The Endocrine System

ICSE Class 10 · Biology · Chapter 12

What this chapter covers

Chemical coordination and hormones
Endocrine and exocrine glands
Location and shape of the endocrine glands
Pancreas: insulin and glucagon
Thyroid: thyroxin
Adrenal gland: cortical hormones and adrenaline
Pituitary: growth hormone, tropic hormones, ADH and oxytocin
Effects of hyposecretion and hypersecretion of hormones
Feedback mechanism with reference to TSH

Key points

Hormones are chemical messengers made by ductless endocrine glands, carried by the blood and acting in tiny amounts on target organs.
Exocrine glands have ducts and release enzymes, sweat or mucus; endocrine glands are ductless and release hormones into the blood; the pancreas is both.
The pituitary is pea-sized at the base of the brain; the thyroid is butterfly-shaped in the neck; the adrenals cap the kidneys; the pancreas is leaf-shaped behind the stomach.
Insulin (beta cells) lowers blood glucose; glucagon (alpha cells) raises it.
Thyroxin contains iodine and controls the basal metabolic rate and normal physical and mental growth.
The adrenal cortex secretes glucocorticoids (cortisol), mineralocorticoids (aldosterone) and sex corticoids; the adrenal medulla secretes adrenaline, the emergency hormone.
The anterior pituitary secretes growth hormone, the tropic hormones TSH, ACTH, FSH and LH, and prolactin; the posterior pituitary releases ADH and oxytocin.
Insulin: too little causes diabetes mellitus, too much causes hypoglycaemia.
Thyroxin: too little causes cretinism in children, myxoedema in adults and simple goitre (iodine lack); too much causes exophthalmic goitre.
Adrenal cortex: too little causes Addison's disease, too much causes Cushing's syndrome.
Growth hormone: too little causes dwarfism; too much causes gigantism in children and acromegaly in adults. Too little ADH causes diabetes insipidus.
Negative feedback keeps thyroxin steady: high thyroxin lowers TSH secretion, low thyroxin raises it.

Questions answered

Define a hormone.

A hormone is a chemical messenger secreted in very small amounts by an endocrine gland directly into the blood, which carries it to a target organ where it produces a specific response.

Give two differences between an endocrine gland and an exocrine gland, with one example of each.

An endocrine gland has no duct and pours a hormone directly into the blood (thyroid); an exocrine gland has a duct and releases enzymes or other secretions onto a surface or into a cavity (salivary gland). Endocrine secretions usually act at a distance; exocrine secretions usually act near the gland.

Why is the pancreas called a heterocrine gland?

It is both exocrine and endocrine: it sends pancreatic juice through a duct into the duodenum, and its islets of Langerhans secrete insulin and glucagon directly into the blood.

State the exact location and shape of the thyroid and adrenal glands.

The thyroid is a butterfly-shaped gland in the front of the neck, its two lobes on either side of the trachea below the larynx, joined by an isthmus. The adrenal glands are cap-like glands on top of each kidney; the right is triangular and the left crescent-shaped.

Name the cells that secrete insulin and glucagon, and state the effect of each hormone on blood glucose.

Beta cells of the islets of Langerhans secrete insulin, which lowers blood glucose; alpha cells secrete glucagon, which raises it.

Why must insulin be injected and not taken as a tablet?

Insulin is a protein, so protein-digesting enzymes in the stomach and small intestine would digest it before it could be absorbed into the blood.

Why is adrenaline called the emergency hormone? Give three of its effects.

It prepares the body to fight or run away in an emergency. It increases the heart rate and blood pressure, widens the bronchioles, and makes the liver release glucose from glycogen (also: dilates pupils, diverts blood to muscles).

Name the hormone that controls the reabsorption of sodium in the kidney tubules and the part of the gland that secretes it.

Aldosterone, a mineralocorticoid secreted by the adrenal cortex.

Past board exam questions

ICSE 2027 sample paper · 1 mark

Pallavi, a 30-year-old woman showed certain male characteristics such as growth of moustache, beard and hair on her chest. The endocrinologist diagnosed it as a hormonal disorder. Mention the biological term for the disorder.

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Adrenal virilism

ICSE 2027 sample paper · 2 marks

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Excess of the cortical sex hormones (androgens) is responsible. They are secreted by the adrenal gland (adrenal cortex).

ICSE 2027 sample paper · 2 marks

Explain the term hormone.

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A hormone is a chemical secretion of an endocrine (ductless) gland that is released directly into the blood and carried to target organs or tissues, where it regulates specific physiological processes.

ICSE 2027 sample paper · 2 marks

Expand the following abbreviations: 1. TSH 2. ACTH

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1. TSH – Thyroid Stimulating Hormone 2. ACTH – Adreno Cortico Tropic Hormone (Adrenocorticotropic hormone)

ICSE 2026 sample paper · 1 mark

Reena gets emotionally stressed when the school examinations are approaching. Which hormone is responsible for this condition?

Adrenaline
Thyroxine
Insulin
Growth hormone

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Adrenaline

ICSE 2026 sample paper · 1 mark

Assertion (A): Pituitary gland is known as the master gland. Reason (R): It regulates the activities of other exocrine glands.

(A) is true and (R) is false.
(A) is false and (R) is true.
Both (A) and (R) are true and (R) is the correct explanation of (A).
Both (A) and (R) are true but (R) is not the correct explanation of (A).

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(A) is true and (R) is false.

ICSE 2026 board paper · 5 marks

Choose the odd one out from the following terms and name the category to which the others belong: (a) Auxin, Oxytocin, Gibberellin, Cytokinin (b) Growth Hormone, Vasopressin, Thyroid Stimulating Hormone, Gonadotropic Hormone (c) Urochrome, Urea, Uric acid, Nucleic acid (d) Cervix, Chordae Tendinea, Papillary Muscles, Sinoatrial node (e) Morula, Blastocyst, Oviduct, Foetus

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(a) Odd one: Oxytocin. The others are plant hormones (plant growth regulators / phytohormones). (b) Odd one: Vasopressin. The others are hormones of the anterior lobe of the pituitary gland. (c) Odd one: Nucleic acid. The others are excretory products / constituents of urine. (d) Odd one: Cervix. The others are parts (structures) of the human heart. (e) Odd one: Oviduct. The others are stages in the development of the human embryo.

ICSE 2026 board paper · 5 marks

Mohit, a 30-year-old man was a software professional leading a sedentary life. He showed signs of high blood sugar during a routine health check-up despite having a normal body weight. Answer the following: (a) The hormonal disorder he is suffering from. (b) The hormone responsible for this disorder. (c) The organ that secretes this hormone. (d) One symptom experienced by Mohit due to this disorder. (e) One change in lifestyle to lower the blood sugar level.

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(a) Diabetes mellitus (Type 2 diabetes). (b) Insulin (its deficiency, or the body's reduced response to it). (c) Pancreas (the β-cells of the islets of Langerhans). (d) Frequent urination (polyuria) / excessive thirst / sugar in the urine (glycosuria) / fatigue / slow healing of wounds (any one). (e) Regular physical exercise (e.g. a daily walk) / a balanced diet low in sugar and refined carbohydrates (any one).