Human Body Systems
Circulatory, digestive and respiratory systems
Circulatory System:
The heart is a double pump. Right side pumps deoxygenated blood to the lungs. Left side pumps oxygenated blood to the body.
- Arteries: thick-walled, carry blood away from heart, high pressure
- Veins: thinner walls, carry blood to heart, have valves to prevent backflow
- Capillaries: one cell thick, allow exchange of oxygen, nutrients and CO₂
Digestive System (mouth to anus):
Mouth (chewing + amylase) → oesophagus → stomach (HCl + protease) → small intestine (absorption of nutrients via villi — large surface area, thin walls, rich blood supply) → large intestine (water absorption) → rectum → anus.
Respiratory System:
Air: nose → trachea → bronchi → bronchioles → alveoli (gas exchange).
Alveoli have: large surface area, thin walls (one cell thick), moist, good blood supply → efficient diffusion of O₂ into blood, CO₂ out.
Breathing in (inspiration): diaphragm contracts (flattens), rib cage rises → lung volume increases → pressure drops → air enters.
Breathing out (expiration): diaphragm relaxes, rib cage falls → air expelled.
Key Points to Remember
- 1Arteries: away from heart; veins: to heart (have valves)
- 2Small intestine villi: large surface area for absorption
- 3Alveoli: large surface area, thin walls for gas exchange
- 4Inspiration: diaphragm contracts, lung volume increases
Pakistan Example
Shaukat Khanum Hospital — Human Systems and Cancer Treatment
Shaukat Khanum Memorial Cancer Hospital in Lahore treats lung cancer (respiratory system), bowel cancer (digestive system), and heart disease (circulatory system). AKU-EB Biology questions often use Pakistani hospital contexts. Understanding the structure of alveoli explains why smoking causes cancer — tar destroys the thin alveolar walls reducing gas exchange efficiency.
Quick Revision Infographic
Biology — Quick Revision
Human Body Systems
Key Concepts
Shaukat Khanum Hospital — Human Systems and Cancer Treatment
Shaukat Khanum Memorial Cancer Hospital in Lahore treats lung cancer (respiratory system), bowel cancer (digestive system), and heart disease (circulatory system). AKU-EB Biology questions often use Pakistani hospital contexts. Understanding the structure of alveoli explains why smoking causes cancer — tar destroys the thin alveolar walls reducing gas exchange efficiency.