Download Animal Histology

Animal Histology:
Form and Function
This presentation includes representatives of the
major animal tissue types. It also includes a
description of the form and function of each tissue
or organ. The photographs are taken from
Carolina’s best microscope slides.
The images used in the following slides are also
included in a separate folder on this CD. You may
use them in your classroom or lab to create your
own presentations or student assessments.
Tissues
Tissues are groups of specialized cells that work
together for a particular function. In humans,
combinations of different types of tissues make up
organs, and groups of organs work together to
form organ systems.
Four Types of Tissue
1. Epithelial
2. Connective
3. Nervous
4. Muscle
Epithelial Tissue
Epithelial tissues cover body surfaces. Skin and the lining
of organs are epithelial tissues. Epithelial tissues play roles
in absorption, secretion, and protection against foreign
substances.
Simple Squamous Epithelium
SS
Simple squamous (SS) tissue is composed of flat, scale-like cells. It
lines the walls of blood vessels, pulmonary alveoli (shown here), and
the lining of the heart, lung, and peritoneal cavities.
Simple Cuboidal Epithelium
This tissue is composed of a single layer of boxy cells
(arrows). It lines the walls of kidney tubules. In describing
epithelium, the term “simple” means one cell-layer thick.
Simple Columnar Epithelium
The cells of simple columnar epithelium (arrows) are taller, as their
name suggests. This tissue is usually associated with secretion or
absorption and is most often found lining the digestive tract. The section
shown here is from an amphibian.
Stratified Squamous Epithelium
The term “stratified” refers to the layered arrangement of cells. The
outer layers of cells appear flat, but the inner cells vary in shape from
cuboidal to columnar. Stratified squamous epithelium serves as a
barrier to the outside environment.
Stratified Cuboidal Epithelium
SC
Stratified cuboidal epithelium (SC) is found in the ducts of
sweat glands and surrounds Graafian follicles of ovaries
(shown above). The outer layer of cells appears smaller
than the inner layer.
Stratified Columnar Epithelium
Stratified columnar epithelium occurs only in parts
of the male urethra and certain excretory ducts.
Ciliated Epithelium
Some epithelial membranes are made up of cells with cilia,
tiny projections that beat in unison to move mucus along
the surface. Ciliated epithelia in the trachea, for example,
sweep debris out of the respiratory tract.
Pseudostratified Columnar Epithelium
BM
Although this tissue appears stratified, it is actually
composed of a single layer of cells of different types.
Although their nuclei are found at different levels, each
cell adjoins the basal membrane (BM). This tissue lines the
larger respiratory passageways. It is often ciliated (arrows).
Transitional Epithelium
Transitional epithelium is found in the lining of the bladder. When the bladder
is full, the epithelium is stretched and the cells appear flat. Cells appear
rounded when the bladder is empty.
Connective Tissue
Connective tissue differs from other tissues
in that it contains large amounts of
intercellular matrix. Connective tissues
function to bind other tissues together,
provide support, provide nourishment, store
wastes, or repair damaged tissues.
Bone
Bone is a type of connective tissue that secretes a
matrix of mineral salts, such as calcium phosphate,
and the protein collagen. The minerals give bones
their hardness, while the protein gives them
strength and resiliency. Bone supports the body,
protects internal organs, provides for muscle
attachment, and serves as a calcium reservoir.
Many bones contain a marrow cavity where red
blood cells and white blood cells are formed.
Compact Bone
Compact bone consists of repeating units called osteons.
Each osteon has concentric layers of the mineralized
matrix deposited around a central canal. The canal contains
blood vessels and nerves that serve the bone cells. Boneforming cells, called osteoblasts, deposit the matrix around
the central canal and ultimately surround themselves with
the mineralized material, forming a pocket called a lacuna.
Once osteoblasts are surrounded by matrix, the cells are
called osteocytes. Narrow connections called canaliculi
extend from lacunae and connect osteocytes to each other
and to the central canal.
Compact Bone
cc
Compact bone is made up of concentric layers of bone
matrix surrounding central canals (CC). A canal and its
associated layers make up an osteon. Osteocytes are
located within cavities called lacunae.
Osteocytes
oc
Osteocytes (OC) are connected by cellular extensions
called canaliculi. These extensions allow nutrients to pass
from cell to cell.
Adipose Tissue
Adipose tissue is a specialized form of loose
connective tissue that stores fat in adipose cells
distributed throughout a non-cellular matrix.
Adipose tissue protects internal organs, insulates
the body, and stores energy as fat molecules. Each
adipose cell contains a large lipid-filled vesicle.
Adipose cells do not reproduce but are long lived,
functioning for many years.
Adipose Tissue
Adipose cells are bundled together by connective tissue. The
connective tissue creates lobules of adipose cells. Each cell appears as
a clear space, representing the site of the large drop of lipid (fat) before
it dissolved during preparation of the microscope slide. The nuclei
appear as small disks on the periphery of cells.
Loose Connective Tissue
Loose connective tissue has few fibers, a number of cell
types, and a large amount of matrix. It functions to bind
epithelia to underlying tissues.
Dense Connective Tissue
Dense connective tissue contains a large number of fibers
with only a few cells. Fibers shown here are all running
parallel to each other, and no cells are present. Tendons are
composed of dense connective tissue.
Hyaline Cartilage
Hyaline cartilage serves in support and acts as a lubricating
surface for some joints. Hyaline cartilage appears as a
translucent mass with chondrocytes embedded in the
matrix within cavities called lacunae.
Fibrous Cartilage
Fibrous cartilage is composed of bundles of dense
collagenous connective tissue with small groups of lacunae
in a hyaline cartilage matrix. This cartilage is found in the
intervertebral discs.
Blood
Blood is considered a connective tissue because it
has an extracellular matrix called plasma. This
liquid matrix is made up of water, salts, nutrients
and an assortment of dissolved proteins.
Suspended in the matrix are two types of cells,
erythrocytes (red blood cells) and leukocytes
(white blood cells), as well as specialized cell
fragments called platelets that function in clotting
blood.
Erythrocytes
RBCs
Red blood cells (RBCs) in humans are flattened disks because the cells lack a
nucleus. The pigment hemoglobin, which gives blood its red color, binds to
oxygen. Red blood cells are responsible for transporting oxygen to all the cells
of the body.
Leukocytes
White blood cells function mostly in fighting diseases.
Some of them move through the walls of blood vessels and
enter body tissues to engulf bacteria. There are five types
of white blood cells: neutrophils, lymphocytes, monocytes,
eosinophils, and basophils.
Neutrophils
Neutrophils are granular with segmented nuclei with 2 to 5
lobes. They are the most numerous leukocytes and are the
first line of defense, actively phagocytizing foreign
substances.
Lymphocytes
Lymphocytes typically have large, round nuclei and lack
granules in the cytoplasm. There are two types of
lymphocyte: B cells produce antibodies, while T cells fight
virally infected cells and cancer cells.
Monocytes
A monocyte is nongranular and has a large nucleus that
tends to be oval or kidney shaped. Monocytes function
outside the bloodstream where they transform into
macrophages.
Eosinophils
An eosinophil has a two-lobed nucleus and
granules that stain a deep red. Eosinophils
phagocytize antigen-antibody complexes outside
the bloodstream. They also attack parasitic worms.
Basophils
Basophils contain granules that appear blue or purple when
stained. The granules contain histamine and heparin.
Basophils function in body-wide allergic responses by
releasing histamine.
Nervous Tissue
Nervous tissue, which occurs throughout the body,
receives and transmits stimuli. It converts a
stimulus, whether chemical or physical in nature,
into an electrical impulse that is conducted by
neurons. Neurons, also called nerve cells, are the
functional unit of nervous tissues.
Neuron
Axon
Cell Body
Dendrites
A neuron consists of a cell body, dendrites, and axons.
Dendrites carry impulses to the cell body, whereas axons
transmit impulses toward another cell body or an effector,
a muscle or organ that responds to the impulse.
Axons
Axons are usually much longer than dendrites, sometimes reaching a
meter in length. Many axons are enclosed in an insulating, lipid layer
called a myelin sheath. This sheath is produced by Schwann cells, a
type of supporting cell for the nervous system. The sheath not only
protects the axon but also allows impulses to move more quickly along
the axon. Axons arranged in ropelike bundles wrapped in connective
tissue make up nerves. Nerves carry sensory impulses to the brain and
transmit motor responses from the brain to effector organs. Nerves that
make up the peripheral nervous system bring impulses from the entire
body to the spinal cord, which then transmits them to the brain. The
spinal cord and brain are the central nervous system.
Axons
The junction of two Schwann cells is called a Node of
Ranvier (arrows). Electrical impulses must jump across the
space between the cells, speeding up the rate of conduction.
Brain
The brain and the spinal cord make up the central
nervous system. In the brain, incoming sensory
information is received and interpreted. A
response leaves the brain and travels down the
spinal cord to peripheral nerves that take motor
impulse to the designated effector organs.
Cerebrum
The cerebrum, the largest region of the brain, is
composed of a right and left hemisphere. The
cerebrum processes conscious thought, complex
movement, sensations, intellect, and memory. A
series of elevated ridges called gyri vastly
increases the surface area of the cerebral cortex.
This convoluted surface allows for the huge
number of cortical neurons required for the
complex functions of the cerebrum.
Cerebrum
Pyramidal cells, like the one shown above, are found at the
surface of the precentral gyrus, in the frontal lobe of the
cerebrum. This is part of the primary motor cortex, whose
neurons control somatic motor neurons of the brainstem and
spinal cord to direct voluntary movements.
Cerebellum
The cerebellum functions in the coordination of
skeletal muscles. The cerebellum receives sensory
information from proprioreceptors about the
position of the joints and the length of muscles. It
also receives information about motor responses
sent by the cerebrum. The cerebellum uses this
information to coordinate muscle movement and
to control balance and posture.
Cerebellum
The surface of the cerebellum is highly fissured. The outer layer is the
molecular layer, which contains some glial cells but consists mostly of
dendrites and unmyelinated axons. The darkly stained area is the
granular layer and is composed mostly of nerve cell bodies of the tiny
granule cells (multipolar neurons that carry impulses to Purkinje cells)
along with some larger Golgi cells. Between the molecular and
granular layers lies the Purkinje layer.
Spinal Cord
WM
GM
CC
The spinal cord is a large tract of nerve fibers and cell bodies. In the
center of the cord is an H-shaped region known as gray matter (GM),
which contains cell bodies. The anterior horns of the gray matter
contain large motor neurons. White matter (WM) surrounds the gray
matter and is composed of myelinated and nonmyelinated axons. A
central canal (CC) runs the length of the spinal cord and contains
cerebrospinal fluid.
Muscle Tissue
Muscle is a contractile tissue. There are
three types of muscle: skeletal, cardiac and
smooth.
Skeletal Muscle
Skeletal muscle is distinguishable by its striations
and its long, unbranched, multinucleate cells or
fibers. The striations are due to the arrangement of
contractile units called sarcomeres, along the
length of the fiber. Skeletal muscle is attached to
bone and is responsible for voluntary movement.
When signaled to contract, all the fibers in a
particular bundle contract. The number and size of
the bundles involved determines the strength of
the contraction.
Skeletal Muscle
Nucleus
Striations are visible. Each fiber runs the entire length of
the muscle. Nuclei can be found around the cell periphery.
Cardiac Muscle
Cardiac muscle makes up the wall of the heart and
is also striated. The cells are branched and usually
contain only one nucleus. Cardiac muscle fibers
are composed of a number of cardiac cells.
Adjacent muscle cells are held together by
intercalated disk. At each disk, the cell membranes
of cardiac muscle cells are intertwined and held
together by gap junctions. Because of these
connections, impulses spread quickly through the
muscular walls of each chamber.
Cardiac Muscle
Striations are evident as well as intercalated disks,
the light bands between cells in each fiber.
Smooth Muscle
Smooth muscle is found in walls of internal organs and
lacks striations. Depending on location, cells of smooth
muscle may be slender and spindle-shaped (gastrointestinal
tract), short and thick (walls of small arteries), or folded
and twisted (walls of large arteries). Generally, smooth
muscle cells are densely packed and are connected where
cells’ projections fit into other cells’ depressions. Smooth
muscle contracts more slowly than skeletal muscle but can
contract for longer periods of time. It is responsible for
involuntary movements.
Smooth Muscle
Arteries
Arteries carry blood away from the heart and have walls
much thicker than veins. Arteries are composed of three
layers. Each layer is called a tunica. The tunica intima (TI)
is the innermost layer and consists of endothelial cells that
rest on a layer of connective tissue. The tunica media (TM)
contains a large amount of smooth muscle and elastic
material. The tunica adventitia (TA), the outermost part,
consists mainly of connective tissue and contains blood
vessels.
Artery
TA
TM
TI
The three layers can be seen in the aorta, the largest artery
in the body. The tunica intima is a relatively thin layer of
endothelial tissue, whereas the tunica media is quite large
and is made up of smooth muscle.
Aorta
The aorta is called an elastic artery because of the
large amounts of elastic material in its walls.
Elastic arteries can expand to hold an increase in
the volume of blood, returning to their previous
size by squeezing the blood out. This arterial
elasticity helps ensure that the blood reaches every
capillary.
Veins
TI
TM
TA
Veins carry blood to the heart. The walls of veins are much
thinner than those of arteries, mostly due to the reduction
in smooth muscle in the tunica media.
Tongue
The tongue is a muscular organ containing skeletal muscle
covered with a mucous membrane. The mucous membrane
consists of stratified squamous epithelium, much of it
containing keratin. Keratin is an insoluble protein that is
also found in fingernails, hair, and skin. Keratinized cells
resist dessication and provide a protective barrier. The
tongue has numerous taste buds that allow us to perceive
flavors. The taste buds are found in the papillae of the
tongue.
Fungiform and Filiform Papillae
Fungiform
Filiform
Fungiform and filiform papillae are shown here. Filiform
papillae occur over the tongue’s entire surface, while
fungiform papillae are more numerous near the tip.
Filiform papillae do not contain taste buds.
Foliate Papillae with Taste Buds
Taste Pore
Gustatory
Cell
Taste Bud
Taste buds are made of several different types of cells. One
type, the gustatory cell, extends slender microvilli, referred
to as taste hairs, through a taste pore, a narrow opening
into surrounding fluids.
Stomach
The stomach is a J-shaped organ that stores food and regulates its entry
into the small intestine. In addition, the stomach secretes digestive
fluid called gastric juice that is mixed with the food by the churning
action of the layers of smooth muscle in the stomach walls. A soupy
mix called chyme results. Gastric juice includes hydrochloric acid and
an enzyme called pepsin. Pepsin helps begin the breakdown of protein.
The acid activates the pepsin enzyme and also kills bacteria that might
have been in the food. The stomach defends itself against its own harsh
internal environment by a coating of mucus, secreted by its lining of
epithelial cells.
Stomach
The wall of the stomach consists of four layers; mucosa,
submucosa, muscularis externa, and serosa. The mucosa is
the innermost layer and contains gastric pits. The surface
of the empty stomach creates folds called rugae. They are
stretched out and disappear when the stomach is full.
Stomach
The surface of the mucosa is made up of simple columnar
mucous cells.
Small Intestine
The small intestine is the longest portion of the digestive tract. Most of
the enzymatic breakdown of macromolecules and most of the
absorption of nutrients occurs here. The duodenum is the first segment
of the small intestine. This portion receives chyme from the stomach as
well as digestive secretions from the liver and pancreas. Most chemical
digestion and absorption occurs in the second segment, called the
jejunum. The third and final segment of the small intestine is the ileum,
which is partially separated from the large intestine by a sphincter.
Smooth muscles within the walls of the small intestine rhythmically
contract to move chyme along the length of the intestine. This
rhythmic contraction is called peristalsis.
Small Intestine
Villi
The small intestine section shown here is from the
mammalian jejunum. The villi are relatively large in the
jejunum. Simple columnar epithelium lines the lumen.
Colon
The function of the colon is the processing of waste and
absorption of water. The colon is a region with closely
packed glands and no villi. The nucleus of these cells lies
near the basal membrane, and the distal portion of the cell
is filled with secretory vesicles.
Liver
The liver is the largest internal organ and has
many diverse functions. It secretes bile, which
functions in the emulsification of fats, into the gall
bladder. It also functions as a storage site for
vitamins, serves as a blood reservoir, and filters
toxins from the body, among other numerous tasks.
The liver is composed of lobules, clusters of cells
arranged in layers radiating like spokes from
central veins.
Liver
CV
Here, in the center of a lobule, the central vein (CV) and
the radiating spokes of cells are easily seen. The light areas
between the rows of cells are sinusoids, vessels similar to
capillaries.
Lung
The lung is the site where oxygen from outside air enters
blood circulation and carbon dioxide, a by-product of cell
metabolism, is taken from blood to be transported to the
outside.
Alveoli, tiny sacs in the lungs, are the functional units of
respiration. Where the gas exchange takes place, the thin
alveolar walls and the thin capillary walls bring the air and
the blood into very close proximity.
Lung Tissue
Aveolus Sac
Aveolus Sac
Cap
Aveolus Sac
The alveoli themselves are spaces. The cells lining the alveolar sacs
are squamous, but the sac walls contain abundant elastic fibers.
Throughout the lungs are capillary beds, closely associated with the
alveolar sacs. A cross section of a capillary (Cap) is seen here,
surrounded by alveolar sacs.
Spleen
The spleen is a highly vascular organ whose primary function is to
filter the blood. The spleen removes abnormal blood cells and other
particles through phagocytosis by white blood cells found there. The
spleen also stores iron, from the red blood cells decommissioned there.
With the large number of lymphocytes present, the spleen is the site of
immune responses by B and T cells activated by antigens circulating in
blood. The spleen contains the largest collection of lymphoid tissue in
the body.
The mass of the spleen is of two types, the white pulp that forms the
splenic nodules, and the red pulp that forms pulp cords and contains
red blood cells.
Spleen
Ovary
The ovaries are the female reproductive organs where eggs
are produced. Each ovary is enclosed by a capsule of
connective tissue and contains many follicles. A follicle
consists of one egg cell, or oocyte, surrounded by layers of
follicle cells that nourish and protect the egg cell. All of a
female’s egg cells are formed before she is born-up to
400,000. Only a fraction of these will be released during
the reproductive years. Starting at puberty and ending at
menopause, usually one follicle matures and is released
during each menstrual cycle. Release of the egg cell from
the follicle is called ovulation.
Ovary
The section shown here is a human ovary section.
A number of maturing follicles can be seen.
Ovarian Follicle
Nucleus
Oocyte
An oocyte can be seen in a mature follicle, also
called a Graafian follicle.
Testis
The testes are the male reproductive organs
in which sperm are produced. The testes are
made up of seminiferous tubules, lined by
cuboidal epithelium. Two types of cells are
present within the tubules. Sertoli cells
provide structure to the tubules and
nutrition to the germ cells. Germ cells give
rise to sperm.
Testis
An outer capsule protects the seminiferous tubules.
Tubules are lined with a highly modified cuboidal
epithelium.
Kidney
The kidneys, ureters, urinary bladder, and urethra comprise
the urinary system. The kidneys have two main functions,
excretory and endocrine. The excretory function is to
remove from the blood the unused products of cellular
metabolism and to help regulate the content, concentration,
and volume of body fluid. The endocrine function is the
production of two important enzymes: renin, which plays a
key role in the regulation of blood pressure and sodium ion
concentration, and erythropoietin, which stimulates
production of red blood cells in bone marrow.
Kidney
The functional unit of the kidney is the nephron, a tubule
closely associated with capillaries in a structure called the
glomerulus. In the glomerulus, the liquid portion of blood
first filters into the nephron. Along with this liquid are
waste products and dissolved substances such as glucose
and sodium. As liquid moves along the nephron, water,
sodium and glucose are reabsorbed into the bloodstream,
while waste products such as urea remain in the tubule.
The tubule empties into a collecting duct that sends the
waste ultimately to the ureter and out of the body.
Kidney
Cortex
Medulla
Pelvis
The renal cortex is the outer region of the kidney and
contains glomeruli. The renal medulla lies next to the
cortex and contains loops of Henle and collecting ducts.
The renal pelvis is continuous with the ureter.
Nephron
Glomerulus
The glomerulus is a meshwork of capillaries surrounded by the Bowman’s
capsule, made up of simple squamous epithelium. Outside the glomerulus are
the proximal and distal convoluted tubules, both lined by simple cuboidal
epithelium.