Composition of Blood
From MyMCAT
Contents |
Introduction
Blood is a specialized biological fluid consisting of millions of different components. Both cellular bodies (such as T-cells and platelets) and non-cellular components (such as hormones, proteins, antibodies, and small compounds) exist in the blood. While the primary function of the blood is to transport oxygen throughout the body, the efficiency of this fluid system also makes it a useful transport system for the body to distribute nutrients, hormonal signals, and even combat infection in.
Composition of Blood
Non-cellular Components
The noncellular component of blood is simply an aqueous solution containing ~92% water, 8% blood plasma proteins, and small amounts of other materials (such as glucose, hormones, mineral ions, and proteins). This noncellular component is often referred to as plasma. Blood plasma can easily be prepared by simply spinning a tube of fresh blood in a centrifuge until the blood cells fall to the bottom of the tube. The blood plasma is then poured or drawn off.
If the fibrinogen and other clotting factors are selectively removed from the blood plasma, it is known as blood serum.
Cellular Components
The primary cells in the circulatory system are the red blood cells (RBCs or erythrocytes), the white blood cells (leukocytes), and platelets (thrombocytes).
Red blood cells perform several important functions. Utilizing hemoglobin, an oxygen carrying protein complex, they transport oxygen to all the other cells of the body. At the same time, the red blood cells can transport carbon dioxide away from respiring cells. To a lesser degree, they are also capable of regulating the acidity of the blood around them. These properties alone make red blood cells ideal as the by product of respiration is carbon dioxide, which complexes with water to form bicarbonate and hydronium ions.
White blood cells are the active defense of the body. They defend the body from invading microorganisms and viruses that have penetrated the bodies primary defenses (such as the skin and digestive enzymes) and have made it into the circulatory system. These white blood cells actively seek foreign cells and either destroy them by engulfing and digesting them whole, or by recruiting other "killer" cells. (See the immune system section for more details)
Platelets, the third major type of blood cell, play an essential role in blood clotting. The massive volume of blood flowing and the pressure at which it is maintained means that any cut or tear in the circulatory system could easily become fatal with the potentially huge blood loss if left untreated. Platelets are the key to preventing this problem by becoming "sticky" and clogging any cuts or tears. This mass of platelets sealing a wound is known as a clot. The clotting process is actually quite a bit more complicated and can be read about in detail below.
Blood Clotting
Blood clotting is used as a means to plug up torn or cut blood vessels to stop bleeding that otherwise might become fatal. Clotting is primarily a result of the platelets in the blood stream. When an injury or tear to any blood vessel occurs, a chain of rapid-fire reactions occur to form a clot and minimize blood loss.
The first step in this chain of events is the breakdown of platelets at the site of a tear/injury. Normal vessels are smooth and have distinctive chemical characteristics but even a slight imbalance or rough/torn spot will trigger passing platelets to fragment, releasing platelet factors.
The second step in this series of events is the formation of thrombin. Prothrombin present in normal blood react with platelet factors, calcium, and other substances to form thrombin. This thrombin however, immediately reacts with another protein present in normal blood, fibrinogen, changing it into a gel matrix called fibrin. Fibrin is often so dense and stringy that red blood cells along with many large proteins get caught in the matrix increasing the size of the plug and thus slowing blood loss.
