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Physiology

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Question
18 out of 33
 

Cyanosis is not commonly seen in anemia because:



A Oxygen binding capacity of hemoglobin improves in anemia

B A certain minimum amount of hemoglobin is needed to produce cyanosis

C Oxygen requirement is reduced in anemia

D Amount of oxygen dissolved in blood is increased in anemia

Ans. B A certain minimum amount of hemoglobin is needed to produce cyanosis

I. Cyanosis occurs when there is excess of desaturated hemoglobin or abnormal hemoglobin in the capillaries.

II. Deoxygenated hemoglobin level above 5 gm% leads to cyanosis Q Therefore presence or absence of cyanosis depends upon the absolute value of deoxygenated hemoglobin As in cases of anemia, hemoglobin concentration is already low (may be less than 5 gm% in severe cases) cyanosis is not commonly seen

III. Cyanosis can be of 3 types:

a. PERIPHERALA CYANOSIS which is due to slow capillary blood flow Q which allows more time for extraction of oxygen from blood to the tissues. It can be due to two conditions:

i. Reduced cardiac output such as in shock, mitral stenosis, etc

ii. Local vasoconstriction due to cold

b. CENTRAL CYANOSIS which occurs due to excess deoxygenated hemoglobin in blood leaving aorta. Q It can be of three type:

i. Due to inadequate oxygenation of blood which may be due to inadequate oxygen supplied to the lungs as occurs in pneumonia or chronic bronchitis or poliomyelitis or fibrosing alveolitis.

ii. Due to shunting of blood from right to left side as it occurs in tetralogy of Fallot.

iii. Due to an absolute excess of desaturated hemoglobin, the percentage saturation being normal This occurs in primary polycythemia.

c. ENTROGENOUS CYANOSIS ( due to abnormal hemoglobin) due to presence of excess sulph-hemoglobin or methemoglobin. Q

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