Embryology 4 - Body Plan Formation Flashcards
Dorsal-Ventral Axis of body is specified by:
Specified by formation of epiblast and hypoblast
Cranial-Caudal Axis of body is specified by:
Specified by the emergence of the primitive streak
Left-Right Axis of body is specified by:
Specified by clockwise rotation of cilia in node
What three Factors Control Organ Shift?
TGF beta (NODAL)
FGF8
Serotonin (5-HT)
What is Heterotaxy?
Abnormal laterality or distribution of visceral organs
What is Situs inversus (totalis)?
Complete inversion of abdominal and thoracic viscera
What is Kartagener Syndrome and its Major Symptoms (3)?
Defective cilia motility due to mutation in dynein (microtubule motor) gene
- Respiratory Infection
- Infertility
- Situs Inversus (in 50% of cases)
How do Dichorionic/Diamniotic Monozygotic Twins form?
Embryo splits before blastocyst formation (days 0-3)
How do Monochorionic/Diamniotic Monozygotic Twins form?
Inner cell mass split after blastocyst formation (days 4-8)
How do Monochorionic/Monoamniotic Monozygotic Twins form?
Two primitive streaks form in one epiblast
What is the amniotic membrane derived from?
Epiblast (inner cell mass)
Where does the chorionic membrane form?
Underneath trophoblast
What is Twin-to-twin Transfusion Syndrome (TTTS)? What is its effect on each twin?
One twin receives most of blood flow due to anastomosis of circulation in placenta
Smaller twin usually dies from lack of sufficient blood flow
Larger twin may also die from congestive heart failure (high blood pressure)
Conjoined Twinning is caused by ___.
duplication of node
Proximal-distal axis of limb is set up by ___.
AER (apical ectodermal ridge) - ectoderm thickening at the distal tip of limb bud
Action of AER is mediated by ___.
FGF (fibroblast growth factor) signaling
Tetra-amelia
Absence of limbs caused by mutation of FGF10
Anterior-posterior axis of limb is set up by ___.
ZPA (zone of polarizing activity) - a small mesenchyme region in the posterior part of the limb bud
Action of ZPA is mediated by ___.
SHH (sonic hedgehog) signaling
What is Triphalangeal thumb caused by?
Linked to mutations that cause activation of SHH signaling
Dorsal-ventral axis of limb is controlled by ___.
WNT signaling
What is Congenital Duplication of the Palm Syndrome and what is linked to?
Linked to mutation in WNT7A gene
Dorsal sides have thick palmar skin with no hair
No nails
What are the three major signals that pattern limbs?
Digits are separated by ___.
Programmed cell death (apoptosis)
What is Syndactyly?
Incomplete separation of digits
What genes regulate limb patterning?
Homeobox (HOX) genes
HOXD11 mutation causes:
Radioulnar synostosis
HOXA13 mutation causes:
Hand-foot-genital syndrome
HOXD13 mutation causes:
Synpolydactyly
What is Amniotic band syndrome?
Fragment of amniotic membrane encircles and constricts fetal structures
What is Oligohydroamnios and what can it cause?
Insufficient amniotic fluid –> physical compression –> deformation (clubfeet)
