Human reproduction

Human reproduction is the reproduction of humans. It is a form of sexual reproduction, by sexual intercourse between human males and females. In the sexual intercourse, interaction between the male reproductive system and the female reproductive system results in pregnancy, which is followed by childbirth

Anatomy

The human male

The male reproductive system contains two main divisions: the penis, and the testes, the latter of which is where sperm are produced. In humans, both of these organs are outside the abdominal cavity. Having the testes outside the abdomen best facilitates temperature regulation of the sperm, which require specific temperatures to survive.

Sperm are the smaller than the female ovum, and live approximately 2 weeks after production, requiring males to produce them continuously from the time of sexual maturity until death. Prior to ejaculation the produced sperm are stored in the seminal vesicle, a small gland that is located just behind the bladder.
A sperm cell is motile and swims via chemotaxis, using its flagellum to propel itself towards the ovum.

The human female

The female reproductive system likewise contains two main divisions: the vagina and uterus, which act as the receptacle for the sperm, and the ovaries, which produce the female's ova. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the Fallopian tubes. At certain intervals, the ovaries release an ovum, which passes through the fallopian tube into the uterus.

If, in this transit, it meets with sperm, the sperm penetrate and merge with the egg, fertilizing it. The fertilization usually occurs in the oviducts, but can happen in the uterus itself. The zygote then implants itself in the wall of the uterus, where it begins the processes of embryogenesis and morphogenesis. When developed enough to survive outside the womb, the cervix dilates and contractions of the uterus propel the foetus through the birth canal, which is the vagina.

The ova, which are the female sex cells, are much larger than the sperm and are normally formed with in the ovaries of the fetus before its birth. They are mostly fixed in location with in the ovary until their transit to the uterus, and contain nutrients for the later zygote and embryo. Over a regular interval, in response to hormonal signals, a process of oogenesis matures one ovum which is released and sent down the Fallopian tube. If not fertilized, this egg is flushed out of the system through menstruation.

Process

Human reproduction is a long process, starting with sexual intercourse, followed by nine months of pregnancy before childbirth. Many years of parental care is required in order to finish with a mature human being.

exual intercourse

Human reproduction takes place as internal fertilization by sexual intercourse. During this process, the erect penis of the male is inserted into the female's vagina until the male ejaculates semen, which contains sperm, into the female's vagina. The sperm then travels through the vagina and cervix into the uterus or fallopian tubes for fertilization of the ovum. Upon successful fertilization and implantation, gestation of the foetus then occurs within the female's uterus, called pregnancy.

Pregnancy

Pregnancy is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta, which is attached to the fetus' abdomen via an umbilical cord. This drain of nutrients can be quite taxing on the female, who is required to ingest slightly higher levels of calories. In addition, certain vitamins and other nutrients are required in greater quantities than normal, often creating abnormal eating habits. Gestation is 40 weeks in humans.

Birth

Once the fetus is sufficiently developed, chemical signals start the process of birth, which begins with contractions of the uterus and the dilation of the cervix. The fetus then descends to the cervix, where it is pushed out into the vagina, and eventually out of the female. The newborn, which is called an infant in humans, should typically begin respiration on its own shortly after birth. Not long after, the placenta is passed as well. The end of the umbilical cord attached to the young’s abdomen eventually falls off on its own.

Parental care

Human's babies and children are nearly helpless and require high levels of parental care for many years. One important type of parental care is the use of the mammary glands in the female breasts to nurse the baby. [ [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Sexual_Reproduction.html Sexual Reproduction in Humans.] 2006. John W. Kimball. Kimball's Biology Pages, and online textbook.]

Political and social

There are groups promoting more human reproduction and those who think reproduction ought to be limited. Natalism is promoting reproduction, while anti-natalism promotes birth control as a solution to overpopulation and its effects.

References