Development Of The Heart

1. Development (MESODERM)

1. Primitive heart tube

- pair of endocardial heart tubes (mesoderm) form within cardiogenic region

-EHT fuse during lateral folding to form primitive heart tube = endocardium

-surrounding mesoderm develops into myocardium and epicardium

-PHT forms five dilations

2. AP septum (aorticopulmonary)

-divides truncus arteriosus into aorta and pulmonary trunk

-neural crest cells migrate into truncal and bulbar ridges

-grow and twist in spiral, fuse to form AP septum

3. AV septum (atrioventricular)

-partitions AV canal into right and left AV canals

-dorsal and ventral AV cushions fuse to form AV septum

4. Atrial septum

-septum primum grows toward AV septum

-foramen primum between edges of septum primum and AV septum; obliterated when SP fuses with AV cushions

-septum segundum (crescent-shaped) forms to right of SP and fuses after birth with SP to form atrial septum

-foramen ovale is opening between upper and lower parts of SS; shunts blood from right atrium to left atrium

-functional closure soon after birth due to pressure changes; anatomical fusion incomplete in 25% of population; incidental (Image, see High-Yield Embryo)

5. IV septum (interventricular)

-muscular IV septum develops into floor of ventricle and grows toward AV septum; stops short to create IV foramen

-membranous IV septum forms following fusion of right and left bulbar ridges and AV septum; closes IV foramen

6. Aortic Arches
   

2. Congenital Anomalies

1. AP septal defects

1. Tetralogy of Fallot

-improper alignment of AP and AV septums

-overriding Aorta, Pulmonary stenosis, VSD (poor AV fusion), right ventricular hypertrophy (right-to-left shunting, cyanosis)

2. TGA (transposition of great arteries)

-AP septum fails to spiral

-right-to-left shunting, cyanosis

3. Persistent truncus arteriosus

-abnormal neural crest cell migration, incomplete development of AP septum

-usually accompanied by defect in IV septum

-cyanosis

2. Atrial septal defects

1. Patent foramen ovale

-foramen secundum defect, excessive resorption of SP or SS

-symptoms may manifest as late as age 30

-most common ASD

3. VSDs

1. Membranous VSD

-most common VSD

-fails to develop

-left-to-right shunting, pulmonary hypertension

-sx: excessive fatigue on exertion

4. Circulatory anomalies

1. Coarctation of aorta

-abnormally constricted inf. to ductus arteriosus

-increased BP in upper extremities, lack of femoral pulse, high risk of cerebral hemorrhage and bacterial endocarditis

2. PDA (patent ductus arteriosus)

-common in premature infants, mothers with rubella during pregnancy

-causes L>R shunting, O2 rich blood back into pulm. circulation

-can treat with indomethacin (prostaglandin synthesis inhibitor; I remember it by saying, Take yo’ PDA indo’, man! Also used for acute gout, as in stay indo’ or go-out)

Category: Anatomy Notes