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Understanding Human Reproductive Systems: Asexual vs. Sexual Reproduction

This chapter explores human reproduction, focusing on both asexual and sexual reproduction methods. Asexual reproduction involves a single parent producing genetically identical offspring, efficiently suited for stable environments. Methods include budding, fragmentation, and parthenogenesis. In contrast, sexual reproduction involves the fusion of gametes, promoting genetic diversity vital for adapting to changing environments. The chapter details mammalian reproductive systems, including male and female anatomy, spermatogenesis, oogenesis, hormonal regulation, and the intricate processes leading to fertilization and development of embryos.

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Understanding Human Reproductive Systems: Asexual vs. Sexual Reproduction

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  1. Chapter 48 Reproduction

  2. Asexual reproduction • A single parent endows its offspring with genes identical to its own • Energy efficient • Most successful in a stable environment

  3. Means of asexual reproduction • Budding • Part of the parent’s body grows and separates from the rest of the body • Fragmentation • The parent’s body breaks into pieces • Each piece can grow into a new animal • Parthenogenesis • An unfertilized egg develops into an adult

  4. Asexual reproductionby budding

  5. Sexual reproduction • Offspring produced by fusion of two gametes • Ovum • Sperm • A fertilized egg (zygote) forms • Promotes genetic variety and is adaptive in an unstable environment

  6. External fertilization • Mating partners typically release eggs into the water simultaneously • Internal fertilization • Male delivers sperm into the female’s body • Hermaphroditism • Single individual produces eggs and sperm

  7. Human male reproductive system • Testes • Housed in the scrotum • Contain the seminiferous tubules, where sperm production takes place • Interstitial cells secrete testosterone • Sertoli cells produce signaling molecules and a fluid that nourishes sperm cells

  8. Human male reproductive system, cont. • Sperm • Stored in the epididymis and vas deferens • During ejaculation, sperm pass from the vas deferens to the ejaculatory duct and into the urethra

  9. Human male reproductive system, cont. • Penis • Three columns of erectile tissue • Two cavernous bodies • One spongy body that surrounds the urethra • Erectile tissue becomes engorged with blood and causes erection

  10. Male reproductivesystem

  11. Spermatogenesis • Takes place in the seminiferous tubules • Spermatogonia divide by mitosis • Head of a sperm consists of the nucleus and an acrosome, containing enzymes that help penetrate the egg

  12. Spermatogenesis in the seminiferous tubules

  13. Spermatogenesis

  14. Sperm pass in sequence through • Seminiferous tubes of the testes • Epididymis • Vas deferens • Ejaculatory duct • Urethra

  15. Structure of amature sperm

  16. Endocrine regulation of reproduction in the human male • Testosterone establishes and maintains • Primary sex characteristics • Secondary sex characteristics

  17. Internal structure of the penis

  18. Endocrine regulation of reproduction involves the • Hypothalamus • GnRH • Pituitary gland • FSH and LH • Testes • Testosterone • ABP and inhibin

  19. Principal male reproductive hormones

  20. Regulation of reproduction in the male

  21. Human female reproductive system • Ovaries • Produce gametes • Steroid hormones estrogen and progesterone • Fertilization takes place in the oviducts

  22. Female reproductive system

  23. Human female reproductive system, cont. • Uterus • Incubator for the embryo • Endometrium thickens each month • Cervix extends into the vagina

  24. Human female reproductive system, cont. • Vagina • Lower part of the birth canal • Vulva includes the labia majora, labia minora, vestibule, clitoris, and mons pubis

  25. Female reproductive system,anterior view

  26. Human female reproductive system, cont. • Breasts • Function in lactation • Prolactin stimulates milk production • Oxytocin stimulates milk ejection from the alveoli into the ducts

  27. Development of a human ovum • Oogenesis takes places in the ovaries • Oogonia differentiate into primary oocytes • Primary oocyte and granulosa cells make up a follicle

  28. Oogenesis

  29. Development of a human ovum, cont. • As the follicle grows • Connective tissue cells form a layer of theca cells • Primary oocyte undergoes meitosis, giving rise to a secondary oocyte and a polar body

  30. Development of follicles in the ovary

  31. Development of a human ovum, cont. • During ovulation • The secondary oocyte is ejected and enters an oviduct to be fertilized • The part of the remaining follicle develops into a corpus luteum

  32. Endocrine regulation of reproduction • Preovulatory phase • GnRH stimulates the pituitary to secrete FSH and LH • Estrogen stimulates endometrium development • LH stimulates final maturation of the follicle and ovulation

  33. Endocrine regulation of reproduction, cont. • Postovulatory phase • LH promotes development of the corpus luteum • The corpus luteum secretes progesterone and estrogen • If fertilization does not occur, the corpus luteum degenerates, hormone levels fall, and menstruation occurs

  34. Principal female reproductive hormones

  35. Feedback mechanisms in endocrine regulation of female reproduction

  36. Physiological changes that occur during sexual response • Sexual excitement • Plateau • Orgasm • Resolution

  37. Human fertilization • Fusion of secondary oocyte and sperm to form a zygote • Embryo implants in the uterus • hCG is the hormone that maintains the corpus luteum • Estrogen and progesterone • Secreted by corpus luteum (first trimester) and then by placenta

  38. Fertilization

  39. Events following fertilization

  40. Human birth process • Several hormones, including estrogen, oxytocin, and prostaglandins regulate parturition • Labor • Divided into three stages • The baby is delivered during the second stage

  41. Contraception • Hormonal methods, such as oral contraceptives • Intrauterine devices • Condoms and contraceptive diaphragms • Sterilization (vasectomy or tubal ligation)

  42. Sterilization

  43. Abortions • Spontaneous miscarriages occur without intervention • Induced abortions • Therapeutic performed to maintain the mother’s health, as birth control, or when the embryo is thought to be grossly abnormal

  44. Common sexually transmitted diseases (STDs) • Chlamydia • Gonorrhea • Syphilis • Pelvic inflammatory disease (PID) • Genital herpes • HIV

  45. Endocrine regulation of reproduction involves the • Hypothalamus • GnRH • Pituitary gland • FSH and LH • Testes • Testosterone • ABP and inhibin

  46. Some types of endocrine signaling

  47. Majorchemical groups of hormones

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