Human blood is a vital fluid that circulates throughout the body, delivering oxygen and nutrients to cells while removing waste products. It consists of red blood cells, which carry oxygen; white blood cells, which help fight infections; and platelets, which assist in blood clotting. The liquid portion, called plasma, contains water, electrolytes, proteins, and hormones. Blood plays a crucial role in maintaining homeostasis, regulating body temperature, and transporting substances like glucose and hormones. The average adult has about 5 to 6 liters of blood, which makes up approximately 7-8% of their body weight. Proper blood function is essential for overall health and well-being.