Understanding your anatomy and physiology -- the body structures and how they work -- can help you make good decisions about health and nutrition. Your blood is the fluid that delivers oxygen and nutrients to your cells. The blood is essentially a water-based mixture of many different chemicals, including a suspension of cells. Specifically, plasma is the liquid portion of blood.
Your blood is a fluid that connects all body cells. Not only does it bring nutrients and oxygen to the cells from the lungs and digestive tract, it carries waste products away from the cells for disposal. Your cells communicate with one another via the blood -- the liquid medium carries chemical messengers from one cell to another. Blood consists of water-based liquid, called plasma, plus a suspension of many different types of blood cells.
Plasma is similar in many ways to seawater -- it's water-based, but contains many salts, including NaCl, or table salt. Plasma also contains many chemicals that aren't found in seawater, including blood proteins, components of clotting and cellular messengers called hormones. Whole blood is approximately 45 percent cells and 55 percent plasma, explains Dr. Lauralee Sherwood in her book "Human Physiology." The plasma itself is mostly water -- about 90 percent.
One of the important roles of blood is to transport nutrients to the body cells. Blood cells don't participate in nutrient transport -- instead, nutrients dissolve in the plasma itself. For instance, notes Dr. Gary Thibodeau in his book "Anatomy and Physiology," when you consume a carbohydrate-containing meal, you digest the carbohydrate and absorb a sugar called glucose into the bloodstream. The glucose dissolves in the blood plasma -- it's then called blood sugar -- and the plasma carries it to the body cells.
To keep cells well-nourished, your body works hard to maintain steady concentrations of certain key nutrients in the bloodstream. Energy-providing nutrients in the bloodstream include amino acids, which come from proteins, and fats, but the most regulated of the bloodstream nutrients is glucose. Your pancreas uses two different hormones to keep blood glucose levels relatively constant. If blood sugar starts to rise too much, the pancreas secretes insulin to decrease blood sugar. If blood sugar starts to fall, the pancreas secretes glucagon to raise it.
Other nutrients affect the blood plasma, even though they don't provide energy to cells. For instance, vitamin K is one of the micronutrients, meaning components of food that you need only in small amounts. Your body uses vitamin K to help in the clotting process that takes place when you damage a blood vessel or cut yourself. Without sufficient vitamin K in the blood plasma, your blood can't clot, and you can develop a bleeding disorder, explains Dr. Sherwood.
- “Human Physiology”; Lauralee Sherwood, Ph.D.; 2004
- “Anatomy and Physiology”; Gary Thibodeau, Ph.D.; 2007