Chapter 15- Lateral mesoderm and endoderm Recall lineages Fig. 12.4 Fig. 14.1- mesoderm lineage Intermediate Kidney , gonads Paraxial Hea d Somit e Cartila ge, skeleta l, dermis Lateral Circulator y, Body cavity, extraembry onic Notocho rd ig. 14.1- mesoderm lineages Somatic mesoderm Splanchnic mesoderm Coelom -becomes the body cavity -becomes body cavity wall and the the heart -becomes body cavity wal
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Chapter 15- Lateral mesoderm and endoderm
Recall lineages
Fig. 12.4
Fig. 14.1- mesoderm lineages
Intermediate
Kidney, gonads
Paraxial
Head Somite
Cartilage,skeletal, dermis
Lateral
Circulatory,Body cavity,
extraembryonic
Notochord
Fig. 14.1- mesoderm lineages
Somatic mesoderm
Splanchnic mesoderm
Coelom -becomes the body cavity
-becomes body cavity wall and the the heart
-becomes body cavity wall
How does the heart develop??
1. Splanchnic mesoderm halves begin to merge
2. These cells differentiate into endocardium (heart lining and valve precursorsand myocardium (heart muscles)
25hr 26hr
Endocardium
3. Endocardium tubes fuse4. Mycocardium fuses
Fig. 15.3
27hr 28hr
5. Heart begins beating even while fusion is occurring
72hr
Myocardium
Lateral mesoderm
Blood vessel formation
Note: Blood vessels form independently of the heart, then link up
Constraints on blood vessel construction1. Physiological- an organism must:
• Obtain nourishment before the intestine develops• Use oxygen before there are lungs• Excrete wastes before there are kidneys
2. Evolutionary-• Six pairs of aortic arches loop
out- these enable primitive fish gills to oxygenate blood, but these serve no obvious purpose in mammals and birds.
3. Physical- Blood flows easier through large vessels, yet efficient diffusion requires small vessels and slow moving blood
Solution- Large vessels branch into very small ones with overall more cumulative volume capacity
Fig. 15.13- “extra” archs in mammal
development
2 steps- vasculogenesis and angiogenesis
Some background Info
Lateral mesoderm
1. Vasculogenesis
Blood vessels and blood cells are intimately
connected
Endothelial cells line blood vessels
Fig. 15.14
Angiogenic cell cluster(blood islands)
Endothelial cellsMesenchyme
Primitive blood cells
Fig. 15.16
Blood vessel formation
BMP
Lateral mesoderm
Transcription factors in vasculogenesis
1. FGF2 is required for hemangioblast formation
2. VEGF is required for blood island and blood vessel formation
3. Ang1 is required proper blood vessel formation (involved in communication between endothelial cell and smooth muscle)
1. Vasculogenesis
VEGF is a target for tumor therapy
“Tumors gotta eat”
Lateral mesoderm
2. Angiogenesis
Definition- Remodeling and pruning of capillary beds, arteries and veins
Note- Capillary networks of each organ arise within the organ itself, not from larger vessels!
VEGF plays key role
TGFstabilizes capillary network
PDGF recruits pericyte cells to ensure flexibility of capillaries
Lateral mesoderm
2. AngiogenesisArteries vs. veins??
•Arteries have EphrinB2 in cell membranes
•Veins have EphrinB2 receptor (called EphB4) in cell membranes
Functions of the EphrinB2/EphB4 system1. Ensure that arteries only link up with veins, not other arteries2. Ensure capillary fusion only occurs with like cells (e.g. only
arteries with arteries)
Arterial(EphrinB2)
Venous(EphB4) Fig. 15.17
Lateral mesoderm
2. Angiogenesis
Many organs make their own angiogenesis factors•Example- placenta
Developing placenta secretes proliferin to promote angiogenesis, then later secretes proliferin-related protein to inhibit angiogenesis
Angiogenesis plays key role in tumor development
•A tumor must induce vascularization in order to enlarge
•Hence, if use a drug that inhibits this angiogenesis, can possibly slow cure some cancers
Lateral mesoderm
Development of Blood Cells
Stem cells – embryonic cells capable of producing many cell types, including other stem cells
Largest population of stem cells is in the bone marrow