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TISSUES

TISSUE--collection of specialized cells and cell products that perform a specific function

--four primary types:

--epithelia; 3 % body weight

--connective tissue; 45% body weight

--muscle; 50% body weight

--neural tissue; 2%

 

1) EPITHELIA

a) WHERE IT'S FOUND

--any surface exposed to the world: skin

--any internal tract that communicates with the outside world: digestive, repiratory, reproductive, and urinary tracts

--lining of internal cavities: dorsal & ventral internal cavities, eye, inner ear, blood vessels

 

b) FUNCTION

--physical protection: from abrasion, dehydration, chemical and biological agents

--permeability: every substance that enters or leaves the body or passes from one cavity to another must pass through epithelia

--epithelia control the movement of substances; some are more permeable than others

--provide sensations

--secretion; epithelia compose glands

--exocrine glands--products travel through ducts outside the body; sweat, milk, digestive enzymes, mucus, oil, wax

--some are unicellular (such as the goblet cells which secrete mucus); others are multicellular

--endocrine glands--ductless; hormones are secreted for the control of metabolism

c) CELL SPECIALIZATIONS

--junctions: most cells are firmly attached to other cells or extracellular protein fibers; cells can be linked by a number of junctions:

--basement membrane: glues epithelia to the connective tissue beneath

--epithelial cells therefore have polarity: the basal surface is attached to the basement membrane while the apical surface faces the body cavity or body exterior

--high reproductive rate: since cells are always being lost to digestive enzymes, abrasion, microbes, etc., worn out cells must constantly be replaced

--avascular: nutrients must diffuse through interfacial canals


--frequently have microvilli (fingerlike extensions of the cell membrane that increase surface area; found in digestive and urinary tracts), cilia (respiratory tract, fallopian tube, uterus, paranasal sinuses, & central canal of spinal cord), sterocilia (hair cells in ear)

--microvilli can increase a cell's surface area 20x for absorption and secretion

 

EPITHELIA

A) Simple Squamous Epithelium: single layer of flat cells, disk-shaped nucleus; located in regions which allow diffusion and filtration; LUNG SLIDE; in the fourth photo the glomerular capsule (on the kidney slide) is composed of simple squamous epithelium)

LUNG LUNG
LUNG

B) Simple Cuboidal Epithelium: single layer of boxlike cells with round nucleus; located in areas that allow secretion and absorption

CUBOIDAL CUBOIDAL
CUBOIDAL

C) Simple Columnar Epithelium: single layer of rectangular cells with oval nucleus; located in areas that allow secretion and absorption

SIMPLE COLUMNAR EPITHELIUM SLIDE; this epithelium lines the lumen of the digestive tract cross section; this epithelium is non-ciliated

--also seen on Ciliated Columnar Epithelium demo slide from oviduct

MONKEY INTESTINE:

COLUMNAR COLUMNAR
COLUMNAR COLUMNAR

D) Stratified Squamous Epithelium: several layers of cells; basal layers are cuboidal or columnar while superficial cells are squamous; functions in protection

--ESOPHAGUS SLIDE; these cells are non-keratinized

STRATIFIED SQUAMOUS STRATIFIED SQUAMOUS
STRATIFIED SQUAMOUS STRATIFIED SQUAMOUS

--PALMAR SKIN SLIDE

--the superficial layer of stratified squamous epithelia is keratinized

SKIN SKIN
SKIN

E) Other

--Pseudostratified Columnar Epithelium on TRACHEA SLIDE

--not really stratified; note the cilia which sweep mucus to the mouth and the goblet cells (one celled exocrine glands which secrete the mucus)

PSEDUOSTRATIFIED PSEDUOSTRATIFIED

--Transitional Epithelium on Bladder Demo Slide

--the cells can be distended (appearing cuboidal when relaxed, squamous when stretched) and occur in parts of the urinary tract that require distention

--Relaxed:

TRANSITIONAL TRANSITIONAL
TRANSITIONAL
                Stretched:
Stretched: Stretched: