Melasma Overview. Patches of melasma are darker than other areas of skin because they have more pigment. The cells that produce pigment in the skin are called melanocytes. Ultraviolet radiation, or UV rays, from the sun stimulate melanocytes to produce pigment.
The human testicle .The two muscles that regulate the temperature of the testes are the dartos andcremaster muscles:â¢ Dartos Muscle The dartos muscle is a layer of smooth muscle fibers in the subcutaneous tissue of thescrotum (surrounding the scrotum).
Specialized endocrine cells known as interstitial cells (the cells of Leydig) are responsible for the production and secretion of the necessary male sex hormones. Because of this, the testes are considered both endocrine glands as well as exocrine glands.