Quick Revision Notes

Class 11 Biology: Chemical Coordination and Integration

MP Board Education

Introduction to Chemical Coordination

Endocrine System: The neural system and the endocrine system jointly coordinate and regulate the physiological functions of the body. Since the nerve fibers do not innervate all cells of the body, a special coordination system is needed. This is provided by hormones.
Hormones: Non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.
Endocrine Glands: Ductless glands (ducts are absent) that release their secretions (hormones) directly into the blood.

Human Endocrine System

The major endocrine glands and structures out of the body include:

Hypothalamus
Pituitary Gland
Pineal Gland
Thyroid Gland
Parathyroid Gland
Thymus
Adrenal Gland
Pancreas
Testis (in males)
Ovary (in females)

1. Hypothalamus

Location: Basal part of diencephalon (forebrain).
Function: Produces neurohormones (releasing and inhibiting hormones).
Key Hormones:
- Releasing hormones: Stimulate secretion of pituitary hormones (e.g., Gonadotropin-releasing hormone - GnRH).
- Inhibiting hormones: Inhibit secretion of pituitary hormones (e.g., Somatostatin).

2. Pituitary Gland (Hypophysis)

Location: Sella turcica (a bony cavity), attached to the hypothalamus.
Division: Divided anatomically into Adenohypophysis (anterior pituitary) and Neurohypophysis (posterior pituitary).

A. Adenohypophysis Hormones:

Growth Hormone (GH): Over-secretion leads to Gigantism; under-secretion leads to Pituitary Dwarfism. Acromegaly is caused by excess GH in adults.
Prolactin (PRL): Regulates growth of mammary glands and milk formation.
Thyroid-Stimulating Hormone (TSH): Stimulates synthesis and secretion of thyroid hormones.
Adrenocorticotropic Hormone (ACTH): Stimulates synthesis and secretion of steroid hormones (glucocorticoids) from the adrenal cortex.
Luteinizing Hormone (LH) & Follicle-Stimulating Hormone (FSH): Collectively called gonadotropins. Stimulate gonadal activity.

B. Neurohypophysis (Pars Nervosa) Hormones:

(Stored and released by posterior pituitary, synthesized by hypothalamus)

Oxytocin: Contracts smooth muscles; triggers uterin contraction during child birth and milk ejection from mammary glands.
Vasopressin (Antidiuretic Hormone - ADH): Acts mainly at the kidney and stimulates resorption of water and electrolytes by distal tubules, thus reducing water loss (diuresis). Deficiency causes Diabetes Insipidus.

3. Pineal Gland

Location: Dorsal side of forebrain.
Hormone: Melatonin
Function: Plays a very important role in regulation of a 24-hour (diurnal) rhythm of our body (e.g., sleep-wake cycle, body temperature, metabolism, pigmentation, defense capability).

4. Thyroid Gland

Location: Composed of two lobes on either side of the trachea.
Hormone: Thyroxine (Tetraiodothyronine - T4), Triiodothyronine (T3), and Thyrocalcitonin (TCT).
Functions:
- Regulation of the basal metabolic rate (BMR).
- Support red blood cell formation.
- Control metabolism of carbohydrates, proteins, and fats.
- TCT regulates calcium levels in blood (hypocalcemic hormone).
Disorders:
- Hypothyroidism: Iodine deficiency leads to Goitre; during pregnancy causes stunted growth and mental retardation (Cretinism); in adult women causes Myxedema.
- Hyperthyroidism: Exophthalmic goitre (Grave's disease) - enlargement of thyroid gland, high BMR, nervousness, protrusion of eyeballs.

5. Parathyroid Gland

Location: Back side of the thyroid gland (4 in number).
Hormone: Parathyroid Hormone (PTH) / Collip's Hormone
Function: Peptide hormone that increases $\text{Ca}^{2+}$ levels in blood (hypercalcemic hormone). It stimulates bone resorption and reabsorption of $\text{Ca}^{2+}$ by renal tubules.

6. Thymus Gland

Location: Lobular structure located between lungs behind sternum on the ventral side of aorta.
Hormone: Thymosins
Function: Play a major role in the differentiation of T-lymphocytes (cell-mediated immunity) and promote antibody production (humoral immunity). Degenerates in older individuals resulting in weak immunity.

7. Adrenal Gland

Location: Anterior part of each kidney.
Structure: Outer Adrenal Cortex and inner Adrenal Medulla.

A. Adrenal Medulla Hormones:

Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine) – collectively called Catecholamines or "Emergency Hormones" / "Fight or Flight hormones".
Functions: Increase alertness, pupillary dilation, piloerection (raising of hair), sweating, heart rate, rate of respiration, glycogen breakdown.

B. Adrenal Cortex Zones & Hormones:

Zona Reticularis (Inner layer): Sex corticoids (Androgens).
Zona Fasciculata (Middle layer): Glucocorticoids (e.g., Cortisol - involved in carbohydrate metabolism, anti-inflammatory).
Zona Glomerulosa (Outer layer): Mineralocorticoids (e.g., Aldosterone - regulates $\text{Na}^+$ and water balance).

Disorder: Addison's Disease – caused by under-secretion of adrenal cortex hormones, resulting in hypoglycemia, weakness, and bronze-like skin pigmentation.

8. Pancreas

Location: Composite gland situated behind the stomach.
Endocrine Part: Islets of Langerhans (contain about 1-2 million islets).
Cell Types & Hormones:
- Alpha ($\alpha$) cells: Produce Glucagon (Hyperglycemic factor - increases blood glucose levels by glycogenolysis).
- Beta ($\beta$) cells: Produce Insulin (Hypoglycemic factor - decreases blood glucose levels by promoting cellular glucose uptake and glycogenesis).
Disorder: Diabetes Mellitus – prolonged hyperglycemia leading to loss of glucose through urine (glucosuria) and formation of harmful compounds known as ketone bodies.

9. Gonads

A. Testis (Male Gonad):

Location: Scrosal sac of males.
Hormone: Androgens (mainly Testosterone).
Function: Regulation of maturation of male accessory sex organs, spermatogenesis, and secondary sexual characters (deepening of voice, facial hair, etc.).

B. Ovary (Female Gonad):

Location: Abdominal cavity of females.
Hormones: Estrogen and Progesterone.
Functions:
- Estrogen: Growth and development of female accessory sex organs, secondary sexual characters, and ovarian follicle growth.
- Progesterone: Supports pregnancy, acts on mammary glands for milk secretion (alveoli formation).

10. Hormones of Heart, Kidney, and Gastrointestinal Tract

Atrial Natriuretic Factor (ANF): Secreted by the atrial wall of the heart; decreases blood pressure by causing vasodilation.
Erythropoietin: Secreted by juxtaglomerular cells of kidney; stimulates erythropoiesis (RBC formation).
Gastrointestinal Hormones:
- Gastrin: Stimulates $\text{HCl}$ and pepsinogen secretion.
- Secretin: Stimulates secretion of water and bicarbonate ions from exocrine pancreas.
- Cholecystokinin (CCK): Stimulates secretion of bile juice and pancreatic enzymes.
- Gastric Inhibitory Peptide (GIP): Inhibits gastric secretion and motility.

Mechanism of Hormone Action

Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues.

Receptors on cell membrane (Peptide/Protein hormones):
- Hormone (First messenger) $\rightarrow$ Binds to membrane receptor $\rightarrow$ Generates second messengers (like cyclic AMP, $\text{IP}_3$, $\text{Ca}^{2+}$) $\rightarrow$ Biochemical responses $\rightarrow$ Physiological response.
- Example: Insulin, Oxytocin, FSH.
Intracellular receptors (Steroid/Iodothyronine hormones):
- Hormone (Lipid soluble) $\rightarrow$ Enters cell $\rightarrow$ Binds to intracellular receptor (mostly in nucleus) $\rightarrow$ Hormone-receptor complex interacts with genome $\rightarrow$ Protein synthesis / Gene expression $\rightarrow$ Physiological response.
- Example: Cortisol, Testosterone, Estrogen, Thyroxine.

Chemical Coordination and Integration

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