Endocrine physiology
Practice questions with explanations

C. Glucagon, promoting hepatic glycogenolysis and gluconeogenesis

Glucagon from pancreatic alpha cells is the primary short-term defence against hypoglycaemia, and its response is often lost in long-standing type 1 diabetes, leaving adrenaline as the main protection. GLP-1 agonists suppress glucagon in a glucose-dependent way, contributing to their effect without causing hypoglycaemia.

D. Negative feedback, in which the hormone or its effect inhibits its own further release

Negative feedback keeps hormone concentrations within a range: rising cortisol suppresses ACTH and CRH, rising thyroid hormone suppresses TSH. Positive feedback exists but is rare and self-limiting, the classic example being the oestrogen surge that triggers the LH surge before ovulation. Understanding the loop is what allows a raised TSH with a low T4 to be read as glandular failure rather than pituitary disease.

A. Suckling and TRH stimulate it, while dopamine from the hypothalamus tonically inhibits it

Prolactin is unique among anterior pituitary hormones in being under tonic inhibition: dopamine travelling down the portal system suppresses it continuously. Anything that blocks dopamine — antipsychotics, metoclopramide, domperidone — raises prolactin and can cause galactorrhoea, amenorrhoea and reduced libido. Conversely dopamine agonists such as cabergoline treat prolactinoma. A stalk lesion also raises prolactin by cutting off the inhibition.