1. The Reproductive Systems

2. By the end of this class you should understand: The key organs and functions of both male and female reproductive systems The nature and behavior of human gametes The key sex hormones and their effects on the body The major biological reasons why teenagers are idiots

3. Reproduction Life is defined by its ability to reproduce The cells of our body can reproduce to make two identical copies (mitosis) – This was the only means of reproduction for a long time To increase the spread of beneficial genes, a new type of reproduction was evolved called sexual reproduction

4. Meiosis Sexual reproduction requires a new type of cell division: meiosis Normal human mitosis takes one cell with 46 chromosomes and produces two cells with 46 chromosomes Meiosis instead produces four cells with 23 chromosomes – 1 of each instead of 2 of each These cells are called haploid, and two haploid cells will make a new whole cell

5. Fertilization Haploid sex cells are called gametes Human gametes are sperm cells (male) and egg cells (female), which are produced by the gonads The human reproductive systems have two purposes: – Initiate fertilization (combine a sperm cell with an egg cell) – Keep this newly-created life form in a safe place until it is able to live on its own (pregnancy)

6. Gamete Formation In men, gamete formation is called spermatogenesis and takes places in the testes – Spermatogenesis requires a precise temperature which is less than normal body temperature, so the testes are placed in a sac of skin called the scrotum – Men produce millions of sperm a day after puberty In women, gamete formation is called oogenesis and takes place in the ovaries – In women, all gametes have begun their formation by the time the baby is born, and will only release a few hundred during her lifetime

7. Sex Hormones The primary mediator of the reproductive system is sex hormones, also produced by the gonads Male gonads: testes (singular: testis) Female gonads: ovaries The gonads produce sex hormones, primarily testosterone (men) and estrogen and progesterone (women) – Actually a broad array of hormones in both

8. Hormonal Activities Sex hormones have major effects on the body – Development of reproductive organs and secondary sexual characteristics – Change brain behavior (e.g. testosterone supposedly increases aggression, though it’s not clear that it does) – Make sexual activity appealing Sex hormones have strong effects on the limbic system, and the frontal lobe must spend its teenage years learning to cope with hormone-originated impulses – This is why teenagers are idiots

9. Reproductive Organs The gonads produce the gametes, but other organs are involved in the meeting of the gametes Male organs are devoted to producing, processing, and delivering sperm cells Female organs are for receiving semen and growing and nourishing the fetus once it is formed

10. Male Reproductive Organs The primary male reproductive organs are the testes that produce sperm and testosterone The other major organ is the penis, used to deliver sperm to inside the woman – The tubes running from the testes to the penis are called the vas deferens, and these also meet with the urethra which carries urine

11. Accessory Male Organs The other male reproductive organs help create semen, which is a mixture of sperm cells with sugars, mucus, and alkaline chemicals to enable them to survive inside the woman – The vagina is acidic and generally hostile to life, so that it does not become infected The most well-known of these is the prostate, which produces the watery alkaline fluid of semen – Enlargement can cause discomfort, also prone to cancer

12. Female Reproductive Organs The female ovaries are attached via the oviducts to the uterus – The oviducts were formerly known as the Fallopian tubes The uterus’s connection to the exterior of the body is a muscular canal called the vagina – The vagina has a small penislike organ called the clitoris at the anterior portion

13. Why Do Women Have A Clitoris? Answer: The same reason men have nipples!

14. Pregnancy The actual fertilization event occurs in the oviduct, which is where the egg cell is initially placed at the peak of the ovarian cycle If fertilized, the egg is migrated into the uterus where it becomes implanted The uterus then develops an organ called the placenta which nourishes the fetus The fetus develops for 9 months before being pushed out of the vagina by uterine contractions, a painful and occasionally lethal process

15. Ovarian Cycle The ovaries do not secrete estrogen and progesterone at a fixed level During the ovarian cycle, estrogen and progesterone levels rise, triggering a release of an egg cell, which is called ovulation If no sperm is present to fertilize the egg, the estrogen and progesterone levels will drop – This causes menstruation

16. Menstruation The increasing hormones from the ovarian cycle trigger growth of the inner lining of the uterus, which is called the endometrium Once the estrogen and progesterone levels fall, the endometrium disintegrates and leaks out of the vagina, a process called menstruation When fertilization occurs, hormonal levels remain high so there is no menstruation – This is how the woman’s body is aware it is pregnant – Hormonal contraceptives trick the body into thinking it’s pregnant when it’s not (“The Pill,” “The Shot,” etc.)

17. Sexual Response In both men and women, the sexual response is the brain and hormones working together to mate and is stimulated by sexual interest – Requires a combination of sympathetic and parasympathetic activity In both sexes, blood is flushed to the genitals (using a molecular mechanism that is duplicated by viagra) – In men this produces an erection, or enlargement of the penis – In women this stimulates glands to secrete mucus to lubricate the vagina

18. Sexual Response The brain is programmed to focus on the sexual response through controlled positive feedback loops As with other systems, positive feedback loops build up to a climax, and in the sexual response the climax is the orgasm In men, orgasm triggers the release of semen – Recall the orgasm also triggers the release of oxytocin If coitus has been occurring, the semen will be released into the vagina

19. Two ways to fail to avoid being pregnant: Withdrawal method (pull-out): Attempting to ejaculate outside the vagina while being in it for the run up – Sperm cells may also be found in the male lubricants secreted before orgasm Periodic abstinence (rhythm method): Attempting to not mate during peak fertility – Fertility can be difficult to estimate based only on menstruation, also sperm may be long-lived in the vagina given the right conditions

20. Contraception As indicated previously, many female contraceptive technologies are hormonal, in that they deceive the body by creating artificial hormone levels – These have an advantage of not interrupting the parasympathetic nervous system’s attempt to relax you into having sex Barrier methods such as condoms also prevent pregnancy and also prevent excessive mucousa-to-mucousa contact – Mucosal layers of the genitals may carry bacterial and/or viral sexually transmitted diseases (STDs)

21. That’s our show! There is no new content (aside from labs) for the semester! Next week is exam #3 The following week is the last week with the cumulative final exam!