Hormones are secreted by :

Question

UnlockIAS · Accepted Answer

Correct — D, Endocrine glands. An endocrine gland is defined by what it lacks: a duct. It releases its product into the surrounding interstitial fluid and from there into the bloodstream, which carries the molecule to distant cells that happen to carry a matching receptor. The Commission's own published remark on this question says exactly that — endocrine glands are ductless glands that secrete hormones directly into the bloodstream — and it then walks the other three options off the page one by one: exocrine glands secrete enzymes through a duct at the target organ, sebaceous glands secrete sebum, and reproductive glands, also called gonads, are a kind of endocrine gland that secretes the male and female sex hormones. The vocabulary is built on the same distinction: 'endocrine' from the Greek endon, within, plus krinein, to separate, against exo, outside. Bloodstream transport is written into the definition of a hormone itself. Ernest Starling coined the word in 1905 from the Greek for 'to arouse or excite', describing hormones as 'the chemical messengers which speeding from cell to cell along the blood stream, may coordinate the activities and growth of different parts of the body'. The human endocrine set is short enough to memorise: the hypothalamus, the pituitary, the pineal, the thyroid, the four parathyroids, the thymus, the two adrenals, the islets of Langerhans embedded in the pancreas, and the gonads — the ovaries and testes. Add the placenta during pregnancy, and a further list of organs that carry endocrine tissue without being called glands: the kidney (erythropoietin, renin, calcitriol), the heart (atrial natriuretic peptide), the stomach and intestine (gastrin, secretin, cholecystokinin), the liver and even adipose tissue (leptin). Every one of those sources answers to the description 'endocrine', and no hormone in the human body comes from anywhere else. That completeness is precisely what the key rewards. Option (d) does not merely contain a true example — it names the whole category to which every hormone-secreting structure in the body, including the gonads of option (b), belongs.

Why the other options are wrong — (a) Sebaceous glands are microscopic EXOCRINE glands of the skin that open into a hair follicle and discharge sebum — roughly 41% triglycerides, 26% wax esters and 12% squalene — by the holocrine route, in which the whole sebocyte ruptures and is secreted along with its contents. They occur on all skin except the palms and soles, and the eyelid's meibomian glands are a specialised type. Crucially they are a TARGET of hormones, not a source: androgens drive them, which is why acne tracks puberty.  (b) Not false — and that is what makes it the real trap on this item. Ovaries and testes genuinely secrete hormones: oestrogen, progesterone, testosterone and inhibin all reach the blood from them. But reproductive glands are a SUBSET of the endocrine glands, not an alternative to them, and the Commission settles it in its own words: gonads 'are a kind of endocrine glands that secrete male and female sex hormones'. UPSC's 2000 matching question does the same thing silently, listing 'Gonads' as the first entry under the heading 'Endocrine glands'. Gonads are also mixed glands, releasing ova and sperm through ducts, so as a category they are both narrower and less pure than (d). Choosing them leaves the pituitary, thyroid, adrenals and islets of Langerhans unaccounted for.  (c) The exact opposite of the answer, and the definitional mirror image. Exocrine glands secrete THROUGH DUCTS on to an epithelial surface or into a body cavity — salivary, gastric, sweat, lacrimal, mammary glands and the pancreatic acini — and their products are enzymes, mucus, milk, tears, sweat and oil, never hormones. It tempts because the pancreas is a mixed gland: its acini are exocrine and pour pancreatic juice down the pancreatic duct, while its islets of Langerhans are endocrine and put insulin and glucagon into the blood. The presence of a duct is the whole test.

Concept: Glands are classified by where their secretion goes, not by what it is. Exocrine glands keep a duct and deliver on to a surface: sweat on to the skin, saliva into the mouth, bile and pancreatic juice into the duodenum, milk through the nipple, tears on to the conjunctiva. They are further sorted by how the cell parts with its product — merocrine, where vesicles fuse with the membrane and the cell survives (salivary glands, sweat glands); apocrine, where the apical part of the cell pinches off; and holocrine, where the entire cell disintegrates into the secretion, the sebaceous gland being the textbook case. Endocrine glands, by contrast, lost their embryonic duct and release into the interstitial fluid and blood. Their products act at extreme dilution, on cells that may be a metre away, and only on cells bearing the right receptor — specificity comes from the receptor, not from the plumbing. Hormones themselves fall into three chemical classes: peptides and proteins (insulin, growth hormone, ADH), steroids derived from cholesterol (cortisol, aldosterone, oestrogen, testosterone) and amines derived from tyrosine (thyroxine, adrenaline). Two organs sit in both camps at once. The pancreas is the standard mixed gland, and the gonads are the other — and it is precisely that dual identity which turns option (b) into a plausible answer rather than an obvious error.

State PCS 2025 Q139 — Science & Technology PYQ with Answer

State PCS 2025 Q139 — Science & Technology PYQ with Answer