Chemical Coordination and Integration – Class 11 Biology Chapter 19 Notes & NCERT PDF

Class 11BiologyChapter 19NCERT book: Biology - Class 11

Notes and a simple summary of Chapter 19 of the NCERT Class 11 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 19: Chemical Coordination and Integration

Introduction

Neural coordination is fast but short-lived, and nerve fibres do not reach every cell. Continuous regulation of cellular functions is provided by hormones. The neural and endocrine systems jointly coordinate and regulate the body's physiological functions.

Key Concepts

19.1 Endocrine Glands and Hormones

Endocrine glands lack ducts (ductless glands); their secretions are hormones. Classical definition: a chemical produced by endocrine glands, released into blood and transported to a distant target organ. Current definition:

Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

Invertebrates have simple endocrine systems; vertebrates have many hormones.

19.2 Human Endocrine System

Organised endocrine bodies: pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus and gonads (testis/ovary). Other organs — GI tract, liver, kidney, heart — also produce hormones.

#### 19.2.1 Hypothalamus

Basal part of the diencephalon (forebrain). Its neurosecretory cells (nuclei) make hormones that regulate pituitary hormones:

Releasing hormones — e.g., GnRH stimulates pituitary synthesis and release of gonadotrophins.

Inhibiting hormones — e.g., somatostatin inhibits release of growth hormone.

These travel down axons and reach the pituitary through a portal circulatory system, regulating the anterior pituitary. The posterior pituitary is under direct neural regulation of the hypothalamus.

#### 19.2.2 Pituitary

In a bony cavity, sella tursica, attached to the hypothalamus by a stalk.

Adenohypophysis:

- Pars distalis (anterior pituitary) — GH, PRL, TSH, ACTH, LH, FSH.

- Pars intermedia — only MSH; in humans almost merged with pars distalis.

Neurohypophysis (pars nervosa, posterior pituitary) — stores and releases oxytocin and vasopressin, which are made in the hypothalamus and transported axonally.

Actions and disorders:

GH — over-secretion: gigantism; low secretion: pituitary dwarfism; excess in adults (middle age): acromegaly (facial disfigurement; hard to diagnose early).

Prolactin — growth of mammary glands and milk formation.

TSH — synthesis/secretion of thyroid hormones.

ACTH — glucocorticoids from the adrenal cortex.

LH and FSH (gonadotrophins) — males: LH → androgens from testis; FSH + androgens regulate spermatogenesis. Females: LH induces ovulation of Graafian follicles and maintains the corpus luteum; FSH stimulates growth of ovarian follicles.

MSH — acts on melanocytes; regulates skin pigmentation.

Oxytocin — contracts smooth muscles; vigorous uterine contraction at childbirth and milk ejection.

Vasopressin (ADH) — water and electrolyte resorption by distal tubules, reducing water loss (diuresis). Impaired ADH → diabetes insipidus (water loss, dehydration).

#### 19.2.3 Pineal

On the dorsal side of the forebrain; secretes melatonin — regulates the 24-hour (diurnal) rhythm (sleep–wake cycle, body temperature) and influences metabolism, pigmentation, menstrual cycle and defence capability.

#### 19.2.4 Thyroid

Two lobes on either side of the trachea, joined by the isthmus; made of follicles and stromal tissue. Follicular cells make thyroxine (T₄, tetraiodothyronine) and T₃ (triiodothyronine). Iodine is essential.

Iodine deficiency → hypothyroidism and goitre.

Hypothyroidism in pregnancy → cretinism (stunted growth, mental retardation, low IQ, abnormal skin, deaf-mutism); in adult women, irregular menstrual cycle.

Hyperthyroidism (thyroid cancer or nodules) — exophthalmic goitre / Graves' disease: enlarged thyroid, protruding eyeballs, raised BMR, weight loss.

Functions: regulate basal metabolic rate, support RBC formation, control carbohydrate/protein/fat metabolism, water–electrolyte balance.

Thyrocalcitonin (TCT) — protein hormone regulating blood calcium (decreases it).

#### 19.2.5 Parathyroid

Four glands on the back of the thyroid (one pair in each lobe); secrete PTH (peptide), regulated by circulating Ca²⁺. PTH increases blood Ca²⁺ — stimulates bone resorption, renal reabsorption of Ca²⁺ and Ca²⁺ absorption from food: a hypercalcemic hormone. With TCT it maintains calcium balance.

#### 19.2.6 Thymus

Lobular gland between the lungs behind the sternum, ventral to the aorta. Secretes thymosins — differentiation of T-lymphocytes (cell-mediated immunity) and antibody production (humoral immunity). It degenerates in old age, weakening immune responses.

#### 19.2.7 Adrenal

One pair, above each kidney; central adrenal medulla and outer adrenal cortex.

Medulla — adrenaline (epinephrine) and noradrenaline (norepinephrine) = catecholamines; emergency / fight-or-flight hormones: increase alertness, pupillary dilation, piloerection, sweating, heart beat, strength of contraction, rate of respiration; stimulate breakdown of glycogen (raising blood glucose), lipids and proteins.

Cortex — three layers: zona reticularis (inner), zona fasciculata (middle), zona glomerulosa (outer). Secretes corticoids:

- Glucocorticoids (main: cortisol) — gluconeogenesis, lipolysis, proteolysis; inhibit amino acid uptake; maintain cardiovascular and kidney functions; anti-inflammatory; suppress immune response; stimulate RBC production.

- Mineralocorticoids (main: aldosterone) — Na⁺ and water reabsorption and excretion of K⁺ and phosphate at renal tubules; maintains electrolytes, fluid volume, osmotic pressure and BP.

- Small amounts of androgenic steroids — axial, pubic and facial hair at puberty.

Underproduction of cortical hormones → Addison's disease (acute weakness, fatigue).

#### 19.2.8 Pancreas

A composite gland (exocrine + endocrine). Endocrine part: Islets of Langerhans — about 1 to 2 million, only 1–2% of pancreatic tissue.

α-cells → glucagon — acts on hepatocytes; glycogenolysis and gluconeogenesis; reduces cellular glucose uptake → hyperglycemic hormone.

β-cells → insulin — acts on hepatocytes and adipocytes; increases glucose uptake and utilisation; glycogenesis → hypoglycemic.

Prolonged hyperglycemia → diabetes mellitus — glucose loss in urine and harmful ketone bodies; treated with insulin therapy.

#### 19.2.9 Testis

In the scrotal sac; primary sex organ and endocrine gland. Leydig (interstitial) cells in intertubular spaces produce androgens, mainly testosterone: development and function of accessory sex organs (epididymis, vas deferens, seminal vesicles, prostate, urethra), muscular growth, facial/axillary hair, low-pitched voice, spermatogenesis, male sexual behaviour (libido), anabolic effects.

#### 19.2.10 Ovary

Produces one ovum each menstrual cycle and steroid hormones estrogen and progesterone. Estrogen — mainly from growing follicles; after ovulation the ruptured follicle becomes the corpus luteum, secreting mainly progesterone.

Estrogen — growth of female secondary sex organs, follicle development, secondary sex characters (e.g., high-pitched voice), mammary gland development, female sexual behaviour.

Progesterone — supports pregnancy; stimulates alveoli formation and milk secretion in mammary glands.

19.3 Hormones of Heart, Kidney and GI Tract

Heart (atrial wall) — ANF: dilates blood vessels, lowers BP.

Kidney (juxtaglomerular cells) — erythropoietin: stimulates erythropoiesis.

GI tract — gastrin (HCl and pepsinogen), secretin (water and bicarbonate from exocrine pancreas), CCK (pancreatic enzymes and bile), GIP (inhibits gastric secretion and motility).

Non-endocrine tissues secrete growth factors for growth and repair.

19.4 Mechanism of Hormone Action

Hormones bind specific hormone receptors in target tissues only, forming a hormone–receptor complex.

Membrane-bound receptors — hormones do not enter the cell; they generate second messengers (cyclic AMP, IP₃, Ca²⁺) that regulate metabolism.

Intracellular (mostly nuclear) receptors — e.g., steroid hormones, iodothyronines; regulate gene expression or chromosome function.

Chemical classes: (i) peptide/polypeptide/protein (insulin, glucagon, pituitary and hypothalamic hormones); (ii) steroids (cortisol, testosterone, estradiol, progesterone); (iii) iodothyronines (thyroid hormones); (iv) amino-acid derivatives (epinephrine).

Diagrams to Know (in words)

Location of endocrine glands on a human outline: hypothalamus, pituitary, pineal, thyroid/parathyroid, thymus, adrenal, pancreas, testis/ovary.

Hypothalamus–pituitary with portal circulation to the anterior lobe and axonal link to the posterior lobe.

Thyroid ventral view with isthmus; four parathyroids dorsally.

Protein hormone (membrane receptor → second messenger) vs steroid hormone (enters cell → nuclear receptor → gene expression).

Key-Facts Sheet

Anterior pituitary: GH, PRL, TSH, ACTH, LH, FSH; pars intermedia: MSH; posterior: oxytocin, vasopressin

Hyperglycemic: glucagon; hypoglycemic: insulin; hypercalcemic: PTH; blood-calcium lowering: TCT

BP-lowering: ANF; RBC formation: erythropoietin

Islets of Langerhans: 1–2 million, 1–2% of pancreas

Exam Focus

Define exocrine gland, endocrine gland and hormone (current definition).

List hormones of each gland; target glands of hypothalamic hormones (pituitary), TSH (thyroid), ACTH (adrenal cortex), LH/FSH (gonads), MSH (melanocytes).

Deficiency causes: diabetes mellitus (insulin), goitre (thyroid hormones, iodine deficiency), cretinism (thyroid hormones in pregnancy).

Match: T₄ — thyroid; PTH — parathyroid; GnRH — hypothalamus; LH — pituitary.

FSH is a protein hormone acting through membrane-bound receptors and second messengers.

Key Terms

Endocrine gland (अंतःस्रावी ग्रंथि)

Hormone (हॉर्मोन)

Hypothalamus (अधश्चेतक)

Pituitary gland (पीयूष ग्रंथि)

Pineal gland (पीनियल ग्रंथि)

Thyroid gland (अवटु ग्रंथि)

Parathyroid gland (परावटु ग्रंथि)

Thymus (थाइमस)

Adrenal gland (अधिवृक्क ग्रंथि)

Islets of Langerhans (लैंगरहैंस द्वीप)

Insulin (इंसुलिन)

Glucagon (ग्लूकागॉन)

Goitre (घेंघा)

Second messenger (द्वितीयक संदेशवाहक)

Hormone receptor (हॉर्मोन ग्राही)

Common Mistakes

Saying the posterior pituitary makes oxytocin and vasopressin — it only stores and releases them; the hypothalamus synthesises them.

Swapping glucagon (hyperglycemic, α-cells) and insulin (hypoglycemic, β-cells).

Confusing diabetes insipidus (ADH problem) with diabetes mellitus (insulin problem).

Stating PTH lowers blood calcium — PTH raises it; TCT lowers it.

💡 Key Learning Points

✓Hormones are non-nutrient chemicals acting as intercellular messengers in trace amounts; they give slower, longer-lasting coordination than nerves.
✓The hypothalamus controls the anterior pituitary through releasing/inhibiting hormones via portal circulation and the posterior pituitary neurally.
✓Each endocrine gland — pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, testis, ovary — has specific hormones, actions and disorders.
✓Heart (ANF), kidney (erythropoietin) and GI tract (gastrin, secretin, CCK, GIP) also secrete hormones.
✓Hormones act via membrane-bound receptors and second messengers, or intracellular receptors that regulate gene expression.

👨‍🏫 Teaching Tips

→Build a gland–hormone–action–disorder chart together, one row per gland.
→Use a body outline for students to place each endocrine gland from memory.
→Explain the hypothalamus–pituitary axis with a 'manager and supervisors' analogy.
→Pair opposite hormones: insulin/glucagon, PTH/TCT, ANF/renin-angiotensin to stress balance.
→Contrast diabetes insipidus and diabetes mellitus explicitly to avoid confusion.
→Draw protein vs steroid hormone action side by side (membrane receptor vs nuclear receptor).
→Use the book's matching and fill-in exercises as a timed quiz.

📋 Assessment Questions

Define hormone and distinguish exocrine and endocrine glands.
List the hormones of the anterior and posterior pituitary and their functions.
Explain how insulin and glucagon maintain glucose homeostasis.
Name the hormones whose deficiency causes diabetes mellitus, goitre and cretinism.
Describe the mechanism of action of a protein hormone such as FSH.

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