MLT GlobeChemistry: Endocrinology
123 Chemistry MCQs on Endocrinology with answers and explanations.
Lack of vitamin D produces soft, poorly mineralised bone. In children and adults this is called, respectively:
Deficient calcitriol reduces calcium and phosphate absorption, impairing mineralisation of osteoid: rickets before growth plates close, osteomalacia afterwards.
A 39-amino-acid peptide from the anterior pituitary that drives cortisol secretion by the adrenal cortex is:
ACTH is a 39-residue peptide cleaved from POMC in anterior pituitary corticotrophs. Glucagon (29 residues) and insulin are pancreatic; oxytocin is a posterior pituitary nonapeptide.
Endemic goitre in inland mountain regions is caused mainly by dietary deficiency of:
Without iodine the thyroid cannot make enough hormone; rising TSH enlarges the gland. Iodised salt prevents this. Copper metabolism relates to Wilson disease, not goitre.
Calcitriol acts as a hormone on three main target tissues to raise plasma calcium. Which are they?
1,25-dihydroxyvitamin D increases intestinal calcium absorption, mobilises bone calcium with PTH, and increases renal calcium reabsorption.
Which pineal hormone, made mainly in darkness, helps set the circadian sleep–wake rhythm?
The pineal gland makes melatonin from serotonin at night. Light suppresses it through the suprachiasmatic nucleus.
Which pancreatic cells release insulin, together with C-peptide in equal molar amounts?
Beta cells cleave proinsulin into insulin and C-peptide. C-peptide shows endogenous secretion and helps separate insulinoma from factitious insulin use.
Oxytocin mainly causes contraction of smooth muscle in which organ?
Oxytocin drives uterine contractions in labour and myoepithelial contraction for milk ejection. It has little effect on gut or vascular smooth muscle.
Which hormone comes from the anterior pituitary?
Somatotrophs release GH, which drives IGF-1 production in the liver. Adrenaline, insulin and thyroxine come from the adrenal medulla, pancreas and thyroid.
Which hormone drives the acute 'fight or flight' response to sudden danger?
The adrenal medulla releases adrenaline within seconds of sympathetic activation. It raises heart rate, blood pressure and blood glucose.
Which effect is NOT caused by adrenaline?
Through beta-1 receptors adrenaline speeds the heart, through beta-2 it dilates bronchi, and it mobilises glucose. Bradycardia is a vagal (cholinergic) effect.
Which hormone is the main mineralocorticoid, causing sodium retention and potassium loss?
Aldosterone from the zona glomerulosa acts on principal cells of the collecting duct. Cortisol is the main glucocorticoid.
Which is the largest purely endocrine gland in an adult?
The thyroid weighs about 15–25 g and wraps around the trachea. The adrenals are about 4–5 g each and the pituitary under 1 g.
Which secretion is released through a duct (exocrine), not into the blood?
Salivary glands empty through ducts into the mouth. Oxytocin, thyroxine and vasopressin are hormones released into the bloodstream.
A morning cortisol sample is requested. At what time is plasma cortisol normally highest?
Cortisol peaks soon after waking and is lowest around midnight. Loss of the midnight low (raised late-night salivary cortisol) suggests Cushing syndrome.
Thyroid hormones are made by iodinating residues of which amino acid within thyroglobulin?
Thyroid peroxidase iodinates tyrosyl residues to MIT and DIT, which couple to form T3 and T4. Thyroglobulin is also a tumour marker after thyroidectomy.
Which single test is the most sensitive first-line screen for primary thyroid dysfunction?
Small changes in free T4 cause large log-linear changes in TSH, so TSH becomes abnormal first. Guidelines recommend TSH first, then reflex free T4.
Calcitonin from thyroid C-cells lowers the blood level of which ion?
Calcitonin inhibits osteoclasts and lowers serum calcium. Clinically it is used as a tumour marker for medullary thyroid carcinoma.
A woman has galactorrhoea and amenorrhoea, and MRI shows a pituitary microadenoma. Which hormone is most likely raised?
A prolactinoma is the commonest functioning pituitary adenoma. High prolactin suppresses GnRH, causing amenorrhoea and galactorrhoea.
Which condition is LEAST likely to cause hyperthyroidism?
Loss of pituitary TSH causes central (secondary) hypothyroidism. Graves disease, thyroiditis in its release phase and toxic nodules all cause thyrotoxicosis.
Which gland is often called the 'master gland' because its trophic hormones control several other endocrine glands?
The anterior pituitary releases TSH, ACTH, FSH, LH and GH, which regulate the thyroid, adrenals, gonads and liver. It is itself controlled by the hypothalamus.