Blood is a specialized fluid that moves constantly through the body, supporting the function of every organ and cell. It is composed of a liquid component called plasma, along with formed elements like red blood cells, white blood cells, and platelets. This complex mixture performs three primary functions required for maintaining a stable internal environment necessary for life.
Transportation of Essential Materials
Blood acts as the body’s primary delivery and collection system, moving necessary substances to tissues and removing waste products. Red blood cells bind oxygen in the lungs and deliver it throughout the body. These cells contain the protein hemoglobin, which reversibly binds to oxygen, significantly increasing the amount of gas carried in the bloodstream.
After delivering oxygen, the blood collects carbon dioxide, a byproduct of cellular metabolism, to transport back to the lungs for exhalation. Blood plasma also carries absorbed nutrients, such as glucose, amino acids, and fatty acids, from the digestive system to the various cells that need them. Chemical messengers, known as hormones, travel via the blood from the endocrine glands to their target organs.
Blood handles the removal of metabolic waste products, such as urea and lactic acid, from the tissues. It carries these compounds to organs designed for excretion, such as the kidneys and liver, which filter and process the waste for elimination. This continuous cycle ensures cells receive a steady supply of fuel while preventing the buildup of toxic byproducts.
Regulation of Internal Body Conditions
Blood plays a significant part in maintaining homeostasis, keeping internal physical and chemical conditions stable. One way blood contributes to this balance is through thermoregulation, or the control of body temperature. When muscles generate heat during activity, the blood absorbs this warmth and distributes it evenly throughout the body.
To cool the body, blood vessels near the skin’s surface dilate (vasodilation), allowing more blood flow so that heat can dissipate into the environment. Conversely, in cold conditions, these vessels constrict (vasoconstrict), which reduces blood flow to the skin and conserves heat in the core. This mechanism helps maintain the core temperature within the optimal range.
The blood is also responsible for maintaining a stable pH level, which must remain within the narrow range of 7.35 to 7.45 for proper cellular function. Blood plasma contains chemical buffers, such as bicarbonate ions, that neutralize excess acids or bases to prevent drastic shifts in acidity. Furthermore, blood helps regulate fluid and electrolyte balance by maintaining the correct osmotic pressure between the blood vessels and the surrounding tissues.
Protection Against Harm and Injury
The third primary function of blood is protection, encompassing physical repair and immunological defense. The immediate response to vascular injury is hemostasis, which stops blood loss. Platelets rapidly aggregate at the site of a damaged blood vessel to form a temporary plug.
Following the initial plug, proteins found in the plasma, known as clotting factors, initiate the formation of a stable fibrin clot over the injury. This mechanism converts liquid blood into a semisolid gel, sealing the wound and preventing excessive blood loss. This rapid repair mechanism is necessary.
For long-term defense, blood transports white blood cells that make up the immune system. These cells identify and neutralize foreign invaders like bacteria, viruses, and fungi. Some white blood cells, such as granulocytes and monocytes, directly engulf pathogens through phagocytosis. Other lymphocytes produce specific antibodies that target and tag foreign antigens for destruction.