Functions of the blood/Blood basics

Blood is a specialized fluid within the body that performs numerous important functions. Blood is made up of various components, including red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes), and plasma. The blood comprises approximately 55% plasma and 45% blood cells. Blood makes up about 7 to 8 % of our total body weight. On average, an adult male has approximately 12 pints (6 liters) of blood, while an adult female has around nine (5 liters) pints.

Blood components and their function

  • Plasma: Plasma is a yellowish fluid that contains water, proteins, sugar, fat, and salts. Plasma transports blood cells along with nutrients, hormones, and waste materials throughout the body. It also helps regulate body temperature and maintains proper fluid balance.
  • White Blood Cells: White blood cells protect the body from infections. There are five types of white blood cells.
    • The most common type of white blood cell is the neutrophil, accounting for 55 to 70 % of the total white blood cell count. Neutrophils have a short lifespan of less than a day, requiring continuous production by the bone marrow to ensure ongoing protection against infections.
    • Lymphocytes are another important type of white blood cell, divided into two main populations. T lymphocytes regulate immune cell function and directly attack infected cells and tumors. B lymphocytes produce antibodies, specialized proteins that target and neutralize bacteria, viruses, and foreign substances. 
    • Eosinophils: White blood cells identify and destroy parasites, eliminate cancer cells, and assist basophils in allergic responses.
    • Basophils: Involved in allergic reactions and can cause symptoms such as coughing, sneezing, or a runny nose.
    • Monocytes: Defend against infections by cleaning up damaged cells in the body.

The normal white blood cell count ranges between 4,000 and 11,000 cells per microliter.

  • Platelets: Platelets are small, colorless cell fragments that take on a plate-like shape. Platelets are involved in blood clotting (coagulation) to prevent excessive bleeding. They form clots at the injury site to stop bleeding and initiate healing. A normal platelet count for adults ranges from 150,000 to 450,000 platelets per microliter of blood.
  • Red Blood Cells: RBCs account for about 40 to 45% of the blood’s volume. The shape of a red blood cell is a flattened disk resembling a donut. The production of red blood cells is regulated by erythropoietin, a hormone primarily produced by the kidneys. Immature cells in the bone marrow develop into red blood cells over approximately seven days and are then released into the bloodstream. On average, a red blood cell survives for about 120 days. Red cells contain a special protein called hemoglobin, which facilitates oxygen transport from the lungs to the body tissues and carries carbon dioxide back to the lungs for exhalation. The high concentration of red blood cells gives blood its red color, derived from hemoglobin.

Normal red blood cell counts:

Men: 4.7 to 6.1 million red blood cells per microliter of blood.

Women: 4.2 to 5.4 million red blood cells per microliter of blood.

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