What Are Primary Sex Characteristics?

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The sex characteristics that are present at birth are known as primary sexual characteristics. These mature when sex hormones are released during puberty. In males this includes the enlarging of the penis and testicles and sperm production. In females this includes the uterus and vagina growing and a monthly shedding of a mucus-like substance that acts as a form of vaginal lubrication (menstruation).

Secondary sexual characteristics are physical traits that develop at puberty. These include facial hair growth and thicker, coarser skin.


The testes (plural: testicles) are two egg-shaped male reproductive organs found in the scrotum. They produce sperm and the male hormone, testosterone. They are homologous to the female ovaries in all bilaterians. The adenohypophysis (anterior pituitary gland) produces the sex hormones luteinizing hormone and follicle-stimulating hormone, which stimulate sperm production. The testes contain germ cells that will eventually become mature sperm, and supporting cells called Sertoli cells and specialized testosterone-producing cells known as Leydig cells.

In order to work efficiently, the testes need a temperature that is cooler than core body temperature. This is why they are outside the body in the scrotum. There are several hypotheses as to why the testes evolved to operate at a colder temperature.

The testes connect to the penis by a tube called the epididymis. The epididymis is a curved, elongated structure that receives the seminal fluid from the testes. The sperm is then stored and matured in the epididymal ducts. If the sperm is not properly matured, it will be unable to fertilize an egg and cause infertility. One of the most common problems associated with the testes is cryptorchidism, which is when the testicles do not descend into the scrotum after birth. Premature infants have a high risk of this condition because they are born before the testicles reach full maturity and can descend into the scrotum.

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The ovaries are located on the front part of the pelvic bones. They produce female sex hormones and they help to create the eggs for conception. They also help to control the menstrual cycle. In humans, the ovaries and uterus are commonly called primary sexual characteristics. These changes are not present in early infancy, but develop just before or during puberty, which happens between ages 10 and 16.

The development of primary sexual characteristics is what makes males and females different from each other. However, there are other things that can distinguish a male from a female. For example, a man’s mane, the bright face and rump of a male lion or the extravagant tail feathers of peacocks are known as secondary sexual characteristics. In addition, pubic hair, facial hair and enlarged breasts are also known as secondary sexual characteristics.

In our society, children are assigned gender at birth. If they have male sex characteristics, they are labeled as boys; and if they have female sex characteristics, they are labeled girls. Despite our cultural assumptions that we only have two options for gender, some children are born intersex (with either male or female genitalia).

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These children are sometimes raised as the opposite gender they are. For example, a girl born with female sex characteristics might be raised as a tomboy, and a boy born with male sex characteristics might be raised as naughty.


The uterus, also called the womb, is a pear-shaped organ in the reproductive system of people assigned female at birth. It is where a fertilized egg implants during pregnancy and where a baby develops until it is ready to be delivered. Each month, the uterus stretches to accommodate a growing fetus and then contracts during childbirth. It also stretches and sheds its lining (endometrium) each month during menstruation.

The female uterus is connected to the vagina by a tube called the cervix. The uterus may be in a position that is straight, or midline, or it can be anteverted or retroflexed. This refers to its tilt in relation to the pelvic bones and rectum. An anteverted uterus is positioned pointing forward toward the abdomen and a retroflexed uterus is positioned tipped backward at the cervix.

For girls, the primary sex characteristics that are visible include the uterus building a lining that is later shed during menstruation and the vagina producing lubrication when sexually aroused. These changes normally start to happen between the ages of 9 and 14 years. Secondary sex characteristics such as pubic hair, breasts and hips may also develop at this time.


A females internal structure known as the uterus or vagina is surrounded by a layer of lining that will eventually be shed through menstruation. This lining is what gives females their feminine appearance. The tube leading from outside a females body to the opening of her uterus is called the vulva, and it is the site where her primary sexual characteristics develop. A woman’s uterus and vulva are controlled by hormones. The Y chromosome from the father determines whether her gonads develop into testes or ovaries during foetal development. If she develops a set of testes, her primary sexual characteristics are male. If she develops a set of ovaries, her primary sexual characteristics are female. If she develops a set of both, her primary sexual characteristics are hermaphrodite.

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These organs are known as primary sexual characteristics because they are present from birth and are directly involved in reproduction. Other physical characteristics that are indicative of a person’s sex and are not related to the reproductive system are called secondary sexual characteristics. Examples of secondary sexual characteristics include a mane in a male lion, an extravagant tail feather in a peacock, or facial hair in a male person.

When a person has the right pair of primary sexual characteristics, it can usually be determined which gender they are. However, the appearance of these characteristics can vary widely between human cultures. For example, a person may wear a dress or skirt and be considered to be female in American culture, but the same person might wear a kilt and be considered to be masculine in many Middle Eastern or Asian cultures.

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