Development of the Cardiovascular System 1

trilaminar disc

• from lateral plate mesoderm

differentiation of mesoderm into cardiac tissue

• mesoderm undergoes vasculogenesis:

  • angioblasts (endothelium of embryonic blood vessels)→ outer part

  • hemocytoblasts (elements of blood itself)→ inner part

• endoderm secretes growth factor→ causes splanchnic division of lateral place mesoderm to diferentiate into cardiac tissue

• form:

  • pericardial cavity

  • heart

lateral folding

• formation of single heart tube and single pericardial cavity

• 3 layers of heart tube:

  • endocardium

  • cardiac jelly

  • myocardium

craniocaudal folding

• heart moves from top of head to lie in the thoracic region

• during this folding, heart tube is pulled inside pericardial cavity

segments of the heart tube

folding of heart tube

• bulbous cordis begins to grow

• insufficient space to grow→ moves down and to the right

• displaced primitive ventricle→ moves to the left and up

• as ventricle moves up, primitive atria dragged out of the way

• primitive atria will displace to move to the top

day 22→ differentiation of sinus venosus

• some cells from sinus venosus move into pericardial cavity and begin to form visceral pericardium

• other cells move into heart itself and begin to form primitive conduction system→ heart can now technically beat

formation of atrioventricular canal

• neural crest cells migrate into heart tube and begin to form endocardial cushions

• eventually endocardial cushions unite to form septum intermedium

  • forms right AV canal and left AV canal

formation of valves

• right and left AV canals have now formed

• neural crest cells move in to form valves

• chordae tendineae and papillary muscles attach to newly formed valves

formation of separate atria

• septum primum grows from the top to ostium primum

• apoptosis happens to form ostium secundum→ forms a gap

• septum secundum’ blocks ostium secundum→ still a small space (foramen ovale) for blood to travel through

  • when baby is born, gap closes leaving fossa ovalis

formation of separate ventricles

• muscular portion of interventricular septum

• as is reaches septum intermedium, membrane forms and fuses to muscular portion

development of inflow tracts

• sinous venousus divides into left and right horns, each having

  1. a. common cardinal vein

  2. b. umbilical vein

  3. c. vitelline vein

• all 3 of the veins feeding into the left form break down, leaving just the horn

• right umbilical vein also breaks down

formation of vena cava

• left horn shifts to right and is absorbed into right horn

• sinus venosus is then absorbed into primitive atria:

  • right common cardinal vein forms SVC

  • left horn becomes coronary sinus

  • right vitelline vein becomes IVC

• whilst right horn is absorbed into right atrium, outgrowth from left atrium forms single pulmonary vein

  • further branches into 4 veins

• week 5→ pulmonary veins incorporated into left atrial wall→ intussusception

formation of outflow tracts

• neural crest cells form truncal ridges in truncus arteriosus and bulbar ridges in bulbous cordis→ left and right

• bulbar ridges from bulbar septum

• as ridges converge to form septa→ structures twist around its central axis

• creates corkscrew formation for blood leaving ventricles to navigate

navigation of blood leaving the ventricles

• blood leaving left ventricle passes posterior to bulbar septum

  • blood leaves by passing anterior to truncal septum

  • will become aortic arch

• blood leaving right ventricle passes anterior to bulbar septum

  • leaves by passing posterior to truncal septum

  • will become pulmonary trunk

rotation of outflow tracts

• once septa have formed further rotation takes place

  • separates structure into aortic arch and pulmonary trunk

foetal circulation

• oxygenated blood enters through umbilical vein

• some blood enter foetus’ liver, rest enters ductus venosus→ lets blood bypass liver and enter IVC

• IVC drains blood to right atrium

• due to foramen ovale, blood passes from right to left atrium, bypassing right ventricle

• blood moves into left ventricle and exits heart via aorta

• any blood that passes into right ventricle passes through ductus arteriosus as it exits heart→ not necessary for blood to travel to lungs in the foetus

circulation after birth

• umbilical circulation no longer necessary

• ductus venosus and closes and becomes ligamentun venosum

• once newborn takes its first breath, pulmonary arteries dilate and alter pressure in the atria

• this causes increased pressure in left atrium→ forces septum primum to push against more stable septum secundum

• foramen ovale is now closed→ seen as fossa ovalis in adults

• blood flows into right ventricle and exits via pulmonary arteries

• first breath alters oxygen saturation in ductus arteriosus→ constructs and forms ligamentum arteriosum

  • means blood will travel to lungs