BIOLOGY

Human reproductive system
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 for approximately nine months, this process is known as pregnancy in humans. Gestation ends with birth, the process of birth is known as labor. Labor consists of the muscles of the uterus contracting, the cervix dilating, and the baby passing out the vagina. 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.
Humans have a high level of sexual differentiation. In addition to differences in nearly every reproductive organ, numerous differences typically occur in secondary sexual characteristics.
Male reproductive system
The human male reproductive system is a series of organs located outside of the body and around the pelvic region of a male that contribute towards the reproductive process. The primary direct function of the male reproductive system is to provide the male gamete or spermatozoa for fertilization of the ovum.
Major secondary sexual characteristics includes: larger, more muscular stature, deepened voice, facial and body hair, broad shoulders, and development of an adam's apple. An important sexual hormone of males is androgen, and particularly testosterone.
Female reproductive system
The human female reproductive system is a series of organs primarily located inside of the body and around the pelvic region of a female that contribute towards the reproductive process. The human female reproductive system contains three main parts: the vagina, which acts as the receptacle for the male's sperm, the uterus, which holds the developing fetus, and the ovaries, which produce the female's ova. The breasts are also a reproductive organ during the parenting stage of reproduction[citation needed]. However, in most classifications breasts are not considered to be part of the female reproductive system.
The vagina meets the outside at the vulva, which also includes the labia, clitoris and urethra; during intercourse this area is lubricated by mucus secreted by the Bartholin's glands. 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, typically approximately every 28 days, the ovaries release an ovum, which passes through the fallopian tube into the uterus. The lining of the uterus, called the endometrium, and unfertilized ova are shed each cycle through a process known as menstruation. when the reproduction takes place,the sperms of man fertilizes the egg and a new embroyo is formed.
Production of gametes

The production of gametes takes place within the gonads through a process known as gametogenesis. Gametogenesis occurs when certain types of germ cells undergo meiosis to split the normal diploid number of chromosomes in humans (n=46) into haploids cells containing only 23 chromosomes.
In males this process is known as spermatogenesis and takes place only after puberty in the seminiferous tubules of the testes. The immature spermatozoon or sperm are then sent to the epididymis where they gain a tail and motility. Each of the original diploid germs cells or primary spermatocytes forms four functional gametes which is each capable of fertilization.
In females gametogenesis is known as oogenesis which occurs in the ovarian follicles of the ovaries. This process does not produce mature ovum until puberty. In contrast with males, each of the original diploid germ cells or primary oocytes will form only one mature ovum, and three polar bodies which are not capable of fertilization.hahaha It has long been understood that in females, unlike males, all of the primary oocytes ever found in a female will be created prior to birth, and that the final stages of ova production will then not resume until puberty. However, recent scientific data has challenged that hypothesis. This new data indicates that in at least some species of mammal oocytes continue to be replenished in females well after birth.
Development of the reproductive system
The development of the reproductive system and urinary systems are closely tied in the development of the human fetus. Despite the differences between the adult male and female reproductive system, there are a number of homologous structures shared between them due to their common origins within the fetus. Both organ systems are derived from the intermediate mesoderm. The three main fetal precursors of the reproductive organs are the Wolffian duct, Müllerian ducts, and the gonad. Endocrine hormones are a well known and critical controlling factor in the normal differentiation of the reproductive system.
The Wolffian duct forms the epididymis, vas deferns, ductus deferens, ejaculatory duct, and seminal vesicle in the male reproductive system and essentially disappears in the female reproductive system. For the Müllerian Duct this process is reversed as it essentially disappears in the male reproductive system and forms the fallopian tubes, uterus, and vagina in the female system. In both sexes the gonad goes on to form the testes and ovaries, because they are derived from the same undeveloped structure they are considered homologous organs. There are a number of other homologous structures shared between male and female reproductive systems. However, despite the similarity in function of the female fallopian tubes and the male epididymis and vas deferens, they are not homologous but rather analogous structures as they arise from different fetal structures.
Diseases of the human reproductive system
Like all complex organ systems the human reproductive system is affected by many diseases. There are four main categories of reproductive diseases in humans. They are: 1) genetic or congenital abnormalities, 2) cancers, 3) infections which are often sexually transmitted diseases, and 4) functional problems cause by environmental factors, physical damage, psychological issues, autoimmune disorders, or other causes. The best known type of functional problems include sexual dysfunction and infertility which are both broad terms relating to many disorders with many causes.
Specific reproductive diseases are often symptoms of other diseases and disorders, or have multiple, or unknown causes making them difficult to classify. Examples of unclassifiable disorders include Peyronie's disease in males and endometriosis in females. Many congenial conditions cause reproductive abnormalities but are better known for their other symptoms, these include: Turner syndrome, Klinefelter's syndrome, Cystic fibrosis, and Bloom syndrome.
It is also known that disruption of the endocrine system by certain chemical adversely affects the development of the reproductive system and can cause vaginal cancer. Many other reproductive diseases have also been link to exposure to synthetic and environmental chemicals. Common chemicals with known links to reproductive disorders include: lead, dioxin, styrene, toluene, and pesticides.
Examples of congenital abnormalities
Kallmann syndrome - Genetic disorder causing decreased functioning of the sex hormone-producing glands caused by a deficiency of a hormone.
Cryptorchidism - Absence of one or both testes from the scrotum.
Androgen insensitivity syndrome - A genetic disorder causing people who are genetically male (i.e. XY chromosome pair) to develop sexually as a female due to an inability to utilize androgen.
Intersexuality - A person who has genitalia and/or other sexual traits which are not clearly male or female.
Examples of cancers
Prostate cancer - Cancer of the prostate gland.
Breast cancer - Cancer of the mammary gland.
Ovarian cancer - Cancer of the ovary.
Penile cancer - Cancer of penis.
Uterine cancer - Cancer of the uterus.
Testicular cancer - Cancer of the testis/(plural:testes.
Cervical Cancer - Cancer of the cervix.
Examples of infections
HIV - Infection by the retrovirus known as human immunodeficiency virus.
Genital warts - Sexually transmitted infection caused by some sub-types of human papillomavirus (HPV).
Herpes simplex - Sexually transmitted infection caused by a virus called herpes simplex virus (HSV) type 2
Gonorrhea - Common sexually transmitted disease caused by the Gram-negative bacterium Neisseria gonorrheae
Yeast infection - Infection of the vagina by any species of the fungus genus Candida.
Pelvic inflammatory disease - Painful infection of the female uterus, fallopian tubes, and/or ovaries with associated scar formation and adhesions to nearby tissues and organs.
Syphilis - Sexually transmitted infection caused by the bacterium Treponema pallidum.
Pubic lice - Infection of the pubic hair by crab lice, Phthirius pubis.
Trichomoniasis - Sexually transmitted infection by the single-celled protozoan parasite Trichomonas vaginalis.
Examples of functional problems
Impotence - The inability of a male to produce or maintain an erection.
Hypogonadism - A lack of function of the gonads, in regards to either hormones or gamete production.
Ectopic pregnancy - When a fertilized ovum is implanted in any tissue other than the uterine wall.
Hypoactive sexual desire disorder - A low level of sexual desire and interest.
Female sexual arousal disorder - A condition of decreased, insufficient, or absent lubrication in females during sexual activity
Premature ejaculation - A lack of voluntary control over ejaculation.