Blood is a specialized fluid connective tissue that circulates throughout the body, performing many essential functions. It consists of a liquid component called plasma, which suspends various cellular components. These cellular components are known as the “formed elements” and include the red blood cells, white blood cells, and platelets.
Red Blood Cells
Red blood cells, also known as erythrocytes, are the most abundant formed elements in the blood, giving blood its characteristic red color. Their primary function is to transport oxygen from the lungs to the body’s tissues and carry carbon dioxide back to the lungs for exhalation. This exchange is facilitated by hemoglobin, a specialized protein rich in iron, which red blood cells contain.
These cells possess a biconcave disc shape, which enhances their flexibility, allowing them to navigate through narrow blood vessels, and maximizes their surface area for efficient gas diffusion. Mature red blood cells lack a nucleus, which limits their lifespan. They typically circulate for approximately 120 days before being removed from the bloodstream.
White Blood Cells
White blood cells, or leukocytes, are components of the body’s immune system, defending against infection and foreign invaders. These cells are generally larger than red blood cells and, unlike red blood cells, they possess a nucleus. They circulate through the bloodstream and tissues, actively responding to injury or illness by locating and combating harmful organisms.
There are several types of white blood cells, each with specialized roles in the immune response. Some types, like neutrophils, are phagocytes that engulf and destroy bacteria and fungi. Other types, such as lymphocytes, include T cells and B cells, which are involved in recognizing and neutralizing specific pathogens or producing antibodies to fight infection. This diverse array of white blood cells coordinates to provide comprehensive protection for the body.
Platelets
Platelets, also known as thrombocytes, are small, irregular-shaped cell fragments, not complete cells, that play a role in blood clotting. Their main function is to prevent excessive bleeding after an injury by initiating hemostasis. Platelets are produced in the bone marrow from larger cells called megakaryocytes.
When a blood vessel is damaged, platelets are signaled to the site of injury. They adhere to the damaged vessel wall and then aggregate, or clump together, forming a temporary plug. This initial plug triggers a series of events known as the coagulation cascade, which involves various proteins called clotting factors. The culmination of this process is the formation of a stable blood clot, which seals the injury and stops blood loss.