Reproductive system

1. Reproductive system

2. Hormonal Regulation of Reproduction • Hypothalamus: pulse generator • Gonadotropin releasing hormone (GnRH) • Anterior pituitary • Luteinizing hormone (LH) • Follicle stimulating hormone (FSH) • Gonads produce steroid and peptide hormones • Gonads are the main source of sex steroids • Peptide hormones: inhibin and activin

3. Feedback Loops Control Gonadotropin Release Internal andenvironmentalstimuli CNS GnRH Hypothalamus Short-loop negative feedback KEY Stimulus Anteriorpituitary Integrating center Efferent pathway Effector Long-loop feedbackmay be negativeor positive Tissue response LH FSH Gonads(ovaries or testes) Females only Endocrinecells Gameteproduction Steroid andpeptide hormones

4. Synthesis Pathways for Steroid Hormones Cholesterol Progesterone Dihydro-testosterone(DHT) Testosterone aromatase Corticosterone Cortisol Estradiol Aldosterone Intermediate steps

5. Male Reproductive System Figure 27.1

6. Testes protection - Testicular Thermoregulation • Sperms are not produced at core body temperature • In the scrotum, the testes are kept 2-3°C cooler than in the pelvic cavity. This is essential for sperm production. • Cooling mechanisms • The cremaster muscle contains strips of the internal abdominal oblique muscle around the spermatic cord. • It can elevate or lower the testes. • The dartos muscle is a subcutaneous layer of smooth muscle that wrinkles skin reducing surface area of scrotum. Can lifts testis upwards • The pampiniform plexus is an extensive network of veins that surround the testicular artery in the spermatic cord, keeping the testes cooler countercurrent heat exchange that cools arterial blood entering testis

7. Cells in the testes – 3 types • 2 populations found in the Seminiferous tubule • Germinal epithelium – lines the lumen of the tubules • consisting of several layers of germ cells in the process of becoming sperm • Sustentacular (Sertoli) cells. • Between the seminiferous tubules are clusters of interstitial (Leydig) cells, the source of testosterone (will be discussed later with hormonal control).

9. The functions of Sertoli cells and BTB • Sertoli cells protect the germ cells and promote their development. Tight junctions between adjacent sustentacular cells form a blood-testis barrier (BTB) • The fluid inside the tubules contains high levels of androgens, potassium and amino acids • The BTB prevents the immune system from attacking the developing spermatozoa (contain specific Ag that are not found on any other cell) • Sertoli cell supply nutrients to the developing sperms • Phagocytize cytoplasm shed by spermatids • Secrete inhibin- negative feedback loop for FSH • Secrete androgen-binding-protein (ABP) – binds testosterone inside tubules to maintain high levels

10. Spermatogenesis • Cells making up the walls of seminiferous tubules are in various stages of cell division • These spermatogenic cells give rise to sperms in a series of events • Mitosis of spermatogonia, forming spermatocytes • Meiosis forms spermatids from spermatocytes • Spermiogenesis – spermatids to sperm

11. Ovulation with Fertilization Is Followed by Final Step of Meiosis FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated (may notoccur) Reproductive adult 4 Second meioticdivision Spermatids Disintegrates Egg releasedfrom ovary atovulation. Secondary gamete divides. develop into 23 chromosomes(haploid) Sperm FERTILIZATION 6 One primary oocyteyields 1 egg. One primary spermatocyteyields 4 sperm. 5 Secondpolar bodydisintegrates. Unfertilized eggpasses out of body. Zygote Figure 26-5, steps 1–6

12. Spermiogenesis: Spermatids to Sperm • Spermiogenesis – spermatids lose excess cytoplasm and form a tail, becoming sperm spermiogenesis spermatogenesis http://distance.stcc.edu/AandP/AP/AP2pages/reprod/spermato.htm

13. Mitosis of Spermatogonia • Spermatogonia – outermost cells in contact with the epithelial basal lamina • Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells • Type A cells remain at the basement membrane and maintain the germ line • Type B cells move toward the lumen and become primary spermatocytes

14. Spermatogenesis Spermatogonium (2n) differentiation Primary spermatocyte (2n) Primary spermatocyte Division – 1st meiosis secondary spermatocyte (n) 2nd meiosis Spermatid (n)

15. Spermiogenesis spermatozoa

16. Hormonal Regulation of Testicular Function • The hypothalamus releases gonadotropin-releasing hormone (GnRH) • GnRH stimulates the anterior pituitary to secrete FSH and LH • FSH causes sustentacular cells to release androgen-binding protein (ABP) • LH stimulates interstitial cells to release testosterone • ABP binding of testosterone enhances spermatogenesis

17. Testosterone Inhibits the Hypothalamus and Anterior Pituitary GnRH Hypothalamus Anteriorpituitary FSH LH Leydigcells Spermatogonium Inhibin Testosterone (T) Spermatocyte Testes Sertolicell Secondmessenger To bodyfor secondaryeffects Cellproducts Sertolicell Androgen-bindingprotein (ABP) ABP T Figure 26-11 (9 of 9)

18. Testosterone • The principal androgen (male sex hormone) is testosterone. • This steroid is manufactured by the interstitial (Leydig) cells of the testes. • Secretion of testosterone increases sharply at puberty and is responsible for the development of the secondary sexual characteristics of men. • Testosterone is also essential for the production of sperm.

19. Effects of Androgens gonads and Secondary Sex Characteristics Table 22.2

20. Accessory Glands Contribute to Semen

21. Ovaries • Ovaries contain the ovarian follicles • Each follicle consists of an immature egg (oocyte) • Cells around the oocyte are called: • Follicle cells (one cell layer thick) • Granulosa and theca cells (when more than one layer is present) • The follicles and the oocytes are going through cyclic development – ovarian cycle

22. The ovarian cycle • Combination of follicles and oocyte development • Divided to 2 major periods (phases) • Follicular phase – period of follicle growth (days 1–14) • Luteal phase – period of corpus luteum activity (days 14–28) • The 2 phases are “separated” by Ovulation (release of the secondary oocyte from a tertiary follicle)

23. Luteal phase Follicular phase ovulation http://biology.clc.uc.edu/courses/bio105/sexual.htm

24. Follicular development - Folliculogenesis • The folliculogenesis occurs during follicular phase • Primordial Follicle –flattened granulosa cell layer, basement membrane, oocyte • Primary Follicle – growth of oocyte, zonapellucida formation, cuboidal granulosa cells • Secondary Follicle – add layers of granulosa cells, formation of theca cells

25. Folliculogenesis • Early Tertiary Follicle – antrum formation, zona pellucida thickens, theca interna and theca externa form, basement membrane is still present between theca and granulosa cells, blood vessels are in the theca cell layer but not in follicle • Tertiary/pre-ovulatory/Graffian – full size follicle ready to ovulate; oocyte surrounded by corona radiata (granulosa cells) and attached to follicular wall by the comulus oophorus

26. Follicular Phase • A few follicles begin to develop from primordial follicle • Oocyte grows, granulosa cells proliferate • Zona pellucida and antrum form

27. Follicular Phase • Dominant follicle continues development, rest regress • Corona radiata develops • Graafian follicle = mature follicle • Ovulation

33. Photomicrograph of an early tertiary follicle http://www.endotext.org/female/female1/femaleframe1.htm

35. Luteal Phase • After ovulation, the ruptured follicle collapses, granulosa cells enlarge, and along with internal thecal cells, form the corpus luteum • The corpus luteum secretes progesterone and estrogen • If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans) • If pregnancy does occur, the corpus luteum produces hormones until the placenta takes over that role (at about 3 months)

36. Luteal Phase • Ruptured follicle  gland = corpus luteum • Corpus luteum secretes mostly progesterone • Corpus luteum reaches max activity 10 days, then degenerates

37. Corpus luteum • The fate of the corpus luteum depends on fertilization: • If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans) • If pregnancy occurs, the corpus luteum produces hormones until the placenta takes over that role (at about 3 months)

38. The Ovarian Cycle

39. Oogenesis – oocyte development FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated (may notoccur) Reproductive adult 4 Second meioticdivision Spermatids Disintegrates Egg releasedfrom ovary atovulation. Secondary gamete divides. develop into 23 chromosomes(haploid) Sperm FERTILIZATION 6 One primary oocyteyields 1 egg. One primary spermatocyteyields 4 sperm. 5 Secondpolar bodydisintegrates. Unfertilized eggpasses out of body. Zygote

40. Oogenesis • Ovum production • Occurs monthly in ovarian follicles • Part of ovarian cycle • Happens during the Follicular phase (preovulatory)

41. Oogenesis • Production of female sex cells by meiosis • In the fetal period, oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients • Primordial follicles appear as oogonia are transformed into primary oocytes • Primary oocytes begin meiosis but stall in prophase I

42. Oogenesis: Puberty • At puberty, one activated primary oocyte produces two haploid cells • The first polar body • The secondary oocyte • The secondary oocyte arrests in metaphase II and is ovulated • If fertilized, the second oocyte completes meiosis II, yielding: • One large ovum (the functional gamete) • A tiny second polar body

43. Oogenesis

44. Oogonia(multiple by mitosis until 5th month of fetal development) Arrested development (until shortly before birth) Primary oocytes (arrest in prophase I) ___________________________________________________________ Puberty Oocyte in Graafian follicle – complete meiosis I Secondary oocyte first polar body Arrested in metaphase II If fertilization occur Complete meiosis II Ovum second polar body

45. Actions of Estrogens from growing follicle

46. Actions of Progesterone from the Corpus luteum

49. Uterine cycle • Repeating series of changes in the endometrium • Menses • Degeneration of the endometrium • Menstruation • Proliferative phase • Restoration of the endometrium • Secretory phase • Endometrial glands enlarge and accelerate their rates of secretion

50. Beginning of new cycle - Menstrual Phase of the Uterus • If fertilization does not occur, the corpus luteum degenerates and estrogen and progesterone levels decrease. • The lack of estrogen and progesterone leads to the collapse of the endometrium, which in turn leads to menstruation.