The Reproductive System

1. The Reproductive System

2. Important notes • Reproduction is to perpetuate the species (not survival, but making sure that there will be humans after your death) • The reproductive organs are somewhat unique in that they are non-functional at birth • Only functional after puberty • Most other organs have SOME function at birth

3. Important notes • Male and female reproductive organs are derived from the SAME embryonic organs • As an embryo, the male and female organs come from the same cells • The female sex is the “default” development pathway • Without the “Y” chromosome, embryo “defaults” to female sex • With “Y” chromosome, a series of genes (proteins coded on the Y region of the DNA) will prevent the female organs from developing

4. Important notes • Because male and females develop from the same embryonic “template”, we share “homologous structures” • Almost every female sex organ has an equivalent male organ (homologous organ)

5. Key words • Gonad = sex organ that produces the gamete (egg or sperm) • Gamete = egg or sperm • Has only HALF the amount of DNA that every other cell in your body has (“haploid”) • When you have “ALL” your DNA, you are “DIPLOID” because you have 2 copies each DNA unit • 1 copy from mother, 1 copy from father • Zygote = fertilized egg • When sperm (only 1) fertilizes an egg and the two cells combine their DNA to form a “diploid” zygote

6. Key words • Mitosis = normal cell division • When a cell divides, it will copy ALL the DNA in the nucleus (so that it has 2 copies of everything) • Then, that cell will divide into 2 cells, and divide the DNA accordingly • This way, every offspring cell has the SAME DNA • Meiosis = gamete cell division • “progenitor” cell (the parent cell) divided WITHOUT copying its DNA • Divides its DNA into ½ (haploid) • Remember that ½ of your DNA is from your father, the other ½ is from your mother • When the progenitor cell divides, it RANDOMLY divides its DNA (so that the “daughter” cells have a MIX of maternal and fraternal DNA) into HALF

7. Key words • Meiosis = gamete cell division • By randomly dividing the DNA into half, you increase the odds of something different • If we didn’t do this, we’d ALL be CLONES of one another • Clones = bad…what if we cloned a person with cancer, or no brain, or who couldn’t reproduce? • As human beings, we’ve been able to make a mess EVERYWHERE on this planet (and are starting to do the same in outer space) • We’re able to do this because we’re “adaptable” • We can take our environment and “shape” it (or wreck it) • This ability to adapt is because we’re ALL DIFFERENT • This inherent difference allows us to see, interpret, work and think differently

8. Meiosis • Dividing DNA into half ? • We have maternal and fraternal (mom and dad’s) DNA • This means, we have 2 copies of EVERY protein that we can produce from our DNA codes • Randomly divide the DNA so that each “offspring/daughter” cell has 1 copy of each DNA code • Remember that this is “random”…your mother’s eyes, your father’s hair etc. • You DO NOT divide the DNA so that 1 daughter cell gets BOTH copies of the eye color DNA, and the other daughter cell gets BOTH copies of the hair color DNA • If you did this, you would have 1 cell without a gene for eye color, and another cell without a gene for hair color…and you’d likely die.

9. Meiosis • Now that you have 2 “daughter” cells (2 cells that have ½ the original DNA), you have the male/female gamete • The goal of reproduction (copulation) is to MIX the two gametes • “fertilize” the egg with the sperm • Thereby MIX the two DNA, starting the process that made you • Literally 2 stages of DNA “mixing” • Meiosis (random division of YOUR OWN DNA) • Fertilization (random mixing of YOUR DNA with your MATE) • More “mixing” = more difference • Remember, difference is good…clones are bad • TWINS are not evil…they “SHARE” the mixed DNA CLONES

10. Homologous Structures • Easy way to think about this concept: • Males = sex organ progenitors descend out of the pelvic cavity • Female = sex organ progenitors remain within the pelvic cavity

11. Adult Reproductive Anatomy • Male GONAD = testis (single) testes (plural) • Have to descend OUT of the abdominal cavity during embryonic development • Pass through the “inguinal canal” • Hole in the abdomen • Very common site for hernia • Contained within scrotum • Male gamete development (sperm development) requires slightly lower body temperature • Place the gonads outside the body cavity to “cool” them

13. Adult Reproductive Anatomy • Sperm are produced in the seminiferous tubules • Are NOT mature yet (this takes about 30-60 days) • Then to epididymis to “mature” • During copulation, epididymis will contract to propel mature sperm up the ductus deferens to the bladder & penis

14. Adult Reproductive Anatomy • Penis is the actual copulatory organ (organ used to deliver sperm into female) • Sperm are delivered via urethra (tube within the penis) • Remember that males use the urethra for 2 purposes • Urination • Ejaculation/reproduction • Along the way, 3 sets of glands add fluids to the sperm • Seminal vesicles (70% ejaculatory volume) • Prostate gland (25% ejaculatory volume) • Bulbourethral glands (pre-ejaculate…to clean urethra) • Note that sperm actually make up less than 1% total ejaculatory volume • Ingredients in the various secretions act to help sperm live longer

15. In order for copulation to occur, the penis must be erect. The body “erects” the penis by parasympathetic and sympathetic nerves that control blood flow to the various regions (corpora) of the penis. The sensory system and the CNS are responsible for initiating this response.

16. Adult Reproductive Anatomy • Female gonad = ovary • While males produce sperm CONSTANTLY, females are “born” with all their gametes (follicles) • Born with 300,000-2 million • By puberty, will have less than 3,000 • Only  300 will actually “develop” into actual eggs until menopause (when egg “production” stops)

17. Adult Reproductive Anatomy • If females have all their gametes at birth, what does “egg production” mean? • Female gametes are actually “diploid” and not really “eggs” • Actually “follicle” or “primary oocytes” (primary eggs) • During the “ovarian cycle” (not the same at the uterine cycle) • 1 follicle will “mature” into an egg (oocyte) and be released from the ovary • The rest of the follicles will “stay put” and not “mature” until the next cycle

18. Adult Reproductive Anatomy • Ovarian cycle: • Monthly process to “mature” an egg for fertilization • In response to the correct hormones (from the pituitary gland…itself stimulated by the hypthalamus) • Lutenizing hormone & follicle stimulating hormone • A single follicle will “mature” and the undergo meiosis • Not a complete meiosis…the egg does not fully “split” • Secondary oocyte + “polar body” • Polar body will “die” if the secondary oocyte is fertilized by a sperm • In essence, the female gamete isn’t truly “haploid” because the polar body never truly breaks free

19. Adult Reproductive Anatomy • Ovarian cycle: • Once the secondary oocyte (the egg) is formed, it will “erupt” from the follicle/ovary • Must then enter the fallopian/uterine tube/oviduct • Tube that “catches” the egg and delivers it to the uterus

20. A unique aspect of the female reproductive system is the fact that the fallopian tube (uterine tube) is not physically connected to the ovary. During ovulation (when the egg leaves the ovary), the egg must rupture from the ovary and find its way into the uterine tube…many actually fall out and enter the abdominal cavity.

21. Adult Reproductive Anatomy • Uterine/menstrual cycle: • This is NOT the same as the ovarian cycle • The monthly “period” because it leads to shedding of the lining of the uterus • Every cycle (roughly a month), the uterus “expects” a fertilized egg • Begins by increasing the thickness of the uterus • If no fertilized egg (zygote) arrives, will shed this lining and start again

22. Adult Reproductive Anatomy • While the ovarian cycle (this deals with the ovaries) and the uterine/menstrual cycle (describes the uterus) are not the same, they are inherently “linked” • The same hormones that trigger the ovarian cycle also play a role in the uterine cycle • Lutenizing hormone (LH) + follicle stimulating hormone (FSH)

23. Adult Reproductive Anatomy • During copulation, the erect penis is inserted into the vagina • Goal is to deliver sperm to the uterus • From the uterus, sperm make their way into the uterine tubes (oviducts) to fertilize an egg

24. Reproduction & Birth Control • Different methods for “prevention” of fertilization: • Abstinence • Physically preventing sperm deposit into the vagina • Sperm is deposited into the vagina, and post-orgasm contractions “draw” this deposit into the uterus and oviducts • Physical barriers = condom, tubule ligation (male or female “tubes”) • Birth control pills = hormones that prevent ovulation (trick the body into believing that it has ovulated when in fact, it has not)

25. Reproduction & Birth Control • Timing: • Sperm can live 2-5 days within the female reproductive tract • Egg is only “alive” for 12-24 hours • In essence, you have 12-24 hours to fertilize the egg before it “dies” • “Rhythm method” is based on forecasting WHEN ovulation (release of a live egg) will occur • Because every ovulation is slightly different, the “sweet spot” is usually 4 days

26. Reproduction & Birth Control • Timing: • How can you tell? • During secondary oocyte/polar body “development”, both lutenizing hormone and follicle stimulating hormone levels must change • Right before “eruption” of the egg (actually the secondary oocyte and polar body), there is a sudden increase in estrogen secretion • Increased estrogen (from the ovary) triggers a rapid increase in lutenizing hormone levels in the blood • A sudden increase in LH concentration will trigger the eruption of the egg

27. Remember that the pituitary gland is where lutenizing hormone is made. In order to rapidly increase the amount of LH in the blood, the pituitary actually “empties” itself of all its LH.

28. The “period” • The first day of bleeding = first day of the menstrual “recycling” stage (uterine recycling) • By this time, the egg has died, and the body realizes that the “enlarged” uterus is “useless” • Sheds the uterus (hence the blood), starts building a “new” uterus lining for the next round

29. Female Reproductive Organs Note the different epithelia of the cervix and vagina. In the case of cervical cancer, the epithelium changes (metaplasia) from columnar epithelium to squamous epithelium (or vice versa). Where else have you seen this “change” in cell phenotype as a risk of cancer?

30. Fertilization • Should the egg be fertilized: • ONLY 1 SPERM can do this…once this happens, the egg “SHUTS” the door and all the rest of the sperm have NO chance of entering the egg • Polar body will “die”, and the egg bursts open the sperm to release the father’s DNA contribution • Fertilized egg will the migrate through the oviduct (fallopian tube) and “implant” into the uterus wall • This is why the uterus “expands”…to give the fertilized egg a spot to “grow”

31. Parturition • Should the embryo develop correctly, maturing into a fetus… • Under the correct conditions, if everything works • Delivery of the baby = parturition