Question

The diagram represents the ‘closed system’ or ‘double circulation’ of blood in mammals.

Justify the above statement.

State two structural and two functional differences between the arteries and veins.

State the changes in the composition of blood as it passes through the following organs:

(a) Lungs (b) Gut (c) Liver (d) Kidneys.

Answer 1

Double circulation or closed system: In human beings, the heart has double circulation as the blood passes through the heart twice.

(1) It first leaves the heart (right ventricle) and goes to lungs and then returns to the heart (left auricle).

(2) From the left auricle it circulates through the entire body and again returns to the heart (right auricle ).

Double circulation means that the blood flows twice in the heart before it completes one full round-the short pulmonary (lung) circulation and the long systemic (general body) circulation.

For this reason the blood circulation in human body is also called double circulation.

(a) In lungs, the blood releases carbon dioxide and picks up oxygen.

Hence before passing through the lungs it contains more CO₂ while it contains more oxygen after it has passed through the lungs.

(b) When blood passes through the gut, it absorbs digested food materials i.e., it contains more carbohydrates, proteins, fats, water, ions and vitamins.

(c) As the blood passes through liver, it contains more urea another waste materials.

(d) As the blood passes through kidneys, it contains less urea and other waste materials.