The
spermatic cord is a complicated structure. One of its many functions
is to serve as a route for blood entering and leaving the testis.
Recall that the optimum temperature for spermatogenesis is typically a few degrees below core body temperature; the cord provides for this with a countercurrent flow mechanism. Blood moving through the arteries to the testis is cooled slightly by transferring its heat to the blood coming from the testis in veins that surround it. You can see these blood vessels in this field, cut in cross section. There are several large arteries with muscular walls, and a plexus of blood filled veins at the top of the field.
The blood coming back to the body core receives heat, and its
temperature is raised. Thus heat loss is minimized. The fact that
the two flows move in opposite directions means that they will always
be encountering new blood with the same temperature gradient and the
two flows will never equilibrate. This greatly enhances the
efficiency of the process.
