Sexual differentiation in humans any androgen can cause external masculinization. The most potent is dihydrotestosterone (DHT), generated from testosterone in skin and genital tissue by the action of 5α-reductase. A male fetus may be incompletely masculinized if this enzyme is deficient. In some diseases and circumstances, other androgens may be present in high enough concentrations to cause partial or (rarely) complete masculinization of the external genitalia of a genetically female fetus. The testes begin to secrete three hormones that influence the male internal and external genitalia. They secrete anti-müllerian hormone, testosterone, and Dihydrotestosterone. anti-Müllerian hormone (AMH) causes the paramesonephric ducts to regress. Testosterone, which
Melanocyte-stimulating hormone when the animal is in a dark location. This causes pigment to be dispersed in pigment cells in the toad's skin, making it become darker, and harder for predators to spot. The pigment cells are called melanophores and therefore, in amphibians, the hormone is often called melanophore-stimulating hormone. An increase in MSH will cause darker skin in humans too. MSH increases in humans during pregnancy. This, along with increased estrogens, causes increased pigmentation in pregnant women. Cushing's disease due to excess adrenocorticotropic hormone (ACTH) may also result in hyperpigmentation, such as acanthosis nigricans in the axilla. Most people with primary