Endocrine Glands and Hormones
நாளமில்லாச் சுரப்பிகளும் ஹார்மோன்களும்
Hormones are non-nutrient chemicals that act as intercellular messengers in trace amounts. Most NEET matching questions in this chapter are just gland → hormone → disorder triplets — learn them as sets.
The idea
The neural system provides a point-to-point rapid coordination among organs, but it is short-lived; since nerve fibres do not innervate all cells of the body and cellular functions need continuous regulation, a special kind of coordination and integration is provided by hormones. Endocrine glands lack ducts and are hence called ductless glands; their secretions are called hormones. Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts. The endocrine glands and hormone-producing diffused tissues or cells located in different parts of the body constitute the endocrine system. The pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus and gonads (testis in males and ovary in females) are the organised endocrine bodies in our body. In addition, some other organs like the gastrointestinal tract, liver, kidney and heart also produce hormones. Hypofunction or hyperfunction of these glands produces characteristic disorders — for example, deficiency of insulin causes diabetes mellitus, of ADH causes diabetes insipidus, of cortisol and aldosterone (adrenal cortex) causes Addison's disease, and excess thyroid hormone causes Graves' disease (exophthalmic goitre).
Why it matters
Nerves give fast, local, short signals; hormones give slower, body-wide, long-lasting control of growth, metabolism and reproduction.
NEET lens
Matching triplets: insulin — diabetes mellitus; ADH — diabetes insipidus; corticoids — Addison's disease; thyroxin (excess) — exophthalmic goitre/Graves'; GH excess — gigantism/acromegaly; GH deficiency — dwarfism; iodine deficiency — goitre; thyroid deficiency in pregnancy — cretinism. Know which organs are not 'true' endocrine glands but still make hormones (GI tract, liver, kidney, heart).
Clinical significance
Diabetes mellitus, thyroid disorders and hormonal imbalances like PCOS are among the most common chronic conditions in India; simple blood tests for hormones and glucose allow early diagnosis.
Introduction
The endocrine system uses hormones — chemical messengers released into blood in trace amounts — to coordinate the body alongside the nervous system.
Core concept
Endocrine glands = ductless glands; secretions = hormones (non-nutrient chemicals, intercellular messengers, trace amounts). Organised endocrine bodies: pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, gonads (testis, ovary). Other hormone-producing organs: gastrointestinal tract, liver, kidney, heart. Neural coordination = fast, point-to-point, short-lived; hormonal = slower, widespread, longer-lasting. Classic disorders: insulin ↓ → diabetes mellitus; ADH ↓ → diabetes insipidus; adrenal cortex ↓ → Addison's disease; thyroid ↑ → Graves' disease (exophthalmic goitre); GH ↑ in childhood → gigantism, in adults → acromegaly; GH ↓ → stunted growth (pituitary dwarfism).
Go deeper
Invertebrates possess very simple endocrine systems with few hormones, whereas a large number of chemicals act as hormones and provide coordination in vertebrates.
From Class 10
Class 10 introduced glands like thyroid and pancreas and diseases like goitre and diabetes. This chapter organises all of them.