1. David Sadava H. Craig Heller Gordon H. Orians William K. Purves David M. Hillis Biologia.blu C – Il corpo umano Reproductive System and Development

2. How do the human male and female reproductive systems work? How does fertilization activate development? What are the stages of development? How can fertility be controlled and sexual health maintained? Reproductive System and Development

3. Semen is made up of sperm and other fluids and molecules. Sperm are produced in the paired male gonads, or testes. The testes are located in the scrotum, outside of the body, to maintain optimal temperature for sperm production. Reproductive System and Development - How do the human male and female reproductive systems work?

4. The reproductive tract of the human male (part 1)

5. Reproductive System and Development - How do the human male and female reproductive systems work? The reproductive tract of the human male (part 2)

6. Reproductive System and Development - How do the human male and female reproductive systems work? The reproductive tract of the human female (part 1)

7. Reproductive System and Development - How do the human male and female reproductive systems work? The reproductive tract of the human female (part 2)

8. Within the seminiferous tubules are germ cells in stages of spermatogenesis. Germ cells are closely associated with Sertoli cells, which provide nutrients for developing sperm. Differentiated sperm cells are shed in the lumen of the seminiferous tubule. Reproductive System and Development - How do the human male and female reproductive systems work?

9. Seminiferous tubules are the site of spermatogenesis (A and B)

10. Reproductive System and Development - How do the human male and female reproductive systems work? Seminiferous tubules are the site of spermatogenesis (C)

11. Reproductive System and Development - How do the human male and female reproductive systems work? Spermatogenesis

12. Reproductive System and Development - How do the human male and female reproductive systems work? The ovarian cycle

13. Reproductive System and Development - How do the human male and female reproductive systems work? Oogenesis

14. Reproductive System and Development - How do the human male and female reproductive systems work? Hormones control male sexual function. At puberty GnRH released by the hypothalamus causes the anterior pituitary to increase LH and FSH release. LH acts on the interstitial cells (Leydig cells) of the testes stimulating them to synthesize and secrete the male sex hormone, testosterone. FSH and testosterone control spermatogenesis in the Sertoli cells. These cells also produce inhibin, which exerts negative feedback on cells that produce and secrete FSH.

15. Reproductive System and Development - How do the human male and female reproductive systems work? Hormones control the male reproductive system

16. The female reproductive cycle consists of two linked cycles: the ovarian cycle that produces eggs and hormones; the uterine cycle that prepares the endometrium for a blastocyst. If a blastocyst does not arrive, the thickened endometrium is shed off. Reproductive System and Development - How do the human male and female reproductive systems work?

17. An ovarian cycle is about 28 days long in the human female, but varies. Ovulation occurs during the first half of the cycle: a primary oocyte matures into an egg and is expelled from the ovary. In the second half of the cycle, ovarian cells develop endocrine functions that stop if the egg is not fertilized. Reproductive System and Development - How do the human male and female reproductive systems work?

18. A human female is born with about one-million primary oocytes in each ovary. Most will degenerate but a woman will go through about 450 ovarian cycles. At menopause, the end of fertility, there may be only a few oocytes left in each ovary. Reproductive System and Development - How do the human male and female reproductive systems work?

19. The functional unit of the ovary is called the follicle: it consists of a primary oocyte and its surrounding ovarian cells. After two weeks of follicular growth, ovulation occurs: the follicle ruptures and the egg is released. Reproductive System and Development - How do the human male and female reproductive systems work?

20. The other follicular cells form the corpus luteum, which remains in the ovary. The corpus luteum functions as an endocrine gland and produces estrogen and progesterone for about two weeks. It degenerates unless a blastocyst implants in the endometrium. Reproductive System and Development - How do the human male and female reproductive systems work?

21. The uterine cycle parallels the ovarian cycle and consists of the buildup and breakdown of the endometrium. The endometrium remains prepared for a blastocyst until about 9 days after ovulation. Menstruation is the sloughing off of the endometrium through the vagina. Reproductive System and Development - How do the human male and female reproductive systems work?

22. The ovarian and uterine cycles (A) Reproductive System and Development - How do the human male and female reproductive systems work?

23. The ovarian and uterine cycles (B-D) Reproductive System and Development - How do the human male and female reproductive systems work?

24. Ovarian and uterine cycles are controlled by hormones. At puberty increased GnRH stimulates production of FSH and LH. FSH and LH stimulate ovarian tissue to grow and produce estrogen, which causes the maturation of secondary sexual characteristics.

25. Reproductive System and Development - How do the human male and female reproductive systems work? Menstruation marks the beginning of both ovarian and uterine cycles. A few days before menstruation: pituitary increases FSH and LH; follicles in ovary grow and increase estrogen production; one follicle matures completely.

26. Reproductive System and Development - How do the human male and female reproductive systems work? Estrogen exerts negative feedback on the pituitary early in the ovarian cycle. Later on estrogen becomes a positive feedback signal, and causes a surge of LH and FSH. The LH surge causes the follicle to release its egg and to develop the corpus luteum. It functions as an endocrine gland and secretes estrogen and progesterone. These sex steroids exert negative feedback on the pituitary, inhibiting GnRH and follicle maturation. Without fertilization, corpus luteum degenerates, steroids decrease, and GnRH, FSH, and LH rise for the next cycle.

27. Hormones control the ovarian and uterine cycles Reproductive System and Development - How do the human male and female reproductive systems work?

28. In females, the ovary releases an egg into the oviduct, or Fallopian tube, where it may be fertilized. The egg is propelled towards the uterus where it will develop if fertilized. The bottom of the uterus is the narrow cervix, which opens into the vagina. Sperm deposited in the vagina must swim to the upper oviduct to fertilize an egg. Fertilization results in the fusion of the haploid sperm and egg nuclei and produces a diploid zygote. Reproductive System and Development - How do the human male and female reproductive systems work?

29. A mammalian egg is surrounded by barriers to sperm

30. The zygote undergoes cell division and becomes a blastocyst. The blastocyst moves down the oviduct and attaches to the lining of the uterus, the endometrium. Implantation occurs when the trophoblast adheres to the endometrium, or uterine lining. Early implantation that occurs in the oviduct is an ectopic or tubal pregnancy. Reproductive System and Development - How do the human male and female reproductive systems work?

31. The mammalian zygote becomes a blastocyst

32. Reproductive System and Development – How does fertilization activate development? A human blastocyst at implantation

33. In mammals, the yolk sac grows from the hypoblast and provides mesodermal tissues to form the chorion. The chorion and uterine tissues form the placenta, which exchanges nutrients, gases, and waste between mother and embryo. The epiblast produces the amnion, which fills with fluid and protects the embryo. The allantois forms the umbilical cord and exchanges nutrients and wastes. Reproductive System and Development – How does fertilization activate development?

34. The placenta

35. Reproductive System and Development - What are the stages of development? Gestation, or pregnancy, in humans is about 266 days and is divided into trimesters. In the first trimester the embryo becomes a fetus: heart begins to beat by week 4; limbs form by week 8.

36. Reproductive System and Development - What are the stages of development? Stages of human development

37. The first trimester is the period during which the fetus is most susceptible to damage from radiation, drugs, chemicals, and agents that cause birth defects. The hormone hCG is released after implantation and is an early indicator of pregnancy. Reproductive System and Development - What are the stages of development?

38. During the second trimester the limbs elongate and facial features form. In the third trimester internal organs mature and organ systems begin to function. The last organs to mature before birth are the lungs. Reproductive System and Development - What are the stages of development?

39. Extraembryonic membranes allow for detection of genetic diseases. Amniocentesis: extraction of amniotic fluid with a needle, after the fourteenth week of pregnancy. Chorionic villus sampling: tissue is removed from the chorion after the eighth week.

40. Sexual behavior can transmit disease organisms. The organisms cause sexually transmitted diseases (STDs). The only contraceptive device effective against STDs is a condom. Reproductive System and Development - How can fertility be controlled and sexual health maintained?