Blood

The Components of Blood and Their Significance

• Plasma

Plasma is the fluid component of blood, comprising a mixture of water, glucose, lipids, proteins, and electrolytes. Its primary function is to transport blood cells throughout the body, along with essential nutrients, metabolic waste products, antibodies, clotting factors, hormones, and proteins that help regulate the body’s fluid balance.

• Red Blood Cells (Erythrocytes)

Erythrocytes, commonly known as red blood cells (RBCs), are the most prevalent cellular component of blood, accounting for approximately 40-45% of its volume. These cells are characterized by their biconcave disc shape, which optimizes their surface area for gas exchange.

Erythropoiesis, the production of red blood cells, is regulated by erythropoietin, a hormone primarily synthesized by the kidneys. Erythrocytes originate as immature cells in the bone marrow and mature over about seven days before entering the bloodstream. Unlike most cells, mature erythrocytes lack a nucleus, enhancing their flexibility to navigate through the body’s vasculature. However, this also limits their lifespan to about 120 days, after which they are removed from circulation.

Haemoglobin, a specialized protein within erythrocytes, binds oxygen in the lungs and releases it to tissues throughout the body, then facilitates the transport of carbon dioxide back to the lungs for exhalation. The hematocrit, a measure of the proportion of blood volume occupied by red blood cells, is a common clinical indicator of erythrocyte levels.

• White Blood Cells (Leukocytes)

Leukocytes, or white blood cells (WBCs), play a crucial role in the body’s immune defence. They are significantly fewer in number than erythrocytes, constituting about 1% of blood volume.

The most abundant type of leukocyte is the neutrophil, which serves as an immediate responder to infection and constitutes 55-70% of the total WBC count. Neutrophils have a short lifespan of less than a day, necessitating constant production by the bone marrow to maintain immune defence.

Lymphocytes, another major class of WBCs, are divided into two main types: T lymphocytes, which regulate other immune cells and directly attack infected or cancerous cells, and B lymphocytes, which produce antibodies targeting specific pathogens.

• Platelets (Thrombocytes)

Platelets, or thrombocytes, are not true cells but small cell fragments. They are essential for the coagulation process, gathering at injury sites, adhering to the vessel lining, and forming a platform for blood clot formation. This results in the creation of a fibrin clot that seals the wound and prevents further bleeding, also providing a scaffold for new tissue growth and healing.

Abnormally high platelet counts can lead to excessive clotting, increasing the risk of strokes and myocardial infarctions. However, advances in antiplatelet therapy offer effective prevention and treatment options. Conversely, low platelet counts can result in excessive bleeding.

Blood Type 

Blood type is determined by two major blood group systems: ABO and Rh, which depend on the presence or absence of specific antigens and proteins on the surface of red blood cells.

• ABO System

The ABO blood group system categorizes blood into four main types based on the presence or absence of antigens A and B:

• Type A: Has the A antigen on the surface of red blood cells.
• Type B: Has the B antigen on the surface of red blood cells.
• Type AB: Has both A and B antigens on the surface of red blood cells.
• Type O: Lacks both A and B antigens on the surface of red blood cells.

• Rh System

The Rh blood group system further classifies blood based on the presence or absence of the Rh factor, a specific protein:

• Rh Positive (Rh+): The Rh factor is present on the surface of red blood cells.
• Rh-Negative (Rh-): The Rh factor is absent on the surface of red blood cells

function

• Delivering oxygen to tissues is facilitated by haemoglobin within red blood cells.
• Providing essential nutrients like glucose, amino acids, and fatty acids, either dissolved in the blood or bound to plasma proteins, such as blood lipids.
• Eliminating waste products, including carbon dioxide, urea, and lactic acid.
• Supporting immune functions by circulating white blood cells and enabling antibodies to detect foreign substances.
• Initiating coagulation to respond to blood vessel injuries, converting blood from a liquid to a semi-solid gel to prevent bleeding.
• Acting as a messenger by transporting hormones and signaling tissue damage.
• Regulating core body temperature.