My recent mail swims with sperms. I send you these items to keep you informed.

Dr Paul Jarrett writes from Arizona:

I don’t know why spermatogenesis, the production of sperm, must take place at a temperature about 2 degrees below body temperature, but it does.

In order to insure propagation of the species – and this includes many other mammals – some means had to be employed so that a cooler environment than that within the peritoneal cavity, (where ovaries are completely comfortable), could be maintained.  The solution is to initiate the testicle at body temperature, an early necessity during organogenesis, and later in pregnancy move it outside where temperatures will be more easily regulated.  

Nerves provide temperature sensing while the cremaster muscles provide raising and lowering of the testes and further feed-back. Responding nerves provide for perspiration glands to produce sweat for evaporation and further cooling.  There are also mechanisms in place to minimize injury which I will not describe at this time.

Moving the testicle outside took a bit of doing.  During development of the embryo, (sometimes later-“Undescended Testicle) the testicle migrates out of the retroperitonal space through the Inguinal Canal to the Scrotum.  The process of peritoneum which forms the lining of the inguinal canal during this passage is pinched off at the Internal Ring if all goes well.  If not, a potential Inguinal Hernia exists with a pre-formed sac waiting for peritoneal contents to also migrate downward into the Inguinal Canal or Scrotal Sac.  This is known as an “Indirect Hernia”.  It happens with sufficient regularity to provide tuition for a Surgeon’s kids. I have repaired these from a few days old to well into old age.  They can occur in animals but are more common in bipeds. Continue reading →