Tissues

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 + neural2. mesoderm - connective + muscle + some epithelial3. endoderm – organs + some epithelial

Epithelial Tissue

= lining epithelium & glands

•multiple functions of epithelial tissue:1. protection - from dehydration, pathogens2. synthesis3. regulation - e.g. body temperature4. excretion - e.g. waste5. 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 crossan epithelial tissue first-permeability varies from location to location-contain pores, channels, transporters and other machinery requiredfor selective permeability-function can be modified by stimuli

e.g. hormones can increase ion transporte.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. Cellularity2. Polarity3. Attachment

1. to each other2. to connective tissue

4. Avascularity5. Regeneration


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 exteriorof the body - apical face-also has an attached base which is anchored to other tissues - basal face-the organelles are not uniformly distributed

3. Attachment: attached to underlying tissues via the basement membrane


-BM is produced by the basal surface of the cells & connective tissue - comprised ofcollagen type IV and laminin

-the BM is comprised of two layersa. closest to epithelial cell = basal lamina(glycoproteins, laminin and actin)

-acts as a barrier to transport

b. furthest from the epithelialcell = reticular lamina

-collagen IV bundles producedby the underlying connectivetissue cells-provides strength



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



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

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

A. # of layerssimple = 1 layerstratified = multiple**pseudo = 1 layer

B. Cell shapecolumnarcuboidal squamous

• catagorizing epithelial tissue types

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

-stratified squamous - where mechanical stresses are severe

-cells on exposed surfaces (exposed to air) contain keratin - an intermediate filament protein that reduces water loss andprovides strength = keratinized epithelium

-non-keratinized epithelium is tough but must be kept moist

e.g. lining of mouth

Squamous 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 ithas several layers-actual number of layers can be seen upondistension

Transitional Epithelium

Cuboidal Epithelium

-cells are cubes-nucleus is in the center of the cell – very round

-simple cuboidal: regions of secretion and absorptione.g. kidney tubules pancreas & salivary glands – secretion of buffers & enzymes thyroid follicles – secretion of thyroid hormones

-stratified cuboidal: relatively rare-ducts of sweat glands and mammary glands

Cuboidal Epithelium

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

-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 lymphocytesmicrovilli

-stratified columnar: relatively rare-two to multiple layers-only outer layer contains truly columnar cells-protection role

Columnar Epithelium

NOT ON PRACTICAL

Stratified 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

Columnar Epithelium

Pseudostratified

-these tissues are generally ciliated

Type:

Simple squamous

Simple cuboidal

Simple columnar

Pseudostratifiedcolumnar

Stratified squamous

Stratified cuboidal

Stratified columnar

Description:

single layer, flattened cells

single layer, cube-shapedcells

single layer, elongatedcells

single layer, elongatedcells

multiple layers, flattened cells

multiple layers, cube-shapedcells

multiple layers, elongatedcells

Function:

filtration, diffusion, osmosis

secretion, absorption

protection, secretion, absorption

protection, secretion, movement of mucus

protection

protection

protection, secretion

Location:

lungs, linings of bloodvessels

ovaries, kidneys, certainglands

linings of uterus, stomachand intestines

linings of respiratorypassages and reproductive

outer layer of skin, oralcavity, throat

larger ducts of sweat glandssalivary glands and pancreas

vas deferens, parts ofpharynx

• epithelial cells specialized to produce and secrete substances

Glandular Epithelium

•gland = single epithelial cell OR multiple cells

•two types of glands: 1) exocrine = secrete into ductse.g. sweat glands

2) endocrine = secrete directly into bloodstreame.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 types1. serous - watery fluid that contains enzymes

e.g. saliva – parotid salivary gland

•exocrine gland types2. mucous - glycoproteins called mucins that absorb water to form a

slippery mucus

•exocrine gland types3. mixed - more than one type of gland cell

-produces different types of secretions - mucus and serouse.g. submandibular salivary gland

Connective Tissue

• binds structures together

•components: matrix + cells

• provides support

• produces blood

• fills cavities

• protects organs

-matrix: non-cellular support material-comprised of extracellular protein fibers – mainly collagense.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 veryspecialized matrix

-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 substancee.g. proteoglycans

Connective Tissues

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

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 Tissues

D. Macrophages (Fixed): engulf damaged and dead cells by phagocytosis-immune cell-derived from monocytes

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

3. Elastic: primarily made up of the proteins fibrillin & elastin-branching and wavy in appearance

2. Reticular: made of collagen type III -2 collagen III 1 + 1 collagen III 2 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

Connective tissue: fibers

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. Loose2. Dense3. Adipose4. Reticular5. Elastic6. Cartilage7. Bone8. Blood9. Lymph

Type:

Loose connective

Adipose

Reticular

Dense

Elastic

Hyaline cartilage

Elastic cartilage

Bone

Blood

Description:

Cells in fluid-gel matrix





Cells in solid-gel matrix

Cells in solid-gel matrix

Cells in solid matrix

Cells in fluid matrix

Function:

Binds organs together,holds tissues, fluidsProtects, insulates andstoresSupports

Binds organs together

Provides elastic quality

Supports, protects, provides frameworkSupports, protects, provides flexible frameworkSupports, protects, provides frameworkTransports gases, defendsagainst disease, clotting

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

Loose connective tissues: types

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 seee.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 directionse.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

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

Supportive Connective tissues: types-cartilage & bone

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 absorbere.g. intervertebral discs meniscus of the knee

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

Supportive Connective tissues: types

-two types of bone – when the matrix classified by histology1. 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

-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 cellsc. basophils - histamined. neutrophils - 1st at infectione. eosinophils - allergic response

3) platelets - blood clotting response

Fluid Connective tissue: Blood

Membranes

-four types:

1. serous

2. mucous

3. cutaneous

4. synovial

-superficial epithelial sheet + underlying connective layer(called a lamina propria)

-cover & protect

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

-you could confuse dense irregular connective tissue and smooth muscle – so be careful!!

-there are more cells/nuclei in smooth muscle

DENSE

Neural Tissue (Nervous Tissue)

•specialized for the conduction of electrical impulses from one bodyregion to another

1) neurons

2) glial cells

•two types of neural cells:

1) glial cells: astrocytes, oligodendrocytes, microglia

-supportive function to neurons

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

2) neuron:

Tissues

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