Human Physiology – Study Notes (BSMS Siddha – Biology)
Purpose – Understand the structure, function, and inter‑relationships of the human body’s systems.
Target – Students of the Bachelor of Siddha Medicine & Surgery (BSMS).
1. Simple Explanation
Human physiology is the branch of biology that investigates how the body’s organs, tissues, and cells work together to maintain life. It explains “how” the body functions, not “what” the body is made of (which is anatomy).
Analogy: Think of the body as a complex machine. Physiology tells you the mechanics—how the gears, pumps, and circuits interact to keep the machine running smoothly.
2. Key Points – Organ Systems & Core Functions
| System | Main Organs / Structures | Core Functions | Interaction Highlights |
|---|---|---|---|
| Circulatory | Heart, blood vessels, blood | Transport oxygen, nutrients, hormones, waste | Drives blood pressure; works with respiratory & renal systems for gas & fluid balance |
| Respiratory | Lungs, trachea, bronchi | Gas exchange (O₂ ↔ CO₂) | Provides O₂ for cellular respiration; CO₂ removal via blood |
| Digestive | Mouth, esophagus, stomach, intestines, liver, pancreas | Break down food, absorb nutrients, eliminate waste | Releases digestive enzymes; produces hormones (e.g., gastrin) |
| Nervous | Brain, spinal cord, peripheral nerves | Control, coordination, and response to stimuli | Sends signals via neurotransmitters; works with endocrine system for homeostasis |
| Endocrine | Glands (pituitary, thyroid, pancreas, etc.) | Secrete hormones to regulate metabolism, growth, reproduction | Hormones act on target cells; feedback loops (e.g., insulin ↔ blood glucose) |
| Muscular | Skeletal, smooth, cardiac muscle | Movement, posture, blood pumping | Skeletal muscle contracts through ATP; smooth muscle in gut & vessels |
| Skeletal | Bones, cartilage | Support, protection, blood cell production | Bone marrow produces RBCs, WBCs, platelets |
| Immune | Lymph nodes, spleen, thymus, white blood cells | Defend against pathogens | Adaptive immunity (antibodies) vs innate immunity (barriers, phagocytes) |
| Reproductive | Male: testes, female: ovaries, uterus | Produce gametes & hormones for reproduction | Hormonal cycles (menstrual, spermatogenesis) |
| Excretory | Kidneys, ureters, bladder, urethra | Filter blood, excrete waste, regulate fluid & electrolytes | Works with circulatory system to maintain osmotic balance |
3. Worked Example – Regulation of Blood Glucose (Insulin–Glucagon Axis)
Scenario
A patient eats a carbohydrate‑rich meal. Blood glucose rises. How does the body restore normal glucose levels?
Step‑by‑Step
| Step | Physiological Event | Key Players | Result |
|---|---|---|---|
| 1. Food Ingestion | Carbohydrates → glucose in bloodstream | Pancreatic β‑cells | ↑ Blood glucose (~120–180 mg/dL) |
| 2. Detection | β‑cells sense high glucose | Glucose transporters (GLUT2) | Trigger insulin secretion |
| 3. Hormone Release | Insulin released into blood | Insulin | Lowers glucose by stimulating cells to uptake glucose |
| 4. Cellular Uptake | Glucose enters muscle, liver, fat cells via GLUT4 | Insulin receptor → PI3K/Akt pathway | ↓ Blood glucose |
| 5. Storage | Liver → glycogen; muscle → glycogen; fat → triglycerides | Glycogen synthase, lipogenesis | Stores excess glucose |
| 6. Feedback | Blood glucose drops to ~70–100 mg/dL | Pancreatic α‑cells sense low glucose | Secrete glucagon |
| 7. Counter‑regulation | Glucagon → liver → glycogenolysis & gluconeogenesis | Hepatocytes | Raises blood glucose back to normal |
| 8. Homeostasis Achieved | Balance of insulin & glucagon keeps glucose ~70–100 mg/dL | Endocrine‑metabolic loop | Prevents hypoglycemia or hyperglycemia |
Take‑away
- Insulin (β‑cells) promotes glucose uptake & storage.
- Glucagon (α‑cells) promotes glucose release from stores.
- Feedback loops maintain glucose within a narrow range (70–110 mg/dL).
4. Quick Revision Summary
| System | Primary Function | Key Hormone / Molecule | Important Feedback |
|---|---|---|---|
| Circulatory | Transport | Blood pressure (vasoconstriction/dilation) | Baroreceptor reflex |
| Respiratory | Gas exchange | CO₂, O₂ | Ventilatory response to CO₂ levels |
| Digestive | Nutrition | Gastrin, secretin | GI hormones regulate secretion and motility |
| Nervous | Control & coordination | Neurotransmitters (ACh, dopamine) | Reflex arcs, CNS ↔ PNS |
| Endocrine | Hormonal regulation | Insulin, cortisol, thyroid hormones | Negative feedback (e.g., cortisol ↔ ACTH) |
| Muscular | Movement | ATP, Ca²⁺ | Calcium‑ATPase pump |
| Skeletal | Support & hematopoiesis | Parathyroid hormone (PTH) | Calcium–phosphate balance |
| Immune | Defense | Antibodies, cytokines | Adaptive vs innate immunity |
| Reproductive | Gamete formation & reproduction | Estrogen, testosterone | Sexual hormone feedback |
| Excretory | Waste removal | Aldosterone, antidiuretic hormone (ADH) | Water & electrolyte balance |
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