Human Being: Blood and Circulation

Blood: a liquid connective tissue. It consists of plasma (≈55%) and formed elements.

• Erythrocytes have no nucleus; with the help of hemoglobin erythrocytes carry O₂.
• Leukocytes perform a protective function (phagocytosis, immunity).
• Thrombocytes take part in blood clotting.

The heart has four chambers.

Circulation circuits

The systemic circuit ends in the right atrium, and begins in the left ventricle.

1. Left ventricle
2. Aorta
3. Organs
4. Venae cavae
5. Right atrium

The pulmonary circuit begins in the right ventricle, and ends in the left atrium.

1. Right ventricle
2. Pulmonary artery
3. Lungs
4. Pulmonary veins
5. Left atrium

Arteries carry blood away from the heart, veins carry blood to the heart. Gas and substance exchange takes place in the capillaries.

Key facts

• Erythrocytes are formed in the red bone marrow and live ≈120 days.
• Blood groups (ABO): I (0) is the universal donor, IV (AB) is the universal recipient. Rh factor: positive and negative.
• Normal arterial pressure is ≈ 120/80 mm Hg. Pulse is ≈ 60-80 beats/min.
• In the pulmonary circuit, venous blood flows in the artery, and arterial blood flows in the vein (in the pulmonary arteries and veins).
• The heart valves ensure that blood flows in one direction only.