Why humans need blood?

Blood is vital to human survival for several reasons:

1. Oxygen Transport: Red blood cells (erythrocytes) contain hemoglobin, an iron-rich protein responsible for carrying oxygen from the lungs to all tissues and organs in the body. Oxygen is essential for cellular respiration, the process by which cells generate energy.

2. Nutrient Delivery: Blood carries essential nutrients, such as glucose, amino acids, vitamins, and minerals, to all body cells. These nutrients are necessary for cellular growth, repair, and function.

3. Waste Removal: Blood transports metabolic waste products, such as carbon dioxide and nitrogenous waste (e.g., urea), from tissues back to the lungs and kidneys for elimination.

4. Defense Mechanisms: Blood contains various immune cells, including white blood cells and platelets, which help defend the body against infections, diseases, and tissue damage. White blood cells fight infections by engulfing and destroying harmful microorganisms, while platelets help stop bleeding by forming clots.

5. Regulation of Body Temperature: Blood vessels dilate or constrict to regulate heat distribution and maintain a consistent body temperature.

6. pH Regulation: Blood helps regulate the pH balance in the body, ensuring that cells have an optimal environment to function.

7. Hormone Transport: Blood transports hormones from endocrine glands to target tissues, enabling communication and coordination between different parts of the body.

8. Fluid Balance: Blood contributes to maintaining the body's overall fluid balance by transporting water and electrolytes throughout the circulatory system.

In summary, blood is essential for sustaining life because it performs numerous critical functions, including oxygen and nutrient delivery, waste removal, immune defense, temperature regulation, pH balance, hormone transport, and fluid balance.