.
IV. Serosa and adventitia
 Where the large intestine is directly in contact with other structures, its outer
layer is adventitia;
 Elsewhere, the outer layer is a typical serosa.
Cecum and appendix
Structure:
 The appendix is a thin, finger-like extension of blind pouch of the cecum.
 The appendix differs from the rest of the colon in having a complete layer of
longitudinal muscle in the muscularis externa.
 The most conspicuous feature of the appendix is the large number of
lymphatic nodules that fuse and extend into the submucosa
Rectum and anus
Structure:
 The rectum is dilated distal portion of the alimentary tract.
 Its upper part is distinguished from the rest of the colon by the presence of
folds called transverse rectal folds.
 The most distal portion of the alimentary canal is the anal canal.
 The upper part of the anal canal has longitudinal folds called anal columns.
 Depressions between the anal columns are called anal sinuses.
 The mucosa of the rectum is similar to that of the rest of the distal colon,
having straight, tubular intestinal glands with many goblet cells.
Anal canal
Structure:
 Anal glands extend into the submucosa and even into the muscularis externa.
 These are branched, straight tubular glands that secrete mucus onto the anal
surface.
 Large apocrine glands, the circumanal glands, are found in the skin
surrounding the anal orifice.
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 The muscularis mucosa disappears at about the level of the rectoanal margin,
but at the same level, the circular layer of the muscularis externa thickness to
form the internal anal sphincter.
Pancreas
The pancreas is an exocrine and endocrine gland.
Exocrine pancreas
Structure:
 The exocrine portion of the pancreas is a compound acinar gland with serous
type of secretion
 The initial portion of the intercalated duct begins within the acinus.
 The intercalated duct cells located inside the acinus are called centroacinar
cells.
 Cells which composed pancreatic acini are called acinar cells.
 They are characterized by acidophilic zymogen granules.
Functions:
 Zymogen granules contain a variety of digestive enzymes in an inactive
form.
 Pancreatic enzymes are capable of digesting most food substances.
 The intercalated duct cells secrete a large volume of fluid rich in sodium and
bicarbonate
 The bicarbonate serves to neutralize the acidity of the chyme that enters the
duodenum from the stomach and to establish the optimum pH for the
activity of the major pancreatic enzymes.
Duct system
1. The intercalated ducts are short and drain to intralobular collecting ducts.
2. The network of intralobular ducts drains to the larger interlobular ducts.
3. The interlobular ducts, in turn, drain directly into the main pancreatic duct.
4. A second large duct, the ductus choledochus (accessory pancreatic duct)
arises in the head of the pancreas.
Endocrine pancreas
Structure:
 The islets of Langerhans, the endocrine component of the pancreas, are
scattered throughout the organ.
 The islets constitute about 1-2% of the volume of the pancreas.
Principal cell types of the islet
 The B cells constitute about 70% of the total islet cells
 They are generally located in its central portion.
Functions:
 They secrete insulin which stimulate:
 uptake of glucose from the circulation
 utilization and storage of glucose by all cells
44
 The A cells constitute about 15-20% of the human islet population
 They are generally located peripherally in the islets.
Functions:
 They secrete glucagon which stimulates:
 release of glucose into the blood-stream
 gluconeogenesis (synthesis of glucose from metabolites of amino
acids) and glycogenolysis (breakdown of glycogen) in the liver
 The D cells constitute about 5-10% of the total pancreatic endocrine tissue.
 They are also located peripherally in the islets.
Functions:
 They secrete somatostatin which inhibit:
 insulin and glucagon secretion
The minor islet cells constitute about 5% of the islet tissue.
 The PP cells secrete pancreatic polypeptide.
 It stimulates gastric chief cells
 It inhibits bile secretion and intestinal motility.
 It inhibits pancreatic enzymes and bicarbonate secretion.
 The D-1 cells secrete vasoactive intestinal peptide.
 Its principal effects are similar to those of glucagon.
 It stimulates pancreatic exocrine secretion.
 The EC cells secrete secretin, motilin and substance P.
 Secretin acts locally to stimulate bicarbonate secretion in pancreatic
fluid and pancreatic enzyme secretion.
 Motilin increases gastric and intestinal motility.
 Substance P function is unclear.
Liver
The liver is the largest mass of glandular tissue in the body and is also the largest
internal organ.
Blood supply to the liver
1. The hepatic portal vein (hpv) and the hepatic artery send blood to the liver.
2. Their branches form the interlobular vessels which branch into distributing
vessels that are located at the periphery of the lobule.
3. The interlobular vessels that form the smallest portal triads send blood into
the sinusoids.
4. In the sinusoids the blood flows centripetally toward the central vein.
5. The central vein courses through the central axis of the classic liver lobule
and empties into a sublobular vein.
6. Several sublobular veins converge to form larger hepatic veins that empty
into the inferior vena cava.
45
Liver lobules
There are three ways of describing the structure of the liver in terms of a functional
unit: the “classic” lobule, the portal lobule, and the liver acinus.
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Classic lobule
The classic hepatic lobule is a roughly hexagonal block of tissue which
consists of stacks of anastomosing plates of hepatic cells, separated by the
anastomosing system of sinusoids that perfuse the cells with the mixed
portal and arterial blood.
At the center of the lobule is the terminal hepatic venule (central vein) into
which the sinusoids drain.
The plates of cells radiate from the central vein to the periphery of the
lobule, as do the sinusoids.
At the angles of the hexagon are the portal areas (portal canals), loose
stromal connective tissue characterized by the presence of the portal triads
(artery, vein and bile duct).
Liver acinus
The liver acinus described as diamond shaped, is the smallest functional unit
in the hepatic parenchyma.
The short axis of the acinus is defined by the terminal branches of the portal
triad that lie along the border between two “classic” lobules.
The long axis is a line drawn between the two central veins closest to the
short axis.
The liver acinus provides the best correlation among blood perfusion,
metabolic activity, and liver pathology.
Portal lobule
 Its outer margins are imaginary lines between the three central veins that are
closest to that portal triad.
 This defines a roughly triangular block of tissue that includes those portions
of three classic lobules that secrete the bile that drains into its axial bile duct.
 The portal lobule emphasizes the exocrine functions of the liver
Sinusoids
 Hepatic sinusoids are lined with a thin discontinuous endothelium.
 Hepatic sinusoids have Kupffer cell or the stellate sinusoidal macrophage.
 The Kupffer cells may be involved in the final breakdown of some damaged
or senile red blood cells that reach the liver from the spleen.
Perisinusoidal space (space of Disse)
 The perisinusoidal space is the site of exchange of materials between blood
and liver cells.
46
 The perisinusoidal space lies between the basal surfaces of the hepatocytes
and the basal surfaces of the endothelial cells and Kupffer cells that line the
sinusoids.
 The lypocyte or adipose cell (commonly called an Ito cell) is found in the
perisinusoidal space.
 These cells are storage site for vitamin A.
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Hepatocytes
Hepatocytes make up the anastomosing cell plates of the liver lobule.
Hepatocytes are large polygonal cells that constitute about 80% of the cell
population of the liver.
Liver cells are capable of considerable regeneration when liver substance is
lost to disease or surgery.
Specific cytoplasmic components include rER, free ribosomes, numerous
mitochondria, glycogen, lipid droplets, small Golgi complexes and a lot of
peroxisomes.
Functions of peroxisomes are metabolism of purines, alcohol and lipids.
The sER involved in degradation and conjugation of toxins and drugs as
well as enzymes responsible for synthesizing cholesterol and the lipid
portion of lipoproteins.
Hepatocyte lysosomes may be a normal storage site for iron.
Biliary tree
The bile canaliculus is small canal formed by grooves in neighboring cells.
The bile canaliculi form a ring about the hepatocyte and drains into small
bile ducts, the canals of Hering, these in turn, drain into the bile duct of the
portal canals.
Bile flows in the canaliculi centrifugal. The flow of bile is in a direction
opposite to the flow of blood, i.e. from the region of the central vein toward
the portal canal.
Near the portal canal, but still within the lobule, bile canaliculi join to form
small ductules, the canals of Hering that are lined with cuboidal cells that are
not hepatocytes.
The ductules carry the bile to the interlobar bile ducts that form part of the
portal triad. Interlobular duct join to form the right and left lobar ducts that
in turn join at the hilum to form the common hepatic duct.
Extra hepatic bile ducts carry the bile to the gall bladder and intestine.
Bile
Structure:
 About 90% of the bile salts a component of bile is reabsorbed and resecreted
by the hepatocytes.
47
 Bile also consists of cholesterol, lecithin, bile pigments, water and
electrolytes.
Functions of the liver:
 The liver has both exocrine and endocrine functions.
 Some of the products of metabolic conversions are carried in the exocrine
secretion of the liver, called bile.
 The endocrine secretions of the liver are released directly into the blood that
supplies the liver parenchyma. These secretions include substances
synthesized by the liver cells, such as albumin, prothrombin, fibronectin and
glycogen.
Gall bladder
The gall bladder concentrates and stores bile.
I. Mucosa
 The empty or partially filled gall bladder has numerous deep mucosal folds.
The mucosal surface consists of a simple columnar epithelium.
 Lamina propria
 Mucin-secreting glands
 large number of lymphocyte and plasma cells
II. Muscularis externa
 The smooth muscle bundles are some what randomly oriented.
III. Adventitia and serosa
 External to the muscularis externa is a thick layer of dense connective tissue.
 Where the gall bladder is attached to the liver surface, this layer is referred
to as the adventitia.
 The unattached surface is covered by a serosa of visceral peritoneum
consisting of a layer of mesothelium and a thin layer of loose connective
tissue.
48
Respiratory system
General structure:
 The respiratory system consists of the paired lungs and a series of air
passages that lead to and from the lungs.
 The air passages consist of a conducting portion and a respiratory portion.
 The conducting portion begins at nasal cavities and ends at terminal
bronchioles
 The respiratory portion consists of respiratory bronchioles, alveolar ducts,
alveolar sacs and alveoli.
Functions:
 air conduction
 air filtration
 warming and moistening of the air
 gas exchange (respiration)
 air passing through the larynx is used to produce speech
 air passing over the olfactory mucosa in the nasal cavities carries the stimuli
for the sense of smell
Nasal cavities
The nasal cavities are paired chambers separated by a bony and cartilaginous
septum. Each chamber is divided into three regions:
 Vestibule (nostril)
 Respiratory segment
 Olfactory segment
Vestibule of the Nasal Cavity
 It is lined with stratified squamous epithelium, and contains the hairs that
filter out large particulate matter.
 Sebaceous glands are also present.


1.
2.
3.
4.
5.



1.
Respiratory Segment of the Nasal Cavity
It is lined by a ciliated, pseudostratified columnar epithelium.
It is composed of five cell types:
Ciliated cells
Goblet cells
Brush cells bear short, blunt microvilli
Small granule cells contain secretory granules
Basal cells stem cells from which the other cell types arise
The lamina propria of the respiratory segment has a rich, vascular network
and contains mucous glands, many with serous demilunes.
Olfactory Segment of the Nasal Cavity
The olfactory segment and are lined with olfactory mucosa.
The olfactory epithelium is composed of the following cell types:
Olfactory cells are bipolar neurons.
49
2. Supporting cells provide mechanical and metabolic support to the olfactory
cells
3. Basal cells are stem cells from which new olfactory cells and supporting
cells differentiate
4. Brush cells
 The lamina propria of the olfactory segment has connective tissue with
numerous blood and lymphatic vessels.
Pharynx
Structure:
 The pharynx connects the nasal and oral cavities to the larynx and
esophagus.
 The pharynx is divided into the nasopharynx and oropharynx
 The auditory tubes connect the nasopharynx to each middle ear.
 Diffuse lymphatic tissue and lymphatic nodules are found in the wall of
the nasopharynx.
 The concentration of such nodules in the posterior wall is called the
pharyngeal tonsil.
Larynx
Structure:
 The passageway for air between the oropharynx and trachea is the larynx.
 It is formed by irregularly shaped plates of hyaline and elastic cartilage.
 The vocal folds are two folds of mucosa that project into the lumen of the
larynx.
 A supporting ligament and skeletal muscle, the vocalis muscle, is
contained within each vocal fold-ligament.
 The ventricular folds located above the vocal folds are the "false vocal
cords".
 The luminal surface of the vocal cords is covered with stratified squamous
epithelium.
 The rest of the larynx is lined with the ciliated, pseudostratified columnar
epithelium.
 The connective tissue of the larynx contains mixed mucoserous glands that
secrete through ducts onto the laryngeal surface.
Function:
 Vocal folds control the flow of air through the larynx and vibrate to produce
sound
Trachea
The trachea is a short tube.
The wall of the trachea consists of four layers:
1. Mucosa composed of ciliated, pseudostratified epithelium which has same cell
types as respiratory portion of the nasal cavity and an elastic fiber-rich lamina
propria (typical loose connective tissue). Basement membrane appears as a
glassy or homogeneous layer.
50
2. Submucosa is a relatively loose connective tissue. Submucosal glands
composed of mucus-secreting acini with serous demilunes.
3. Cartilaginous layer composed of C-shaped hyaline cartilages. Fibroelastic
tissue and smooth muscle bridge the gap between the free ends of the Cshaped cartilages.
4. Adventitia, which binds the trachea to adjacent structures. It consists of
loose connective tissue.
Bronchi
 The trachea divides into two branches forming extrapulmonary bronchi.
 On entering the lungs the bronchi become the intrapulmonary bronchi,
which branch immediately to give rise to the lobar bronchi.
 The lobar bronchi divide to give rise to segmental bronchi.
Bronchial Structure
The wall of the bronchus consists of five layers.
 Mucosa is composed of a pseudostratified epithelium having the same
cellular composition as the trachea.
 Muscularis is a continuous layer of smooth muscle in the larger bronchi.
It may appear discontinuous in smaller bronchi.
 Submucosa remains as a relatively loose connective tissue.
 Cartilage layer consists of discontinuous cartilage plates that become
reduced in size as the bronchial diameter diminishes.
 Adventitia is dense connective tissue.
Bronchioles
 large bronchioles
 terminal bronchioles
 respiratory bronchioles
Structure:
 Bronchioles are air-conducting ducts.
 Cartilage and glands are not present in bronchioles
 The larger diameter bronchioles initially have a ciliated, pseudostratified
columnar epithelium.
 Thick layer of smooth muscle.
 The terminal bronchioles are lined with a simple cuboidal epithelium in
which Clara cells are found among the ciliated cells.
 Clara cells are nonciliated cells secrete a surface-active agent which prevent
luminal adhesion during expiration.
 A small amount of connective tissue underlies epithelium.
 A circumferential layer of smooth muscle underlies the connective tissue.
 Respiratory bronchioles are the first part of the bronchial tree that allows
gas exchange to occur.
 They are lined by a cuboidal epithelium.
 Scattered, thin-walled outpocketings, alveoli, extend from the lumen of the
respiratory bronchioles.
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ALVEOLI
 Alveoli are the terminal air spaces of the respiratory system and are the
actual site of gas exchange between the air and the blood.
 At some point, each alveolus is confluent with a respiratory bronchiole, by
means of an alveolar duct, and an alveolar sac.
 Alveolar epithelium is composed of type I and II alveolar cells and
occasional brush cells.
 Type I alveolar cells, also known as type I pneumocytes, are extremely
thin squamous cells that line most of the surface of the alveoli.
 Type II alveolar cells are secretory cells. Their apical cytoplasm is filled
with granules which rich in phospholipids, among which is the surface
active agent surfactant.
 Without adequate secretions of surfactant, the alveoli would collapse on
exhalation.
The alveolar septum is the site of the air-blood barrier which consists of:
 Alveolar epithelial cells
 Basal lamina of the alveolar epithelium
 Basal lamina of the capillary endothelium
 Endothelial cells of the rich capillary network
 Other connective tissue elements, including fibroblasts, macrophages,
collagen fibers, and elastic fibers
Function of air-blood barrier:
 It is place across which gases must diffuse between the alveolar
compartment and capillary compartment.
52
Urinary system
The urinary system consists of the paired kidneys, the paired ureters, which lead
from the kidneys to the bladder, and the urethra, which leads from the bladder
to the exterior of the body.
Functions of kidneys:
 Production of urine
 Synthesis and secretion of erythropoietin
 Synthesis and secretion of renin
KIDNEY STRUCTURE
1. Capsule
 The kidney surface is covered by a thin connective tissue capsule.
2. Cortex
 It has renal corpuscles with their tubules and medullary rays.
 Each medullary ray contains straight collecting tubules and straight tubule
components of the nephrons.
3. Medulla
 It has straight tubules, collecting ducts, and a special capillary network.
 The tubules in the medulla form a number of conical structures called
pyramids.
 Usually 8— 12 pyramids may occur in the human kidney.
 The bases of the pyramids face the cortex and the apices face the renal
sinus.
 The caps of cortical tissue that lie over the pyramids form the renal
columns.
Nephron
The nephron is the basic functional and structural unit of the kidney.
They are responsible for the production of urine and correspond to the secretory
part of other glands.
 The renal corpuscle represents the beginning of the nephron.
 It consists of the glomerulus, a tuft of capillaries, surrounded by a doublelayered epithelial cup, the renal or Bowman's capsule.
 The glomerular capillaries are supplied by an afferent arteriole and are
drained by an efferent arteriole that then branches, forming a new capillary
network to supply the kidney tubules. This is then an arterial portal system.
 Continuing from Bowman's capsule, the remaining segments of the
nephron, namely, the tubular parts, are:
 Proximal thick segment, consisting of the proximal convoluted tubule and
the proximal straight tubule.
 Thin segment, which constitutes the thin limb of the loop of Henle.
 Distal thick segment, consisting of the distal straight segment and the
distal convoluted tubule.
53
 The distal convoluted tubule connects to the collecting tubule, often through
a connecting tubule, thus forming the uriniferous tubule, i.e., the nephron
plus collecting tubule.
Types of Nephrons
The types of nephrons are based on where their renal corpuscles are located in the
cortex:
 Cortical or subcapsular nephrons have their renal corpuscles located in
the outer part of the cortex.
 Juxtamedullary nephrons have their renal corpuscles in proximity to the
base of a medullary pyramid.
 Intermediate nephrons have their renal corpuscles in the midregion of the
cortex.
Renal (Malpighian) Corpuscle
Structure:
 The renal corpuscle consists of the glomerular capillary tuft and the
surrounding visceral and parietal epithelial layers of Bowman’s capsule.
 The outer layer of Bowman's capsule, called the parietal layer, is a simple
squamous epithelium
 The inner layer of Bowman's capsule, called the visceral layer, constitute
podocytes cells
 The space between the visceral and parietal layers of Bowman's capsule is
called the urinary or Bowman's space.
 The renal corpuscle contains group of cells called mesangial cells.
 The renal corpuscle contains the filtration apparatus of the kidney.
The filtration apparatus consists of three components:
1. endothelium of the glomerular capillaries with numerous fenestrations
2. basal lamina (the glomerular basement membrane)
3. visceral layer of Bowman’s capsule
Functions:
 Bowman's capsule is the initial portion of the nephron where blood flowing
through the glomerular capillaries undergoes a filtration process to
produce the initial urine filtrate (I filtration phase of urine production).
 Filtration apparatus restricts the movement of albumin and hemoglobin.
 Mesangial cells are phagocytic; they can remove trapped residues and
aggregated proteins from the glomerular basement membrane.
 Mesangial cells and their matrix provide structural support for the
podocytes where the epithelial basement membrane is absent or
incomplete.
Juxtaglomerular Apparatus
Structure:
 The juxtaglomerular apparatus includes the macula densa, the
juxtaglomerular cells, and the extraglomerular mesangial cells.
54
 Lying directly adjacent to the afferent and efferent arterioles of the renal
corpuscle is the terminal portion of the distal thick segment of the nephron.
 It contains cells that collectively are referred to as the macula densa.
 The smooth muscle cells of the adjacent afferent arteriole are modified.
 These smooth muscle cells are referred to as juxtaglomerular cells.
 The granules of the juxtaglomerular cells contain renin that is synthesized,
stored, and released into the blood.
 Some extraglomerular mesangial cells are located along the vascular pole
where they are also designated as lacis cells
Functions:
 Renin increases blood pressure, stimulates the release of the hormone
aldosterone which raising blood volume and pressure.
 The cells of the macula densa monitor the NaCl concentration in the
afferent arteriole and regulate the release of renin by the juxtaglomerular
cells.
KIDNEY TUBULE FUNCTION
Proximal Thick Segment
Structure:
 The proximal convoluted tubule receives the primary filtrate from the
urinary space of Bowman's capsule.
 The cuboidal cells of the tubule have the following features:
 A brush border, composed of numerous, relatively long microvilli
 A terminal bar apparatus, consisting of a narrow tight junction and a
zonula adherens
 Extensive interdigitation of basal processes of adjacent cells
 Basal striations, consisting of elongate mitochondria concentrated in the
basal processes
Functions:
 reabsorption of 80% of the primary filtrate (II phase of urine production)
 reabsorption of fluid is driven by active transport of Na + into the lateral
intercellular space and into the peritubular capillary network
 reabsorption of amino acids, sugars, and proteins
Proximal Straight Segment
 The cells of the straight segment of the proximal tubule, i.e., the thick
descending limb of the loop of Henle, are not as specialized for
absorption as are those of the convoluted segment.
Thin Segment
Structure:
 The thin segment has four types of epithelial cells which possess few
organelles.
Functions:
55
 The descending portion of the thin segment is permeable, permitting free
passage or equilibration of salt and water between the lumen of the
nephron and the peritubular connective tissue.
Distal Thick Segment
Structure:
 The straight segment of the distal tubule, like the ascending thin segment,
transports ions from the tubular lumen to the interstitium.
 The large, cuboidal cells of the distal tubule have extensive basal-lateral
plications and numerous large mitochondria associated with these basal
folds.
 They have considerably fewer and less well-developed microvilli than
proximal tubule cells.
Functions:
 Reabsorption of Na+ and secretion of K+ in order to conserve Na+
 Continued reabsorption of bicarbonate ion
 Antidiuretic hormone can act on the terminal portion of the distal
convoluted tubule to increase the permeability of the tubule to water,
thereby producing more concentrated urine.
Collecting Tubules and Collecting Ducts
Structure:
 Both the collecting tubules and ducts are composed of a simple epithelium.
 The arched and cortical collecting tubules have flattened cells, somewhat
squamous to cuboid in shape.
 The medullary collecting ducts have cuboidal cells, with a transition to
columnar cells as the ducts increase in size.
Cytologically, two distinct types of cells are present in the collecting system:
 Light cells have basal infoldings, true infoldings rather than processes that
implicate with those of adjacent cells. They possess a single cilium and have
relatively few short microvilli.
 Dark cells, occur in considerably smaller numbers. They have many
mitochondria. Numerous vesicles are present in the apical cytoplasm.
Functions:
 Final III secretory phase of urine production occurs in the collecting
tubules
 H+ ions are secreted in the cortical and medullary collecting tubules.
 The collecting tubules responsible for the final concentration of the urine.
INTERSTITIAL CELLS
 The connective tissue of the kidney parenchyma, called interstitial tissue,
surrounds the components of the nephrons, the ducts, and the blood and
lymphatic vessels.
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 In the medulla, the principal interstitial cells resemble myofibroblasts. These
cells may secrete a hormone-like material that reduces blood pressure.
 Prostaglandins and prostacyclin are synthesized in the interstitium.
Excretory passages
 All excretory passages except the urethra have the same general structure,
namely, a mucosa, a muscularis, and an adventitia (or in some regions
serosa)
 Transitional epithelium lines all of the excretory passages.
 Transitional epithelium is essentially impermeable to salts and water. The
apical surface of the cell is very irregular, with deep clefts.
 In the ureters and urethra there are usually two layers of smooth muscle
longitudinal inner layer and circular outer layer
 The smooth muscle of the urinary passages is mixed with connective tissue,
so that it forms parallel bundles rather than pure muscular sheets.
 The smooth muscle of the bladder wall is more random mixing of muscle
and collagen bundles.
Ureters
 The ureters conduct urine from the renal pelvis to the bladder and follow an
oblique path through the wall of the bladder.
 The terminal portion of the ureters is a thick outer layer of longitudinal
muscle.
Urinary Bladder
 The bladder is a distensible reservoir for urine; its size and shape change as
it fills.
 The smooth muscle of the bladder wall forms an internal sphincter, a
ring-like arrangement of muscle around the opening of the urethra.
 The triangular region defined by these three openings the trigone, is
relatively smooth.
Urethra
In the male, the urethra is about 20 cm long and serves as the terminal duct of both
the urinary and genital systems. It has three distinct segments:
 Prostatic urethra extends for 3-4 cm from the neck of the bladder through
the prostate gland
 Membranous urethra extends for about 1 cm from the apex of the prostate
gland through the body wall
 Penile urethra extends for about 15cm through the length of the penis to
open the body surface at the glans penis.
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Male reproductive system
 The male reproductive system consists of the testes, epididymides and
genital ducts, accessory reproductive glands, and penis.
TESTIS
Functions:
 The testes produce sperm and androgens.
 They influence embryonic development,
reproductive function.
sexual
maturation,
and
Structure:
 The testes have a thick connective tissue capsule, the tunica albuginea.
 Each testis is divided into approximately 250 lobules by incomplete
connective tissue septa that project from the capsule.
 Each lobule contains several highly convoluted seminiferous tubules which
produce the sperm.
 They continuous with tubuli recti which connect with the rete testis.
 Tubuli recti are lined only by Sertoli cells.
 Near their termination, the tubuli recti are lined by simple cuboidal
epithelium.
 A simple cuboidal or low columnar epithelium lines the channels of the
rete testis.
 Interstitial or Leydig cells are found in a connective tissue stroma.
 They are large, polygonal, acidophilic cells that typically contain lipid
droplets and secrete testosterone.
 The seminiferous tubules consist of a seminiferous epithelium which
composed of two basic populations of cells:
 Spermatogenic cells
 Sertoli cells
 The tunica propria is a multilayered connective tissue that lacks typical
fibroblasts.
 It consists of three to five layers of myoid cells and collagen fibrils
external to the basal lamina of the seminiferous epithelium.
 Rhythmic contractions of the myoid cells help move spermatozoa and
testicular fluid to the excurrent duct system.
Sertoli cells
Structure:
 The Sertoli cells are columnar cells with complex apical and lateral
processes.
 They surround the adjacent spermatogenic cells and fill the spaces
between them.
Functions:
58
 The Sertoli cells give structural organization to the tubules.
 They divides the seminiferous epithelium into basal and luminal
compartments.
 They exchange metabolic substrates and wastes between the developing
spermatogenic cells and the circulatory system.
 They phagocytized and break down any spermatogenic cells that fail to
differentiate completely.
 The Sertoli-Sertoli junctional complex is the site of the blood-testis barrier.
 They secrete androgen-binding protein.
EXCURRENT DUCT SYSTEM
Efferent Ductules
 The efferent ductules connect the rete testis to the epididymis.
 They are highly coiled and form 6-10 conical masses.
 The efferent ductules are lined with a pseudostratified columnar epithelium.
 Interspersed among the columnar cells are a few basal cells and
intraepithelial lymphocytes.
 The smooth muscle forms a circular sheath in the wall of the ductule.
Ductus Epididymis
Structure:
 The ductus epididymis is a highly coiled tube which lies along the posterior
surface of testis.
 It consists of the ductus epididymis and its associated vascularized
connective tissue, smooth muscle, and a fibrous connective tissue tunic.
 The ductus epididymis is divided a head (caput), a body (corpus), and a
tail (cauda).
 The ductus epididymis is lined with a pseudostratified columnar
epithelium. It contains principal cells (tall) and basal cells (short).
 In the head of the epididymis and most of the body, the smooth muscle coat
consists of a thin layer of circular smooth muscle.
 In the tail, inner and outer longitudinal layers are added.
 These three layers are then continuous with the three smooth muscle
layers of the ductus deferens.
Functions:
 Epididymal cells function in both absorption and secretion.
 Maturation of the sperm cells.
Ductus deferens
 The ductus deferens is a direct continuation of the epididymis and
connects to the prostatic urethra.
 The distal end of the ductus deferens enlarges to form the ampulla.
 The ampulla has branched mucosal folds.
 The ductus deferens is lined with a pseudostratified columnar epithelium.
 The tall columnar cells also have long microvilli that extend into the lumen.
 The rounded basal cells rest on the basal lamina.
59
 The lumen of the duct appears to be thrown into deep longitudinal folds
throughout most of its length, probably due to contraction.
Accessory sex glands
Seminal vesicles
Structure:
 The seminal vesicles are paired, elongate tubular glands that have a
muscular and fibrous coat.
 The pseudostratified columnar epithelium contains tall, nonciliated columnar
cells and short round cells.
Functions:
 Prostaglandins are synthesized in large amounts in the seminal vesicles.
 Secrete the fluid that is rich in fructose.
Prostate Gland
Structure:
 The prostate consists of a collection of 30—50 tubuloalveolar glands that
surround the proximal urethra.
 The glands are arranged in three concentric layers: a mucosal layer, a
submucosal layer, and the most peripheral layer containing the main
prostatic glands.
 The epithelium is generally columnar but may have patches that are
cuboidal, squamous, or pseudostratified.
 Prostate has fibromuscular tissue.
Functions:
 It secretes protein enzymes, acid phosphatase, fibrinolysin, and citric acid.
Bulbourethral Glands
Structure:
 The paired bulbourethral glands are pea-sized structures located in the
urogenital diaphragm.
 They are compound tubuloalveolar glands.
 They are lined by simple columnar epithelium.
Functions:
 Produce the major portion of the preseminal fluid
 Serves as a lubricant of the penile urethra.
Penis
 The urethra, which originates at the bladder and extends through the penis,
carries both semen and urine to the exterior.
 The penis consists principally of two corpora cavernosa, and the corpus
spongiosum, in which the urethra is embedded.
 A dense fibroelastic layer, the tunica albuginea, binds the three
together and forms a capsule around each one.
 The skin of the penis is thin and loosely attached to the underlying loose
connective tissue except at the glans, where it is very thin and tightly
attached.
The Female Reproductive System
60
The female reproductive system consists of internal sex organs and external
genital structures
OVARY
Functions of the ovary:
 Production of the estrogen and progesterone
 Production of gametes.
Structure:
 The ovaries are paired structures covered by tunica albuginea.
 The ovary is composed of a cortex and a medulla.
1. Medulla located in the central portion of the ovary. It contains loose
connective tissue, blood vessels, lymphatic vessels, and nerves.
2. Cortex found in the peripheral portion of the ovary. It contains the ovarian
follicles.
 Types of follicles
1. Primordial follicles
2. Growing follicles (primary and secondary) follicles
3. Mature or Graafian follicles
The Primordial Follicle
 The primordial follicles are found in the stroma of the cortex.
 A single layer of squamous follicular cells surrounds the oocyte.
The Primary Follicle
 Follicular cells proliferate and become cuboidal.
 Zona pellucida appears between the oocyte and the adjacent follicular cells.
 Follicular cells undergo stratification to form the granulosa layer of the
primary follicle.
 Connective tissue cells form the theca interna and externa layers of the
primary follicle.
 Under the plasma membrane the oocytes exhibit cortical granules.
The Secondary Follicle
 In the secondary follicle begins to form a single cavity called the antrum,
which contain liquor with estrogen.
 The granulosa cells form the cumulus oophorus.
The Graafian follicle
 The mature follicle, also known as a Graafian follicle, has a diameter of 10
mm or more.
 The cells of the cumulus oophorus which surround the oocyte are called
corona radiata.
Ovulation
 Ovulation is the process by which an oocyte is released from the Graafian
follicle due to increasing volume and pressure of the follicular fluid and
enzymatic proteolysis of the follicular wall.
Corpus Luteum
61
At ovulation, the follicular wall, composed of the remaining granulosa and thecal
cells, is transformed into the corpus luteum (yellow body), which produces
progesterone.
1. If fertilization and implantation do occur, the corpus luteum forms the
corpus luteum of pregnancy. It remains active 12 weeks.
2. If fertilization and implantation do not occur, the corpus luteum forms the
corpus luteum of menstruation. It remains active 14 days.
3. The corpus luteum degenerates after pregnancy or menstruation. A white
scar forms the corpus albicans.
Most ovarian follicles are lost by atresia.
OVIDUCT
The oviducts (Fallopian tubes) are paired tubes that extend bilaterally from the
uterus toward the ovaries.
The oviduct wall consists of next layers.
 The serosa.
 The muscularis.
 The mucosa is lined with simple columnar epithelium composed of
ciliated and nonciliated cells.
Uterus
The human uterus is a hollow, pear-shaped organ. The uterine wall is composed
of three layers.
1. Endometrium, the mucosa of the uterus which consists of stratum functionale
and stratum basale. The stratum functionale is lined with a simple columnar
epithelium with secretory and ciliated cells and contain uterine gland (simple
tubular).
2. Myometrium, the thick muscular layer which is composed of three indistinctly
defined layers of smooth muscle.
3. Perimetrium consists of a mesothelium and a thin layer of loose
connective tissue. The perimetrium covers the entire posterior surface of the
uterus but only part of the anterior surface. The remaining part of the anterior
surface consists of connective tissue or adventitia.
 The endometrium undergoes cyclic changes each month that prepare it for
the implantation of the embryo.
 The discharge of tissue and blood from the vagina, which usually
continues for a period of 3-5 days, is referred to as menstruation.
Menstrual cycle
The menstrual cycle has 3 phases:
1. Proliferative phase, occurring concurrently with follicular maturation and
influenced by ovarian estrogen secretion
62
2. Secretory phase, coinciding with the functional activity of the corpus luteum
and primarily influenced by progesterone secretion
3. Menstrual phase, commencing as hormone production by the ovary declines
with the degeneration of the corpus luteum
I. The proliferative phase of the menstrual cycle is regulated by estrogen.
Following changes can be seen:
1. Epithelial cells in the basal portion of the glands reconstitute the glands
2. Spiral arteries lengthen as the endometrium is reestablished.
3. Thickness of endometrium is about 3 mm.
4. Duration of this phase is from 5 up to 14 days of menstrual cycle.
II. The secretory phase of the menstrual cycle is under the control of progesterone.
Following changes can be seen:
1. The endometrium becomes edematous.
2. Thickness of endometrium is about 5-6 mm.
3. The glands enlarge and become corkscrew shaped.
4. The lumen of the glands is filled with secretory products (glycogen).
5. The spiral arteries lengthen and become more coiled.
6. Stromal cells undergoing transformation into decidual cells.
III. The menstrual phase results from a decline in the ovarian secretion of
progesterone and estrogen.
Following changes can be seen:
1. As the hormone levels rapidly decline, periodic contraction of the walls of
the spiral arteries cause the stratum functionale to become ischemic and than
sloughed off.
2. At the end of the menstrual phase, thickness of endometrium is about 1 mm.
This layer is the stratum basale; the layer that was sloughed off was the
stratum functionale.
Vagina
 The vagina is a fibromuscular tube lined by nonkeratinized stratified
squamous epithelium
The vaginal wall consists of:
1. Inner mucosal layer (without glands) consists of lamina propria and
submucosa.
2. Intermediate muscular layer is smooth muscle layers, an outer longitudinal
and an inner circular layer.
3. Outer adventitial layer consists of an inner dense connective tissue and an
outer loose connective tissue.
MAMMARY GLANDS
 Mammary glands are modified apocrine sweat glands that develop under the
influence of sex hormone.
63
Structure:
 It is composed of 15-20 irregular lobes of branched tubuloalveolar glands
which radiate from the mammary papilla or nipple and are further
subdivided into numerous lobules.
 Abundant adipose tissue is present in the interlobular spaces.
 The epidermis of the adult nipple and areola is highly pigmented and
somewhat wrinkled.
 Deep to the areola and nipple, bundles of smooth muscle fibers are arranged
radially and circumferentially in the dense connective tissue and
longitudinally along the lactiferous ducts.
 The areola contains sebaceous glands, sweat glands, and modified
mammary glands and fewer sensory nerve endings.
 Each tubuloalveolar gland ends in a lactiferous duct that opens through a
constricted orifice onto the nipple.
 Beneath the areola, the pigmented area surrounding the nipple, each duct
has a dilated portion, the lactiferous sinus.
The morphology of the secretory portion of the mammary gland varies with the
menstrual cycle.
Mammary glands undergo dramatic proliferation and development during
pregnancy
1. Decreasing of the amount of connective and adipose tissues.
2. Infiltration of plasma cells, lymphocytes, and eosinophils of fibrous
component of the connective tissue.
3. Branching of ducts and developing of alveoli.
4. Hypertrophy of the secretory cells and accumulation of secretory product
in the alveoli.
Both merocrine and apocrine secretion are involved in production of milk.
The secretory cells produce two distinct products that are released by different
mechanisms:
1. Merocrine secretion: The protein component of the milk is synthesized in
the rER and released from the cell by fusion of the granule's limiting
membrane with the plasma membrane.
2. Apocrine secretion: The lipid coalesces to form large droplets that pass
to the apical region of the cell and project into the lumen of
the acinus. The droplets are invested with an envelope of plasma membrane
as they are released. A thin layer of cytoplasm is trapped between the
plasma membrane and lipid droplet and is released with the lipid, but the
cytoplasmic loss in this process is minimal.
The secretion released in the first few days after childbirth is known as colostrum.
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