embryology Flashcards
sonic hedgehog gene
made in base of limbs in the zone of polarizing activity —anterior/posterior patterning; involved in CNS development
Wnt-7 gene
made at apical ectodermal ridge (distal end of growing limbs); for dorsal/ventral organization
FGF gene
made at apical ectodermal ridge; stimulates mitosis for limb lengthening
Hox (homeobox) genes
segmental organization of embryp in a craniocaudal fashion
hox mutation causes…
appendage in wrong place
10 weeks of early fetal development
day 0 - fertilization forms a zygote; embryogenesis initiated week 1 - hCG secretion and implantation of blastocyst week 2 - 2 wks = 2 layers –> bilaminar disc (epiblast and hypoblast) week 3 - 3 wks = 3 layers –> trilaminar disc; gastrulation; primitive streak, notochord, mesoderm, and neural plate begin to form weeks 3-8 - extremely susceptible to teratogens week 4 - heart begins to beat; limb buds begin to form (4wks = 4 limbs) week 6 - fetal cardiac activity visible by transvaginal ultrasound week 10 - sex specific genitalia
gastrulation
process that forms the trilaminar disc (ectoderm, mesoderm, and endoderm germ layers) starts with the epiblast invaginating to form the primitive streak
what forms the CNS? PNS?
cns = neuroectoderm pns = neural crest
mesodermal defects
VACTERL vertebral anal atresia cardiac trachea-esophageal fistula renal limb (bone and muscle)
what is derived from surface ectoderm?
eye lens, oral cavity linings, ear sensory organs and olfactory epithelium, anal canal below pectinate line, parotid/sweat/mammary glands
what is derived from the neuroectoderm?
CNS brain, retina, optic nerves, spinal cord
what is derived from neural crest?
pns dorsal root ganglia, schwann cells, melanocytes, bones of skull, odontoblasts, aorticopulmonary septum, chromaffin and parafollicular cells
what is derived from the mesoderm?
muscle, bone, CT, serous linings of cavties (peritoneum), spleen, CV structures, lymphatics, blood, wall of gut tube, vagina, kidneys, dermis, testes, ovaries,
endoderm forms the…
gut tube epithelium, anal canal above pectinate line, urethra and luminal epithelium derivatives (lungs, liver, gallbladder, Eustachian tube, thymus, etc)
agenesis
absent organ due to absent primordial tissue
aplasia
absent organ despite present primordial tissue
hypoplasia
incomplete organ development
disruption
secondary breakdown of a previously normal structure
malformation vs deformation
M = intrinsic disruption; during the embryonic period (wks 3 - 8) D = extrinsic disruption; after the embryonic period
sequence error
abnormalities result from a single embryological event ex: oligohydramnios –> potter sequence
when is embryo most susceptible to teratogens?
weeks 3-8 (embryonic period) during organogenesis before week 3 –> all or none effect after week 8 –> growth and function affected
fetal alcohol syndrome
mothers consume a lot of alcohol during pregnancy –> increased risk for congenital malformations —intellectual disability, retardation, microcephaly, holopresencephaly, facial abnormalities, limb dislocation, and heart defects
dizygotic twins
arises from 2 eggs that are separately fertilized by 2 different sperm (always 2 zygotes) –2 different amniotic sacs and 2 separate placentas (chorions)
monozygotic twins
from 1 fertilized egg (1 egg + 1 sperm) that splits into 2 zygotes in early pregnancy
what determines degree of separation of monozygotic twins?
depends on when the fertilized egg splits into 2 zygotes –timing determines the number of chorions and amnions
amnion vs chorion
Amnion is the inner layer that surrounds the amniotic cavity while chorion is the outer layer that covers amnion, yolk sac and the allantois amnion does not contain any vessels or nerves
early separation of monozygotic twins? middle latest separation of monozygotic twins?
before morula (0-4 days) –> dichorionic diamniotic after morula, before blastocyst (4-8 days) –> monochorionic diamniotic after blastocyst stage (8+ days) –> monochorionic monoamniotic
where are nutrient and gas exchanged between mother and fetus?
placenta
three components forming the placenta?
cytotrophoblast, syncytiotrophoblast, and decidua basalis
cytotrophoblast
inner layer of chorionic villi of placenta (fetal component)
syncytiotrophoblast
outer layer of chorionic villi; secretes hCG; fetal component of placenta
hCG stimulates what?
stimulates the corpus luteum to secrete progesterone during first trimester
decidua basalis
derived from the endometrium; maternal blood in lacunae; layer on outside of placenta where maternal veins and arteries pass through into placenta
umbilical cord contains…
2 unbilical arteries, 1 umbilical vein, allantoic duct, wharton jelly, and amniotic epithelium
what do umbilical arteries do?
returns deoxy blood from fetal internal iliac arteries to placenta
what does umbilical vein do?
supplies oxy blood from placenta to fetus; drains IVC via liver or ductus venosus
what are umbilical arteries and veins derived from?
the allantois
allantois
made from yolk sac in 3rd week, and becomes the urachus
urachus
formed from the allantois
the urachus is a duct between fetal bladder and yolk sac
failure of urachus to obliterate can result in three conditions–>
1 - patent urachus (urine comes out umbilicus)
2 - urachal cyst (fluid filled cavity between umbilicus and bladder, can cause infection or adenocarcinoma)
3 - vesicourachal diverticulum (bladder outpouching)
vitelline duct
connects yolk sac to midgut lumen
obliterates in week 7
failure of vitelline duct to obliterate can cause these 2 conditions…
vitelline fistula - meconium comes out the umbilicus
meckel diverticulum – partial closue, with patent portion attached to ileum (TRUE diverticulum)
1st-6th branchial arches
1 = Ms to CHEW (meckel cartilage, mandible, malleus, mandibular ligament, muscles of mastication, massetter, medial pterygoid, mylohyoid) — CNV2 and V3
2 = S/SMILE (stapes, styloid process, stylohyoid ligament, muscles of facial expression, stapedius, stylohyoid, platySma) —CN7
3 = SWALLOW STYLishly/CN9 ( stylopharyngeus/glossopharyngeal nerve)
4= CNX superior laryngeal (swallow) - cricothyriod, pharyngeal constrictors, levator veli palatini
6 = CNX recurrent laryngeal branch (talk) - intrinsic muscles of larynx
treacher collins syndrome
1st arch neural crest fails to migrate –> mandibular hypoplasia, facial abnormalities
congenital pharyngocutaneous fistula
persistence of cleft and pouch –> fistula between tonsillar area and lateral neck (2nd arch abnormality)
digeorge syndrome
aberrant development of 3rd and 4th pouches –> T cell deficiency (thymic aplasia) and hypocalcemia (failure of parathyroid development)
associated with cardiac defects (conotruncal abnormalities)
MEN 2a
mutation of RET (neural crest cells) that causes:
pheochromocytoma (adrenal medulla)
parathyroid tumor (3/4 pharyngeal pouch)
parafollicular cells/medullary thyroid cancer (4/5 pharyngeal pouches)
cleft lip
failure of fusion of the maxillary and medial nasal processes (formation of the primary 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 the secondary palate)
cleft lip and cleft palate…..
often occur together but have different etiologies
default genital development
is the female form
–mesonephric duct degenerates and paramesonephric duct develops
male genital development
SRY gene on ch. Y produces testis-determining factor –> testes development
Sertoli cells secrete Mullerian inhibitory factor (MIF) that suppresses development of paramesonephric ducts
Leydig cells secrete androgens that stimulate the development of the mesonephric ducts
mullerian duct
aka the paramesonephric duct
default; develops into female structures –> fallopian tubes, uterus, and upper vagina
mullerian duct abnormalities results in…
presents as primary amenorrhea in females with fully developed secondary sex characteristics (indicates functional ovaries)
wolfian duct
aka the mesonephric duct
develops into male internal structures (except prostate) –> Seminal vesicales, Epididymis, Ejaculatory duct, and Ductus deferens (SEED)
bicornuate uterus
results from incomplete fusion of the paramesonephric ducts
can cause anatomical defects –> recurrent miscarriages
complete failure of paramesonephric ducts fusion causes –?
incomplete fusion…?
complete failure –> double uterus and vagina
incomplete failure –> bicornuate uterus
where do you find sertoli and leydig cells?
testes
what produces testis determining factor (TDF)?
SRY gene on Y ch.
sertoli cells produce?
leydig cells produce?
Sertoli –> MIF (mullerian inhibitory factor)
leydig –> testosterone
MIF causes…
degeneration of the paramesonephric duct (so no female genitalia)
if there are not sertoli cells or MIF –>
develop both male and female internal genitalia and male external genitalia
5alpha reductase deficiency
inability to convert testosterone to DHT –> has male internal genitalia, ambiguous external genitalia until puberty (when increased testosterone causes masculinization)
gubernaculum
1) male remnant
2) female remnant
1 - anchors testes within scrotum
2 - ovarian ligament + round ligament of uterus
processus vaginalis
1) male remnant?
2) female remnant?
1 - forms tunica vaginalis
2 - obliterated
hypospadias
vs
epispadias
H - abnormal opening of urethra on INFERIOR/VENTRAL side of penis due to failure of urethral folds to close
E - abnormal opening of urethra on SUPERIOR/DORSAL side of penis due to faulty positioning of genital tubercle; associated with exstrophy of bladder ( Epispadias hits your EYE when you pEE)
genital tubercle becomes what…
1) with DHT (dihydrotestosterone)
2) with estrogen
1) glans penis, corpus cavernosum, and songiosum
2) glans clitoris and vestibular bulbs
urogenital sinus becomes what…
1) with DHT (dihydrotestosterone)
2) with estrogen
1 - bulbourethral glands and prostate gland
2 - greater vestibular glands of bartholin and urethral and paraurethral glands of skene
urogenital folds becomes what…
1) with DHT (dihydrotestosterone)
2) with estrogen
1 - ventral shaft of penis (penile urethra)
2 - labia minora
labioscrotal swelling becomes what…
1) with DHT (dihydrotestosterone)
2) with estrogen
1 - scrotum
2 - labia majora
