Which one of the following hormones increases the heartbeat in mammals?
- (a)Insulin
- (b)Melatonin
- (c)Thyroxine
- (d)Adrenaline
Correct — D, Adrenaline. Adrenaline (epinephrine) is secreted by the medulla of the adrenal glands and is the hormone of the fight-or-flight response. Released in situations of anger, fear or danger, it speeds up the heart rate and strengthens each beat, raises blood pressure, widens the airways and shifts blood towards the skeletal muscles, so the body is ready for sudden effort.
- (a)Insulin — Insulin comes from the beta cells of the pancreas and lowers blood glucose by helping cells take glucose up. It has no role in driving up the heart rate.
- (b)Melatonin — Melatonin is secreted by the pineal gland and regulates the sleep-wake cycle. It is associated with settling the body down for sleep, not with speeding the heart up.
- (c)Thyroxine — Thyroxine from the thyroid gland sets the body's overall metabolic rate, and a long-term excess of it does push the resting heart rate up. But it is not the hormone responsible for the direct, immediate rise in heartbeat that this question describes — that is adrenaline's job.
Hormones are chemical messengers made by endocrine (ductless) glands and carried in the blood to distant target organs. Each adrenal gland sits like a cap on top of a kidney and has two parts; the inner medulla makes adrenaline and noradrenaline, the chemicals that produce the body's emergency response.
The trap here is thyroxine, because students remember that it 'controls metabolism' and that metabolism has something to do with the heart. Sort the options by their headline job — insulin for glucose, melatonin for sleep, thyroxine for metabolic rate, adrenaline for emergencies — and only one of them has a fast, direct action on the heart.
- Adrenaline is secreted by the adrenal medulla, the inner part of the adrenal gland that caps each kidney.
- Adrenaline drives the fight-or-flight response — faster and stronger heartbeat, higher blood pressure, wider airways and more blood sent to skeletal muscles.
- Insulin comes from the pancreas and lowers blood glucose; thyroxine comes from the thyroid, contains iodine and sets the metabolic rate.
- Melatonin is produced by the pineal gland and regulates the sleep-wake cycle.
- A threat is sensed — anger, fear or danger
- The adrenal medulla, on top of the kidney, releases adrenaline into the blood
- Adrenaline reaches the heart and the blood vessels
- Heart beats faster and harder, blood pressure rises, airways widen, blood is diverted to the muscles
Adrenaline is carried by the blood from the adrenal medulla to the heart, which is why the response is fast and body-wide.
- Picking thyroxine because it also affects the heart — the question asks which hormone increases the heartbeat, and that is adrenaline's direct action.
- Confusing hormones of the adrenal cortex, such as cortisol, with adrenaline from the adrenal medulla.
A one-line hormone-to-function match, using the four most examined hormones — insulin, melatonin, thyroxine and adrenaline — as options.
Match the hormones in List I with items in List II and select the correct answer using the codes given below the Lists: List I — I. Adrenaline, II. Estrogen, III. Insulin, IV. Pheromones; List II — A) Anger, fear, danger, B) Attracting partners through sense of smell, C) Females, D) Glucose
- (a) I-C, II-A, III-D, IV-B
- (b) I-A, II-C, III-B, IV-D
- (c) I-A, II-C, III-D, IV-B
- (d) I-C, II-A, III-B, IV-D
Answer(c) I-A, II-C, III-D, IV-B
UPSC pairs adrenaline directly with 'anger, fear, danger' — the fight-or-flight situations in which the hormone is released and the heartbeat rises. The same question also separates insulin (glucose) from the rest.
Thyroid gland produces a hormone called "Thyroxine" which
- (a) controls blood glucose levels.
- (b) controls ovulation.
- (c) controls metabolic rate.
- (d) maintains pregnancy.
Answer(c) controls metabolic rate.
The companion question on the distractor here — NDA has separately tested that thyroxine's job is the metabolic rate, which is exactly why it must not be chosen for the hormone that raises the heartbeat.
- practice — not a real PYQ
Adrenaline is secreted by which part of the adrenal gland?
- (a)Cortex
- (b)Medulla
- (c)Capsule
- (d)Hilum
Answer(b) Medulla — the inner part of the adrenal gland secretes adrenaline and noradrenaline.
- practice — not a real PYQ
Melatonin, the hormone that regulates the sleep-wake cycle, is secreted by the
- (a)thyroid gland
- (b)pineal gland
- (c)pituitary gland
- (d)pancreas
Answer(b) pineal gland — a small gland in the brain that releases melatonin, mainly in darkness.