Blood is an important body fluid in the form of fluid connective tissue present in the circulatory system. The presence of hemoglobin gives red color to blood. Blood components include blood plasma, white blood cells, red blood cells and platelets.
Blood is made up of fluid component plasma is of 55% and blood forming elements -

• Erythrocytes or RBC
• White blood cells or WBC
• Platelets and thrombocytes.

The PH of blood is 7.35 -7.42 and the specific gravity is 1055 to 1060.

Functions of blood

• The blood transports oxygen from lungs to tissue site and carries carbon dioxide from tissues to lungs.
• Supply of various nutrients to tissues and carrying of waste material s for excretion,
• Transport of hormones, vitamins, drugs and chemicals,
• Blood helps to maintain acid- base balance in the body.
• Blood helps in Regulation of body temperature.
• The immune system of blood protects the body against infection.
• Components of blood help in clotting of blood during emergency.

The total volume of blood is around 5 lit in an average adult male.

Plasma of Blood

Plasma is the fluid portion of blood. Normal blood plasma volume is 3500 ml. Plasma is mainly composed of water and other substances present in the plasma are
Inorganic substances such as Sodium, potassium, calcium ions and copper and
Organic substances such as Proteins, lipids, glucose, urea and creatinine.

The plasma without clotting factors is called as Serum.

Plasma proteins: Plasma proteins are the proteins present in the plasma. Most of the plasma proteins are synthesized in the liver. The important plasma proteins are
Albumin

• Globulin
• Fibrinogen and
• Prothrombin

Albumin: Albumin has molecular weight of 66,000 and is produced in liver. Plasma half life of albumin is 19 days. The albumin maintains the colloidal atmospheric pressure. Albumin present in the blood mainly helps in transportation of bilirubin, hormones and drugs.

Globulin: Globulin helps in the transportation of proteins and immunoglobulin. The globulin mainly consists of

• Alpha globulin
• beta globulin
• Gama globulin.

Fibrinogen: The blood fibrinogen helps in blood coagulation. Fibrinogen is the main factor responsible for the clotting of blood.

Total proteins in the blood plasma are
Albumin 6-8gms/dl
Globulin 4.5-5.5 gm/dl
Fibrinogen 0.2-0.4gms/dl
Prothrombin 0.1gm/dl
Albumin globulin ratio is 1:7:1

Prothrombin: Prothrombin is an inactive precursor of thrombin. Prothrombin concentration in plasma is 15 mg/dl. Prothrombin is formed in the liver with the help of vitamin k.

Functions of plasma protein

Plasma protein maintains colloidal osmotic pressure.
Plasma proteins are responsible for maintenance of viscosity of blood.
Plasma protein acts as buffer to regulate PH.
Plasma protein act as protein reserve.
Gama globulins provide immunity to body.
Plasma proteins are also responsible for blood clotting.
These proteins help in transport of hormones, drugs and metabolites in the body.

Erythrocytes

Erythrocytes or red blood cells are abundantly present in blood. These cells don’t have nucleus, mitochondria or ribosome.
The coloring pigment present in blood is hemoglobin in jelly form. Erythrocytes or red blood cells are biconcave in shape as it helps in easily pass through the narrow capillaries. RBCs are flexible in nature.

• Mean red cell diameter is 7.2 micron.
• Thickness is 2.2 at the periphery and 1 micron at the center.
• Normal life span of RBC is 120 days.

Normal count of RBC

Normal RBC in Males: 5 to 5.5 million cells/cu mm
Normal RBC in Females: 4.5 to 5 million cells/cu mm.
Normal RBC in Infants: 6-7 million cells/cu mm.

Functions of RBCs

The hemoglobin present in blood helps in the blood
Transport of oxygen from lungs to tissue site.
Transports carbon dioxide from tissues to lungs.
RBCs Regulate acid base balance in the body.

Erythropoiesis: Erythropoiesis is the process of formation of red blood cells. Erythropoiesis starts in the third week of intra uterine life in the mesoderm of yolk sac.
From the third month of intra uterine life it is in the liver and spleen. After 5th month of intrauterine life fetal bone marrow starts producing red cells.

Bone marrow is of two types.

• Red bone marrow
• Yellow bone marrow

Red bone marrow produces RBC. During birth Red bone marrow is present in all the bones. In case of adults Red bone marrow is present in the flat bones like cranial bones, vertebrae, pelvic bones, ribs, sternum, upper end of long bones like femur and humorous.
The yellow bone marrow is mainly made up of adipose tissue.

Fate or Life span of RBC

The old and fragile RBCs are phagocyted by reticulo endothelial system. In the reticulo endothelial cells, red blood cells are broken down and HB is released. Subsequently HB or hemoglobin is broken-down into haem and globulin. The Iron liberated during this process is used again for synthesis of new hemoglobin. The remaining portion of haem called biliverdin. It is reduced to bilirubin in the liver and excreted through bile.

Polycythemia

Polycythemia is a condition where RBC count is increased above 8 million cells/cu mm.

Hemoglobin

Hemoglobin is a conjugated protein present in the erythrocytes or RBC. Hemoglobin forms 95% of the dry weight of RBC. Hemoglobin is a globular molecule made up of subunits.

Hemoglobin is a globular molecule made up of subunits. Each subunit contains a hememoity conjugated to a polypeptide. It is also involved in transport of carbon dioxide. Hemoglobin acts as a buffer.

ESR: Erythrocytes sedimentation rate

Erythrocytes sedimentation rate is the rate at which red blood cells settle down. ESR or the Erythrocytes sedimentation rate is the measure of supernatant plasma separated out at the end of one hour when a column of blood is kept disturbed.
The normal value of Erythrocytes sedimentation rate or ESR in males is : 0 to 5 mm at the end of an hour.
Erythrocytes sedimentation rate in females is:  o to 8 mm / hr.

ESR is increased in pregnancy and menstruation. Erythrocytes sedimentation rate is also increased in infections like tuberculosis, rheumatoid arthritis, malignancy, anemia and other systemic diseases.

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