Chemical Coordination and Integration

NCERT Line-by-Line Breakdown for NEET 2026

Unit 5: Human Physiology

The neural system provides point-to-point coordination but is short-lived. To regulate cellular functions continuously, we need a special kind of coordination: Chemical Coordination. This is performed by Hormones secreted by Endocrine Glands (Ductless glands).

1. The Master Controllers

A. Hypothalamus (Basal part of Diencephalon)

Contains Neurosecretory cells (Nuclei) that produce hormones regulating the pituitary.

Releasing Hormones: Stimulate pituitary (e.g., GnRH → Release of Gonadotrophins).
Inhibiting Hormones: Inhibit pituitary (e.g., Somatostatin → Inhibits Growth Hormone).

B. Pituitary Gland (Master Gland)

Located in a bony cavity called Sella Tursica. Attached to hypothalamus by a stalk.

[Image of pituitary gland anatomy anterior posterior lobes]

Adenohypophysis (Anterior)
• GH (Growth Hormone): Over-secretion → Gigantism/Acromegaly. Low → Dwarfism.
• PRL (Prolactin): Milk formation.
• TSH: Thyroid stimulation.
• ACTH: Adrenal cortex stimulation.
• LH & FSH (Gonadotrophins): Gonadal activity.

Neurohypophysis (Posterior)
Stores hormones synthesized by Hypothalamus.
• Oxytocin: Milk Ejection (Let-down reflex) & Childbirth (Uterine contraction).
• Vasopressin (ADH): Water reabsorption (prevents Diuresis).

2. Thyroid & Parathyroid

A. Thyroid Gland

Two lobes on either side of trachea. Composed of follicles and stromal tissues. Requires Iodine.

T3 & T4 (Thyroxine): Regulate BMR (Basal Metabolic Rate), RBC formation, and metabolism of carbs/proteins/fats.
TCT (Thyrocalcitonin): Lowers blood calcium levels (Hypocalcemic).

⚠️ Disorders: Goitre (Iodine deficiency), Cretinism (Hypothyroid in pregnancy – mental retardation), Exophthalmic Goitre (Graves’ disease – Hyperthyroid).

B. Parathyroid Gland

4 glands on back side of Thyroid. Secrete PTH (Parathyroid Hormone).

Hypercalcemic: Increases blood Ca++ levels (Bone resorption/dissolution).
Antagonistic to TCT.

3. Adrenal & Pancreas

A. Adrenal Gland (Supra-renal)

Cortex (Outer)
• Mineralocorticoids (Aldosterone): Balance Water & Electrolytes (Na+ reabsorption).
• Glucocorticoids (Cortisol): Anti-inflammatory, Gluconeogenesis, Lipolysis. (Stress response).

Medulla (Inner)
• Catecholamines (Adrenaline/Nor-adrenaline): Fight or Flight hormones. Increase Heart rate, Alertness, Sweating.

B. Pancreas (Islets of Langerhans)

Cell	Hormone	Function
Alpha Cells	Glucagon	Hyperglycemic: Increases blood glucose (Glycogenolysis).
Beta Cells	Insulin	Hypoglycemic: Decreases blood glucose (Transport into cells/Glycogenesis).

Diabetes Mellitus: Loss of glucose through urine + formation of harmful Ketone bodies.

4. Other Glands & Mechanism

Pineal Gland: Secretes Melatonin. Regulates 24-hour Diurnal rhythm (Sleep-wake cycle).
Thymus: Secretes Thymosins. Differentiation of T-Lymphocytes (Cell-mediated immunity). Degenerates in old age.
Heart: ANF (Lowers BP).
Kidney: Erythropoietin (RBC formation).

Mechanism of Hormone Action

Membrane Bound Receptors
For Protein/Peptide hormones (Insulin, Pituitary hormones). Cannot enter cell. Generate Second Messengers (cAMP, Ca++).

Intracellular Receptors
For Steroids (Testosterone, Cortisol) & Iodothyronines. Cross membrane, bind to nuclear receptors, and interact with Genome.

📝 Rapid Fire MCQs

Q1. Which hormone is responsible for the ‘Let-down reflex’ in lactation?

A) Prolactin
B) Oxytocin
C) Estrogen
D) Progesterone

Click to check Answer

Answer: B) Oxytocin (Milk Ejection). Prolactin is for Milk Synthesis.

Q2. Which of the following is an amino acid derivative hormone?

A) Epinephrine
B) Ecdysone
C) Estradiol
D) Estriol