Revision: Class 11 >> Chemical Coordination and Integration NEET (UG) Chemical Coordination and Integration

An exocrine gland is a gland that secretes its products (such as enzymes, sweat, or mucus) through a duct directly onto an epithelial surface or into a body cavity, rather than into the bloodstream.

An endocrine gland is a ductless gland that secretes hormones directly into the bloodstream to regulate various physiological processes and maintain homeostasis in the body.

The endocrine system is defined as a group of organs performing an overall common function. The endocrine glands secrete certain chemicals called hormones.

A group of glands and glandular cells that secrete hormones to regulate and coordinate various functions in the body through chemical control.

Hormone is a molecule that is created and secreted in very minute quantities into the blood stream by an endocrine gland or a specialized nerve cell that governs the growth or functioning of a specific tissue organ in a distant area of the body, e.g., insulin

Myxoedema is a condition that affects an adult if his thyroid does not function properly; in this condition, the person becomes sluggish with swelling of the face and hands.

Exophthalmic goitre a form of hyperthyroidism in which the thyroid gland is overactive and secretes excess thyroxine, producing an enlarged thyroid (goitre) together with protrusion of the eyes (exophthalmos).

Hypothyroidism is a medical condition in which the thyroid gland is underactive and fails to produce sufficient thyroid hormone to meet the body’s metabolic needs.

Hyperglycemia is a medical condition characterized by an abnormally high level of glucose (sugar) in the bloodstream.

Beta cells are specialized endocrine cells located within the islets of Langerhans in the pancreas. They are critical to human metabolism because they are the primary source of insulin production in the body.

Diabetes mellitus is a chronic metabolic condition characterised by elevated blood glucose (hyperglycemia). It occurs when the body either cannot produce enough insulin or cannot use the insulin it produces effectively.

• Glands that discharge secretions into ducts are known as exocrine glands.
• Sebaceous glands in the skin, salivary glands in the buccal cavity, etc. are examples of exocrine glands.

• The neural system provides rapid, point-to-point coordination among organs.
• Neural coordination is fast but short-lived.
• Nerve fibres do not innervate all body cells.
• Cellular functions require continuous regulation.
• Hormones provide special coordination and integration.
• Neural and endocrine systems jointly regulate physiological functions.

• Endocrine glands are ductless glands (they do not have ducts).
• Their secretions are called hormones.
• Hormones are chemical messengers that travel through the blood to target organs.
• They are non-nutrient substances produced in very small amounts.
• Hormones help in the coordination and regulation of body functions.

• Endocrine system controls body activities through chemical messengers called hormones, which are released directly into the bloodstream (no ducts).
• Hormones act as intercellular messengers — they inhibit, stimulate, or modify specific body processes like growth and development, and act only on specific target organs.
• Types of Hormones — Steroid (aldosterone, sex corticoids); Amine (thyroxine, adrenaline); Peptide (ADH, GnRH); Protein (TSH, FSH); Fatty acid derivatives (prostaglandins).
• Endocrine glands are ductless glands — they secrete hormones directly into the blood. Examples: thyroid, pituitary, pancreas, hypothalamus, adrenal glands.
• All endocrine glands work in a coordinated manner, activating each other to bring about overall chemical coordination in the body.

• Controls Pituitary - Hypothalamus regulates the anterior pituitary via Releasing (RH) and Inhibiting (IH) hormones.
• Oxytocin - Stored in the posterior pituitary; causes uterine contractions during childbirth and milk ejection.
• ADH (Vasopressin) - Stored in the posterior pituitary; promotes water reabsorption in the kidneys, reducing urine loss.
• GnRH - Stimulates the pituitary to release gonadotropins (reproductive hormones).
• Somatostatin - Inhibits the release of growth hormone from the pituitary.

• Pineal gland is a small endocrine gland located on the roof of diencephalon, between the two cerebral hemispheres, on the dorsal side of the forebrain.
• It consists of neuroglia and secretory cells called pinealocytes.
• It secretes Melatonin — an amine hormone derived from tryptophan, also called the sleep hormone.
• Melatonin regulates the body's biological clock (circadian rhythm) — the 24-hour diurnal rhythm, including the sleep-wake cycle and body temperature.
• It also influences pigmentation, metabolism, defense capability, and reproductive/menstrual cycle.

1. The thyroid gland is a butterfly-shaped gland located in the neck and secretes thyroxine and calcitonin.

2. Thyroxine controls basal metabolic rate, influences growth, mental development, bone formation, and body temperature.

3. Hypothyroidism may cause:

• Simple goitre (due to iodine deficiency),
• Cretinism (dwarfism and mental retardation in children),
• Myxoedema (sluggishness and swelling in adults).

4. Hyperthyroidism leads to exophthalmic goitre with symptoms like protruding eyes, neck swelling, high metabolism, rapid heartbeat, and breathlessness.

5. Use of iodised salt helps prevent thyroid-related issues caused by iodine deficiency.

• Four glands on posterior surface of thyroid; secrete peptide hormone Parathormone (PTH) / Collip's hormone.
• PTH Function - Increases blood Ca²⁺ by bone resorption, renal Ca²⁺ reabsorption, and intestinal Ca²⁺ absorption.
• PTH and Calcitonin (TCT) are antagonistic - together maintain calcium-phosphate balance. PTH is under feedback control of blood Ca²⁺.
• Hyposecretion → low Ca²⁺ → muscle twitch/spasm = Hypocalcaemic Tetany.
• Hypersecretion → excess bone demineralisation → softening/fracture = Osteoporosis (common in post-menopausal women).

• Located in the upper thorax, dorsal side of the heart; soft, pinkish, bilobed mass of lymphoid tissue.
• Prominent at birth but gradually atrophies in adults — hence called a temporary gland.
• Secretes hormone Thymosin, which plays a key role in the development of the immune system.
• Thymosin promotes differentiation and maturation of T-lymphocytes → provides cell-mediated immunity.
• Also promotes production of antibodies → provides humoral immunity.

• Pancreas functions both as an exocrine gland (secreting pancreatic juice into the duodenum) and an endocrine gland (secreting hormones into the blood).
• The Islets of Langerhans contain beta cells (secrete insulin) and alpha cells (secrete glucagon), which regulate blood sugar levels.
• Insulin lowers blood glucose by promoting glucose uptake by cells and storing excess glucose as glycogen in the liver and muscles.
• Under-secretion of insulin causes diabetes mellitus (hyperglycemia), with symptoms like excessive urination, thirst, weakness, and sugar in urine.
• Glucagon raises blood sugar by converting glycogen to glucose in the liver; overdose of insulin can lead to hypoglycemia or insulin shock.

• Location & Function - Testes are in the scrotal sac; act as both sex organs (sperm) and endocrine glands (hormones).
• Structure - Made of seminiferous tubules + stromal/interstitial tissue.
• Leydig Cells - Produce testosterone, which matures male accessory organs (epididymis, prostate, etc.).
• Androgen Functions - Control spermatogenesis, muscle/hair growth, low voice pitch, and libido (via CNS).
• Metabolic Effect - Androgens have anabolic effects on protein and carbohydrate metabolism.

• Location & Function - Pair of ovaries in the abdomen; produce one ovum/cycle + secrete estrogen & progesterone.
• Structure - Made of ovarian follicles + stromal tissue; follicles secrete estrogen.
• Corpus Luteum - After ovulation, the ruptured follicle becomes the corpus luteum, which secretes progesterone.
• Estrogen Functions - Develops female sex organs, ovarian follicles, a high-pitched voice, and regulates sexual behaviour.
• Progesterone Functions - Supports pregnancy; stimulates alveoli formation and milk secretion in mammary glands.

• Some non-endocrine tissues also secrete hormones (e.g., heart, kidney, gastrointestinal tract).
• The heart secretes Atrial Natriuretic Factor (ANF), which reduces blood pressure by dilating blood vessels.
• ANF is released when blood pressure increases, helping to bring it back to normal.
• Kidneys (juxtaglomerular cells) secrete erythropoietin, which stimulates RBC formation.
• The gastrointestinal tract secretes hormones that regulate digestion.
• Gastrin → stimulates secretion of HCl and pepsinogen.
• Secretin, CCK, and GIP → regulate pancreatic secretion, bile release, and inhibit gastric activity.

• Hormones bind to specific receptors in target tissues only, forming a hormone-receptor complex → causes biochemical changes.
• Two receptor types — Membrane-bound (cell surface) and Intracellular (inside cell/nucleus).
• Membrane Receptor — Water-soluble hormones bind surface receptor → adenylate cyclase → ATP converts to cAMP (2nd messenger) → enzyme activation. Other 2nd messengers: Ca²⁺, cGMP, IP₃.
• Intracellular Receptor — Lipid-soluble hormones cross membrane → bind cytoplasm receptor → complex enters nucleus → activates DNA → mRNA → protein synthesis.
• Membrane receptor = faster, short-lived; Intracellular receptor = slower, long-lasting.