Human Blood: Components and Functions
Blood
The human body contains several extracellular fluids that constitute the internal environment. These include the interstitial fluid of the intercellular matrix and circulating fluids such as blood and lymph. These fluids act as intermediaries between the highly variable external environment and the intracellular environment, where metabolic reactions occur.
Blood is a liquid tissue, part of the internal environment, that circulates through blood vessels.
Blood performs a wide variety of functions:
- It transports hormones, nutrients from the digestive system, oxygen from the respiratory system to cells, and waste products from cellular metabolism for elimination.
- It regulates body temperature, acid-base balance, and the concentration of the internal environment.
- It defends the body against infectious agents.
Blood circulates rapidly throughout the body. To prevent loss in case of blood vessel rupture, the body has developed a complex defense mechanism known as coagulation.
Blood is composed of two distinct components: plasma and blood cells.
Plasma
Plasma is the liquid component of blood. It is an aqueous solution in constant exchange of substances with the interstitial fluid surrounding cells.
Its chemical composition includes water, various proteins, ions, nutrients, hormones, waste substances, and gases.
The most important plasma proteins are:
- Albumins: The most abundant proteins, performing various functions, including enhancing water retention in the blood.
- Globulins: A diverse group including antibodies or immunoglobulins, which play a role in immune defense.
- Fibrinogen: A soluble protein that transforms into insoluble fibrin during blood clotting.
Blood Cells
There are three main categories: erythrocytes, leukocytes, and platelets.
Erythrocytes (Red Blood Cells)
Also known as Red Blood Cells (RBCs). They are the most abundant blood cells, specialized in oxygen transport using a special protein, Hemoglobin. In mammals, mature red blood cells lack a nucleus.
Leukocytes (White Blood Cells)
Also known as White Blood Cells (WBCs). These cells function to defend the body. They possess a nucleus. Two main groups are distinguished:
Granulocytes
Cells with granules in their cytoplasm that show different affinities for staining dyes, allowing distinction into three types:
- Eosinophils: Stain with acid dyes. Participate in defense against parasites.
- Basophils: Stain with basic dyes. Involved in inflammatory reactions.
- Neutrophils: Do not show a specific affinity for particular dyes. They are the most abundant leukocytes and participate in defense by engulfing pathogens (phagocytosis).
Agranulocytes
Do not show granules visible under light microscopy. There are two main types:
- Lymphocytes: Cells responsible for specific immune responses.
- Monocytes: The largest blood cells. They can move into other tissues, transforming into macrophages, cells with high phagocytic capacity.
Platelets
These are cell fragments without nuclei. When a blood vessel is broken, they aggregate and adhere to its walls to form a platelet plug and release factors involved in blood clotting.