L10-11: Body Plan

Question 1

what are the 3 zones of the mesoderm

Answer 1

paraxial mesoderm – segmental plate

intermediate mesoderm

lateral plate mesoderm

Question 2

origins of the mesoderm

Answer 2

originates from epiblast

passes thru primitive streak as bottle cells

spreads laterally to form continuous layer between ectoderm and endoderm

Question 3

paraxial mesoderm

Answer 3

thick column of mesoderm closest to notochord

becomes segmented into somites

Question 4

intermediate mesoderm

Answer 4

narrow column
lateral to paraxial

gives rise to urogenital system

Question 5

lateral plate mesoderm

Answer 5

thin plate
lat to intermediate meso

splits to form:
lining of body cavities
mesoderm of most internal organs and limbs

Question 6

define somitomeres

Answer 6

initial pairs of segments of mesenchyme that begin to develop along, on either side of the neural plate in the paraxial mesoderm

11 pairs are kept constant at the caudal end of the paraxial mesoderm

Question 7

new somitomeres are added ?

Answer 7

caudally as the primitive streak regresses

Question 8

after 20 days, ___ pairs of somitomeres have formed and then ?

Answer 8

20 pairs

the first pair of somites forms behind the 7th pair of somitomeres at the expense of the 8th

Question 9

define somites

Answer 9

dense blocks of mesoderm that form along the notochord

Question 10

what are the 2 theories of somite differentiation

Answer 10

Wavefront mechanism

segmentation clock

Question 11

properties of Wavefront mechanism

Answer 11

–also called determination front

–Mesp-2 is important for determination step

Question 12

why is it called the determination front?

Answer 12

because of the balance between FGF-8 and retinoic acid

which results in cellular determination towards somitogenesis

Question 13

Wavefront mechanism

Answer 13

increase in [FGF-8]
=mitosis in mesenchymal cells in post primitive streak

increase in [retinoic acid]
=anteriorly opposes action of FGF-8

Question 14

describe the name segmentation clock

Answer 14

oscillating expression of molecules in the notch pathway, Wnt, FGF pathways leading to pattern of somite formation

which is expressed along a timeline = segmentation clock

Question 15

critical locations that will serve to divide adjacent somites – segmentation clock theory

Answer 15

lunatic fringe – conc at future ant border

c-hairy – conc at future post

Question 16

expression resulting in fissure between 2 adjacent somites – segmentation clock

Answer 16

calls at ant border express Eph A receptor

cells at post border express Eph B ligand

resulting in fissure

Question 17

steps in somite differentiation: beginning to somitocoel formation

Answer 17

1. ectoderm dorsal to somites send SM Wnt-6
2. somite gene paraxis activated
3. paraxis + down regulation of gene snail
   = mesenchymal cells convert to epithelial cells

and formation of somitocoel

Question 18

steps in somite differentiation: somitocoel to dermomyotome

Answer 18

1. notochord uses SM Shh + noggin to
2. activate genes Pax1 + Pax9 in ventral somite
   = sclerotome
3. Wnt genes in dorsal neural tube activated
4. dorsal half of somite is transformed into dermomyotome

Question 19

steps in somite differentiation: dermomyotome

Answer 19

1. dermo expresses genes Pax3, Pax7 and paraxis

2. dermo is separated into dorsal dermatome and ventral myotome

Question 20

how do Wnt and Shh signaling affect the myotome portion of the dermomyotome?

Answer 20

Shh from notochord
Wnt from dorsal neural tube

create a balance to cause myotome to commit to myogenic lineage

Question 21

BMP-4 and relationship w/ myogenesis

Answer 21

from lat plate
normally suppresses myogenesis

is inhibited by noggin to allow the myotome to commit to myogenic lineage

Question 22

_____ from the myotome signals the sclerotome to produce ______, which causes ?

Answer 22

FGF (SM)
scleraxis (gene)

ant and post borders of each somite to form syndetome

Question 23

syndetome

Answer 23

precursor of tendons

Question 24

creation of intermediate mesoderm

Answer 24

future IM responds to BMP and activin to become IM
IM expresses Pax2

BMP from lat ectoderm
activin from paraxial meso

Question 25

intermediate mesoderm is associated with the formation of ?

Answer 25

pronephros then later mesonephros

Question 26

cranial and _____ extent of intermediate mesoderm is dependent on expression of what genes?

Answer 26

caudal Hox4 Hox11

Question 27

early heart forming cells arise in the ______ and migrate through ?

Answer 27

epiblast | primitive streak

Question 28

cells that form the outflow tract of the heart

Answer 28

are the cells that migrate thru the ant primitive streak

Question 29

cells that form the ventricles of the heart

Answer 29

the cells that migrate thru the middle of the primitive streak

Question 30

cells that form the atria of the heart

Answer 30

cells that enter prim streak most posteriorly

Question 31

what causes these cells to commit to the heart forming pathway?

Answer 31

inductive influence by endoderm | ant visceral endoderm use signaling molecules BMPs and FGFs --causing cardiac crescent formation

Question 32

expression of what genes by migrating cells form transcription factors necessary for early heart formation

Answer 32

Nkx2-5 MEF2 GATA4

Question 33

______ plate arises from splanchnic mesoderm and forms ?

Answer 33

cardiogenic plate cardiac tubes

Question 34

define cardiac tubes

Answer 34

bilaterally paired tubes that form from the cardiogenic mesoderm fuse under foregut to form single tube

Question 35

cardiac tubes consist of ?

Answer 35

an outer and inner layer outer forms myocardium inner forms endocardium

Question 36

what forms between the layers of the cardiac tubes

Answer 36

cardiac jelly forms between the 2 layers of the cardiac tubes has a specialized EC matrix

Question 37

what is the source of pericardium and myocardial fibroblasts

Answer 37

proepicardial primordium

Question 38

relationship of forming heart of foregut

Answer 38

oropharyngeal memb contact between endoderm of gut and oral area of embryo disillusion is this area results in mouth opening due to no mesoderm separating the two

Question 39

initial signaling for endoderm formation occurs during ?

Answer 39

gastrulation depends on nodal expression during this

Question 40

endoderm formation - ant/post gradient

Answer 40

high levels nodal ant lower levels of nodal FGF-4 presence posteriorly

Question 41

endoderm formation posterior gut

Answer 41

expresses Cdx-2 which promotes hindgut development suppresses formation of ant gut structures

Question 42

endoderm formation - anterior gut

Answer 42

expresses | Hex, Sox2, Foxa2

Question 43

more refined differentiation of gut structures depends on ____ genes

Answer 43

Hox genes

Question 44

what are the 3 circulatory arcs in 4-wk embryos?

Answer 44

vitelline arc allantoic arc embryonic arc

Question 45

allantoic arc consists of what vessels?

Answer 45

umbilical or allantoic vessels

Question 46

list the components of the embryonic arc

Answer 46

dorsal aorta aortic arches ant, common, post cardinal veins atrium, ventricle, ventral aorta

Question 47

list the extraembryonic tissues

Answer 47

amnion yolk sac chorion allantois

Question 48

what are the amnion and yolk sac origins

Answer 48

inner cell mass -- epiblast derivative icm -- hypoblast derivative

Question 49

chorion

Answer 49

trophoblast derivative part of maternal fetus interface

Question 50

allantois

Answer 50

icm | interfaces w/ placenta via umbilical cord

Question 51

list the fetal-maternal interfaces

Answer 51

placenta | chorion

Question 52

where are the maternal-fetus interfaces derived from ?

Answer 52

trophoblast derivatives

Question 53

list the stages of placenta development -- what are they based on ?

Answer 53

based on changes in the villi previllous embryo primary villous stage 2ndary villous stage tertiary villous stage final development

Question 54

previllous embryo

Answer 54

no villi have been formed on the trophoblast

Question 55

primary villous stage

Answer 55

solid, cytotrophoblastic, | ectodermal primary villi appear

Question 56

secondary villous stage

Answer 56

mesodermal cores appear w/in the primary villi

Question 57

tertiary villous stage

Answer 57

characterized by the appearance of BVs w/in the mesenchymal core of the 2ndary villi

Question 58

final development of the placenta includes

Answer 58

cytotrophoblastic columns cytotrophoblastic shells anchoring villi

Question 59

cytotrophoblastic shells

Answer 59

formed by expansion of the cytotrophoblastic columns over the maternal decidual cells

Question 60

anchoring villi

Answer 60

villi anchored to cytotrophoblastic shell --as opposed to floating villi

Question 61

list layers - uterus to baby

Answer 61

1. uterus lumen 2. decidua pariatalis 3. decidua capsularis 4. outer cytotrophoblastic shells 5. villi and intervilli space 6. chorionic plate or extraembryonic meso 7. chorionic cavity 8. amnion

Question 62

what layers must be torn for baby to be born?

Answer 62

decidua paratalis and capsularis chorionic plate amnion 4 layers