Chapter 19 — Chemical Coordination and Integration

Chapter 19 of the Class 11 Biology NCERT textbook, "Chemical Coordination and Integration", explains this topic. Chemical coordination is carried out by hormones—non-nutrient chemicals produced by endocrine glands and other tissues that act as intercellular messengers—working alongside the neural system to regulate metabolism, growth, development, and homeostasis.

• The endocrine network — The chapter maps the endocrine system as organized glands plus scattered hormone-secreting cells in organs like the heart, kidney, and gut, together forming a slow, chemical control system that complements nerves.
• Hormones that run metabolism — It explains how specific hormones govern body chemistry—thyroid hormones set metabolic rate, pancreatic insulin and glucagon balance blood glucose, and adrenal catecholamines drive the fight-or-flight response.
• Mechanisms and disorders — The chapter shows two ways hormones act—membrane receptors making second messengers versus intracellular receptors altering gene expression—and links imbalances to disorders like diabetes, hypothyroidism, and Addison's disease.

1. 01The endocrine system comprises organized glands (pituitary, thyroid, adrenal, pancreas, parathyroid, thymus, pineal, gonads) plus hormone-secreting cells in the heart, kidney, and gastrointestinal tract
2. 02The hypothalamus regulates the pituitary through releasing and inhibiting hormones via a portal circulatory system, controlling anterior pituitary; the posterior pituitary is under direct neural regulation
3. 03Thyroid hormones (T3, T4) regulate basal metabolic rate, carbohydrate/protein/fat metabolism, and require iodine; deficiency causes hypothyroidism (goitre, cretinism); excess causes hyperthyroidism (Graves' disease)
4. 04Pancreatic insulin (β-cells) decreases blood glucose by promoting uptake and glycogenesis, while glucagon (α-cells) increases blood glucose via glycogenolysis and gluconeogenesis; imbalance causes diabetes mellitus
5. 05Adrenal catecholamines (epinephrine, norepinephrine) trigger fight-or-flight responses increasing heart rate, respiration, and glucose availability; cortical glucocorticoids regulate metabolism and immunity, mineralocorticoids control electrolyte balance
6. 06Hormone action occurs via two pathways: membrane-bound receptors generate second messengers (cAMP, IP3, Ca²⁺) for protein hormones; intracellular receptors regulate gene expression for steroids and thyroid hormones