During puberty, the uterus of young girls begins to build a lining that can later be shed in menstruation. Girls also produce a mucus-like discharge, which serves as an early form of vaginal lubrication.
These changes are called primary sex characteristics, and they are directly involved in reproduction. Secondary sexual characteristics, which are not related to reproduction, include a deeper voice and broader shoulders for males.
Testes
The testicles (or testis) are a pair of egg-shaped glands that sit in a pouch on the outside of the body called the scrotum. They produce sperm and testosterone, the male sex hormone. The scrotum protects the testes and helps them stay at a temperature that’s a little cooler than your body’s core temperature for optimal sperm development. Special muscles in the scrotum allow it to contract (tighten) to pull your testicles closer to your body for warmth and protection and to relax to cool them.
The sperm develop in the testicles in tiny tubes called seminiferous tubules. At birth, these tubules contain simple round cells that produce testosterone and other hormones needed for sperm production (spermatogenesis). Then the sperm cells grow and change until they have a head with a tail, like tadpoles. Then they move into a coiled tube called the epididymis to prepare to’swim’ through the prostate gland and urethra for fertilization.
Boys go through a growth spurt during puberty, which can lead to an increase in the size of their penis and testicles. They also produce millions of sperm each day.
Penis
A man’s penis is a tube- or cylinder-shaped organ that has an opening at its tip called the glans. It’s covered by a loose layer of skin (foreskin), which healthcare providers sometimes remove surgically (circumcision). The penis contains special sponge-like tissue with thousands of small spaces that fill with blood during sexual arousal and make the penis hard and rigid (erection).
The glans opens into the urethra, a tube that carries pee from the bladder to the outside of the body. The urethra also transports sperm. The sperm exit the penis through a special opening (the ejaculatory ducts) during orgasm. The sperm contain androgens, which are male reproductive cells that help fertilise eggs.
The testicles (testes) are oval sex glands that produce sperm. The sperm are used to fertilize an egg, which contains the man’s genetic material. The sperm travel to the ejaculatory ducts through a tube called the vas deferens. The scrotum is a sac of skin that hangs behind the penis and holds the testicles. The scrotum also contains the epididymis, which collects and stores sperm. The prostate gland and seminal vesicles are accessory sex glands that provide sperm with nourishing fluid.
Ovaries
The ovaries make female gametes, or eggs. If these are fertilised by sperm from the male, they can combine with the genetic material of the father to produce a new baby. The ovaries are housed in the uterus, which is lined with a mucus-like substance that is shed during menstruation or when a girl becomes sexually aroused. Girls may also begin to squirt a thick liquid from the vagina during this period.
A study of chickens has shown that DMRT1 is a key switch that determines whether a developing gonad becomes a testis or an ovary. When DMRT1 was blocked in ZW embryos that were destined to become testis, the gonads became ovary-like, with a cortex that expressed estrogen (E2) marker proteins such as FOXL2 and aromatase.
The ovaries can be distinguished from the testicles by their larger size. Similarly, the sperm in the testicles are distinguishable from the egg in the uterus by their size and shape. The reproductive organs of both boys and girls become fully functional at the onset of puberty, when the internal sex characteristics grow, such as the testes and penis in males and the ovaries and uterus in females.
Uterus
The uterus is the organ in most female mammals that accommodates and nurtures a fertilized egg or embryo until birth. The uterus is also known as the “womb”.
When a girl begins puberty, her internal and external sex characteristics become fully functional. The reproductive organs grow in size, the scrotum develops and the vagina begins to produce a mucus-like discharge. The uterus starts to build a lining and the cervix narrows or widens in preparation for pregnancy.
The uterus is a hollow muscular organ in the pelvis that is about 3 inches long. It sits behind the bladder and in front of the rectum. It has three layers: an inner layer called the endometrium that responds to hormones, a middle muscle layer and a neck (cervix) that projects into the vagina. The uterus accepts a fertilized ovary (a zygote) that travels down the fallopian tube and derives nourishment from blood vessels that develop exclusively for this purpose. The uterus nurtures the fertilized ovum through embryonic and fetal development until childbirth. It also plays a role in sexual response by directing blood flow to the pelvic bones, ovaries and genitals.
Vagina
The female external genitalia is known as the vagina. It is connected to the uterus through the fallopian tubes and ovaries. The ovary is a repository of immature eggs, called gametes. Females have a monthly reproductive cycle, during which the ovaries release mature eggs that pass to the fallopian tube and on to the uterus.
The development of the male and female internal and external sex characteristics is a natural process that occurs during the prepubescent through postpubescent stages of life. These changes are known as puberty and usually begin between 8 and 14 years of age, depending on the individual.
During this period, the male external sex characteristics typically grow in size, and the scrotum may become larger. In females, the uterus grows in size and the menstrual flow begins. There are some individuals whose sex characteristics do not develop in the usual way. This is called Diverse Sexual Development and is sometimes referred to as intersex or gender nonconforming. The underlying causes can be genetic or hormonal, and the symptoms vary from person to person.
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