Why the scrotum is colder than the body and how upright walking caused male infertility
Just a few million years ago, human ancestors switched to upright walking, which, on the one hand, ensured the high survival rate of Homo sapiens throughout the planet, but on the other hand, it came into conflict with its more ancient animal physiology and backfired on modern man with the appearance of unique diseases.
Why is the scrotum colder than the body
During pregnancy, billions of lymphocytes mature in the thymus of the fetus, each of which is equipped with a unique receptor capable of binding a molecule strictly specific to it according to the “key-lock” principle. This guarantees the immune system the ability to withstand the whole variety of existing and even not yet created by nature infections. It is inevitable that among the billions there are lymphocytes capable of binding the molecules of their own body. The task of immunity is to get rid of such autospecific lymphocytes, which can cause autoimmune diseases in later life.
For this, all lymphocytes maturing in the thymus are programmed to self-destruct as soon as their receptor binds something. And since there are normally no foreign molecules and infections inside the fetus, only autospecific lymphocytes self-destruct.
All other lymphocytes, whose receptors have not found anything suitable for themselves in a sterile fetus, survive. After birth, these lymphocytes leave the thymus and for the first time encounter their natural targets – infections. But instead of self-destruction, now lymphocytes go into activation mode, multiply and mature into killer cells or memory cells. Thus, a newborn has lymphocytes to bind anything, but not the molecules of his body. This ensures the tolerance of immunity to the tissues and cells of its own body.
The trouble is that mature spermatozoa appear in the body much later than birth, so the lymphocytes capable of binding them successfully survived negative selection and now recognize the germ cells as something foreign. One of the mechanisms of protection of sperm from immunity is to lower the temperature of the testicles to + 33 ° C, due to which the strength of binding of receptors and antibodies to sperm decreases.
Testicular cooling mechanism
In all extremities, hot arterial blood flows through the arteries at a maximum depth close to the bones. Then, passing through the capillaries, the blood cooled in the limbs is collected in the veins at the very surface of the body. Due to this separation of the inflow and outflow of blood, a stable temperature of the extremities of about + 37 ° C is ensured.
But unlike the arms and legs, in the testicles, the blood outflow system forms a dense lobate plexus of veins, closely intertwined with the arteries. The venous blood cooled in the scrotum enters this plexus and cools the arteries through which the previously cooled arterial blood enters the testicles. This makes the testicles noticeably colder in relation to the rest of the body.Поділитися цим: