Introduction
The human body is organised into several interconnected systems, each with a specialised function. This
chapter covers the major organ systems tested most frequently across Railway exams — digestive,
circulatory, respiratory, nervous, and skeletal.
Digestive System
| Organ | Function |
|---|
| Mouth | Mechanical digestion (chewing) and salivary amylase begins starch digestion |
| Stomach | Secretes gastric juices (HCl, pepsin) for protein digestion |
| Small Intestine | Main site of digestion and nutrient absorption |
| Large Intestine | Absorbs water, forms and stores solid waste |
| Liver | Produces bile (fat digestion), detoxifies blood |
| Pancreas | Produces digestive enzymes and insulin |
Circulatory System
| Component | Function |
|---|
| Heart | Four-chambered muscular pump; circulates blood throughout the body |
| Arteries | Carry oxygenated blood AWAY from the heart (except pulmonary artery) |
| Veins | Carry deoxygenated blood TOWARDS the heart (except pulmonary vein) |
| Capillaries | Tiny vessels where exchange of gases/nutrients occurs |
📌 Blood Composition: Plasma (55%, liquid part), Red Blood Cells (carry oxygen via haemoglobin), White Blood Cells (immune defence), Platelets (blood clotting).
| Blood Component | Also Known As | Function |
|---|
| Red Blood Cells | Erythrocytes | Oxygen transport |
| White Blood Cells | Leukocytes | Fight infection |
| Platelets | Thrombocytes | Blood clotting |
Respiratory System
| Organ | Function |
|---|
| Nose/Nasal Cavity | Filters, warms, and moistens incoming air |
| Trachea (Windpipe) | Carries air to the lungs |
| Lungs | Site of gas exchange (oxygen in, carbon dioxide out) |
| Alveoli | Tiny air sacs in the lungs where actual gas exchange occurs |
| Diaphragm | Muscle that contracts/relaxes to enable breathing |
Nervous System
| Component | Function |
|---|
| Brain | Central control centre — divided into cerebrum, cerebellum, and medulla oblongata |
| Spinal Cord | Relays signals between the brain and the rest of the body |
| Neurons | Basic functional unit of the nervous system; transmit electrical impulses |
| Brain Part | Function |
|---|
| Cerebrum | Largest part; controls thought, memory, voluntary movement |
| Cerebellum | Controls balance and coordination |
| Medulla Oblongata | Controls involuntary functions (heartbeat, breathing) |
Skeletal System
| Fact |
|---|
| An adult human skeleton has 206 bones |
| A newborn baby has about 300 bones (many fuse together with age) |
| The Femur (thigh bone) is the longest and strongest bone in the human body |
| The Stapes (in the ear) is the smallest bone in the human body |
Excretory System
| Organ | Function |
|---|
| Kidneys | Filter blood, remove waste as urine (basic unit: Nephron) |
| Ureters | Carry urine from kidneys to the bladder |
| Bladder | Stores urine before elimination |
Q. Which blood vessel carries deoxygenated blood away from the heart, unlike typical arteries?
The Pulmonary Artery is the exception — it carries deoxygenated blood from the heart to the lungs
Answer: Pulmonary Artery
✅ Exam Focus: Digestive organ-function matching · Blood component functions and artery/vein exceptions · Respiratory system organs (especially alveoli) · Brain part functions (cerebrum, cerebellum, medulla) · Skeletal facts (206 bones, longest/smallest bone) · Nephron as the kidney's functional unit.