Blood : plasma, components, functions of red blood cells

Blood Cell:-

As one of the important body fluid, blood is a fluid connective tissue present in the circulatory system. the presence hemoglobin gives red color to blood.
blood made up of fluid component plasmas 55%, and formed elements –

* Erythrocytes or RBC

* Leukosis or WBC

* Platelets and thrombocytes.

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

Functions of blood:-

1. Transport of oxygen from lungs to tissue site. and carrying carbon dioxide from tissues to lungs.

2. Supply of various nutrients to tissues. carrying of waste material s for excretion.

3. Transport of hormones, vitamins, drugs and chemicals.

4. Maintains acid- base balance.

5. Regulation of body temperature.

6. The immune system of blood protects against infection.

7. Helps in clotting of blood.

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


Plasma is the fluid portion of blood. Its normal volume is 3500 ml. it is mainly composed of water.

Other substances:-

Inorganic substances : Sodium, potassium, calcium ions and copper.

organic substances: Proteins, lipids, glucose, urea and creatinine.

Serum is plasma without clotting factors.

Plasma Proteins:-

They are the proteins present in the plasma. Most of the plasma proteins are synthesized in the liver.

important plasma proteins are:

* Albumin
* Globulin
* Fibrinogen
* Prothrombin

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

Globulin: it helps in the transportation of proteins and immunoglobulin. it consists of:-
1. Alpha globulin
2. beta globulin
3. Gama globulin.

Fibrinogen: It helps in blood coagulation. Total proteins in the 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 1:7:1

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

Functions of plasma protein:-

* It maintains colloidal osmotic pressure.
* They are responsible for maintenance of viscosity of blood.
* They acts as buffer to regulate PH.
* They act as protein reserve.
* Gama globulin provide immunity.
* They are responsible for blood clotting.
* These proteins help in transport of hormones, drugs and metabolites.


* erythrocytes or red blood cells are abundantly present in blood. These cells don’t have nucleus, mitochondria or ribosomes.
* the coloring pigment present in blood is hemoglobin in jelly form. These are biconcave in shape as it helps in easily pass through the narrow capillaries. They 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:
Males- 5 to 5.5 million cells/ cu mm
Females-4.5 to 5 million cells/cu mm.
Infants- 6-7 million cells/ cu mm.

Functions of RBC:-

* The hemoglobin present in blood helps in
* transport of oxygen
* transport of carbon dioxide.
* regulation of acid base balance.

Erythropoiesis: Is the process of formation of red blood cell. Erythropoiesis starts in the third week of intrauterine life in the mesoderm of yolk sac.
From the third month of intrauterine 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.
1]  Red bone marrow
2]  Yellow bone marrow.

Red bone marrow produces RBC. During birth it is present in all the bones. In case of adults it 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 of RBC:-

The old and fragile RBC are phagocytized by reticuloendothelial system. In the reticuloendothelial cells they are broken down and HB is released. Subsequently HB is broken-down into haem and globulin. The Iron liberated is used again for synthesis of new HB. The remaining portion of haem called biliverdin. It is reduced to bilirubin in the liver and secreted through bile.


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


Hemoglobin is a conjugated protein present in the RBC. It forms 95% of the dry weight of RBC. Hemoglobin is a globular molecule made up of subunits. It is  involved in transport of carbon dioxide. It acts as a buffer.


It is the rate at which red blood cells settle down. It 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 in males – 0 to 5 mm at the end of an hour. In females – o -8 mm / hr.

ESR is increased in pregnancy and menstruation. it is increased in infections like tuberculosis rheumatoid arthritis, malignancy and anemic.

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