MLT GlobePhysiology: Endocrine physiology – page 2
40 Physiology MCQs on Endocrine physiology with answers and explanations.
Which islet cells secrete somatostatin, which inhibits both insulin and glucagon release?
Delta cells make somatostatin, a local inhibitor of other islet hormones. Alpha cells make glucagon, beta cells insulin, and PP cells pancreatic polypeptide.
An obese adult has high fasting glucose despite raised insulin levels, because insulin receptor number and signalling are reduced. This fits:
Type 2 diabetes is driven by insulin resistance, including fewer or less responsive receptors. Type 1 is autoimmune loss of beta cells; diabetes insipidus involves ADH, not insulin.
Compared with nervous signalling, endocrine signalling typically has:
Hormones travel in the blood and act over minutes to days, often on widespread targets. Neurones act within milliseconds at specific synapses.
Which effect is NOT produced by cortisol?
Cortisol is a counter-regulatory hormone that raises glucose via gluconeogenesis, protein catabolism and lipolysis. Excess cortisol can therefore cause hyperglycaemia.
Which hormone acts mainly through an intracellular receptor rather than a G-protein coupled receptor?
Aldosterone is a lipid-soluble steroid that binds cytoplasmic mineralocorticoid receptors and alters gene transcription. Epinephrine, histamine and muscarinic acetylcholine signal via GPCRs.
In a patient with high cortisol levels, what happens to amino acid release from skeletal muscle?
Glucocorticoids promote muscle protein breakdown, releasing amino acids for hepatic gluconeogenesis. This explains muscle wasting in Cushing syndrome.
What is the main role of thymosin?
Thymosin, from thymic epithelial cells, supports T-cell maturation. The thymus involutes after puberty, so its hormone output declines with age; it is unrelated to the thyroid or spleen.
Which organ produces hormones even though its primary role is immunological rather than endocrine?
The thymus is chiefly a lymphoid organ for T-cell development but secretes thymosins, a secondary endocrine function. The other glands are primarily endocrine.
Which action is attributed to calcitonin?
Calcitonin, from parafollicular C cells, inhibits osteoclasts and lowers blood calcium. Raising calcium and enhancing renal reabsorption are parathyroid hormone actions.
The fetal thyroid begins secreting its own thyroid hormones at about which stage?
The fetal thyroid starts trapping iodine and producing T4 around 10–12 weeks (third month); before this the fetus depends on maternal thyroxine.
In a healthy adult, the thyroid gland weighs approximately:
The normal adult thyroid weighs about 15–25 g. Substantially heavier glands indicate goitre.
When collecting samples for a circadian study, which hormone reaches its lowest level around midnight?
ACTH and cortisol peak in the early morning and are lowest near midnight. GH, TSH and prolactin rise during the night or sleep.
A child has proportionate short stature, normal intelligence and delayed bone age. Which deficiency best explains this?
Childhood GH deficiency causes proportionate pituitary dwarfism with normal intellect. Congenital hypothyroidism causes short stature with intellectual impairment; somatostatin deficiency would increase GH.
An adolescent's height gain stops when the epiphyseal plates fuse. Which hormone is chiefly responsible for plate closure in both sexes?
Oestrogen, including that made from testosterone by aromatase, drives epiphyseal fusion in both sexes; aromatase-deficient men keep growing. Growth hormone promotes growth rather than fusion.
Besides the kidney, aldosterone also increases sodium reabsorption in which epithelium?
Aldosterone acts on distal colon, sweat and salivary gland ducts as well as the renal collecting duct, conserving Na+ and excreting K+.
Binding of insulin to its receptor first activates which process?
The insulin receptor is a tyrosine kinase; insulin binding makes it phosphorylate itself, then insulin receptor substrates, triggering downstream signalling such as GLUT4 translocation.
Glucagon binds a G-protein-coupled receptor on hepatocytes. Which enzyme does this directly activate?
Glucagon activates Gs, which stimulates adenylyl cyclase to make cAMP; protein kinase A then promotes glycogenolysis and gluconeogenesis.
Hormones acting via Gq-coupled receptors generate diacylglycerol and inositol trisphosphate by activating:
Phospholipase C splits membrane PIP2 into IP3, which releases Ca2+ from the ER, and DAG, which activates protein kinase C. Phospholipase A2 releases arachidonic acid.
After a high-protein meal glucagon rises. Which amino acid is a particularly strong stimulus for glucagon secretion?
Arginine and alanine strongly stimulate alpha cells. The glucagon prevents hypoglycaemia that insulin released by the same meal could otherwise cause.
Signalling through which receptor depends on ligand-induced dimerization and JAK2 activation?
The GH receptor is a cytokine-type receptor; GH binding brings two receptor molecules together, activating JAK2–STAT signalling. The others are GPCRs or ion channels.