Embryo - Heart Development Flashcards
What layer does the Heart develop from?
Basics:
- splanchnic layer of lateral mesoderm
Other Facts:
- Earliest organ to develop (~day 18)
- Heart beats (~day 21-22)
- detected by sonography (~week5)
What is cardiogenic mesoderm and what does it split into?
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)
What is the importance of flexion and folding?
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
What are the 5 subdivisions of the Single Heart Tube in early embryonic development?
Sinus venosus –> Primordial Atrium –> Primodial Ventricle –> Bulbus Cordis –> Truncus Arteriosus
Embryological fates of the heart tube components?
Truncus arteriosus gives rise to?
Ascending aorta & pulmonary trunk
Bulbus cordis gives rise to?
Smooth parts (outflow tract) of left and right ventricles
Endocardial cushion gives rise to?
- Atrial septum
- Membranous interventricular septum
- AV & semilunar valves
Primitive atrium gives rise to?
Trabeculated part of left & right atria
Primitive ventricle gives rise to?
Trabeculated part of left & right ventricles
Primative pulmonary vein gives rise to?
Smooth part of left atrium
Left horn of sinus venosus gives rise to?
Coronary Sinus
Right horn of sinus venosus gives rise to?
Smooth part of the right atrium (sinus venarum)
Right common cardinal vein and Right anterior cardinal vein give rise to?
Superior vena cava (SVC)
What is Cardiac Looping ?
What defect can arise?
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
What is involved in Left-Right Partitioning?
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
Separation of the Atrial chambers involves what 5 steps?
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.
What is the Fate of aortic arches?
-
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
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
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
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:
- rubella in early pregnancy
- Down Syndrome (trisomy 21)
- coarctation of aorta
- transposition of great vessels
- Failure of TGF-B induction after birth
Note:
- 2 of 3 anomalies of arches
What is Coarctation of aorta?
Basics:
- abnormal partial involution (constriction) of dorsal aorta
3 Types:
-
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
-
Preductal
- proximal to ductus arteriosus
- Extensive
Note:
- May be associated w. Turner Syndrome
What are the major features of Right Atrium?
-
Pectinate muscle
- trabiculated part
- from primordial atrium
- trabiculated part
-
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
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
What are the 2 important features of Fetal Circulation?
-
Lung = non functional
- collapsed in fetus
- high pulmonary resistance
-
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)
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:
-
VSD
- membranous VSD
-
Pulmonary stenosis
- uneven separation leads to small pulm. artery
-
Right ventricular hypertrophy
- increased workload resulting from pulm. stenosis
-
Overridinig aorta
- Aorta “rides over the IV septum; receives blood from both ventricles
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
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
