HISTO - DM

Question 1

Explain the role of the venous portal system in the pituitary gland (5) Answer

Answer 1

Different embryonic origins for anterior & posterior pituitary (1)

Axons from hypothalamus terminate in upper pituitary stalk (median eminence) (1)

Secreted Hypothalamic neurohormones are taken up into capillary plexus (1) and transported from the neural lobe to the anterior pituitary (1) to regulate the release of anterior pituitary hormones (1).

Question 2

In a table, compare the histological features between an inactive and highly active state of the thyroid [3]

Answer 2

Follicles are large and filled with colloid (1)

Follicles are variable in size with numerous resorption vacuoles (1)

Principal cells are squamous/low cuboidal (½)

Principal cells are tall (½)

Question 3

Name the endocrine gland (other than the pituitary) and the specific region/s of the gland involved in both the acute and chronic stress responses (2)

Answer 3

Adrenal gland, cortex/zona fasciculata and medulla

Question 4

State the route/mechanism by which the cells above receive their stimuli and name the hormones released by these cells (3) [adrenal cortex and medulla]

Answer 4

Cells of the adrenal cortex receive signals (Adrenocorticotropic hormone (ACTH)) via the blood from the pituitary to release cortisol (1½)

Adrenal medullary cells are stimulated to release their hormones (epinephrine/norepinephrine) via direct neuronal signalling (arising from the hypothalamus) via preganglionic nerve endings in the adrenal medulla (1½)

Question 5

Name three (3) cells that make up the endocrine pancreas and outline their functions (6)

Answer 5

• Beta cells produce insulin which is secreted after intake of a meal/ raised blood glucose/ stimulation from the vagal nerve.
• Alpha cells secrete glucagon in response to low blood glucose/ increase in serum arginine and alanine/ stimulation of the parasymphatetic nervous system.
• Delta cells produce somatostatin which negatively regulates glucagon and insulin secretion in a paracrine manner, and also secretes gastrin which stimulates HCl secretion in the stomach.
• PP cells (F cells) secrete pancreatic polypeptide that inhibits the secretion of somatostatin and inhibits the secretion of pancreatic digestive enzymes.

Question 6

Name two (2) pancreatic hormones that regulate glucose homeostasis via the endocrine route and state their main action/function (2x1½ = 3)

Answer 6

Insulin: Cellular uptake of glucose (via Glut 4 receptors)

Glucagon: Increases hepatic glycogenolysis (subsequent release of glucose into the blood).

Question 7

State the role of somatostatin in the Islets of Langerhans (1½)

Answer 7

Inhibits/ reduces glucagon and insulin release

Question 8

State by which signalling route somatostatin acts on islet cells (½)

Answer 8

Paracrine

Question 9

Name two other anatomical locations where somatostatin is synthesised and secreted (1)

Answer 9

Hypothalamus, gut epithelium

Question 10

List two (2) functions of pancreatic polypeptide and state by which signalling route each of these functions act (3)

Answer 10

Inhibits somatostatin secretion – paracrine signalling

Inhibits secretion of pancreatic enzymes and bile from gall bladder – endocrine route

Question 11

Name the biochemical class of hormones produced by the cells of the islets of Langerhans and name the typical intracellular feature that is associated with cells producing these class of hormones (1)

Answer 11

Peptide hormones – membrane bound secretory vesicles

Question 12

Briefly discuss the integrated mechanisms that are involved in regulating pancreatic islet function (5)

Answer 12

Involves integrated neural (autonomic), paracrine, autocrine, vascular signals/ direct parasympathetic and parasympathetic signalling of alpha and beta cells. Regulation of vascular flow via Innervation of arterioles - regulates intra-islet blood flow - important for vascular-based signals (e.g. glucose).

Paracrine signalling: Provide one example e.g. glucagon released from alpha cells assist with regulation of insulin release: somatostatin regulates insulin release (reduces rate) & inhibits glucagon release; Insulin from β-cells regulates nearby α-cells.

Autocrine e.g. this can occur by the release of secretory products such as neuropeptides (glutamate) from alpha cells to stimulate glucagon release. Also insulin and glucagon act on beta and alpha cells respectively via autocrine feedback.

Question 13

If you could “see” inside a type 1 diabetic’s pancreas, would his islets contain beta cells or not? Explain your answer (1)

Answer 13

No, beta cells would have been destroyed by the immune system.