Epithelial Cells Flashcards
What is the difference between simple and stratified epithelia?
Simple = one cell-layer thick. Stratified = more than one cell-layer thick.
Define epithelial cells.
Sheets of contiguous (adjacent) cells of varied embryonic origin which cover the external surface of the body and line internal surfaces.
What is the basement membrane, what is it’s role and position.
A thin, flexible acellular layer between epithelial cells and the subtending connective tissue (basal lamina and reticular fibrils).
Cellular and molecular filter e.g. tight junctions in gut prevent food particles slipping between epithelial cells.
Where are simple squamous epithelia located, and how does that relate to function?
Endothelium of blood & lymphatic vessels (barrier).
Mesothelium of serous body cavities (lubrication & barrier).
Alveoli epithelium (gas exchange, lubrication, barrier).
Bowman’s capsule/Loop of Henle (active transport).
Where are simple cuboidal epithelia located, and how does that relate to function?
Thyroid follicles (hormone synthesis, storage & mobilisation). Kidney tubules (absorption & conduit). Exocrine gland ducts (absorption, secretion & conduit). Surface of ovary (barrier/covering).
Where are simple columnar epithelia located, and how does that relate to function?
Stomach lining (absorption) & gastric glands (secretion & conduit).
Microvilli of small intestine & colon (absorption).
Gallbladder (conduit).
Exocrine gland ducts (secretion & conduit).
Oviducts (transport).
Testes’ ductuli efferentes (transport).
Uterus.
Where are pseudostratified epithelia located, and how does that relate to function?
Nasal cavity, trachea & bronchi lining (mucus secretion, particle trapping = muco-ciliary escalator). Tear duct (secretion). Ductus deferens & epididymis (secretion, conduit & absorption). Excretory ducts (secretion & conduit).
Where are stratified, non-keratinised squamous epithelia located, and how does that relate to function?
Oral cavity, oesophagus, larynx.
Vagina, anal cavity.
Surface of cornea, inner surface of the eyelid.
(protection against abrasion, reduces water loss whilst still remaining moist).
Where are stratified, keratinised squamous epithelia located, and how does that relate to function?
Surface of the skin.
Limited distribution in oral cavity.
(protection against abrasion and trauma, prevention of water loss, regulating heat loss, shields against UV damage, barrier to microbes).
Where is transitional epithelia located, and how does that relate to function?
Ureter/urethra/bladder (distensibility and protection of underlying tissues from toxic chemicals).
Why do the rates of renewal of epithelia differ?
Depends on location & function, accelerated with injury.
Epidermis: 28 days basal layer -> keratinisation -> sloughed off
Small intestine: 4-6 days (replaced by regenerative cells in Crypts of Lieberkuhn).
Where are microvilli found and what is their function?
Apical finger-like extensions which increases the surface area for selective absorption and secretion.
Brush border of the small intestine.
Where are stereocilia found and what is their function?
Elongated microvilli.
Epididymal epithelium.
Function not confirmed.
Where are cilia located and what is their function?
Elongated, mobile extensions of plasma membrane and cytoplasm. Move material across cells surface.
Trachea and bronchi, oviduct.
What is the difference between metaplasia and neoplasia?
Metaplasia = reversible conversion from one differentiated epithelia to another
e.g. Barrett’s oesophagus: stratified squamous —> simple columnar + goblet cells
Neoplasia = permanent change resulting from disease
