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The reproductive system

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The reproductive system

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  1. The reproductive system • Overview • Male reproductive system • Female reproductive system • Fertilization, implantation and pregnancy • Parturition and lactation

  2. The reproductive system • Overview • Male reproductive system • Female reproductive system • Fertilization, implantation and pregnancy • Parturition and lactation

  3. Role of the reproductive system: Gamete production Fertilization Zygote (offspring) development Overview

  4. The reproductive system • Overview • Male reproductive system • Female reproductive system • Fertilization, implantation and pregnancy • Parturition and lactation

  5. Testes: main organs: - produce gametes (spermatocytes) - secrete male hormone, testosterone (Leydig cells = interstitial cells) Male reproductive system

  6. Spermatogonia multiply at the base of the seminiferous tubules. Their growth, development and maturation are supported by the Sertoli’s cells. They migrate toward the lumen while undergoing meiosis  spermatocytes

  7. At puberty, the hypothalamus secretes GnRH  Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) LH: stimulates secretion of testosterone by the Leydig cell FSH: promotes sperm production by the Sertoli’s cell. Testosterone must also be present for the Sertoli’s cells to work adequately Testosterone produces a negative feed-back on LH Inhibin, secreted by the Sertoli’s cell have a negative feedback on FSH Control of spermatogenesis and hormone production in males

  8. 1- to help spermatogenesis 2- promote the development of secondary sexual characters and behavior: - stimulate the development of the reproductive organs - stimulate the male pattern growth of hair (chest, legs...) - the skin become thicker, coarser and darker - cause hypertrophy of the larynx with a deepening of the voice - stimulate increase of bone and muscle mass - stimulate the activity of the sebaceous glands - increase the metabolic rate - promote also epiphyseal disc closure so growth in length will stop - promote male sexual behavior 3- has a negative feed-back effect on the hypothalamus Testosterone

  9. 1- Arousal: Thoughts, visual impulses, massages of the penis  sacral parasympathetic NS dilatation of the arteries supplying blood to the penis ---> erection. 2- Ejaculation: sympathetic NS  rhythmic peristaltic waves in the ducts and perineal muscles  ejection of semen or ejaculation. climax or orgasm. The semencontains the secretion from the various glands along the reproductive ducts with 20 to 100 millions sperm per ml. Sperm can survive up to 72 h in the female body. 3- Resolution: Ejaculationt is followed by a relaxation period during which a man cannot achieve another orgasm (NE in synapse has been exhausted and needs to be resynthesized). Sexual response in males

  10. The reproductive system • Overview • Male reproductive system • Female reproductive system • Fertilization, implantation and pregnancy • Parturition and lactation

  11. Role: - form gametes (oocytes) - support zygote development Characteristics: - cyclic changes in activity - restricted period of fertility - limited gamete production Female reproductive system

  12. Oocytes mature during fetal development  at birth, arrest in meiosis I Development resumes during each menstrual cycle: upon ovulation, egg is arrested in meiosis II Development will resume only upon fertilization by a spermatocyte Gamete development

  13. The menstrual cycle • Several cycles: • Hypothalamus-pituitary gland cycle • Ovarian cycle - follicular cycle - hormonal cycle • Uterine cycle

  14. At puberty, GnRH stimulates the release of FSH FSH promotes follicle (egg and its surrounding layers) development LH secretion peaks in mid-menstrual cycle Secretions of LH and FSH are controlled by negative feedback from progesterone and estrogen, respectively (see ovarian cycle) Menstrual cycle: Hypothalamus-pituitary gland

  15. Under the influence of FSH: - Several follicles develop. Only one will mature to ovulation. Follicular cells multiply - Primordial follicle primary follicle  secondary follicle  Graafian follicle - Synthesis of estrogen by granulosa cells Ovarian cycle: follicular phase

  16. promotes rapid growth in young girl, follow by closing of the epiphyseal disc induces development of the breasts stimulates fat deposit under the breast, in the hip areas promotes widening of the pelvis induces hair growth in the pubic, axillary areas Promote female behavior Promotes a negative feedback on FSH Role of estrogen

  17. Under the influence of LH: Burst of antrum fluid secretion by Graafian follicle rupture  the oocyte and its corona radiata are ejected toward the Fallopian tube  ovulation Ovarian cycle: ovulation

  18. Under the influence of LH mostly (and some FSH): Remaining granulosa cells form the corpus luteum The corpus luteum synthesizes progesterone under the influence of LH and estrogen under the influence of FSH. Ovarian cycle: luteal phase 1

  19. High levels of progesterone and estrogen have a negative feedback on LH and FSH (respectively) LH and FSH levels drop Corpus luteum no longer active  corpus albicans Progesterone and estrogen levels drop The negative feedback loop weakens FSH can increase against  beginning of a new cycle Ovarian cycle: luteal phase 2

  20. Proliferative phase- Estrogen promotes uterine endometrium development (multiplication of endometrial cells) Secretory phase- under the influence of progesterone  promotes nutrient secretion from lining for egg implantation Uterine cycle

  21. Figure 22.15

  22. Figure 22.16

  23. Figure 22.17

  24. The reproductive system • Overview • Male reproductive system • Female reproductive system • Fertilization, implantation and pregnancy • Parturition and lactation

  25. Maximum survival of sperm: up to 5 days Maximum survival of oocyte: 24 h If coitus during fertile period  oocyte fertilization in Fallopian tube. The fertilized oocyte completes meiosis II, the nuclei fuse  diploid zygote formed Fertilization

  26. What is the difference between identical twins and fraternal twins? Twins

  27. What is the difference between identical twins and fraternal twins? Twins

  28. The fertilized egg undergoes several division as it is sliding toward the uterus where it implants after about 6 days (unfertilized eggs are destroyed and phagocytized by macrophages) Some cells of the eggs develop into the embryo, other cells form the membrane and placenta. The placental cells start (within 10 days) secreting human chorionic gonadotropin (hCG) hCG has a role similar to LH: it sustains the activity of the corpus luteum (LH level decreases due to negative feedback from progesterone) Implantation

  29. At 3 months of pregnancy, the placenta secretes large enough amount of estrogen and progesterone to replace the corpus luteum (which then disappears) Estrogen promotes: development of breast duct tissue, breast fatty deposit growth of uterine muscle Progesterone promotes: - mammary gland development - suppress uterine contraction - maintain secretory glands in uterus - lactogen secretion (hormone involved in mammary gland development) Pregnancy

  30. A teratogen is a compound which can induce congenital malformations in developing babies Can you name some of these compounds? Clinical applications

  31. A teratogen is a compound which can induce congenital malformations in developing babies Can you name some of these compounds? Which stage of development is most susceptible? Prior to implantation First 3 months (embryonic stage) 3 months to birth (fetal stage) Clinical applications thalidomide dioxin

  32. Which stage of development is most susceptible? Prior to implantation First 3 months (embryonic stage) 3 months to birth (fetal stage) Embryonic stage, because all organs are being formed at this stage. Organs mature during the fetal stage and are not as susceptible to malformation. Clinical applications thalidomide dioxin

  33. The reproductive system • Overview • Male reproductive system • Female reproductive system • Fertilization, implantation and pregancy • Parturition and lactation

  34. Pregnancy should last 9 months Stretch of the uterus triggers increased contraction and oxytocin release Oxytocin reinforces uterine contraction  Baby’s birth Parturition

  35. First few days after birth, secretion of colostrum, a watery liquid rich in proteins. Then, milk is secreted by the mammary glands under the influence of prolactin Milk release is promoted by oxytocin (milk-let-down reflex) Lactation

  36. Clinical applications: Birth control

  37. Clinical applications: male circumcision phimosis

  38. Female genital mutilation

  39. Clinical application: female genital mutilation