Chapter 27 REPRODUCTION

1. Chapter 27 REPRODUCTION

2. Asexual versus Sexual Reproduction Asexual Reproduction: A single parent gives rise to two or more offspring by: • Fission (Splitting): One individual splits into two or more of about equal size. • E.g.: Bacteria, sea anemone. • Budding: New individual(s) are generated from a portion of the parent and are smaller than parent. • E.g.: Many plants, budding yeast. • Fragmenting: Can regenerate body parts. • E.g.: Sea stars when cut into several pieces will regenerate into several new star fish. • Parthenogenesis: “Virgin development”. Unfertilized egg develops into an adult animal. Adaptation for stressful times. • Whiptail lizard • Several insects

3. Asexual versus Sexual Reproduction Sexual Reproduction: • The most common type of animal reproduction. • Occurs through the fusion of gametes (sperm and egg). • Male: Produces sperm cells. Small and motile, propels itself by whiplike flagellum. • Female: Produces eggs (ova). Large and nonmotile. • Zygote: Egg cell fertilized by a sperm cell. Fertilization: Creation of zygotes by fusion of ova and sperm cells. Two types: • Internal Fertilization: Gametes fuse inside the female’s body. • Usually requires copulation (intercourse) in which male delivers sperm directly into body of female. • Practiced by most terrestrial animals, aquatic reptiles, birds, and mammals. Sexual Reproduction: • Only organ system that is not essential for individual survival. • Continuation of species. • Gamete formation (eggs and sperm cells. Homeostatic Role: • Maintains secondary sexual characteristics.

4. Asexual versus Sexual Reproduction • External Fertilization: Gametes fuse outside the female’s body. • Mating partners release eggs and sperm simultaneously into the water. • Practiced by most aquatic animals: fish, amphibians. • Many eggs are lost and eaten by predators. Therefore, many must be made and released for a few to survive. Hermaphroditism: • A single individual produces both sperm and eggs. • Some such as the tapeworm are capable of self-fertilization. • Others (e.g.: earthworm) must mate with other animals. • In some species self-fertilization is prevented by development of testis and ovaries at different times. • Used by “solitary” animals.

5. Advantages of Sexual Reproduction: • Genetic diversity among offspring. • If environment changes drastically, the population may survive if a few individuals have genetic traits that allow them to adapt to changes. Disadvantages of Sexual Reproduction: • Need to invest considerable time, resources, and energy searching for suitable mate. • Only pass on 50% of your genetic material to each offspring.

6. Advantages of Asexual Reproduction: • Don’t need to invest time and energy searching for suitable mate. • Replicates a given genotype rapidly and precisely. • Pass on 100% of your genetic makeup to each offspring. • Useful for organisms well adapted to a stable environment. Disadvantages of Asexual Reproduction: • No genetic diversity among offspring. • If environment changes drastically, the entire population may die out.

7. Reproductive System of Humans Reproductive Functions of Female: • Produces eggs (ova) • Receives sperm • Incubates and nourishes the embryo and fetus • Gives birth • Produces milk for young All of these processes are regulated and coordinated by hormones secreted by: • Hypothalamus • Pituitary gland (anterior portion) • Ovaries

8. Endocrine Glands Regulate Sexual Functions

9. Reproductive System of Humans Major Organs of Female Reproductive System: • Ovaries: Produce ova (oogenesis) and sex hormones. • Size and shape of large almonds. • Located close to lateral walls of pelvic cavity and held in place by connective tissue. • Mainly connective tissue containing scattered eggs (ova) in different stages of development. • Follicles: A single egg with surrounding cells that nourish and protect it. • Women are born with all of their follicles (40,000 to 400,000). • Only a fraction of follicles release eggs during a woman’s reproductive life.

10. Frontal View of Female Reproductive System

11. Side View of Female Reproductive System

12. Female Reproductive System: • Ovulation & Oogenesis: After puberty, each month one immature egg (oocyte), is released from ovary. • Each follicle contains a primary oocyte, arrested in prophase I of meiosis. • Pituitary hormones FSH (follicle stimulating hormone) and LH (luteinizing hormone) cause a follicle to enlarge and complete meiosis I. • One large cell (secondary oocyte) and a tiny cell (polar body) are produced. • LH (luteinizing hormone) causes the secondary oocyte to be released by the ovary during ovulation. • Oocyte will not finish meiotic division, until fertilized. • In the end, one large ovum (egg) and 3 small polar bodies are made from oogenesis.

13. Oogenesis and Ovary Structure

14. Major Organs of Female Reproductive System: • Oviducts (Fallopian Tubes): Transport the egg from the ovary to the uterus. • Peristalsis of smooth muscle in oviduct and beating of cilia, help the egg move along. • Fertilization occurs in the first third of oviduct. • Scarring of oviducts is a common consequence of sexually transmitted diseases: chlamydia and gonorrhea. • Ectopic Pregnancy: Fertilized egg does not reach the uterus. Usually starts to develop in oviduct. • Usually due to a blocked oviduct. • Occurs in 1% of all pregnancies in the U.S. • Must be surgically removed. • May cause death and severe hemorrhage.

15. Fertilization Occurs in the Oviducts

16. Ectopic Pregnancy of Twins Ectopic pregnancies occur in about 1% of pregnancies in U.S. and usually require surgical removal of embryos.

17. Reproductive System of Humans Major Organs of Female Reproductive System: • Uterus: Incubates the embryo/fetus. • Size of a fist, in center of pelvic cavity. • Oviducts open into upper corners of uterus. • Has thick walls of smooth muscle (myometrium) responsible for uterine contractions and cramps. • Endometrium: Inner mucous lining, which thickens each month in preparation for pregnancy. • If fertilization does not occur, endometrium breaks down and is discharged during menstruation. • If fertilization occurs, the egg implants in the endometrium which supports its growth until the placenta develops.

18. The Uterus Incubates and Nourishes the Fetus

19. Reproductive System of Humans Major Organs of Female Reproductive System: • Cervix: Lower portion of the uterus, which projects into the vagina. • Pap smear: Examination of cervical tissue to detect abnormalities. Recommended yearly. • Cervical cancer: Most cases caused by a viral infection with human papillomavirus. • Women are infected through intercourse with asymptomatic male. • Takes about 20 to 30 years to develop. • Men don’t appear to be affected.

20. Reproductive System of Humans Major Organs of Female Reproductive System: • Vagina: Thin walled, muscular chamber. • Receives the sperm and penis • Acid pH kills bacteria and sperm cells • Part of birth canal • Vulva: External structures. • Clitoris: Equivalent to male penis. • Labia minora: Skin folds that border vaginal opening. • Labia majora: Protect entire genital region. • Hymen: Ring of tissue that forms a border around vaginal entrance. No known function. • Bartholin’s gland: Secrete lubricating fluid during sexual arousal. • Breasts: Lactation

21. Female Hormones Controlling Reproduction • Follicle Stimulating Hormone (FSH) • Secreted by pituitary gland • Stimulates growth of ovarian follicle • Luteinizing Hormone (LH) • Secreted by pituitary gland • Stimulates growth of follicle and completion of meiosis I • Induces ovulation • Promotes development of corpus luteum and hormone secretion. • Estrogen • Secreted by ovarian follicle • Low levels inhibit FSH and LH secretion • High levels stimulate FSH and LH secretion • Promotes growth of endometrium • Progesterone and Estrogen • Secreted by corpus luteum • Maintain endometrium, sharp drop causes menstruation • High levels inhibit inhibit FSH and LH secretion

22. Female Menstrual Cycle: Approximately 28 days. • Menstruation: Day 1 of cycle. • Walls of endometrium break down. • Caused by falling levels of progesterone and estrogen. • Lasts 3 to 7 days. • Pre-Ovulatory phase: Starts around day 5 of cycle. • Rising estrogen levels cause the endometrium to start thickening. • Ovulation: Occurs around day 14 of cycle. • FSH stimulates growth of ovarian follicle. • LH causes follicle to finish meiosis I (secondary oocyte) and to be released by ovary. • Corpus luteum: Starts to secrete estrogen and progesterone. • Post-ovulatory Phase: Starts around day 15. • Endometrium continues to grow in response to rising estrogen and progesterone. • If no fertilization occurs, corpus luteum degenerates and menstruation occurs. • If fertilization occurs, embryo maintains corpus luteum.

23. Stages of Female Reproductive Cycle

24. Reproductive System of Humans Reproductive Functions of Male: • Produces sperm • Delivers sperm to female reproductive tract All of these processes are regulated and coordinated by hormones secreted by: • Hypothalamus • Pituitary gland (anterior portion) • Testes (Sing. Testis)

25. Side View of Male Reproductive System

26. Front View of Male Reproductive System

27. Major Organs of Male Reproductive System: • Testes: Paired male gonads. • Produce sperm through spermatogenesis, which produces four sperm cells of equal size. • Spermatogenesis occurs in a vast system of hollow tubes called seminiferous tubules. • Each mature sperm has a head, a midpiece, and a flagellum. • Sperm head has an acrosome, which produces enzymes that help it penetrate the egg. • Human sperm cannot develop at body temperature. • Testicles descend from abdominal cavity into scrotum, a skin covered sac, about two months before birth. • Undescended testicles (cryptorchidism) may cause infertility.

28. Spermatogenesis Occurs in Seminiferous Tubules of Testes

29. Sperm Cell Structure

30. Reproductive System of Humans Major Organs of Male Reproductive System: • Epididymus: • Large coiled tube (23 ft long) that surrounds testes. • Stores sperm while they develop fertilizing ability and motility (about 20 days). • During ejaculation, sperm cells are propelled from epididymus. • Vas Deferens: • Long muscular ducts from scrotum to back of bladder. • During ejaculation, the sperm pass from epididymus into these two ducts. • Vasectomy: Each vas deferens is cut to prevent sperm from entering urethra.

31. Reproductive System of Humans Major Organs of Male Reproductive System: • Ejaculatory Duct: • Short duct after two vas deferens ducts unite. • Urethra: • Deliver sperm to the exterior. • In males, urine and sperm pass through the urethra. • Females have a separate urethra from the reproductive system.

32. Reproductive System of Humans Major Organs of Male Reproductive System: Accessory Glands: Produce semen. • Functions of semen: • Activate sperm cells • Provide nutrients for motility • Counteract acidity of vagina and male urethra • Stimulate contractions of female reproductive tract • Antimicrobial action • Ejaculation volume 4 to 5 ml. • One ejaculation has 50-500 million sperm cells • Sperm cells account for less than 5% of semen volume. • Secretions from 3 different accessory glands make up the rest of the volume: Seminal vesicles (2), prostate, and bulbourethral glands (2).

33. Major Organs of Male Reproductive System: Accessory Glands: A. Seminal vesicles (2): Secrete fluid that nourishes sperm. • Contribute about 60% of semen volume. • Thick, clear, alkaline fluid. • Contains: • Fructose: Provides energy for sperm motility. • Prostaglandins: Stimulate smooth muscle contractions of female and male reproductive tracts. • Fibrinogen: Forms temporary clot in vagina. • Sperm cells become highly motile when mixed with this fluid.

34. Accessory Glands: B. Prostate gland: Produces a thin milky secretion. • Largest of semen secreting glands. • Contributes 30% of semen volume. • Produces an antibiotic that may prevent urinary tract infections in men. • Benign (noncancerous) prostate enlargement is common among older men. • 50% of men over 40. • Almost all men over 70. • Prostate cancer is the second leading cause of cancer and cancer deaths in men. • Over 330,000 new cases/year and 40,000 deaths. • Average age at diagnosis: 72 • Detected by blood test or digital rectal exam. • Treated surgically or with drugs to reduce prostate size or activity.

35. Benign Prostate Enlargement Usually Procedes Prostate Cancer Normal prostate is 2 to 3 cm in diameter

36. Major Organs of Male Reproductive System: Accesory Glands: C. Bulbourethral glands (2): Release a mucous secretion that lubricates penis and facilitates its entry into vagina. • Pair of small glands below the prostate. • Contribute 5-10% of semen volume. • Before ejaculation secrete a clear mucus that neutralizes acid from remaining urine in urethra. • Bulbourethral fluid also carries some sperm that is released before ejaculation. One cause of high failure rate of withdrawal method.

37. Major Organs of Male Reproductive System: • Penis: Copulatory organ that delivers sperm to female body. • Composed of three cylinders of erectile tissue. • During sexual arousal, the penis fills with blood from the arteries. • Erection is essential for penetration. • Impotence is the inability to maintain an erection. • May be caused by alcohol, drugs, illness, and/or emotional problems. • Viagra acts by relaxing smooth muscle of penis blood vessels, allowing blood to enter erectile tissue. • Penis structure: • Shaft: Long cylinder with thick skin. • Glans: Enlarged tip of penis. Thin skin, covered by prepuce or foreskin.

38. Fertilization: Sperm Cell Penetrates Egg with Acrosomal Enzymes

39. Fertilization and Early Embryonic Development

40. Developing Embryo is Nourished by Placenta

41. Pregnancy and Human Development • Gestation: In humans starts at conception and lasts approximately 38 weeks (266 days). • Due date typically 40 weeks after last menstruation. • First Trimester: By the end of week 13 • Sex distinguished externally • Fetus weighs about 150 grams • Second Trimester: By the end of week 26 • Fetus weighs about 1000 g • May survive if born at this point. • Third Trimester: By the end of week 38 • Fetus weighs about 3500 g (7 ½ lb.) • Testes have descended in males.

42. Critical Stages of Embryonic and Fetal Development

43. Childbirth (Labor) and its Three Stages Hormonal triggers: • Rising estrogen levels causes the formation of oxytocin receptors on smooth muscle of uterus. • Oxytocin is secreted by fetal cells and mother’s pituitary. • Prostaglandins are released by placenta. Stages of Childbirth • First Stage: Dilation • Cervix opens from 1 cm to 10 cm. • Lasts several hours or days. • Second Stage: Expulsion • Strong uterine contractions every 2 to 3 min push baby through birth canal. • Lasts 20 min to a couple of hours. • Third Stage: Delivery of placenta (afterbirth) • Usually within 15 minutes of delivery

44. Labor Contractions Are Induced by Several Hormones

45. Birth of Human Child Requires Dilation of Cervix

46. Different Contraceptive Methods 1. Prevent Release of Gametes: • Birth control pill (combination): Prevents ovulation 2. Prevent Fertilization • Vasectomy: Male sterilization • Tubal ligation: Female sterilization • Minipill: Progestin only, blocks cervical opening • Norplant implant: Releases progestin for 5 years • Rhythm (calendar): Avoid intercourse around ovulation • Withdrawal: Remove penis before ejaculation • Condom: Latex or sheepskin barrier • Diaphragm, cervical cap: Block cervical opening • Spermicide: Kill sperm cells 3. Prevent Implantion • Intrauterine device (IUD) • Morning after pills l

47. Effectiveness of Methods of Contraception

48. Effectiveness of Methods of Contraception

49. Incidence (New Cases) of Sexually Transmitted Diseases in the U.S. (1996)

50. Reproductive System Diseases 1. Gonorrhea • Characteristics: Acute infection of urethra, anus, vagina, cervix, and fallopian tubes. Yellow foul discharge (more common in men). Causes pelvic inflammatory disease (PID) in women. Major cause of infertility in both men and women. May also result in throat and eye infections. In a large percentage of cases, symptoms are mild or absent. • Pathogens: Neisseria gonnorrhoea (bacterium). • Transmission: Direct sexual or mucous membrane contact. Mother to infant transmission during childbirth. • Incubation period: 2 to 7 days.