1. Transporter: the most familiar function of blood is that of a transporter. Blood is responsible for supplying the body oxygen that it gets from the lungs. After delivering oxygen to body cells blood becomes deoxygenated but it also picks up carbon dioxide and is then transported back to the lungs to dump off the carbon dioxide and pick up fresh oxygen (oxygenation). Blood is also responsible for transporting nutrients released from the breakdown of macromolecules. Some of these nutrients include carbohydrates, amino acids, fatty acids, vitamins, and minerals. Cellular waste products are transported to the lungs, liver and/or kidneys to be eliminated. Blood also serves to transport hormones from the endocrine system to target tissues throughout the body. This highlights the fact that blood is an important contributor to homeostasis as it helps with regulation and signaling systems. Blood is also responsible for the transportation and distribution of various components of the immune system which will help ward off invasion from harmful pathogens and toxins.
2. pH regulation: The pH of the human body must be carefully regulated, ideally in the range of 7.35-7.45. If the pH deviates too far above or below this range, serious consequences will result. Through the use of CO2 and buffers like HCO3-, blood is able to maintain pH in a strict range.
3. Body fluid Regulation: Various salts and proteins in the bloodstream help regulate the fluid volume through the use of osmotic gradients.
4. Body Temperature Regulation: Blood also plays a critical role in maintaining a strict body temperature. As blood flows throughout the circulatory system, it absorbs heat generated from skeletal muscles and organs and disperses the heat throughout the body. Eventually, blood flows near the surface of the skin where heat is expelled. Moisture on the skin facilitates this heat loss and this is why we sweat. Water molecules are in constant motion with the fastest moving water molecules having the most heat energy (they move faster when they are hotter). When water evaporates, the fastest moving molecules are more likely to leave the liquid and enter the surrounding air. This leaves the cooler molecules behind. The evaporating molecules in your sweat actually carry heat away from your body.
5. Hemostasis: When a blood vessel or tissue is damaged, blood vessels can constrict and clotting occurs to halt the improper flow of blood out of the vessels. Clotting is often the first step to begin the process of repair.