Blood Components

Blood is a vital fluid that circulates throughout the body, providing oxygen and nutrients to cells and removing waste products. It is made up of different components that work together to perform various functions. In this lesson, we will explore the different components of blood and their functions.


Plasma is the liquid component of blood, making up approximately 55% of total blood volume. It is a clear, yellowish fluid that contains various proteins, electrolytes, hormones, and other substances. The functions of plasma include:

  • Transporting nutrients, hormones, and waste products to and from cells.
  • Regulating the pH balance of blood.
  • Maintaining blood volume and pressure.
  • Helping to fight infections by carrying antibodies and other immune system components.

Red blood cells (RBCs)

Red blood cells, also known as erythrocytes, are the most abundant cells in the blood. They make up about 45% of total blood volume. RBCs are responsible for carrying oxygen from the lungs to the rest of the body and removing carbon dioxide from the body. They contain a protein called hemoglobin, which binds to oxygen and gives RBCs their red color.

White blood cells (WBCs)

White blood cells, also known as leukocytes, are a critical part of the body’s immune system. They make up less than 1% of total blood volume. WBCs help to fight off infections and diseases by identifying and attacking foreign invaders such as bacteria, viruses, and parasites. There are several types of white blood cells, each with a specific function:

  • Neutrophils: the most common type of WBC, responsible for attacking bacteria and other foreign invaders.
  • Lymphocytes: responsible for producing antibodies and other immune system responses.
  • Monocytes: responsible for engulfing and digesting pathogens.
  • Eosinophils: involved in fighting parasitic infections and allergic reactions.
  • Basophils: involved in allergic reactions and inflammation.


Platelets, also known as thrombocytes, are small fragments of cells that help to form blood clots. They make up less than 1% of total blood volume. When a blood vessel is damaged, platelets quickly clump together to form a plug, which helps to stop bleeding. Platelets also release chemicals that help to stimulate the repair of damaged blood vessels.

Blood is composed of plasma, red blood cells, white blood cells, and platelets. Each of these components has a specific function, working together to maintain the health and wellbeing of the body. Understanding the components of blood is essential for understanding the body’s immune system, as well as diagnosing and treating various diseases and conditions.

Blood Vessels

Blood Types