Human Reproductive System Gametogenesis Occurs in the gonads

Human Reproductive System

Gametogenesis • Occurs in the gonads (ovaries and testes) • Meiosis that results in the production of gametes (haploid) from germ cells (diploid cells) • Spermatogenesis and Oogenesis Slide 2 of 18

Oogenesis • Occurs in the ovaries— results in the production of 1 egg (and 3 polar bodies) • Begins when the female is an embryo—all primary oocytes form before birth and remain “frozen” in this stage indefinitely Slide 3 of 18

Oogenesis • Each month after puberty, one primary oocyte completes Meiosis I and begins Meiosis II • Meiosis II is completed only after fertilization occurs. Slide 4 of 18

Oogenesis • Characterized by unequal division of cytoplasm. • Why does it make sense for this to happen? – Allows for more nutrients to be available to the egg in case fertilization occurs. Slide 5 of 18

Spermatogenesis • Occurs in the testes in the seminiferous tubules— results in the production of 4 sperm • Mature in the epididymis and gain motility • Produced constantly after puberty Slide 6 of 18

Spermatogenesis • The midpiece contains lots of mitochondria —why? – The sperm have a long journey they need a lot of energy (hence the need for lots of mitochondria) Slide 7 of 18

Male Reproductive System • Testes – where spermatogenesis takes place • Epididymis – where sperm mature • When sperm leaves the body, it will go up the vas deferens, past the following glands: – Bulbourethral gland – Prostate gland – Seminal vesicles Slide 8 of 18

Male Reproductive System • Secretions of these 3 glands, contribute to the semen • Bulbourethral glands - produce an alkaline solution to neutralize acidity of urethra • Prostate gland – clotting enzyme to make semen gelatinous, solution to make environment in uterus more “friendly” • Seminal vesicles – solution that contains food (fructose) for the sperm. Slide 9 of 18

Pathway of Semen • Epididymis Vas Deferens Urethra • A vasectomy is a procedure in which the vas deferens is cut so that the man will no longer be able to father children. Slide 10 of 18

Female Reproductive System • Ovaries – where oogenesis takes place • Oviduct (Fallopian Tube) – where fertilization takes place • Uterus – where the embryo grows and develops • Vagina – birth canal Slide 12 of 18

Female Reproductive Hormones • See hormone chart in notes • Gn. RH released from hypothalamus causes the release of LH and FSH from the pituitary gland • LH and FSH act on the ovaries and cause them to produce estrogen and progesterone – Feedback mechanisms will be discussed in the next few slides Image taken without permission from http: //bcs. whfreeman. com/thelifewire/ Slide 13 of 18

Female Menstrual Cycle • Each month, a woman’s body prepares for the possible fertilization of an egg • Ovarian Cycle = an egg matures (from a primary oocyte) and is released • Uterine Cycle = the endometrium (lining) of the uterus builds up (becomes ready to have a fertilized egg implant) then breaks down (if no fertilization occurs). Slide 14 of 18

Female Menstrual Cycle • An oocyte & the cells around it = follicle • Usually, only one follicle fully matures during each ovarian cycle • Ovulation – release of egg from ovary triggered by a surge of LH. Slide 15 of 18

Female Menstrual Cycle • The corpus luteum is the remaining cells of the follicle – Continues to produce estrogen and progesterone for approximately 2 weeks maintains the thickness of the endometrium – If no fertilization occurs, it degenerates endometrium is no longer maintained. – This starts the whole cycle over again. Slide 16 of 18

Female Menstrual Cycle • Day 1 = first day of a woman’s period • Hormonal control is complicated! – During different times of the cycle, Estrogen can either stimulate or inhibit other hormones Image taken without permission from http: //bcs. whfreeman. com/thelifewire/ Slide 17 of 18

Female Menstrual Cycle • If fertilization occurs, the embryo secretes HCG which maintains the corpus luteum – Eventually cells derived from embryo will secrete estrogen and progesterone to take over for the corpus luteum – h. CG is what is tested for in pregnancy tests • Birth control pills are synthetic progesterone and estrogen that “trick” the body into thinking the woman is pregnant – no ovulation occurs Slide 18 of 18