HEMOGLOBIN

 

HEMOGLOBIN

  Blood is a connective tissue in form of fluid.Red blood cells (erythrocytes) are the non-nucleated formed elements of blood. While hemoglobin is the iron containing protein in blood that is responsible for the transport of respiratory gases. It is a chromoprotein and has a molecular weight of 68000. Hemoglobin increases oxygen solubility in blood by about a  hundredfold. 

NORMAL HEMOGLOBIN CONTENT;Average hemoglobin content in blood is 14-16 g/dL. 

The value  varies depending  upon  the age and sex. 

AGE 

At birth : 25 g/dL  

After 3rd month : 20 g/dL

After 1 year : 17 g/dL

From puberty onwards : 14 to 16 g/dL 

SEX 

In adult males :  15 g/dL

In adult females : 14.5g/dL.

STRUCTURE AND TYPES OF HEMOGLOBIN

Hemoglobin is a conjugated protein.

 Its molecule is globular in shape, and is made up of 4 sub units. It consists of a protein combined with an iron containing pigment. The protein part is globin and the iron containing pigment is heme.

Globin;Contains four polypeptide chains. Among the four polypeptide chains, two are beta-chains and two are alpha-chains.

Heme;This is the iron containing pigment of the hemoglobin. Free  heme  is  very  sensitive to oxygen and, therefore, can bind with oxygen.

Types Of Normal Hemoglobin

1.  Adult hemoglobin – HbA

2.  Fetal hemoglobin – HbF

 Both differ structurally and functionally. 

FUNCTIONS OF HEMOGLOBIN

Transport of Oxygen;Oxygen binds with hemoglobin,resulting in the formation of oxyhemoglobin.Oxyhemoglobin is an unstable compound and the combination is reversible.When oxygen is released from oxyhemoglobin, it is called reduced hemoglobin.

Transport of Carbondioxide;When carbon dioxide binds with hemoglobin,  carbhemoglobin is formed. It is also an unstable compound and the combination  is reversible.By removal and transport of carbon dioxide from tissues to the lungs where it is expired, hemoglobin plays a role in maintenance of acid balance. 

HEMOGLOBIN SYNTHESIS

Hemoglobin synthesis begins in the proerythroblast stage of RBCs development.

Heme is synthesized in the mitochondria. 

Globin is synthesized in the ribosomes.

ABNORMAL HEMOGLOBIN

 Abnormal hemoglobin are pathologic mutant forms of hemoglobin.Occurs due to structural changes in polypeptide chains caused by mutation in gene.Hemoglobin can bind to other molecules and result in formation of Abnormal Hemoglobin Derivatives some of which are:

Carboxyhemoglobin.

Methemoglobin.

Sulfhemoglobin.

HEMOLYSIS

Red blood cells have a lifespan of 120days.They are destroyed in the reticuloendothelial system along with hemoglobin.Hemoglobin is split into heme and globin.

Globin is reutilized for hemoglobin synthesis.

Heme is eventually broken iron and prophyrin.

Iron is stored in the body as ferritin and hemosiderin.

Porphyrin is eventually broken to form biliverdin which would be converted to bilirubin (bile pigment).

PATHOPHYSIOLOGY

Anemia 

The most common blood disorder is Anemia.  It is caused by too few red blood cells or too little hemoglobin in blood.

The most common symptom is fatigue.

Aplastic anemia can cause fever, and skin rashes.

Folic acid deficiency anemia irritability and diarrhea.

Hemolytic anemia can cause jaundice, dark  urine, a  fever,  and abdominal pain. 

Sickle cell anemia can cause painful swelling  in the  feet and hands, as well as fatigue and jaundice.

 Treatment includes iron supplements taken by  mouth, transfusion of  RBCs,  folic  acid and Vit. B12  supplements.

REFERENCES

• Arthur C. Guyton and John E. Hall. Guyton and Hall textbook of medical physiology (11th edition), 419.

• K. Sembulingam and Prema Sembulingam. Essential of Medical Physiology. (6th edition), 45-78.

• Magdi Sabry. Human Physiology for Medical Students. Blood and Body Fluids (fourth edition), 33.