BPSC 71st CCE Prelims General Studies · Question 139 of 150

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.

• (a)Sebaceous glands — 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)Reproductive glands — 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)Exocrine glands — 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.

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.

Work the stem's verb, then the set relations. 'Hormones are secreted by' asks for the source category of hormones in general, with no restriction to a system or a sex. Two options can be discarded on definition alone: exocrine glands are defined by having a duct and by not producing hormones, and sebaceous glands are one named example of exactly that class. That leaves a contest between (b) and (d) which is not a contest about truth — both statements are true — but about set membership. Reproductive glands are inside the endocrine category; the endocrine category is not inside them. When two options are both true and one is a proper subset of the other, an unrestricted stem takes the superset, because the subset leaves most of the phenomenon unexplained: pick 'reproductive glands' and you have no account of insulin, thyroxine, cortisol, ADH or growth hormone. Had the stem read 'Testosterone is secreted by', the subset would have been the answer. The single discriminating fact is therefore the word 'ductless' — it is what defines the class the question is really naming, and it is what the Commission's remark states. One further exam-craft point: BPSC scores +1 for a right answer and, under its own booklet instruction 9, −1/3 for a wrong one, so on a two-way subset/superset choice like this, marking the broader category is both the better physiology and the better arithmetic.

• Endocrine glands are ductless and release hormones directly into the interstitial fluid and blood, which carries them to distant target cells bearing specific receptors; exocrine glands retain a duct and deliver enzymes, mucus, sweat, milk or oil on to a surface or into a cavity.
• Ernest Starling coined 'hormone' in 1905 from the Greek for 'to arouse or excite', defining hormones as chemical messengers travelling by the bloodstream to coordinate distant parts of the body. Secretin, isolated by William Bayliss and Starling in 1902, is conventionally called the first hormone identified, though Oliver and Schäfer's adrenal extract of 1894 — containing adrenaline — has the earlier claim.
• The human endocrine glands are the hypothalamus, pituitary, pineal, thyroid, four parathyroids, thymus, two adrenals, the islets of Langerhans of the pancreas and the gonads, joined by the placenta in pregnancy; the kidney (erythropoietin, renin, calcitriol), heart (atrial natriuretic peptide), gut (gastrin, secretin, cholecystokinin) and adipose tissue (leptin) also carry endocrine tissue.
• The pancreas is the standard mixed gland — exocrine acini sending digestive juice down the pancreatic duct, endocrine islets of Langerhans putting insulin and glucagon into the blood. The gonads are mixed in the same way: gametes leave through ducts, steroid hormones enter the blood.
• Sebaceous glands are microscopic exocrine glands opening into hair follicles; sebum is about 41% triglycerides, 26% wax esters and 12% squalene, released holocrine so the sebocyte itself ruptures. They occur on all skin except the palms and soles, the eyelid's meibomian glands being a specialised variety, and they respond to androgens rather than producing any hormone.

• Treating 'reproductive glands' as wrong. They are right but incomplete — they are one member of the endocrine class, and they are also exocrine because gametes leave through ducts
• Forgetting that the pancreas is a mixed gland, and so concluding that exocrine glands must sometimes make hormones. The acini make juice, the islets make insulin; only the islets are endocrine
• Confusing a hormone target with a hormone source. Sebaceous glands, hair follicles and the endometrium all respond to hormones without secreting any

BPSC asks the classification itself in four bare words and plants a subset among the options, so the mark turns on recognising a set relationship rather than on recalling a fact. UPSC never asks it that flat. It goes one level finer — matching Gonads, Pituitary, Pancreas and Adrenal to progesterone, growth hormone, insulin and cortisone in 2000; asking which endocrine gland functions independently of the pituitary in 1997; asking which hormone regulates blood calcium and phosphate in 2007. Learn the category for BPSC and the gland-hormone table for UPSC.

• practice — not a real PYQ

  Which one of the following is a mixed gland, having both exocrine and endocrine functions?

  • (a)Thyroid gland
  • (b)Pancreas
  • (c)Parathyroid gland
  • (d)Pineal gland

  Answer(b) Pancreas — its acini are exocrine and pour pancreatic juice into the duodenum through the pancreatic duct, while the islets of Langerhans are endocrine and release insulin and glucagon into the blood. The thyroid, parathyroid and pineal are purely endocrine.

• practice — not a real PYQ

  The essential difference between an endocrine gland and an exocrine gland is that an endocrine gland

  • (a)secretes only proteins, while an exocrine gland secretes only lipids
  • (b)has no duct and releases its secretion directly into the blood
  • (c)is found only in the abdominal cavity
  • (d)is controlled by nerves, while an exocrine gland is not

  Answer(b) has no duct and releases its secretion directly into the blood — that is the defining criterion. Both kinds secrete substances of varied chemistry, both occur throughout the body, and both can be under nervous or hormonal control; only the presence or absence of a duct separates them.