Unit 1.L1-Gametogenesis Fertilization Flashcards
(141 cards)
1
Q
What are the two periods of human development?
A
- Prenatal….Period 1
- Postnatal……Period 2
2
Q
What is Period 1 of human development?
A
- Prenatal Growth (development in utero, before birth)
- Starts from fertilization of an oocyte→Birth is the prenatal period
Also called Intrauterine growth
3
Q
What are the 2 periods of Prenatal Growth (period 1)?
A
1a. Embryonic
1b. Fetal
4
Q
Explain the Embryonic Period (1a) including the stages and number of days
Prenatal Period
A
- 23 stages; Day 1-Day 56 (carnegie stages)
- Defined by morphological changes
- Stage 1: Fertilization: Day 1
- Stage 23: Embryonic period over: Day 56
5
Q
What is the Fetal Period (1b)? When do we see the most visible organ structures?
Prenatal Period
A
- 9th week to birth: differentiaiton and growth of tissues and organs
- Most visible organ structures form b/w 3rd-8th weeks
By the time you are at day 56 (9th week) organ fate is already set, you are just tiny. Fetal period you are now growing
6
Q
What is period 2 of human development? How many phases and what is occuring?
A
- Postnatal Growth: w/ 5 phases
- Extrauterine development
7
Q
What is the 1st phase of POSTnatal growth (period 2) of human development? What is the duration and what occurs?
A
- Infancy: Neonate: up to 1 month or younger(neonatal period)
- Transition from intrauterine to extrauterine exsistence
- Many changes in cardiovascular and respiratory system during transition
Many changes occurs in 1st month and need to remove fluid from lung and heart needs to change circulation
8
Q
What is the 2nd phase of POSTnatal growth (period 2) of human development? What is the duration and what occurs?
A
-
Childhood: period between infancy up to puberty (1 month to puberty)
1. Teeth: The primary (deciduous) teeth continue to appear –> replaced by the secondary (permanent) teeth.
2. Bones: Active ossification (formation of bones, length of the body).
- Ossification occurs all the way until 25
- Lungs grow unti 8
9
Q
What is the 3rd phase of POSTnatal growth (period 2) of human development? What occurs?
A
Pre-pubertal growth: Rapid acceleration of weight (growth spurt)
10
Q
What is the 4th phase of POSTnatal growth (period 2) of human development?
A
- Puberty: Functionally capable of procreation (reproduction)
- Female: 1st signs by 8-11
- Males: 1st begins at age 9-12
11
Q
What is the 5th phase of POSTnatal growth (period 2) of human development?
A
- Adulthood: Attainment of full growth/maturity
- 18-21 years of age (early phase)
- 21-25 years of age: Complete ossification (mature adult)
12
Q
In the lateral view of a 7-week embryo, a frontal coronal section can be seen. What is the rostral view?
A
90 degree cut to coronal section on face/nose
13
Q
The vertebral column (spine) develops ____ in the embryo
A
dorsally
14
Q
The lungs develop ____ to the esophagus
A
ventrally
15
Q
The sternum develops ____.
A
Ventrally
16
Q
List the steps of Gametogenesis (Meiosis I & Meiosis II)
Week 1
A
- Homologous chromatids pairs & align: Total 23 pairs (2n=46 chromatids)
- Synthesis phase (S-phase): Chromatid pairs duplicate (4 chromatids-4n=92)
- Meiosis I: TWO DIPLOID homologous chromosomes does allelic crossover
- Metaphase: The two pairs (4n) arrange at meiotic spindle (4n=92 chromatids)
- Anaphase: The diploid chromosomes with the new alleles seperate (4n=92 chromatids)
- Telophase: The chromosomes goes to poles and cytokines begins (4n=92 chromatids)
- New diploid cells for Gametogenesis: (2n=46 chromosomes w/ newly swapped alleles)
- Meoisis II: Each diploid cells give rise to 2 haploid cells. (4 haploid gametes are formed from each diploid gonadal precursor cell in spermatogenesis; in oogenesis only one gamate formed, rest become polar bodies and dies)
17
Q
What can abnormal gametogenesis cause?
A
- Causes Nondisjuction in chromosomes→abnormal gametes (sperm/egg).
- After fertilization, the gametes w/ numeric chromosome abnormalities (3n) cause: Trisomy 21 or Down Syndrome
- Examples
1. Nullisomy: loss of both pairs of chromosomes (ex. Turner’s syndrome)
2. Disomy: 2 pairs of chromosomes from same parent, none from the other
3. Trisomy: numeric chromosome abnormalities (3n)
18
Q
Explain the steps of Meiosis I & II in Spermatogenesis?
A
- Dominant Spermatogonia in the seminiferous tubules mature in sperm at puberty
- At puberty mitosis of Spermatogonia→primary spermatocytes (largest cell)
- In Meiosis I: Primary spermatocyte (46 x 2n; XY, n=92 chromatids)→Secondary spermatocyte (smaller cells; 23 x 2n; XY=46)
- In Meiosis II: Secondary spermatocytes→4 haploid spermatids (smallest cells)
- SpermIOgenesis: converts spermatids into four mature sperms (Haploid)
- Sertoli cells lining the seminiferous tubules support and nurture the sperm
- Mature Sperms→seminiferous tubules & are stored in the epididymis
- Spermatogonia takes 2 months to form mature sperm
19
Q
What is Oogenesis?
A
PGCs (progenitor germ cells) make Oogonia→Mature Oocytes
20
Q
Explain the steps of Meiosis I & II in Oogenesis?
A
- Oogenesis (Ovaries): Diploid Oogonium (PGCs)→grow/mature into primary oocytes (in follicles)
- The pimary oocyte start meoisis I but STOP at prophase I in Embryo
- At puberty : Primary oocytes completes Meoisis I→ 1 st polar body + Diploid (2n) Secondary oocyte
- At ovulation, secondary occyte undergoes Meiosis-II up metaphase and stalls
- Completion of Meiosis II occurs after sperm entry and the haploid secondary occyte (23 single chromatids, 1n) is called the Ootid (has male & female nucleus) before male & female chromosome mixing and deplodization/zygotization occcurs
21
Q
What is the two stages of Oocyte Maturation?
A
- Prenatal/pre-puberty Maturation
- Postnatal/at puberty Maturation
22
Q
Explain the Prenatal/pre-puberty Maturation of Oocyte maturation
A
- In the fetus, Oogonia proliferate by mitosis to form Primary Oocytes at birth.
- A single layered folliculae cells surround the Oocyte: Primordial Follicle
- The primary oocytes remain dormant in a Growing Follicle until puberty
- At puberty, the Primordial Follilcle→Ovarian Follicle
23
Q
Explain the Postnatal/at puberty Maturation of Occyte maturation
A
- At Puberty the Primary Oocyte enlarges w/ follicular cells changing shape: Squamous→Cudoidal→Columnar cells→Ovarian Follicle
- Primary Oocyte is surrounded by Zona Pellucida (acellular glycoproteins)
- Meiosis-I:Primary Oocyte divides→Secondary Oocyte + First polar body & follicular fluid-filled space Antrum is formed
- Meosis II up to metaphase: At ovulation, secondary oocyte undergoes meiosis II & stalls at metphase
- Meiosis II is completed during fertilization, to form a Zygote + second polar body
- At puberty: One Ovarian follicle matures each month and Ovulation occurs
24
Q
How long does Oogenesis continue for and when does it stop?
A
- Continues til menopause
- Stops when menstral cycle cease
25
How many primary oocyte do you have as a neonate compared to puberty?
2 Million primary oocyte; neonate→40,000 remains at puberty
26
On average how many secondary oocytes ovulate (if contraceptive are not used)?
* Only 400 (20-35 yrs of age)
27
Describe the structure of a mature human sperm
* The Head: Nucleus + cap-like acrosome (hydrolytic enzymes)
* The Tail: Middle piece, Principle piece and End piece
28
Describe the structure of a mature secondary oocyte (after Meiosis I)
Surronded by **zona pellucida** and **corona radiata**
29
Explain the Maturation of an Ovarian Follicle
1. Primary Oocyte→Continues to grows & later differentiate
2. Proliferation of follicular cells→**Estrogen production**
3. **Zona pellucida** is formed around the oocyte
4. **Theca folliculi** (2 layered): Inner & outer
* Inner (Vascular theca interna)
* Outer (Glandular theca externa)
5. Follicle splits, giving a fluid space **Antrum** & becomes: →Secondary Oocyte→Mature Oocyte
6. **FSH** (follicle stimulating hormone) in **early** ovarian development
7. **LSH** (luetinizing hormone) in **late** ovarian development **induces Ovulation**
30
What is the function of the inner and outer layer of the Theca folliculi (derived from ovarian follicle)?
## Footnote
* Inner: Vascular theca interna
* Outer: Glandular theca externa
* Inner (Vacular theca interna): Nutrtion to the follicle→**produce Estrogen**
* Outer (Glandular theca externa): Intestitial gland of the ovary→**produce Prostaglandins**
31
Explain the steps that induce Ovulation
1. Under **FSH and LH**, at mid menstrual cycle, a bulge or **Stigma** appears
2. **Secondary oocyte detaches** from the follicle→**mature oocyte**
3. **High Blood Estrogen** causes a **spike in LH, inducing Ovulation.**
4. **Ovulation**: *(i) Increase in Intrafollicular pressure* & *(ii) Contraction of theca externa smooth muscle mediated by prostaglandins*, **ruptures the Stigma→Oocyte is expelled**
5. Oocyte (covered with Zona pellucida & Corona radiata)ready to be fertilized.
6. The finger like **fimbriae of uterine tube** sweep the oocyte into the **infundibulum**
## Footnote
Stigma can pentrate wall of ovaries
32
What causes Ovulation?
High Blood estrogen causes a spike in LH which induces ovulation
33
When ovulation occurs what mediates the increase of intrafollicular pressure and contraction of theca externa smooth muscle?
Prostaglandins
34
What happens after the LH surge and ovulation?
LH surge→empty follicle & theca follculi→**Glandular Corpus Luteum**
35
**Corpus Luteum**
* Secretes what?
* Prepares for what?
* Secretes: Progesterone and Estrogen
* Prepares: the Endomertrium for the implantation of the fertilized Oocyte
36
What happens to the Corpus Luteum after fertilization?
* Enlarges to form a **corpus luteum of pregnancy** and increases its hormone production which helps convert the **Zygote into multicellular Blastocyst**
37
What does the **Blastocyte** make and explain its function?
Makes **hCG (Human Chronic Gonadotropin) hormone** and prevents **degeneration of corpus luteum**, which maintains secretion of progesterone and estrogen in a positive feed-back loop
38
What are the 3 parts of the Early Embryonic Phase?
1. Blastogenesis
2. Implantation of the Embryo
3. Ceasing of the Menstrual Cycle
39
# Early Embryonic Phase
Explain Blastogenesis
| Part 1/3
* Cleavage of the zygote and formation of a blastocyst
* The **blastocyst** prepares to implant in the endometrium
40
# Early Embryonic Phase
Explain what helps the Implantation of the Embryo
| Part 2/3
* **HCG** is secreted by the **outer epithelial cells** of the blastocyst-the **trophoblast (Syncytiotrophoblast)**
* HCG keeps the corpus luteum secreting estrogens and progesterone (setting a positive feed-back loop, preparing the endometrium for implantation)
## Footnote
Trophoblast (Syncytiotrophoblast)-layer that attachs to endometrium
41
# Early Embryonic Phase
Explain the Ceasing of Menstrual Cycle
| Part 3/3
Endometrium is now ready for the pregnancy phase
## Footnote
No ischemia or loss of endometrium lining
42
What are the steps of transportation of the oocyte?
1. The expelled *secondary oocyte floats* in the follicular fluid.
2. The *fimbriated end* of the uterine tube turns to the **ovary**
3. The finger-like fimbriae moves back & forth over the ovary in a sweeping action.
4. The fluid current is produced by the mucosal cell cilia of the of the fimbriae, which *“sweep” the oocyte* into the **funnel-shaped infundibulum** of the uterine tube.
5. The fertilized oocyte then goes→ampulla of the uterine tube by peristalsis and reaches the uterine lumen in 3-4 days.
43
What are the two phases in sperm discharge?
1. Emmision
2. Ejaculation
44
What is emission?
* Peristalsis of the **ductus deferens** pushes the sperms to the prostatic part of the urethra through *ejaculatory ducts*
* Secretions d/t Symphathetic response from the: *seminal glands (vesicle), prostate and bulbourethral glands*, produce sperm filled Semen
45
What are the secretions of sperm due to?
D/t Sympathetic response from the: seminal glands (vesicle), prostate, & bulbourethral glands, produce sperm filled Semen (keeps sperm healthy)
46
How does ejaculation work (sequence of events)?
1. *Closer* of the *vesicle sphincters* of the bladder
2. Contraction of the *urethral & penial erectile muscle*
3. Semen is expelled via uretheral orifice **~600 mill sperms** are deposited at the **external OS & fornix** of the vagina during intercourse
47
How does the transport of the sperms to the oviduct happen?
**Capacitation**
* Changes in *cell surface of the sperm*
* Required for proper *attachment* and *penetration* of the *zona pellucida* when the sperm encounter the oocyte
48
How does the activation of sperms in the oviduct happen?
**Capacitation, Acrosome Reaction and Penetration in the Oocyte**
1. Capacitation: *Removal of Glycoproteins + Seminal Proteins* from the **Acrosome** (initiating "Acrosome Reaction"
* Occurs in 7 hrs in the ovidult d/t uterine secretions
2. Acrosomal perforations release *hydrolytic enzymes* when the sperm touchs the **"Corona radiata"**
3. Acrosome binds *glycoprotein (ZP3)* on the zona pellucida & acrosome enzymes **digests the zona pellucida**
4. Sperm nucleus (head) & tail enters the cytoplasm of the oocyte.
49
How does Fertilzation occur at a cellular level?
1. Oocyte with 23 identical chromatid pairs (Meiosis-II-Metaphase)
2. Sperm entry completes meiosis-II, forming the female haploid pronucleus (n=23 haploid) + 2nd polar body
3. The sperm head becomes the male pronucleus (n=23 haploid).
(This cell with the male + female pronuclei is called the OOTID)
4. *Fusion of Pronuclei*→ Zygote with **23 diploid chromosomes**
50
List the main points that summarizes phases of Fertilization
1. *Passage of a sperm* through the **corona radiata.**
2. Penetration of the **zona pellucida.**
3. Fusion of cell membranes of the oocyte and sperm.
4. Second meiotic division of the oocyte to form the pronucleus.
5. Formation of the male pronucleus.
6. Formation of the **Ootid** with male & female pronucleus.
7. Chromosomal mixing & **sex determination** at fertilization by the kind of sperm (X or Y) that fertilizes the oocyte.
51
What happens with the cleavage of the zygote?
| Week 1
Zygote: Cleavage stages: 30 hrs p.f. (post fertilization), Zygote divides→smaller blastomeres.
* **A-D:Morula**: 12-32 cell stage (3-4 days)
* **E:Early blastocyst**: The zona pellucida degrades (5 days).
* **F: Late Blastocyst**: Zona pellucida degenerates; blastocyst enlarges & blastomeres align, tighten & undergo cell-cell adhesion, causing “Compaction” during morula stage.
* **F: Embryoblast**: Compaction segregates cells into inner cell mass (ICM) or (1) embryoblast outer cells ((2) trophoblast layer) and a uterine fluid filled space; (3) Blastocystic cavity
## Footnote
Morula also 8-32 cell stage; after 8 cell stage changes occur in the cytoplasm
52
What is the state of the blastocystic cavity and zona pellucida at day 4 compared to day 4.5?
| Week 1
## Footnote
!2 hrs difference
* Day 4: The blastocytic cavity is just beginning to form. The zona pellucida is undergoing degradation.
* Day 4.5: The blastocyst cavity has enlarged and the embryoblast and trophoblast are clearly defined. The zona pellucida has completely dissolved.
53
How does implatation of the embryo occur?
| Week 1
* At Day 6: the **trophoblast** of the blastocyst attaches to the *endometrial epithelium* at the **embryonic pole**(the ICM side)
* By the end of Day 6: Finger-like processes of **"Syncytiotrophoblast"** produces enzymes that invade and *'"dissolves"* the endometrial epithelium and the connective tissue surrounding it
## Footnote
ICM: Inner cell mass
54
What occurs at the end of the first week (Day 7)?
* The **Attached Trophblast** proliferates rapidly and differentiaties into two layers
1. **Cytotrophoblast** (inner layer)
2. **Syncytiotrophoblast** (outer layer) consisting of a *mutlinucleated protoplasmic mass* w/ no cell boundaries
* **Attached Blastocyst**
1. The **implanted blastocyst** is nourished by the **endometrium**
2. The **primary endoderm (Hypoblast**; yellow cuboidal cell lining) appears on the bottom surface of the embryoblast facing the blastocystic cavity
55
Where is the primary endoderm located?
**Hypoblast**
* Appears on the bottom-surface of the embryoblast facing the blastocystic cavity
56
List the main points that summerize the first week of embryo development
1. **Oogenesis**: Oocytes made in ovaries are expelled in the Oviduct.
2. **Fertilization**: Fimbriae of the uterine tubes sweep the oocyte into the *ampulla*, where it is fertilized by a sperm.
3. (Oocyte touches sperm to *completes meiosis II*, becoming a mature oocyte (haploid; 23, 1n) & the 2nd polar body.
4. The sperm enter the oocyte forming **OOTID**
5. M + F pronuclei fuse & chromosome mixing (46; 2n) → **Zygote**
6. *Day 3*: Zygote divides into 8-32 Blastomeres→ **“Morula” stage**
6. *Day 5*, after Cell Compaction, it becomes a **Blastocyst (ICM): (1) Embryoblast (2) Trophoblast and (3) Blastocystic cavity**
7. *Day 6*: Zona pellucida dissolves & trophoblast attaches to the endometrial epithelium via finger-like projections of the **syncytiotrophoblast**
8. *Day 7*: A cuboidal cell layer of **hypoblast** forms on the inner-deep surface of the embryoblast, giving rise to *primary endodermal layer (hypoblast)*
57
What is Mittelschmerz?
* Pain during Ovulation
* A variable of mild abdominal pain occurs during ovulation in some women
* Ovulation cause bleeding into the peritoneal cavity, leading to abrupt, constant pain in the lower abdomen.
* **Mittelschmerz is a secondary indicator of ovulation; primary being elevation of basal body temperature**
## Footnote
Occurs in girls around 15
58
What is Anovulation?
* Women may not ovulate (anovulation) due to **lack of gonadotropins**
* Ovulation can be induced by giving gonadotropins or an ovulatory agent such as **CLOMIPHENE**
* CLOMIPHENE stimulates the release of pituitary gonadotropins **(FSH and LH)**, resulting in multiple ovulations with high chance of multiple pregnancies (7-8 embryos survive to birth)
* Clomiphene binds to estrogen receptors so estrogen does not bind and the body thinks it has low estrogen
59
What is Anovulatory Menstrual Cycles & Ovarian Hypofunction?
* Without ovulation, an anovulatory menstrual cycle occurs. (no egg)
* Proliferative endometrium is seen, but no luteal phase seen→as corpus luteum does not form. ⭐️
* Estrogen/estrogenic birth control pills acts on the hypothalamus/pituitary gland; inhibits secretion of FSH/ LH→no ovulation. ⭐️
60
What is the normal amount of sperm in semen?
100 million sperms/per mL of semen in normal males & is variable in normal males (range: 20-100 million).
## Footnote
Male Infertility (30-50% of involuntary childless couples)
61
What are five reasons of male infertility?
1. Low sperm count (< 10 million sperms/mL of semen)
2. Immotile and abmormal sperm
3. >50% of spern non-motile after 2 hrs
4. Medications, drugs, endocrine disorders, pollutants, cigarette smoking
5. Obstruction of a gential duct (blocked ductus deferens)
62
What is a vasectomy?
1. Surgical removal or blocked ductus deferens (vas deferens); no sperms in the semen
2. Reversal of vasectomy is surgically feasible
63
What is dispermy and tripoidy?
* Normally one sperm enters the oocyte and fertilizes it due to polymerization of glycoprotein in Zona Pellucida
* If **TWO SPERMS** fertilize an ovum **(dispermy)**, a **Triploid zygote (69 chromosomes)** is formed, causing *spontaneous abortions* and *death to fetus* shortly after birth
64
What are the 3 periods of the "in Utero" Phase
1. Initial Period: 1st week of development
2. Embryonic Period: 2-8th week
3. Fetal Period: 9th week→Birth
## Footnote
"in Utero"- from embryo to fetus
65
What is the Embryoblast doing on Day 7 (Week 1)?
Forming a disc like structure attached to the endometrium
66
Where does the implanted blastocyst starts getting nourishment?
| Day 7 (Week 1)
From the endometrium
67
Where does the primary endoderm (Hypoblast) appear on Day 7 (week 1)?
On the bottom-surface of the embryoblast facing the blastocystic cavity
68
What happens the Embryoblast disc at the beginning of Week 2 (Day 8)?
* Becomes *"bilaminar"*
1. **Epiblast**
2. **Hypoblast**
69
What does the Embryo disc later form?
| Wk 2, Day 8
**3 germ layers & Progenitor Germ Cells (PGCs)**, i.e., all tissues of the body
| Day 8: Implantation of the Blastocyst & the Bilaminar Embryo
70
The trophoblast contacts the endometrium and gives rise to what?
| Wk 2, Day 8
**5 The Extraembryonic Structures**
1. Amnion
2. Amniotic cavity
3. Umbilical Vesicle (Blastocystic cavity)
4. Connecting stalk
5. Chrionic Sac
## Footnote
NOTE: 4&5 are not formed yet
71
What is another name for implantation?
How big is the embryo?
| Wk 2, Day 8
Conceptus (0.1 mm)
## Footnote
Cannot see it
72
Explain the roof and floor of the embryoblast
| Wk 2, Day 8
* Roof: Aminoblast that are cuboidal
* Floor: Columnar cells and this is where the embryo grows from
* The amniotic cavity is between the two
73
What are the 2 layers the Trophoblast differentiate into?
| Wk 2, Day ~8
1. Cytotrophoblast
2. Syncytiotrophoblast
74
What is the Cytotrophoblast?
| Wk 2, Day ~8
(Inner layer of trophoblast) Cells, which migrate out of the endoderm & surrounds the *Exoceolomic cavity*
75
What is the Exocoelomic cavity?
(Also blastocystic cavity), or umbilical vesicle or yolk sac
76
What is the Syncytiotrophoblast?
| Day ~8
(outer layer of trophoblast) Cells invading & hydrolyzing the endometrium. This helps in **implantation**
77
What is the epithelial type of:
* Cytotrophoblast
* Hypoblast
* Exocelomic membrane
* Cytotrophoblast: Cuboidal
* Hypoblast: Cuboidal
* Exocelomic membrane: Squamous
## Footnote
Hyoblast differentiates into exocoelomic membrane (cuboidal to squamous)
78
Where is the blastocyst located by Day ~8?
| Wk 2, Day ~8
Half inside the endometrium
79
What are important structures formed by day ~8 and how are they formed?
| Wk 2, Day ~8
**Amnion, Amniotic Cavity & Exocoelomic Membrane**
* **Amnion** emerges from the top-most layer of the epiblast
* A slit-like **amniotic cavity** emerges below the Amnion
* **Exocoelomic membrane** is made of *squamous hypoblast* derivates
80
What structure emerges from the top layer of the epiblast?
| Wk 2, Day ~8
Amnion
81
What emerges from below the Amnion (aminoblasts)?
| Wk 2, Day ~8
A slit-like amniotic cavity
82
* Roof of amnion is made up of what?
* Amniotic cavity form what?
| Wk 2, Day ~8
* Aminoblasts
* Entire Embryo
83
What is produced by the endometrium and what does it cause during day 9?
| Wk 2, Day 9
* Produces Microvilli, integrins, cytokines, prostaglandins, hormones (hCG, progesterone), growth factors and proteinases that cause **endometrial cell apoptosis** and makes it **receptive to attach to the blastocyst**
* Known as **Synchronization**
## Footnote
If this does not occur (when estrogen: progesterone ratio is off), there will be a miscarriage
84
What does the Syncytiotrophoblast produce during day 9?
| Wk 2, Day 9
Produces hCG, which enters the maternal blood via endometrial lacunae
85
What is the function of hCG produced by Syncytiotrophoblast?
| Wk 2, Day 9
Enhances **estrogen/progesterone** production in the *corpus luteum* in the ovary during pregnancy
86
Why does the corpus luteum secrete estrogen/progesterone?
| Wk 2, Day 9
To pepare and maintain the *placenta* for **nourishment** of the embryo
87
What is the basis for pregnancy test?
| Wk 2, Day 9
hCG in maternal blood
88
Together blood islands and synctiotrophoblast form what?
| Wk 2, Day 9
**Lacunae**, where pumping blood of mom into synctiotrophoblast
89
What is the endometrial epithelial defect?
| Wk 2, Day 9
Damage to the endometrium and the blood will come out on the 9th or 10th day of pregnancy
90
On Day 10: Amniotic cavity appears above the ___________
| Wk 2
Embryoblasts
91
On Day 10: What seperates from the epiblast and what does it form?
| Wk 2
**Aminoblasts** seperate from the epiblast and form the **Amnion**, around the amniotic cavity
92
What is the Epiblast?
| Wk 2, Day 10
Thick columnar cells facing the amniotic cavity
93
What is the Hypoblast?
| Wk 2, Day 10
Small cuboidal cells facing the *Exocoelomic cavity*, which is now called the **Primary Umbilical Vesicle (PUV)**
94
Amnion roof has what type of cells and what do they do?
| Wk 2, Day 10
Squamous cells and secrete fluid b/c the cells cannot be dry
95
Where does the Extraembryonic mesoderm come from?
| Wk 2, Day 10
Transdifferentiation of the hypoblast (goes out) and trophoblast (goes in)
96
Where is the Primary Umbilical Vesicle (PUV) cells derived from?
| WK 2, Day 10
**Hypoblast + Cytotrophoblast** which form the *Extraembryonic mesoderm*
97
What does the Extraembyronic mesoderm surround?
| Wk 2, Day 10
The **Amnion, Embryonic disc & Primary Umbilical Vesicle w/ Exocoelomic cavity/Yolk sac**
98
What is the function of eroded glands and blood in the lacunar network?
| Wk 2, Day 10
Provide nutrition to the embryo via **Primordial "uteroplacental circulation"**
99
What closes the Endometrial Epithelial Defect?
| Wk 2, Day 10
Blood Coagulum (fibrin plug)
100
How is the "Intervillous spaces" of the placenta formed?
| Wk 2, Day 12
By Uterine glands erode, Lacunar networks form and make the synctiotrophoblast sponge-like
101
* The endometrial capillaries form what?
* Under the influence of what?
* What do sinusoid form?
| Wk 2, Day 12
* **Maternal sinusoids** under the influence of **estrogen & progesterone.**
* Sinusoids form **blood vessels** in the endometrial stroma
102
The Extraembryonic mesoderm splits to form what?
| Wk 2, Day 12
* **Extraembryonic Coelomic space**→the future Chronic cavity
103
Hypoblast cells contribute to what?
| Wk 2, Day 12
Extra-embryonic endodermal lining (exocoelomic membrane) of the primary umbilicial vesicle (yolk sac)
104
Endometrial epithelial defect persists at Day12 & remains plugged by?
| Wk 2, Day 12
Fibrin plug
105
When does the endometrial epithelial defect disappears and contagious endometrial epithelial layer is seen?
Day 13 (Week 2)
106
What does the primary umbilical vesicle do? and what surrounds it?
| Wk 2, Day 13
Extends downwards & is surrounded by the extraembryonic coelom
107
What structure appears at Day 13 and will fuse with sinuosids?
| Wk 2, Day 13
Primary Chrionic Villi
108
How does the extraembryonic *coelom* splits the extraembryonic *mesoderm*?
| Wk 2, Day 13
1. **Extraembryonic Somatic Mesoderm** (top): lines the amnion & the embryo body (soma) & trophoblast
2. **Extraembryonic Splanchnic Mesoderm**(bottom): surrounds the umblicial vesicle
109
What happens to the primary umbilical vesicle (PUV)?
| Wk 2. Day 14
* "Pinching off" to form the **Secondary umbilical yolk sac**, leaving a remnant of the primary yolk sac
110
Where does the Primary Chorionic Villi protrudes at?
| Wk 2, Day 14
The connecting stalk of the outermost fetal layer, the **"Chorion"**
111
What is the Chorion and how is it made?
| Wk 2, Day 14
* The outermost fetal layer
* Made of extraembryonic somatic mesoderm (top) and the two layers of the cytotrophoblast
112
What does the Chorion form?
| Wk 2, Day 14
A sac called the **Chrionic Sac** with the **chorionic cavity**
113
At Day 14: The embryo "hangs" in the _________ and is only attached by the ___________ for nourishment from the __________ and later ___________
| Wk 2, Day 14
The embryo “hangs” in the **chorionic cavity** and is only attached by the **connecting stalk** for nourishment from the **chorionic villi** & later *placenta*.
114
At Day 14: What does the Hypoblast cells form and how?
| Wk 2, Day 14
Hypoblastic cells (in a localized area) become columnar and form a thicken circular area, **the prechordal plate**
115
What does the prechordal plate do?
| Wk 2, Day 14
* Demarcating (determining) the future mouth and head region
* Embryonic Cranial-Caudal directionality is established
116
At day 14 what structure is large? And which structures are visible?
| Wk 2, Day 14
* The *Extraembryonic coelom* is large
* The *connecting stalk, amnion, chorion & chorionic villi* and future chorinic cavity are visible
117
What does the Epiblast eventually become?
* Ectoderm of amnion
* Embryonic ectoderm (1 of 3 germ layers)
* Primative streak (origin of the 2 other germ layers)
118
Summary of Implantation I from Days 5-10
* Day 5:the zona pellucida (zp) degenerates post fertilization (pf).
* Day 6: Loss of zona pellucida allows the blastocyst to grow & adhere to the endometrial epithelium
* Day 7: Initiation of blastocyst attachment begins: Trophoblast differentiates into syncytiotrophoblast and the cytotrophoblast.
* Day 8: The syncytiotrophoblast secrets hydrolytic enzymes and erodes endometrial tissues.
* Day 8: Hypoblast & Epiblast are well defined after the embryoblast splits
* Day 8-9: Amnion and Amniotic cavity is well-defined; roof of the embryoblast forms the Amnioblast (Amnion)
* Day 9: the blastocyst begins to embed in the endometrium.
* Day 10: blood-filled lacunae appear in the syncytiotrophoblast
119
Summary of Implantation II from Day 10 to Day 14
* Day 10-11: the blastocyst is buried in the endometrial epithelium closing the plug
* Day 11: Lacunar networks form
by fusion of adjacent lacunae.
* Day 11-12: the syncytiotrophoblast erodes endometrial blood vessels, allowing maternal blood to diffuse in and out of lacunar networks, which initiates the uteroplacental circulation.
* Day 12-13: the endometrial epithelium defect is repaired & contiguous epithelium is formed.
* Day 13-14: Primary chorionic villi, Chorion & its Sac develop
* Day 14: Thick columnar Hypobastic cells develop into prechordal plate
* Day 14: Connecting stalk, Chorion, Chorionic Villi & Future Chorionic cavity formed.
120
Summary of Embryonic Second Week
1. Rapid proliferation and differentiation of the trophoblast during blastocyst implantation in the uterine endometrium.
2. Decidual reaction dissolves the endometrial tissues and makes it receptive to implantation of the blastocyst.
3. The embryoblast differentiates into a bilaminar embryonic disc (upper layer-epiblast & lower layer-hypoblast).
4. The primary umbilical vesicle forms and extraembryonic mesoderm develops.
5. The amniotic cavity appears between the cytotrophoblast and embryoblast.
6. Cavities form & fuse in the extraembryonic mesoderm, forming the extraembryonic coelom (cavity).
7. The secondary umbilical vesicle develops by pinching of the primary umbilical vesicle (degenerates!)
8. The Extraembryonic coelom becomes the chorionic cavity in the surrounding layer, the chorionic sac.
9. Thickening of the hypoblast (Cuboidal→Columnar cells) forms the Prechordal plate, a precursor to the head & mouth,
defining the Cranio-Caudal directionality of the embryo.
121
What is Extrauterine Implantations?
* Blastocyst implanted outside the uterus (ectopic sites); a clinical condition called **“Ectopic Pregnancy”**
* Ampulla is the most common
* Ovary has the least common implantation
122
Where does Tubal Pregnancies moslty occur?
| ~95%-98% of ectopic implantation
* In the Uterine tubes (mostly ampulla & isthmus)
## Footnote
Increase in Ectopic pregnancy (1 in 80)=2% of all pregnancies
123
What is the main cause of maternal deaths (1st trimester)?
Tubal pregnancy
124
How do you diagnosis Ectopic pregnancies?
Endovaginal axial sonogram
125
What is Abdominal pregnancy?
## Footnote
Rare cases of Extrauterine Implantations
* Expulsion of the embryo from the fimbriated end into the abdominal cavity, leads to **Rectouterine pouch implantation** (abdominal).
* It may continue to full term and the *fetus is delivered alive* by **laparotomy**
126
What is Lithopedion?
## Footnote
Rare cases of Extrauterine Implantations
If an **abdominal conceptus dies** and is not detected; the **fetus becomes calcified**, forming a “stone fetus,” or lithopedion.
127
Explain Heterotopic pregnancies and Placenta Previa
## Footnote
Rare cases of Extrauterine Implantations
1. **Heterotrophic pregnancies**: Simultaneous intrauterine and extrauterine pregnancies (1:8000). With “super-ovulation drugs” the chance of heterotopic pregnancies increase by 25 fold! (~3:1000).
2. **Placenta Previa**: Implantation at the Internal Orifice (OS). Painless bleeding during the third trimester as the placenta partially or totally covers the opening of the mother's cervix.
128
What are the signs, symptoms & diagnosis of Extrauterine Implantations?
* **Abdominal pain & tenderness** due to *distention of the uterine tube.*
* **Abnormal vaginal bleeding** & pain in the *pelvic peritoneum (peritonitis)*.
* Ectopic pregnancies have **low secretion rate of β-human chorionic gonadotropin (β-hCG)**,
giving *false-negative pregnancy blood test (dangerous!).*
* **Transvaginal ultrasonography** can detect early ectopic tubal pregnancies
129
What are complications of Extrauterine Implantations?
**Rupture of the Uterine Tube**
* **Hemorrhage** into the *peritoneal cavity* & **death of the embryo by week 8.**
* **Tubal rupture** and hemorrhage causes **maternal mortality**
130
What are treatments of Extrauterine Implantations?
1. Prompt diagnosis, aggressive intervention & **surgical removal of the tube and conceptus.**
2. **Extrauterine pregnancies** in the abdomen is removed by **laparotomy.**
3. Rare **Cervical implantations** needs removal of the uterus **(hysterectomy)**
131
What is the definition of Abortion?
* “A premature stoppage of development and expulsion of a conceptus or embryo or fetus from the uterus before it is viable & capable of living outside the uterus”.
* An "abortus" is any product (or all products) of an abortion
## Footnote
Abortion is derived from latin “aboriri”, means to miscarry.
132
What are the different types of Abortion?
1. Threatened abortion
2. Spontaneous abortion (miscarriage)
3. Habitual abortion
4. Induced abortion
5. Complete abortion
6. Missed abortion
133
Explain Threatened abortion
* Profuse vaginal bleeding with high possibility of abortion
* 25% of all clinically apparent pregnancies have this symptom and half of these (~12-13%) embryos ultimately abort, despite utmost clinical care.
134
Explain Spontaneous abortion (miscarriage)
**Definition: “Pregnancy loss that occurs naturally before the 20th week of gestation”**
* Highest Frequency: 3rd week of fertilization.
* ~15% of diagnosed pregnancies end in spontaneous abortion (first 12 weeks).
* >50% of all known spontaneous abortions result from chromosomal abnormalities→Older women have high probability of nondisjunction during oogenesis→ abortion
135
Explain Habitual abortion
≥ 3 consecutive pregnancies result in spontaneous expulsion
of a dead or nonviable embryo or fetus
136
Explain Induced abortion
A medically induced birth before 20 weeks when the fetus is NOT viable ex vivo.
137
Explain Complete abortion
It is a process in which all products of conception (embryo and its membranes) are expelled from the uterus
138
Explain Missed abortion
It is the retention of a conceptus in the uterus after death of the embryo or fetus
139
What are ways to inhibit the implantation
1. Morning-after pills
2. Intrauterine devices (IUDs)
140
Explain the morning-after pills
* Large doses of progestins/estrogens for several days, right after unprotected sexual intercourse, usually may not prevent fertilization but often prevents implantation of the blastocyst.
* Examples:
1. High dose of Diethylstilbestrol (DES): Taken twice daily for 5- 6 days, accelerates passage of the cleaving zygote along the uterine tube. Mechanism: Huge amounts of estrogen alters estrogen:progesterone ratio & disrupts the endometrial preparation for implantation. (DO NOT USE-cancerious agents)
2. Plan B Drug (1999): Progestin-only (Levonorgestrel), Emergency Contraceptive Pill (ECP) taken within 72 hrs. after unprotected sex will prevent unwanted pregnancy (89% of times); but will not work in over-weight women >164 lbs). Mechanism: It stops release/movement of egg & prevent a sperm from fertilizing; thickens the vaginal fluid & alters the uterine wall.
141
Explain Intrauterine devices (IUDs)
* **Interferes with implantation by causing a local inflammatory reaction**
* Examples:
1. IUDs (Slow-release Progesterone): Disrupts the endometrial preparation for implantation.
2. IUDs with Copper Wire:
* Copper is directly toxic to sperms
* Copper induces uterine endothelial secretions that is toxic to sperms.
* Copper induces local inflammation, rendering endometrial wall incompetent for implantation
