Lecture 15 Notes
Animal Reproduction
| I. Two major ways to reproduce
A. Asexually 1. animal simply divides, splits or buds off 2. benefits: efficient, fast, and partner not required 3. costs: no genetic variation introduced into population B. Sexually 1. male and female partners needed to exchange genetic material 2. benefits: genetic recombination insures genetic variability in population, may reduce parasite loads, allows better coping with environmental variation 3. costs: is time consuming (searching for partner, gestation period), dangerous (could be eaten during reproduction, or die during pregnancy) C. will concentrate on human reproduction in this class (see Chapter 27) 1. Males a. penis and testes main parts i. penis - organ for transmitting sperm to female 1. part of intricate system for producing sperm and transmitting them (see Figure 27.3 A and B, pg. 538) 2. sperm produced in testis, then stored in epididymis 3. during ejaculation, sperm are moved out of epididymis through tubes called vas deferens 4. three glands associated with reproductive system a. seminal vesicle - produces thick clear fluid that lubricates and nourishes sperm b. prostate gland - secretes a milky fluid that balances acidity due to any trace amounts of urine and protects sperm against acidity of vagina c. bulbourethral gland - secretes a few drops of fluid into urethra that may help lubricate pathway for sperm 5. All fluids + sperm constitute semen 6. about 4 mls are ejected (teaspoon) during each ejaculation 7. this may contain 200-500 million sperm!! 8. penis is composed of tissue that can fill with blood during arousal a. when aroused, more blood flows in than goes out, and penis becomes stiff (NO, or laughing gas, nitric oxide, is involved!) b. muscle contractions result in ejection of semen 2. Females a. see Figure 27.2A and B and C for details on anatomy b. eggs are produced in ovaries, surrounded by other cells - entire complex is called a follicle c. ovaries connected to oviducts that lead to the uterus d. uterus connected to vagina by small opening called the cervix e. vagina is organ that receives the penis and sperm f. uterus is where embryo develops g. clitoris - stimulatory area analogous to male penis 3. Both sperm and egg are haploid - that is, the result of meiosis and only have half the chromosomes of somatic, or other body cells 4. when follicle matures, it releases the egg to the oviducts (called ovulation) 5. left over follicle without egg is known as the corpus luteum 6. Menstrual Cycle and Hormonal Control a. usually cycle takes about 28 days b. consult Figure 27.5 to fully understand this part c. Brain (hypothalamus) releases a hormone that stimulates the pituitary to release two hormones (FSH and LH, which are follicle stimulating hormone and luteinizing hormone, respectively) d. these hormones travel to female reproductive system in blood stream e. FSH stimulates a follicle to begin maturing f. as follicle grows and matures, it begins producing estrogen, a female hormone g. estrogen travels back to the brain, and inhibits further production of of FSH, effectively preventing more than one follicle from maturing at a time - it also slows production of LH also h. but as estrogen gets higher and higher in blood stream, there comes a time when this causes a burst of production of FSH and LH, near the midpoint of the cycle i. the increase in LH triggers ovulation and release of the egg. We still do not know what the increase in FSH does at this time in the cycle j. LH also stimulates the uterus to produce another hormone, called progesterone - this prevents bleeding and keeps the endometrium intact for eventual implantation of the embryo. Endometrium is the inner wall of the uterus k. production of estrogen and progesterone then stops further production of anymore FSH or LH l. corpus luteum produces progesterone for a while - but if no fertilization takes place, it dies, and the lack of progesterone allows menstrual bleeding to occur, and the cycle begins anew m. if fertilization does occur, then the embryo begins to secrete a new hormone called human chorionic gonadotropin (HCG) that acts like LH and keeps the endometrium intact for implantation. It is this hormone the pregnancy kits use to see if you are pregnant (if you detect HCG, there must be an embryo producing it - the kit works by binding an antibody to HCG, and then reacting it with a chemical that turns color in its presence) n. once fertilization occurs, embryo implants on uterus wall, and develops 7. Birth Control Methods (see pgs. 544-545) a. best method is the pill (not including abstinence!) b. rhythm method is much less reliable (accidents do occur, and knowing when ovulation occurs is difficult sometimes) |