Mesoderm - Heart + Blood Vessels

Lateral Plate Mesoderm Derivatives

Somatic and splanchic

Basic Steps of Heart Dev

• Cardiovascular system formation

• Heart formation

• Blood vessels

• Blood cells

• Remodeling for complexity

Frog Heart Dev

Has 4 major tissues

• endocardium

• myocardium

• pericardial cavity

• pericardium

Frog: Endocardium

Cells detach from the mesoderm and migrate inwards

Frog: Myocardium

Thicker tissue layer that is the result of convergence of the ends of splanchnic mesoderm

Frog: Pericardial Cavity

Forms from the coelomic cavity

Frog: Pericardium

Somatic mesoderm detaches and surrounds the coelomic cavity

Chick Heart Dev

Has some main requirements

• Cardiac precursor cells

• Myocardium

• Endocardium

Chick: Cardiac Precursor Cells

Migrate ventrally along the endoderm

• guided by tinman

• eventually forms two tubes

Chick: Endocardium

Forms from two tubes converging on the ventral surface of the embryo after precursor migration

Chick: Myocardium

Forms from splanchnic mesoderm sheet convergence

Vertebrate Heart Dev

Begins as two tubes that become regionalized and loop to form chambers

• sinus venosus

• atrium

• ventricle

• truncus arteriosus

Vertebrate: Looping

The heart is a tube that is anchored on either end

1. truncus arteriosus grows ventrally

2. atrium grows dorsally and anteriorly

3. atrium widens and forms two chambers

4. ventricle widens and forms two chambers

Human Heart Dev

• Cardiac crescent at day 15

• Tube heart at day 21

• Looping at day 28

• Complex heart at day 50

Foramen Ovale

Embryonic structure that does not have a purpose after birth

• Between atria, allows blood to get to the left ventricle

• At first breath, the blood pressure on the left side of the heart increases and forces the foramen ovale closed

• Separates the pulmonary and systemic circulations

Ductus Arteriosus

• Between the aorta and pulmonary artery

• Allows most blood to bypass lungs

• At first breath the increase in prostaglandins causes ductus arteriosus to vasoconstrict and close

2 Chambered Hearts

Present in adult fish and all vertebrate embryos

3 Chambered Hearts

Present in adult amphibians, many reptilian adults, and some vertebrate embryos

• as a result of incomplete ventricle division

4 Chambered Hearts

Present in crocodiles, mammals, and birds

Sinus Venosus

• Persists in the circulatory systems of some vertebrates (fish)

• Integrated into the wall of the atrium as the sinoatrial node in mammals

Truncus Arteriosus

Becomes part of the base of the ventricle, and contributes to the base of the aorta and pulmonary artery

• Also the name of the rare congenital heart disease whereby a single tube drains both ventricles allowing too much blood to enter the lungs

Chick Circulation

Vitelline arteries and veins

• gas exchange and nutrient uptake

Blood islands

• where 1st blood vessels form

Mammalian Circulation

• Placenta and yolk must be vascularized

• Vessels grow over the yolk sac

Blood Vessels

Mesenchyme derived

• unique patterns within organisms like fingerprints

• form independently and then join up

• adhere to physical and physiological constraints

Blood Vessel Formation

Require precursor angioblasts that are attracted by signaling from neurons

1. Vasculogenesis

2. Angiogenesis

Vasculogenesis

Process of forming new blood vessel from lateral plate mesoderm

• relies on FGF and VEGF

Angiogenesis

Process of sprouting and remodeling existing blood vessels

• relies on VEGF and PDGF

V - FGF

Involved in the generation of angioblasts from lateral plate mesoderm

V - VEGF

• Role in the multiplication and differentiation of angioblasts

• High levels may lead to defects in vessel formation and have cancer implications

• Green tea and wine inhibited (kinda)

A - VEGF

• Degrades ECM that supports primary vessels

• Involved in endothelial sprouting

A - PDGF

• Attracts cells such as smooth muscle and pericytes to form vessel wall