Blood is a vital fluid that circulates throughout our body. It carries oxygen from the lungs to tissues through arteries, shown in red. After delivering oxygen and picking up carbon dioxide, blood returns to the heart through veins, shown in blue. The exchange of gases and nutrients occurs in tiny capillaries that connect arteries and veins.
When blood is separated in a test tube, we can see its four main components. Plasma, the liquid portion, makes up about fifty-five percent and appears yellow. Red blood cells comprise forty-five percent and carry oxygen throughout the body. White blood cells and platelets make up less than one percent but are crucial for immune defense and blood clotting.
The three types of blood vessels have distinct structures. Arteries have thick muscular walls to withstand high pressure as they carry oxygenated blood from the heart. Veins have thinner walls and contain valves to prevent backflow as they return blood to the heart under low pressure. Capillaries are only one cell thick, allowing efficient exchange of oxygen, nutrients, and waste products between blood and surrounding tissues.
The circulatory system has two main circuits. In pulmonary circulation, the right side of the heart pumps deoxygenated blood to the lungs where it picks up oxygen and releases carbon dioxide. The oxygenated blood then returns to the left side of the heart. In systemic circulation, the left side pumps oxygen-rich blood through the aorta to all body organs and tissues. After delivering oxygen and nutrients, the deoxygenated blood returns through veins to the right side of the heart, completing the cycle.
Blood performs four essential functions in our body. First, it transports oxygen from lungs to tissues and carries nutrients while removing waste products. Second, it provides defense through white blood cells that fight infections and produce antibodies. Third, platelets enable blood clotting to stop bleeding and heal wounds. Finally, blood helps regulate body temperature, pH balance, and hormone distribution. To maintain healthy blood and circulation, we should exercise regularly, eat nutritious foods, stay hydrated, and avoid harmful habits like smoking.