Embryo - Heart Development Flashcards
1
Q
What layer does the Heart develop from?
A
Basics:
- splanchnic layer of lateral mesoderm
Other Facts:
- Earliest organ to develop (~day 18)
- Heart beats (~day 21-22)
- detected by sonography (~week5)
2
Q
What is cardiogenic mesoderm and what does it split into?
A
Basics:
- horseshoe shaped region of mesoderm
- extending from anterior of embryo –> both sides of foregut
Approx 18 days:
- Cardiogenic Mesoderm = cranial to precordal plate (mouth)
Pericardial coelom splits it into:
- somatic part (dorsal)
- splanchnic part (ventral)
- primordial heart tubes dev. from this layer
Pericardial coelom eventually is divided by folds to form:
- pericardial space (heart)
- pleural space (lungs)
- peritoneal space (abdomenal structures)
3
Q
What is the importance of flexion and folding?
A
Basics:
- Folding & flexion –> migration of developing heart into normal anatomical position
- ventral to foregut
- proximal to diaphragm
Longitudinal Folding:
-
Brings everything caudal into correct place
- Heart tube = now caudal to head & ventral to foregut
- Septum transversum = caudal to heart
- future diaphragm
- Secondary Yolk sac —> forms gut/GI structure
Lateral folding:
- fuses heart tubes together
- parietal pericardium
- forms from somatic layer of mesoderm
- visceral pericardium
- forms from splanchnic layer of mesoderm
- phrenic nerve found in folds
Results:
-
Pleural cavitites lie along the sides of the foregut
- airways develop from foregut
- Peritoneal cavities lie dorsally at sides of gut
- Pericardial cavity moves to position vental to foregut
4
Q
What are the 5 subdivisions of the Single Heart Tube in early embryonic development?
A
Sinus venosus –> Primordial Atrium –> Primodial Ventricle –> Bulbus Cordis –> Truncus Arteriosus
5
Q
Embryological fates of the heart tube components?
A
6
Q
Truncus arteriosus gives rise to?
A
Ascending aorta & pulmonary trunk
7
Q
Bulbus cordis gives rise to?
A
Smooth parts (outflow tract) of left and right ventricles
8
Q
Endocardial cushion gives rise to?
A
- Atrial septum
- Membranous interventricular septum
- AV & semilunar valves
9
Q
Primitive atrium gives rise to?
A
Trabeculated part of left & right atria
10
Q
Primitive ventricle gives rise to?
A
Trabeculated part of left & right ventricles
11
Q
Primative pulmonary vein gives rise to?
A
Smooth part of left atrium
12
Q
Left horn of sinus venosus gives rise to?
A
Coronary Sinus
13
Q
Right horn of sinus venosus gives rise to?
A
Smooth part of the right atrium (sinus venarum)
14
Q
Right common cardinal vein and Right anterior cardinal vein give rise to?
A
Superior vena cava (SVC)
15
Q
What is Cardiac Looping ?
What defect can arise?
A
Cardiac Looping:
- Primary heart tube loops to establish left-right polarity/heart laterality
- begins at week 4 of gestation
- D-Loop (normal)
- apex = left
When things go wrong:
-
Dextrocardia (L-loop)
- apex = right
- Seen in Kartagener syndrome
- primary ciliary dyskinesia
-
Complete situs inversus
- all organs = reversed
16
Q
What is involved in Left-Right Partitioning?
A
Basics:
- ALL of the heart tube MUST BE PARTITIONED:
Partitioning = accomplished by the growth/dev of:
- Endocardial cushions (AV cushions)
- neural crest cells = important for this formation
- Interatrial septum
- Interventricular sepum
- muscular & membranous parts
- Spiral (aortico-pulmonary) septum
17
Q
Separation of the Atrial chambers involves what 5 steps?
A
Atrial Chambers in Utero:
-
Septum primum grows toward endocardial cushions
- narrows foramen primum
-
Foramen secundum forms in septum primum
- foramen primum disappears
- Septum secundum develops as f_oramen secundum_ maintains right-to-left shunt
-
Septum secundum expands and covers most of foramen secundum
- opening btw septum secundum + septum primum = foramen ovale
- Remaining portion of septum primum forms valve of foramen ovale
After Birth:
- Septum secundum & septum primum fuse to form the atrial septum
-
Forman ovale usually closes due to ↑ L.A. pressue
- fossa ovale = reminant that can be seen in R.A.
18
Q
What are the 3 Steps for the Separation of Ventricle Chambers?
A
-
Muscular interventricular septum forms
- opening = interventricular foramen
-
Aorticopulmonary septum rotates & fuses w/ muscular ventricular septum
- forms membranous interventricular septum
- closes interventricular foramen
-
Growth of endocardial cushions separates atria from ventricles
- contributes to both atrial septation & membranous portion of the interventricular septum
19
Q
Explain outflow tract formation.
What happens when things go wrong?
A
Outflow tract formation:
- Neural crest & endocardial cell migrations
- truncal & bulbar ridges
- spiral & fuse to form aorticopulmonary septum
- ascending aorta & pulmonary trunk
- truncal & bulbar ridges
When things go wrong:
- Conotruncal abnormalities assoc. w/ failure of neural crest cells to migrate:
- Transposition of great vessels
- Tetralogy of Fallot
- Persistent truncus arteriosus
20
Q
Valve Development
A
Aortic/Pulmonary:
- derived from endocardial cushions of outflow tract
Mitral/Tricuspid:
- derived from fused endocardial cushions of the AV canal
When things go wrong…
-
Valvular anomalies:
- Stenotic
- Regurgitant
- Atretic
- tricuspid atresia
- Displaced
- Abstein anomaly
21
Q
Fetal Circulation
A
Fetal Circulation:
- Placental circulation
- source of oxygentated blood
- Right-to-left shunts
- Foramen ovale
- connects R.A. + L.A.
- Ductus arteriosus
- connects R.V. –> pulmonary artery + descending aorta
- Foramen ovale
- Little pulmonary blood flow
- Non-functional lungs
Note:
- Limbs & GI = less oxygenated blood
22
Q
What are the 3 important Shunts in Fetal Circulation?
A
Basics:
- Blood in umblical vein:
- Po2 = 30mmHg
- ~ 80% saturated w/ O2
- Umbilical arteries have low O2 saturation
3 Important Shunts
-
Ductus Venosus
- Blood entering fetus via umbilical vein –> IVC
- Bypasses hepatic circulation
- Blood entering fetus via umbilical vein –> IVC
-
Foramen Ovale
- Oxygenated blood reaches heart via IVC
- Blood directed from R.A. –> L.A. –> L.V. –> Aorta
- Most blood pumped thru Aorta
-
Ductus Arteriosus
-
De-oxygenated blood from SVC
- R.A. –> R.V. –> main pul. artery –> Ductus arterious –> Decending Aorta
- Shunt is due to HIGH fetal pul. artery resistance
- cause by partly low O2 tension
-
De-oxygenated blood from SVC
After Birth:
- infant takes breath = ↓ Resistance in pul vasculature
- ↑ L.A. pressue
- Foramen ovale closes –> Fossa ovalis
-
↑ O2 (from respiration) + ↓ Prostaglandins (from placental separation) = closure of Ductus Arteriosus
- Indomethacin = helps close PDA
- Prostaglandins E1, E2 = kEEp PDA open
- Reminant = Ligamentum arteriosum
23
Q
What is the Fate of aortic arches?
A
-
1st arch
- maxillary artery
-
2nd arch
- stapedial a.
- tympanic branch of internal carotid a.
- stapedial a.
-
3rd arch
- common carotid
- proximal part of internal carotid a.
-
4th arch
- arch of aorta (left)
- left subclavian a.
- right subclavian
- right 7th cervical intersegmental branch
- arch of aorta (left)
-
5th arch
- completely disappears
-
6th arch
- right pulm. a.
- left pulm. a
- ductus arterious
24
Q
What are the Disappearing arteries?
A
Partially disappearing:
- 1st arch
- 2nd arch
- Right 6th arch
- Righ Dorsal Aorta
Totally disappearing:
- 5th arch
25
What aortic branches do the Recurrent laryngeal nerves wrap around?
**Left Recurrent laryngeal nerve**
* _wraps around 6th aortic arch_
* lateral to ductus arteriosus
**Right Recurrent laryngeal nerve**
* _wraps around 4th arch_ - right subclavian a.
* 5th & 6th arches disappear
26
What are the 3 Major Anomalies of the arch system?
1. Double aortic arch
2. Patent Ductus Arteriosis
3. Coarctation of Aorta
27
What is a Double aortic arch?
**Basics:**
* _Persistence of RIGHT dorsal aorta_
* Caudal to 7th cervical intersegmental a.
* Forms ring around trachea & esophagus
**Results:**
* _Encloses esophagus & trachea_
* Causes:
* dyspnea (trouble breathing)
* dysphagia (trouble eating)
**Note:**
* 1 of 3 anomalies of the arch system
28
What is a Patent Ductus Arteriosus?
**Basics:**
* Ductus arteriosus should close after 72 hrs (3 days)
* Becomes ligamentum arteriosum
* _Patent Ductus arteriosus = FAILURE TO CLOS_E
**Natural causes of closure:**
* _Increase in partial pressure of O2_ after birth
* _Drop in prostaglandin_ levels after birth
**Treatment of Patent Ductus arteriosus:**
* Give high concentration of O2 to baby
* Give anti-prostaglandins to baby
**Fun Facts:**
* More common in _females_
* Associated with:
1. **rubella** in early pregnancy
2. **Down Syndrome (trisomy 21)**
3. coarctation of aorta
4. transposition of great vessels
* Failure of TGF-B induction after birth
**Note:**
* 2 of 3 anomalies of arches
29
What is Coarctation of aorta?
**Basics:**
* abnormal partial involution (constriction) of dorsal aorta
**3 Types:**
1. _Postductal_
* **distal** to ductus arteriosus
* **collateral circulation =\> less severe effects**
* subclavian a. --\> internal thoracic a --\> superior epigastric a. --\> inferior epigastric a. (branch of external iliac a.);
* will NOT affect tissue O2 much b/c of collateral circulation
* _Upper limb = HTN & Heart Failure_
* Lower limb = diminished femoral pulse
2. _Preductal_
* __**proximal** to ductus arteriosus
3. _Extensive_
**Note:**
* May be associated w. _Turner Syndrome_
30
What are the 2 major categories of Congenital Heart Defects?
**Acynotic**
* Volume load
* _Left --\> Right shunt_
1. ASD
2. VSD
3. AV Canal
4. Patent ductus arteriosus
* Pressure load
* _Obstr. Ventricle Outflow_
1. Pulmonary Valve stenosis
2. Aortic Valve stenosis
3. Coarctation of aorta
**Cyanotic**
* _↑ Pulm. flow_
* Transposition of Great Vessels
* Single Ventricle
* Trucus Arteriousus
* _↓ Pulm. flow_
* Tetralogy of Fallot
* Pulm atresia
* Tricuspid atresia
31
What are the 4 Causes of Congenital Heart Defects?
**Causes of CHD:**
1. 80% = UNKNOWN
2. Infection
* Rubella
3. Chromosomal
* Turners syndrome = Coarctation of aorta
* Downs/Trisomy 21 = ASD/VSD/PDA
4. Poorly defined familial susceptibility
32
What are the 5 Clinical effects of CHD?
1. Failure to thrive
2. Cyanosis
* Right --\> Left shunt
3. Cardiac Failure
4. Pulm. HTN
5. Infective endocarditis
33
How does the Single Heart Tube grow?
**Future Right Atrium**
* rough part = primordial atrium
* smooth part =
* right horn of sinus venosus = sinus venarum
* left horn of sinus venosus = coronary sinus
**Future Left Atrium**
* rough part = primordial atrium
* smooth part = pulmonary arteries
**Future Right Ventricle**
* trabeculated part = primordial ventricle
* smooth part = bulbus cordis = conus arteriosus
**Future Left Ventricle**
* trabeculated part = primordial ventricle
* smooth part = bulbus cordis = aortic vestibule
**Future Aorta & Pulm artery**
* from truncus arteriosus
34
What are the major features of Right Atrium?
* **Pectinate muscle**
* trabiculated part
* from primordial atrium
* **Crista terminalis**
* junction of smooth & rough parts
* **Fossa ovalis**
* closed shunt; fetal reminant
* **Tricuspid valve**
* leads to right ventricle
* **Coronary sinus**
* from left horn of sinus venosus
* venous return from heart veins
35
What are the major components of the Left Atrium & Left Ventricle?
**Left Atrium**
* Mostly smooth due to absorption of pulm. veins
* 4 pulmonary veins = bring O2 rich blood
* _Left auricle_
* rough part
* reminant of primordial atrium
**Left Ventricle**
* _Aortic vestibule_
* left ventricle outflow tract (LVOT)
* form bulbus cordis
* entry into aorta
* _Aortic (semilunar) valve_
36
What are the major components of the Right Ventricle?
* **Conus arteriosus**
* Right ventricle outflow tract (RVOT)
* entry into pulm. artery (pulm valve)
* **Moderator band**
* septomarginal trabeculum
* anchors papillaries to interventricular septum
* **Tendinous cords**
* hold tricusptid valve open
* attached to papillary muscles
* **Trabeculae carnae**
* rought part
* from primordial ventricle
37
What are the 2 important features of Fetal Circulation?
1. **Lung = non functional**
* collapsed in fetus
* high pulmonary resistance
2. **Nutrients & O2 rich blood from maternal circulation**
* Placenta --\> Umbilical vein --\> Ductus Venosus --\> IVC --\> R.A. --\> Foramen Ovale --\> L.A. --\> L.V. --\> Ascending Aorta --.\> Body (Brain)
* Blood from SVC --\> R.A. --\> R.V. --\> Pulm Artery --\> Ductus arterious --\> Descending Aorta (mixed venous blood to lower limb)
38
What are the 3 Important Changes from Fetal to Adult Circulation?
1. **Closure of foramen ovale**
* breathing = lungs expand = resistance in pulmonary system DECREASES
* right pressure in heart DECREASES
* left pressure in heart INCREASES
* change in pressure = closes formaen ovale
* becomes _Fossa Ovalis_
2. **Closure of ductus arteriosus**
* becomes _ligamentum arteriosum_
3. **Closure of ductus venosus**
* becomes _ligamentum venosum_
39
Explain Ventricular Partitioning
**Basics:**
* Interventricular septum separates RV & LV by week 7
* aorta & pulm trunk = formed by partitioning truncus arteriosus
**Structures:**
* Ventricular septum has 2 parts:
* Muscular part - dev. from primordial interventricular septum
* Membranous part - dev. from endocardial cushions & bulbar ridges
* Partition of aorta & pulm trunk:
* continuation of bulbar ridges, truncal ridges, and endocardial cushions
* forms aorticopulmonary/spiral septum
**Both:**
* have rough (trabeculated) part dev. from primordial ventricle
40
What are Ventricular Septal Defects (VSD)?
**Basics:**
* Failure of tissue from endocardial cushions to fuse w/ primordial IV setum & bulbar ridges
* Left --\> Right Shunt
* Acyanotic
**Most Common:**
* Membranous type of VSD
* ~25% of all CHD
**Note:**
* Can have associated AV valve (mitral) abnormality
41
What are the 4 Abnormal Divisions of Truncus Arteriosus?
**Basics:**
* Caused by faulty migration of NEURAL CREST cells
**4 Defects:**
1. Tetralogy of Fallot
2. Transposition of Great Vessels
3. Persistent Truncus
4. Aorticopulmonary septal defects
42
What is Tetralogy of Fallot?
**Basics:**
* truncus arteriousus divides unevenly
* larger aorta, smaller pulm. artery
* Right --\> Left shunt
* Cyanosis!
**Cause:**
* Faulty migration of neural crest cells
* Failed fusion of endocardial cushions, truncal & bulbar ridges
**Results:**
1. _VSD_
* membranous VSD
2. _Pulmonary stenosis_
* uneven separation leads to small pulm. artery
3. _Right ventricular hypertrophy_
* increased workload resulting from pulm. stenosis
4. _Overridinig aorta_
* Aorta "rides over the IV septum; receives blood from both ventricles
43
What is the Transposition of the Great Vessels?
**Basics:**
* Switching of aorta & pulmonary trunk
**Cause:**
* Faulty migration of neural crest cells --\> absence of spiral twist in aortico-pulmonary septum
**Result**:
* Immediately lethal unless combined w/ other defect - PDA, ASD, VSD
44
What is Persistent Truncus Arteriosus?
**Basics:**
* No formation of aortico-pulmonary septum
**Cause:**
* Failure of neural crest cells to migrate
**Result:**
* Associated w/ VSD
* Cyanotic
