TOB: Glandular tissue Flashcards
Define a gland
An epithelial cell or collection of cells specialised for secretion
What does exocrine mean?
Glands with ducts that secrete onto an epithelial surface
What does endocrine mean?
‘Ductless’ glands whcih secrete into the bloodstream
Give an example of a unicellular gland and where it can be found
Goblet cell in the upper respiratory epithelium, tubular colonic crypts and epithelium of the intestinal villus.
What is the mucocilliary escalator?
The action of trapping particles and bacteria in mucous in the respiratory tract and moving it with the cillia back up to the oropharynx where it is swallowed
What is the mechanism by which cystic fibrosis sufferers get pulmonary infections?
- The ion channel CFTR is not present in the apical membrane of the epithelial cells of individuals with cystic fibrosis.
- Therefore chloride ion transport across the membrane is substantially compromised.
- Therefore the mucous lining the surface of the epithelial tract is not as rich in Na+ and Cl- ions and therefore not enough water leaves the epithelial cells to adequately hydrate the mucus.
- The mucous becomes more viscous and less readily moved to the oropharynx for swallowing.
- Therefore the respiratory tract is less able to remove particles and bacteria, so infection is more likely to occur.
What affects can cystic fibrosis have on the gastrointestinal tract?
Viscous mucus in the GI tract can cause:
- meconium ileum in newborns: inability to pass first faeces
- In older CF suffered can lead to constipation and invagination of parts of the GI tract
What do mucous glands secrete and how do they stain with H&E?
Their secretions are rich in Mucins (hgihly glycosylated polypeptides).
They stain poorly with H&E sections.
What do serous glands secrete and how do they stain with H&E?
Their secretions are often rich in enzymes, are watery and free of mucus.
They are eosinophilia (pink) in H&E sections.
Describe the mechanism of merocrine secretion. Give an example of a gland that secretes this way.
THIS IS THE SAME AS EXOCYTOSIS!
- Membrane bound component approaches cell surface
- Bounding membrane fuses with the plasma membrane
- Contents are in continuity with the extracellular space
- Plasma membrane transiently larger
- Membrane retrieved, stabilising cell surface area
Majority of glands secrete this way: apocrine (merocrine despite name) sweat glands in the axillae, areolar of nipples and genital and perineal regions. Eccrine sweat glands
Describe the mechanisms of apocrine secretion. Give an example of an apocrine gland that secretes this way.
Non-membrane bounded structur (e.g. Lipid) approaches cell surface. It makes contact and pushed up the apical membrane. A thin layer of cytoplasm drapes around the droplet. The membrane surrounding the droplet pinches off from the cell. Cell membrane is transiently smaller, so membrane added to regain original area.
Example: Apocrine secretion of fat droplet during lactating mammary glands.
Why do individuals with CF have salty sweat?
The absence of the CFTR molecule in the apical membrane of epithelial cells lining the duct of the sweat gland, results in poor reabsorption of chloride ions. As a result sweat is rich in chloride and sodium ions.
Describe the mechanism of holocrine secretion. Give an example of a gland that secretes this way.
- Disintegration of cell
- Release of contents
- Discharge of whole cell
E.g. Sebaceous glands undergo holocrine secretion, to fill hair follicles with sebum.
Describe the mechanisms of endocytosis
Engulfing material initially outide cell. Opposite of EXOCYTOSIS (merocrine secretion)
Describe how endocytosis and secretion combine to give transepithelial transport
- Material endocytosed at one surface
- Transport vesicles shuttles across cytoplasm
- Material exocytosed at opposite surface
NB: This is a good way of shunting across molecules that are too big to penetrate the membrane.
NB2: Vesicle contents can be changed in this process.
