Fertilization

3. Question: What are some key structures of a mature spermatozoon? Answer: Key structures include the head (containing the acrosome and nucleus), the midpiece (containing mitochondria), and the flagellum (tail). The readings also mention the nucleus and acrosome.

4. Question: What are some key structures of an oocyte? Answer: Key structures include the cytoplasm, nucleus, granulosa cells, zona pellucida, and cortical granules.

5. Question: What are the mature gonads in males and females? Answer: In males, the mature gonads are the testes which contain seminiferous tubules. In females, they are the ovaries which contain ovarian follicles.

6. Question: Name some parts of the male reproductive tract. Answer: Parts of the male reproductive tract include the testes, spermatic cord, excurrent duct system, accessory sex glands, and the penis with associated muscles. The scrotum and prepuce are also mentioned in relation to male gross anatomy.

7. Question: Name some parts of the female reproductive tract. Answer: Parts of the female reproductive tract include the ovary, oviduct, uterus, cervix, and vagina.

8. Question: How are non-motile spermatozoa transported in the male reproductive tract before ejaculation? Answer: Non-motile, infertile spermatozoa are passively transported to the epididymis for spermiation. This process takes 4-12 days.

9. Question: What are the sources and components of secretions that mix with spermatozoa upon ejaculation? Answer: Secretions come from:

• Seminal vesicles: provide fructose and prostaglandins.

• Prostate gland: provides citric acid, acid phosphatase, zinc, and magnesium ions.

10. Question: Where is ejaculated sperm deposited in the female reproductive tract? Answer: Ejaculated sperm is deposited in the upper vagina.

11. Question: What are the stages of sperm transport in the female reproductive tract? Answer: The stages are:

1. Sperm deposited in the upper vagina (rapid elevation of pH).

2. Passage through the cervix (fast & slow phases).

3. Passage through the uterus/uterine horns.

4. Entry into the oviducts.

5. Passage up the oviducts by flagellar movement & contractions.

12. Question: What is the significance of seminal fluid in the upper vagina? Answer: Seminal fluid protects spermatozoa from the acidity of the upper vagina and causes a rapid elevation of pH from 4.3 to 7.2 within 10 seconds. This buffering effect, lasting a few minutes, allows sperm to approach the cervix at an optimal pH (~6-6.5) for motility.

13. Question: What are the two main functions of the cervix in sperm transport? Answer: The cervix functions as:

1. A major barrier to spermatozoa due to viscous, gelatinous mucus secreted by cervical cells and physical inhibition by cervical rings and folds.

2. A sperm reservoir where sperm get trapped in cervical folds and crypts, facilitated by cervical mucus.

14. Question: What are sialomucin and sulfomucin, and how do they affect sperm motility in the cervix? Answer: Sialomucin is watery and facilitates sperm motility, while sulfomucin is viscous and prevents sperm motility.

15. Question: Describe the rapid transport of sperm through the cervix. Answer: Rapid transport involves spermatozoa penetrating sialomucin and being quickly transported through the cervical canal, aided by muscular contractions of the female tract, to reach the uterus.

16. Question: Describe the slow transport of sperm through the cervix. Answer: Slow transport involves spermatozoa swimming through cervical mucus (2-3 mm/hr) and the sequential release of stored sperm from cervical crypts, ensuring continued availability of spermatozoa for fertilization for up to 3-4 days after ejaculation.

17. Question: What factors aid sperm transport in the uterus? Answer: Spermatozoa are drawn to a chemoattractant secreted by the COC and ovary. The contractile activity of the myometrium (uterine smooth muscle) also supports movement towards the oviducts.

18. Question: What is capacitation and where does it begin? Answer: Capacitation is defined as the alteration of the glycoprotein surface of spermatozoa under the influence of female tissue secretions within the reproductive tract, which enables zona pellucida penetration. Capacitation is initiated in the uterus.

19. Question: What structural changes occur in sperm cells during capacitation? Answer: Capacitation involves structural changes in the sperm cells. Specifically, it involves the alteration of the glycoprotein surface.

20. Question: Name the different parts of the oviduct. Answer: The different parts of the oviduct are the isthmus, fimbriae, ampulla, and infundibulum.

21. Question: Where does sperm storage occur in the oviduct? Answer: Sperm storage occurs in the isthmus of the oviduct.

22. Question: What is sperm hyperactivation? Answer: Sperm hyperactivation is a state of hyperactive motility achieved in the oviduct.

23. Question: What is the cumulus oocyte complex (COC)? Answer: The cumulus oocyte complex consists of the oocyte surrounded by cumulus cells. It is released when the dominant follicle ruptures.

24. Question: How is the COC captured by the oviduct? Answer: The fimbriae of the infundibulum capture the COC after it is released from the ovary. Ciliated epithelium then guides it towards the ampulla.

25. Question: How is the cumulus cloud surrounding the COC degraded by sperm? Answer: The cumulus cloud is degraded by:

1. Hyaluronidase: a hydrolytic enzyme on the surface of capacitated sperm that disintegrates cumulus cells.

2. Sperm motility: physically disrupts the cloud.

26. Question: What is the role of ZP proteins? Answer: ZP proteins allow species-specific binding of capacitated sperm, prevent any other spermatozoa from entering the ovum after fertilization, and trigger the acrosome reaction upon binding.

27. Question: Describe the acrosomal reaction. Answer: The acrosomal reaction involves:

1. Fusion of the spermatozoa plasma membrane & outer acrosomal membrane.

2. The release of acrosomal enzymes (acrosin + hyaluronidase) through pores, which digest the zona pellucida.

3. The inner acrosomal membrane and fusion proteins become exposed.

28. Question: How does sperm-oocyte fusion occur? Answer: After a sperm penetrates the zona pellucida, cortical granules migrate to the periphery of the oocyte. The oocyte plasma membrane fuses with the equatorial segment of the sperm, leading to immediate membrane depolarization and the engulfment of the fertilizing sperm. The sperm nuclear membrane disappears, and the nucleus decondenses.

29. Question: What is membrane depolarization and what is its role? Answer: Membrane depolarization is a rapid depolarization of the vitelline membrane, triggered by the influx of Na+ ions. It acts as a fast block to prevent polyspermy by creating an electrical barrier to sperm entry.

30. Question: Describe the cortical granule reaction and its purpose. Answer: The cortical granule reaction involves the release of enzymes into the perivitelline space. These enzymes include peroxidases (harden glycoproteins to form an impenetrable layer), glycosaminoglycans (attract water, forming the fertilization envelope), and proteases (destroy sperm binding sites). This serves as a slow block to prevent polyspermy.

31. Question: What cellular changes occur in the oocyte upon activation? Answer: Calcium oscillations trigger DNA synthesis, resumption of the cell cycle, NAD+ Kinase activation (leading to membrane biosynthesis), degradation of cyclin (inactivating MAP kinase and restoring meiotic cell division), and the stimulation of protein synthesis, DNA replication, and cytoplasmic maturation. The Ca2+ wave also triggers the completion of meiosis and the extrusion of the 2nd polar body and the formation of the maternal pronucleus.

32. Question: Describe the process of zygote formation. Answer: Zygote formation involves:

1. Completion of meiosis, resulting in a female pronucleus.

2. Decondensation of the sperm nucleus to form the male pronucleus.

3. The sperm centriole forming microtubules that integrate with ovum microtubules, drawing the pronuclei closer.

4. Fusion of the two pronuclei: cellular membranes break down, and chromatin intermixes before condensing into chromosomes. Embryonic development then begins.

33. Question: What is infertility defined as? Answer: Infertility is the inability to conceive after one year of regular unprotected intercourse.

34. Question: What are some potential causes of infertility? Answer: Causes can include a myriad of endogenous and exogenous factors, such as hormones, reproductive tract development, homeostasis, epigenetics and genetics, and damage related to disease conditions like cancer and its treatment.

35. Question: What are some factors contributing to male infertility? Answer: Male infertility can be caused by conditions affecting spermatogenesis, sperm quantity, sperm quality, environmental factors, and problems with sperm reaching the female reproductive tract.

36. Question: What are some factors contributing to female infertility? Answer: Female infertility can be caused by ovulation disorders, conditions of the uterus, fallopian tube damage or blockage, endometriosis, and primary ovarian insufficiency.

37. Question: What is artificial insemination (AI) or intrauterine insemination (IUI)? Answer: AI/IUI involves washing sperm and then injecting it directly into the uterus.

38. Question: Briefly describe in-vitro fertilization (IVF). Answer: IVF involves harvesting oocytes and fertilizing them in a lab, followed by the transfer of the embryo into a carrier or surrogate.

39. Question: What is intracytoplasmic sperm injection (ICSI) and when is it used? Answer: ICSI is a treatment for severe male factor sterility where a sperm is injected directly into the secondary oocyte cytoplasm after assessing sperm quality (motility and morphology).

40. Question: How is the early embryo transported after fertilization? Answer: After fertilization, the ciliated epithelium of the oviduct moves the embryo towards the uterus.

41. Question: What is the general timeline of mammalian cleavage? Answer: Mammalian cleavage occurs approximately every 12-24 hours.

42. Question: What is the end goal of early embryo transport and cleavage? Answer: The end goal is implantation of the embryo via burrowing into the uterine endometrium.

43. Question: What is early embryonic cleavage? Answer: Early embryonic cleavage refers to the initial divisions of the zygote to form the early embryo, involving rapid mitotic divisions with no growth phases, resulting in identical daughter cells called blastomeres that become smaller with each division. Blastomeres up to the 8-cell stage are totipotent.

44. Question: What occurs during compaction at the 8-cell stage? Answer: At the 8-cell stage, blastomeres tightly adhere, forming the 16-cell morula. The embryo becomes more compact, and cells lose individual identity. This is mediated by calcium-activated cell adhesion molecules, including E-cadherin and epithin.

45. Question: What is blastulation and what is the structure formed? Answer: Blastulation is the process of forming a blastocyst. The blastocyst structure includes the inner cell mass (embryoblast) which becomes the embryo proper, and the outer cell mass (trophoblast) which contributes to the fetal placenta and other extraembryonic membranes.

46. Question: What is blastocyst hatching and why is it important? Answer: Blastocyst hatching occurs prior to implantation when the embryo breaks through the zona pellucida due to proteases secreted by the blastocyst. Inability to hatch is a cause of infertility.

47. Question: Describe the apposition and adherence phases of implantation. Answer: Apposition involves the embryonic pole becoming adjacent to the uterine endometrium. Adherence is mediated by cell adhesion molecules, with the involvement of LIF, L-selectin, and trophinin.

48. Question: Describe the penetration phase of implantation. Answer: Penetration involves the syncytiotrophoblast, a differentiated multinucleated trophoblast, which is invasive and secretes digestive enzymes to work its way into the uterine tissue and establish contact with maternal blood vessels.

49. Question: What is the decidual reaction? Answer: The decidual reaction is the uterine tissue's response to the invasion of the trophoblast, setting up an immunological barrier called the decidua, which becomes the maternal portion of the placenta.

50. Question: What is gastrulation and what are the embryonic germ layers formed? Answer: Gastrulation is a series of changes in the embryonic disc (which transitions from a bilaminar disc with epiblast and hypoblast) by week 3 to form the three embryonic germ layers: ectoderm, mesoderm, and endoderm.

51. Question: What are some tissues and systems derived from the ectoderm? Answer: The ectoderm gives rise to the integumentary system (epidermis) and the nervous system.

52. Question: What are some tissues and systems derived from the mesoderm? Answer: The mesoderm gives rise to the circulatory system, the integumentary system (dermis), the musculoskeletal system, and the urogenital system.

53. Question: What are some tissues and systems derived from the endoderm? Answer: The endoderm gives rise to the digestive system, glandular tissues, and the respiratory system.

54. Question: What is the chorion and what is its function? Answer: The chorion is the fetal portion of the placenta and provides fetal oxygen and nourishment.

55. Question: What is the amnion and what is its function? Answer: The amnion encloses the embryo, is filled with amniotic fluid, and provides physical protection from impact.

56. Question: What is the yolk sac's role in early development? Answer: The yolk sac is the initial site of blood cell production (hematopoiesis), synthesizes various proteins, and contains primordial germ cells (PGCs).

57. Question: What is the allantois' function in non-mammals? Answer: In non-mammals, the allantois functions in independent waste storage and respiration.

58. Question: What are the three stages of prenatal development and their approximate timelines? Answer:

• Germinal Period: Fertilization until implantation (zygote until embryonic disc).

• Embryonic Period: Gastrulation until the 8th week of pregnancy (Neurulation à Organogenesis).

• Fetal Period: From the 9th week of pregnancy until parturition (Age of viability 22 to 28 weeks).

59. Question: What hormones are necessary for maintaining early pregnancy and where are they synthesized? Answer: Elevated levels of estrogens (E2) and progesterone (P4) are necessary. The corpus luteum synthesizes progesterone (P4). Syncytiotrophoblast cells synthesize human chorionic gonadotropin (hCG).

60. Question: What is the role of hCG in early pregnancy? Answer: hCG maintains the corpus luteum (CL) until gestational week 5-6.

61. Question: What hormones are synthesized by the placenta during mid/late pregnancy? Answer: The placenta synthesizes hCG, estriol (E3), progesterone (P4), PTHrP (parathyroid hormone-related peptide), and CRH (corticotropin-releasing hormone).

62. Question: What are some functions of estriol (E3) during pregnancy? Answer: Estriol (E3) is involved in uterine myometrium regulation, increasing oxytocin receptors, and the development of breast ducts.

63. Question: What are some functions of progesterone (P4) during pregnancy? Answer: Progesterone (P4) suppresses uterine contractions, maintains the cervical plug, and promotes the development of milk glands.

64. Question: What is the role of oxytocin and prostaglandins in labor? Answer: Oxytocin (produced in the hypothalamus, released by the posterior pituitary, and produced in the uterus) and prostaglandins (produced by uterine glands, specifically PGF2α & PGE2) mediate uterine contractions. They stimulate Ca2+ channels in the plasma membrane for muscle contraction.

65. Question: What are the three pathways activated during parturition by fetal adrenal gland hormones? Answer: The three pathways are: I. Positive Feedback II. Uterine Sensitivity III. Maternal Hypothalamic-Pituitary-Oxytocin Pathway

66. Question: Describe the positive feedback loop involving CRH in parturition. Answer: The fetal hypothalamus releases CRH, which stimulates the fetal anterior pituitary to release ACTH. ACTH stimulates the fetal adrenal gland to release fetal cortisol. The placenta also produces CRH, and fetal cortisol stimulates the placenta to produce more CRH, creating a positive feedback loop. The accumulation of CRH is the most important determinant of primate parturition and stimulates fetal lung maturation and surfactant production.

67. Question: How does the fetal adrenal gland influence uterine sensitivity during parturition? Answer: The fetal adrenal gland releases DHEAS, which is converted to estriol (E3) in the placenta. The placenta also produces prostaglandins and oxytocin, which stimulate changes in the maternal myometrium, including more oxytocin receptors, more prostaglandin receptors, and more gap junctions.

68. Question: Describe the maternal hypothalamic-pituitary-oxytocin pathway during labor. Answer: The maternal hypothalamus produces oxytocin, which is released from the posterior pituitary. Oxytocin binds to the myometrium, stimulating Ca2+ opening and muscle contraction. Cervical stretch during labor also triggers a positive feedback loop, leading to more oxytocin release.

69. Question: What are the roles of oxytocin after labor? Answer: After labor, oxytocin maintains myometrium muscle tone, reduces hemorrhaging from uterine arteries, and promotes uterus involution (size reduction). The uterus reduces in weight from about 1 kg after birth to 60 g 6 weeks post-partum.