Epithelia Flashcards
What epithelia are derived from ectoderm?
Epidermis, corneal epithelium.
Define epithelia
Sheets of contiguous cells of varied embryonic origin which cover the external surfaces of the body and line internal surfaces.
What epithelia are derived from mesoderm?
Epithelium of urogenital tract.
Endothelium of blood and lymphatic vessels.
Pericardial and pleural dad lining.
Peritoneal lining.
What epithelia are derived from endoderm?
Epithelial lining of GI tract.
Epithelial lining of respiratory tract.
Many glands - thymus, salivary, thyroid.
Epithelium of liver.
What is basement membrane?
Thin acellular layer, lies between epithelia and subtending connective tissue.
Consists of a basal lamina laid down by epithelial cells - type four collagen and laminin
And lamina reticularis - type three collagen - elaborated by connective tissue
What is the function of the basement membrane?
Cellular and molecular filter.
Surface for cells to adhere to.
What implication does penetration of the basement membrane by malignant cells have?
Highly relevant to prognosis.
Where might simple squamous epithelia be found?
Glomerulus; arteriole, venule, lymphatics, capillaries (endothelium); lining pericardium, peritoneum, pleural sac (mesothelium); alveoli; loop of henle; inner and middle ear.
What are the functions is simple squamous epithelia?
Lubrication - pleural sac, pericardium, peritoneum.
Gas exchange
Barrier
Active transport - mesothelium and endothelium. (Pinocytosis)
Where is simple cuboidal epithelia found?
Collecting ducts in kidney.
Thyroid follicles
Ducts of many exocrine glands (pancreas)
Surface of ovary (germinal epithelium)
What is the function of the epithelium covering the ovary?
Barrier and covering.
What is the function of the epithelia in the thyroid?
Hormone secretion, storage and mobilisation.
What is the function of the epithelia in the kidney tubules?
Absorption and secretion.
What is the function of epithelia in the ducts of exocrine glands?
Absorption and conduit.
Where is simple columnar epithelium found?
Lining the crypts of Lieberkuhn, small intestine and colon.
Lining of stomach and gastric glands.
Lining the gall bladder
Striated duct of parotid gland
Fallopian tube - some cells ciliated, and uterus.
Large ducts of exocrine glands including striated duct of parotid gland.
Ductuli efferentes of testes.
What is the function of the simple columnar epithelium in the gall bladder?
Removes water and electrolytes, reduces volume of bile.
What is a striated duct?
Characterised by infoldings of basal membrane - basal portion of each cell is striated.
What makes saliva hypotonic?
Removal of sodium ions
What is the zonula occludens?
Two adjacent plasma membranes bound tightly together by occludin.
What is the function of the zonula occludens?
Segregation of membrane proteins to apical/lateral/basal surface.
Separate lumen and intercellular space - control the movement of fluid across the epithelium.
What can disrupt the zonula occludens?
Cholera toxins.
What connective tissue is found in the villi of the small intestine?
Lamina propria.
What is a lacteal?
Dilated lymphatic vessel.
What is the function of the simple columnar epithelium in the small intestine and colon?
Absorption, secretion, lubrication.
What is the function of the simple columnar epithelium in the gall bladder?
Absorption
What is the function of the simple columnar epithelium in the stomach and gastric glands?
Secretion
What is the function of the simple columnar epithelium in the fallopian tube?
Transport of oocyte (ciliated)
Where is pseudostratified epithelium found?
Upper respiratory tract - nasal cavity, trachea, bronchi. Epididymis and ductus deferens. Lacrimal sac. Large excretory ducts. Auditory tube and tympanic cavity.
What cells are present in the epididymis?
Basal cells - stem cells.
Proncipal cells - absorb fluid, and secrete substances that promote sperm maturation, phagocytose degenerate sperm and residual bodies.
What cell surface modifications are present in the pseudostratified epithelium of the epididymis?
Stereocilia
What happens to sperm as they pass through epididymis?
Sperm mature and acquire motility
How long is the epididymis?
4-6m - highly coiled!
What cell surface modifications are found in the pseudostratified epithelium of the respiratory tract?
Cilia
What specialised cells are found in the pseudostratified epithelium f the upper respiratory tract? What is their function?
Goblet cells - secrete mucous.
What frequency do the cilia beat at?
12hZ
Where is stratified squamous epithelium found?
Vagina, oral cavity, oesophagus, larynx, part of anal canal, surface of cornea, inner surface of eyelid.
What is the function of stratified squamous non keratinised epithelium?
Protection.
Reduces water loss but remains moist.
How does the vagina maintain a low pH?
Cells are rich in glycogen which is a substrate for lactobacilli, which produce lactate.
What happens to the epithelial cells of the vagina in the absence of hormonal stimulation - pre puberty and post menopausal?
Atrophy.
Where is stratified squamous keratinised epithelium found?
Skin.
Limited distribution in oral cavity.
What is the function of stratified squamous keratinised epithelium?
Protect against UV, abrasion.
Prevents water loss.
Physical barrier to microbes.
Where is transitional epithelium found?
Bladder, ureters, urethra, renal calyces.
What is the function of transitional epithelium?
Protect underlying tissues from toxins.
Distends.
What is the time from cell division to being sloughed off for a cell in the epidermis?
28 days.
What is the time from cell division to being sloughed off for a cell in the small intestine?
4-6 days.
What is the function of microvilli?
Increase cell surface area for diffusion/active transport.
