Epithelial Cells Flashcards
1
Q
What is the polarity in epithelial cells?
A
- Epithelial cell membrane organisms into discrete domains by formation of junctions
- This membrane polarity key to generating a distinct polarity with an apical domain at the lumen (open) surface and a basolateral domain
- The basal surface in contact with the extracellular matrix
- The membrane between these two surfaces where membranes of adjacent cell appose each other, is the lateral membrane
- Most epithelial functions are directional e.g. secure, fluid and sill transport and absorption and these processes are highly organised
- Epithelial polarity is required to give the directionality needed for epithelial function
- Polarity in epithelial cells is seen as diff region ion of the cell surface being different from one another, with discretely organised cellular contents
- Pumps and channels need to be polarised, can achieve directional flow and flow only
- Polarity needed for secretion as usually only secrete one way either in apical or basal aspect (if secrete both way could be catastrophic)
2
Q
What are secretory epithelium?
A
- In tissues main purpose secretion, epithelium often arranged in tubules and glands of varying complexity
- In may epithelial tissues, individual, dispersed secretory cells can be present in epithelium
- Exocrine secretion (into duct or lumen)
- Endocrine (into bloodstream)
- Pancreas carries out both exocrine and endocrine secretory functions
- Also classify on way they secrete
3
Q
What are the different ways they secrete?
A
- Constitutive: secretory vessels as they are formed move directly to the palms membrane and relate their contents e.g production of plasma proteins by hepatocytes (constitutive endocrine secretion)
- Stimulated: secretory vesicles are soured in cytoplasm and only fuse with the plasma membrane to release their contents e.g. the release of adrenaline from cells of adrenal medulla after a fight-or-flight stimulus (stimulated endocrine secretion); when stomach contents enter the duodenum, pancreatic acinar cells are stimulated to relate their digestive enzymes into ducts (stimulated exocrine secretion)
4
Q
What is epithelial proliferation?
A
- Cell that are lost by cell death or mechanical removal e.g. abrasion are replaced by proliferation fo stem cells within epithelium
1. Cells in intestinal crypts replacing cells lost from the tips of intestinal villi
2. Cells of the basal layer of stratified squamous epithelia dividing to replace cells lost form the surface
5
Q
What is the epithelial turnover in small intestine like?
A
- As cell marked cell migrates up the villus epithelium new cells constantly being procured by th e crypt stem cells to replace the cells constantly being lots from the villus tip
- Inhibition of the proliferation of intestinal crypto cells e.g. in cancer chemotherapy results in loss of finger-like intestinal villi and flattening of the intestinal mucosa
- This is responsible for many of gastro-intestinal disturbances that are side effects of chemo
6
Q
What is the epithelial turnover like in the epidermis?
A
- Epidermis is the keratinising stratified squamous epithelium of our body surface
- Surface cells constantly lost but are replace dby new cells formed in basal layer which migrate up while undergoing programme of differentiating that mentally leads to them flattening out and keratinising
- Hyper proliferation results in increased cell numbers and thickening of cell layers (can begin response to repeated or constant pressure) - if increase in cell production greater than cell loss from cell surface, cells accumulate form this heard layer e.g. corns or hard skin
- Infectious agents as well like papilloma virus induces hyperproliferation by jijack cellular machinery of stratified squamous epithelia and inducing increased cell proliferation result in surface grow e.g. a wart
7
Q
What are some cell-cell junctions in epithelia?
A
- Tight junctions (sealing gap between cells)
- Adherence junction
- Desmosomes
- Gap junction (channel forming)
8
Q
What are epithelial cells?
A
- Epithelial cells make organized, stable cell-cell junctions
- Transport, absorption, secretion, protection
9
Q
What is an example of simple squamous?
A
Lung alveolar, mesothelium, endothelium
10
Q
What is an example of simple cuboidal?
A
Kidney collecting duct
11
Q
What is an example of simple columnar?
A
Enterocytes
12
Q
What is an example of Stratified squamous?
A
Epidermis, lining of mouth/anus/cervix/vagina
13
Q
What is an example of pseudostraitifed?
A
Upper airway (bronchi) epithelium
14
Q
What is the transporting function of epithelial cells?
A
- Plasma membrane have high conc. of ion transporters
- Mitochondria closely associated with extensive basal membrane infoldings
- Infoldings ion and water pump density
15
Q
What are the absorptive function of epithelial cells?
A
- Found on brush-border membranes – enterocytes, kidney PCT cells
- Secretory cells interspersed through absorptive cells
