Human Reproduction

• Human reproduction is exclusively sexual and involves the production of sex cells or gametes and their fusion during fertilization.
• The process of reproduction in humans must be followed by various developmental processes during gestation that lead to the formation of a fully functional individual.
• Human life cycle consists of infancy (ages 0 to 2 years old with a continuous physical development), childhood (ages 1 to 12 years old; locomotor and cognitive skills development), adolescence (ages 13 to 19 years old; undergoing various changes related to puberty), and adulthood (ages 20 years onwards; sexually mature physically and behaviorally).
• Human reproduction involves the production of sex cells or gametes and their fusion during fertilization.
• Testis is a male gonad that produces and nourishes sperm cells.
• Scrotum is an external sac that regulates temperature for testis.
• Epididymis stores sperm cells produced and transports them to vas deferens.
• Urethra is a common exit duct for both the urine and semen.
• Vas deferens is a pathway of sperms from testis to the urethra.
• Seminal vesicle contributes alkaline fluid that nourishes and protects sperm cells.
• Prostate Gland contributes a fluid that neutralizes semen and vaginal fluid.
• Bourethral Gland contributes a fluid that functions for lubrication.
• Penis is a copulatory organ that conveys sperm to female reproductive tract.
• Fallopian Tubes are ducts that serve as fertilization site and leads to the uterus.
• Fimbriae are appendages of the fallopian tubes that catch eggs during ovulation.
• Uterus is a highly vascularized sac that nourishes the developing embryo.
• Cervix is a narrow channel that prevents further entry of foreign materials.
• Vagina receives the sperm cells and serves as the birth canal.
• External Genitalia are accessory structures of the female reproductive system.
• Bartholin’s Gland produces fluid that serves as lubrication during intercourse.
• Gametogenesis involves the reduction of the chromosome number through spermatogenesis (♂) or oogenesis (♀), making sperm cells sufficiently motile and producing egg cells with enough nutrients.
• Spermatogenesis refers to the process of sperm cell production and development in males, occurring in the seminiferous tubules of the testes, which contain cells that develop into sperm cells.
• Spermatogenesis begins during puberty and is continuous throughout their lives.
• Oogenesis occurs in the ovaries and fallopian tubes.
• The follicles of the ovary exert hormonal influence during oogenesis.
• Oogenesis starts during the pregnancy of the mother.
• The four major stages of oogenesis are Proliferation, Growth, Maturation, and Differentiation.
• Proliferation in oogenesis involves the mitotic division of oogonia to produce more oogonia.
• Growth in oogenesis involves the significant growth of oogonia to become primary oocytes.
• Maturation in oogenesis involves the meiotic division of primary oocyte to reduce chromosome number.
• Meiosis I of the primary oocyte produces a secondary oocyte and a polar body in oogenesis.
• Meiosis II of the secondary oocyte produces an ootid and another polar body in oogenesis.
• Differentiation in oogenesis involves the ootid, a very transient stage, becoming the ovum, but with very minimal differentiation.
• The polar body in oogenesis is a small meiotic product of the unequal division that allows to concentrate the cytoplasmic contents into one ovum.
• Human fertilization produces the zygote with normal or restored chromosome number with slow-block and fast-block mechanisms against polyspermy.
• Human development during the pre-implantation phase involves the zygote undergoing repeated cell division and reorganization, traveling down into the uterus through the fallopian tube, and implantation occurring during the blastocyst stage.
• During the third week from conception, the offspring becomes a three-layered embryo through the process of gastrulation.
• The placenta, which is both maternal and fetal in origin, is formed eventually, and the yolk sac and allantois give rise to the umbilical cord.
• The placenta is a structure during gestation that supplies the developing fetus with oxygen and nutrients from the mother and removes the wastes accumulated by the fetus.
• At the start of the embryonic stage, the developing embryo becomes susceptible to the effects of teratogens.