anat and phys lecture 5

function of epithelial tissue

a structural barrier/boundary for inside and outside of the body

physiological processes: absorption, secretion, diffusion

characteristics of epithelial tissue

• avascular: no blood vessels are present in the epithelial tissue so epithelial tissue must be close enough to blood vessel in order for oxygen and nutrients to diffuse

• innervative: receives nervous innervation

• highly regenerative: undergoes mitosis rapidly, regenerates from below

fluid/fibers of epithelial tissue

• fluid: epithelial cells are always close together and often mechanically attached through desmosomes and tight junctions - little fluid

• fibers: very little fibers

desmosomes

spanning between two cells fibers (cell adhesion molecules) tether them together but there is enough space in between cells to allow for molecules to pass through

• more common

tight junctions

proteins (cell adhesion molecules) hold neighboring cells together but the gap between the neighboring cells is not big enough to material to move between cells (often found in the brain as a form of protective mechanism to limit what gets into the brain)

• not common

apical/basal surface

• apical surface: the surface of the epithelial cell that is oriented towards the air/liquid

• basal surface: the surface of the epithelial cell that is oriented/attached to the basal membrane

basement membrane

anchors epithelial tissue to connective tissue

• basement lamina: at least one layer of epithelial cells are attached to

• reticular lamina: layer of connective tissue, connects skin directly/indirectly to muscle or bone

simple squamous

function: diffusion and filtration

• found in the alveoli of lung, inner layers of the blood vessel, lining of the heart

simple cuboidal

function: absorption and secretion

• found in the nephrons of the kidney

  • nephrons are tubes with hallowed space called lumen and the lumen is filled with liquid and the walls of the nephron is simple cuboidal

• fluid of bloodstream is pushed into the nephron

• simple cuboidal cells absorb useful nutrients and water from the filtrate in the lumen (absorption) and return them back into the blood stream (secretion)

simple columnar

function: absorption and secretion

• only found in the digestive tract (cells lining the stomach, small and large intestine)

• because there is fluid inside the intestine there must be epithelial tissue present (simple columnar)

• microvilli are on top of columnar cells to increase surface area and to allow cell to absorb more nutrients and other substances

• pinocytosis occurs as simple columnar cells move materials out of the intestine and deposit them to underlying connective tissue

intestine

inner surface of the intestine folds to create more surface areas (the folds are called villas and villae)

• small intestine: absorbs nutrients

• large intestine: absorbs water

pseudostratified columnar

function: trapping and moving material

• unique characteristics of pseudostratified columnar are that the cells that reach the apical surface are ciliated (hair like projections and motor proteins on top of the cell to allow cell to mechanically move things)

• located in the respiratory tract

stratified squamous

function: protections

• located on body in areas that need protection and places that experience friction

stratified cuboidal

function: more protection than absorption since multiple layers and secretion

glandular epithelial tissue is always stratified cuboidal: cells that secret often die so there must be a population

structural stratified cuboidal: only in the ureter of the urinary system

• ureter is constantly pushing liquid from kidney to the bladder so it must be stratified

stratified columnar

function: more protection than absorption since multiple layers and secretion

located in the urethra of the urinary system (moves bladder to the outside world) and ducts of exocrine glands

• ducts connect glands to another part of the body and fluid is moving in the duct