Biology 3201 Unit 2 section 5-7

Section 5: Human Reproductive System

Gonads produce gametes (sperm in males, eggs in females) and sex hormones controlling primary and secondary sex characteristics.The male reproductive system produces and stores sperm, while the female system provides an environment for fertilization, fetal development, and childbirth.Sperm travels through the following structures in males: testes, scrotum, seminiferous tubules, interstitial cells, epididymis, vas deferens, penis, seminal vesicle, prostate gland, Cowper's gland, and urethra.In females, eggs travel through: ovaries, follicle, fimbriae, oviducts (fallopian tubes), uterus, endometrium, cervix, and vagina. Sexual reproduction occurs through intercourse, where fluid exchange and close contact can transmit STIs. STIs can result from viruses, bacteria, or parasites. Viral STIs are typically incurable but manageable; bacterial STIs can be treated with antibiotics.

Section 6: Regulation of the Human Reproductive System

The hypothalamus governs the pituitary gland via releasing hormones. The pituitary gland, with anterior and posterior lobes, releases tropic hormones that stimulate target glands to produce hormones, regulated by negative feedback.In males, testosterone promotes sperm formation. In females, estrogen stimulates uterine lining growth, and progesterone prevents contractions. The negative feedback loop maintains sperm levels in males and regulates the menstrual cycle in females.The menstrual cycle lasts about 28 days and comprises two cycles: ovarian and uterine.

Follicular Stage: Rising FSH stimulates the follicle to produce estrogen and progesterone, inhibiting further FSH production. Increased estrogen triggers GnRH release, causing an LH spike that leads to ovulation.
Luteal Stage: After ovulation, LH turns the follicle into a corpus luteum, secreting progesterone and estrogen. Rising hormone levels inhibit FSH and LH, but as the corpus luteum degenerates, hormone levels drop, prompting a rise in FSH and LH.
Uterine Cycle: Starts with menstruation, involves endometrium thickening due to estrogen from the developing follicle. If there is no fertilization, hormone levels drop, causing endometrium breakdown and menstruation.

Section 7: Human Development - Fertilization to Birth

During ovulation, an egg is released and moves to the uterus. The male releases millions of sperm that must reach and fertilize the egg within 12-24 hours.The egg's protective layers include the zona pellucida (a selective filter) and the corona radiata (nourishing layer). Sperm undergo the acrosome reaction to penetrate these layers. Upon fertilization, the egg's plasma membrane prevents other sperm from entering.Cleavage rapidly divides without growth, leading to the morula, then the blastocyst with an outer trophoblast layer forming the chorion (placenta) and an inner cell mass developing into the embryo.Implantation occurs between days 10-14, with the trophoblast releasing hCG to maintain the endometrium.Embryonic Development: The inner cell mass forms the primary germ layers: ectoderm (skin, organs), mesoderm (muscles, heart), and endoderm (digestive tract).Neurulation: The mesoderm develops further, forming the notochord for skeletal framework, while the ectoderm develops into the central nervous system.Supporting the Embryo: Extra-embryonic membranes (amnion, yolk sac, allantois, and chorion) provide protection and nourishment.Placenta and Umbilical Cord: The placenta, a disk-shaped organ, connects the fetus to maternal blood through the umbilical cord which contains two arteries (carrying deoxygenated blood) and one vein (carrying oxygenated blood).Twins: Identical (monozygotic) twins arise from one fertilized egg; fraternal (dizygotic) twins occur from two fertilized eggs.Teratogen: Agents that disrupt normal embryonic development.

Hormones

GnRH: From hypothalamus, stimulates FSH and LH release in both sexes.
FSH: From anterior pituitary, promotes sexual organ and gamete development.
LH: From anterior pituitary, stimulates testosterone in males and ovulation in females.
Estrogen: Produced in ovaries; promotes female reproductive system development.
Progesterone: Secreted by ovaries, regulates uterine changes.
Testosterone: From testes, develops male reproductive traits.
Inhibin: Produced in testes; inhibits FSH secretion.
Oxytocin: Triggers muscle contractions for milk release.
Prolactin: Stimulates lactation.