What hormones are responsible for the expression of secondary sexual characteristics in human male & females?

Q. Which hormones are responsible for secondary sex male and female characteristics?

Answer:

• Testosterone - produced by the testes - controls the development of male secondary sexual characteristics.
• Oestrogen - produced by the ovaries - controls the development of female secondary sexual characteristics.

Secondary Sex Characteristics

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Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a species, but unlike the sex organs, are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which display fitness, giving an individual an advantage over its rivals in courtship and aggressive interactions. They are distinguished from the primary sex characteristics, the sex organs, which are directly necessary for sexual reproduction to occur.

In humans, visible secondary sex characteristics include pubic hair, enlarged breasts and widened hips of females, and facial hair and Adam's apple on males.

In humans, sexual differentiation begins during gestation, when the gonads are formed. The general structure and shape of the body and face, as well as sex hormone levels, are similar in preadolescent boys and girls. As puberty begins and sex hormone levels rise, differences appear, though some changes are similar in males and females. Male levels of testosterone directly induce the growth of the genitals, and indirectly (via dihydrotestosterone (DHT)) the prostate. Estradiol and other hormones cause breasts to develop in females. However, fetal or neonatal androgens may modulate later breast development by reducing the capacity of breast tissue to respond to later estrogen.

Females

In females, breasts are a manifestation of higher levels of estrogen; estrogen also widens the pelvis and increases the amount of body fat in hips, thighs, buttocks, and breasts. Estrogen also induces growth of the uterus, proliferation of the endometrium, and menses.

• Enlargement of breasts and erection of nipples.
• Growth of body hair, most prominently underarm and pubic hair
• Greater development of thigh muscles behind the femur, rather than in front of it (as is typical in mature males)
• Widening of hips; lower waist to hip ratio than adult males
• Elbows that hyperextend 5-8° more than male adults
• Face is more rounded, with softer features
• Smaller Waist
• Upper arms approximately 2 cm longer, on average, for a given height
• Changed distribution in weight and fat; more subcutaneous fat and fat deposits, mainly around the buttocks, thighs, and hips
• Labia minora, the inner lips of the vulva, may grow more prominent and undergo changes in color with the increased stimulation related to higher levels of estrogen.

Males

A beard is a human male secondary sexual characteristic

In males, testosterone directly increases size and mass of muscles, vocal cords, and bones, deepening the voice, and changing the shape of the face and skeleton. Converted into DHT in the skin, it accelerates the growth of androgen-responsive facial and body hair but may slow and eventually stop the growth of head hair. Taller stature is largely a result of later puberty and slower epiphyseal fusion.

• The growth of body hair, including underarm, abdominal, chest hair and pubic hair. Loss of scalp hair due to androgenic alopecia can also occur.
• Greater mass of thigh muscles in front of the femur, rather than behind it (as is typical in mature females)
• Growth of facial hair
• Enlargement of larynx (Adam's apple) and deepening of voice Increased stature; adult males are taller than adult females, on average
• Heavier skull and bone structure
• Increased muscle mass and strength
• Hands, feet and nose grow larger
• Larger bodies
• Face is square, with more angular features
• Small waist, but wider than females
• Broadening of shoulders and chest; shoulders wider than hips
• Increased secretions of oil and sweat glands
• Coarsening or rigidity of skin texture due to less subcutaneous fat
• Higher waist-to-hip ratio than prepubescent or adult females or prepubescent males, on average
• Lower bodyfat percentage than prepubescent or adult females or prepubescent males, on average