Human Body: Nutrition, Digestion, Respiration, Circulation and Excretion

Biology · 6 min read

Nutrition and food

Nutrient	Source	Function	Deficiency
Carbohydrates	Rice, wheat, potato, sugar	Main energy source (4 kcal/g)	Weakness
Proteins	Pulses, milk, eggs, meat, soybean	Growth and repair; made of amino acids	Kwashiorkor, marasmus
Fats	Oils, ghee, nuts	Stored energy (9 kcal/g), insulation
Vitamins	Fruits, vegetables	Protective; needed in small amounts	See below
Minerals	Milk, vegetables, salt	Bones, blood, nerves	See below
Water	Drinks, food	Transport, temperature control	Dehydration
Roughage (dietary fibre)	Vegetables, whole grains	Prevents constipation	Constipation

Balanced diet has all nutrients in the right amount. Energy is measured in calories (1 kcal = 4.2 kJ). BMR is the energy used at rest.
Tests: iodine turns starch blue-black; Benedict's solution shows glucose (orange-red); copper sulphate + caustic soda (biuret) shows protein (violet); paper shows fat (grease spot).

Vitamins

Vitamin	Chemical name / source	Deficiency disease
A	Retinol; carrot, papaya, liver, fish oil	Night blindness, xerophthalmia
B1	Thiamine; whole grain, yeast	Beri-beri
B2	Riboflavin; milk	Cracked lips, skin
B3	Niacin	Pellagra
B6	Pyridoxine	Anaemia, convulsions
B9	Folic acid	Anaemia, birth defects
B12	Cobalamin; milk, meat (contains cobalt)	Pernicious anaemia
C	Ascorbic acid; amla, citrus fruits, guava	Scurvy (bleeding gums)
D	Calciferol; sunlight, fish oil, egg yolk	Rickets (children), osteomalacia (adults)
E	Tocopherol; oils, nuts	Sterility, muscle weakness
K	Phylloquinone; green vegetables	Delayed blood clotting

Fat-soluble vitamins: A, D, E, K. Water-soluble: B and C. Vitamin D is made by skin in sunlight; vitamin K by gut bacteria.
Minerals and deficiency: calcium (bones and teeth; rickets, osteoporosis), iron (haemoglobin; anaemia), iodine (thyroxine; goitre), phosphorus, sodium and potassium (nerves), fluorine (teeth; excess causes fluorosis), zinc, copper.
Protein-energy malnutrition: kwashiorkor (protein deficiency), marasmus (protein and calories).

Human digestive system

Organ	Function
Mouth	Teeth chew; saliva (salivary amylase/ptyalin) starts starch digestion into maltose
Oesophagus	Peristalsis pushes food down
Stomach	Gastric juice: HCl (kills germs, makes acidic), pepsin (digests proteins), rennin (curdles milk), mucus protects the wall
Liver	Largest gland; makes bile (emulsifies fats, neutralises acid); stores glycogen; detoxifies
Gall bladder	Stores bile
Pancreas	Pancreatic juice: amylase, trypsin, lipase; also makes insulin and glucagon
Small intestine	Digestion is completed and absorption occurs through villi; about 6 to 7 m long; duodenum receives bile; intestinal juice has maltase, lipase and others
Large intestine	Absorbs water; forms faeces
Anus	Egestion

Teeth: 32 in adults (20 milk teeth in children). Incisors (cutting), canines (tearing), premolars and molars (grinding). Enamel is the hardest substance in the body.
Enzymes are biological catalysts: amylase (starch), pepsin and trypsin (protein), lipase (fats).
Peristalsis is the wave-like movement of the gut.

Respiration

Breathing is moving air in and out; cellular respiration releases energy from glucose in cells: C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP).
Aerobic respiration uses oxygen (38 ATP); anaerobic does not: in yeast it gives ethanol + CO2; in muscles it gives lactic acid (causing cramps) (2 ATP).
Path of air: nose, pharynx, larynx, trachea, bronchi, bronchioles, alveoli. Gas exchange happens in the alveoli. Haemoglobin carries oxygen.
Diaphragm and intercostal muscles control breathing: inhaling: diaphragm contracts and flattens, ribs lift; exhaling: they relax.
Lungs: right lung has 3 lobes, left has 2.
Breathing rate (adult at rest): about 12 to 20 per minute. Air we breathe out has about 4% CO2.
Other animals: earthworm (skin), insects (tracheae), fish (gills), frog (skin and lungs), birds and mammals (lungs).

Circulation

Part	Facts
Heart	Muscular organ, size of a fist; 4 chambers: two atria (upper), two ventricles (lower); beats about 72 times a minute; located slightly left
Valves	Prevent backflow of blood
Arteries	Carry blood away from the heart; thick walls; oxygenated (except pulmonary artery)
Veins	Carry blood to the heart; valves; deoxygenated (except pulmonary vein)
Capillaries	Thinnest; exchange of materials
Blood pressure	Normal 120/80 mm Hg; measured by a sphygmomanometer
Pulse	About 72 per minute

Double circulation: blood passes through the heart twice in one circuit (pulmonary and systemic). William Harvey discovered blood circulation.
Pacemaker (SA node) starts the heartbeat. ECG records the heart's activity; the stethoscope was invented by Laennec.

Blood

Component	Function
Plasma (55%)	Liquid; 90% water; carries nutrients, hormones, waste
Red blood cells (RBC, erythrocytes)	Haemoglobin (iron) carries oxygen; no nucleus; made in bone marrow; lifespan about 120 days; about 5 million/mm^3
White blood cells (WBC, leucocytes)	Fight infection (immunity); lifespan short; about 5000 to 10,000/mm^3
Platelets (thrombocytes)	Blood clotting; about 1.5 to 4 lakh/mm^3

Blood groups (Karl Landsteiner): A, B, AB, O. O is the universal donor (no antigens); AB is the universal recipient. Rh factor was found in rhesus monkey; Rh-negative mother with Rh-positive baby can cause problems.
Adult blood volume: about 5 to 6 litres. Haemoglobin: 12 to 16 g/dl. Anaemia is low haemoglobin.
Lymph is a colourless fluid with WBCs; lymphatic system returns fluid and fights infection. Spleen is the graveyard of RBCs; bone marrow makes blood cells.
Blood clotting needs platelets, vitamin K and calcium.

Excretion

Excretion removes metabolic wastes. Human excretory system: two kidneys, two ureters, urinary bladder, urethra.
Kidney (bean-shaped) has about a million nephrons (structural and functional unit) which filter blood; urine is formed by filtration, reabsorption and secretion.
Urine is about 95% water, urea, uric acid, salts; pale yellow due to urochrome. Normal urine is slightly acidic.
Dialysis (artificial kidney) treats kidney failure; kidney transplant is another option.
Other excretory organs: skin (sweat), lungs (CO2), liver (bile pigments, urea formation).
Excretory products: ammonia (fish, ammonotelic), urea (humans, ureotelic), uric acid (birds and reptiles, uricotelic).
Kidney stones are calcium oxalate. Diabetes and hypertension harm kidneys.

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Prepared for exam revision from the NCERT Science textbooks for Classes 6 to 10 and standard sources. Space missions, awards and records change, so check official sources for recent facts. Found a mistake? Tell us.