Heart Development Flashcards
When do the primordial heart and vascular system begin to appear in an embryo?
middle of the 3rd week
When does the heart start to function?
beginning of the 4th week
From what three main embryonic structures does the cardiovascular system develop?
- splanchnic mesoderm - forms heart promordium
- paraxial and lateral mesoderm - near otic placodes
- neural crest cells - from between otic vesicles and caudal end of 3rd somite pair
What is the structure whose name is crossed out in blue?
What is its origin and significance?
It is paired. What do the two of them form and how?
angioblastic cords
- earliests signs of heart dev. (during 3rd week)
- paired endothelial cell groups which leave the cardiogenic splanchnic mesoderm just below the pericardial intraembryonic coelom
- later canalize to form endocardial tubes
What are the steps of the general process for the initial formation of the embryonic vascular system?
(acronym)
A B C F V A
All Boston Cabbies Find Vagina Appealing
- begin at end of 3rd week
- Angioblast Differentiation - mesenchymal cells > angioblasts
- Blood Island Formation - angioblasts aggregate > blood islands
- Cavities - intercellular clefts combine to form cavities in islands
- Flattening - angioblasts flatten to form endothelium
- Vasuculogenesis - endothelium-lined cavities fuse to form vessels
- Angiogenesis - endothelial budding > new vessels sprout from old
What forms from the endocardial tubes?
How and when?
Tubular Heart
- endocardium of the heart
- the 2 endocardial tubes fuse medially during “rolling” or transverse folding
- 4th week
What induces early development of the heart?
stimulation from the anterior endoderm
What 3 paired veins drain into the tubular heart of a 4-week embryo?
They are marked here by the red dots.
- anterior, posterior + common cardinal veins - return O2 poor blood from embryo body
- vitelline veins - return O2 poor blood from yolk sac
- umbilical veins - carry O2 rich blood from placenta
(orientation of veins around heart seen below)
What is this cavity on the caudal end of the embryonic heart?
sinus venosus
- receives blood from umbilical, vitelline and cardinal veins
What is this paired structure?
What does it come from and later become?
Myoepicardial Mantle
- thickening of the splanchnic mesoderm
- it is the dorsal wall of the primordial pericardial cavity
- later becomes the epi- and myocardium layers
(shown w/ red arrow below, eventually even the dorsal side of the MEM fuses to completely surround the heart tube )
What two embryonic movements explain the movement and fusion of the parts of the primordial heart?
Flexion (AKA head/tail fold, longitudinal folding)** **- explains hearts movement from “above” head to in the chest
Rolling (AKA transverse folding) - explains joining of paired heart primordia in the mesoderm
What is #7?
How does it form and what is its fate?
Dorsal Mesocardium
- a dorsal suspension of the heart tube and its surroundings by a stalk of mesoderm
- forms when the intraembryonic coelom fuses ventrally, but not dorsally
- eventually disappears as the coelom fuses completely to form the pericardial cavity
What eventually becomes the parietal pericardium?
**somatic mesoderm **of the cardiogenic area
What is the area marked by the question mark?
What does it become and how?
Truncus Arteriosus
- cranial end of the primitive heart tube coming from the primitive ventricle and bulbus cordis
- becomes the aorta and pulmonary trunk after septation by the spiral aorticopulmonary septum
What is the area indicated by the question mark?
What does it become?
bulbus cordis
- rounded structure in primitive heart tube distal to primitive ventricle
- gives rise to outflow part of the right ventricle (infundibulum)
What is the red question mark?
What does it become?
Right Sinus Horn
- differentiates into the SVC and IVC leading into the sinus venarum
What is the blue question mark?
What does it become and how?
Left Sinus Horn
AKA Duct of Cuviér
- becomes the coronary sinus when the sinu-atrial opening moves rightward
What are the green structures at the sinu-atrial opening?
The dorso-cranial fusion of these two structures forms what?
And what is its fate?
right and left veinous valves
- form the septum spurium as they fuse cranially
- septum spurium and left venous valve incorporate into septum primum
How do the ends of the primitive heart tube move in order for the chambers to arrange normally?
What is this new, folded arrangement called?
venous end moves backwards and upwards to form atria
arterial end moves forwards and downwards to form ventricles
- called the bulboventricular or cardiac loop
How does the atrioventricular canal septate?
- paired dorsal and ventral AV endocardial cushions form centrally within the canal
- the AV cushions proliferate dorsoventrally until they fuse
- tissue around the resulting right and left AV canals is induced by the surrounding myocardium to become the bi- and tricuspid valves
What forms from the inferior portion of the right venous valve?
Eustachian and Thebesian Valves
How do the pulmonary veins form?
- a single primordial pulmonary vein grows out of the dorsal left atrium near the septum primum
- atrial growth incorporates the primordial pulmonary vein and its main tributaries into the atrial wall, forming the final 4 pulmonary veins
What are the origins of the smooth and rough parts of the atria?
smooth parts - sinus venarum cavarum and smooth left atria form from incorporation of veinous tissue into atrial wall
rough parts - auricles and pectinate muscles form from common atrium
How is the primordial atrium partitioned?
- thin, cresecent-shaped septum primum grows antero-inferiorly towards EC cushions from the postero-superior wall of the common atrium
- foramen primum forms as septum approaches EC cushions
- apoptotic holes in septum primum form **foramen secundum **above f. primum
- foramen primum closes when septum primum fuses with left side of EC cushions
- thicker **septum secundum **grows just right of primum in opposite direction
- **foramen ovale **forms from overlap of the two septa at foramen secundum
- cranial septum primum disappears forming valve of foramen ovale
How does the interventricular septum form?
- muscular IV septum arises as a ridge in the floor of the ventricle
- at first, just ventricular dilation pushes muscular septum upward
- then, myoblast proliferation increases size further
- an IV foramen persists at the caudal end of the septum
- membranous IV septum forms finally from 3 sources:
- left and right bulbar ridges
- endocardial cushions
What forms the parietal pericardium?
somatic mesoderm
what forms the visceral pericardium?
mesothelial cells from septum transversum
What forms the ridges which go on to septate the heart tube during the formation of the large arteries?
**mesenchymal cells **from neural crest cells which migrate through pharyngeal arches
Describe the septation of the bulbus cordis and truncus arteriosus.
- mesenchymal cells originating from neural crest cells migrate into bulbus cordis
- these cells form bulbar and truncal ridges which spiral 180-270 degrees through the bulbus cordis and truncus arteriosus
- ridges proliferate centrally into the bulbotruncal lumen and fuse to complete the septum
- a hook septum forms superiorly from the spiral septum to complete the separation of the pulmonary circulation
How do the semilunar valves form?
left and right valvulae - bulbar ridges (AKA primary endocardial cushions)
anterior and posterior valvulae - secondary endocardial cushions
What is the malformation in which all viscera are mirrored?
situs inversus totalis
What is the malformation in which only the heart is mirrored to the other side of the thorax?
dextrocardia
What is the name of incomplete closure of septum primum and secundum?
atrial septal defect or persisting foramen ovale
What is the name of the malformation resulting in faulty separation of ventriculars?
How does it occur?
Ventricular Septal Defect
- muscular and membranous parts do not fuse
How does a transposition of the great vessels occur?
What is it?
- aorticopulmonary septum twists only 90 degrees
- a swapping of the vessels that each ventricle feeds into such that:
- deoxygenated blood from the right ventricle feeds into the aorta and systemic circulation
- oxygenated blood from the left ventricle feeds into the pulmonary trunk and circulation
What is the name of the malformation with four parts?
What are the four parts?
Tetralogy of Fallot
- narrow pulmonary valve
- thick right ventricular wall
- aortic displacement over IV septal defect
- IV septal defect
