ICSE Class 10 Biology: Endocrine System — Hormones Notes 2026

Introduction to Endocrine System

• Ductless glands secrete hormones directly into bloodstream
• Hormones: chemical messengers; produced in tiny amounts; act on distant target organs
• Compared to nervous system: slower, longer-lasting effects; systemic

Pituitary Gland — Master Gland

• Pea-sized; located below hypothalamus in brain; anterior and posterior lobes
• Anterior: secretes GH (growth), TSH (thyroid), ACTH (adrenal), FSH/LH (gonads)
• Posterior: releases ADH (water balance) and oxytocin (uterine contractions, lactation)

Thyroid and Parathyroid

• Thyroid: secretes thyroxine (T4) — regulates BMR, growth, brain development; requires iodine
• Hypo-thyroidism: goitre (iodine deficiency), cretinism in infants; hyperthyroidism: exophthalmia
• Parathyroid: secretes PTH — raises blood calcium; antagonistic to calcitonin

Adrenal Glands

• Adrenal cortex: cortisol (stress, anti-inflammatory), aldosterone (Na⁺/K⁺ balance)
• Adrenal medulla: adrenaline (epinephrine) — fight-or-flight: ↑ heart rate, ↑ blood glucose, ↑ breathing
• Over-secretion of cortisol: Cushing's syndrome; under-secretion: Addison's disease

Pancreas — Islets of Langerhans

• Alpha cells: glucagon — raises blood glucose by stimulating liver glycogenolysis
• Beta cells: insulin — lowers blood glucose by promoting glucose uptake into cells and glycogen synthesis
• Diabetes mellitus Type 1: insufficient insulin; Type 2: insulin resistance; managed by diet, exercise, insulin

Gonads — Sex Hormones

• Testes: testosterone — male secondary sexual characteristics (puberty), sperm production
• Ovaries: oestrogen and progesterone — female characteristics, menstrual cycle, pregnancy
• Feedback mechanism: low hormone levels trigger pituitary to secrete more tropic hormones

ICSE Exam — Endocrine System

• Name the hormone responsible for regulation of blood glucose and its source gland
• Explain why the pituitary is called the master gland
• State the effect of adrenaline on the body during emergency situations