Like islands just off the coast of a big city, testicles have a few bridges to the mainland. As islands, the testes are closer to factory towns than vacation destinations, owing to their dual role in supporting reproduction and the endocrine system. Sperm cells are produced and mature in the testes, and testosterone for the rest of the body is made in the testes as well.
Arteries import the oxygen, nutrients, and hormones needed to produce sperm cells and support the surrounding infrastructure, and veins carry out cellular waste and androgenic hormones. The vasa deferentia export mature sperm cells ready to exit the body.
Since there is a narrow temperature range ideal for sperm cell maturation, the body has a muscle to help to regulate the temperature of each testicle. In cold places, the cremaster muscles draws the testicles closer to the body core for warmth. When the external temperature is high enough, the same muscles allows the testicles to hang free. The cremaster muscle also draws the testicles in during sex for protection and to prepare for ejaculation. The cremasters cover the testes and attach to the internal oblique muscles. If you’re looking to add a new group to your workout regimen, “Kegel” exercises can be done to strengthen the cremaster muscles, the pubococcygeus muscle, and other muscles of the pelvic floor: just clench the same muscles used for holding in urine, and then let go.