Blood is the fluid that transports oxygen nutrients through the whole body and carries away the waste products of the organism. An average human adult has about five liters of blood, which constitutes 8% of the entire body weight (Shier et al., 2019). Due to its complex nature and transport function, a single drop of blood can contain a countless number of viruses. Therefore, the extraction of blood requires the strictest precautions to avoid infection.
It is essential to analyze its structure to have a better understanding of blood’s functions. Blood consists of white and red blood cells, and platelets, which are cellular fragments. Shier et al. (2019) explain the origin of blood cells: “Blood cells originate in red bone marrow from hematopoietic stem cells, also known as hemocytoblasts” (p. 531). The function of red blood cells lies in carrying oxygen from the lung to the rest of the body. They are shaped into a biconcave disc, with a thinner layer in the middle and a thicker layer around the rims. Such a shape allows them to increase the area of the surface, which, in turn, creates space for the diffusion of gases into and out of the cell (Shier et al., 2019). Moreover, this shape shortens the distance for diffusion, where the cell membrane is set closer to hemoglobin molecules. Therefore, red blood cells assist the transference of oxygen across the organism, which supplements the body with needed nutrients.
Another significant part of blood is white blood cells, or leukocytes, that serve as protectors of the organism. They fight bacteria, viruses, and other damaging bodies that threaten human health. They are responsible for preventing illnesses, and a person’s health directly depends on the quality of their work. There are five main types of white blood cells in circulating blood. They differ in the shape of their nucleus, size, and the nature of the cytoplasm. These are neutrophils, eosinophils, basophils, monocytes, and lymphocytes. The first three belong to the granulocytes group, while the last two to the agranulocytes group. They differ in the composition of their cytoplasmic granules, where granulocytes have a more prominent granular cytoplasm. Shier et al. (2019) describe the functions of each type of white blood cell. Neutrophils are the blood cells that come first at the site of the infection. Their task is to phagocytize bacteria, some viruses, and fungi. Eosinophils manage allergic reactions and protect the rest of the body from the infestation of parasitic worms. Basophils respond to neutrophils by migrating “to damaged tissues where they release histamine, which promotes inflammation and heparin, which inhibits blood clotting, actions that increase blood flow to injured tissues” (Shier et al., 2019, p. 537-39). Therefore, the function of the granulocytes group is to take the first act in fighting the infection.
Agranulocytes are responsible for the composition of the organism’s adaptive immunity to prevent potential reoccurring infections. For example, monocytes are similar to neutrophils because they also phagocytize bacteria and other debris in the tissues, only outside the bloodstream. Lymphocytes divide into two groups: T cells and B cells which are essential for the immune system. While “T cells directly attack microorganisms, tumor cells, and transplanted cells, B cells produce antibodies, which are proteins that attack foreign molecules” (Shier et al., 2019, p. 537-39). Thus, granulocytes and agranulocytes represent the protectors of the body from infections and help to develop a stronger immune system.
Reference
Shier, D., Butler, J., & Lewis, R. (2019). Hole’s human anatomy and physiology (15th ed.). McGraw-Hill Education.