Human Physiology: Chemical Coordination and Integration

1. Endocrine System:

• Definition and Location:

• Endocrine system: Network of glands that secrete hormones directly into the bloodstream.

• Pituitary gland: Pea-sized gland located at the base of the skull. (NCERT Biology Class 11, Chapter 22, Page 281)

• Thyroid gland: Butterfly-shaped gland located in front of the neck. (NCERT Biology Class 12, Chapter 21, Page 219)

• Parathyroid glands: Four small glands located behind the thyroid gland. (NCERT Biology Class 11, Chapter 22, Page 282)

• Pancreas: Organ with both exocrine and endocrine functions, located behind the stomach. (NCERT Biology Class 11, Chapter 16, Page 191)

• Adrenal glands: Pair of glands located on top of each kidney. (NCERT Biology Class 11, Chapter 22, Page 286)

• Testes (males) and ovaries (females): Primary reproductive organs.

• Hormone Structure and Function:

• Hormones are chemical messengers that regulate various physiological processes.

• Peptide hormones: Composed of amino acids, e.g., insulin, glucagon.

• Steroid hormones: Derived from cholesterol, e.g., estrogen, testosterone.

• Regulation of Hormone Secretion:

• Feedback mechanisms:

• Positive feedback: Increases the response to a stimulus (e.g., oxytocin during childbirth).

• Negative feedback: Decreases the response to a stimulus (e.g., insulin and glucagon).

2. Pituitary Gland:

• Location, Structure, and Hormones:

• Located at the base of the brain. (NCERT Biology Class 11, Chapter 22, Page 281)

• Secretes growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin.

• Regulation and Function:

• Controlled by the hypothalamus.

• GH: Regulates growth and development.

• TSH: Stimulates the thyroid gland.

• ACTH: Controls the release of hormones from the adrenal glands.

• LH: Involved in ovulation and testosterone production.

• FSH: Involved in sperm production and development of ovarian follicles.

• Prolactin: Stimulates milk production.

3. Thyroid Gland:

• Location, Structure, and Hormones:

• Situated in the neck region, consists of two lobes connected by an isthmus.

• Produces thyroxine (T4) and triiodothyronine (T3).

• Regulation and Function:

• Controlled by the pituitary gland’s TSH.

• T4 and T3 regulate metabolism, growth, and development.

• Calcitonin: Regulates blood calcium levels.

4. Parathyroid Glands:

• Location, Structure, and Hormone:

• Located near the thyroid gland, usually four in number.

• Secretes parathyroid hormone (PTH).

• Regulation and Function:

• PTH regulates calcium and phosphate homeostasis.

• Maintains calcium levels in blood and bones.

5. Adrenal Glands:

• Location, Structure, and Hormones:

• Situated on top of each kidney.

• Consists of two regions: adrenal cortex and medulla.

• Cortex produces corticosteroids (e.g., cortisol, aldosterone).

• Medulla produces catecholamines (e.g., adrenaline, noradrenaline).

• Regulation and Function:

• Corticosteroids regulate metabolism, immune response, and water and electrolyte balance.

• Catecholamines prepare the body for “fight or flight” responses.

6. Pancreas:

• Location, Structure, and Hormones:

• Located behind the stomach, with both exocrine (pancreatic juice) and endocrine functions.

• Endocrine pancreas produces insulin and glucagon.

• Regulation and Function:

• Insulin: Lowers blood sugar levels by facilitating glucose uptake into cells.

• Glucagon: Raises blood sugar levels by promoting the breakdown of stored glycogen.

7. Reproductive Hormones:

• Male Reproductive System:

• Testosterone: Primary sex hormone in males, produced by the testes.

• Regulates male sexual development, secondary sexual characters, and sperm production.

• Female Reproductive System:

• Estrogen: Primary sex hormone in females, produced by the ovaries.

• Progesterone: Produced by the ovaries and corpus luteum.

• Regulate the menstrual cycle, prepare the uterus for pregnancy, and maintain it.

8. Feedback Mechanisms:

• Positive Feedback:

  • Oxytocin during childbirth, triggering stronger uterine contractions.

• Negative Feedback:

• Insulin secretion lowers blood sugar, inhibiting further insulin release.

9. Neuroendocrine Integration:

• Hypothalamic-Pituitary Axis:
• Hypothalamus: Part of the brain that regulates hormone release.
• Pituitary gland: Secretes hormones that influence other glands.
• Hypothalamic hormones control pituitary hormone secretion.

10. Disorders and Dysfunctions:

• Diabetes:

• Type 1: Autoimmune destruction of insulin-producing cells.

• Type 2: Insulin resistance, impaired insulin secretion, or both.

• Thyroid Disorders:

• Hypothyroidism: Insufficient thyroid hormone production.

• Hyperthyroidism: Excessive thyroid hormone production.

• Growth Hormone Deficiency:

• Reduced GH secretion, leading to stunted growth.

• Cushing’s Syndrome:

• Excessive cortisol secretion, causing various symptoms including weight gain, high blood pressure, and mood changes.

• Addison’s Disease:

• Insufficient adrenal hormone production, leading to fatigue, weight loss, and low blood pressure.

Note: This covers important subtopics for the JEE exam. Consult standard textbooks and additional resources for a more comprehensive understanding.