The human body is made of trillions of cells working together in organized groups called systems. Questions on body organs, blood, vitamins and diseases appear often in the general science part of Lok Sewa exams. This note gives the most important facts in a simple, easy-to-revise form, ending with basic first aid ideas that every citizen should know.
1. Digestive system
The digestive system breaks food into simple substances that the body can absorb.
- Mouth: teeth chew food; saliva contains an enzyme (amylase) that starts digesting starch.
- Oesophagus (food pipe): carries food to the stomach by wave-like movements.
- Stomach: produces hydrochloric acid and enzymes that start digesting protein; the acid also kills many germs.
- Small intestine: the longest part of the digestive canal, where most digestion and absorption take place. Its inner wall has tiny finger-like villi that increase the surface for absorption.
- Large intestine: absorbs water from the remaining waste.
- Liver: the largest gland of the body; it makes bile, which helps digest fats. Bile is stored in the gall bladder.
- Pancreas: releases digestive juice into the small intestine.
2. Respiratory system
The respiratory system takes in oxygen and removes carbon dioxide. Air passes through the nose, pharynx, larynx (voice box), trachea (windpipe) and bronchi into the two lungs. Inside the lungs are millions of tiny air sacs called alveoli, where gas exchange happens: oxygen enters the blood and carbon dioxide leaves it.
The dome-shaped muscle below the lungs, the diaphragm, moves down when we breathe in and up when we breathe out. Breathing is the physical movement of air; respiration is the process in cells where food is broken down with oxygen to release energy.
3. Circulatory system
The circulatory system carries blood around the body. Its main parts are the heart, blood vessels and blood.
- The human heart has four chambers: two upper atria and two lower ventricles.
- Arteries carry blood away from the heart; most carry oxygen-rich blood. The pulmonary artery is the exception, as it carries oxygen-poor blood to the lungs.
- Veins carry blood back to the heart; the pulmonary vein carries oxygen-rich blood from the lungs.
- Capillaries are very thin vessels where substances pass between blood and body cells.
Normal blood pressure of a healthy adult is about 120/80 mm Hg. William Harvey is known for describing the circulation of blood.
4. Nervous system
The nervous system controls and coordinates all activities of the body. Its basic unit is the neuron (nerve cell).
| Part | Main function |
|---|---|
| Cerebrum | Largest part of the brain; thinking, memory, intelligence and voluntary actions |
| Cerebellum | Balance of the body and coordination of movements |
| Medulla oblongata | Controls involuntary actions such as heartbeat and breathing |
| Spinal cord | Carries messages between brain and body; controls reflex actions |
A reflex action is a quick, automatic response, such as pulling your hand back from a hot object before you even think about it.
5. Excretory system
The excretory system removes waste from the body. The main organs are the two kidneys, which filter blood and make urine. The working unit of the kidney is the nephron. Urine flows through the ureters to the urinary bladder and leaves through the urethra. The skin (through sweat), lungs (carbon dioxide) and liver also help remove waste. When both kidneys fail, blood can be cleaned with a machine in a process called dialysis.
6. Skeletal system
The skeleton gives the body shape, protects organs and helps movement with the muscles.
- An adult human has 206 bones.
- The femur (thigh bone) is the longest and strongest bone.
- The stapes in the middle ear is the smallest bone.
- The skull protects the brain and the rib cage protects the heart and lungs.
- Places where bones meet are joints; bones are joined to each other by ligaments, and muscles are joined to bones by tendons.
- Bones get their hardness mainly from minerals of calcium and phosphorus (calcium phosphate).
The skin is the largest organ of the body.
7. Blood and blood groups
Blood is a fluid connective tissue. Its liquid part is plasma, which is mostly water. Floating in the plasma are three kinds of blood cells (platelets are really small cell fragments):
| Component | Main job |
|---|---|
| Red blood cells (RBC) | Carry oxygen using haemoglobin, an iron-containing protein; live about 120 days |
| White blood cells (WBC) | Fight infection and protect the body |
| Platelets | Help blood to clot at a wound |
Blood cells are produced mainly in the bone marrow. The ABO blood groups were discovered by Karl Landsteiner. The four groups are A, B, AB and O. Each can be Rh positive or Rh negative.
- O negative is called the universal donor, because its red cells can be given to people of any group in an emergency.
- AB positive is called the universal recipient, because it can receive red cells from any group.
8. Important glands and hormones
Endocrine glands are ductless glands that release chemical messengers called hormones directly into the blood.
| Gland | Hormone | Main role |
|---|---|---|
| Pituitary | Growth hormone and others | Called the master gland because it controls other glands |
| Thyroid | Thyroxine | Controls the rate of metabolism; needs iodine |
| Pancreas (islets of Langerhans) | Insulin | Lowers blood sugar; lack of insulin, or the body not using it properly, causes diabetes |
| Adrenal | Adrenaline | Prepares the body for emergencies, called the fight or flight hormone |
| Testes | Testosterone | Male characteristics |
| Ovaries | Oestrogen and progesterone | Female characteristics and pregnancy |
9. Vitamins and minerals
| Nutrient | Good sources | Deficiency disease |
|---|---|---|
| Vitamin A | Carrot, green vegetables, milk | Night blindness |
| Vitamin B1 (thiamine) | Whole grains, pulses | Beriberi |
| Vitamin B3 (niacin) | Meat, grains, groundnut | Pellagra |
| Vitamin B12 | Meat, eggs, milk | Pernicious anaemia |
| Vitamin C | Lemon, orange, amla, guava | Scurvy (bleeding gums) |
| Vitamin D | Sunlight, fish oil, egg yolk | Rickets in children |
| Vitamin K | Green leafy vegetables | Slow clotting of blood |
| Iron | Green vegetables, meat | Anaemia |
| Iodine | Iodized salt, sea food | Goitre |
| Calcium | Milk, curd, cheese | Weak bones and teeth |
Vitamins A, D, E and K are fat-soluble; vitamins B and C are water-soluble. The body makes vitamin D in the skin when it is exposed to sunlight.
10. Communicable diseases and their causes
Communicable diseases spread from one person to another through air, water, food, contact or insects.
| Cause | Diseases |
|---|---|
| Bacteria | Tuberculosis (TB), typhoid, cholera, tetanus, diphtheria, leprosy, whooping cough |
| Virus | Measles, polio, rabies, influenza, hepatitis, dengue, AIDS (caused by HIV) |
| Protozoa | Malaria (spread by female Anopheles mosquito), kala-azar (spread by sandfly), amoebic dysentery |
Dengue is spread by the Aedes mosquito. Vaccines protect against many of these diseases, and antibiotics work against bacteria but not against viruses.
11. Basic first aid
First aid is the immediate help given to an injured or sick person before medical help arrives.
- Bleeding: press firmly on the wound with a clean cloth and raise the injured part if possible.
- Burns: hold the burnt area under cool, clean running water for several minutes; do not apply toothpaste, oil or ice.
- Fracture: keep the broken part still with a splint and do not try to straighten it.
- Snakebite: keep the person calm and still, keep the bitten limb at rest, and take them quickly to a health facility; do not cut or suck the wound.
- Diarrhoea: give ORS (Oral Rehydration Solution) to replace lost water and salts.
- Unconscious but breathing: place the person on their side (recovery position) and call for help.
📌 Key points to remember
- The small intestine is where most digestion and absorption happen; the liver is the largest gland.
- Gas exchange takes place in the alveoli of the lungs.
- The heart has four chambers; arteries carry blood away from it, veins bring it back.
- The cerebrum is the largest part of the brain; the cerebellum controls balance.
- The nephron is the working unit of the kidney.
- An adult has 206 bones; the femur is the longest, the stapes the smallest.
- O negative is the universal donor; AB positive is the universal recipient.
- The pituitary is the master gland; insulin lack causes diabetes.
- Vitamin C lack causes scurvy, vitamin D lack rickets, iodine lack goitre.
- Malaria is caused by a protozoan; TB by bacteria; polio by a virus.
- Use ORS for diarrhoea and cool running water for burns.
Test yourself: Human Body and Health
50 questions on Digestive system, Skeletal system and Basic first aid. Each attempt picks 25 at random.