SSC CGL - Detailed Guide 2025
Self-Paced Course
Circulatory and Excretory Systems
Reference: NCERT Class 10-12, Lucent GK
1. Circulatory System
The circulatory system is responsible for the transport of oxygen, nutrients, hormones, and waste products throughout the body.
A. Heart
| Feature | Description |
|---|---|
| Type | Muscular organ, about the size of a fist |
| Location | In the thoracic cavity, slightly left of center |
| Chambers | 4 chambers: 2 atria (upper), 2 ventricles (lower) |
| Valves | Prevent backflow (e.g. tricuspid, bicuspid/mitral, pulmonary, aortic) |
| Beats per minute | Average: 72 bpm |
| Double Circulation | Blood passes twice through the heart in one complete cycle (systemic + pulmonary) |
Path of Blood Flow:
- Deoxygenated blood: Body → Right Atrium → Right Ventricle → Lungs
- Oxygenated blood: Lungs → Left Atrium → Left Ventricle → Body
B. Blood
| Component | Description | Function |
|---|---|---|
| Plasma | Yellow fluid (55% of blood); contains proteins, hormones | Transports nutrients, hormones |
| RBCs (Erythrocytes) | Contain hemoglobin; biconcave; no nucleus | Carry oxygen |
| WBCs (Leukocytes) | Nucleated; various types (lymphocytes, neutrophils, etc.) | Fight infection (immune defense) |
| Platelets | Cell fragments, help in blood clotting | Prevent bleeding |
Blood Groups:
| Group | Antigen on RBC | Antibody in Plasma | Can Receive From |
|---|---|---|---|
| A | A | Anti-B | A, O |
| B | B | Anti-A | B, O |
| AB (Universal Recipient) | A & B | None | A, B, AB, O |
| O (Universal Donor) | None | Anti-A, Anti-B | O |
| Rh Factor | Rh+ or Rh- | Determines + or - | Rh- can donate to Rh+, not vice versa |
C. Blood Vessels
| Type | Structure & Function | Direction of Blood Flow |
|---|---|---|
| Arteries | Thick-walled, elastic; carry oxygenated blood (except pulmonary artery) | Heart → Body |
| Veins | Thin-walled, valves present; carry deoxygenated blood (except pulmonary vein) | Body → Heart |
| Capillaries | One-cell thick; site of exchange between blood and tissues | Connect arteries to veins |
2. Excretory System
The excretory system removes nitrogenous wastes (mainly urea), excess salts, and water from the body.
A. Excretory Organs
| Organ | Function |
|---|---|
| Kidneys | Filter blood to form urine |
| Ureters | Transport urine from kidneys to urinary bladder |
| Urinary Bladder | Stores urine |
| Urethra | Removes urine from body |
| Skin (accessory) | Removes salts, water through sweat |
| Lungs (accessory) | Remove CO₂ and water vapor |
| Liver (accessory) | Converts ammonia to urea |
B. Kidney: Structure & Function
- Bean-shaped, 2 in number
- Located in the abdominal cavity (retroperitoneal)
- Each kidney contains ~1 million nephrons
- Blood enters via renal artery, filtered blood exits via renal vein
C. Nephron: The Functional Unit
| Part | Function |
|---|---|
| Bowman's Capsule | Cup-like structure that encloses glomerulus; filtration of blood |
| Glomerulus | Network of capillaries; filters small molecules from blood |
| Proximal Tubule | Reabsorption of water, glucose, ions |
| Loop of Henle | Creates concentration gradient in medulla |
| Distal Tubule | Secretion of ions and drugs |
| Collecting Duct | Collects urine and sends to ureter |
Urine Formation Steps:
- Filtration – in glomerulus (filters blood)
- Reabsorption - in tubules (useful substances reabsorbed)
- Secretion - excess ions/drugs added to filtrate
- Excretion - urine formed & passed to bladder
Normal Urine Composition:
- Water (~95%)
- Urea
- Salts
- Uric acid
- Creatinine
Quick Facts
- • The heart pumps about 70 ml of blood per beat (5 liters/minute)
- • Hemoglobin gives blood its red color and can carry 4 oxygen molecules
- • Kidneys filter 180 liters of blood daily but produce only 1-2 liters of urine
- • Dialysis is an artificial process that performs kidney functions when kidneys fail
- • The pulmonary artery is the only artery that carries deoxygenated blood
Developed By Satyam Kumar
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