Blood cells

Blood is one among the most important body fluids. Blood is a type of connective tissue. It has various important functions. Primarily it delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells, transporting hormones and other signals throughout the body. Blood plays an important role in regulating the body’s systems, maintaining homeostasis, regulating body pH and core body temperature. The average person has about 5 liters (more than a gallon) of blood.

A liquid called plasma makes up about half of the content of blood. Plasma contains proteins that help blood to clot, transport substances through the blood, and perform other functions. Blood plasma also contains glucose and other dissolved nutrients. Blood is conducted through blood vessels (arteries and veins). Blood is prevented from clotting in the blood vessels by their smoothness, and the finely tuned balance of clotting factors.

Constituents of Blood

Blood constituents

  • Erythrocytes (red blood cells, RBCs),
  • Leukocytes (white blood cells),
  • Thrombocytes (platelets).

By volume, the red blood cells constitute about

  • 45% of whole blood,
  • the plasma about 54.3%,
  • white cells about 0.7%.


One ml of blood contains:

  • 7 to 6.1 million (male), 4.2 to 5.4 million (female)Erythrocytes (RBC)
  • 4,000–11,000Leukocytes (WBC)
  • 200,000–500,000Thrombocytes ( Platelets)


Plasma is a fluid that is the blood’s liquid medium, which by itself is straw-yellow in color. The blood plasma is about 55% of blood, its volume totals of 2.7–3.0 liters (2.8–3.2 quarts) in an average human. It is essentially an aqueous solution containing 92% water, 8% blood plasma proteins, and trace amounts of other materials.

Plasma circulates dissolved nutrients, such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins), and removes waste products, such as carbon dioxide, urea, and lactic acid.

Other important components include:

  • Serum albumin
  • Blood-clotting factors (to facilitate coagulation)
  • Immunoglobulins(antibodies)
  • lipoprotein particles
  • Various other proteins
  • Various electrolytes (mainly sodium and chloride)

The term serum refers to plasma from which the clotting proteins have been removed. Most of the proteins remaining are albumin and immunoglobulins.

Narrow range of pH values

Blood Ph is regulated to stay within the narrow range of 7.35 to 7.45, making it slightly basic.

Functions of Blood

  • Red blood cells, which carry oxygen to the tissues
  • White blood cells, which fight infections
  • Platelets, smaller cells that help blood to clot
  1. Transportation
  • Transporting important nutrients and materials to and from the cells and molecules that make up our body.
  • It is the duty of blood to first take the oxygen processed by the lungs to all the cells of the body and then to collect the carbon dioxide from the cells and deliver it to the lungs.
  • Collecting metabolic waste from up and down the body and take it to the kidneys for excretion.
  • Delivering the nutrients and glucose generated by the organs of the digestive system
  • To carry out the transportation of hormones
  1. Protection
  • Protecting the body from the threat of infections and disease-causing bacteria.
  • The white blood cells found in blood are responsible for safeguarding the different organs of the body by producing antibodies and proteins.
  • The platelets present in blood handle the task of limiting blood loss in the wake of an injury by helping the blood to clot quickly.
  1. Regulation
  • It oversees the temperature of the body and maintains it to a level that is tolerated by the body with ease.
  • Controlling the concentration of Hydrogen ions in the body, which are also known as pH balance.
  • The administration of the levels of water and salt required by each cell of the body also falls under the regulation duties of blood.
  • To control the blood pressure and maintain it under a normal range.

Blood transfusion

Blood transfusion is a medical treatment that replaces blood lost through injury, surgery, or disease. The blood goes through a tube from a bag to an intravenous (IV) catheter and into your vein.

Need of Blood transfusion

  • Patients with poor oxygen saturation may need more blood.
  • In cases where patients have low levels of hemoglobin but are cardiovascularly stable,parenteral iron is increasingly a preferred option based on both efficacy and safety.
  • Injury or major surgery.
  • An illness that causes bleeding, such as a bleeding ulcer.
  • An illness that destroys blood cells, such as hemolytic anemia or thrombocytopenia.
  • If you have an illness in which your bone marrow doesn’t make enough blood, such as aplastic anemia, you may need transfusions.

Blood donor requirements:

  • Be aged between 16 and 70 years
  • Weigh at least 45kg
  • Be in good health, including normal temperature and blood pressure

Different types of blood collection

The main ways in which blood is collected include:

  • Homologous– whole blood is collected from the donor, separated into different components and given as a transfusion to people with compatible (matching) blood types.
  • Apheresis– only some components, either plasma or platelets, are taken from the blood of the donor. A machine centrifuges the cells and gives the red cells, or red cells and plasma, back to the donor.

Less common ways in which blood is collected include:

  • Autologous– prior to a scheduled operation or transfusion, a person donates blood specifically for their own use.
  • Directed or designated– prior to a scheduled transfusion, a person requests that only blood collected from family members or friends be used for transfusion.


  • A single unit of blood taken during a whole blood donation is about less than 450mL , which is less than 10% of your total blood volume
  • Donors must wait eight weeks (56 days) between whole blood donations but only seven days between platelet pheresis donations.

Blood Types

  • Every person has one of the following blood types: A, B, AB, or O. Also, every person’s blood is either Rh-positive or Rh-negative. So, if you have type A blood, it’s either A positive or A negative.
  • ‘O’ People who have this blood type are called universal donors. Type O blood is used for emergencies when there’s no time to test a person’s blood type.

People who have type AB blood are called universal recipients. This means they can get any type of blood.


Dr. Keerthi Shetty

Dr. Keerthi Shetty

Ayurveda Doctor and Panchakarma Expert

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