Heart Development Embryo Flashcards
When does the heart start beating?
Day 22
What embryonic tissue is the heart derived from?
Splanchnic mesoderm
What are heart fields and what do they become?
Primary heart field: comes from the primitive streak, develops into left and right atria, and the left ventricle
Secondary heart field: comes from pharyngeal arches, develops into right ventricle, outflow tract and the venous pole of the atria
What is the outflow tract
Bulbus cordis (conus cordis) and truncus arteriosis -> they both eventually become the aorta and pulmonary tract
What does intraembryonic coelom give rise to?
Pericardial cavity
What is the cardiogenic cord also called?
Primary heart field or heart tubes
What is dorsal mesocardium?
A double layer of splanchnic mesoderm that forms from the fusion of the two endocardial heart tubes (eventually it pinches off to give transverse pericardial sinus).
It provides route for blood vessels, lymph and nerves to get to/from organs
What are the three layers of heart mesenchyme?
Endocardium: internal endothelial lining
Myocardium: muscular wall
Epicardium: (visceral pericardium) outer covering of heart
What does the transverse sinus do?
Separates outflow tract from venous flow
What do neural crest cells participate in? And what structures do they migrate through?
Originating in the medulla (myencephalon), they migrate through parygeal arches 3, 4, 6 and help to form the truncus arteriosus and aorticopulmonary septa (b/w aorta and pulmonary tract)
What regulates cardiac neural crest migration/differentiation?
Retinoic acid, Hox genes, Nf-1 and Pax3.
Note: too much vitamin A in pregnancy can cause cardiac defects d/t disruption of NC migration. (Accutane is a vitamin A derivative)
What is the order of heart formation?
Day 20: 2 heart tubes approach and fuse
Day 21: fusion into primitive heart tube
Day 22: heart starts to beat, have truncus arteriosus, bulbus cordis, primitive ventricle and primitive atrium
Day 23: heart starts to bend down on itself and to the right (bulboventricular loop)
Days 24-25: atrium and sinus venosus come to lie dorsally in back, ventricle moves down
What is dextrocardia?
When cardiac folding happens in the opposite direction (to the left) and the heart becomes a mirror image of normal folding.
Can cause other defects unless it presents with sinus inversus: where all abdominal contents are in mirror image, then it can go unnoticed for years
What are the different septation events, and when are they taking place?
Atrioventricular (AV) septum, Atrial septation, Interventricular (IVS) septum, Conotruncal septum
All are happening at the same time, start mid 4th week and end in the 8th week of development
Describe atrioventricular (AV) canal septation
Dorsal and ventral endocardial (AV) cushions grow together, giving right and left AV canals, separating atria from ventricle
Note: formation remodeling of the AV cushions is retinoic acid-dependent, so disruption of retinoid signaling often produces AV canal defects
What are the endocardial cushions derived from?
Mesodermal growth from the dorsal and ventral walls
What is pectinate muscle derived from?
The primitive heart tube
What does the left horn of sinus venosus remodel into?
The coronary sinus
What does the right horn of the sinus venosus become?
It becomes the sinus venarium and is incorporated into the atrium
Where do the orfices of superior and inferior vena cava veins come from?
The right horn of sinus venosus
Where does the orifice of the coronary sinus come from?
The ORIFICE comes from the right horn, the sinus itself comes from the left horn of sinus venosus
What is the sinus venosus
The venous structure that comes into the atrium, delivering blood
What is the crista terminalis?
Crest separating smooth muscle from pectinate muscle in the atria
Describe the septation of the atrium
- Septum primum grows toward the endocardial cushion, forming the foramen primum
- When the septum fuses with the cushion, foramen primum apoptoses and the foramen secundum forms (formation ensures shunting b/w right and left atrium)
- Septum secundum grows, overlapping septum primum, and forms the foramen ovale
What does the foramen ovale become?
It becomes the fossa ovale, giving rise to the first sptum
Note: tissue around the fossa ovale is the second septum (septum secundum)
What prevents backflow of blood between atria?
Pressure from blood wanting to flow backwards causes the foramen to close, sealing the hole
What is unique about ventricular septation?
The interventricular septum (splanchnic mesoderm) tries to migrate up to meet the endocardial cushion, but it doesnt make it -> does not fuse
What septation event are neural crest cells associated with?
Outflow tract septation ( bulbus cordis and truncus arteriosis)
Neural crest cells migrate into truncus arteriosus and bulbus cordis, forming ridges
The ridges spiral down (180 degrees) and fuse with endocardial cushion, giving Aorticopulmonary septum
What does the Aorticopulmonary septum separate?
It divides bulbus cordis and truncus arteriosus into ascending aorta and pulmonary trunk
What fuses to give membranous part of interventricular septum?
Endocardial cushion, right bulbar ridge (NC), left bulbar ridge (NC)
Complete fusion results in separation of right and left ventricles, and left ventricle from right atria (due to heart folding)
How are the cardiac valves formed?
Process begins once partition of truncus arteriosus is almost done.
- Blood travels through vessel, relaxing valve
- Backflow pressure tries to pull blood backward, which erodes the relaxed valve and leads to cusps that help to close valve and prevent backflow
What does the sinoatrial fold cause?
A deep fold which separates the left part of the sinus venosus from the left side of the atrium, which narrows the opening and causes a right shift, allowing the right horn to grow
Where does the SA node come from?
A portion of the right sinus horn and right common cardinal vein
