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Pediatrics Exam 1 > Embryology > Flashcards

Embryology Flashcards

(72 cards)

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1
Q

Follicular phase

A

(days 1–14)
– Selection of the dominant
“ovulatory” follicle
– ↑ estrogen levels
– Endometrial thickening

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2
Q

Luteal phase

A

(days 14–21)
– Corpus luteum produces
estrogen and progesterone
– Endometrium prepared for
implantation

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3
Q

How would implantation occur?

A

Blastocyst produces human chorionic gonadotropin (hCG) thus maintaining progesterone production

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4
Q

Gestational Age or Menstrual Age

A

Time since the 1st day of the last menstrual period (LMP), which predates conception

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5
Q

EDC & Naegele rule

A

Estimated Date of Confinement (EDC)
– Naegele Rule
1st Day of LMP + 7 day − 3 months = EDC

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6
Q

Fertilization timeline

A

Takes place within hours (no more than a day) after ovulation
* Fusion of the nuclei of the maternal & paternal gametes
* Haploid chromosome sets intermingle & create the Zygote

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7
Q

Fertilization Steps

A
  1. Passage of sperm through the corona radiata
  2. Penetration of the zona pellucida
  3. Fusion of plasma membranes of oocyte &
    sperm
  4. Completion of 2nd meiotic division of oocyte
  5. Formation of male pronucleus
  6. Breakdown of pronuclear membranes
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8
Q

What happens 24 hrs after fertilization?

A

The diploid cell with 46 chromosomes undergoes cleavage –> forming 2 blastomeres.
* Blastomeres & polar body
are surrounded by the zona
pellucida
* Blastomeres divide & form a solid
a 16-cell morula

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9
Q

What happens 3 days post fertilization?

A
  • Morula enters the uterine cavity
  • Fluid forms between the cells of
    the morula creating the
    early blastocyst
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10
Q

What happens ~5 days postfertilization?

A
  • 58-cell blastula differentiates into
    the inner cell mass
    – 5 embryo-producing cells
    – 53 outer cells
    (trophectoderm) will become
    trophoblasts
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11
Q

What is the 107-cell blastocyst composed of?

A
  • 8 embryo-producing cells surrounded by 99 trophoblastic cells
  • Secretory-phase endometrial glands release proteases
    – Releases blastocyst from the
    zona pellucida
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12
Q

What happens ~6-7 day postfertilization?

A

Implantation into the uterine wall
1. Apposition—Initial contact of the blastocyst to the uterine wall
2. Adhesion— ↑contact between the blastocyst & decidua (thick modified mucous membrane, lines pregnant uterus)
3. Invasion—Penetration & invasion of
syncytiotrophoblasts & cytotrophoblasts into the functional layer of the endometrium

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13
Q

The placenta will develop from the
_____ encircling the blastocyst

A

trophoblast cell layer

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14
Q

What happens ~Day 8 postfertilization?

A
  • Trophoblasts have differentiated
    – Outer layer
  • primitive syncytiotrophoblast
    – Inner layer
  • cytotrophoblasts
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15
Q

After implantation is complete, trophoblasts further differentiate & give rise to _____

A

villous & extravillous trophoblasts

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16
Q

What do Villous trophoblasts do?

A

generate chorionic villi (fingerlike projections)
– Transport oxygen, nutrients, & other compounds between
the fetus & mother

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17
Q

What do Extravillous trophoblasts do?

A

are further classified as interstitial
trophoblasts & endovascular trophoblasts

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18
Q

What do Interstitial trophoblasts do?

A

invade the decidua & myometrium to
form placental-bed giant cells & surround spiral arteries

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19
Q

What do Endovascular trophoblasts do?

A

invade & transform spiral arteries
during pregnancy to create low-resistance blood flow that is characteristic of the placenta

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20
Q

What happens ~9-10 days postfertilization?

A
  • Blastocyst wall facing the uterine
    lumen is a single layer of flattened cells
  • Becomes totally encased within the
    endometrium
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21
Q

What happens ~12 days postfertilization?

A
  • Maternal blood fills lacunar network
  • Large cavities appear in the
    extraembryonic mesoderm
  • Extraembryonic endodermal cells
    form on the inside of the primitive
    yolk sac
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22
Q

What are Chorionic Villi?

A
  • Primary villi arise from buds of
    cytotrophoblasts
  • Lacunae join & form a complicated
    labyrinth partitioned by cytotrophoblastic
    columns
  • Trophoblast-lined channels form the
    intervillous space, & the solid cellular columns
    form the primary villous stalks
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23
Q

What happens ~15-17 days postfertilization?

A
  • Mesenchymal cords from extraembryonic
    mesoderm invade the solid trophoblast columns
    & form secondary villi
  • Angiogenesis* in the mesenchymal cords forms tertiary villi
  • Maternal arterial blood enters the intervillous
    space & fetal blood vessels become functional
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24
Q

Postovulatory age:

A

~15-17 (week 3)
* Organogenesis begins
* Gastrulation = Conversion of
bilaminar embryonic disc to a
trilaminar embryonic disc
* Morphogenesis begins
* Primitive streak forms

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25
Largest susceptibility to developmental defects occurs when?
Postovulatory age: ~15-17 (week 3)
26
Week 3
* Development of the Notochord – Migrates ventral and cranial to the primitive streak/node – Defines the axis of the embryo * Neurulation begins = formation of the neural tube * Primitive tube (heart) develops (cardiogenic mesoderm) * Mesonephric duct
27
Week 5
* Chorionic/gestational sac measures ~1 cm in diameter * Embryo ~3 mm long * Arm & leg buds developed * Amnion begins to ensheath the body stalk
28
Week 6
* Embryo ~9 mm long – Neural tube closed * cranial end 38 days from LMP * caudal end closes 40 days from LMP * Cardiac motion is discernable sonographically
29
Week 8
End of the embryonic period * Crown-rump length ~22 mm * Fingers & toes are present * Arms bend at the elbows * Upper lip is complete
30
Week 9
* ~24 mm in length * Most organ systems have begun to develop
31
Week 10
* Bone growth of the front of the skull * Placenta supplants the yolk sac
32
Week 11
* Neck has lengthened * Eyes & ears are visible, but not functional
33
Week 12
* Crown-rump length ~5 to 7 cm * Most bones have centers of ossification * Fingers & toes forming * Patches of hair; skin & nails develop * Male/female external genitalia show * Spontaneous movements
34
Week 13
* Crown-rump length ~7 cm * Wt ~25 gm * Pancreas producing insulin * Female clitoris, labia have formed
35
End of 1st Trimester
End of week 13
36
Week 14
* Forearms, wrists, hands, fingers are differentiated * Eyes migrate toward midline; behind the sealed eyelids
37
Week 15
* Jaw lengthens, chin held away from the chest * Hands & outstretched fingers are commonly close to the face * Canaliculi (small channels/ducts) of the lungs begin to form
38
Week 16
* Crown-rump length* ~12 cm; Wt ~100 gm * Biparietal diameter, head circumference, abd. circumference, & femur length are measured & used to estimate weight * Eyes can blink * Finger/toe-prints form * Male penis, urethra, & scrotum formed
39
Week 17
* ~12.7 cm; ~140 gm – Would fit comfortably in your palm * Cranial bone replacing cartilage * Blood vessels/supply proliferating * Small fat deposits begin to develop * Heart pumps 25+ oz of blood/day * Moving joints
40
Week 18
* Full movement of the arms & legs * Yawning * Nerves developing/myelinating * Hearing developing * Vision developing * Female uterus is formed * Vaginal canalization begins
41
Week 19
* ~15 cm & Wt ~240 gm * Skin wrinkled, vernix caseosa * Umbilical cord coiled (prevents kinking) * Teeth forming, bones ossifying * Muscles developing * Kidneys producing urine * Digestive tract producing meconium
42
Week 20
– Midpoint of gestation * ~15 cm & Wt ~300 gm * Thumb sucking, stretching * Facial movements * “Quickening” (mom feels movement) * Brown fat forming; skin less transparent * Lanugo covers the body; some scalp hair present
43
Week 21
* Head to heal length ~26 cm long * Wt ~355 gm * Intestines contract & relax * Heart rate is ~120-160 BPM * Red blood cell production begins to shift from liver to bone marrow
44
Week 22
* Hearing internal & external sound * Sense of touch developing * Fingers moving * Taste buds developing * Liver begins breaking down bilirubin * Male testes begin descent
45
Week 23
* ~29 cm & Wt ~450 gm * Eyes fully formed, no iris pigment * Skin pigment developing * Organs continue development
46
Week 24
* ~30 cm ~565 gm * Secretory type II pneumocytes secrete surfactant – Terminal alveoli not yet fully formed * Neural pain system is developed
47
Week 25
~34 cm ~680 gm * Spine structures begin to form * Lungs rapidly developing
48
Week 26
* ~35.5 cm ~900 gm * Active brain growth * Male testes descended
49
End of 2nd Trimester
End of week 26
50
Week 27
* ~36.8 cm ~907 gm * Able to stick out the tongue out – Esp. before or after a particularly large gulp of amniotic fluid
51
Week 28
* ~37.5 cm ~925 gm * Brain activity indicates dreaming
52
Week 29
* ~38 cm ~1200 gm * Fat deposition continues * Skin smoothing
53
Week 30
* ~39 cm ~1400 gm * Brain sulci & gyri becoming prominent * Lanugo diminishing * Bone marrow producing more RBC * Digestive tract nearly fully formed
54
Week 31
* ~41 cm ~1500 gm * May be positioned head down * All 5 senses intact * Eye lids blink
55
Week 32
* ~42 cm ~1800 kg * Skin smooth & thickening * Bones calcifying
56
Week 33
* ~43 cm ~2000 gm * Hair on the head is growing * Regularly practicing “breathing”: Would likely need some support breathing if born this early
57
Week 34
* ~44.5 cm ~2500 gm * Fat deposition increases
58
Week 35
* ~46 cm ~2500 gm * Kidney development complete * Lung development nearly complete
59
Week 36
* 47 cm ~2.7 gm * Body fat increases * Skin is pink 2° to blood vessel proliferation subcutaneously
60
Week 37
* ~48 cm ~2800 gm * No longer considered a “preemie” * ACOG: – Babies born 37 – 38 weeks 6 days – Early-Term
61
Week 38
* ~46 cm ~3000 gm * Rooting reflex initiates suckling at every opportunity (parts of the hands, thumbs or fingers)
62
Week 39
* ~50 cm ~3-3500 gm * ACOG: – Babies born at 39 weeks 0 days – Full Term
63
When do ovaries develop?
11-13 weeks gestation
64
When do testes develop
6 weeks gestation
65
– Disorders of Sex Development (DSD)
DSD are congenital conditions in which development of chromosomal, gonadal, or anatomic sex is atypical
66
DSDs Classification: 46,XX DSD
virilized female – Disorders of androgen excess – Disorders of gonadal development
67
46,XY DSD
undervirilized male – Disorders of androgen action or synthesis – Disorders of gonadal development
68
Ovotesticular DSD
– Ovarian & testicular tissue – abnormal vagina – hypoplastic uterus – Usually 46,XX
69
Mixed gonadal dysgenesis
– 45,X/46,XY mosaicism » 42% = phenotypic ♀(Turner syndrome) » 42% = ambiguous external genitalia, asymmetrical gonads » 15% = phenotypic ♂(incomplete) – Phenotype dependent on % of blood & gonadal tissue genetic variation
70
Klinefelter syndrome
47, XXY – ♂ phenotype, typically
71
Turner syndrome
(45,XO) – ♀ phenotype, typically
72
Precursors of external genitalia =
urogenital tubercle, swelling, & folds

Pediatrics Exam 1 (6 decks)

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