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Pediatrics Exam 1 > Embryology > Flashcards

Embryology Flashcards

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
Q

Largest susceptibility to
developmental defects occurs when?

A

Postovulatory age: ~15-17 (week 3)

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26
Q

Week 3

A
  • 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
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27
Q

Week 5

A
  • Chorionic/gestational sac
    measures ~1 cm in diameter
  • Embryo ~3 mm long
  • Arm & leg buds developed
  • Amnion begins to ensheath
    the body stalk
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28
Q

Week 6

A
  • 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
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29
Q

Week 8

A

End of the embryonic period
* Crown-rump length ~22 mm
* Fingers & toes are present
* Arms bend at the elbows
* Upper lip is complete

30
Q

Week 9

A
  • ~24 mm in length
  • Most organ systems have
    begun to develop
31
Q

Week 10

A
  • Bone growth of the front of the
    skull
  • Placenta supplants the yolk sac
32
Q

Week 11

A
  • Neck has lengthened
  • Eyes & ears are visible, but not
    functional
33
Q

Week 12

A
  • 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
Q

Week 13

A
  • Crown-rump length ~7 cm
  • Wt ~25 gm
  • Pancreas producing insulin
  • Female clitoris, labia have formed
35
Q

End of 1st Trimester

A

End of week 13

36
Q

Week 14

A
  • Forearms, wrists, hands, fingers are
    differentiated
  • Eyes migrate toward midline; behind
    the sealed eyelids
37
Q

Week 15

A
  • 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
Q

Week 16

A
  • 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
Q

Week 17

A
  • ~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
Q

Week 18

A
  • Full movement of the arms & legs
  • Yawning
  • Nerves developing/myelinating
  • Hearing developing
  • Vision developing
  • Female uterus is formed
  • Vaginal canalization begins
41
Q

Week 19

A
  • ~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
Q

Week 20

A

– 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
Q

Week 21

A
  • 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
Q

Week 22

A
  • Hearing internal & external sound
  • Sense of touch developing
  • Fingers moving
  • Taste buds developing
  • Liver begins breaking down bilirubin
  • Male testes begin descent
45
Q

Week 23

A
  • ~29 cm & Wt ~450 gm
  • Eyes fully formed, no iris pigment
  • Skin pigment developing
  • Organs continue development
46
Q

Week 24

A
  • ~30 cm ~565 gm
  • Secretory type II pneumocytes
    secrete surfactant
    – Terminal alveoli not yet fully formed
  • Neural pain system is developed
47
Q

Week 25

A

~34 cm ~680 gm
* Spine structures begin to form
* Lungs rapidly developing

48
Q

Week 26

A
  • ~35.5 cm ~900 gm
  • Active brain growth
  • Male testes descended
49
Q

End of 2nd Trimester

A

End of week 26

50
Q

Week 27

A
  • ~36.8 cm ~907 gm
  • Able to stick out the tongue out
    – Esp. before or after a particularly
    large gulp of amniotic fluid
51
Q

Week 28

A
  • ~37.5 cm ~925 gm
  • Brain activity indicates dreaming
52
Q

Week 29

A
  • ~38 cm ~1200 gm
  • Fat deposition continues
  • Skin smoothing
53
Q

Week 30

A
  • ~39 cm ~1400 gm
  • Brain sulci & gyri becoming
    prominent
  • Lanugo diminishing
  • Bone marrow producing more RBC
  • Digestive tract nearly fully formed
54
Q

Week 31

A
  • ~41 cm ~1500 gm
  • May be positioned head down
  • All 5 senses intact
  • Eye lids blink
55
Q

Week 32

A
  • ~42 cm ~1800 kg
  • Skin smooth & thickening
  • Bones calcifying
56
Q

Week 33

A
  • ~43 cm ~2000 gm
  • Hair on the head is growing
  • Regularly practicing “breathing”: Would likely need some support breathing if born this early
57
Q

Week 34

A
  • ~44.5 cm ~2500 gm
  • Fat deposition increases
58
Q

Week 35

A
  • ~46 cm ~2500 gm
  • Kidney development complete
  • Lung development nearly complete
59
Q

Week 36

A
  • 47 cm ~2.7 gm
  • Body fat increases
  • Skin is pink 2° to blood vessel
    proliferation subcutaneously
60
Q

Week 37

A
  • ~48 cm ~2800 gm
  • No longer considered a “preemie”
  • ACOG:
    – Babies born 37 – 38 weeks 6 days
    – Early-Term
61
Q

Week 38

A
  • ~46 cm ~3000 gm
  • Rooting reflex initiates suckling at
    every opportunity (parts of the
    hands, thumbs or fingers)
62
Q

Week 39

A
  • ~50 cm ~3-3500 gm
  • ACOG:
    – Babies born at 39 weeks 0 days
    – Full Term
63
Q

When do ovaries develop?

A

11-13 weeks gestation

64
Q

When do testes develop

A

6 weeks gestation

65
Q

– Disorders of Sex Development (DSD)

A

DSD are congenital conditions in which development of
chromosomal, gonadal, or anatomic sex is atypical

66
Q

DSDs Classification: 46,XX DSD

A

virilized female
– Disorders of androgen
excess
– Disorders of gonadal
development

67
Q

46,XY DSD

A

undervirilized male
– Disorders of androgen action
or synthesis
– Disorders of gonadal
development

68
Q

Ovotesticular DSD

A

– Ovarian & testicular
tissue
– abnormal vagina
– hypoplastic uterus
– Usually 46,XX

69
Q

Mixed gonadal dysgenesis

A

– 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
Q

Klinefelter syndrome

A

47, XXY
– ♂ phenotype, typically

71
Q

Turner syndrome

A

(45,XO)
– ♀ phenotype, typically

72
Q

Precursors of external genitalia =

A

urogenital tubercle, swelling, & folds

Pediatrics Exam 1 (6 decks)

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