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EHD Block 1 > Gametogenesis and Fertilization/ First week of development > Flashcards

Gametogenesis and Fertilization/ First week of development Flashcards

1
Q

What are Primordial germ cells?

A
  1. Originate in the epiblast
  2. Migrate through the primitive streak into the wall of the yolk sac (end of 3rd week)
  3. Migration proceeds in to the dorsal mesentery of the hindgut (4th week)
  4. From the mesentery of the hindgut PGCs migrate to the dorsal body wall

*They multiply by mitotic divisions

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2
Q

What are Teratomas?

A
  1. Arise from primordial germ cells that fail to migrate to the gonadal ridge
  2. Composed of all 3 germ layers

*Tumor-containing derivatives from all three germ layers

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3
Q

What are the Formation of the genital ridges?

A
  1. Arrival of PGCs into the presumptive gonad region leads to:
    a. Proliferation of the coelomic epithelium
    b. Formation of the somatic support cells

*These cells provide nourishment and regulate development of the gametes

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4
Q

What is Gametogenesis?

A
  1. Converts PGCs into mature male and female gametes
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5
Q

What is Male Gametogenesis?

A
  1. In males gonocytes remain dormant from the 6th week of embryonic development until puberty
  2. At puberty, seminiferous tubules mature
  3. Gonocytes differentiate into spermatogonia
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6
Q

What is Female Gametogenesis?

A
  1. Gonocytes differentiate into oogonia
  2. 5th month of fetal development all oogonia begin meiosis (Called primary oocytes)
  3. During early phase of meiosis all oogonia enter a state of dormancy until sexual maturity
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7
Q

What is Meiosis?

A

Is a specialized process of cell division that occurs only in the germ line

*In females only 1 gamete will survive; the others are polar bodies and die

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8
Q

What is Spermatogenesis?

A
  1. Starts in Puberty
  2. Testes secrete testosterone
  3. Growth of testes
  4. Maturation of seminiferous tubules
  5. Commencement of spermatogenesis begins

*The dormant PGCs resume development, divide several times by mitosis, and then differentiate into spermatogonia

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9
Q

What is the process of spermatogonia to seminiferous tubules?

A
  1. Spermatogonia to primary spermatocyte
  2. 1st meiotic division occurs
  3. 2 Secondary speramtocytes form (haploid)
  4. 2nd meiotic division begins
  5. 4 Spermatids form (haploid)
  6. Spermiogenesis occurs
  7. 4 mature sperms form and enter the seminiferous tubules

*74 day process (to form new spermatocytes)

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10
Q

What is Spermiogenesis?

A
  1. The formation of the acrosome
  2. Condensation of the nucleus
  3. The formation of neck, middle piece, and tail
  4. The shedding of most of the cytoplasm as residual bodies that are phagocytized by Sertoli cells

*Acrosome covers the head of the sperm and contains enzymes

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11
Q

What is Spermiation?

A
  1. The last connections with Sertoli cells break
  2. The spermatozoa are released into the tubule lumen
  3. Then transported passively from the seminiferous tubules to the epididymis (where they are stored and become mature)
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12
Q

What is epididymis?

A
  1. The elongated coiled duct along the posterior border of the testes
    * It is continuous with the ductus deferens, which transports the sperms to the urethra
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13
Q

What is Mature sperms?

A
  1. Free-swimming, actively motile with a head and tail
  2. Head: contains haploid nucleus
  3. Anterior 2/3 of the head is covered by the acrosome
  4. The enzyme in the acrosome penetrate the zona pellucida during fertilization
  5. The tail contains three sigments; middle (contains mitochondria), principal, and end
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14
Q

What occurs during ejaculation?

A
  1. Sperm are propelled through the vas deferens and urethra

2. Mixed with nourishing secretions from the seminal vesicles, prostate, and bulbourethral glands

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15
Q

What is Capacitation?

A
  1. Is the changes in the acrosome
  2. Release of the enzyme penetrates the zona pellucida (7 hours)
  3. Takes place within female genital tract
  4. Requires contact with secretions of the Fallopian tube

Capacitated sperms show no morphologic changes, but they are more active

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16
Q

What is a germinal vesicle?

A

Is the nucleus of an oocyte that is arrested in prophase of meiosis I

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17
Q

What is the primordial follicle?

A

A single-layered, squamous capsule of epithelial follicle cells derived from the somatic support cells tightly encloses each primary oocyte

*This is made up of the capsule and the enclosed primary oocyte

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18
Q

What is the primary follicle?

A
  1. At puberty the follicular epithelial cells become cuboidal in shape and then columnar forming the primary follicle
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19
Q

What is the Zona pellucida?

A
  1. Consist of the primary oocyte that becomes surrounded by a covering of amorphous acellular glycoprotein material
    * Composed of 3 glycoproteins (ZPA, ZPB, ZPC), which form a network of filaments with multiple pores
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20
Q

What is an Antrum?

A
  1. A central fluid-filled cavity developed by follicles

2. Follicles called antral or vesicular follicles

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21
Q

What are 2 layers of the ovarian stroma?

A
  1. Theca interna

2. Theca externa (outer fibrous capsule)

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22
Q

What occurs to the secondary oocyte during ovulation?

A
  1. The secondary oocyte begins the 2nd meiotic division, but progresses only to metaphase
  2. If a sperm penetrates the secondary oocyte, the 2nd meiotic division is completed
  3. Forming the second polar body
23
Q

What is the Female Reproductive cycles?

A
  1. A gonadotropin-releasing hormone is synthesized in the hypothalamus
  2. It stimulates the release of 2 hormones produced by the hypophysis
    a. Follicle-stimulating hormone
    b. Luteinizing hormone
  3. Both induce growth of the ovarian follicles and the endometrium
24
Q

What is the Follicle-stimulating hormone?

A
  1. Stimulates the development of ovarian follicles and the production of estrogen by the follicular cells
25
Q

What is Luteinizing hormone?

A
  1. Serves as the “trigger” for ovulation and stimulates the follicular cells and corpus luteum to produce progesterone
26
Q

What is Follicular development?

A
  1. Growth and differentiation of primary oocyte
  2. Proliferation of follicular cells
  3. Formation of Zona pellucida
  4. Development of the theca folliculi
27
Q

What occurs during Ovulation?

A
  1. Day 13-14 of the menstrual cycle, levels of FSH and LH suddenly rise
  2. The primary oocyte of the mature graafian follicle resumes meiosis (about 15 hours from ovulatory surge)
  3. By 20 hours the chromosomes are lined up in metaphase
  4. Cell division to form the secondary oocyte and first polar body rapidly ensues
  5. The secondary oocyte promptly begins the 2nd meiotic division
  6. About 3 hours before ovulation, is arrested at the 2nd meiotic metaphase
  7. The graafian follicle produces a cystic bulge
  8. The STIGMA (a small avascular spot) appears on it
  9. Before ovulation, the secondary oocyte and some cells of the cumulus oophorus detach from the distended follicle inferiorly
  10. Ovulation follows the LH peak by 12 to 24 hours
  11. The stigma ballon outs, which forms a vesicle after the LH surge
  12. The stigma ruptures
  13. The secondary oocyte with the follicular fluid expel out

*The expelling secondary oocyte is surrounded by the zona pellucida

28
Q

What is the Corona radiata?

A

Formed by some of the cumulus oophorus cells then rearrange themselves around the zona pellucida

29
Q

What is the Corpus luteum formation?

A
  1. After ovulation, the membrane granulosa cells of the ruptured follicular wall proliferate and give rise to the luteal cells of the corpus luteum
30
Q

What occurs if embryo implants?

A
  1. The corpus luteum enlarges to form a corpus luteum of pregnancy and increases its hormone production
31
Q

What occurs if an embryo does not implant?

A
  1. The corpus luteum degenerates after about 14 days and is converted to a scarlike structure (CORPUS ALBICANS)
32
Q

What is the menstrual cycle?

A
  1. The average menstrual cycle is 28 days

2. Day 1 is the day the menstrual flow begins

33
Q

What occurs during the Menstrual phase?

A
  1. 4-5 days

2. The functional layer of the uterine wall is sloghed off and discarded with the menstrual flow (menses)

34
Q

What occurs during the Proliferative phase?

A
  1. 9 days
  2. Coincides with the growth of the ovarian follicles
  3. Controlled by estrogen, which is secreted by the follicles
  4. The endometrial glands increase in number and length and the spiral arteries elongate
35
Q

What occurs during the Luteal phase?

A
  1. 13 days
  2. Progesterone stimulates the glandular epithelium to secrete a glycogen-rich material
  3. The glands widen and the endometrium thickens
  4. The SPIRAL ARTERIES grow into the superficial compact layer, becoming very coiled
  5. The venous network becomes complex and large LACUNAE (venous spaces) develop

*Direct arteriovenous anastomoses are prominent features of this stage

36
Q

What occurs during the Ischemic phase?

A
  1. Occurs when the oocyte is not fertilized
  2. The spiral arteries constrict causing the endometrium to have a pale appearance
  3. A stoppage of glandular secretion, a loss of interstitial fluid, and a shrinkage on the endometrium occurs
  4. The VENOUS STASIS and patchy ischemic necrosis develops in the superficial tissues
  5. Rupture of damaged vessel walls follows and blood seeps into the surrounding connective tissue
37
Q

What occurs during oocyte transport?

A
  1. The secondary oocyte is expelled with the follicular fluid
  2. During ovulation, the fimbriated end of the uterine tube becomes closely applied to the ovary
  3. The fimbriae of the tube moves back and forth over the ovary
  4. The sweeping action of the fimbriae and fluid currents produced by the cilia of the mucosal cells of the fimbriae “sweep” the secondary oocyte into the INFUNDIBULUM of the uterine tube
  5. The oocyte then passes into the ampulla of the tube, mainly as the result of peristalsis
38
Q

What are the 2 phases of the reflex ejaculation?

A
  1. Emission (semen is delivered to the prostatic part of the urethra)
  2. Ejaculation (semen is expelled from the urethra through the external urethral orifice)
  • Volume of ejaculation is about 3.5ml, with a range of 2 to 6 ml
  • Sperm moves 2 to 3 mm per minute (pH can affect movement)
39
Q

What is the Sperm transport process?

A
  1. Sperm passes through the uterus into the uterine tubes due to muscular contractions of the walls of these organs
  2. Prostaglandins in the semen stimulates uterine motility at the time of intercourse and assist in the movement of sperms to the site of fertilization in the ampulla of the uterine tube

*Fructose, secreted by the seminal glands, is an energy source for the sperms in the semen

40
Q

What occurs during Fertilization?

A
  1. Occurs in the ampulla of the uterine tube
  2. Goes through 3 phases:
    a. Penetration of the corona radiata
    b. Penetration of the zona pellucida (by the release of acrosomal enzymes)
    c. Fusion of the oocyte and sperm cell membranes
  • Sperm penetration causes cortical granules to release their contents, which render the zona pellucida impenetrable to further sperm
  • Each phase take 24 hours
41
Q

What occurs during the Penetration of the Corona radiata?

A
  1. Dispersal of the follicular cells of the corona radiata and zona pellucida by the hyaluronidase released from the acrosome of the sperm
  2. Tubal mucosal enzymes are released
  3. Screw-like movements of the tail of the sperm assist
42
Q

What occurs during the Penetration of the Zona Pellucida?

A
  1. Results from the release of the enzymes from the acrosome (esterases, acrosin, and neuraminidase)
  2. Causes lysis of the zona pellucida, forming a path for the sperm to reach the oocyte
  3. A zona reaction (a change in the properties of the zona pellucida) occurs when the sperm penetrates the zona pellucida, which prevents other sperm to enter.

*Zona reaction is from the action of the lysosomal enzymes released by cortical granules near the plasma membrane of the oocyte

43
Q

What occurs during the Fusion of the oocyte and sperm cell membranes?

A
  1. The plasma membranes of the oocyte and sperm fuse and break down at the area of fusion
  2. The head and tail of the sperm enter the cytoplasm of the oocyte (the cell membrane and mitochondria remain behind)
  3. This activates the oocyte into completing the 2nd meiotic division and forming a mature oocyte and 2nd polar body
  4. The nucleus of the mature oocyte becomes the female pronucleus
  5. The nucleus of the sperm enlarges to form the male pronucleus and the tail of the sperm degenerates

*As the pronuclei fuse into a single diploid aggregation of chromosomes, the ootid becomes a zygote

44
Q

What is an Ootid?

A

A haploid cell formed by the meiotic division of a secondary oocyte

45
Q

What is Human oocyte viability?

A
  1. Are usually fertilized within 12 hours after ovulation

2. The oocyte cannot be fertilized after 24 hours and degenerates shortly after

46
Q

What is the viability of human sperms?

A

Do not survive for more than 48 hours in the female genital tract

47
Q

What is Triploid conceptions?

A
  1. Account for 20% of chromosomally abnormal spontaneous abortions
  2. Triploid embryos (69 chromosomes) may appear normal, but they nearly always abort or die shortly after birth
48
Q

What is the Cleavage process?

A
  1. Occurs 30 hours after fertilization
  2. Occurs as the zygote passes along the uterine tube toward the uterus
  3. Consist of repeated mitotic divisions of the zygote (results in the rapid increase in the number of cells; blastomeres)
  4. Blastomeres become smaller with each successive cleavage division
  5. After the 9-cell stage, the blastomeres change their shape and tightly align themselves into a compact ball (COMPACTION)

*During cleavage, the zygote is within the zona pellucida

49
Q

What is a Morula?

A

A formation of 12 to 32 blastomeres

*The morula forms 3 days after fertilization as it enters the uterus

50
Q

What is the formation of the blastocyst?

A
  1. Morula enters the cavity of the uterus at 4 days after fertilization
  2. Fluid penetrates the intercellular spaces
  3. The spaces become confluent and form the BLASTOCELE
  4. Cells of the inner mass, the EMBRYOBLAST, are at one pole
  5. Cells of the outer cell mass, or TROPHBLAST, flatten and form the epithelial wall of the BLASTOCYST
  6. The zona pellucida disappears, allowing for implantation to begin
51
Q

What is the beginning of implantation?

A
  1. Around 6 days after fertilization
  2. The blastocyst attaches to the endomentrial epithelium
  3. The adjacent cells of the endometrial stroma differentiate inot metabolically active DECIDUAL CELLS
  4. This response is called the DECIDUAL REACTION
52
Q

What is Ectopic pregnancy?

A
  1. Threaten the life of the mother because the blood vessels that form at the abnormal site are about to rupture as a result of growth of the embryo and placenta
    * Symptoms include: abdominal pain and/or vaginal bleeding
53
Q

What are 6 types of Contraception?

A
  1. Barrier methods (male and female condoms)
  2. Oral contraceptives (prevent ovulation and implantation)
  3. Injected or implanted sources of progesterone (Hormone patch, Intrauterine devices, or vaginal rings)
  4. Antiprogesterone Compound RU-486 (mifepriston)
  5. Postcoital (emergency) contraception
  6. Sterilization
54
Q

What are 5 Assisted reproductive technologies?

A
  1. In Vitro fertilization (IVF)
  2. Embryo transfer
  3. Intracytoplasmic sperm injection (ICSI)
  4. Gamete intrafallopian transfer (GIFT)
  5. Zygote intrafallopian transfer (ZIFT)

EHD Block 1 (6 decks)

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