Reproduction in Humans

1. Reproduction in Humans

2. Male and female reproductive systems Function together to produce offspring Female reproductive system nurtures developing offspring Produce important hormones Introduction

3. Male Reproductive system

4. Male reproductive System • Essentially 4 parts: • Testes • Gonads, in scrotum; make gamates and releases sex hormones • Ducts • Epididymis, sperm ducts • Glands • Seminal vesicles, prostate gland • Penis • Urethra and erectile tissue. Arousal leads to filling of the tissue with blood  erection. Enables it to function as a penetrating organ in intercourse

5. Sperm cells Head Nucleus with 23 chromosomes Acrosome – enzyme-filled sac Helps sperm penetrate ovum Midpiece Mitochrondria that generate cell’s energy Tail Flagellum that propels sperm forward Male Reproductive System (cont.)

6. Male Reproductive System: Erection, Orgasm, and Ejaculation • Erection • Parasympathetic nervous system stimulates erectile tissue • Become engorged with blood • Orgasm • Sperm cells propelled out of testes into urethra • Secretions from accessory organs also released into urethra • Ejaculation • Semen is forced out of urethra • Sympathetic nerves then stimulate erectile tissue to release blood • Penis returns to flaccid state

7. Female Reproductive system

8. Female reproductive System I • Function is to: • Produce gamates (ova) • Receive the male gamates • Provide a suitable environment for: • fertilisation • Development of fetus • Provide a means of expelling the developed fetus during parturition (birth)

9. Female reproductive System II • Consists of: • Ovaries • Produce Ova, secrete progesterone + oestrogen • Oviducts (Fallopian Tubes) • Uterus • Hollow, pearshaped, muscular. Lining – endometrium – undergoes cyclical changes. Cervix part of uterus that projects thru’ from vagina • Vagina • Muscular tube adapted for reception of the penis and passage of baby out during birth.

10. Internal Female Organs

11. Gamete Production

12. Production of Gametes • Production of Gametes – Gametogenesis • Involves special cell division – meiosis • Spermatogenesis • Oogenesis

13. Spermatogenesis 1 • Each testis is packed with seminiferous tubules • In these Spermatogenesis takes place • Spermatogonia (germ cells) line the tubules dividing my mitosis to give more spermatogonia (Type A and Type B)

14. Spermatogenesis 2 • Type B Spermatogonia will undergo meiosis to eventually form spermatozoa • Type B also known as primary spermatocytes • After the first meiotic division they become secondary spermatocytes

15. Spermatogenesis 3 • Secondary spermatocytes rapidly under go the second meiotic division to form spermatids • Spermatids undergo development into spermatozoa

16. Spermatogenesis 4

17. Spermatogenesis 5 • During spermatogenesis, cells are supported by Sertoli Cells • Testes also produce testosterone from Leydig cells • Controls rate of sperm production and male characteristics

18. Spermatogenesis 6

19. Spermatogenesis 6 • Testes controlled by the anterior pituitary gland • Follicle stimulating hormone (FSH) • Interstitial Cell Stimulating Hormone (ICSH) • ICSH stimulates leydig cells to secrete testosterone  inhibits FSH and ICSH secretion. Negative feedback.

20. Oogenesis 1 • The process primordial germ cells (oogonia) become ova • Begins in fetus – oogonia divide by mitosis • By 4 or 5months, some are enlarged – potential to become gametes • Now called primary oocyte

21. Oogenesis 2 • Primary oocytes begin first stage of meiosis • By month 7 they are surrounded by follicular cells to form primary follicles • Then Meiosis stops until puberty

22. Oogenesis 3 • Once a month some of the primary oocytes continue meiosis • move to surface of ovary • One reaches maturity, others degenerate • First meiotic division finishes – secondary oocyte • Ovulation  follicle ruptures, oocyte released (once released called ovum) • 2nd Meiotic division doesn’t occur until the head of a spermatozoan enters the ovum

23. Oogenesis 4

24. Oogenesis 5 • After ovulation, the ruptured follicle fills with a blood clot • Cells enlarge •  temporary endocrine structure, the corpus luteum • Grows for 7 – 8 days secreting progesterone and oestrogen • If fertilisation/implantation don’t occur, corpus luteum degenerates after 12 – 14 days.

25. Oogenesis 6

26. Fertilisation & Pregnancy

27. Pregnancy: Fertilisation • Pregnancy – condition of having a developing offspring in the uterus • Fertilisation – process in which a sperm cell unites with an ovum; results in pregnancy • Only one sperm cell penetrates the follicular cells and the zonapellucidathat surround the ovum’s cell membrane

28. Acrosome reaction

29. After fertilization, ovum releases enzymes that cause the zonapellucida to become impenetrable to other sperm • Zygote forms from union of ovum and sperm • Contains 46 chromosomes

30. Fertilisation & Implantation

31. Pregnancy: The Prenatal Period • Time before birth • Zygote – undergoes rapid mitosis • First week after fertilization • Cleavage – rapid cell division • Morula – ball of cells resulting from cleavage • Travels down fallopian tube to uterus • Becomes blastocystwhich implants in endometrial wall • Blastocyst • Some cells (inner cell mass) become embryo • Others, along with cells from uterus, form placenta

32. Fertilisation & Implantation (brief) • Sperm motile – 1mm/min • With muscular movements of uterus get through cervix into oviducts • Fertilisation takes place (diploid) • Fertilised ovum – zygote – begins mitosis • 3 days – morula – 16 cells, enters uterus • Fluid enters morula, cells rearrange to become hollow – blastocyst • Blastocyst implants into endometrium – total 10 days

33. Pregnancy: Hormonal Changes • Embryonic cells secrete human chorionic gonadotropin(HCG) • Maintains the corpus luteum • Estrogen and progesterone • Secreted by corpus luteum and placenta • Functions • Stimulate uterine lining to thicken, development of mammary glands, enlargement of female reproductive organs • Inhibit release of FSH and LH from anterior pituitary gland (preventing ovulation) and uterine contractions

34. Pregnancy Testing Kits • These use monoclonal antibodies to test for hormone hCG • hCG produced by placenta • The test relies on the reaction between hCG and antibodies bound to coloured latex beads