Hormones & Functions: Endocrine Glands Table
Quick answer: Hormones are chemical messengers secreted by endocrine (ductless) glands directly into the blood, acting on distant target organs to regulate growth, metabolism, reproduction and homeostasis. Their action is slow but long-lasting, and tiny quantities produce large effects. The master table below lists every major gland, its hormones and their functions.
Key Facts: Hormones
- Hormones are chemical messengers secreted by endocrine (ductless) glands directly into the blood, acting on distant target organs.
- The pituitary is the master gland: its hormones (GH, TSH, ACTH, FSH, LH, prolactin) control other endocrine glands, but it is itself commanded by the hypothalamus.
- ADH and oxytocin are made in the hypothalamus and only stored and released by the posterior pituitary, not manufactured there.
- Insulin (beta cells) lowers blood glucose; glucagon (alpha cells) raises it; their imbalance causes diabetes mellitus.
- Thyroxine (thyroid) sets the basal metabolic rate; deficiency in childhood causes cretinism, in adults myxoedema.
- Adrenaline (adrenal medulla) drives the fight-or-flight response; cortisol (adrenal cortex) manages long-term stress.
- Most hormones are switched off by negative feedback; the classic positive feedback example is estrogen triggering the LH surge before ovulation.
Hormones are the body's postal service: chemical letters sent through the blood from endocrine glands to distant target organs. Unlike nerve impulses (fast, brief, wired), hormonal messages are slow, long-lasting, and wireless. This table-first guide covers every major hormone, its gland, and its function, in the exact format examiners expect: gland, hormone, one-line function.
What Are Hormones? Properties of Hormones
Hormones are organic compounds secreted in minute amounts by endocrine glands. Their defining properties separate them sharply from nerve impulses and enzymes:
- They are produced in one organ but act on a different (target) organ.
- They are transported through the blood, not through ducts, which is why endocrine glands are called ductless glands.
- They act in very small quantities and are usually destroyed after action.
- They do not initiate a reaction; they regulate the rate of physiological processes such as growth and metabolism.
- Their secretion is controlled by feedback mechanisms, mostly negative feedback.
Master Table: Hormones and Their Functions
| Gland | Hormone | Target / Function |
|---|---|---|
| Hypothalamus | Releasing / inhibiting hormones (e.g. GnRH, TRH, CRH, somatostatin) | Control the anterior pituitary; link the nervous and endocrine systems |
| Anterior pituitary | Growth hormone (GH / somatotropin) | Stimulates growth of bones and tissues; controls body growth |
| Thyroid-stimulating hormone (TSH) | Stimulates the thyroid gland to release thyroxine | |
| Adrenocorticotropic hormone (ACTH) | Stimulates the adrenal cortex to release cortisol | |
| Follicle-stimulating hormone (FSH) | Gamete formation: follicle development (female), spermatogenesis (male) | |
| Luteinizing hormone (LH) | Triggers ovulation; stimulates testosterone secretion in males | |
| Prolactin | Stimulates milk production (lactation) in mammary glands | |
| MSH (melanocyte-stimulating hormone) | Regulates skin pigmentation (melanin) | |
| Posterior pituitary (hormones made in hypothalamus, only released here) | ADH (vasopressin) | Increases water reabsorption by kidney tubules; concentrates urine (osmoregulation) |
| Oxytocin | Stimulates uterine contraction during childbirth and milk ejection | |
| Thyroid | Thyroxine (T4) & triiodothyronine (T3); calcitonin | Regulate basal metabolic rate; calcitonin lowers blood calcium |
| Parathyroid | Parathormone (PTH) | Raises blood calcium (releases calcium from bones; opposes calcitonin) |
| Adrenal cortex | Glucocorticoids (cortisol) | Raise blood sugar; anti-stress, anti-inflammatory action |
| Mineralocorticoids (aldosterone) | Regulate salt and water balance (Na+ reabsorption by kidneys) | |
| Adrenal medulla | Adrenaline (epinephrine) & noradrenaline | Fight-or-flight: raise heartbeat, blood pressure, blood sugar, alertness |
| Pancreas (islets of Langerhans) | Insulin (beta cells), glucagon (alpha cells) | Insulin lowers blood sugar (glycogenesis); glucagon raises it (glycogenolysis): blood-glucose homeostasis |
| Pineal | Melatonin | Regulates sleep–wake cycle (biological clock); seasonal rhythms |
| Thymus | Thymosin | Development and maturation of T-lymphocytes (immunity) |
| Testes (Leydig cells) | Testosterone | Development of male secondary sexual characters and sperm production |
| Ovaries | Estrogen, progesterone | Female secondary sexual characters; regulate the menstrual cycle and pregnancy |
Reading tip: work through the hormones and their functions table row by row, gland, then hormones, then what each hormone does. Seen this way, the whole endocrine system reads as one connected control network, with the hypothalamus–pituitary axis at its centre.
Endocrine vs Exocrine Glands
Examiners often pair hormones with their opposites, the exocrine glands. The two differ in how they deliver their products:
| Feature | Endocrine glands | Exocrine glands |
|---|---|---|
| Ducts | Ductless; secretion released directly into blood | Have ducts; secretion carried to a surface or cavity |
| Product | Hormones (chemical messengers) | Enzymes, sweat, saliva, milk |
| Target | Distant target organs via blood | Nearby surfaces or cavities |
| Examples | Pituitary, thyroid, adrenal, pineal | Salivary glands, sweat glands, gastric glands |
| Mixed example | Pancreas: exocrine acinar cells secrete digestive enzymes; endocrine islets of Langerhans secrete insulin and glucagon | |
The Hypothalamus–Pituitary Axis: The Real Command Chain
The pituitary is called the master gland, but the true commander is the hypothalamus. Control flows down a chain, with each level driving the next:
- Hypothalamus (brain) senses internal conditions and releases releasing or inhibiting hormones.
- TRH (thyrotropin-releasing hormone) → stimulates TSH release
- CRH (corticotropin-releasing hormone) → stimulates ACTH release
- GnRH (gonadotropin-releasing hormone) → stimulates FSH and LH release
- Somatostatin → inhibits GH release
- Anterior pituitary responds by secreting its tropic hormones (TSH, ACTH, FSH, LH) into the blood.
- TSH → thyroid; ACTH → adrenal cortex; FSH/LH → gonads
- Target glands release their own hormones (thyroxine, cortisol, sex hormones), which act on the body and feed back on the hypothalamus and pituitary to switch them off (negative feedback).
Three Chemical Classes of Hormones
Every hormone in the master table belongs to one of three chemical classes, and the class decides how the hormone reaches and acts on its target:
- Steroid hormones (lipid-soluble, made from cholesterol; pass straight through cell membranes and act inside the cell)
- Adrenal cortex: cortisol, aldosterone
- Testes: testosterone
- Ovaries: estrogen, progesterone
- Peptide / protein hormones (chains of amino acids; bind receptors on the cell surface)
- Anterior pituitary: GH, TSH, ACTH, FSH, LH, prolactin
- Pancreas: insulin, glucagon
- Others: parathormone, calcitonin, ADH, oxytocin, thymosin
- Amine hormones (derived from single amino acids; mostly act at the cell surface)
- From tyrosine: thyroxine (T3/T4), adrenaline, noradrenaline
- From tryptophan: melatonin
How Is Hormone Secretion Controlled? Feedback Loops
Most hormones are regulated by negative feedback: when the hormone's effect reaches the required level, the effect switches off further secretion. The thyroid axis is the textbook example:
- Low thyroxine in blood → hypothalamus releases TRH
- TRH → anterior pituitary releases TSH
- TSH → thyroid releases thyroxine (T4)
- High thyroxine → inhibits both the hypothalamus and pituitary → TRH and TSH fall → thyroxine returns to normal
Positive feedback is rare: instead of switching secretion off, the effect amplifies it. The classic exam example is estrogen triggering the LH surge before ovulation, which drives follicle rupture in the menstrual cycle.
Antagonistic Hormone Pairs
Many body variables are held steady by antagonistic pairs: two hormones pulling in opposite directions around a set point.
- Blood glucose: insulin lowers it (glycogenesis, glucose uptake by cells); glucagon raises it (glycogenolysis, gluconeogenesis). After a meal insulin dominates; between meals glucagon dominates.
- Insulin deficiency → diabetes mellitus (high blood sugar, glucose in urine)
- Excess insulin → hypoglycemia (dangerously low blood sugar)
- Blood calcium: parathormone raises it (calcium released from bone, absorbed from gut, conserved by kidneys); calcitonin lowers it (calcium deposited into bone).
- PTH deficiency → tetany (low blood calcium, muscle spasms)
- PTH excess → bone weakening as calcium is drained from bone
- Stress response: adrenaline (adrenal medulla) drives the rapid fight-or-flight burst; cortisol (adrenal cortex) manages the slower, long-term stress response.
Hormonal Disorders Asked in Exams
| Hormone | Deficiency | Excess |
|---|---|---|
| Growth hormone | Dwarfism (childhood) | Gigantism (childhood) / acromegaly (adulthood) |
| Thyroxine | Cretinism (children), myxoedema (adults); simple goitre (iodine deficiency) | Exophthalmic goitre / Graves' disease (protruding eyes, high BMR) |
| Insulin | Diabetes mellitus (high blood sugar, glucose in urine) | Hypoglycemia (low blood sugar) |
| ADH | Diabetes insipidus (large volumes of dilute urine) | — |
| Parathormone | Tetany (low blood calcium, muscle spasms) | Bone weakening (excess calcium loss from bone) |
| Cortisol | Addison's disease | Cushing's syndrome |
Questions that ask "complete the table: gland — hormone — effect" are pure recall; prepare the table above row by row. Examiners love the anterior vs posterior pituitary distinction (ADH and oxytocin are made in the hypothalamus and only released by the posterior pituitary) and the insulin–glucagon pair for blood-sugar control. For disorders, always link the condition to the gland: goitre → thyroid, diabetes → pancreas, dwarfism → pituitary.
Frequently Asked Questions
Why is the pituitary gland called the master gland?
Because it secretes tropic hormones (TSH, ACTH, FSH, LH) that control the secretion of other endocrine glands: the thyroid, adrenal cortex and gonads. It is itself controlled by the hypothalamus, which is the true commander of the system.
Which gland secretes both hormones and enzymes?
The pancreas: its exocrine part (acinar cells) secretes digestive enzymes in pancreatic juice, while the endocrine islets of Langerhans secrete insulin and glucagon. It is therefore a mixed (heterocrine) gland.
What is the difference between diabetes mellitus and diabetes insipidus?
Diabetes mellitus is caused by insulin deficiency (pancreas): high blood sugar and glucose in urine. Diabetes insipidus is caused by ADH deficiency (posterior pituitary): excretion of large volumes of dilute, sugar-free urine. The names differ, but both cause excessive urination.
What does adrenaline do in the fight-or-flight response?
Adrenaline (and noradrenaline) from the adrenal medulla increases heartbeat and blood pressure, dilates the airways, raises blood sugar and sharpens alertness, preparing the body for emergency action. It acts within seconds but fades quickly; cortisol handles the longer stress response.
Which hormone regulates the sleep–wake cycle?
Melatonin, secreted by the pineal gland, regulates the circadian (sleep–wake) rhythm and seasonal biological clocks. It is an amine hormone derived from the amino acid tryptophan.
What hormones does the pituitary gland secrete?
The anterior pituitary secretes growth hormone (GH), TSH, ACTH, FSH, LH, prolactin and MSH. The posterior pituitary releases ADH and oxytocin, which are actually made in the hypothalamus and only stored and released here.
Practice MCQs
Q1. Which gland is known as the master gland?
- Thyroid
- Adrenal
- Pituitary
- Pineal
Answer: C — The pituitary controls other endocrine glands through its tropic hormones (TSH, ACTH, FSH, LH).
Q2. Insulin is secreted by which cells of the pancreas?
- Alpha cells
- Beta cells
- Delta cells
- Acinar cells
Answer: B — Beta cells of the islets of Langerhans secrete insulin; alpha cells secrete glucagon.
Q3. Deficiency of thyroxine in childhood causes:
- Gigantism
- Cretinism
- Acromegaly
- Addison's disease
Answer: B — Cretinism is stunted physical and mental growth due to thyroid hormone deficiency in children.
Q4. The fight-or-flight hormones are secreted by the:
- Adrenal cortex
- Adrenal medulla
- Thyroid gland
- Posterior pituitary
Answer: B — The adrenal medulla secretes adrenaline (epinephrine) and noradrenaline for emergency responses.
Q5. Which hormone increases water reabsorption by the kidney tubules?
- Oxytocin
- Prolactin
- ADH (vasopressin)
- Aldosterone
Answer: C — ADH, released by the posterior pituitary, increases water reabsorption, producing concentrated urine.
Q6. ADH and oxytocin differ from other pituitary hormones because they:
- Are made in the hypothalamus and only released by the posterior pituitary
- Are produced by the anterior pituitary like TSH and GH
- Are steroid hormones secreted into ducts
- Act only on the brain and never on target organs
Answer: A — ADH and oxytocin are synthesized in the hypothalamus and merely released by the posterior pituitary; they are not made there.
Q7. Which hormone lowers blood calcium, opposing parathormone?
- Calcitonin
- Thyroxine
- Aldosterone
- Parathormone
Answer: A — Calcitonin from the thyroid lowers blood calcium, while parathormone raises it by releasing calcium from bones.
Q8. The classic exam example of positive feedback in hormonal control is:
- High blood sugar switching off insulin release
- Low thyroxine stimulating TSH secretion
- Low blood calcium stimulating parathormone
- Estrogen triggering the LH surge before ovulation
Answer: D — Before ovulation, estrogen exerts positive feedback on the pituitary to trigger the LH surge; most other hormone control is negative feedback.
Q9. Which cells of the islets of Langerhans secrete glucagon?
- Beta cells
- Alpha cells
- Delta cells
- Acinar cells
Answer: B — Glucagon is secreted by the alpha cells of the islets of Langerhans and raises blood sugar by glycogenolysis.
Q10. Acromegaly is caused by excess growth hormone in:
- Adults
- Childhood
- Newborn infants
- Pregnant women
Answer: A — Excess growth hormone causes gigantism in childhood but acromegaly in adulthood, after the long bones have stopped growing.
Q11. Melatonin, the hormone that regulates the sleep–wake cycle, is secreted by the:
- Thymus
- Thyroid gland
- Pineal gland
- Posterior pituitary
Answer: C — Melatonin is secreted by the pineal gland and regulates the sleep–wake cycle and seasonal rhythms.
Q12. Tetany (low blood calcium with muscle spasms) results from deficiency of:
- Thyroxine
- Insulin
- Cortisol
- Parathormone
Answer: D — Parathormone deficiency lowers blood calcium, causing tetany (muscle spasms); excess weakens bone by draining calcium from it.
Short Questions
Q1. What are hormones? State three defining properties of hormones. See answer
Hormones are organic chemical messengers secreted in minute amounts by endocrine (ductless) glands directly into the blood, through which they reach distant target organs and regulate growth, metabolism and reproduction. Unlike enzymes, which act where they are produced, hormones act far from their site of secretion.
Three defining properties: (1) they are produced in one organ but act on a different (target) organ; (2) they are transported through the blood, not through ducts; (3) they act in very small quantities and are usually destroyed after action. Two more exam points: they do not initiate a reaction but regulate the rate of physiological processes, and their secretion is controlled by feedback mechanisms, mostly negative feedback.
The properties are easy to contrast with nerve impulses: hormonal action is slow but long-lasting and wireless, while nervous action is fast, brief and wired.
Q2. Why is the pituitary gland called the "master gland"? Who commands it? See answer
The pituitary is called the master gland because it secretes tropic hormones (TSH, ACTH, FSH, LH) that control the secretion of other endocrine glands: the thyroid, adrenal cortex and gonads. Through these hormones it indirectly governs metabolism (via thyroxine), stress response (via cortisol) and reproduction (via sex hormones).
The true commander, however, is the hypothalamus, which links the nervous and endocrine systems. The hypothalamus controls the anterior pituitary with releasing hormones (TRH, CRH, GnRH) and inhibiting hormones (somatostatin). It also manufactures ADH and oxytocin, which travel down nerve axons to the posterior pituitary for storage and release.
An examiner's favourite trap is asking which pituitary hormones are actually made elsewhere: the answer is ADH and oxytocin, made in the hypothalamus and only released by the posterior pituitary.
Q3. How is blood sugar regulated by insulin and glucagon? See answer
Insulin, secreted by the beta cells of the islets of Langerhans, lowers blood glucose by promoting glycogenesis (conversion of glucose to glycogen in the liver) and increasing glucose uptake by body cells. It dominates after a meal, when blood sugar rises.
Glucagon, secreted by the alpha cells, raises blood glucose by promoting glycogenolysis (breakdown of liver glycogen) and gluconeogenesis (formation of glucose from non-carbohydrates). It dominates between meals and during fasting, keeping the brain supplied with glucose.
The two form an antagonistic pair under negative feedback control: high blood sugar stimulates insulin release, and as sugar falls, insulin secretion stops, allowing glucagon to take over. Diabetes mellitus results from insulin deficiency or resistance, producing persistent high blood sugar with glucose in the urine.
Q4. Differentiate between diabetes mellitus and diabetes insipidus. See answer
Diabetes mellitus is caused by insulin deficiency (or insulin resistance) in the pancreas: blood glucose stays high and excess glucose spills into the urine. It is treated with insulin or glucose-lowering drugs and diet control.
Diabetes insipidus is caused by ADH deficiency (posterior pituitary): the kidneys cannot reabsorb water, so the patient excretes large volumes of dilute, sugar-free urine and suffers constant thirst. It is treated with ADH (vasopressin) replacement.
The shared word "diabetes" refers only to the excessive urination common to both; the causes, the gland involved, and the urine chemistry are completely different.
Q5. What is the fight-or-flight response and which hormones drive it? See answer
The fight-or-flight response is the body's rapid emergency reaction to danger or stress: the heartbeat pounds faster, airways widen, blood pressure rises, blood sugar spikes and blood shifts toward the muscles, preparing the body to fight or flee within seconds.
It is driven by adrenaline (epinephrine) and noradrenaline, secreted by the adrenal medulla under sympathetic nervous stimulation. Because the medulla is wired directly to the nervous system, adrenaline reaches its targets almost instantly, which is why it acts in seconds and fades in minutes.
Cortisol from the adrenal cortex manages the slower, long-term stress response: it raises blood sugar and suppresses inflammation over hours.
Q6. Why does iodine deficiency cause simple goitre? See answer
Thyroxine (T4) production requires iodine: each thyroxine molecule carries four iodine atoms. When dietary iodine is deficient, the thyroid cannot make enough thyroxine, so the basal metabolic rate falls.
Low thyroxine removes negative feedback on the pituitary, which keeps releasing TSH, overstimulating the thyroid gland. The gland enlarges in a futile attempt to make more hormone, producing the visible neck swelling called simple goitre.
Contrast this with exophthalmic goitre (Graves' disease), caused by thyroxine excess, which raises BMR and produces protruding eyes. In childhood, thyroxine deficiency causes cretinism (stunted physical and mental development).
References
- Hickman, C.P., Roberts, L.S. & Larson, A. Integrated Principles of Zoology, 18th ed. McGraw-Hill. (Chemical coordination; endocrine system.)
- Miller, S.A. & Harley, J.P. Zoology, McGraw-Hill. (Hormones and endocrine glands.)
- OpenStax, Anatomy & Physiology, Chapter 17: The Endocrine System: OpenStax A&P 2e.
- NCBI Bookshelf — Physiology of the Endocrine System: NCBI Bookshelf.
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