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The Reproductive System / All About the Reproductive System
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submitted by Dr. Gary Farr - Contact the author here.
Last Updated December, 7, 2011
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The Reproductive System
What is it?
Humans belong to that group of mammals characterized by the bearing of live offspring that have attained considerable development within the uterus, or womb. Provided all organs are present, normally constructed, and functioning properly, the essential features of human reproduction are:
- liberation of an egg from the ovary at the right time in the reproductive cycle
- internal fertilization by spermatozoa (sperm, or male sex cells) of the ovum in the uterine tube
- transport of the fertilized ovum along the uterine tube to the uterus
- implantation of the blastocyst, the early embryo that develops from the fertilized ovum, in the wall of the uterus
- formation of a placenta and maintenance of the intra-uterine existence of the unborn child
- birth of the child and expulsion of the placenta; and
- suckling and care of the child, with an eventual return of the maternal organs virtually to their original state
For this biological process to be carried out, certain organs and structures are required in both male and female bodies. The source of the ova, the female germ cells, is the female gonad or ovary; that of spermatozoa is the testis. In human beings, the two ovaries are situated in the pelvic cavity, and the two testes are enveloped in a sac of skin, the scrotum, lying below and outside the abdomen. Besides producing the germ cells, or gametes, the ovaries and testes are the source of hormones that cause full development of secondary sexual characteristics and also the proper functioning of the genital (reproductive) tracts. These tracts comprise the uterine tube, the uterus, vagina, and associated structures in females, and, in males, the penis, the sperm channels, epididymis, ductus deferens, and ejaculatory ducts, and other related structures and glands. The function of the uterine tube is to convey an ovum, which is fertilized in the tube, to the uterus, where gestation (development before birth) takes place. The function of the male ducts is to convey spermatozoa from the testis, to store them, and, when ejaculation occurs, to eject them with secretions from the male glands through the penis.
 At copulation the erect penis is inserted into the vagina and spermatozoa contained in the seminal fluid are ejaculated into the female genital tract. Spermatozoa then pass from the vagina through the uterus to the uterine tube to fertilize the ovum in the outer part of the tube. Human females exhibit a periodicity in the activity of their ovaries and uterus, which starts at puberty and ends at the menopause. The periodicity is manifested by menstruation at intervals of about 28 days; important changes occur in the ovaries and uterus during each reproductive or menstrual cycle. Periodicity is suppressed during pregnancy and lactation.
The sex of a human child is determined at the time of fertilization of the ovum by the spermatozoon. The differences between a man and a woman are genetically determined by the chromosomes that each possesses in the nuclei of the cells. This stage in the development of the individual is detailed in the article human embryology: Early stages.
Once the genetic sex has been determined there normally follows a succession of changes that will result, finally, in the development of an adult male or female. There is, however, no external indication of the sex of a human embryo during the first eight weeks of its life within the uterus. This is a neutral or indifferent stage during which the sex of an embryo can be ascertained only by examination of the chromosomes in its cells. The next phase, one of differentiation, begins first in gonads that are to become testes, and a week or so later in those destined to be ovaries. Embryos of the two sexes are initially alike in possessing similar duct systems linking the undifferentiated gonads with the exterior and in having similar external genitalia, represented by three simple protuberances. The embryos each have four ducts, the subsequent fate of which is of great significance in the eventual anatomical differences between men and women. Two ducts closely related to the developing urinary system are called mesonephric, or wolffian, ducts. In males, each mesonephric duct becomes differentiated into four related structures: a duct of the epididymis, a ductus deferens, an ejaculatory duct, and a seminal vesicle (see below). In females, the mesonephric ducts are largely suppressed. The other two ducts, called the paramesonephric or mllerian ducts, persist, in females, to develop into the uterine tubes, the uterus, and part of the vagina; in males they are largely suppressed. Differentiation also occurs in the primitive external genitalia, which in males become the penis and scrotum, and in females the clitoris and labia.
More detailed information about the male reproductive system can be found here.
At birth the organs appropriate to each sex have developed and are in their adult positions but are not functioning. Various abnormalities can occur during development of sex organs in human embryos, leading to hermaphroditism, pseudohermaphroditism, and other chromosomally induced conditions. During childhood until puberty there is steady growth in all reproductive organs and a gradual development of activity. Puberty marks the onset of increased activity in the sex glands and the steady development of secondary sexual characteristics.
In males at puberty the testes enlarge and become active, the external genitalia enlarge, and the capacity to ejaculate develops. Marked changes in height and weight occur as hormonal secretion from the testes increases. The larynx, or voice box, enlarges, with resultant deepening of the voice. Certain features in the skeleton, as seen in the pelvic bones and skull, become accentuated. The hair in the armpit and the pubic hair becomes abundant and thicker. A beard, a moustache, and cheek hair develop, as well as hair on the chest, abdomen, and limbs. Hair at the temple recedes. Skin glands become more active, especially apocrine glands (a type of sweat gland that is found in the armpit and groin and around the anus).
These secondary sex characteristics do not develop in individuals castrated before puberty, but the administration of androgens (male sex hormones) to such persons and to males having poorly developed testes can correct, in large measure, some of the poorly developed secondary characteristics. Large amounts of androgen, however, by preventing production of the hormone gonadotrophin by the pituitary, suppress testicular activity, thus depressing formation and release of sperm. Some derivatives of the male sex hormone testosterone can promote general bodily development.
In females at puberty, the external genitalia enlarge and the uterus commences its periodic activity with overt menstruation. The mammary glands develop, and there is a deposition of body fat in accordance with the usual contours of the mature female. Growth of axillary (armpit) and pubic hair is more abundant, and the hair becomes thicker. In a female receiving androgens, the typical male secondary sex characteristics may develop, menstruation may be suppressed, and the mammary glands may atrophy.
What parts make-up the female anatomy?
 The female reproductive anatomy includes internal and external structures.
The function of the external female reproductive structures (the genital) is twofold: To enable sperm to enter the body and to protect the internal genital organs from infectious organisms. The main external structures of the female reproductive system include:
- Labia majora: - The labia majora enclose and protect the other external reproductive organs. Literally translated as "large lips," the labia majora are relatively large and fleshy, and are comparable to the scrotum in males. The labia majora contain sweat and oil-secreting glands. After puberty, the labia majora are covered with hair.
- Labia minora: - Literally translated as "small lips," the labia minora can be very small or up to 2 inches wide. They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body).
- Bartholin's glands: - These glands are located next to the vaginal opening and produce a fluid (mucus) secretion.
- Clitoris: - The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect.
The internal female reproductive organs include:
- Vagina: - The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.
- Uterus (womb): - The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit.
- Ovaries: - The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.
- Fallopian tubes: - These are narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants to the uterine wall.
More detailed information about the female reproductive system can be found here.
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