Glands Flashcards
What is the general definition of a ‘gland’?
A gland is a collection of epithelial cells which together has been functionally specialised for secretion.
What is the difference between an endocrine and an exocrine gland?
An endocrine gland is a ductless gland which functions to secrete substances into the blood stream. Examples include the thyroid, adrenals and endocrine pancreas. An exocrine gland is a collection of epithelial cells which secretes the substances into a duct, destined for the external environment. Examples include the salivary glands, sweat glands and the exocrine pancreas.
What is a unicellular gland?
A single celled secretory unit, the main example is the goblet cell, interspersed within epithelia for the production of mucus. Such areas include the intestines, stomach and trachea.
What are the crypts of Lieberkuhn?
The crypts of Lieberkuhn are invaginations between the villi of the intestinal tract. They extend into the mucosa down to the muscularis mucosa. Cells located writhing these crypts include stem cells, goblet cells and Paneth cells (cells which secrete antimicrobial proteins for immune defence, mainly defensins).
What is a ‘simple’ gland as opposed to a ‘compound’ gland?
A simple gland is one whose structure does not involved branching of their ducts. They can have one of more gland structures coming of them, secreting into a single duct. For instance, they may be simple tubular, simple coiled, simple branched tubular, simple alveolar and simple branched alveolar.
What is a ‘compound’ gland as opposed to a ‘simple’ gland?
A compound gland is one whose ducts branch. They can be compound tubular, alveolar or tubuloalveolar.
What is the difference between a mucus and a serous gland?
A mucus gland secretes substances rich in mucins, which do not stain well using H/E stains so appear pale. Serous glands secrete a more watery substance, often rich in enzymes, which stain better so appear darker.
Describe the three mechanisms of secretion
- Merocrine - exocytosis of intracellular secretory vesicles in which the two membranes fuse, releasing the contents into the duct or blood. This is the most common mechanism, with examples including the thyroid, pancreas and apocrine + eccrine sweat glands.
- Apocrine - formation of a secretory vesicle in which the intracellular substance to be secreted buds off from the cell. The main example is the mammoth gland secretion during lactation.
- Halocrine - the breakdown of the cell membrane in order to release the cellular contents. The main example include the sebaceous gland of the pilosebaceous units.
Describe the mechanisms by which secretion can be regulated.
Endocrine control, for instance through a hypothalamic pituitary axis such as the HPG or HPT axes.
Nervous control, for instance secretion of oxytocin or ADH through nervous innervation from the hypothalamus, or of chromaffin cells in the secretion of adrenalin.
Negative feedback control, such as that involved in thyroid hormone secretion.
Describe the histological difference between the three major paired salivary glands.
Parotid glands are entirely serous and so appear as well stained acini and a simple columnar duct.
Submandibular glands are mixed seromucus glands which main secrete serous fluid but have some mucus function. They therefore appear as poorly stained acini and well stain serous demilunes.
Sublingual glands are mixed glands but almost entirely mucus secreting. As such they appear as poorly stained acini.
What is the underlying pathology involved in system fibrosis
Cystic fibrosis is an autosomal recessive condition characterised by an absence or deficiency of function CFTR proteins. The CFTR protein is expressed in epithelial cells of the pancreatic ducts, respiratory tract, digestive tract and uterine tubes/vas deferens. A dysfunctional CFTR protein results in reduced chloride, sodium and water movement into secretions, creating an abnormally thick secretion which can trap pathogens and block tubes. In skin there is a reduced reputable of chloride back into cells, causing salty sweat.
What is the normal function of the CFTR protein?
It normally functions to allow passage of chloride ions out of the cell into secretions, creating an electrical gradient for the moment of sodium ions into the secretions, followed by water. This hydrates secretions for normal thickness and function. This is relevant to areas such as the reproductive tract (I.e. Uterine tubes/vas), respiratory tract, digestive tract and pancreatic ducts.
