GPS: Anatomy & Embryology (Wondisford) - 10/31/16 Flashcards
The heart tubes fused to form one tube, which differentiates from most superior to most inferior.
What do the following embryonic structures give rise to?
- Truncus arteriosus
- Bulbus cordis
- Endocardial cushion
- Primitive atrium
- Primitive ventricle
- Primitive pulmonary vein
- Left horn of sinus venosus
- Right horn of sinus venosus
- Right common cardinal vein and right anterior cardinal vein
- Truncus arteriosus (b/w sac and bulbus cordis) –> Ascending aorta and pulmonary trunk
- Bulbus cordis –> Smooth parts (outflow tract) of LV and RV
- Endocardial cushion –> Atrial septum, membranous IV septum; AV and semilunar valves
- Primitive atrium –> trabeculated part of LA and RA
- Primitive ventricle –> trabeculated part of LV and RV
- Primitive pulmonary vein –> Smooth part of LA
- Left horn of sinus venosus –> Coronary sinus
- Right horn of sinus venosus –> Smooth part of RA (sinus venarum)
- Right common cardinal vein and right anterior cardinal vein –> SVC
The heart is the first functional organ in vertebrate embryos. By what week of development does it begin to spontaneously beat?
Week 4
Cardiac Looping
Why does the primary heart tube loop?
When does cardiac looping begin?
What structure plays an important role in normal heart rotation?
Potential defect?
Why: To establish L-R polarity
When: Week 3.5-4 of gestation
What: cilia
Potential defect: Defect in L-R dynein (involved in L/R asymmetry) → dextrocardia (heart points to R side of chest instead of L)
- Dextrocardia seen in Kartagener syndrome (primary ciliary dyskinesia)
After looping, the heart needs to be divided.
- AV endocardial cushions are invaded by NC cells
- Approach each other
- Fuse in ventral-dorsal direction → AV canal divided into R and L canals
- Canals partially separate primordial atrium from primordial ventricle
- Valves will eventually form here
What are the steps in the septation of the atrial chambers?
- Septum primum (green) grows toward endocardial cushions → foramen primum narrows
- Foramen secundum forms in septum primum → foramen primum disappears
- Septum secundum (blue) develops → foramen secundum maintains R-to-L shunt
- Septum secundum expands and covers most of foramen secundum → Residual foramen = foramen ovale
- Remaining portion of septum primum → valve of foramen ovale formed
- (Not shown) Septum secundum and septum primum fuse → atrial septum formed
- (Not shown) After birth, inc. LA pressure → Foramen ovale usually closes
What causes a patent foramen ovale?
What can a PFO lead to?
Failure of septum primum + septum secundum to fuse after birth; most left untreated (occurs in 25% of population)
- NOT a congenital heart defect (no true hole at rest in the septum)
Can lead to paradoxical emboli (venous thromboemboli that enter systemic arterial circulation), similar to those resulting from an ASD (congenital heart defect)
Blood clot travels from R side to L side of heart through patent foramen ovale → ends up in systemic circulation → brain → stroke
What are the steps in the septation of the ventricle chambers?
Ventricular septal defect
- Muscular IV septum forms → Opening is called IV foramen
- Aorticopulmonary septum rotates and fuses with muscular ventricular septum to form membranous IV septum, closing IV foramen
* This requires NC cells - Growth of endocardial cushions separates atria from ventricles and contributes to both atrial septation and membranous portion of IV septum
Ventricular septal defect (VSD)
- Most common congenital heart defect (25% of all defects)
- Most commonly occurs in membranous septum
- Not cyanotic at birth due to L → R shunt
Purpose of yolk sac in human?
What is vitelline circulation?
Yolk sac → critical for blood cell development
The system of blood flowing from the embryo to the yolk sac and back again.
All venous drainage to the primordial heart occurs via ______________.
What paired sets of veins is received by this structure?
Sinus venosus
- Umbilical vessels from the chorion.
- Vitelline vessels draining from the umbilical vesicle (yolk sac equivalent); source of blood cells
- Dorsal aorta and cardinal vessels (both paired) draining body wall of embryo
Fetal erythropoiesis
“Young Liver Synthesizes Blood”
- Yolk sac (3-8 wks)
- Liver (6 wks-birth)
- Spleen (10-18 wks)
- Bone Marrow (18 wks-adult)
Hemoglobin development
- What is the structure of hemoglobin?
- What are the embryonic globins?
- Fetal hemoglobin (HbF)?
- Adult hemoglobin (HbA1)?
- All hemoglobin have 4 subunits, each which contain a globin and a heme group.
- So you have 2 alpha globin + 2 beta globin, each with its own iron containing pigment
- What are the embryonic globins? zeta & epsilon
- Fetal hemoglobin (HbF)? a2g2
- Adult hemoglobin (HbA1)? a2b2
“Alpha Always, Gama Goes, Becomes Beta”
Why does HbF have a higher affinity for oxygen than HbA?
Shape of dissociation curve of HbF and HbA
Less avid binding of 2,3-BPG → allows HbF to extract oxygen across placentra from maternal hemoglobin (HbA)
HbF: hyperbolic
HbA: sigmoidal
Which type of hemoglobin circulates at low levels in adults and under what circumstances can it be increased?
Hemoglobin A2 (a2d2)
Inc. in patients with beta thalassemia or sickle cell disease
Heart Morphogenesis
- Heart tubes (horseshoe) begin superior to mouth and ventral to intra-embryonic coelom (future pericardial, pleural, and peritoneal cavities)
- As the head grows at 3 weeks, heart tubes fold ventrally → trap foregut on either side by paired dorsal aorta
- Pericardial cavity now becomes ventral (anterior in newborn); head and mouth are now superior
- Heart tubes approach each other in midline and venous drainage develops
- Pericardioperitoneal canals arise from pericardial cavity
- Pass on either side of foregut to join peritoneal cavity
- Septum transversum (primodrium of central tendon of diaphragm) will separate the heart and lungs from the peritoneal cavity
- Paired aorta now trap foregut
Veinous drainage of the embryo
- Majority of venous drainage is via umbilical arteries (return blood to the placenta)
- Venous drainage to sinus venosus as embryo develops
Morphogenesis of sinus venosus
- Starts out with paired (L and R) structures (common cardinal, vitteline, umbilical)
- R vitelline vein → hepatic vein (drains into IVC)
- L vitelline vein → degrades
- R umbilical vein → degrades
- L umbilical vein remains
- Anterior and posterior cardinal veins (paired) drain into paired common cardinal veins
- Anterior cardinals → jugular, subclavian veins, and SVC on R
- Posterior cardinals → replaced by smaller veins → eventually form azygos system and IVC
Neural Crest Cell Derivatives (from ectoderm)
Ectoderm
- Surface ectoderm
- Neuroectoderm
- Neural crest
- PNS
- Dorsal root ganglia
- Cranial nerves
- Autonomic ganglia
- Schwann cells
- Melanocytes
- Chromaffin cells of adrenal medulla
- Parafollicular (C) cells of thyroid
- Pia
- Arachnoid
- Osteoblasts/osteoclasts
- Odontoblasts (produce dentin)
- Aorticopulmonary septum
- Endocardial cushions
- PNS
Neural Crest Cells migrate to outflow tract and cardiac cushion. They also organize tissue movement.
Outflow tract formation
Conotruncal abnormalities associated with failure of NC cells to migrate (3)
NC and endocardial cell migrations → truncal and bulbar ridges that spiral and fuse → form aorticopulmonary septum → ascending aorta and pulmonary trunk
Abnormalities - all cause blue babies:
- Transposition of great vessels (if rotation doesn’t happen, aorta comes off RV and PA comes off LV)
-
Tetralogy of Fallot
- VSD
- Overriding aorta
- Pulmonary outflow tract stenosis (most important prognostic factor)
- RV hypertrophy
- Persistent truncus arteriosus (one big channel that doesn’t septate - RV and LV both drain into it)
Kartagener’s Syndrome
- Rare, autosomal recessive disorder
- Type of primary ciliary dyskinesia
- Defects in dynein (involved in L/R asymmetry) → ciliary dysfunction
- Recurrent chest, ear, and sinus infections
- Infertility
- Defects in dynein (involved in L/R asymmetry) → ciliary dysfunction
- Comprises a triad:
-
Situs inversus (organs sit on opposite side)
- Dextrocardia (heart points R instead of L)
- Chronic sinusitis
- Bronchiectasis (walls of bronchi thickened from infection/inflammation)
-
Situs inversus (organs sit on opposite side)
Atrial Septal Defects (ASD) (2)
Route of embolus from leg or pelvis
- Ostium Secundum Type (90%)
- Abnormal growth (not enough) of septum primum or secundum
- Ostium Primum Type (5%)
- Septum primum doesn’t fuse with endocardial cushion
- Seen in Down Syndrome
- Associated with AV valve defects
ASD can lead to paradoxical emboli (venous thromboemboli that enter systemic arterial circulation)
Embolus from leg or pelvis:
- Passes through ASD and enters LA → LV → CNS → stroke
- Process increases with age as L to R shunt in atrium overloads the lung → pulmonary HTN + reversal of atrial shunt
What is cyanosis?
Two types:
Early vs. Late
Cyanosis - presence of desaturated hemoglobin → blood has bluish tinge
Early:
“Blue babies” due to R to L shunts
- Deoxygenated blood reaches systemic circulation
- Transposition of great vessels
- Tetralogy of Fallot
- Persistent truncus arteriosus
Late:
“Blue kids” due to L to R shunts
- Eventually overwhelm lungs → increase PVR →Reverse shunt to R to L (Eisenmenger’s Syndrome)
- ASD
- VSD
- Patent Ductus Arteriosis (PDA)
Aortic arch derivatives → develop into arterial system
Where do the R and L recurrent laryngeal nerves loop?
R recurrent laryngeal nerve: wraps around R subclavian
L recurrent laryngeal nerve: loops around aortic arch distal to ductus arteriosus
Coarctation of the aorta
3 types
Aortic narrowing (stenosis) near insertion of ductus arteriosus
-
Postductal
- Constriction just distal to DA → collateral circulation possible during fetal period → assist w passage of blood to lower lobdy
- Presents later in life with:
- Weak LE pulses
- UE HTN
- Rib notching
-
Preductal
- Constriction is proximal to DA
- Before birth, blood flows through DA to descending aorta for distribution to lower body
- Collaterals do not develop in utero → preductal coarctation can be life-threatening in neonate
- Symptom of Turner Syndrome (XO)
-
Juxtaductal
- At the DA (most common)
- Behaves most like postductal if unrecognized at birth
Fetal Circulation:
PO2 of blood in umbilical vein and % saturation
3 important shunts
PO2 of blood in umbilical vein = 30 mmHg
% saturation = 80%
3 important shunts:
- Blood entering fetus through umbilical vein → ductus venosus → IVC (bypass hepatic circulation)
- Most of highly oxygenated blood reaching the heart via IVC directed through foramen ovale and pumped into aorta to supply head + body
- Deoxygenated blood from SVC passes through RA → RV → main pulmonary artery → patent ductus arteriosus → descending aorta
- Shunt due to high fetal pulmonary artery resistance (due partly to low O2 tension)
Where is the space posterior to the crista in the RA derived from?
Right horn of sinus venosus
- Smooth, thin walls
- Both vena cava empty into this space
Fetal-postnatal derivatives
Umbilical vein
Umbilical arteries
Ductus arteriosus
Ductus venosus
Foramen ovale
Allantois
What does it mean to have Right Dominant Circulation
RCA supplies back of heart (85%)
Defined by which artery supplies the PDA (aka PIvA)
SA and AV nodes usually supplied by RCA
Describe the blood supply of AV, SA nodes and bundle of His
AV node supplied by PDA (supplies posterior 1/3 of IV septum, AV node, and posterior wall of ventricles)
SA node supplied by RCA
Bundle of His from AV node travels anteriorly (supplied by anterior circulation → LCA)
Conducting System of the Heart: master is on the top
What is the source of somatic sensation (pain) from the parietal pericardium (outside pericardial cavity)?
Where is the pain referred to?
Contrast this with cardiac “pain”
Somatic afferent fibers in phrenic nerves
Referred pain → shoulder/lateral neck area (C3, C4, C5)
Cardiac “pain” - referred pain (more vague) to the chest b/c visceral pericardial afferents return to T1-5 via SNS (autonomic)
What are the following structures?
Which structure is a derivative of the cardinal veins?
- Ascending Aorta
- Descending Aorta
- SVC
- Trachea
- Pulmonary Artery
- L main bronchus
