Embryology 4 - Body Plan Formation

Question 1

Dorsal-Ventral Axis of body is specified by:

Answer 1

Specified by formation of epiblast and hypoblast

Question 2

Cranial-Caudal Axis of body is specified by:

Answer 2

Specified by the emergence of the primitive streak

Question 3

Left-Right Axis of body is specified by:

Answer 3

Specified by clockwise rotation of cilia in node

Question 4

What three Factors Control Organ Shift?

Answer 4

TGF beta (NODAL)

FGF8

Serotonin (5-HT)

Question 5

What is Heterotaxy?

Answer 5

Abnormal laterality or distribution of visceral organs

Question 6

What is Situs inversus (totalis)?

Answer 6

Complete inversion of abdominal and thoracic viscera

Question 7

What is Kartagener Syndrome and its Major Symptoms (3)?

Answer 7

Defective cilia motility due to mutation in dynein (microtubule motor) gene

1. Respiratory Infection
2. Infertility
3. Situs Inversus (in 50% of cases)

Question 8

How do Dichorionic/Diamniotic Monozygotic Twins form?

Answer 8

Embryo splits before blastocyst formation (days 0-3)

Question 9

How do Monochorionic/Diamniotic Monozygotic Twins form?

Answer 9

Inner cell mass split after blastocyst formation (days 4-8)

Question 10

How do Monochorionic/Monoamniotic Monozygotic Twins form?

Answer 10

Two primitive streaks form in one epiblast

Question 11

What is the amniotic membrane derived from?

Answer 11

Epiblast (inner cell mass)

Question 12

Where does the chorionic membrane form?

Answer 12

Underneath trophoblast

Question 13

What is Twin-to-twin Transfusion Syndrome (TTTS)? What is its effect on each twin?

Answer 13

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)

Question 14

Conjoined Twinning is caused by ___.

Answer 14

duplication of node

Question 15

Proximal-distal axis of limb is set up by ___.

Answer 15

AER (apical ectodermal ridge) - ectoderm thickening at the distal tip of limb bud

Question 16

Action of AER is mediated by ___.

Answer 16

FGF (fibroblast growth factor) signaling

Question 17

Tetra-amelia

Answer 17

Absence of limbs caused by mutation of FGF10

Question 18

Anterior-posterior axis of limb is set up by ___.

Answer 18

ZPA (zone of polarizing activity) - a small mesenchyme region in the posterior part of the limb bud

Question 19

Action of ZPA is mediated by ___.

Answer 19

SHH (sonic hedgehog) signaling

Question 20

What is Triphalangeal thumb caused by?

Answer 20

Linked to mutations that cause activation of SHH signaling

Question 21

Dorsal-ventral axis of limb is controlled by ___.

Answer 21

WNT signaling

Question 22

What is Congenital Duplication of the Palm Syndrome and what is linked to?

Answer 22

Linked to mutation in WNT7A gene

Dorsal sides have thick palmar skin with no hair

No nails

Question 23

What are the three major signals that pattern limbs?

Answer 23

Question 24

Digits are separated by ___.

Answer 24

Programmed cell death (apoptosis)

Question 25

What is Syndactyly?

Answer 25

Incomplete separation of digits

Question 26

What genes regulate limb patterning?

Answer 26

Homeobox (HOX) genes

Question 27

HOXD11 mutation causes:

Answer 27

Radioulnar synostosis

Question 28

HOXA13 mutation causes:

Answer 28

Hand-foot-genital syndrome

Question 29

HOXD13 mutation causes:

Answer 29

Synpolydactyly

Question 30

What is Amniotic band syndrome?

Answer 30

Fragment of amniotic membrane encircles and constricts fetal structures

Question 31

What is Oligohydroamnios and what can it cause?

Answer 31

Insufficient amniotic fluid –> physical compression –> deformation (clubfeet)