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Animal Transport

Circulation, heart, blood vessels, blood

Double Circulation

Two separate circuits: heart → lungs → heart → body

Pulmonary circuit: Heart → lungs (pick up O₂, drop CO₂) → back to heart

Systemic circuit: Heart → body cells (deliver O₂, pick up CO₂) → back to heart

Ensures high pressure in systemic circulation for efficient delivery

Heart Structure — Four Chambers

Right atrium: Receives deoxygenated blood from body (via vena cava)

Right ventricle: Pumps deoxygenated blood to lungs (via pulmonary artery)

Left atrium: Receives oxygenated blood from lungs (via pulmonary vein)

Left ventricle: Pumps oxygenated blood to body (via aorta). Thickest muscle.

Valves prevent backflow: Atrioventricular (AV) valves, semilunar valves

Coronary Arteries & Heart Health

Coronary arteries: Supply blood & O₂ to heart muscle itself

Atherosclerosis: Cholesterol deposits narrow arteries → reduced blood flow → angina (chest pain)

Heart attack: Complete blockage → heart muscle doesn't get O₂ → tissue dies

Prevention: exercise, low-fat diet, no smoking, manage stress

Blood Vessels — Structure & Function

Vessel	Structure	Pressure	Function
Artery	Thick elastic walls, narrow lumen	High	Carry blood AWAY from heart
Capillary	One cell thick, tiny	Medium	Exchange of O₂/CO₂ and nutrients
Vein	Thin walls, wide lumen, valves	Low	Carry blood TO heart; prevent backflow

Capillaries — Exchange Sites

One cell thick: Enables diffusion (short distance)

Large total surface area: Network of tiny vessels

Narrow lumen: Blood cells close to walls for exchange

Exchange: O₂ & glucose OUT to cells; CO₂ & urea IN from cells

Blood Composition

Plasma (55%): Liquid part. Carries glucose, amino acids, urea, hormones, antibodies, clotting factors.

Red blood cells (RBCs, 44%): No nucleus. Contain haemoglobin. Carry O₂. Live ~120 days.

White blood cells (1%): Have nucleus. Fight infection. Phagocytes (engulf bacteria), lymphocytes (make antibodies).

Platelets (<1%): Cell fragments. Cause clotting. Stop bleeding.

Haemoglobin & Oxygen Transport

Haemoglobin: Iron-containing protein in RBCs. Binds O₂ reversibly.

In lungs (high O₂): Haemoglobin + O₂ → oxyhaemoglobin (bright red)

In body (low O₂): Oxyhaemoglobin → haemoglobin + O₂ (released to tissues)

CO₂ transport: 85% as bicarbonate ions in plasma; 15% bound to haemoglobin

Exam Tips

✓ Double circulation: heart → lungs → heart → body

✓ Left ventricle is thickest (pumps to whole body)

✓ Artery (thick wall, high pressure) vs vein (thin wall, valves, low pressure)

✓ Capillaries: one cell thick, exchange site

✓ Blood: plasma, RBCs (haemoglobin + O₂), WBCs, platelets

Key Takeaways

✅ Double circulation: pulmonary (heart-lungs) & systemic (heart-body)

✅ Heart: 4 chambers, valves prevent backflow

✅ Artery: thick wall, high pressure, no valves

✅ Vein: thin wall, low pressure, valves

✅ Capillary: one cell thick, exchange O₂/CO₂/nutrients

✅ Blood: plasma, RBCs (haemoglobin), WBCs, platelets

Your heart keeps you alive! ❤️✓