Transport in Humans

Unlike plants, humans are active animals. We need a fast, high-pressure transport system to deliver oxygen and nutrients. Our system includes the heart, blood vessels, and blood.

The nature of blood
Blood is a living tissue. About 55% of it is plasma, a watery fluid that carries nutrients, hormones, and waste materials.

Blood cells include:

1. Red blood cells: These carry oxygen using hemoglobin. They do not have a nucleus, which gives more space for oxygen transport.
2. White blood cells: These protect the body by fighting bacteria and viruses.
3. Platelets: These help in clotting and stop bleeding when a blood vessel is damaged.

Blood groups and safe transfusions
Human blood has different types based on antigens on red blood cells. In the ABO system, blood can be A, B, AB, or O.

If wrong blood types are mixed, the immune system attacks the foreign cells, causing clumping. Type O blood is called the universal donor because it has no A or B antigens.

The heart and circulation
The heart works as two pumps separated by a wall.

Right side (lung pump): Sends deoxygenated blood to the lungs to get oxygen.

Left side (body pump): Sends oxygen-rich blood to the whole body with strong force. The left ventricle is the strongest chamber because it pumps blood to the entire body.

Valves in the heart act like one-way doors that prevent backflow.

Blood vessels
Blood moves through three types of vessels:

1. Arteries: Carry blood away from the heart under high pressure. They have thick, elastic walls.
2. Veins: Carry blood back to the heart. They have thinner walls and valves to prevent backflow.
3. Capillaries: Tiny vessels with walls one cell thick. They allow exchange of oxygen, nutrients, and wastes between blood and body tissues.