Question

60. The majority of carbon dioxide is transported in the body:

Select one:

a. bound to haemoglobin

b. dissolved directly in the plasma

c. as bicarbonate ions

d. as carbaminohemoglobin

e. as carbon monoxide (CO)

Answer 1

ANSWER :

60.OPTION C- as bicarbonate ion

The majority of carbon dioxide is transported in the body as bicarbonate ions.

REASON :

Transport of carbon dioxide in the blood :

1.Dissolution directly into the blood(5-7%).

2.Binding to haemoglobin(10%).

3 Carried as bicarnonate ion(85%).

1.Dissolution directly into the blood:

• Carbon dioxide is more soluble in blood than in oxygen ,about 5-7% of all carbon dioxide is dissolved in plasma.

2.Binding to haemoglobin :

• Carbon dioxide has the ability to attach to haemoglobin molecules and forms carbaminohaemoglobin.
• This form transports about 10% of carbon dioxide.
• Binding of carbon dioxide to haemoglobin is reversible.Therefore, when it reaches the lungs ,carbon dioxide freely dissociates from the haemoglobin and can be expelled from the body.

3.Carried as bicarbonate ion:

• Majority of the carbon dioxide molecules (85%) are carried as part of the bicarbonate buffer system.
• In this system, when carbon dioxide diffuses into the RBC,carbonic anhydrase within the RBC quickly converts the carbon dioxide into carbonic acid.
• Carbonic acid is unstable , immediately dissociates into bicarbonate ions and hydrogen ions.
• Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for continous uptake of carbon dioxide into the blood,down its concentration gradient.