Mammals have a closed, double circulation.

a. State what is meant by the term double circulation.

b. Explain why the wall of the artery is thicker than the wall of the vein.

c. Suggest one role for the pre-capillary sphincter muscle shown in the figure.

The figure below shows part of the circulation in a mammalian tissue. The central part is enlarged to show a capillary, a cell supplied by the capillary, and vessel Z.

d. With reference to the figure, describe the role of capillaries in forming tissue fluid. 

e. i. Describe three ways in which plasma differs from tissue fluid.

ii. Name the fluid in vessel Z.

Transcribed Image Text:

pre-capillary sphincter muscle vein artery plasma arteriole tissue fluid