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OBGYN Clerkship > Embryology > Flashcards

Embryology Flashcards

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

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2
Q

Anatomy of the upper and lower gubernaculum at 15 weeks in a female fetus

A
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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
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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.

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5
Q

Four layers of the placental membrane

A
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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
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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
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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.
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9
Q

Risk factors for abnormal placentation

A
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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
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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

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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.

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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.

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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
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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
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16
Q

Risk factors for placenta accreta

A

Previous cesarean section

Previous myotomy

Previous dilation and curetage

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17
Q

Basic embryology of the GU system

A
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18
Q

The Mullerian ducts give rise to. . .

A

. . . the fallopian tubes, uterus, and and upper 2/3 of vagina

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19
Q

The Wolfian ducts give rise to. . .

A

. . . the ureters, seminal vesicles, vas deferens, and epididymis

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20
Q

How a fetus becomes “male”

A
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21
Q

How a fetus becomes “female”

A
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22
Q

How the Mullerian ducts / Paramesonephric ducts form the uterus

A
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23
Q

Three main types of error in Mullerian anomalies

A
  1. 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)
  2. Errors in septal resorption: The septum between fused ducts persists, resulting in a septate uterus or an arcuate uterus (indentation where the septum was)
  3. 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.
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24
Q

Transverse vaginal septum

A
  • Results from failed Mullerian fusion or failed vaginal canalization
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25
Q

Longitudinal vaginal septum

A
  • Defective lateral fusion or incomplete septal resorpton of the caudal portion of the Mullerian ducts
  • Often seen with uterine didelphys (double uterus)
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26
Q

Disorders of Mullerian duct development have no effect on. . .

A

. . . 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.

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27
Q

Once a Mullerian anomaly is confirmed, women must also be evaluated for ___, which tend to occur with Mullerian anomalies.

A

Once a Mullerian anomaly is confirmed, women must also be evaluated for renal anomalies, which tend to occur with Mullerian anomalies.

28
Q

Women with unicornuate uterus are at risk for ___

A

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
Q

Gold standard for diagnosing uterine anomalies

A

MRI

30
Q

Order of female egg cell progenitors in oogenesis

A
  1. Oogonium
  2. Primary oocyte
  3. Secondary oocyte
31
Q

By week ___, the embryo is referred to as a fetus

A

By week 9, the embryo is referred to as a fetus

32
Q

Site of fetal hematopoiesis over time

A
33
Q

“Periods” of development

A

Embryonic: Wk 1-8

Fetal: Wk 9-birth

34
Q

The time from fertilization to implantation of the blastocyst is approximately. . .

A

. . . 1 week

35
Q

The major event that takes place during week 3 of embryogenesis

A

Gastrulation begins w/ formation of primitive streak and primitive node

36
Q

The yolk sac and amnion develop. . .

A

. . . simultaneously during week 2 of embryogenesis

37
Q

Role of serotonin in early gastrulation

A

Serotonin regulates the orientation of mesoderm development during gastrulation, effectively deciding which end forms the head. It drives expression of the NODAL gene (normal development of laterality), 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
Q

Heterotaxy

A
  • 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
Q

Timeline of embryonic organ development (and consequentially, timeline of which phases of development are affected by insults at any given time)

A
40
Q

Frequent fevers or hot-tub or sauna use early in pregnancy may result in. . .

A

. . . defects in neural tube development and microcephaly

41
Q

A beta hCG over ___ is consistent with pregnancy (or GTD)

A beta hCG over ___ is highly likely to be GTD.

A

A beta hCG over 2000 is consistent with pregnancy (or GTD)

A beta hCG over 100,000 is highly likely to be GTD.

42
Q

Trophoblasts differentiate into which two cell types?

A

Cytotrophoblasts

Syncytiotrophoblasts

43
Q

Steps in implantation

A
  • 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
Q

Resumption of Meiosis I during puberty

A

The resultant haploid oocyte arrests in metaphase II until fertilization

45
Q

5 common aneuploidys which may result in a viable fetus

A
  • Down’s (trisomy 21)
  • Edward’s (trisomy 18)
  • Patau’s (trisomy 13)
  • Turner’s (45, X)
  • Kleinfelter’s (47, XXY)
46
Q

A fertilized zygote will remain in the zona pellucidum as it divides to the 2-cell, 4-cell, 8-cell stage, etc. until. . .

A

. . . 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
Q

Blastocyst to amnionic-fetal unit

A
48
Q

All dizygotic twins are __ __ during development

A

All dizygotic twins are dichorionic, diamniotic during development

49
Q

Timing of the split of monozygotic twins and resultant chorionicity and amnionicity

A
  • 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
Q

Diagnosing dichorionic pregnancies

A
  • Observance of the lambda sign on ultrasound:
    • Visualizing the septum between two separate chorions
    • Most specific between 10-14 weeks
51
Q

Diagnosing monochorionic diamniotic pregnancies

A
  • Visualization of the thin membrane between two amnionic sacs on ultrasound:
52
Q

Diagnosing monochorionic monoamniotic pregnancies

A

No lambda sign or thin amniotic dividing membrane on ultrasound

53
Q

Possible complications of twin pregnancies

A
  • Uneven distribution of nutrients:
    • Dichorionic by mechanism of unequal placentation
    • Monochorionic by mechanism of uneven chorio-fetal flow or anastamoses
54
Q

Complication unique to monochorionic twins

A
  • 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
Q

Complication unique to non-conjoined monochorionic monoamniotic twins

A

Higher prevalence of fetal cord entanglement and intrauterine death due to the presence of two cords in the same amnion

56
Q

When does amniotic fluid start to be produced?

A

~16 weeks gestation

In otherwords, this is when the fetal kidneys start producing urine!

57
Q

The corpus luteum is the main source of progesterone until about ___ weeks gestation

A

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
Q

Risk of congenital defects for infants delivered by “true” gestational diabetics

A

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
Q

If beta-hCG is above ___, you should be able to see a viable intraterine pregnancy if one is present.

A

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
Q

Management of threatened abortion

A
61
Q

Progesterone in viable vs nonviable gestations

A

Progesterone > 25 ng/mL almost always indicates viable intrauterine gestation

Progesterone < 5 ng/mL almost always indicates nonviable gestation

62
Q

After ANY delivery or abortion, you should ALWAYS follow. . .

A

. . . 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
Q

The defining historical feature in distinguishing between inevitable abortion and cervical insufficiency

A

The presence or absence of uterine contractions

Present in abortion, absent in cervical insufficiency

64
Q

Management of spontaneous abortion and cervical insufficiency based on clinical history

A
  • 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
Q

Indications for using methotrexate for an ectopic pregnancy

A
  • 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

OBGYN Clerkship (30 decks)

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