Why a Pinch of Iodised Salt Protects Your Thyroid
Define hormones and tell endocrine from exocrine glands, meet the hypothalamus and the hormones of the anterior and posterior pituitary, study the pineal, thyroid and parathyroid glands, and see how adrenal, pancreatic and gonadal hormones act.
How do glands control the body without any nerves?
Growing taller over years, calming down after a fright, and keeping blood sugar steady are all controlled by hormones — chemical messages released by glands into the blood.
This part covers what hormones are, the hypothalamus and pituitary, the pineal, thyroid and parathyroid glands, and the adrenal glands, pancreas and gonads.
This part covers what hormones are, the hypothalamus and pituitary, the pineal, thyroid and parathyroid glands, and the adrenal glands, pancreas and gonads.
What are hormones, and how do endocrine glands differ from exocrine glands?
Hormones are non-nutrient chemicals produced in trace amounts that act as intercellular messengers; endocrine glands are ductless and release them straight into blood, while exocrine glands release their secretions through ducts.
The definition. Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts. This covers hormones from organised glands and from scattered hormone-producing tissues.
Endocrine glands:
- Ductless — secretions pass directly into blood
- Act on target organs, often far away
- Examples: pituitary, thyroid, adrenal
Exocrine glands:
- Have ducts carrying secretions to a surface or cavity
- Examples: salivary, sweat and gastric glands
A gland that is both. The pancreas secretes digestive juice through a duct, while its islets of Langerhans release hormones into blood.
An everyday example. Sweat on your forehead on a hot afternoon reaches the skin through ducts of exocrine glands, while the adrenaline behind a racing heart before an exam travels in blood.
The substance. A hormone affects only cells with matching receptors, which is why a hormone carried everywhere acts only on its targets.
The definition. Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts. This covers hormones from organised glands and from scattered hormone-producing tissues.
Endocrine glands:
- Ductless — secretions pass directly into blood
- Act on target organs, often far away
- Examples: pituitary, thyroid, adrenal
Exocrine glands:
- Have ducts carrying secretions to a surface or cavity
- Examples: salivary, sweat and gastric glands
A gland that is both. The pancreas secretes digestive juice through a duct, while its islets of Langerhans release hormones into blood.
An everyday example. Sweat on your forehead on a hot afternoon reaches the skin through ducts of exocrine glands, while the adrenaline behind a racing heart before an exam travels in blood.
The substance. A hormone affects only cells with matching receptors, which is why a hormone carried everywhere acts only on its targets.
What do the hypothalamus and pituitary do, and which hormones do the adenohypophysis and neurohypophysis release?
The hypothalamus makes releasing and inhibiting hormones that control the anterior pituitary, as well as hormones stored in the posterior pituitary; the adenohypophysis releases GH, PRL, TSH, ACTH, LH, FSH and MSH, and the neurohypophysis releases oxytocin and vasopressin.
Hypothalamus:
- The basal part of the diencephalon, with groups of neurosecretory cells
- Releasing hormones stimulate pituitary secretion — GnRH stimulates gonadotrophin release
- Inhibiting hormones stop it — somatostatin inhibits growth hormone release
- These reach the anterior pituitary through a portal circulatory system; posterior pituitary hormones travel along axons
Adenohypophysis (anterior pituitary):
- Growth hormone (GH) — body growth
- Prolactin (PRL) — mammary gland growth and milk formation
- TSH — stimulates thyroid hormone synthesis
- ACTH — stimulates glucocorticoid synthesis in the adrenal cortex
- LH and FSH — stimulate gonadal activity
- MSH — acts on melanocytes, regulating skin pigmentation
Neurohypophysis (posterior pituitary) stores and releases:
- Oxytocin — contraction of smooth muscles, such as the uterus at childbirth, and milk ejection
- Vasopressin (ADH) — water reabsorption by distal tubules, reducing water loss
An everyday example. Children of the same age differ in height at a school health check-up, partly because of differences in growth hormone.
The substance. The posterior pituitary makes no hormones of its own — it stores and releases those made by the hypothalamus.
Hypothalamus:
- The basal part of the diencephalon, with groups of neurosecretory cells
- Releasing hormones stimulate pituitary secretion — GnRH stimulates gonadotrophin release
- Inhibiting hormones stop it — somatostatin inhibits growth hormone release
- These reach the anterior pituitary through a portal circulatory system; posterior pituitary hormones travel along axons
Adenohypophysis (anterior pituitary):
- Growth hormone (GH) — body growth
- Prolactin (PRL) — mammary gland growth and milk formation
- TSH — stimulates thyroid hormone synthesis
- ACTH — stimulates glucocorticoid synthesis in the adrenal cortex
- LH and FSH — stimulate gonadal activity
- MSH — acts on melanocytes, regulating skin pigmentation
Neurohypophysis (posterior pituitary) stores and releases:
- Oxytocin — contraction of smooth muscles, such as the uterus at childbirth, and milk ejection
- Vasopressin (ADH) — water reabsorption by distal tubules, reducing water loss
An everyday example. Children of the same age differ in height at a school health check-up, partly because of differences in growth hormone.
The substance. The posterior pituitary makes no hormones of its own — it stores and releases those made by the hypothalamus.
What do melatonin, thyroxine, PTH and calcitonin do, and why does the thyroid need iodine?
Melatonin from the pineal gland regulates the daily sleep-wake rhythm, thyroid hormones control the basal metabolic rate and need iodine to be made, and parathyroid hormone raises blood calcium while thyrocalcitonin from the thyroid lowers it.
Pineal gland:
- On the dorsal side of the forebrain
- Secretes melatonin, which regulates the diurnal rhythm of sleep, waking and body temperature, and influences metabolism, pigmentation, the menstrual cycle and defence
Thyroid gland:
- Two lobes on either side of the trachea, joined by an isthmus, made of follicles
- Follicular cells make **thyroxine (T) and triiodothyronine (T)
- Iodine is essential for normal thyroid hormone synthesis; deficiency causes hypothyroidism and enlargement of the gland, goitre
- Thyroid hormones regulate basal metabolic rate and support RBC formation
- The thyroid also secretes thyrocalcitonin (TCT), which lowers blood calcium
Parathyroid glands:
- Four glands on the back of the thyroid, a pair in each lobe
- Secrete parathyroid hormone (PTH), which raises blood Ca** by stimulating bone resorption, Ca reabsorption by kidney tubules and absorption from digested food
- PTH is hypercalcaemic; TCT is hypocalcaemic
An everyday example. Most table salt sold in India is iodised, a simple step that protects people from iodine-deficiency goitre.
The substance. PTH and TCT act antagonistically — one raises blood calcium and the other lowers it, keeping the level balanced.
Pineal gland:
- On the dorsal side of the forebrain
- Secretes melatonin, which regulates the diurnal rhythm of sleep, waking and body temperature, and influences metabolism, pigmentation, the menstrual cycle and defence
Thyroid gland:
- Two lobes on either side of the trachea, joined by an isthmus, made of follicles
- Follicular cells make **thyroxine (T) and triiodothyronine (T)
- Iodine is essential for normal thyroid hormone synthesis; deficiency causes hypothyroidism and enlargement of the gland, goitre
- Thyroid hormones regulate basal metabolic rate and support RBC formation
- The thyroid also secretes thyrocalcitonin (TCT), which lowers blood calcium
Parathyroid glands:
- Four glands on the back of the thyroid, a pair in each lobe
- Secrete parathyroid hormone (PTH), which raises blood Ca** by stimulating bone resorption, Ca reabsorption by kidney tubules and absorption from digested food
- PTH is hypercalcaemic; TCT is hypocalcaemic
An everyday example. Most table salt sold in India is iodised, a simple step that protects people from iodine-deficiency goitre.
The substance. PTH and TCT act antagonistically — one raises blood calcium and the other lowers it, keeping the level balanced.
What do adrenaline, cortisol, insulin, glucagon, testosterone, oestrogen and progesterone do?
Adrenaline from the adrenal medulla prepares the body for emergencies, cortisol from the adrenal cortex raises blood glucose and dampens immune responses, insulin lowers and glucagon raises blood glucose, testosterone controls male sex characters, and oestrogen and progesterone control female characters and support pregnancy.
Adrenal gland — one on the anterior part of each kidney, with an outer cortex and inner medulla:
- Adrenal medulla — adrenaline and noradrenaline, the fight-or-flight hormones; they increase alertness, pupil dilation, sweating, heart rate and breathing rate, and raise blood glucose by glycogen breakdown
- Adrenal cortex — cortisol, a glucocorticoid, raises blood glucose, has anti-inflammatory effects and suppresses the immune response; aldosterone, a mineralocorticoid, increases **Na and water reabsorption
Pancreas — islets of Langerhans:
- Alpha cells secrete glucagon, a hyperglycaemic hormone that stimulates glycogen breakdown and gluconeogenesis in the liver
- Beta cells secrete insulin, a hypoglycaemic hormone that increases glucose uptake by liver and fat cells and promotes glycogen formation
Gonads:
- Testis — Leydig cells make testosterone, which controls male accessory sex organs, secondary sex characters and sperm production
- Ovary — oestrogen from growing follicles drives female sex organs, secondary sex characters and mammary gland development; progesterone from the corpus luteum supports pregnancy
An everyday example. The pounding heart and sweaty palms just before a stage performance are adrenaline at work.
The substance. Insulin and glucagon are antagonists** — together they hold blood glucose within a narrow range.
Adrenal gland — one on the anterior part of each kidney, with an outer cortex and inner medulla:
- Adrenal medulla — adrenaline and noradrenaline, the fight-or-flight hormones; they increase alertness, pupil dilation, sweating, heart rate and breathing rate, and raise blood glucose by glycogen breakdown
- Adrenal cortex — cortisol, a glucocorticoid, raises blood glucose, has anti-inflammatory effects and suppresses the immune response; aldosterone, a mineralocorticoid, increases **Na and water reabsorption
Pancreas — islets of Langerhans:
- Alpha cells secrete glucagon, a hyperglycaemic hormone that stimulates glycogen breakdown and gluconeogenesis in the liver
- Beta cells secrete insulin, a hypoglycaemic hormone that increases glucose uptake by liver and fat cells and promotes glycogen formation
Gonads:
- Testis — Leydig cells make testosterone, which controls male accessory sex organs, secondary sex characters and sperm production
- Ovary — oestrogen from growing follicles drives female sex organs, secondary sex characters and mammary gland development; progesterone from the corpus luteum supports pregnancy
An everyday example. The pounding heart and sweaty palms just before a stage performance are adrenaline at work.
The substance. Insulin and glucagon are antagonists** — together they hold blood glucose within a narrow range.
Exam tip
What earns full marks on the endocrine glands?
Make one line per gland — location, hormone, main action — and learn antagonistic pairs together.
- Hypothalamus: releasing and inhibiting hormones such as GnRH and somatostatin
- Anterior pituitary: GH, PRL, TSH, ACTH, LH, FSH, MSH; posterior: oxytocin, vasopressin
- Pineal: melatonin; thyroid: T, T, TCT; parathyroid: PTH
- Adrenal: adrenaline, cortisol, aldosterone; pancreas: insulin from beta cells, glucagon from alpha cells
- Gonads: testosterone; oestrogen and progesterone
The trap. Saying oxytocin is made by the posterior pituitary. It is made by the hypothalamus and only released from the posterior pituitary.
- Hypothalamus: releasing and inhibiting hormones such as GnRH and somatostatin
- Anterior pituitary: GH, PRL, TSH, ACTH, LH, FSH, MSH; posterior: oxytocin, vasopressin
- Pineal: melatonin; thyroid: T, T, TCT; parathyroid: PTH
- Adrenal: adrenaline, cortisol, aldosterone; pancreas: insulin from beta cells, glucagon from alpha cells
- Gonads: testosterone; oestrogen and progesterone
The trap. Saying oxytocin is made by the posterior pituitary. It is made by the hypothalamus and only released from the posterior pituitary.
Did you know
Why do you start feeling sleepy once it gets dark?
Your pineal gland releases more melatonin as darkness falls and much less in bright light.
Rising melatonin in the evening is one of the signals that make you drowsy and lower your body temperature for sleep.
This is why bright screens late at night can make it harder to fall asleep — the light tells the pineal gland it is still daytime, delaying the melatonin signal the body relies on.
Rising melatonin in the evening is one of the signals that make you drowsy and lower your body temperature for sleep.
This is why bright screens late at night can make it harder to fall asleep — the light tells the pineal gland it is still daytime, delaying the melatonin signal the body relies on.
Exam relevance
How are the endocrine glands and their hormones tested in NEET?
Chemical Coordination and Integration is part of the Human Physiology unit of NEET Biology, and matching glands, hormones and actions dominates it.
What gets asked. Hormones of the anterior and posterior pituitary, hypothalamic releasing and inhibiting hormones, the role of iodine, calcium control by PTH and TCT, adrenal medullary and cortical hormones, insulin and glucagon from specific islet cells, and the sources of testosterone, oestrogen and progesterone.
Question types. Match-the-column lists, statement-based questions and assertion-reason questions.
The trap that costs marks. Calling glucagon hypoglycaemic — glucagon raises blood glucose; insulin lowers it.
What gets asked. Hormones of the anterior and posterior pituitary, hypothalamic releasing and inhibiting hormones, the role of iodine, calcium control by PTH and TCT, adrenal medullary and cortical hormones, insulin and glucagon from specific islet cells, and the sources of testosterone, oestrogen and progesterone.
Question types. Match-the-column lists, statement-based questions and assertion-reason questions.
The trap that costs marks. Calling glucagon hypoglycaemic — glucagon raises blood glucose; insulin lowers it.
Key takeaways
What must you be able to do from this part?
- Hormones: non-nutrient intercellular messengers in trace amounts; endocrine glands are ductless, exocrine glands have ducts
- Hypothalamus and pituitary: releasing and inhibiting hormones; anterior pituitary GH, PRL, TSH, ACTH, LH, FSH, MSH; posterior pituitary oxytocin and vasopressin
- Pineal, thyroid, parathyroid: melatonin and diurnal rhythm; T and T need iodine; PTH raises and TCT lowers blood calcium
- Adrenal, pancreas, gonads: adrenaline, cortisol and aldosterone; insulin and glucagon; testosterone, oestrogen and progesterone
Pick three pairs of hormones that work against each other, and for each pair say which one raises and which one lowers the level it controls.
- Hypothalamus and pituitary: releasing and inhibiting hormones; anterior pituitary GH, PRL, TSH, ACTH, LH, FSH, MSH; posterior pituitary oxytocin and vasopressin
- Pineal, thyroid, parathyroid: melatonin and diurnal rhythm; T and T need iodine; PTH raises and TCT lowers blood calcium
- Adrenal, pancreas, gonads: adrenaline, cortisol and aldosterone; insulin and glucagon; testosterone, oestrogen and progesterone
Pick three pairs of hormones that work against each other, and for each pair say which one raises and which one lowers the level it controls.