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Tissues
-four primary tissue types:
1. Epithelial
2. Connective
3. Muscle
4. Neural
-however: all tissues in the body develop from three germ layers
1. ectoderm - epithelial + neural
2. mesoderm - connective + muscle + some epithelial
3. endoderm – organs + some epithelial
Epithelial Tissue
= lining epithelium & glands
•multiple functions of epithelial tissue:
1. protection - from dehydration, pathogens
2. synthesis
3. regulation - e.g. body temperature
4. excretion - e.g. waste
5. immune response
• lining epithelium = line body surfaces and cavities
• glandular epithelium = secretion
Lining Epithelium Functions
1. Physical protection: are found on exposed surfaces of the body
-protection from abrasion, dehydration, and entrance by toxins
2. Control permeability: every substance that enters the body must cross
an epithelial tissue first
-permeability varies from location to location
-contain pores, channels, transporters and other machinery required
for selective permeability
-function can be modified by stimuli
e.g. hormones can increase ion transport
e.g. stress can alter the physical structure and thus permeability
3. Sensitivity: innervated by sensory nerves
-many epithelial tissues can detect differences in the environment
(e.g. heat, pressure)
-convey these changes to the nervous system
-one type of specialized sensory epithelium = neuroepithelium
-found in special sense organs (ear, eyes, tongue)
Epithelial characteristics
1. Cellularity
2. Polarity
3. Attachment
1. to each other
2. to connective tissue
4. Avascularity
5. Regeneration
Epithelial characteristics
1. Cellularity: composed almost entirely of cells held together by cell
junctions
-very little extracellular matrix
2. Polarity: possesses an exposed surface the faces the exterior
of the body - apical face
-also has an attached base which is anchored to other tissues basal face
-the organelles are not uniformly
distributed
Epithelial characteristics
3. Attachment: attached to underlying tissues via the basement membrane
-BM is produced by the basal
surface of the cells & connective
tissue - comprised of
collagen type IV and laminin
-the BM is comprised of two layers
a. closest to epithelial cell = basal lamina
(glycoproteins, laminin and actin)
-acts as a barrier to transport
b. furthest from the epithelial
cell = reticular lamina
-collagen IV bundles produced
by the underlying connective
tissue cells
-provides strength
Epithelial characteristics
characteristics
Epithelial
1. Tight junctions: lipid portions of PMs are
bound together by interlocking membrane
proteins
-very tight union - prevents passage of
water and solutes between the two cells
3. Attachment: also form extensive connections between each other
Epithelial characteristics
characteristics
Epithelial
2. Gap junctions: two cells held together
by proteins called connexons
-connexons are channel
proteins
-materials can freely move between
the two cells
-passage of materials helps to
coordinate the activities of the two
cells
e. g beating rhythm of cilia
3. Desmosomes: comprised of cellular
adhesion proteins/CAMs and proteoglycans
-also form plaques and contain cadherins
-the plaque attaches to the intermediate
filaments of the cytoskeleton (keratin)
-several types known: belt, hemi, button
-hemidesmosome: attaches the cell to the
basement membrane of the tissue
-link to a basement membrane protein =
laminin
Epithelial characteristics
4. Avascularity: do not contain blood vessels
-must obtain nutrients via diffusion or absorption
5. Regeneration: damaged cells are replaced through differentiation of
stem cells located deep within the tissue
-rate of renewal depends on rate of cell death
-stem cells = germinative cells
-these cells are found closest to the basement membrane
-migrate towards the surface and differentiate
Classification of Epithelia
• catagorizing epithelial tissue types
A. # of layers
simple = 1 layer
stratified = multiple
**pseudo = 1 layer
B. Cell shape
columnar
cuboidal
squamous
Simple Epithelium
-relatively thin
-cells have the same polarity - nuclei are generally aligned
-very fragile - cannot provide mechanical/physical protection
-line internal compartments
-relatively permeable - absorptive surfaces, secretion, filtration
Stratified Epithelium
-thicker due to multiple layers
-found in areas subject to mechanical and chemical stress
e.g. skin, mouth
-tougher than simple epi.
-organelles do not align
Pseudostratified Epithelium
-appears to be stratified
-yet the basal surface of every cell contacts basement membrane
-apical surface of the cells may possess cilia (ciliated epithelium)
-often has glandular epithelial cells embedded in it - cells secrete mucus
-found lining absorptive organs
e.g. respiratory epithelium
Squamous Epithelium
-tile-like cells - cells are thin, flat and
irregular in shape
-cells interlock like tiles
-simple squamous - most delicate
tissue in the body
-found in protected regions
-many types: mesothelium - lines
ventral body cavity
(i.e. peritoneum of the
abdomen)
endothelium - lines
heart and vessels
Squamous Epithelium
-stratified squamous - where
mechanical stresses are severe
-cells on exposed surfaces
(exposed to air) contain keratin an intermediate filament protein
that reduces water loss and
provides strength = keratinized
epithelium
-non-keratinized epithelium is
tough but must be kept moist
e.g. lining of mouth
Transitional Epithelium
-permits stretching
-located in walls of the bladder, renal pelvis and the ureters
e.g. bladder wall - when empty the epi. looks as if it
has several layers
-actual number of layers can be seen upon
distension
Cuboidal Epithelium
-cells are cubes
-nucleus is in the center of the cell – very round
-simple cuboidal: regions of secretion and absorption
e.g. kidney tubules
pancreas & salivary glands – secretion of buffers & enzymes
thyroid follicles – secretion of thyroid hormones
Cuboidal Epithelium
-stratified cuboidal: relatively rare
-ducts of sweat glands and mammary glands
NOT ON PRACTICAL
Columnar Epithelium
-height is greater than their width
-nuclei is close to the BM
-simple columnar: provides some protection
-also in areas of absorption and secretion
Simple columnar epithelium
microvilli
-usually lines organs involved in secretion
and absorption
-located in the gallbladder, larger ducts of
exocrine glands, gastric pits of stomach,
lining of the small intestine
-basally located nuclei aligned with one
another
-frequently the apical face is modified
with cellular extensions
e.g. microvilli – intestinal lining
= brush border
-short-lived cells – replaced every 4 to 5
days
-frequently found with Goblet cells
(intestine and stomach)
wandering lymphocytes
Columnar Epithelium
-stratified columnar: relatively rare
-two to multiple layers
-only outer layer contains truly columnar cells
-protection role
NOT ON PRACTICAL
Stratified columnar epithelium
Columnar Epithelium
-pseudostratified columnar: only a single layer
-every cell contacts the BM
-nuclei are at varying levels - appearance of multiple layers
-exposed apical surface typically bears cilia
e.g. respiratory epithelium
Pseudostratified
-these tissues are generally ciliated
Type:
Description:
Function:
Simple squamous
single layer, flattened cells
filtration, diffusion, osmosis lungs, linings of blood
vessels
single layer, cube-shaped
cells
secretion, absorption
ovaries, kidneys, certain
glands
single layer, elongated
cells
protection, secretion,
absorption
linings of uterus, stomach
and intestines
single layer, elongated
cells
protection, secretion,
movement of mucus
linings of respiratory
passages and reproductive
multiple layers, flattened
cells
protection
outer layer of skin, oral
cavity, throat
Location:
Simple cuboidal
Simple columnar
Pseudostratified
columnar
Stratified squamous
Stratified cuboidal
Stratified columnar
protection
multiple layers, cube-shaped
cells
multiple layers, elongated
cells
protection, secretion
larger ducts of sweat glands
salivary glands and pancreas
vas deferens, parts of
pharynx
Glandular Epithelium
• epithelial cells specialized to produce and secrete substances
•gland = single epithelial cell OR multiple cells
•two types of glands: 1) exocrine = secrete into ducts
e.g. sweat glands
2) endocrine = secrete directly into bloodstream
e.g. thyroid, pituitary
** one gland is mixed - e.g. pancreas
•exocrine gland structure:
• Unicellular: single-celled glands
e.g. goblet cells
•Multicellular glands – multiple cells grouped together
•Can be classified based on:
•1. Mode of secretion
•Merocrine
•Apocrine
•Holocrine
•2. Consistency of secretion
•Serous
•Mucus
•Mixed
•3. Structure
•shape of the secretory portion
•branching pattern of the duct
• simplest multi-cellular gland is a secretory sheet
•e.g. gastric epithelium
SIMPLE COLUMNAR with GOBLET CELLS
-goblet cells = unicellular exocrine glands that secrete mucus
•exocrine gland types
1. serous - watery fluid that contains enzymes
e.g. saliva – parotid salivary gland
•exocrine gland types
2. mucous - glycoproteins called mucins that absorb water to form a
slippery mucus
•exocrine gland types
3. mixed - more than one type of gland cell
-produces different types of secretions - mucus and serous
e.g. submandibular salivary gland
Connective Tissue
• provides support
• binds structures together
• fills cavities
• produces blood
• protects organs
•components: matrix + cells
-matrix: non-cellular support material
-comprised of extracellular protein fibers – mainly collagens
e.g. 1. collagen fibers (white) – type I
2. elastic fibers (yellow)
3. reticular fibers – collagen type III
4. fibronectin
-plus a ground substance = water + hyaluronan (sugar),
proteoglycans and glycoproteins
-cells: secrete the matrix
-some have become very specialized and make a very
specialized matrix
Connective Tissues
-cell types found in connective tissues:
A. fibroblasts: immature cell type found in basic connective tissues
-secrete the extracellular matrix
-secrete main component of matrix = collagens
-also produce hyaluronan = glycosaminoglycan (sugar)
that gives the ground substance a viscous quality
-also produces the other components of the ground substance
e.g. proteoglycans
B. adipocytes: mature cell type of adipose tissue
-more specialized type of fibroblast – fat storage
-fill with lipid upon maturation
C. melanocytes: synthesize and secrete melanin
-dark, brown pigment that absorb light
Connective Tissues
D. Macrophages (Fixed): engulf damaged and dead cells by phagocytosis
-immune cell
-derived from monocytes
E. free macrophages: wander rapidly through the connective tissue
-called monocytes when circulating in blood
F. mast cells: another immune cell
-synthesize and secrete histamine - inflammation response
-synthesize and secrete heparin - inflammation response
G. lymphocytes - immune cells (T and B cells)
-differentiate into plasma cells (type of B cells) - antibodies
-differentiate into T cell subtypes - assist B cells
Connective tissue Matrix fibers: collagen, reticular and elastic
1. Collagen fibers: long, straight and unbranched fibers made of CN type I
-very concentrated and dense in tendons and ligaments
-long chains of collagen protein subunits forming a triple helix
-these helices are wound together - “rope” or a bundle = fibril
-fibrils are then stacked together = collagen fiber
-triple helix – three subunits = 2 alpha 1 chains + 1 alpha 2 chain
e.g. CNI - 2 chains of CNIa1 and one chain of CNIa2
-there are nineteen types of collagen in the body = 80-90% are CNI, CNII,
CNIII & CIV
Connective tissue: fibers
2. Reticular: made of collagen type III
-2 collagen III a1 + 1 collagen III a2 subunits = reticular fiber
-reticular fibers interact in a different way – 3D network rather than
bundles
-thinner than collagen type I fibers - more flexible
-abundant in the walls of hollow organs
-form a supportive stroma (3D network) that supports
the functional cells of these organs
3. Elastic: primarily made up of the proteins fibrillin & elastin
-branching and wavy in appearance
Classification
Embryonic: first to appear = mesenchyme
-derived from mesoderm germ layer
-cells are star-shaped
-matrix - fine protein filaments
-Mucus connective tissue - jelly-like, many regions of embryo
The way I organize Connective
tissues
•
•
•
•
Loose – areolar CT, fat & reticular
Dense – dense (regular, irregular), elastic
Supportive – bone & cartilage
Fluid – blood (& lymph)
Types:
1. Loose
2. Dense
3. Adipose
4. Reticular
5. Elastic
6. Cartilage
7. Bone
8. Blood
9. Lymph
Type:
Description:
Loose connective Cells in fluid-gel matrix
Function:
Adipose
Cells in fluid-gel matrix
Reticular
Cells in fluid-gel matrix
Binds organs together,
holds tissues, fluids
Protects, insulates and
stores
Supports
Dense
Cells in fluid-gel matrix
Binds organs together
Elastic
Cells in fluid-gel matrix
Provides elastic quality
Hyaline cartilage
Cells in solid-gel matrix
Elastic cartilage
Cells in solid-gel matrix
Bone
Cells in solid matrix
Blood
Cells in fluid matrix
Supports, protects,
provides framework
Supports, protects,
provides flexible framework
Supports, protects,
provides framework
Transports gases, defends
against disease, clotting
Loose connective tissues: types
1. Loose Areolar tissue
-cells: are mainly fibroblasts, spaced far apart
-matrix: sparse collagen I fibers, elastic fibers, mostly ground substance
-cushions and can be distorted due to loose organization
e.g. beneath the dermis
2. Adipose tissue = fat
-cells: adipocytes (fat storing fibroblasts)
-matrix: small amounts in between the adipocytes (mainly CNIV)
-cushions joints and organs
-stores energy
-insulates
liposuction: suction assisted lipoplasty
-removal of SQ fat
3. Reticular tissue:
-matrix: thin collagen III/reticular fibers woven into a 3D network
– fibers are secreted by reticular cells (specialized fibroblasts)
-supports walls of certain organs – e.g. liver, spleen, lymph nodes
e.g. liver, spleen
NOT ON PRACTICAL
Dense connective tissues: types
-most of the tissue is densely packed extracellular matrix fibers of
collagen type I
-often called fibrous or collagenous tissue
-type types: 1) dense regular – densely packed collagen I and elastic fibers
e.g. tendons, ligaments
2) dense irregular - interwoven meshwork of fibers of CNI and
elastic
-e.g. dermis of skin, perichondrium of joints
and periosteum of bone
1. Dense Regular:
-cells: few fibroblasts
- matrix: multiple, closely packed collagen fibers – collagen type I
-PLUS - fine network of elastic fibers – harder to see
e.g. tendons, ligaments
1. Dense Irregular:
-cells: few fibroblasts
- matrix: similar to dense regular but with little to no organization
-gives the tissue strength and flexibility in multiple directions
e.g. dermis of the skin
Dense irregular tissue
• Found in the deepest
layers of the dermis =
also called the reticular
layer (don’t confuse it
with reticular tissue)
2. Elastic:
-yellow, elastic fibers in parallel or branching networks
-walls of larger vessels, airways, hollow organs
NOT ON PRACTICAL
Supportive Connective tissues: types
-cartilage & bone
1. Cartilage:
-cells = chondrocytes
-matrix = collagen fibers embedded in a gel-like
ground-
substance
-collagen type II
-ground substance - water + proteoglycans
-proteoglycans - protein + sugars
e.g. chondroitin sulfate
glucosamine
-functions in support, attachment, protection
-in developing child - model for future bone
(endochondral bone)
-avascular tissue - produces anti-angiogenic
chemicals (inhibits growth of blood vessels)
-therefore diffusion is the main mode of transport
Proteoglycan
-3 types: 1) Hyaline - most common
- “glass”
- ends of bones, within joints (synovial, articular),
- end of nose, supports respiratory passages
2. Elastic - flexible cartilage
- external ears and parts of larynx
3. Fibrocartilage - very tough -> more collagen fibers
- shock absorber
e.g. intervertebral discs
meniscus of the knee
Supportive Connective tissues: types
2. Bone = osseous tissue
-most rigid connective tissue
-cells = osteoblasts, osteocytes
-matrix = collagens, proteoglycans, other specialized bone proteins
-secreted by osteoblasts – as an unmineralized matrix = osteoid
-mineralized as the cells mature into osteocytes
-cells are held in lacunae
-matrix is laid in concentric circles = lamellae
-if lamellae surrounds a central canal = Haversian canal, containing vessels
-two types of bone – when the matrix classified by histology
1. Compact - shaft of long bones, outer layer of short, flat
and irregular bones
-very dense appearing bony matrix
-matrix is made up of units called osteons
2. Spongy - ends of bones, middle layer of short, flat
and irregular bones
-thin bars or “plates” (called trabeculae) of bone
separated by irregular spaces filled with red marrow
-lighter than compact – yet stronger
Fluid Connective tissue: Blood
-cells suspended in a fluid matrix = plasma
-plasma ~ 55% blood volume
-inorganic salts
-organic substances - e.g. sugars, proteins
-cells: 1) RBCs - biconcave, disc-shaped
-contains hemoglobin - 4 globin proteins
+ heme group (iron)
2) WBCs - fight infection
= leukocytes
- many types: a. monocytes/macrophages
b. lymphocytes - T and B cells
c. basophils - histamine
d. neutrophils - 1st at infection
e. eosinophils - allergic response
3) platelets - blood clotting response
Membranes
-superficial epithelial
sheet + underlying
connective layer
(called a lamina
propria)
-cover & protect
-four types:
1. serous
2. mucous
3. cutaneous
4. synovial
Muscular Tissue
•specialized for contraction
•very distinct organelles within the cells
•3 types
•1. skeletal – voluntary muscle
•2. cardiac – involuntary muscle
•3. smooth – involuntary muscle
3 types:
1) striated/skeletal – voluntary nervous control
-repeating banding patterns of actin & myosin = striated
appearance
-mature cells = multi-nucleated cells – made from fusion of
hundreds of muscle cells called myocytes
-cells are very long – sometimes called muscle fibers
-cannot divide – but new cells form from differentiation of myogenic
stem cells = satellite cells
-attached to bones via tendons
3) cardiac - involuntary control
- only found in heart
-cells are striated but uninuclear =
cardiomyocytes
-incapable of dividing – PLUS there are
no satellite cells
-therefore damaged heart muscle cannot
be regenerated
-cells are connected end to end by
intercalated discs
-these discs are areas of communication
between cardiomyocytes through gap
junctions
-the discs also help channel the forces of
contraction
2) smooth – involuntary control
-lines blood vessels, airways and organs
-non-striated
-control their own rate of contraction
through action of pacemaker cells
-nervous system can also control
contraction
-slow, sustained contraction
-spindle shaped cells - single
nucleus/uninucleated
-many types of smooth muscle cells found
in many organs (i.e. not the same in every
organ)
-many kinds of smooth muscle cells
incapable of division – no stem cells
SMOOTH
DENSE
-you could confuse dense irregular connective tissue and smooth muscle – so
be careful!!
-there are more cells/nuclei in smooth muscle
Neural Tissue (Nervous Tissue)
•specialized for the conduction of electrical impulses from one body
region to another
•two types of neural cells:
1) neurons
2) glial cells
1) glial cells: astrocytes, oligodendrocytes, microglia
-supportive function to neurons
2) neuron:
cell body, dendrites, axon with an axon terminal
-therefore cell has polarity
-dendrite receives and/or generates signal
-cell body = soma
-axon - conducts the nerve impulse
-forms a synapse with: another neuron or a muscle cell