Human Anatomy and Physiology

1. Human Anatomy and Physiology Chapter 27 – Reproductive System

2. The Reproductive System • Functions: • Produce sex cells (eggs and sperm) • Permit the joining of the sex cells • Provide an environment for the development of a fertilized egg (only in the female)

3. Male Reproductive System • The male gonads (organs that produce sex cells) are the testes. • The testes are held within the scrotum • Optimum sperm production occurs at about 3° C cooler than internal body temperature • The scrotum helps to regulate the temperature of the testes • The dartos and cremaster muscles • Figures 27.1 and 27.2

4. Male Reproductive System • The penis contains erectile tissue – Figure 27.4

5. Male Reproductive System • Inside the testes there is a series of coiled tubes called seminiferous tubules (ST) • these are the site of sperm production • they have a total length of nearly half a mile! • Outside the ST are the interstitial or Leydig cells that produce testosterone • Figure 27.3

6. Male Reproductive System (cont.) • Spermatogenesis • about 400 million sperm are produced each day! • Inside the ST there are two cell types: • Spermatogenic cells – these will become sperm • Sertioli cells (sustentacular cells) – help nourish the germ cells • They also form the blood-testis barrier • Figure 27.8

7. Male Reproductive System (cont.) • Germ Cells • Spermatogonia – around the periphery of the ST • Divide by mitosis to start the process of sperm production • One cell  spermatocyte, One cell  spermatogonia • The spermatocytes then proceed through meiosis to produce functional sperm cells • Figure 27.8

8. Male Reproductive System (cont.) • Mature sperm have three distinct parts: • head - nucleus and acrosome • midpiece - contains mitochondria • tail - flagellum for motility • Figure 27.9

9. Male Reproductive System (cont.) • Sperm produced in the testes mature in the epididymis • They are also stored here for as long as several months • the epididymis is connected to the urethra by a long tube called the vas deferens (ductus deferens) • vasectomy - severing of the vas deferens • Figure 27.1 and Figure from other text

10. Male Reproductive System (cont.) • Before leaving the body, sperm are mixed with a fluid • seminal fluid + sperm = semen

11. Male Reproductive System (cont.) • Seminal fluid is produced by three glands: • seminal vesicles – (60%) mucus, fructose, fibrinogen, prostaglandins • prostate gland – (30%) enzymes, clotting factors • bulbourethral gland – (5%) mucus • The remaining 5% of semen is composed of sperm • Normal sperm count is 75-400 million sperm per ml of semen • Figure 27.1

12. Male Reproductive System (cont.) • Hormonal Regulation in Males • Hypothalamus – Gonadotropin-releasing hormone (GnRH) • Stimulates the release of the gonadotropins from the anterior pituitary gland: • Luteinizing Hormone (LH) – increases testosterone production in the Leydig cells • Follicle-Stimulating Hormone (FSH) – binds to Sertioli cells and stimulates sperm cell production • Figure 27.10

13. Male Reproductive System (cont.) • Puberty – onset of sexual maturity • Human chorionic gonadotropin is produced by the placenta during fetal development • This stimulates the release of testosterone for initial male sex organ development • After birth, very little testosterone is produced until puberty

14. Male Reproductive System (cont.) • At puberty the hypothalamus increases GnRH secretion • This in turn increases LH and FSH secretion resulting in testosterone production • Effects of testosterone • Development and enlargement of male reproductive system • Stimulates hair production on face, legs, chest, pubic region (and back, occasionally)

15. Male Reproductive System (cont.) • Increases rate of sebaceous gland secretion • Can result in acne • Increases metabolism, RBC production, and protein synthesis • Causes rapid bone growth (but also stimulates the closure of the epiphyseal growth plate)

16. Female Reproductive System • The female gonads are the ovaries • the ovaries alternate in producing one egg per month • The ovaries also produce estrogen and progesterone (the female sex hormones) • Anatomy - Figures 27.11 and 27.14

17. Female Reproductive System (cont.) • Oogenesis • There are many follicles within the ovaries • each follicle contains an immature egg • there are about 2 million follicles at birth • 300,000-400,000 at puberty • only ~400 are ever released as mature eggs • the egg is released from the ovaries during ovulation • The corpus luteum is a hormone-secreting gland in the ovary • Figures 27.12 and 27.19

18. Female Reproductive System (cont.) • Puberty • Marked by menarche (the first menstrual period) • Reproductive organs and breasts enlarge and develop • Puberty results from estrogen and progesterone production

19. Female Reproductive System (cont.) • The Menstrual Cycle • Typically the cycle lasts 28 days • Includes both the ovarian and uterine cycles

20. Female Reproductive System (cont.) • The Ovarian Cycle: • Days 1-14 are the Follicular Phase • Day 14 – Ovulation • Days 14-28 are the Luteal Phase

21. Female Reproductive System (cont.) • The Follicular Phase • Early in the cycle GnRH secretion increases • Effect? • FSH and LH stimulate the development of a follicle and • The production of estrogen by the ovary

22. Female Reproductive System (cont.) • A surge of LH results in ovulation • It also leads to the development of the corpus luteum • The corpus luteum secretes estrogen and progesterone • If fertilization does not occur, the cells of the corpus luteum degenerate • Estrogen and progesterone secretion then rapidly declines and the cycle starts over • Figures 27.21 and 27.22

23. Female Reproductive System (cont.) • The Uterine Cycle: • Days 1-5: Menstrual Phase • the endometrium is sloughed off • Days 6-14: Proliferative Phase • endometrium thickens and prepares for pregnancy • Caused by estrogen and progesterone • Days 15-28: Secretory Phase • endometrium continues to thicken and secretions increase • Figure 27.22, Figure from other text, and CD

24. Female Reproductive System (cont.) • Menopause - period when uterine cycles and ovulation cease • usually occurs between the ages of 45 and 55

25. Fertilization and Pregnancy • Fertilization occurs in the fallopian tubes • If the egg is fertilized, human chorionic gonadotropin is released • This keeps the corpus luteum from degenerating and stops the uterine cycle • The embryo can become embedded in the uterine wall • Figures from other text and 28.4

26. Fertilization and Pregnancy • Timing of intercourse: • The egg is only viable for 12-24 hours after ovulation • Sperm cells can survive for 24-72 hours • Therefore intercourse must occur between days 11-15 in the menstrual cycle • Even given the right timing, fertilization is not certain • Figure 28.2 and other figure

27. Fertilization and Pregnancy • Twins: • Fraternal – 2 eggs released and fertilized • Identical Twins – 1 egg separates to form 2 babies • Figures from other text

28. Methods of Birth Control • Table and Figures from other text

29. Methods of Birth Control • Discussion

30. Infertility • 15% of all couples in the US cannot have children • these couples would be considered sterile • Another 10% have fewer children than they wish • these couples are termed infertile • The most frequent causes of infertility in females are: • blocked oviducts • endometriosis - presence of uterine tissue outside the uterus • The most frequent cause of infertility in males is: • low sperm count

31. Alternative Methods of Reproduction • Artificial Insemination - sperm are placed in the vagina by a physician • sperm from donor • concentrated sperm from husband with low sperm count • In Vitro Fertilization - sperm and egg are mixed in a test tube • fertilized egg is placed in the female’s uterus

32. Alternative Methods of Reproduction (cont.) • Gamete Intrafallopian Transfer - eggs and sperm are mixed in a test tube • they are immediately injected into the fallopian tubes • Surrogate Mothers - individuals donate eggs and/or sperm • the surrogate mother carries the fetus