Reproductive and Developmental Biology: A Closer Look at Sexual Reproduction and Environmental Contaminants

1. Chapter 14 Is There Something in the Water?Reproductive and Developmental Biology 0

2. 1 Principles of Animal Reproduction – Asexual Reproduction In asexually reproducing organisms (mold, banana, yeast, sponges), one parent produces offspring that are genetically identical to the parent Binary fission – cells break away from parent to form similarly-sized offspring (e.g., sponges) Budding – smaller daughter cell remains attached to parent and breaks away when mature (e.g., yeast)

3. 1 Principles of Animal Reproduction – Sexual Reproduction Sexual reproduction combines genomes and creates variable offspring. Gametes = cells that combine to make the next-generation organism (eggs and sperm) Organs that produce gametes are called gonads. Ovaries produce eggs in females and testes produce sperm. Zygote results from the fusion of two gametes (in humans and vertebrates, we call it a fertilized egg).

4. 1 Principles of Animal Reproduction – Sexual Reproduction Sexual reproduction involves two different individuals. Females individuals that have only ovaries and produce large, immobile gametes Males = individuals that have only testes produce small mobile gametes In species possessing males and females, a male and female need to interact sexually to make a zygote Hermaphrodites have both male and female reproductive systems (earthworms, roundworms). In hermaphroditic species, two individuals need to interact with each other to make a zygote, but both individuals can harbor zygotes.

5. 1 Principles of Animal Reproduction – Sexual Reproduction Method of fertilization is variable. Internal fertilization – sperm deposited in or near female reproductive tract. Mammals, birds, reptiles, and sharks use internal fertilization. External fertilization – eggs laid, male deposits sperm over eggs (usually in water). Most fish and amphibians use external fertilization. Very susceptible to contaminants

6. 1 Principles of Animal Reproduction – Environmental Contaminants and Sexual Reproduction Gender change during development is seen in many fish Several fish species are born as one gender, with dominant individuals or schools changing to the opposite gender Developing frogs are extremely sensitive to environmental chemicals. Research showed that some chemicals can act as endocrine disruptors, interfering with normal gonad development. Male amphibians have been feminized. These chemicals affect animals living in water. Are humans affected by drinking contaminated water?

7. 2 Human Reproduction – Male Reproductive Anatomy In addition to producing sperm, testes also produce hormones.

8. 2 Human Reproduction – Female Reproductive Anatomy

9. 2 Human Reproduction – Sexually Transmitted Diseases – common bacterial agents

10. 2 Human Reproduction – Sexually Transmitted Diseases – common viral agents

11. 2 Human Reproduction – Sexually Transmitted Diseases – common fungal/animal/protozoa

12. 2 Human Reproduction – Endocrine Disruptors DES is a chemical known to act as an endocrine disruptor. It was an early-generation estrogen agonist DES was used from 1947 through the 1970s believing that it helps reduce pregnancy complications (miscarriage, deformities) DES was found to cause cancer in women Daughters of women who took DES have a higher rate of infertility.

13. 2 Human Reproduction – Gametogenesis Gametogenesis is the production of gametes It involves the process of meiosis. Reduces number of chromosomes by ½ (homologous pairs are split between cells) Human body cells contain 46 chromosomes, gametes contain 23 Male and female gametes undergo further development to become functional (called spermatogenesis and oogenesis)

14. 2 Human Reproduction – Spermatogenesis Only fully developed sperm participate in fertilization

15. 2 Human Reproduction – Oogenesis Eggs pause development at two stages: Pause until ovulation Pause again until fertilization

16. 2 Human Reproduction – Male Infertility 90% of male infertility related is to problems with sperm formation or production. Low sperm counts Improperly shaped sperm (sperm formation must occur below body temperature) Low motility Chemical exposure (e.g., pesticides) can decrease sperm viability (sperm formation, shape, and motion are highly ordered processes, easy to corrupt) Male infertility increases with alcohol and drug use, including cigarettes

17. 2 Human Reproduction – The Menstrual Cycle The Menstrual cycle is the cyclic changes in the uterus and ovaries in response to hormones. Menstruation is the sloughing off of the endometrial lining in the absence of implantation of a fertilized egg. Day one of the cycle involves the bleeding due to the sloughing off of the endometrium. During day one the hypothalamus releases gonadotropin releasing hormone (GnRH) to stimulate the release of follicle-stimulating hormone (FSH) from the anterior pituitary gland. FSH triggers the ovaries to start maturing a follicle and to produce estrogen. – process takes half a cycle

18. 2 Human Reproduction – The Menstrual Cycle Once the follicle is mature and ready for ovulation the GnRH triggers the release of LH from the anterior pituitary gland. The LH surge triggers ovulation. After the release of the egg, progesterone is produced to finish rebuilding the endometrium and get the uterus ready for implantation. If the egg is not fertilized then it does not implant, and negative feedback by progesterone triggers menstruation and day one again.

19. 2 Human Reproduction – The Menstrual Cycle Changes that occur in the uterus and ovaries are dependent upon the interaction between the uterus, ovaries, brain, and endometrium.

20. 2 Human Reproduction – The Menstrual Cycle The menstrual cycle is self-regulating through feedback loops.

21. 2 Human Reproduction Birth control methods vary widely because there are many ways to interact with the endocrine system. Some are hormonally based; others rely on prevention of fertilization through a variety of means.

22. 2 Human Reproduction Table 21.2

23. 2 Human Reproduction

24. 2 Human Reproduction

25. 2 Human Reproduction – Female Infertility One cause of female infertility is endometriosis, a condition where tissues that line the uterus also grow (and shed) in the ovaries and oviducts. Can cause damage and scarring to ovarian tissue Can disrupt ovulation Painful (far worse than regular periods) Scientists are trying to determine if it is related to exposure to environmental chemicals.

26. 3 Human Development – Fertilization Development is the series of events that take place after fertilization. About 300 million sperm are ejaculated, but only about 200 actually reach the egg in the oviduct (fallopian tubes).

27. 3 Human Development – Endocrine Disruptors and Fertilization Industrial solvents can mimic hormones and interfere with sperm development and fertilization. Misshapen sperm cannot swim effectively and are unable to fertilize egg. Males who are exposed to solvents, such as those working as mechanics or dry cleaners, have a larger number of abnormal sperm. The impact of hormone mimics on the developing fetus is unknown.

28. 3 Human Development – Human Embryonic Development Human zygote undergoes a series of cleavage to produce an embryo.

29. 3 Human Development – Human Embryonic Development The three tissue layers ultimately give rise to all body structures. Ectoderm is the outer layer and gives rise to the skin, nervous system, and sense organs. Mesoderm is the middle layer and gives rise to the bulk of the body. Endoderm is the inner layer and gives rise to the digestive and respiratory organs. Growth of a particular tissue or organ relies on chemical stimulus. Development is very sensitive to disruption.

30. 3 Human Development – Development of Human Reproductive Organs Until week 7 of development, male and female reproductive organs begin to form and take shape but are not committed differentiated to one gender or another. They require hormonal stimulus to become male or female.

31. 3 Human Development – Development of Human Reproductive Organs

32. 3 Human Development – Endocrine Disruptors and Development of Reproductive Organs Endocrine disruptors have been thought to increases the rate of cryptorchidism. Cryptorchidism occurs when the testes do not descend into the scrotum. This decreases reproductive success due to the increased temperature the testicles are exposed to in the abdomen. Testicles must be held at about 90 degrees for proper sperm development Higher temperatures lead to defects in sperm.

33. 3 Human Development – Pregnancy Pregnancy, or gestation, involves carrying a developing baby inside the female reproductive tract; in humans this takes about 38 weeks. Embryo implants in the wall of the uterus A placenta must develop to sustain pregnancy Maternal and fetal blood supplies are closely intertwined in the placenta, allowing exchange of nutrients and wastes Endocrine disrupter exposure during pregnancy can lead to low birth weight and premature birth.

34. 3 Human Development – Childbirth The hormone oxytocin uses a positive feedback loop to induce labor.

35. 3 Human Development - Stages of Labor

36. 4 Is the Water Safe to Drink? The idea of endocrine disruptors in the water supply is disturbing, but do we need to be concerned? What is being done about this issue? EPA requires monitoring of municipal water supplies. It’s unclear what is a safe level of chemicals, and the EPA often sets levels as a compromise between what is economically possible and what is necessary for human health Studies show the human body can be affected by endocrine disruptors, but there is no evidence yet of this happening from contaminated water.

37. A yeast cell undergoes cell division to produce a daughter cell that remains attached to the parent until it achieves sufficient growth to break away. What is this process called? sexual reproduction budding self-fertilization binary fission

38. A yeast cell undergoes cell division to produce a daughter cell that remains attached to the parent until it achieves sufficient growth to break away. What is this process called? sexual reproduction budding self-fertilization binary fission

39. Which of the following does not describe a zygote? gamete 2n diploid fertilized egg

40. Which of the following does not describe a zygote? gamete 2n diploid fertilized egg

41. What is the function of the prostate gland? The many coiled tubes are the location of sperm formation. It secretes a thin, milky white fluid for the sperm’s nutrition. This sperm carrying duct propels the sperm from the epididymis. It is where androgens are produced.

42. What is the function of the prostate gland? The many coiled tubes are the location of sperm formation. It secretes a thin, milky white fluid for the sperm’s nutrition. This sperm carrying duct propels the sperm from the epididymis. It is where androgens are produced.

43. One or more eggs mature and are released from what structure(s)? ovaries corpus luteum uterine or fallopian tubes endometrium

44. One or more eggs mature and are released from what structure(s)? ovaries corpus luteum uterine or fallopian tubes endometrium

45. How many chromosomes do human gametes contain? 13 chromosomes 23 chromosomes 26 chromosomes 46 chromosomes

46. How many chromosomes do human gametes contain? 13 chromosomes 23 chromosomes 26 chromosomes 46 chromosomes

47. What is the cell called after the first meiotic division in spermatogenesis? spermatid sertoli cell primary spermatocyte secondary spermatocyte

48. What is the cell called after the first meiotic division in spermatogenesis? spermatid sertoli cell primary spermatocyte secondary spermatocyte

49. What layer of the gastrula gives rise to the skin, nervous system, and sense organs? ectoderm mesoderm endoderm blastocyst

50. What layer of the gastrula gives rise to the skin, nervous system, and sense organs? ectoderm mesoderm endoderm blastocyst