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What is Haemoglobin Definition and Normal Values,Disadvantages,Function

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 HAEMOGLOBIN Definition ➽ the red, oxygen carrying pigment in the RBCs of vertebrates is haemoglobin.Synthesis of haemoglobin requires the provision of nutrients e.g. proteins, vitamins, minerals (specially iron). 
 It consists of the protein globin (polypeptide) united with the pigment haem (heme). there are 4 haem to the one molecule of haemoglobin, contains 4 iron atoms and can carry 4 molecules (8 atoms) of oxygen. Haemoglobin reacts with oxygen very rapidly requiring less than 0.01 second. Similarly, deoxygenation of haemoglobin is also very rapid. 
Molecular weight of haemoglobin is 68,000.
•Note – Approx. 0.3 gm of haemoglobin is destroyed and 0.3 gm synthesized every hour. 


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STRUCTURE 
l. Haem is an iron containing porphyrin, called iron protoporphyrin IX. 
The porphyrin nucleus is tetrapyrrole i.e. it consists of 4 ‘pyrrole rings’ joined together by 4 methine (= CH-) bridges. 
The pyrrole rings are numbered I, II, III and IV; the carbon atoms of the methine bridges are labelled a, ~, y and o; the position on pyrrole rings to which side chains are attached are numbered 1 to 8. The side chains at 1, 3, 5 and 8 position are methyl (-CH:0; 2 and 4 are vinyl (-CH= CH2 ); 6 and 7 are propionic acid👉 (-CH2.CH2.COOH).  

2. 👉The iron in haem is in the ferrous (Fe2+) form. 
The iron is attached to the ‘N’ of each pyrrole ring. Each Fe2+ combines loosely and reversibly with one molecule of oxygen. Combination of haem with oxygen is called oxygenation and not oxidation, because, after combination with oxygen, iron in the haem stays in Fe2+ state. Therefore, the oxygen does not become ionic oxygen but is carried as molecular oxygen.

3.Globin is a protein built from 4 polypeptide chains, two ‘ a ‘ and two ‘W chains. Therefore, the normal adult haemoglobin (HbA) is written as HbA (CJ.i~2). Of two a-chains each contains 141 amino-acids and of two ~-chains each contains 146 amino-acids.

Each polypeptide chain is associated with one haem group. Thus, there are 4 haem to the one molecule of haemoglobin, contains 4 iron atoms and can carry 4 molecules (8 atoms) of oxygen. 

4. Oxygenation of 1st haem molecule in haemoglobin, increases the affinity of 2nd haem for oxygen and oxygenation of 2nd haem increases the affinity of the ” ~– 3rd and so on. Therefore, the affinity of haemoglobin • for the 4th oxygen molecule is many times that of the 1st. This shifting affinity of haemoglobin for oxygen results in: 
(i) Sigmoid shape of oxygen-haemoglobin dissociation curve.
(ii) Haemoglobin reacts with oxygen very rapidly requiring less than 0.01 second. Similarly, deoxygenation of haemoglobin is also very rapid. 

5. Molecular weight of haemoglobin is 68,000.


                                      SOME IMPORTANT DEFINITIONS     
1. OXYHAEMOGLOBIN –  Haemoglobin reacts with oxygen to form oxyhaemoglobin and is represented as Hb02.
The affinity of haemoglobin for oxygen is influenced by pH, temperature and concentration of 2, 3, diphosphoglycerate (2,3 DPG) in the RBCs, a product of metabolism of glucose
As concentration of 2,3 DPG rises, the affinity of haemoglobin for oxygen falls and the oxygen-haemoglobin dissociation curve is shifted to the right; as a result more oxygen is released by blood to the tissues. 

                                                                                                                                                                       
Important Notes                                                                                                                                            
1. At high altitude (e.g. 5000 metres above sea level) 2,3 DPG concentration in RBCs increases by    50% and this makes more oxygen available to the tissues.                                                                    
2. Stored blood loses its 2,3 DPG and oxygen affinity of haemoglobin increases resulting in less       release of oxygen.                                                                                                                                                                                                     

 2. CARBAMINO-HAEMOGLOBIN – Carbon dioxide reacts with haemoglobin to form cnrbnminohaemoglobi11. CO2 + HbNHz HbNH COOH 

3. REDUCED (DEOXYGENATED) HAEMOGLOBIN – Haemoglobin from which oxygen has been removed is called reduced or deoxygenated haemoglobin and is represented as Hb. 

4. CARBOXY HAEMOGLOBIN or CARBON MONOXY HAEMOGLOBI Carbon monoxide (CO) reacts with haemoglobin to form carboxy haemoglobin or carbon monoxy haemoglobin. The affinity of haemoglobin for CO is 210 times than its affinity for oxygen which consequently displaces oxygen on haemoglobin, reducing the oxygen carrying capacity of blood. 

5. METHAEMOGLOBIN – When either reduced or oxygenated haemoglobin is exposed to various drugs or oxidising agents, the ferrous (Fe2+) is oxidised to ferric (Fe3+) form and the compound is called methaemoglobin. It is represented as HbOH. 

Disadvantages ➧ 
(i) It cannot unite reversibly with gaseous oxygen. 
(ii) It is dark coloured and when it is present in large quantities (more than 1.5% gm/ dL) in circulation it resembles cyanosis i.e. blue colouration of skin. 

Some oxidation of haemoglobin to methaemoglobin occurs normally, but an enzyme in RBCs, the NADH (dihydronicotinamide adenine dinucleotide)- methaemoglobin reductase system, converts methaemoglobin back to haemoglobin. Congenital absence of this  system causes hereditanJ metliaemog lobillemia, a fatal condition. 

Haemoglobin level and NORMAL VALUES ➧

1. At birth: 23 gm/ dL, because RBC count is more. 

2. At the end of 3 months: 10.S gm/ dL, as an infant is totaUy on milk feed which is devoid of iron. 

3. After 3 months, haemoglobin increases gradually and at the end iof 1 year it becomes 12.S gm/dL. 

4. Adults Males : 14-18 gm/ dL (Average: 15.S gm/dL) Females: 12-15.5 gm/dL (Average: 14 gm/ dL) Clinically 14.8 gm/ dL haemoglobin irrespective of sex is regarded as 100% haemoglobin. When blood is equilibrated with 100% oxygen (p02 = 760 mmHg), the normal haemoglobin becomes 100% saturated. 1 gm/ dL haemoglobin when fully saturated combines with 1.34 mLoxygen, therefore, haemoglobin concentration is an index of oxygen-Carrying Capacity of blood. 

Normal values – ma/es: 21 mL/ dL,femnles: 18 mL/ dL.

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FUNCTIONS OF HAEMOGLOBIN 
1. Facilitate transport of oxygen from lungs to the tissues. 
2. Facilitate transport of CO2 from the tissues to the lungs . 
3. It acts as an excellent acid-base buffer, being a protein . It is responsible for 70% buffering power of whole blood. 
4. It has additional nitric oxide (NO) binding site on the ~-chain which is increased by 0 2. Therefore, haemoglobin binds with NO in the lungs and releases it in the tissues where it promotes vasodilation. 

DISADVANTAGES OF ‘FREE’ HAEMOGLOBIN (Why haemoglobin is contained within the RBCs?) 
1. If haemoglobin was dissolved in the plasma (called free haemoglob;in) it would lead to: 
(i) increase in the viscosity of plasma, hence of whole blood, causing BP to rise, and 
(ii) increase in the osmotic pressure of plasma to 100 mmHg. 
(i) and (ii) interfere with the mechanism of fluid exchange between capillaries and tissue spaces.

2. Loss of free haemoglobin by the kidneys in urine (hemoglolmmria)) also results in kidney damage.
3. Free haemoglobin is taken up and rapidly destroyed by the tissue-macrophage system. 
  

SYNTHESIS OF HAEMOGLOBIN Synthesis of haemoglobin requires the provision of nutrients e.g. proteins, vitamins, minerals (specially iron). 

It only takes place in the developing RBCs . Factors controlling haemoglobin formation 

1. Role of proteins – A low protein intake decreases haemoglobin regeneration even in the presence of excess of iron; the limiting factor here is lack of globin formation. 
2. Role of Minerals 
    (i) Iron 
    (a) it helps in formation of haem; 
    (b) iron content of haemoglobin is 0.33%, therefore 100 mL of blood containing 15 gm of                              haemoglobin contains 15 x 0.33/ 100 = approx. 50 mg of iron.                            
    (c) as life span of RBC is 120 days, therefore, 0.8% (1/ 120 x 100) of total blood haemoglobin contained in 50 mL (6 litres x 0.8%) of blood, is destroyed daily, releasing approx. 25 mg of iron. This iron is reused for fresh synthesis of haemoglobin. 
 
   (ii) Copper – helps in promoting the absorption, mobilization and utilization of iron. Very little copper is required; adequate amount occurs in diet and most iron preparations contain traces of copper. 

   (iii) Cobalt – is necessary for manufacture of vitamin B12 by bacterial action in the lumen of GIT. It also increases the production of a hormone erythropoietin  which, in turn, stimulates the development of RBCs. 

     (iv) Calcium – increases iron absorption from GIT. 

3. Role of vitaminsVitamin C, vitamin B12 and folic acid help in synthesis of nucleic acid which in tum, is required for the development of RBCs.  

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Dr .Lalit Choudhary
Hii everyone, I'm Dr Lalit Choudhary PT. Born and brought up in delhi. Practicing as a professional PHYSIOTHERAPIST. As a therapist I love to interact with others and and get myself updated regarding all the social issues which are leading my countrymen to distress themselves. Yes, I agree that Iam a workaholic but my work gives me immense pleasure but there are sometimes when I feel stressed up so to relax myself I travel to new places, meet new people and try to adopt their culture. Most of the time I like to travel hills as it helps me to relax and enjoy our nature beauty. For being a good therapist and to deal with all the difficulties I always prefer to be good listener and have good patience that is what my strength is. I also work as a social worker and the Founder of thesocialphysiofitnessclub and PHYSIO FIT INDIA. In last I just want to say that " I believe that physical therapy is not just a therapy but actually a remedy which not only make you physically fit but also adds happiness, joy and more days to your life." So don't just sit and thought now it's time to stand and work on yourself.

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