10/31 Cardiovascular Embryology and Anatomy - Wondisford Flashcards
importance of yolk sac in human devpt
allantois and yolk sac both don’t have as significant a role as they do in other organisms’ devpt (ex. chicken) bc the PLACENTA serves as the clearinghouse for nutrients and waste
importance of yolk sac: critical for blood cell development (devpt of vitelline system)
- umbilical vessels establish connections with chorion
- vitelline vessels establish connections to umbilical vesicle, serve as source of blood cells
- dorsal aorta and cardinal vessels (paired) → body
- venous drainage to primordial heart goes through sinus venosus
fetal erythropoiesis
mnemonic
site shifts throughout embrynoic devpt
“young liver synthesizes blood”
- yolk sac (3-8wk)
- liver (6wk-birth)
- spleen (birth→10-18wk)
- bone marrow (18wk-adulthood)
hemoglobin devpt
mnemonic
diff bw fetal and adult Hb
HbF (alpha2gamma2) → HbA (alpha2beta2)
“alpha always, gamma goes, becomes beta”
- HbF binds 2,3BPG less avidly → higher affinity for oxygen than HbA
- important diff: allows HbF to extract oxygen from HbA across placenta
- seen in leftward shift of HbF oxygen dissociation curve
heart morphogenesis
(horseshoe model)
- heart tubes (horseshoe) start off…
- superior to the mouth
- ventral to intra-embryonic coelom (develops into pericardial, pleural, peritoneal cavities)
- distal part of each limb of intraembryonic coelom is continuous with extraembryonic coelom at the lateral edges
as head grows, heart tubes fold ventrally → trap foregut on either side by paired dorsal aorti
- pericardial cavity is now anterior
- head and mouth are now superior
heart tubes approach each other in midline → venous drainage develops
septum transversum (primordium of central tendon of diaphragm) will separate heart and lungs from peritoneal cavity!
embryologic derivatives
1. truncus arteriosus segment
- aortic sac → pharyngeal arches
- truncus arteriosus (b/w sac and bulbus cordis) → ascending aorta and pulmonary trunk
2. bulbus cordis segment
- bulbus cordis → outflow tract (smooth part) of LV and RV
3. ventricle segment
- primitive ventricles → trabeculated part of both ventricles
- primitive atria → trabeculated part of both atria
4. atrium segment
- left horn of sinus venosus → coronary sinus
- right horn of sinus venosus → smooth part of RA
- right cardinal veins → SVC
- primitive pulmo veins → smooth part of LA
embryologic derivatives of key veins
- R vitelline v
- L vitelline v
- R umbilical v
- L umbilical v
- anterior cardinal v
- posterior cardinal vv
- R vitelline v → hepatic vein
- L vitelline v degrades
- R umbilical v degrades
- L umbilical v → remains
- anterior cardinal v → SVC, jugular, sublavian
- posterior cardinal vv → IVC, azygos system
heart morphogenesis
basic development timeline
division of heart
- heart is the first functional organ in vertebrate embryos
- beats spontaneously by week4
- primary heart tube loops to establish L/R polarity beginning in week 3.5 of gestation
- cilia appear to be important in normal heart rotation
division of heart
- AV endocardial cusions (invaded by NC cells) approach each other and fuse in ventral-dorsal direction
- AV canal is split into L and R canals, where AV valves will eventualy form
neural crest cell derivatives
- PNS (dorsal root ganglia, CNs, autonomic ganglia, Schwann cells)
- melanocytes
- chromaffin cells of adrenal medulla
- parafollicular (C) cells of thyroid
- pia and arachnoid
- bones of skull
- odontoblasts
- aorticopulmonary septum
- endocardial cushions
Kartagener’s syndrome
rare autosomal recessive disorder
type of primary ciliary dyskinesia
- defects in dynein (involved in L/R asymmetry) cause ciliary dysfx
- defective movement of cilia → recurrent chest, ear, sinus infections and infertility
triad:
- situs inversus
- chronic sinusitis
- brinchiectasis
most common positional defect of heart: DEXTROCARDIA
atrial septal devpt
key players: septum primum, septum secundum, foramen primum, foramen secundum
Q: why have holes in the heart?
typical fate of foramen ovale
- septum primum grows toward endocardial cushions → foramen primum narrows
- foramen secundum forms as small hole within septum primum
- foramen primum disappears afer fusion of septum primum with endocardial cushion
foramen secundum maintains a R→L shunt!!! so heart grows another septum to take care of it
- septum secundum develops and expands to cover most of foramen secundum
- residual foramen is called foramen ovale
- remaining portion of septum primum → valve of foramen ovale!
- Q: what’s the point of having holes in the heart?*
- A: during devpt, want to be able to bypass the lungs!
*foramen ovale usually closes and fuses soon after birth bc of increased LA pressure as blood flows from lungs to LA
- doesn’t happen in 25% of population → patent foramen ovale
atrial septal defects
3 types
common consequence of all three & correlation with age
1. ostium secundum type (90%)
- caused by abnormal/insufficient growth of septum primum or secundum
2. ostium primum type (5%)
- when septum primum doesnt fuse with endocardial cushion
- seen in Down syndrome, assoc with AV valve defects
3. patent foramen ovale (common: 25% of adults)
- caused by faulre of septum primum and secundum to fuse after birth
- not considered a true ASD and tx (closure) is controversial
both ASD and PFO can lead to paradoxical emboli (venous thromboemboli entering systemic arterial circ)
- pathway: embolus from leg/pelvis → through ASD → into LV → CNS → stroke
- unlikely in patients without ASD bc clots would typically just go to lungs → pulmonary embolism
- likelihood increases with age bc L→R shunt in atrium overloads the lung, leading to pulmo HTN (due to vasoconst) and reversal of atrial shunt
- Eisenmenger’s syndrome!
ventricular septation
most common congenital heart defect (25% of all defects)
most commonly occurs in membranous septum
NOT CYANOTIC AT BIRTH due to L→R shunt
- muscular ventricular septum forms first; opening = interventricular foramen
-
aorticopulmonary septum rotates and fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen
- requires neural crest cells
conotruncal abnormalities
due to failure of neural crest cells to migrate to heart
- transposition of great vessels (aorta off of RV, pulmonary trunk off of LV)
- Tetralogy of Fallot
- LVH
- ventricular septal defect
- aorta that overrides LV and RV
- infundibular stenosis (R→L shunt)
- persistent truncus arteriosus (deoxy blood going into blood)
cyanosis
early vs late
- direction of shunt
- pathophys
- examples
early cyanosis
- “blue babies” due to R→L shunts : deoxy blood reaches systemic circulation
- transposition of great vessels
- Tetralogy of Fallot
- persistent truncus arteriosus
late cyanosis
- “blue kids” due to L→R shunts : eventually overwhelm lungs → incr PVR → reverse shunt to R→L (Eisenmenger’s Syndrome)
- ASD
- VSD
- patent ductus arteriosus
valve development
aortic/pulmonary : derived from endocardial cushions of outflow tract
mitral/tricuspic : derived from fused endocardial cushions of AV canal
*valvular anomalies may be…
- atretric/stenotic/regurgitant (ex. tricuspic atresia)
- displaced (ex. Ebstein anomaly)
- Ebstein anomaly: portion of RV is atrialized bc tricuspid valve is too low → functional RV is small.
- assoc with lithium tx for bipolar disorder in moms)
Ebstein anomaly
portion of RV is atrialized bc tricuspid valve is too low → functional RV is small.
assoc with lithium tx for bipolar disorder in moms)
Tetralogy of Fallot
why squat?
characterized by 4 findings:
- large VSD (vent septal defect)
- overriding aorta
- obstruction of RV outflow tract
- RV hypertrophy
due to obstruction of RV outflow tract, blood is shunted through the VSD from R→L
- long periods of squatting can help kids become less cyanotic. why?*
- squatting increases systemic vascular resistance → harder to unload LV → harder for R to L shunt to push blood to left side
summary 2
read
CORRECTION: late cyanosis is L to R shunt
evolution of pharyngeal arch arteries
in humans, aortic arch arteries arise in cranio-caudal sequence and form a basket of arteries around the pharynx
aortic arch derivatives
1st arch : maxillary a
2nd arch : stapedial and hyoid aa
3rd arch : common carotid a and proximal part of internal carotid a
4th arch : left? aortic arch. right? prox part of R subclavian a
6th arch : prox part of pulmonary a and (L side only…) ductus arteriosus
coarctation of aorta
postductal coarctation : constriction distal to ductus arteriosus
- permits devpt of collateral circ during fetal period → assists with passage of blood to lower body
- presents later in life with weak lower extremity pulses, upper extremity HTN, rib notching from collateral circ
preductal coarctation : Turner Syndrome : constriction proximal to DA
- before birth, blood flows through DA to desc aorta for distribution to lower body
- collateral do not develop in utero → can be life-threatening condition in neonate
juxtaductal coarctation : constriction at DA
- most common
- behaves most like a postductal coarctation if unrecog’d at birth
preductal vs postductal coarctation of aorta
which one has collateral formation? why?
preductal coarctation of aorta DOES NOT result in formation of collaterals
- since blood can flow through DA in utero, lower limbs stay perfused
- after birth, when DA closes, lower limbs experience significant sudden drop in perfusion → potentially life-threatening
postductal coarctation of aorta DOES result in formation of collaterals
- DA is not useful in providing lower limbs with blood supply → lower limbs signal for angiogenesis → collaterals form
- after birth, when DA closes, collateral system is able to continue taking on task of perfusion, so no sudden drop in flow
umbilical veins
- chars of blood
- 3 imp shunts
blood in umb vv has PO2 of 30mmHg
80% saturated with )2
three shunts:
- blood entering fetus: via ductus venosus into IVC
- most O2-rich blood reaching heart: via IVC, diverted into foramen ovale
- deoxy blood entering RA: from SVC→RA→RV→main PA→patent ductus arteriosus→descending aorta
how does ductus arteriosus close at birth?
what do you give to close it?
what do you give to keep it open?
at birth, infant takes a breath
- low resistance in pulmonary vasculature → incr LA pressure
- foramen ovale closes
- increase in 02 (from respiration) and decrease in prostaglandins → closure of ductus arteriosus
- remnant of DA = ligamentum arteriosum
INDOMETHACIN : closes PDA
PGE1 and E2 : keep PDA open
