Embryo 13

Front 1

Lateral plate mesoderm forms

Back 1

somatic - parietal - mesoderm and ectoderm form somatopleure

splanchnic - visceral - mesoderm and endoderm forn splanchnopleure

Space between is coelom -origionally two but they fused

Front 2

Similarity between the chick and amphibian embryo

Back 2

If we take out the chick yolk and fold it, it appears similar to the xenopus

Front 3

Presumptive heart cells

Back 3

-originate from two patches of epiblast close to anterior of primitive streak

-proliferate and migrate through the streak

-form two groups of mesodermal cells called the cardiogenic mesoderm

-found in splanchnic mesoderm, one on each side

-combine to form cardiac crescent

Front 4

How are heart precursor cells specified?

Back 4

Endoderm induces BMP and FGF - differentiation of heart

Neural tube induces Wnt - promote blood formation, inhibit heart formation

Anterior mesoderm inhibits Wnt - inhibit inibition of heart

Front 5

Cardiac cells are specified where

Back 5

BMPs are present and Wnts are inhibited

Front 6

Nkkx2.5

Back 6

is expressed where wnt is blocked by crescent and Dkk and where BMPs are expressed

Front 7

Wnt inhibitors

Back 7

Crescent and Dkk

Front 8

After cardial crescent grows...

Back 8

-body folding forces the anterior cardiac crescent down under the gut endoderm

-further folding brings the right and left sides together and they fuse together

Front 9

Cardiac crescent gives rise to the FHF

Back 9

First heart field - linear heart tube

Expands over time as additional cells origionating from pharyngeal mesoderm are added to the poles

This becomes the SHF

Starts beating, rightwards looping, rapid growth

Front 10

Migration of cardiac precursor cells

Back 10

Directionality of the movement is controlled through endoderm morphogens

Endocardial primordial tubes - brought together through infolding of the gut (splanchnopleure)

Myocardial layers - enwrap endocardial tubes

Tube formed as endocardial primordia fuse and myocardia form tube

Front 11

Migration directed by endodermal proteins

Back 11

Cardia bifida - infolding of the gut is prevented - forms two hearts

Front 12

Initial heart beats

Back 12

Heart primordia fusion at 3 weeks

Vitelline veins conduct blood from yolk sac to sinus venosus

Umbilical veins carry oxygen rich blood from chorion

Flap in future atrial region

Trancus arteriosus contracts after cardiac tube is formed

Front 13

Cardiac looping

Back 13

Converts AP polarity to LR polarity

Dependent on nodal lefty2 and pitx2

Front 14

Three sources of heart precursor cells

Back 14

1. cardiogenic mesoderm

2. proepicardial organ

3. cardiac neural crest cells

Front 15

Each nodal cell has a single cilium

Back 15

Cells in the central region - motile cilia, can move nodal fluid

Cells which surround - non motile cilia

Nodal flow causes non motile cilia to bend over activating the ca channel

Front 16

Ca+ gradient causes establishment of the LR axis

Back 16

higher Ca+ on left side

symmetry breaks, activates nodal signalling cascade causing left specific expression of some genes

Front 17

Blood vessel development

Blood cell development

Common precursor

Back 17

vasculogenesis and angiogenesis

hematopoesis

hemangionblast

Front 18

Vasculogenesis

Angiogenesis

Back 18

Creation of primary network of blood vessels from the lateral plate mesoderm

Primary network further remodels into capillary bed, arteries and veins

Front 19

Constrains on blood vessel construction

Back 19

Physiological - feeding and respiration through blood

Evolutionary - blood vessels extend to yolk sac, 6 pairs of aortic arches which converge

Physical - diffusion and hydraulics

Front 20

Two regions of vasculogenesis

Back 20

Extraembryonic vasculogenesis - blood islands (BMP) formed in yolk sac, critical to amniote development - vitaline and umbilical veins that bring nutrients and gas to embryo

Intraembryonic vasculogenesis - blood island formed by embryo from spanchnic mesoderm

Front 21

Extraembryonic vasculogenesis

Back 21

blood islands are formed from primitive streak migration

form hemangioblasts

Outer cells become flat endothelial and inner cells become primordial blood - differentiation depends on notch

Form capillary network draining into vitaline and umbilical veins

Front 22

Intraembryonic vasculogenesis

Back 22

Blood vessels are created de novo

splanchnic cells aggregate along future path, form hollowed out tubes

Front 23

First phase

Back 23

splanchnic mesoderm cells become hemangioblasts and aggregate into blood islands.

inner - hematopoietic stem cells - generate all blood types

outer - angioblasts - blood vessel cells

Front 24

Second phase

Back 24

angioblasts multiply and differentiate into endothelial cells which line blood vessels

Front 25

Third phase

Back 25

endothelial cells form tubes and connect to form network of cappilaries

FGF, VEGF, Angioprotiens

Front 26

Angioproteins mediate

Back 26

interaction between endothelial cells and pericytes - recruited by endothelial to cover them

Front 27

Formation of lumen in hollowing tubes

Back 27

Cord hollowing - vacuoles form in endothelial cells and fuse with cell membrane to form lumen

Cell hollowing - vacuoles form intracellular lumina in each celland fuse so that each lining is of the cell its in