The word erythrocyte is derived from the Greek words erythros meaning red and kytos meaning cell. The biconcave disk-like cells of red color of blood are called red blood cells or hematids or erythrocytes or RBCs. In the human body, red blood cells travel around the body once every 60 seconds. The body contains 20-30 trillion red blood cells which are 70% of all cells in the body. A percentage measurement of the volume of red blood cells in the blood is called hematocrit (HCT). If it is deficient in the body, it causes anemia and if it is more, it causes polycythemia. Children have the highest number of red blood cells in their blood.

Cells immersed in plasma are called blood cells. Because they do not divide, they are called granules rather than cells. The process of making blood cells is called Hematopoiesis. Blood cells make up 45% of blood. There are three types of blood cells in the body.
1. Red blood cells
2. White blood cells
3. micro cycle

1. Transport of nutrients: Amino acids, glucose, fructose, fatty acids, glycerol etc. are transported through plasma.
2. Water Transport: It regulates water transport and water balance in the body.
3. Excretion: Plasma participates in the elimination of harmful waste products produced in the body.
4. Heat balance: It regulates the heat balance throughout the body.
5. Immunity: It helps the body to resist diseases.
6. Osmotic Pressure: Plasma maintains the osmotic pressure of the blood with the help of plasma proteins.
7. Blood Coagulation: It helps in blood clotting as it contains plasma proteins.
8. Contains blood cells: It contains red blood cells, white blood cells and platelets.
9. Maintains blood fluidity: As it contains 91% water, it maintains blood fluidity.
10. Acid-base balance: Maintains blood acid-base balance.

(i) Liquid content: It contains 90%-92% water.
(ii) Inert matter: It contains 9% inert matter.
(iii) Gaseous substances: Gaseous substances are- O2, CO2, N2 etc.
(iv) Minerals: Sodium, Potassium, Calcium, Magnesium, Iron etc.
(v) Ions: Na+, K+, Ca++, Cl-, HCO3-, HPO4- etc.

(i) Nutrients: glucose, amino acids, vitamins etc.
(ii) Plasma proteins: albumin, fibrinogen, prothrombin, albumin, globulin etc. (7.5%).
(iii) Lubricants: neutral lipids, cholesterol, phospholipids, lecithin etc.
(iv) Pigments: bilirubin, biliverdin, carotene, xanthophyll etc.
(v) Organic acids: citric acid, lactic acid etc.
(vi) Excretory substances: urea, uric acid, creatinine, xanthine, ammonia etc.

The light yellow liquid part of blood is called plasma. 55% of blood is plasma. It consists of 90-92% water and 8-10% solids. There are two types of components of plasma. Organic material and inorganic material
1. organic matter
(i) Nutrients: glucose, amino acids, vitamins etc.
(ii) Plasma proteins: albumin, fibrinogen, prothrombin, albumin, globulin etc. (7.5%).
(iii) Lubricants: neutral lipids, cholesterol, phospholipids, lecithin etc.
(iv) Pigments: bilirubin, biliverdin, carotene, xanthophyll etc.
(v) Organic acids: citric acid, lactic acid etc.
(vi) Excretory substances: urea, uric acid, creatinine, xanthine, ammonia etc.
2. inorganic material
(i) Liquid content: It contains 90%-92% water.
(ii) Inert matter: It contains 9% inert matter.
(iii) Gaseous substances: Gaseous substances are- O2, CO2, N2 etc.
(iv) Minerals: Sodium, Potassium, Calcium, Magnesium, Iron etc.
(v) Ions: Na+, K+, Ca++, Cl-, HCO3-, HPO4- etc.

1. It is composed of plasma and blood cells.
2. It consists of 55% plasma and 45% blood cells.
3. Its relative importance is 1.05-1.06.
4. Its pH is 7.35-7.45 (average 7.40).
5. Temperature 36-38০C.
6. 7-8% or 12th of the total body weight is blood.
7. It is red.
8. It is highly alkaline.
9. It is salty in nature.

The word Hematology is derived from the Greek word Haima meaning blood. The branch of biology that deals with blood is called Hematology.

Blood is a type of fluid connective tissue. The red opaque, alkaline, viscous and salty fluid flowing through the blood vessels is called blood. The amount of blood in the body is 5-6 liters. Blood in a test tube is spun in a centrifugal machine 3000 times per minute to separate the blood into two layers. Plasma and blood cells.

Consisting of the heart, blood vessels and blood, the system through which blood moves throughout the body is called the circulatory system. The Greek physician Gallon (130-210) and later scientists for more than 1,400 years believed that the heart produced blood and pumped it throughout the body. In 1628, British physician William Harvey was the first to present the correct method of blood circulation in the human body. For this reason, he is called the father of the circulatory system. De Viussens (1706) described the chambers and tubules of the heart. Stephen Hales first measured blood pressure in 1733. Wren Linnec (1816) invented the stethoscope. In 1952, John Lewis performed the first open heart surgery. Christian Barnard (1967) established the heart in the human body. In 1982, Robert Jarvik created the artificial heart and Willem de Vries implanted it in the human body.