Embryology Flashcards
(65 cards)
1
Q
Gubernaculum
A
Connective tissue that aids in the descent of the gonads by steering them into place in both males and females.
It has developed by ~8 weeks and is only present during the development of the genitourinary systems, after which it atrophies. However, females retain two vestigial reminants: the ovarian ligament and the round ligament of the uterus
2
Q
Anatomy of the upper and lower gubernaculum at 15 weeks in a female fetus
A
3
Q
Timecourse of embryonic vili development
A
- They’re always one week behind
- The primary form by week 2
- The secondary by week 3
- The tertiary by week 4
4
Q
Chorionic villus structure
A
Note that the terminal villi are the region of gas and nutrient exchange.
In this diagram, the intervillous space is filled with maternal blood.
5
Q
Four layers of the placental membrane
A
6
Q
Placental sources of VEGF
A
- The initial source of VEGF is the cytotropoblast
- Later, the Hofbauer cells and stromal cells take over
- Hofbauer cells are placental macrophages
7
Q
Fibrin-type fibrinoid, matrix-type fibrinoid, and Nitabuch’s layer
A
- Fibrin-type fibrinoid is a product of maternal clotting which replaces degenerating syncytiotrophoblasts
- Matrix-type fibrinoid is secreted by invasive extravillous extratrophoblastic cells
- Together, they form Nitabuch’s layer, a band of fibrinoid tissue thought to serve the role of preventing excessively-deep implantation. Loss of this layer can lead to abnormal placentation invasion
8
Q
Fate of the two layers of the trophoblast
A
- Outer layer: The syncytiotrophoblast. After implantation, it is replaced by fibrinoid tissue to form Nitabuch’s layer.
- Inner layer: Cytotrophoblast. Stimulates vasculogenesis in the chorion.
9
Q
Risk factors for abnormal placentation
A
10
Q
Placenta previa
A
- Form of abnormal placentation
- Pathogenesis not currently understood
- Risks include previous surgery and previous pregnancy
- Generally speaking, the placenta is in front of the cervical os
- Involves areas of sub-optimal vascularized descidua, promoting movement of trophoblasts to the lower uterine cavity
11
Q
Vasa previa
A
Sub-group of placenta previa
In vasa previa, fetal blood vessels from the placenta or umbilical cord cover the cervical os
Major risks include velamentous or succenturiate-morphology placenta
12
Q
If placenta previa of any form is detected, ___ is contraindicated due to risk of placental hemorrhage.
A
If placenta previa of any form is detected, any form of vaginal manipulation (vaginal exam, sexual intercourse, etc) is contraindicated due to risk of placental hemorrhage.
13
Q
In placenta previa, ___ is at risk of bleeding.
In vasa previa, ___ is at risk of bleeding.
A
In placenta previa, the mother is at risk of bleeding.
In vasa previa, the infant is at risk of bleeding.
14
Q
Placenta accreta
A
- Anchoring placental villi attach to the myometrium instead of the decidua, resulting in a placenta which adheres to the uterine lining
- Prior cessarian section is the main risk factor
- Down the road, the decidua basalis is absent
- Nitabuch’s layer is often disrupted
15
Q
Placenta accreta, increta, and percreta
A
- Accreta: Decidua basalis is missing, but the placenta is not infriltrative
- Increta: Placenta infiltrates the myometrium, but does not penetrate the serosa
- Percreta: Placenta penetrates through the myometrium into the serosa
16
Q
Risk factors for placenta accreta
A
Previous cesarean section
Previous myotomy
Previous dilation and curetage
17
Q
Basic embryology of the GU system
A
18
Q
The Mullerian ducts give rise to. . .
A
. . . the fallopian tubes, uterus, and and upper 2/3 of vagina
19
Q
The Wolfian ducts give rise to. . .
A
. . . the ureters, seminal vesicles, vas deferens, and epididymis
20
Q
How a fetus becomes “male”
A
21
Q
How a fetus becomes “female”
A
22
Q
How the Mullerian ducts / Paramesonephric ducts form the uterus
A
23
Q
Three main types of error in Mullerian anomalies
A
- Error in fusion: The ducts do not properly fuse, resulting in a “horned” uterus (bicornuate), a uterus with a dominant side (unicornuate), or two completely separate small uteri (uterine didelphys)
- Errors in septal resorption: The septum between fused ducts persists, resulting in a septate uterus or an arcuate uterus (indentation where the septum was)
- Errors in organogenesis: All or part of the Mullerian tract fails to form. Namely causes Mullerian agenesis, where the vagina is absent and uterine development is variable.
24
Q
Transverse vaginal septum
A
- Results from failed Mullerian fusion or failed vaginal canalization
25
Longitudinal vaginal septum
* Defective lateral fusion or incomplete septal resorpton of the caudal portion of the Mullerian ducts
* Often seen with uterine didelphys (double uterus)
26
Disorders of Mullerian duct development have no effect on. . .
. . . **the ovaries**
The ovaries are **NOT derived from the Mullerian ducts**. And, they will function endocrinologically **regardless of the status of the Mullerian ducts.**
So, individuals with even Mullerian agenesis will be phenotypically female with normal estrogen levels and breast development.
27
Once a Mullerian anomaly is confirmed, women must also be evaluated for \_\_\_, which tend to occur with Mullerian anomalies.
Once a Mullerian anomaly is confirmed, women must also be evaluated for **renal anomalies**, which tend to occur with Mullerian anomalies.
28
Women with unicornuate uterus are at risk for \_\_\_
Women with unicornuate uterus are at risk for **retromenstruation**
Endometriosis in the non-communicating portion of the uterus may result in blood back-up into the peritoneal cavity
29
Gold standard for diagnosing uterine anomalies
MRI
30
Order of female egg cell progenitors in oogenesis
1. Oogonium
2. Primary oocyte
3. Secondary oocyte
31
By week \_\_\_, the embryo is referred to as a fetus
By week **9**, the embryo is referred to as a fetus
32
Site of fetal hematopoiesis over time
33
"Periods" of development
Embryonic: Wk 1-8
Fetal: Wk 9-birth
34
The time from fertilization to implantation of the blastocyst is approximately. . .
. . . **1 week**
35
The major event that takes place during week 3 of embryogenesis
Gastrulation begins w/ formation of primitive streak and primitive node
36
The yolk sac and amnion develop. . .
. . . **simultaneously during week 2 of embryogenesis**
37
Role of serotonin in early gastrulation
Serotonin regulates the **orientation of mesoderm** development during gastrulation, effectively deciding which end forms the head. It drives expression of the NODAL gene (**no**rmal **d**evelopment of **la**terality), which ensures normal left-right positioning of organs.
If this is disrupted, it can lead to anatomical anomalies such as **dextrocardia**, **heterotaxy,** or **situs inversus.**
38
Heterotaxy
* Congenital anatomical anomaly due to disruption of serotonin in week 3 of development.
* Characterized by a constellation of:
* **Abnormal organ laterality** (hypoplastic left or right heart syndrome)
* **Cardiac defects**
* **Absent spleen OR multiple spleens**
39
Timeline of embryonic organ development (and consequentially, timeline of which phases of development are affected by insults at any given time)
40
Frequent fevers or hot-tub or sauna use early in pregnancy may result in. . .
. . . **defects in neural tube development and microcephaly**
41
A beta hCG over ___ is consistent with pregnancy (or GTD)
A beta hCG over ___ is highly likely to be GTD.
A beta hCG over **2000** is consistent with pregnancy (or GTD)
A beta hCG over **100,000** is highly likely to be GTD.
42
Trophoblasts differentiate into which two cell types?
Cytotrophoblasts
Syncytiotrophoblasts
43
Steps in implantation
* Begin on day 6-7
* **Apposition:** Loose connection forms between trophoblasts and endometrium
* **Adhesion:** Blastocyst anchors to the endometrium
* **Invasion:** Trophoblasts invade maternal capillaries to form the maternal-fetal circulation
44
Resumption of Meiosis I during puberty
The resultant haploid oocyte arrests in metaphase II until fertilization
45
5 common aneuploidys which may result in a viable fetus
* Down's (trisomy 21)
* Edward's (trisomy 18)
* Patau's (trisomy 13)
* Turner's (45, X)
* Kleinfelter's (47, XXY)
46
A fertilized zygote will remain in the zona pellucidum as it divides to the 2-cell, 4-cell, 8-cell stage, etc. *until*. . .
. . . **it reaches the uterus as a blastocyst**
Here **endometrial proteases** will break down the zona pellucidum
This step helps avoid ectopic pregnancy and facilitates proper implantation of the trophoblasts into the endometrium
47
Blastocyst to amnionic-fetal unit
48
All dizygotic twins are __ \_\_ during development
All dizygotic twins are **dichorionic,** **diamniotic** during development
49
Timing of the split of monozygotic twins and resultant chorionicity and amnionicity
* **First 3 days after fertilization**: (prior to morula stage) _Dichorionic, diamniotic_
* **Days 4-8 after fertilization:** (after trophoblast differentiation, before amnion has formed) _Monochorionic, diamniotic_
* **Days 8-12 after fertilization**: (after differentiation of the chorion and amnion, but before formation of embryonic disk) _Monochorionic, monoamniotic_
* **Day 13 or later:** (after formation of embryonic disk) _Monochorionic, monoamniotic, conjoined_
50
Diagnosing dichorionic pregnancies
* Observance of the **lambda sign** on ultrasound:
* Visualizing the septum between two separate chorions
* Most specific between 10-14 weeks
51
Diagnosing monochorionic diamniotic pregnancies
* Visualization of the thin membrane between two amnionic sacs on ultrasound:
52
Diagnosing monochorionic monoamniotic pregnancies
No lambda sign or thin amniotic dividing membrane on ultrasound
53
Possible complications of twin pregnancies
* Uneven distribution of nutrients:
* **Dichorionic** by mechanism of **unequal placentation**
* **Monochorionic** by mechanism of **uneven chorio-fetal flow** or **anastamoses**
54
Complication unique to monochorionic twins
* **Twin-to-twin transfusion syndrome**
* AV anastamosis in the chorion Results in a unidirectional blood shunt from one twin to the other
* Interventions:
* Laser ablation of anastamosis
* Septostomy
* Amnioreduction
* Selected reduction
55
Complication unique to non-conjoined monochorionic monoamniotic twins
Higher prevalence of fetal cord entanglement and intrauterine death due to the presence of two cords in the same amnion
56
When does amniotic fluid start to be produced?
~16 weeks gestation
In otherwords, this is when the fetal kidneys start producing urine!
57
The corpus luteum is the main source of progesterone until about ___ weeks gestation
The corpus luteum is the main source of progesterone until about **10** weeks gestation
Therefore, if the corpus luteum is removed prior to ~10 weeks EGA, exogenous progesterone is needed to maintain a pregnancy. However, if it is removed following ~10 weeks EGA, the placenta can take over without exogenous help.
58
Risk of congenital defects for infants delivered by "true" gestational diabetics
Since gestational diabetes trypically does not cause a substantial elevation in blood glucose until ~2nd term, blood glucose levels are relatively normal during organogenesis, which is the time when these anomalies first develop.
So, if an individual has "true" gestational diabetes, their rate of congenital anomalies is approximately the same as that of the general population.
For the same reason, true diabetics with tightly-controlled blood glucose and an A1c \< 7% at the beginning of their pregnancy are not at increased risk either.
59
If beta-hCG is above \_\_\_, you should be able to see a viable intraterine pregnancy if one is present.
If beta-hCG is above **2000**, you should be able to see a viable intraterine pregnancy if one is present.
Otherwise, it is likely ectopic or non-viable
60
Management of threatened abortion
61
Progesterone in viable vs nonviable gestations
Progesterone **\> 25 ng/mL** almost always indicates **viable** intrauterine gestation
Progesterone **\< 5 ng/mL** almost always indicates **nonviable** gestation
62
After ANY delivery or abortion, you should ALWAYS follow. . .
. . . **hCG until it reaches zero**
For a completed abortion it should halve every 48-72 hours. If they plateau, this likely indicates retained tissue (incomplete abortion OR ectopic pregnancy) and the cervix will often remain partially open
63
The defining historical feature in distinguishing between inevitable abortion and cervical insufficiency
The presence or absence of uterine contractions
Present in abortion, absent in cervical insufficiency
64
Management of spontaneous abortion and cervical insufficiency based on clinical history
* Premature cervical dilation without passage of material or contractions: **Cervical insufficiency, treat w/ cerclage**
* Premature cervical dilation without passage of material and with ongoing contractions: **Inevitable abortion, follow hCG and cervical status**
* Premtaure cervical dilation without passage of material and with contractions which have since stopped: **Missed abortion, treat with D&C**
* Premature cervical dilation with passage of material and with ongoing contractios: **Incomplete abortion, treat with D&C**
65
Indications for using methotrexate for an ectopic pregnancy
* 100% certainty of the diagnosis (visualization of an adnexal or ectopic mass on ultrasound)
* Features of ectopic make it susceptible:
* Size \< 3.5 cm
* No heart tones
* bHCG \< 5000 mIU/mL
