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).
1 The testes are responsible for making testosterone, the primary male sex hormone, and for generating sperm. 2  Within the testes are coiled masses of tubes called seminiferous tubules.3  These tubes are responsible for producing sperm cells. Most men have two testes. 2  The testes are responsible for making testosterone, the primary male sex hormone, and for generating sperm. 3  Within the testes are coiled masses of tubes called seminiferous tubules.