Reproductive system

1. Reproductive system

2. Chromosomes • Each cell has 46 chromosomes • One pair of sex chromosomes • female XX • male XY • 22 pairs of autosomes • Each chromosome in pair (homologous pair) contains genes for same traits at same positions (allelles) • One chromosome in each pair came from each parent

3. Male reproductive system • Male reproductive structures include: • testes • ducts • accessory sex glands • supporting structures

4. Testes • Testes (testicles) • contain seminiferous tubules in which spermatozoa are made • Reproduction and survival of sperm require temperature lower than normal core body temperature

5. Spermatogenesis • Spermatogenesis • production of haploid sperm in the seminiferous tubules of the testes • Crossing-over occurs in conversion from primary - secondary spermatocyte (haploid) • Sperm produced at rate of approx 300 million per day • once ejaculated life expectancy of 48 hours

6. Spermatogenesis • Sperm cell consists of: • Head • Acrosome contains enzymes which aid penetration of secondary oocyte • Midpiece • Mitochondria for ATP production • Tail

7. Hormonal control of spermatogenesis • At puberty GnRH stimulates anterior pituitary secretion of FSH and LH • LH - assists spermatogenesis by stimulating production of testosterone • FSH - (together with testosterone) initiates spermatogenesis

8. Hormonal control of spermatogenesis • Testosterone • stimulates sperm maturation • controls • Growth, development, functioning and maintenance of sex organs • also stimulates • bone growth • protein anabolism

9. Hormonal control of spermatogenesis • Inhibin- produced by Sertoli cells and inhibits FSH to stop spermatogenesis

10. Semen • Semen • mixture of sperm and accessory sex gland secretions (seminal fluid) • Accessory sex gland secretions: • provide fluid medium for transport of sperm • provide nutrients (fructose etc) for sperm ATP production • neutralizes acidity of male urethra and female vagina • contains antibiotic (seminal plasmin)

11. Female reproductive system • Female organs of reproduction include: • ovaries • fallopian tubes • uterus • vagina • vulva • mammary glands

12. Ovaries • Paired glands homologous to testes • Follicles in cortex contain oocytes in various stages of development • Mature follicle expels oocyte - ovulation • Corpus luteum - remnants of ovulated follicle • produces hormones that promote uterine preparation for acceptance of fertilized ovum

13. Female reproductive cycle • Female reproductive cycle encompasses: • ovarian cycle • series of events associated with maturation of ovum • uterine (menstrual) cycle • changes in endometrium to prepare for reception of fertilized ovum

14. Phases of female reproductive cycle • 3 phases of reproductive cycle: • menstrual phase (~ 5 days) • ovarian follicles begin to develop (FSH) • stratum functionalis layer of endometrium shed

15. Phases of female reproductive cycle • preovulatory phase and ovulation (6-14 days) • one or more follicles mature • LH stimulates mature follicle to produce more estrogen • Estrogen (+ inhibin) from mature follicle inhibits secretion of FSH so no more follicles mature • endometrial repair

16. Phases of female reproductive cycle continued • ovulation (usually occurs on day 14 in 28 day cycle) • high estrogen exerts +ve feedback on LH and GnRH • GnRH promotes more LH (and FSH) release by anterior pituitary • LH surge causes ovulation • LH stimulates corpus luteum development

17. Phases of female reproductive cycle continued • Post ovulatory (luteal) phase (days 15 - 28) • large secretion of estrogen and progesterone (+ inhibin) by corpus luteum • if no fertilization and implantation - corpus luteum degenerates and fall in estrogen and progesterone initiates menstrual cycle • if fertilization and implantation - corpus luteum maintained by HcG from developing embryo until placenta takes over hormone production

18. Hormonal contraception • Normally, high estrogen exerts positive feedback on LH causing ovulation • Moderate levels of estrogen inhibit LH secretion • Progesterone inhibits positive feedback of estrogens on LH • Oral contraceptive pill contains progesterone and moderate levels of estrogens • Inhibition of LH prevents ovulation

19. Aging and the reproductive systems • Puberty • Increased GnRH secretion • Stimulates increased secretion of FSH and LH • secondary sexual characteristics begin to develop and potential for sexual reproduction attained • Leptin appears to play a role in onset of puberty • Mice lacking functional leptin gene remain in prepubertal state

20. Aging and the reproductive systems continued • Menopause • 40-50 yo • Pool of ovarian follicles decline • Ovaries less responsive to LH and FSH • estrogen and progesterone decrease and follicles do not undergo normal development • hot flashes, copious sweating, headache, vaginal dryness, depression, weight gain, emotional fluctuations • also increased incidence of osteoporosis, uterine cancer and breast cancer

21. Aging and the reproductive systems continued • Males often retain reproductive capacity into 80s and 90s • Decreasing levels of testosterone • decreased muscle strength • decreased sexual desire • decreased viable sperm • Prostate disorders increasingly common with age, particularly benign hypertrophy

22. Fertilisation and growth

23. Fertilisation and growth • Sperm must undergo capacitation in order to be able to fertilise ovum • Capacitance mediated by female reproductive secretions • Plasma membrane over acrosome removed • Tail beats more vigorously • Fusion of sperm with secondary oocyte (syngamy) blocks polyspermy • Fast block – depolarisation of membrane • Slow block – exocytosis of molecules that harden zona pellucida and block sperm receptors (ZP3) • Fertilisation • genetic material from haploid sperm cell and haploid oocyte merges into single diploid nucleus

24. Fertilisation and growth • Fertilized ovum (zygote) undergoes rapid mitotic divisions • Forms blastocyst which implants in endometrium approx 6 days post-fertilisation • Embryonic period (first 8 weeks) • rudiments of all adult organs formed • placenta functioning • Fetal period (8 weeks to full term (38 weeks)) • final development of organ systems

25. Maternal changes - anatomical and physiological • Enlarging uterus compresses a number of structures • stomach - leads to heartburn etc • bladder - stress incontinence (40% increase in GFR) • Weight gain • Lower back pain • lordosis

26. Maternal changes - anatomical and physiological continued • Cardiovascular changes • increase in SV • increase in cardiac output • increase in HR at given work load • increase in blood volume (mostly during latter half of pregnancy) • Uterus may compress large blood vessels reducing venous return

27. Maternal changes - anatomical and physiological continued • Pulmonary changes: • increase in tidal volume • decrease in ERV • increase in minute volume of ventilation • decrease in airway resistance • increase in oxygen uptake at given work load • Dyspnea (difficulty breathing)

28. Maternal changes - anatomical and physiological continued • other changes: • increase in appetite and decreased motility - can result in constipation • nausea, vomiting and heartburn • increased skin pigmentation • stretch marks • increased hair loss • pregnancy-induced hypertension • preeclampsia - impaired renal function due to large amounts of protein in the blood. • eclampsia - preeclampsia combined with convulsions and coma

29. Labor • Initiated by interaction of placental and fetal hormones • Inhibition of progesterone plays a role • Progesterone inhibits uterine contraction • Once initiated, labor maintained by positive feedback involving: • Stretch of cervix • Oxytocin • Three stages of labor: • Dilation • Expulsion • Placental stage

30. Exercise and pregnancy • Moderate physical activity • No evidence of inadequate blood flow to placenta • Avoid overheating • Neural tube defects

31. Inheritance

32. Inheritance • Passage of hereditary traits from one generation to the next • Homologous chromosomes • One chromosome from each parent – determines genotype • Alleles – alternative forms of a gene coding for same trait (at same location on each chromosome) • Homozygous - person with same alleles on homologous chromosomes • Heterozygous – person with different alleles on homologous chromosomes • Phenotype – physical expression of a gene

33. Inheritance • Dominant – Recessive inheritance • Dominant allele - masks presence of another allele • Recessive allele – presence masked completely • Phenotypic expression of a gene not usually simple Dominant-Recessive relationship • generally influenced by other genes and environment

34. Inheritance • Incomplete dominance • Neither allele is dominant over the other • Heterozygote has phenotype intermediate between homozygous dominant and homozygous recessive • Eg sickle cell anaemia • heterozygote has hemoglobin which is half normal and half not

35. Inheritance • Multiple allele inheritance - result of some genes having more than two alternate forms • Only two forms of allele inherited (one from each parent) • Example ABO blood group • Four ABO blood groupings result from six combinations of three different alleles of the I gene • Allele IA produces the A antigen • Allele IB produces the B antigen • Allele i produces neither the A nor B antigen

36. Inheritance • Complex inheritance • Most inherited traits controlled by effects of: • two or more genes (polygenic inheritance) • Many genes and environmental factors • One genotype can have many phenotypes or one phenotype can have many genotypes • Eg person may inherit many genes for tallness, but potential height may not be reached due to environmental factors

37. Inheritance • Sex chromosomes • Female sex chromosomes – XX • One X chromosome inactivated so only one chromosome used for protein synthesis • Male sex chromosomes – XY • Spermatocytes undergoing meiosis produce 2 sperm with X chromosomes and 2 with Y • Oocytes undergoing meiosis produce 4 ova with X chromosomes • Gender determined by father’s chromosomes

38. Inheritance • Sex chromosomes also responsible for transmission of several non-gender traits • Sex-linked inheritance • Most genes for these traits present on larger X chromosome but absent from Y chromosome • eg red-green colour blindness

39. From: http://www.come-over.to/FAS/WhoseBabyIsThis.htm Inheritance • Teratogens • Any agent or influence that causes developmental defects in the embryo • May act directly on developing embryo, or indirectly (eg on placenta) • eg fetal alcohol syndrome • Characteristic features – thin upper lip, sunken bridge of nose • Brain damage • Defective heart and other organs • Malformed limbs • Genital abnormalities