Human Body Systems, Health and Nutrition
This domain tests how the digestive, circulatory, respiratory, skeletal and nervous systems work together, and how diet, hygiene and vaccination protect health.
Digestion and absorption
Digestion breaks large food molecules into small soluble ones. Teeth grind food, saliva begins starch digestion, the stomach churns food with acid, and enzymes from the pancreas and small intestine complete the job. The small intestine has villi - tiny finger-like projections with a large surface area and thin walls - that absorb nutrients into the blood. The large intestine absorbs water.
Circulation and gas exchange
The heart has four chambers; arteries carry blood away from the heart, veins carry it back, and capillaries allow exchange with cells. In the lungs, air reaches alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out.
Nutrition and health
Carbohydrates and fats supply energy, proteins build and repair the body, vitamins and minerals keep systems working, fibre prevents constipation and water is needed for all reactions. Deficiency diseases include scurvy (vitamin C), rickets (vitamin D and calcium) and anaemia (iron). A balanced diet, clean water, handwashing, vaccination and exercise protect health.
Worked example
A patient with damaged villi loses weight although eating normally. Reasoning: fewer working villi mean a smaller surface area, so less glucose and amino acid is absorbed into the blood; the body then breaks down fat and muscle for energy.
Traps that cost marks
Do not confuse breathing with respiration. Arteries are named by direction, away from the heart, not by oxygen content. Vitamins do not supply energy.