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.
How are newly synthesised proteins glycosylated in the Golgi apparatus?
The Golgi apparatus consists of stack of cisternae. Glycosylation occurs in the cisternae as the newly synthesised proteins are transported from the RER to the cis- end (C-shaped) of the Golgi body and through the cisternae by pinching off as migratory Golgi vesicles.
What are the 3 Golgi product destinations?
- Majority extruded in secretory vesicles
- Some retained for use in cells (e.g. Lysosomes)
- Some enter the plasma membrane (glycocalyx)
List the functions of the Golgi apparatus
- Sorts proteins into different compartments
- Packages through condensation of contents
- Adding sugars to proteins and lipids (glycosylation)
- Transport of resultant vesicles
What are the two pathways for exocytosis in the Golgi apparatus?
- Regulated secretory pathways
2. Constitutive secretory pathways
In which direction do vesicles travel through the Golgi apparatus?
From cis- to trans-
Glycosylation gives proteins branched sugars and offers complex shapes that can give them specific interactions in the glycocalyx. List some of these functions
- Adhesion to substrates and neighbouring cells
- Mobility of cells
- Communication with neighbouring cells
- Contact inhibition of movement and division
How can secretions be controlled?
- Nervous control - e.g. Sympathetic NS stimulation of adrenal medullary cells to release adrenaline.
- Endocrine control - ACTH stimulates the cortex of adrenal glands to secrete cortisol.
- Neuro-endocrine control - e.g. Nervous cells of the hypothalamus control ACTH secretion from the anterior pituitary
- Negative feedback chemical mechanism - e.g. T3 and T4 negatively feedback to the anterior pituiatry inhibiting synthesis of TSH.
What type of secretions does the parotid gland make?
Serous NOT mucous or mixed
What type of secretions does the submandibulary gland make?
Mixed: serous and mucus
NB: Look out for serous demilunes
What type of secretions does the sublingual gland make?
Mainly mucus but some serous secretions, therefore some serous demilunes can be seen
Describe an artifact that is seen in submandibulary and sublingual glands?
Serous demilunes are artefactual. In reality the mucous and serous secreting cells are mixed together in the Acinus.
Why is the exocrine section of the pancreas affected more than the endocrine section by cystic fibrosis?
The secretions of the exocrine pancreas contain too little water resulting in the ducts becoming blocked-> pancreatitis and malabsorption in the gut.
The endocrine pancreas does not have ducts and therefore deteriorates more slowly.
What do chief cells secrete?
PTH - parathyroid hormone
Name the three distinctive cell types in the parathyroid
Chief cells, oxyphil cells
(Few found near centre) and adipose cells.
Where is thyroglobulin synthesised?
In the follicle cells - simple cuboidal epithelium -surrounding the colloid.
Where is T3 and T4 synthesised in the thyroid?
By oxidative coupling reactions in the colloid.
Name a hormone that undergoes transepithelial transport in the thyroid
T3 and T4 are endocytosed from the colloid, tranported across the cell in vesicles and then exocytosed, to then travel into capillaries.
Name two hormones secreted by the adrenal medulla?
Adrenaline and noradrenaline
Name the three zones of the adrenal cortex from superficial to deep and what they secrete
- Zona glomerulosa - mineralocorticoids (aldosterone)
- Zona fasiculata - glucocorticoids (cortisol)
- Zona reticulares - sex hormones/ gonadocorticoids
