Maarg Manthan · Topic 3.8

Endocrine System: Hypothalamus, Pineal Body, Pituitary Gland, Thyroid, Adrenal Glands, Reproductive Glands

Science & Technology › Human Physiology – Organ Systems · Topic 3.8

The endocrine system is a set of ductless glands that release chemical messengers called hormones directly into the blood, which carry them to target organs. Hormones control growth, metabolism, reproduction, mood and the balance of water, salts and sugar. The main glands are the hypothalamus, pineal gland, pituitary gland, thyroid, parathyroids, adrenal glands, pancreas, thymus and the reproductive glands, the testes and ovaries. The pituitary is called the master gland because its hormones control other glands, but it is itself controlled by the hypothalamus. Hormone levels are regulated by negative feedback. Disorders arise from too little or too much of a hormone, as in diabetes, goitre and gigantism.

5 min read · UPSC Prelims · Science & Technology · Human Physiology – Organ Systems

At a Glance

Master gland Pituitary
Sleep hormone Melatonin (pineal)
Metabolism hormone Thyroxine (thyroid)
Stress hormones Adrenaline, cortisol (adrenal)
Blood sugar Insulin and glucagon (pancreas)
Exam link UPSC Prelims, Science & Technology: Human Physiology – Organ Systems

Where Does It Fit?

This is the eighth topic of the macro on human physiology and organ systems. It describes the chemical control of the body, which works along with the nervous system, and it links to several earlier topics. Previous topic: Immune System and Immunity. Next topic: Respiratory System: External and Internal Respiration in Humans, Animals, Plants and Insects.

What Are the Main Glands and Their Hormones?

Gland	Hormones and effects
Hypothalamus	Links the nervous and endocrine systems. Releasing and inhibiting hormones control the pituitary, and it makes ADH and oxytocin
Pineal gland	Makes melatonin, which controls the sleep-wake cycle and circadian rhythm
Anterior pituitary	Growth hormone, thyroid stimulating hormone, ACTH, FSH, LH and prolactin
Posterior pituitary	Stores and releases ADH and oxytocin, which makes the uterus contract in childbirth and releases milk
Thyroid	Thyroxine and triiodothyronine, which control metabolism and need iodine. Calcitonin lowers blood calcium
Parathyroid	Parathyroid hormone raises blood calcium
Adrenal cortex	Cortisol for stress and sugar, and aldosterone for salt balance
Adrenal medulla	Adrenaline and noradrenaline for the fight or flight response
Pancreas	Insulin lowers blood glucose and glucagon raises it
Testes and ovaries	Testosterone, oestrogen and progesterone control sexual development and reproduction

What Are the Common Disorders?

Growth hormone: too little in childhood causes dwarfism, too much causes gigantism, and too much in adults causes acromegaly.
Thyroid: lack of iodine causes goitre, an enlarged thyroid. Low thyroxine causes cretinism in children and myxoedema in adults, and excess causes hyperthyroidism, such as Graves’ disease.
Diabetes mellitus: caused by lack of insulin or poor response to it. Type 1 is an autoimmune loss of insulin-making cells and type 2 is linked to insulin resistance and lifestyle. Frederick Banting and Charles Best isolated insulin in 1921.
Adrenal disorders: Addison’s disease from too little cortisol and aldosterone, and Cushing’s syndrome from too much cortisol.
Diabetes insipidus: low ADH, as in Osmoregulation, ADH and Formation of Urine; Thermoregulation.
Reproductive hormone problems: polycystic ovary syndrome in women and low testosterone in men.

What Else Should You Remember?

Negative feedback: when a hormone level rises it inhibits further release, as thyroxine suppresses the secretion of thyroid stimulating hormone. Blood sugar is controlled by the opposite actions of insulin and glucagon.
Exocrine and endocrine glands: exocrine glands have ducts, such as sweat and salivary glands, while endocrine glands do not. The pancreas and gonads are both kinds.
Hormones in plants: auxins, gibberellins, cytokinins, ethylene and abscisic acid control growth, ripening and dormancy.
Insect hormones: ecdysone controls moulting and juvenile hormone controls metamorphosis.
Pheromones: chemical signals released outside the body to affect other members of the species, as in ants and moths.
Thymus: makes thymosin, which helps T cells to mature and shrinks after puberty, as in Immune System and Immunity.
Synthetic hormones: insulin made by recombinant DNA technology and growth hormone, as in Recombinant DNA Technology.
Iodised salt: India’s National Iodine Deficiency Disorders Control Programme promotes iodised salt to prevent goitre.
Endocrine disruptors: chemicals such as some pesticides and plastics additives that interfere with hormones.
Pituitary gland: the pituitary gland is about the size of a pea and lies at the base of the brain, and its anterior and posterior parts have different origins.
Thyroid gland: the thyroid gland is the largest purely endocrine gland, shaped like a butterfly in the neck.
Adrenal glands: the adrenal glands sit on top of the kidneys and are also called suprarenal glands.

Why Does It Matter for the Exam?

Matching questions: gland, hormone and function, and disorders caused by excess or lack.
Health link: diabetes is a major public health problem in India, which is often called the diabetes capital of the world.
Policy link: iodised salt and screening of newborns for hypothyroidism.
Technology link: insulin pumps, oral drugs and new weight-loss medicines that act on hormones.
Common errors: treating the pancreas as only an exocrine gland or the pituitary as the top of the hierarchy.

As an analytical point, the endocrine system uses slow, long-lasting signals, while the nervous system uses fast, short ones. Together they keep the body in balance through feedback.

Why Is This Topic Important?

Facts Gland-hormone matching asked
Disorders Excess and deficiency
Link Diabetes and iodine

What Came Next?

The next topic covers the respiratory system in humans, animals, plants and insects. Next topic: Respiratory System: External and Internal Respiration in Humans, Animals, Plants and Insects.

Key People and Terms

Hormone Chemical messenger in blood
Target organ Organ that responds to a hormone
Negative feedback Output reduces the signal
Insulin Lowers blood sugar
Goitre Enlarged thyroid from iodine lack
Pheromone Chemical signal between individuals

Exam Corner

Points to Remember

Pituitary is the master gland.
Melatonin from the pineal gland.
Iodine lack causes goitre.
Banting and Best isolated insulin in 1921.
Adrenaline: fight or flight.

Do Not Confuse With

Insulin and glucagon Lowers versus raises blood sugar
Gigantism and acromegaly Excess GH in childhood versus adulthood
Endocrine and exocrine glands Ductless versus with ducts

Memory Hook

Pituitary master, thyroid thyroxine with iodine; pineal melatonin, adrenal fights, insulin and glucagon keep sugar in line.

Mains Angle

Questions ask about hormonal control and its disorders. These points add depth.

Glands Hormones and functions
Control Feedback loops
Disorders Diabetes, goitre

A Question You May Face

An original practice question, not a past paper question.

“Describe the major endocrine glands, the hormones they secrete and the disorders associated with them.”

How to Answer

Glands List.
Hormones Roles.
Control Feedback.
Disorders Diabetes, goitre.

GS Relevance

Prelims: glands, hormones and their effects, disorders, feedback. GS Paper 3: science and technology, health.

Frequently Asked Questions

Why is the pituitary called the master gland?

The pituitary gland is called the master gland because its hormones, such as thyroid stimulating hormone, ACTH, FSH and LH, control other endocrine glands such as the thyroid, adrenal cortex and gonads. It is itself controlled by the hypothalamus, so the hypothalamus is the real link between the nervous and endocrine systems.

What is the function of the thyroid gland?

The thyroid gland, in the neck, makes thyroxine and triiodothyronine, which control the rate of metabolism and need iodine to be made. It also makes calcitonin, which lowers blood calcium, and lack of iodine causes goitre, while too little thyroxine in infancy causes cretinism.

What do insulin and glucagon do?

Insulin, made by beta cells of the pancreas, lowers blood glucose by helping cells to take it up and by storing it as glycogen in the liver. Glucagon, made by alpha cells, raises blood glucose by breaking down glycogen, and together they keep blood sugar steady.

What are the hormones of the adrenal gland?

The adrenal cortex makes cortisol, which helps to handle stress and controls blood sugar, and aldosterone, which controls sodium and potassium balance. The adrenal medulla makes adrenaline and noradrenaline, which speed up the heart, raise blood sugar and prepare the body for the fight or flight response.

What is negative feedback in hormone control?

Negative feedback is a control system in which a rise in the level of a hormone or its effect reduces further release of that hormone. For example, high thyroxine in blood suppresses the pituitary release of thyroid stimulating hormone, which keeps thyroxine within a narrow range.

PYQ Practice — Statement Analysis

1 Melatonin is secreted by the pineal gland.

True

It regulates sleep.

2 Insulin raises blood sugar levels.

False

It lowers them.

3 Goitre is caused by lack of iodine.