Cell Bio Gametogenesis (11)

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Cell Bio Gametogenesis (11)
2013-09-23 17:03:53
Cell Biology

Exam 2
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  1. embryonic period
    weeks 0-8; type of prenatal (before birth) development period
  2. fetal period
    weeks 9-38; type of prenatal (before birth) developmental period
  3. gametes
    specialized germ cells from the male and the female; haploid as a result of meiosis
  4. gametogenesis
    • formation of fully-developed gametes
    • in males this starts in puberty
    • in females it starts before birth and ENDS at fertilization
  5. During which period of fetal development is the embryo usually not susceptible to teratogens?
    the first two weeks of pregnancy
  6. What type of cells does mitosis produce?
    all of the somatic cells (all cells in the body EXCEPT for the gametes)
  7. oogonia that have already undergone mitosis then begin meiosis to become primary oocytes, which are arrested in _______________ from before birth until puberty
    • primary oocytes are arrested in prophase of meosis I from before birth until puberty
    • - they don't proceed to meiosis II until ovulation
  8. What's one difference between male and female meiotic division?
    • In females there are unequal meiotic divisions that produce a primary oocyte and a small polar body --> then another unequal meiotoc division that produces a secondary oocytes and a second small polar body
    • In males, meiotic divisions are all equal and all meiotic derivatives produce spermatids

  9. Describe the structure of sperm:
    • 1) Acrosome: specialized golgi derived structure; found in the head; enzyme filled
    • 2) Mid-piece: houses mitochondria to provide energy for flagellum (tail)
    • 3) flagellum tail
  10. primary spermatocytes
    (4N; 92; tetraploid) formed from spermatogonial stem cells dividing by mitosis; are initially diploid and are undergo meiosis
  11. secondary spermatocytes
    (2N; 46; diploid) primary spermatocytes that have undergone meosis I; they undergo a meiosis II which results it HAPLOID spermatids
  12. one primary spermatocyte produces:
    four spermatids
  13. spermiogenesis
    • the process by which spermatids are remodeled to form mature sperm (spermatozoa)
    • elongation, tail development, cytoplasm shed
  14. Sertoli cells
    line the periphery of seminiferous tubules; support and nurture the germ cells and regulate spermatogenesis (analogous to zona pellucida)
  15. Leydig cells
    make testosterone (analogous to theca cells)
  16. When is the primary oocyte in a primordial follicle?
    After the zona pellucida and the single layer of follicle cells form
  17. When is the primary follicle formed?
    when the primary oocyte enlarges during puberty; follicular epithelial cells become cuboidal and then columnar, forming the primary follicle
  18. HPO Axis
    • Hypothalamus-Pituitary-Ovary Axis refers to the effects of the hypothalamus, pituitary gland, & gonads as a whole because they often behave in cooperation

    • • the hypothalamus produces GnRH
    • • the anterior pituitary produces LH & FSH
    • •the gonads produce estrogen and testosterone
  19. Gonadotropin Releasing Hormone (GnRH)
    released from the hypothalamus and targeted for the anterior pituitary; causes the synthesis and secretion of LH and FSH
  20. Follicle Stimulating Hormone (FSH)
    released from the anterior pituitary and targeted for the ovary; stimulates ovarian follicle growth, differentiation, and steroidogenesis
  21. What does FSH do?
    stimulates 4-12 ovarian (primordial) follicles to grow, differentiate, and secrete estrogen (as well as other steroid hormones)
  22. Luteinizing Hormone (LH)
    released from the anterior pituitary and targeted for the ovary; stimulates ovulation, corpus luteum formation and steroidogenesis
  23. What does LH do?
    stimulates ovulation, corpus luteum formation, and steroid hormone production, like progesterone
  24. Estrogens
    released from the follicle cells in the ovary and targeted for the uterus, vagina, oviduct, & mammary glands; controls growth & differentiation of targets
  25. Progestins
    released from the follicle cells in the ovary and targeted for the uterus, vagina, oviduct, & mammary glands; controls growth & differentiation of targets
  26. What are the sources, targets, and actions of the following hormones?
  27. Ovarian stroma
    a highly vascular tissue that consists of spindle-shaped stromal cells similar to fibroblasts and arranged in a characteristic whorled texture
  28. Corpus luteum ('yellow body')
    develops from ovarian follicle during luteal phase of the menstrual cycle after a secondary oocyte from the follicle is released during ovulation; involved in the production of progesterone
  29. corpus albicans
    regressed form of the corpus luteum; may persist as a scar on the surface of the ovary
  30. cumulus cells
    epithelial cells that have lots of cytoplasmic ridges directly connecting them to the oocyte; they're an important source of nutrients for the oocyte
  31. What does the hypothalamus synthesize at the beginning of menstrual cycle?
    GnRH (gonadotropin releasing hormone)
  32. What determines whether a follicle grows quickly or not?
    • the number of FSH receptors on it's membrane surface; the more receptors, the faster and larger the follicle will get
    • a dominant follicle continues to mature and is ultimately ovulated (takes 2-3 menstrual cycles to complete)
    • remaining developing follicles degenerate via apoptosis
  33. As estrogen levels rise, they stimulate the ________ to rapidly make __
    • pituitary makes FSH
    • stimulates estrogen synthesis from ovarian follicle
    • once a threshold is reached, it signals the PITUITARY to rapidly synthesize & secrete LH
    • FSH --> threshold estrogen --> LH surge
  34. LH surge
    the trigger for ovulation and release of the primary oocyte from prophase of Meiosis I
  35. What happens after a primary oocyte finishes Meiosis I?
    • It releases the first polar body and then enters Meiosis II where it is arrested at METAPHASE (II)
    • arrested at metaphase II it's called a mature, secondary oocyte
  36. What triggers a secondary follicle to rupture, expelling the secondary oocyte by contraction of the smooth muscle-like _____ cells?
    • prostaglandins - lipid paracrine hormone
    • the smooth muscle-like THECA cells contract and expel the secondary follicle
  37. What surrounds the ovulated secondary oocyte?
    the zona pellucida & one or more layers of follicle cells called the corona radiata
  38. How soon after the LH surge does ovulation occur?
    within 12-24 hours
  39. Down's Syndrome
    caused by non-disjunction or translocation of chromosome 21
  40. oocyte atresia
    process of oocyte death; over 99% of oocytes are apoptosed, with under .01% actually ovulated
  41. What are 9 human health issues that revolve around gametogenesis?
    • Thalidomide birth defects
    • Rubella (German Measles) birth defects
    • Down's Syndrome (Trisomy 21)
    • Angelman Syndrome (Chromosome 15 deletion) Prader-Willi syndrome (Chromosome 15 deletion) Premature menopause (accelerated oocyte atresia) Egg donation
    • Infertility
    • Effect of maternal age on birth defects
  42. mittelschmerz
    the abdominal pain associated with ovulation in some women caused by slight bleeding into the peritoneal cavity (abdomen)
  43. What is an outer physical indicator of ovulation? What is a better indicator?
    • mittelschmerz (abdominal pain)
    • a better indicator is a slight drop in basal body temperature followed by a gradual rise after ovulation
  44. anovulation
    • a menstrual cycle where the ovaries don't release an oocyte therefore ovulation doesn't happen
    • often caused by inadequate release of FSH and LH from the anterior pituitary
  45. What are three things that can be used to induce ovulation?
    • FSH, LH (gonadotropins) or clomiphene citrate
    • a side effect of gonadotropin ovulation induction is a 10-fold increase in the incidence of multiple pregnancies
  46. miscarriage
    • spontaneous end of a pregnancy before fetal viability
    • almost 1/5 spontaneous abortions are caused by insufficient progesterone production
    • some women who have had multiple miscarriages are given progesterone
  47. contraception
    prevents ovulation because increased estrogen levels (with or without increased progesterone levels) act to negatively feedback on the hypothalamus and/or the AP to inhibit GnRH, FSH, and/or LH
  48. After penetration what is the basic pre-fertilization step?
    • sperm swim up the cervical canal and are drawn up through the uterus & fallopian tubes by muscular contractions/ciliary movements
    • females do 2/3 of the work
    • makes do 1/3 of the work
  49. When does fertilization officially begin?
    • when there's contact between the sperm and the secondary oocyte plasma membrane
    • after this occurs the oocyte finishes meiosis II and becomes a mature oocyte
  50. What is the site of fertilization?
    • the ampulla (out-pouching of fallopian tube)
    • the fallopian tube is therefore what transfers the zygote to the body of the uterus
  51. ovaries
    • almond shaped glands that produce estrogen and progesterone, hormones responsible for secondary female sex characteristics and pregnancy regulation
    • they produce and maintain oocytes
  52. What happens to the corpus luteum IF an oocyte is fertilized?!
    • it becomes the corpus luteum of pregnancy, fortified by increased progesterone production
    • this corpus luteum of pregnancy is functional for 20 weeks
    • after this 20 weeks the placenta makes enough estrogen & progesterone to support the pregnancy
  53. What prevents the corpus luteum from degenerating and where is the source of this prevention?
    • human chorionic gonadotropin (hCG) prevents the corpus luteum from degrading
    • hCG comes from the implanted blastocyst (embryo)
  54. What is one major cause of spontaneous abortions?
    progesterone insufficiency
  55. How many sperm are there in one ejaculation?
    • approximately 200-600 million
    • usually 100 million/mL
    • ejaculate volume ~ 2-6 mL
  56. Counts of less than how many sperm per mL are associated with infertility?
    • less than 10 million/mL
    • motility levels below 20% (even if the count is normal) are also associated w/ infertility
  57. What stimulates reproductive tract muscular contractions that push the sperm up the cervical canal, through the uterus, and into the fallopian tube?
    prostaglandins from the SEMEN
  58. What are four really important steps of fertilization?
    • 1) capacitation
    • 2) acrosome reaction
    • 3) eureka moment - oozyte and sperm PMs fuse
    • 4) block of polysperm (Corticol reaction)
  59. capacitation
    • freshly ejaculated sperm are unable to fertilize until they undergo capacitation, a process where the glycoprotein coat and seminal proteins are removed from the acrosome surface (takes about 7 hours)
    • in vivo this step typically occurs in the female reproductive tract after ejaculation
  60. acrosome reaction
    • begins with the sperm penetrating the zona pellucida of the oocyte
    • ZP3 is the sperm receptor on the oocyte and when it detects sperm it initiates the reaction
    • the acrosome membrane of the sperm perforates due to the action of angiotensin converting enzyme (ACE)
    • the acrosome membrane fuses with the sperm membrane
    • this fusion causes release of hyaluronidase and proteases from the sperm that break down and permit sperm penetration through the zona pellucida
  61. ZP3
    • a glycoprotein receptor in the zona pellucida that binds sperm and initiates the acrosome reaction
    • it's unique among species, thus it is the protein that determines specieality
  62. angiotensin converting enzyme (ACE)
    • enzyme derived from the acrosome that perforates the sperm's acrosome membrane
    • this perforation releases enzymes that break down the matrix and allow the sperm to penetrate through the follicle and zona pellucida
  63. cortical (zona) reaction
    • oocyte cortical granule contents are released and they modify the zona pellucida through cross-linking and proteolysis, making it impenetrable to other sperm (mostly done by lysosomal enzymes from granules)
    • called the block to polyspermy and it occurs within seconds to minutes of sperm penetration
  64. In addition to the cortical (zona) reaction, what other event helps prevent polyspermy?
    a calcium pulse within seconds of penetration that gets repeated across the oocyte membrane
  65. What is the next step of fertilization after Ca 2+ pulses:
    • oocyte chromosomes decondense and form a pronucleus and a second polar body
    • the newly arrived sperm nucleus enlarges and forms the male pronucleus
  66. What happens to the chromosomes as the oocyte and sperm pronuclei form?
    all the chromosomes replicate
  67. After the plasma membranes of the sperm and oocyte fuse, what parts of the sperm enter the oocyte and what parts are left behind?
    • the head and tail of sperm to enter the cytoplasm of the oocyte
    • the sperm plasma membrane is left behind
  68. What is the only contribution sperm makes to the zygote besides paternal DNA?
    • the centriole that used for building the zygote's mitotic spindles
    • that and male DNA are the only contributions the sperm makes to the zygote, everything else is maternally derived
  69. When does fertilization officially end?
    • when maternal and paternal chromosomes intermingle during metaphase of the FIRST zygotic division
    • the pronuclear membranes break down, chromosomes condense, and line up for the first metaphase
    • approximately 24 hours after fertilization began
  70. What are three key results of fertilization?
    • 1) the secondary oocyte is stimulated to complete meiosis II
    • 2) a normal diploid number of chromosomes are restored
    • 3) determines the SEX of the embyro
  71. What are two examples of faulty/defective fertilization?
    • 1) parthenogenesis
    • 2) polyspermy
    • the two p's
  72. parthenogenesis
    • embryonic development without sperm
    • artificial induction of oocyte cleavage is possible in some animals, but not in humans
    • parthenos "virgin" + genesis "beginning, birth"
  73. polyspermy
    • an egg that has been fertilized by more than one sperm
    • several sperm usually begin to penetrate the zona pellucida, but only one enters normally
    • although rare, cases of dispermy result in a TRIPLOID zygote, which account for 20% of chromosomally-abnormal spontaneous abortions (SABs)
  74. Menstrual Cycle Phases (4)
    • 1) Menstrual Phase: days 1-5
    • 2) Proliferative Phase: days 5-14
    • estrogen levels rise, stimulate re-growth of endometrium functional layer
    • 3) Secretory Phase: days 14-27
    • estrogen levels peak then fall
    • progesterone levels are high
    • if no fertilization occurs, corpus luteum degenerates, estrogen & progesterone levels fall, and the secretory endometrium enters the ischemic phase
    • 4) Ischemic Phase: days 27-28
    • progesterone & estrogen levels fall rapidly and the functional endometrium becomes ischemic