Chemical Coordination and Integration - Master Notes

I. Endocrine Glands and Hormones

Endocrine glands lack ducts and are called ductless glands. Their secretions are called hormones.

[i] Modern Definition: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

II. The Hypothalamus and Pituitary Axis

Hypothalamus contains Neurosecretory cells (nuclei) which produce hormones. They regulate the synthesis and secretion of pituitary hormones.

Releasing Hormones: e.g., GnRH (stimulates pituitary to release gonadotrophins).
Inhibiting Hormones: e.g., Somatostatin (inhibits release of growth hormone).

[!] Posterior Pituitary: Is under strictly Direct Neural Regulation of the hypothalamus. It stores Oxytocin and Vasopressin (ADH).

III. Major Endocrine Glands

Gland	Main Hormones	Function
Pineal	Melatonin	Diurnal rhythm (Sleep-wake cycle).
Thyroid	T3, T4, TCT	BMR, RBC formation, Blood Ca++ lower.
Parathyroid	PTH	Increases Blood Ca++ levels.
Thymus	Thymosins	T-lymphocytes differentiation (Immunity).
Adrenal Medulla	Adrenaline	Emergency (3F - Fight, Flight, Fright).
Pancreas	Insulin, Glucagon	Glucose homeostasis (Islets of Langerhans).

IV. Non-Endocrine Tissues

Heart: ANF (Atrial Natriuretic Factor) - Decreases Blood Pressure.
Kidney: Erythropoietin - Stimulates RBC formation.
GI Tract: Gastrin, Secretin, CCK, GIP - Regulate digestion.

V. Mechanism of Hormone Action

Hormones produce their effects by binding to specific proteins called Hormone Receptors.

Peptide/Protein Hormones: Bind to membrane-bound receptors. Generate second messengers (e.g., cAMP, IP3, Ca++).
Steroid Hormones/Iodothyronines: Interact with intracellular receptors. Mainly regulate gene expression in the nucleus.

VI. Important Disorders

Cretinism: Hypothyroidism during pregnancy; stunted growth.
Diabetes Mellitus: Failure of Insulin action; high blood glucose.
Diabetes Insipidus: Deficiency of ADH; excessive water loss.
Exophthalmic Goitre: Hyperthyroidism (Grave's disease).

[Q] Why is the Pituitary gland often called the "Master Gland" even though it is controlled by the Hypothalamus?

[A] Explanation:

The Pituitary coordinates the activity of almost all other endocrine glands (Thyroid, Adrenals, Gonads) by secreting trophic hormones like TSH, ACTH, FSH, and LH. While it follows the Hypothalamus's "commands," it is the primary executioner of hormonal control in the body.

[Q] "PTH and TCT are antagonistic hormones." Explain this statement.

[A] Explanation:

PTH (Parathyroid Hormone) increases blood calcium levels by mobilizing it from bones (resorption). TCT (Thyrocalcitonin) decreases blood calcium levels by encouraging its deposition in bones. Together, they maintain calcium homeostasis.

[Q] Differentiate between Diabetes Mellitus and Diabetes Insipidus.

[A] Explanation:

Diabetes Mellitus is caused by Insulin deficiency or resistance, leading to high blood sugar and glucose in urine. Diabetes Insipidus is caused by ADH (Vasopressin) deficiency, leading to excessive excretion of very dilute urine and extreme thirst, without high blood sugar.

[Q] Why does use of iodised salt prevent Goitre?

[A] Explanation:

Iodine is essential for the synthesis of thyroid hormones (T3 and T4). If iodine is deficient, the thyroid gland cannot produce enough hormones, leading to a compensatory enlargement of the gland called Goitre.

[Q] What is the role of 'Second Messengers' in hormone action?

[A] Explanation:

Protein hormones are water-soluble and cannot cross the lipid cell membrane. They bind to outer receptors and trigger the production of Second Messengers (like cAMP or Calcium) inside the cell. These messengers then transmit the signal to achieve the desired metabolic effect.

[Q6] Why is Adrenaline the "emergency hormone"?

Increases alertness, pupil dilation, heart rate, and glycogen breakdown instantly.

[Q7] Function of melatonin.

Regulates 24-hr diurnal rhythm; body temp, sleep, and menstrual cycle.

[Q8] Alpha cells vs Beta cells in Pancreas.

Alpha: Glucagon (increases sugar). Beta: Insulin (decreases sugar).

[Q9] ANF function.

Heart hormone; causes vasodilation to lower blood pressure.

[Q10] Why is Thymus important for immunity?

Site for T-lymphocytes differentiation (Cell-mediated immunity).

[Q11] Exophthalmic goitre symptoms.

Grave's disease: High BMR, weight loss, and protrusion of eyeballs.

[Q12] FSH and LH together called?

Gonadotrophins.

[Q13] Every steroid hormone binds to?

Intracellular (usually nuclear) receptors.

[Q14] Secretin function.

Stimulates exocrine pancreas to secrete water and bicarbonate ions.

[Q15] CCK role in digestion.

Stimulates gallbladder contraction and pancreatic enzyme secretion.

[Q16] Why does Thymus degenerate in old age?

Causes weak immune responses in the elderly.

[Q17] Primary role of Cortisol.

Gluconeogenesis, Anti-inflammatory, and Immune suppression.

[Q18] Estrogen vs Progesterone.

Estrogen: Secondary sexual traits. Progesterone: Pregnancy maintenance.

[Q19] Hypothalamic hormones are?

Releasing or Inhibiting factors.

[Q20] Somatostatin effect.

Inhibits the release of Growth Hormone from the pituitary.

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Hormones: Non-nutrient intercellular messengers in trace amounts.

Hypothalamus: Contains neurosecretory nuclei; master of master gland.

Pituitary Gland: Located in a bony cavity called Sella turcica.

Somatotrophin: Another name for Growth Hormone (GH).

Gigantism: Result of hypersecretion of GH during childhood.

Acromegaly: Severe disfigurement due to high GH in adults.

Prolactin: Regulates growth of mammary glands and milk formation.

TSH: Stimulates production of thyroid hormones.

ACTH: Stimulates adrenal cortex to secrete glucocorticoids.

LH (in males): Stimulates Leydig cells to produce androgens.

FSH (in males): Along with androgens, regulates spermatogenesis.

MSH: Produced by pars intermedia; affects skin pigmentation.

Oxytocin: Stimulates vigorous uterine contraction during birth.

ADH (Vasopressin): Decreases water loss; stimulates water reabsorption in kidneys.

Diabetes Insipidus: Caused by inability of kidney to reabsorb water (low ADH).

Pineal Gland: Secretes Melatonin; on the dorsal side of forebrain.

Thyroid Gland: Composed of follicles and stromal tissues.

Thyroxine: Requires Iodine for synthesis in the thyroid.

Goitre: Enlargement of thyroid gland due to iodine deficiency.

Cretinism: Hypothyroidism in infants; results in mental retardation.

Grave's Disease: Exophthalmic goitre (hyperthyroidism).

TCT (Calcitonin): Lowers blood calcium levels.

Parathyroid Hormone: Increases blood Ca++ (Hypercalcaemic hormone).

Bone Resorption: Dissolution of bones stimulated by PTH.

Thymus: Lobular structure between lungs; secretes Thymosins.

Thymosins: Help in T-cell differentiation and antibody production.

Adrenal Medulla: Secretes Catecholamines (Adrenaline and Noradrenaline).

3F Hormones: Adrenaline/Noradrenaline for Fear, Fight, or Flight.

Adrenal Cortex: Divided into glomerulosa, fasciculata, and reticularis zones.

Aldosterone: Main mineralocorticoid; regulates water and electrolytes.

Cortisol: Involved in gluconeogenesis and anti-inflammatory action.

Addison's disease: Fatigue due to low secretion of adrenal cortex hormones.

Islets of Langerhans: Endocrine part of the Pancreas (~1-2 million).

Glucagon: Hyperglycaemic hormone produced by alpha cells.

Insulin: Hypoglycaemic hormone produced by beta cells.

Diabetes Mellitus: Loss of glucose through urine and ketone bodies.

Androgens: Male steroid hormones like Testosterone.

Estrogen: Synthesized by growing ovarian follicles.

Progesterone: Secreted by Corpus Luteum; maintains pregnancy.

ANF: Secreted by Atrial walls of heart to decrease BP.

Erythropoietin: Peptide hormone from Kidney for RBC production.

Gastrin: Acts on gastric glands for HCl secretion.

Secretin: Stimulates secretion of water and bicarbonates from Pancreas.

CCK: Stimulates secretion of bile and pancreatic enzymes.

Hormone receptors: Specific proteins where hormones bind.

Membrane receptors: For water-soluble hormones like FSH.

Second Messengers: cAMP, IP3, and Ca++ for protein hormones.

Intracellular receptors: For steroid hormones and T3/T4.

Feedback mechanism: Regulates the amount of hormone secretion.

Trophic hormones: Pituitary hormones that affect other glands.

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