Kids Research Express

After birth, the process of sex-role socialization begins immediately. There may be small, physiologically-based differences present at birth that lead girls and boys to perceive the world or behave in slightly different ways. There are also well-documented differences in the ways that boys and girls are treated from birth onward. The behavioral differences between the sexes, such as differences in toy and play preference and in the degree of aggressive behavior, are most likely the product of complex interactions between the way that the child perceives the world and the ways that parents, siblings, and others react to the child. The messages about appropriate behavior for girls and boys intensify differences between the sexes as the child grows older. It is not uncommon for children to touch or play with their genitals or to play games, such as “doctor” or “house,” that include sexual exploration. Such experiences are usually not labeled sexual by the children. Adults will often disc

. About six weeks after conception, if a Y chromosome is present in the embryo's cells (as it is in normal males), a gene on the chromosome directs the undifferentiated gonads to become testes. If the Y chromosome is not present (as in normal females), the undifferentiated gonads will become ovaries. If the gonads become testes, they begin to produce androgens (male hormones, primarily testosterone) by about eight weeks after conception. These androgens stimulate development of the one set of the genital ducts into the epididymes, vas deferens, and ejaculatory duct. The presence of androgens also stimulates development of the penis and the scrotum. The testes later descend into the scrotum. Males also produce a substance that inhibits the development of the second set of ducts into female organs. In the absence of such hormonal stimulation, female structures develop. Prenatal hormones also play a role in the sexual differentiation of the brain. For example, prenatal hormones direc

. There are two periods of marked sexual differentiation in human life. The first occurs prenatally and the second occurs at puberty. Although adult women and men may differ greatly in genital appearance and secondary sexual characteristics, they are almost identical during prenatal development. When an egg and a sperm unite during fertilization, they each bring to the new cell half the number of chromosomes (threadlike structures that contain genetic material) present in other cells. From fertilization through about the first six weeks of development, male and female embryos differ only in the pair of sex chromosomes they have in each cell—two X chromosomes (XX) in females and one X and one Y chromosome (XY) in males. At this stage, both male and female embryos have undifferentiated gonads (ovaries or testes), two sets of ducts (one set capable of developing into male internal organs and the other into female organs), and undifferentiated external genital folds and swellings. See Embr

. The external sex organs of men are the penis and the scrotum. The penis is a sensitive organ important to reproduction and urination and to sexual pleasure. At its tip is the glans, which contains the urethral opening, through which urine passes. The ridge that separates the glans from the body of the penis is called the corona (Latin for “crown”), or coronal ridge. The glans and the corona are the most sensitive parts of the penis. The glans is covered with a foreskin (prepuce) unless the man has been circumcised, in which case the foreskin has been surgically removed. The penis contains three cylinders of tissue that run parallel to the urethra. During sexual arousal, these tissues become engorged with blood and expand, causing the penis to enlarge and become erect (erection or tumescence). Men do not have a penis bone or a muscle that causes erection, as do some other animals. The scrotum is a pouch that hangs below the penis and contains the two testes, which produce sperm (the m

. Primary sexual characteristics of women include the external genitalia (vulva) and the internal organs that make it possible for a woman to produce ova (eggs) and become pregnant. The vulva includes the mons pubis, the most visible part of the woman's external genitalia, which is the pad of fatty tissue that covers the pubic bone and is commonly covered by pubic hair; the labia majora, the large outer lips; and the labia minora, the smaller, hairless inner lips that run along the edge of the vaginal opening and often fold over to cover it. The labia minora come together in front to form the clitoral hood, which covers the clitoris, a sensitive organ that is very important to the woman's sexual response. The opening of the urethra, the tubular vessel through which urine passes, is located midway between the clitoris and the vaginal opening. The area where the labia majora join behind the vagina is called the fourchette. The area of skin between the vaginal opening and the anu

Sexual characteristics are divided into two types. Primary sexual characteristics are directly related to reproduction and include the sex organs (genitalia). Secondary sexual characteristics are attributes other than the sex organs that generally distinguish one sex from the other but are not essential to reproduction, such as the larger breasts characteristic of women and the facial hair and deeper voices characteristic of men. Sub-topics: A. Female Sexual Organs B. Male Sexual Organs

.. Structure of Human Gonads Gonads—in the male, the testes (singular, testis), and in the female, the ovaries—are the organs that produce gametes and sex hormones. The male gamete is the spermatozoan, produced by cell division in the seminiferous tubules of the adult testes. Typically, several hundred million sperm reach maturity in the epididymis and are stored in the vas deferens each day. Whatever is not released in ejaculation is reabsorbed, part of a continuous cycle. In the female, the ovaries produce eggs, or ova. At birth, about 2 million oocytes, or immature eggs, are present in the ovaries. Once the female reaches puberty, one egg matures approximately every 28 days inside a saclike Graafian follicle. Ovulation occurs when the mature egg bursts from the follicle and the ovary, beginning its journey down the fallopian tube toward the uterus. Organs that contain germ cells which later develop into male gametes or spermatozoa are known as testes or male gonads. Organs that cont