The Heart
A. 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 (First Aid p. 94)
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 (First Aid p. 92)
B. Congenital
Anomalies
1. AP
septal defects
a.
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)
b. TGA (transposition of great arteries)
-AP septum fails to spiral
-right-to-left shunting, cyanosis
c.
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
a. 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
a.
Membranous
VSD
-most common VSD
-fails to develop
-left-to-right shunting,
pulmonary hypertension
-sx: excessive fatigue on
exertion
4. Circulatory
anomalies
a. 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
b. 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)
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