Welcome back, today’s topic is the reproductive system. This has the major function of reproducing offspring of a species to continue its survival. Major organs include the vagina, penis, ovary, and testes, with functional units such as eggs and sperm produces by meiosis.
The female human goes through a menstrual cycle where ovulation occurs at a time in the cycle when the uterus lining thickens to develop a blood supply to prepare to nourish an embryo. If the egg is not fertilized the lining sheds from the uterus and out the vagina, and this bleeding is called menstruation. The menstrual cycle is also called the uterine cycle and is caused by the ovarian cycle. The hormones gonadotropin-releasing and gonadotropins follicle-stimulating and luteinizing are involved in this cycle.
The ovarian cycle begins when GnRH is released that stimulates the pituatary gland to secrete FSH and LH. FSH stimulates follicle growth and the cells of the follicles secrete estrogen. This is called the follicular phase. FSH and LH levels increase when estrogen levels rises. Due to this the sensitivity to LH increases so the follicles develop LH receptors and respond strongly to the hormone LH causes a final mature follicle that grows large and the follicular phase ends with ovulation. The follicle and wall of the ovary ruptures releasing a second oocyte, a cell that can develop into an ovum or egg. After ovulation, during the luteal phase, LH stimulates the follicle to change into the corupus luttellum. This corupus produces estrogen and progesterone that inhibits LSH and FSH and once the corups disintigrates the cycle restarts.
The uterine cycle begins when the estrogen and progesterone thickens and the uterus lining, so the follicular phase of the ovarian cycle is continued by the proliferative phase. Before ovulation the uterus is ready for an embryo, and after ovulation, estrogen and progesterone secreted by the corpus lutellum continue maintaining the lining. The luteal phase is controlled by the secretory phase of the uterine cycle. As ovarian hormones drop, arteries spasm in the uterine lining. Menstruation occurs and a new cycle begins.
If fertilization does occur, the egg is fertilized by a sperm and this is also called conception in the oviduct. After 24 hours the zygote divides which is called cleavage. Cleavage continues till it becomes a ball called a blastula reaching the uterus 3 days after. A week after fertilization, cleavage produces a blastocyst. Then the embryo secretes hormones like human chorionic gonadtropin that maintains progesterone and estrogen to stop entrance into menstruation and the HCG levels are detected in pregnancy tests through urine.
Then the 3 trimester period occurs, each 3 months long. In the first trimester the trophoblast, outer layer of blastocyst, grows and joins with the lining to form the placenta. Organogenesis occurs and this is the development of body organs. the mother’s breasts grow and she produces mucus in the cervix for protection. In the second trimester the fetus grows, hormones stabilize, the corpus lutellum deteriorates, and the placenta controls progesterone levels. The third trimester is when the fetus grows so large that it causes the mother’s organs to strain causing constant urination. Oxytocin levels and estrogen increase in the mother which induces contracting and finally labor. The baby is birthed or parturitioned. The mother’s breasts start lactating, or producing milk.
Thank you and I hope you learned something today!
Written by: Neil 6/11/2019