Basics of Human Reproduction

The reproduction cycle may seem simple but it is more complex than we may think about. In a human female there are gonads which are a pair of ovaries. The ovaries produce immature eggs known as oocytes. The ovaries also secrete sex hormones. The ovary will then release these eggs to the oviducts which are also known as the Fallopian tubes. The oviducts then lead to the uterus. The uterine lining is known as the endometrium and it consists of connective tissues, blood vessels, and glands. The uterus has a narrow part which is called the cervix and this connects to the vagina by a muscular tube. Females have a menstrual cycle which means they are fertile intermittently. Females can still be receptive to sex even when they are not fertile. To begin explaining the cycle, meiosis resumes in one primary oocyte at a time. A cell layer will start forming around it. A follicle, whose growth is stimulated by hormones, consists of the cell layer and the oocyte. The hormones are known as FSH, LH, estrogen, and progesterone. They stimulate oocytes to mature and prime the endometrium for pregnancy. The next thing that happens is that the zona pellucida, which is a transparent layer, starts forming around the primary oocyte. A fluid- filled cavity then starts to form in the follicle’s cell layer. About halfway through the cycle the pituitary responds to the increases in estrogen in the blood. It starts to secrete LH. Because of this, the follicles swell up in response and rupture. From this, fluid and the secondary oocyte are released. The mid-cycle surge is what triggers ovulation. At ovulation, the estrogen has made cells of the cervical canal to release a thin, clear mucus that will help sperm to swim through. After the follicle has ruptured, a corpus luteum forms from the pieces. The corpus luteum will not last more than 12 days, so prostaglandin is the signaling molecule that tells the corpus luteum to self-destruct. Once the corpus luteum is gone, the levels of progesterone...