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Flashcards in Reproductive - Embryology Deck (40):
1

Important genes of embryogenesis

  • Sonic hedgehog gene
    • Produced...
    • Function(s)
  • Wnt-7 gene
    • Produced...
    • Function(s)
    • Mutation(s) -->
  • FGF gene
    • Produced...
    • Function(s)
  • Homeobox (Hox) genes
    • Function(s)
    • Mutation(s) -->

  • Sonic hedgehog gene
    • Produced at base of limbs in zone of polarizing activity.
    • Function(s)
      • Involved in patterning along anterior-posterior axis.
      • Involved in CNS development
    • Mutation can cause holoprosencephaly.
  • Wnt-7 gene
    • Produced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb). 
    • Necessary for proper organization along dorsal-ventral axis.
  • FGF gene
    • Produced at apical ectodermal ridge.
    • Stimulates mitosis of underlying mesoderm, providing for lengthening of limbs.
  • Homeobox (Hox) genes
    • Involved in segmental organization of embryo in a craniocaudal direction.
    • Hox mutations -->Ž appendages in wrong locations.

2

Early fetal development (552)

  • Day 0 
  • Within week 1 
  • Within week 2
  • Within week 3
  • Weeks 3–8 (embryonic period)
  • Week 4
  • Week 6
  • Week 10

  • Day 0
    • Fertilization by sperm, forming zygote, initiating embryogenesis.
  • Within week 1
    • hCG secretion begins around the time of implantation of blastocyst.
  • Within week 2
    • Bilaminar disc (epiblast, hypoblast).
      • 2 weeks = 2 layers.
  • Within week 3
    • Trilaminar disc.
      • 3 weeks = 3 layers. 
    • Gastrulation.
    • Primitive streak, notochord, mesoderm and its organization, and neural plate begin to form.
  • Weeks 3–8 (embryonic period)
    • Neural tube formed by neuroectoderm and closes by week 4.
    • Organogenesis.
    • Extremely susceptible to teratogens.
  • Week 4
    • Heart begins to beat.
    • Upper and lower limb buds begin to form.
      • 4 weeks = 4 limbs.
  • Week 6
    • Fetal cardiac activity visible by transvaginal ultrasound.
  • Week 10
    • Genitalia have male/female characteristics.

3

Gastrulation

  • Process that forms the trilaminar embryonic disc.
  • Establishes the ectoderm, mesoderm, and endoderm germ layers.
  • Starts with the epiblast invaginating to form the primitive streak.

4

Embryologic derivatives:
Surface ectoderm

  • Derivatives
  • Craniopharyngioma

  • Derivatives
    • All Epidermis PALE
    • Adenohypophysis (from Rathke pouch)
    • Epidermis
    • Parotid, sweat, and mammary glands
    • Anal canal below the pectinate line
    • Lens of eye
    • Epithelial linings of oral cavity, sensory organs of ear, and olfactory epithelium
  • Craniopharyngioma
    • Benign Rathke pouch tumor with cholesterol crystals, calcifications.

5

Embryologic derivatives:
Neuroectoderm

  • Brain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland)
  • Retina and optic nerve
  • Spinal cord
  • Neuroectoderm—think CNS.

6

Embryologic derivatives:
Neural crest ectoderm

  • BAMCOPPP
  • Bones of the skull
  • Aorticopulmonary septum
  • Melanocytes
  • Chromaffin cells of adrenal medulla
  • Odontoblasts
  • PNS (dorsal root ganglia, cranial nerves, celiac ganglion, Schwann cells, ANS)
  • Parafollicular (C) cells of thyroid
  • Pia and arachnoid
  • Neural crest—think PNS and non-neural structures nearby.

7

Embryologic derivatives:
Mesoderm

  • Derivatives
  • Notochord 
  • Mesodermal defects

  • Derivatives
    • Muscle
    • Bone
    • Connective tissue
    • Serous linings of body cavities (e.g., peritoneum)
    • Spleen (derived from foregut mesentery)
    • Cardiovascular structures
    • Lymphatics
    • Blood
    • Wall of gut tube
    • Vagina
    • Kidneys
    • Adrenal cortex
    • Dermis
    • Testes
    • Ovaries
  • Notochord
    • Induces ectoderm to form neuroectoderm (neural plate).
    • Its only postnatal derivative is the nucleus pulposus of the intervertebral disc.
  • Mesodermal defects (VACTERL)
    • Vertebral defects
    • Anal atresia
    • Cardiac defects
    • Tracheo-Esophageal fistula
    • Renal defects
    • Limb defects (bone and muscle)

8

Embryologic derivatives:
Endoderm

  • Gut tube epithelium (including anal canal above the pectinate line)
  • Most of urethra (derived from urogenital sinus)
  • Luminal epithelial derivatives (e.g., lungs, liver, gallbladder, pancreas, eustachian tube, thymus, parathyroid, thyroid follicular cells)

9

Types of errors in organ morphogenesis

  • Agenesis
  • Aplasia
  • Hypoplasia
  • Deformation
  • Disruption
  • Malformation
  • Sequence

  • Agenesis
    • Absent organ due to absent primordial tissue.
  • Aplasia
    • Absent organ despite presence of primordial tissue.
  • Hypoplasia
    • Incomplete organ development
    • Primordial tissue present.
  • Deformation
    • Extrinsic disruption
    • Occurs after the embryonic period.
  • Disruption
    • 2° breakdown of a previously normal tissue or structure
    • e.g., amniotic band syndrome
  • Malformation
    • Intrinsic disruption
    • Occurs during the embryonic period (weeks 3–8).
  • Sequence
    • Abnormalities result from a single 1° embryological event
    • e.g., oligohydramnios -->Ž Potter sequence

10

Teratogens

  • When most susceptible
  • Before
  • After

  • Most susceptible in 3rd–8th weeks (embryonic period—organogenesis) of pregnancy.
  • Before week 3: all-or-none effects.
  • After week 8: growth and function affected.

11

Effects of these teratogens (medications) on fetus

  • ACE inhibitors
  • Alkylating agents
  • Aminoglycosides
  • Carbamazepine
  • Diethylstilbestrol (DES)
  • Folate antagonists
  • Lithium

  • ACE inhibitors
    • Renal damage
  • Alkylating agents
    • Absence of digits, multiple anomalies
  • Aminoglycosides
    • CN VIII toxicity
    • A mean guy hit the baby in the ear.
  • Carbamazepine
    • Neural tube defects, craniofacial defects, fingernail hypoplasia, developmental delay, IUGR
  • Diethylstilbestrol (DES)
    • Vaginal clear cell adenocarcinoma, congenital Müllerian anomalies
  • Folate antagonists
    • Neural tube defects
  • Lithium
    • Ebstein anomaly (atrialized right ventricle)

12

Effects of these teratogens (medications) on fetus

  • Methimazole
  • Phenytoin
  • Tetracyclines
  • Thalidomide
  • Valproate
  • Warfarin

  • Methimazole
    • Aplasia cutis congenita
  • Phenytoin
    • Fetal hydantoin syndrome: microcephaly, dysmorphic craniofacial features, hypoplastic nails and distal phalanges, cardiac defects, IUGR, intellectual disability
  • Tetracyclines
    • Discolored teeth
    • Teethracyclines”
  • Thalidomide
    • Limb defects (phocomelia, micromelia—“flipper” limbs)
    • Limb defects with “tha-limb-domide.”
  • Valproate
    • Inhibition of maternal folate absorption -->Ž neural tube defects
    • Valproate inhibits folate absorption
  • Warfarin
    • Bone deformities, fetal hemorrhage, abortion, ophthalmologic abnormalities
    • Do not wage warfare on the baby; keep it heppy with heparin (does not cross placenta).

13

Effects of these teratogens (substance abuse) on fetus

  • Alcohol 
  • Cocaine 
  • Smoking (nicotine, CO)

  • Alcohol
    • Common cause of birth defects and intellectual disability
    • Fetal alcohol syndrome
  • Cocaine
    • Abnormal fetal growth and fetal addiction
    • Placental abruption
  • Smoking (nicotine, CO)
    • A leading cause of low birth weight in developed countries
    • Associated with preterm labor, placental problems, IUGR, ADHD

14

Effects of these teratogens on fetus

  • Iodine (lack or excess)
  • Maternal diabetes 
  • Vitamin A (excess) 
  • X-rays
  • Other

  • Iodine (lack or excess)
    • Congenital goiter or hypothyroidism (cretinism)
  • Maternal diabetes
    • Caudal regression syndrome (anal atresia to sirenomelia), congenital heart defects, neural tube defects
  • Vitamin A (excess)
    • Extremely high risk for spontaneous abortions and birth defects (cleft palate, cardiac abnormalities)
  • X-rays
    • Microcephaly, intellectual disability
  • Other
    • Fetal infections and certain antibiotics can also cause congenital malformations

15

Fetal alcohol syndrome

  • One of the leading causes of...
  • Newborns of mothers who consumed significant amounts of alcohol during pregnancy have an increased incidence of...

  • One of the leading causes of congenital malformations in the United States.
  • Newborns of mothers who consumed significant amounts of alcohol during pregnancy have an increased incidence of congenital abnormalities, including...
    • Intellectual disability
    • Pre- and postnatal developmental retardation
    • Microcephaly
    • Holoprosencephaly
    • Facial abnormalities (smooth philtrum, thin upper lip, small palpebral fissures, hypertelorism)
    • Limb dislocation
    • Heart defects

16

Twinning (555)

  • Dizygotic twins
    • Arise from...
    • Will have...
  • Monozygotic twins
    • Arise from...
  • The degree of separation between monozygotic twins depends on...
  • The timing of this separation determines...

  • Dizygotic twins
    • Arise from 2 eggs that are separately fertilized by 2 different sperm (always 2 zygotes)
    • Will have 2 separate amniotic sacs and 2 separate placentas (chorions)
  • Monozygotic twins
    • Arise from 1 fertilized egg (1 egg + 1 sperm) that splits into 2 zygotes in early pregnancy.
  • The degree of separation between monozygotic twins depends on when the fertilized egg splits into 2 zygotes.
  • The timing of this separation determines the number of chorions and the number of amnions.

17

Twinning (555)

  • 0-4 days
  • 4-8 days
  • 8-12 days
  • > 13 days

  • 0-4 days (2 cell stage --> morula)
    • Diamniotic
    • Dichorionic
  • 4-8 days (morula --> blastocyst)
    • Diamniotic
    • Monochorionic
  • 8-12 days (blastocyst --> formed embryonic disc)
    • Monoamniotic
    • Monochorionic
  • > 13 days (formed embryonic disc --> dichorionic / diamniotic)
    • Monoamnioitc
    • Monochorionic
    • Conjoined twins

18

Placental development

  • 1º site of...
  • For each
    • Fetal or maternal component
    • Definition
  • Cytotrophoblast 
  • Syncytiotrophoblast
  • Decidua basalis 

  • 1º site of nutrient and gas exchange between mother and fetus.
  • Cytotrophoblast
    • Fetal component
    • Definition
      • Inner layer of chorionic villi.
      • Cytotrophoblast makes Cells.
  • Syncytiotrophoblast
    • Fetal component
    • Definition
      • Outer layer of chorionic villi
      • Secretes hCG (structurally similar to LH; stimulates corpus luteum to secrete progesterone during first trimester).
  • Decidua basalis
    • Maternal component
    • Definition
      • Derived from the endometrium.
      • Maternal blood in lacunae.

19

Umbilical cord

  • Umbilical arteries
  • Umbilical veins
  • Umbilical artery and vein derivation

  • Umbilical arteries (2)
    • Return deoxygenated blood from fetal internal iliac arteries to placenta [A].
    • Single umbilical artery is associated with congenital and chromosomal anomalies.
  • Umbilical vein (1)
    • Supplies oxygenated blood from placenta to fetus
    • Drains into IVC via liver or via ductus venosus.
  • Umbilical arteries and veins are derived from allantois.

20

Urachus

  • Derivation
  • Failure of urachus to obliterate results in:

  • Derivation
    • In the 3rd week the yolk sac forms the allantois, which extends into the urogenital sinus.
    • Allantois becomes the urachus, a duct between fetal bladder and yolk sac.
  • Failure of urachus to obliterate results in:
    • Patent urachus
      • Urine discharge from umbilicus.
    • Urachal cyst
      • Partial failure of urachus to obliterate
      • Fluid-filled cavity lined with uroepithelium, between umbilicus and bladder.
      • Can lead to infection, adenocarcinoma.
    • Vesicourachal diverticulum
      • Outpouching of bladder.

21

Vitelline duct

  • Derivation
  • Failure of vitelline duct to close results in:

  • Derivation
    • 7th week—obliteration of vitelline duct (omphalo-mesenteric duct), which connects yolk sac to midgut lumen.
  • Failure of vitelline duct to close results in:
    • Vitelline fistula
      • -->Ž meconium discharge from umbilicus.
    • Meckel diverticulum
      • Partial closure, with patent portion attached to ileum (true diverticulum).
      • May have ectopic gastric mucosa and/or pancreatic tissue -->ŽŽ melena, periumbilical pain, and ulcers.

22

Aortic arch derivatives

  • Develop into...
  • 1st 
  • 2nd
  • 3rd
  • 4th
  • 6th

  • Develop into the arterial system.
  • 1st
    • Part of maxillary artery (branch of external carotid).
    • 1st arch is maximal.
  • 2nd
    • Stapedial artery and hyoid artery.
    • Second = Stapedial.
  • 3rd
    • Common Carotid artery and proximal part of internal Carotid artery.
    • C is 3rd letter of alphabet.
  • 4th
    • On left, aortic arch; on right, proximal part of right subclavian artery.
    • 4th arch (4 limbs) = systemic.
  • 6th
    • Proximal part of pulmonary arteries and (on left only) ductus arteriosus.
    • 6th arch = pulmonary and the pulmonary-to-systemic shunt (ductus arteriosus).

23

Branchial apparatus

  • Also called...
  • Composed of...

  • Also called pharyngeal apparatus.
  • Composed of...
    • Branchial clefts
      • Derived from ectoderm.
      • Also called branchial grooves.
    • Branchial arches
      • Derived from mesoderm (muscles, arteries) and neural crest (bones, cartilage).
    • Branchial pouches
      • Derived from endoderm.
  • CAP covers outside to inside:
    • Clefts = ectoderm
    • Arches = mesoderm
    • Pouches = endoderm

24

Branchial cleft derivatives

  • 1st cleft develops into...
  • 2nd through 4th clefts form...
  • Persistent cervical sinus -->

  • 1st cleft develops into external auditory meatus.
  • 2nd through 4th clefts form temporary cervical sinuses, which are obliterated by proliferation of 2nd arch mesenchyme.
  • Persistent cervical sinus -->Ž branchial cleft cyst within lateral neck.

25

Branchial arch derivatives:
1st arch

  • Cartilage
  • Muscles
  • Nerves
  • Abnormalities / comments

  • Cartilage
    • Meckel cartilage: Mandible, Malleus, incus, spheno-Mandibular ligament
  • Muscles
    • Muscles of Mastication (temporalis, Masseter, lateral and Medial pterygoids), Mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini
  • Nerves
    • CN V2 and V3 chew
  • Abnormalities / comments
    • Treacher Collins syndrome: 1st-arch neural crest fails to migrate -->Ž mandibular hypoplasia, facial abnormalities

26

Branchial arch derivatives:
2nd arch

  • Cartilage
  • Muscles
  • Nerves
  • Abnormalities / comments

  • Cartilage
    • Reichert cartilage: Stapes, Styloid process, lesser horn of hyoid, Stylohyoid ligament
  • Muscles
    • Muscles of facial expression, Stapedius, Stylohyoid, platySma, belly of digastric
  • Nerves
    • CN VII (facial expression) smile
  • Abnormalities / comments
    • Congenital pharyngocutaneous fistula: persistence of cleft and pouch Ž--> fistula between tonsillar area and lateral neck

27

Branchial arch derivatives:
3rd arch

  • Cartilage
  • Muscles
  • Nerves

  • Cartilage
    • Cartilage: greater horn of hyoid
  • Muscles
    • Stylopharyngeus (think of stylopharyngeus innervated by glossopharyngeal nerve)
  • Nerves
    • CN IX (stylopharyngeus) swallow stylishly

28

Branchial arch derivatives:
4th–6th arches

  • Cartilage
  • Muscles
    • 4th arch
    • 6th arch
  • Nerves
    • 4th arch
    • 6th arch
  • Abnormalities / comments
    • Arches 3 and 4
    • Arch 5

  • Cartilage
    • Cartilages: thyroid, cricoid, arytenoids, corniculate, cuneiform
  • Muscles
    • 4th arch: most pharyngeal constrictors; cricothyroid, levator veli palatini
    • 6th arch: all intrinsic muscles of larynx except cricothyroid
  • Nerves
    • 4th arch: CN X (superior laryngeal branch) simply swallow
    • 6th arch: CN X (recurrent laryngeal branch) speak
  • Abnormalities / comments
    • Arches 3 and 4 form posterior 1⁄3 of tongue
    • Arch 5 makes no major developmental contributions

29

Branchial arch derivatives

  • Nerves
  • Mnemonic

  • Nerves
    • These are the only CNs with both motor and sensory components (except V2, which is sensory only).
  • Mnemonic
    • When at the restaurant of the golden arches, children tend to first chew (1), then smile (2), then swallow stylishly (3) or simply swallow (4), and then speak (6).

30

Branchial pouch derivatives

  • 1st pouch
  • 2nd pouch
  • 3rd pouch
  • 4th pouch

  • 1st pouch
    • Develops into middle ear cavity, eustachian tube, mastoid air cells.
    • 1st pouch contributes to endoderm-lined structures of ear.
  • 2nd pouch
    • Develops into epithelial lining of palatine tonsil.
  • 3rd pouch
    • Dorsal wings—develops into inferior parathyroids.
    • Ventral wings—develops into thymus.
    • 3rd pouch contributes to 3 structures (thymus, left and right inferior parathyroids).
    • 3rd-pouch structures end up below 4th-pouch structures.
  • 4th pouch
    • Dorsal wings—develops into superior parathyroids.
  • Ear, tonsils, bottom-to-top:
    • 1 (ear),
    • 2 (tonsils),
    • 3 dorsal (bottom for inferior parathyroids),
    • 3 ventral (to = thymus),
    • 4 (top = superior parathyroids).

31

DiGeorge syndrome

  • Aberrant development of 3rd and 4th pouches Ž--> T-cell deficiency (thymic aplasia) and hypocalcemia (failure of parathyroid development).
  • Associated with cardiac defects (conotruncal anomalies).

32

MEN 2A

  • Mutation of germline RET (neural crest cells):
    • Adrenal medulla (pheochromocytoma).
    • Parathyroid (tumor)
      • 3rd/4th pharyngeal pouch.
    • Parafollicular cells (medullary thyroid cancer)
      • Derived from neural crest cells
      • Associated with the 4th/5th pharyngeal pouches.

33

Cleft lip and cleft palate

  • Cleft lip
  • Cleft palate
  • Comparison

  • Cleft lip
    • Failure of fusion of the maxillary and medial nasal processes (formation of 1° palate).
  • Cleft palate
    • Failure of fusion of the two lateral palatine processes or failure of fusion of lateral palatine processes with the nasal septum and/or median palatine process (formation of 2° palate).
  • Comparison
    • Cleft lip and cleft palate have two distinct etiologies, but often occur together.

34

Genital embryology

  • Female 
    • Development
    • Mesonephric duct
    • Paramesonephric duct
  • Male 
    • SRY gene
    • Sertoli cells
    • Leydig cells

  • Female
    • Default development.
    • Mesonephric duct degenerates
    • Paramesonephric duct develops.
  • Male
    • SRY gene on Y chromosome—produces testisdetermining factor (testes development).
    • Sertoli cells secrete Müllerian inhibitory factor (MIF) that suppresses development of paramesonephric ducts.
    • Leydig cells secrete androgens that stimulate the development of mesonephric ducts.

35

Genital embryology

  • Paramesonephric (Müllerian) duct
  • Mesonephric (Wolffian) duct
  • Bicornuate uterus

  • Paramesonephric (Müllerian) duct
    • Develops into female internal structures
      • Fallopian tubes, uterus, and upper portion of vagina (lower portion from urogenital sinus).
    • Müllerian duct abnormalities result in anatomical defects that may present as 1° amenorrhea in females with fully developed 2° sexual characteristics (indicator of functional ovaries).
  • Mesonephric (Wolffian) duct
    • Develops into male internal structures (except prostate)
    • Seminal vesicles, Epididymis, Ejaculatory duct, and Ductus deferens (SEED).
  • Bicornuate uterus
    • Results from incomplete fusion of the paramesonephric ducts (vs. complete failure of fusion, resulting in double uterus and vagina).
    • Can lead to anatomic defects -->Ž recurrent miscarriages.

36

SRY gene

  • No Sertoli cells or lack of Müllerian inhibitory factor
  • 5α-reductase deficiency

  1. No Sertoli cells or lack of Müllerian inhibitory factor
    • Develop both male and female internal genitalia and male external genitalia
  2. 5α-reductase deficiency
    • Inability to convert testosterone into DHT
    • Male internal genitalia, ambiguous external genitalia until puberty (when increase testosterone levels cause masculinization)

37

Male/female genital homologs (562)

  • For each
    • Dihydrotestosterone (male) -->
    • Estrogen (female) -->
  • Genital tubercle
  • Urogenital sinus
  • Urogenital folds
  • Labioscrotal swelling

  • Genital tubercle
    • Dihydrotestosterone --> glans penis, corpus cavernosum, spongiosum
    • Estrogen --> glans clitoris, vestibular bulbs
  • Urogenital sinus
    • Dihydrotestosterone --> bulbourethral glands (of Cowper), prostate gland
    • Estrogen --> greater vestibular glands (of Bartholin), urethral and paraurethral glands (of Skene)
  • Urogenital folds
    • Dihydrotestosterone --> ventral shaft of penis (penile urethra)
    • Estrogen --> labia minora
  • Labioscrotal swelling
    • Dihydrotestosterone --> scrotum
    • Estrogen --> labia majora

38

Hypospadias

  • Congenital penile abnormality
  • Abnormal opening of penile urethra on inferior (ventral) side of penis due to failure of urethral folds to close.
  • Hypospadias is more common than epispadias. 
  • Fix hypospadias to prevent UTIs.
  • Hypo is below.

39

Epispadias

  • Congenital penile abnormality
  • Abnormal opening of penile urethra on superior (dorsal) side of penis due to faulty positioning of genital tubercle.
  • Exstrophy of the bladder is associated with Epispadias.
  • When you have Epispadias, you hit your Eye when you pEE.

40

Descent of testes and ovaries

  • For each
    • Male remnant
    • Female remnant
  • Gubernaculum (band of fibrous tissue)
  • Processus vaginalis (evagination of peritoneum)

  • Gubernaculum (band of fibrous tissue)
    • Male remnant: Anchors testes within scrotum.
    • Female remnant: Ovarian ligament + round ligament of uterus.
  • Processus vaginalis (evagination of peritoneum)
    • Male remnant: Forms tunica vaginalis.
    • Female remnant: Obliterated.

Decks in First Aid Class (92):