Flashcards in L26, L27 – Development of the Heart Deck (98):
What does gastrulation involve? (think primitive streak and action of germ layers)
Formation of 3 germ layers
Epiblast migrate through primitive streak
Mesoderm spread between ectoderm and endoderm
What happens to hypoblast cells during gastrulation?
Displaced by invaginating definitive mesoderm
What are the three segments of mesoderm?
Starting from medial, next to notochord to lateral edge:
Paraxial mesoderm > Intermediate mesoderm> Lateral plate mesoderm
What does lateral plate mesoderm further divide into?
Somatic mesoderm and Splanchnic mesoderm
What structure does paraxial mesoderm give rise to?
What do somites give rise to? (give 4 examples)
What system does intermediate mesoderm give rise to?
Gives rise to urogenital system
What does somatic mesoderm contribute to? What tissue and where specifically?
connective tissue of
What does splanchnic mesoderm give rise to? (give the 2 blast cells name and the walls of 2 organs)
Cardiomyoblasts > Heart
Hemangioblasts > Blood, lining of blood vessels
Wall of Gut
Wall of Respiratory tract
Which germ layer does the heart arise from?
What is the movement and direction of heart progenitor cells in Day 18 which establishes the primary heart field?
Heart progenitor cells in EPIBLAST move through primitive streak > migrate in CRANIAL-LATERAL direction within SPLANCHNIC MESODERM > form HORSESHOE SHAPE clusters of cells lateral to neural folds
How does the progenitor heart cells, after moving through primitive streak and splachnic mesoderm, form the primitive heart?
Horseshoe shape clusters = primary heart field/ cardiogenic area in cranial-lateral area
Clusters UNITE TO FORM HEART TUBE
What cells surrounds the heart tube after establishment of primary heart field?
Cardiomyoblasts (from splanchnic mesoderm)
What 5 structures of the primitive heart is predetermined in the primary heart field?
How many layers does the heart tube have?
What are the layers of the heart tube?
What is the heart tube endocardium's fate and origin?
Origin: epiblast-derived mesenchymal cells in splanchnic mesoderm
Fate: Forms internal endothelial lining of heart
What is the heart tube myocardium's fate and origin?
Origin: Splachnic mesoderm
Fate: form cardiac myocytes
What is the heart tube epicardium's fate and origin?
Origin: Proepicardial organ near sinus venous, adjacent to atrium in mesoderm
Fate: Covering of heart tube
What exists between the endocardium and myocardium in heart tube?
Cardiac jelly, Endocardial cushion
When is the primary heart field + heart tube formed?
When is the secondary heart field formed?
Where are the cells forming secondary heart field from?
Splachnic mesoderm ventral of pharynx (pharyngeal mesoderm)
What is the secondary heart field's fate?
contribute to development of:
Outflow tract (connected to right ventricle)
Part of the atria
Both heart fields are from which germ layer? Do the 2 heart fields form the same chambers?
No, each contribute to different chambers, some overlap e.g. formation of atria involves both fields
Summarize the structures from the the two heart fields.
Primary heart field :
Left Ventricle, Part of Atria,
Secondary heart field:
Right Ventricle, Outflow tract, Part of Atria
After formation of the 2 heart fields, What are the 4 key events in human heart development? (PClCsO)
1) Position of heart tube
2) Cardiac looping
3) Chamber septation
4) Outflow tract division and Valves formation
What 2 foldings are involved in positioning of heart tube?
Cephalic folding + Lateral folding
How does cephalic folding bring heart tube to different position? (3 points)
Centre of cardiogenic area originally anterior to oropharyngeal membrane
Subsequent growth of CNS/ Nerual plate extends over Cardiogenic area and Pericardial cavity > curvature towards foregut
Cephalic folding brings heart tube to cervical > thorax region
What fuses in primitive heart during lateral folding of embryo?
Fusion of paired endocardial tubes (heart tubes)
What is the role of dorsal mesocardium?
Attach primitive heart tube (after fusion) to dorsal side of pericardial cavity
What do endocardial tubes fuse into?
Primitive heart tube
What are the 4 segments of primitive heart tube after 2 endocardial tubes fuse?
Truncus arteriosus >
Bulbus cordis >
Primitive ventricle >
Primitive atrium >
When does cephalic and lateral folding of the embryo take place?
When does the cardiac looping occur?
Cardiac looping involves translocation of 2 portions of primitive heart tube. How does the anterior portion translocate?
Anterior portion (ventricles) bends:
To the right
How does the caudal portion of primitive heart tube shift in cardiac looping?
Caudal portion (atrial) shifts:
To the left
What structure is incorporated in cardiac looping into the pericardial cavity?
Atrial/ caudal portion of primitive heart tube
When does the endocardial/ heart tubes start draining and pumping blood?
Drain at caudal sinus venosus
Pump at cranial dorsal aorta
How is the bulboventricular sulcus formed in cardiac looping?
After ventricle (anterior) portion shift Ventrally, Caudally and to the right
Bulbis cordis lies anterior to ventricles. Sulcus inbetween bulbis cordis and ventricle
What is dextrocardia an abnormality of?
Adnormal cardiac looping
When is dextrocardiac induced?
During gastrulation when laterality is established
During cardiac looping
How come dextrocardia results in heart lying in right? (think about which portion loops wrong)
Mistake in cardiac looping: Ventricle (anterior) portion shifts to the LEFT instead of the right
What is the specific location of endocardial/ heart tubes after cephalic folding?
Ventral to foregut
Neck of embryo
What process follows cardiac looping?
When are the major septa of heart formed?
27th to 37th day
What is the layer between endocaridum and myocardium in primitive heart tube that causes septation?
Cardiac jelly/ endocardial cushion
In what structures is septation simultaneous during chamber septation?
Truncus arteriosus and conus cordis
What 2 steps are there for endocardial cushions to form a septum?
1. endocardial cushion in opposite ridges grow
2. Cardiac chambers expand passively > walls elongate and merge to form septum
Does the endocardial tissue completely seal off structures in chamber septation?
Always leave a small gap to be filled by other tissue
What is the initial direction of blood flow in atria after chamber septation?
From right to left
What structure grows first in spetation of common atrium?
How does Septum primum start dividing the atria?
Septum primum extends downwards toward the endocardial cushion in AV canal
What is the Opening between BOTTOM edge of septum primum and endocardial cushions? What does it allow?
Allow blood flow from RA to LA
How many endocardial cushions frow in the AV canal?
Left, right, anterior, posterior
What happens before the closure of ostium primum?
Cell death in UPPER portion of septum primum > form perforations that coalesce > form ostium secundum
What is the difference between ostium primum and ostium secundum?
Formation: Primum is a gap left between encardial cushion and septum primum
Secundum is cell death > perforation coalesce to form hole
Location: Primum is at bottom edge of septum primum, secundum is at upper edge
Timing: Primum first, then Secundum
What is the function of the ostium primum and secundum?
Allow passage of blood from RA to LA
Where does the Septum secundum form?
From UPPER WALL of RA, grow downwards towards AV canal
How does the Septum secundum form?
Growth of RA results in invagination of muscular atrial roof
How does septum secundum relate to ostium secundum?
Septum secundum's free edge overlaps with ostium secundum
What is the small passageway between the septum secundum and the ostium secundum?
What is the role of foramen ovale?
shunts oxygenated blood from placenta via inferior vena cava from right atrium to left atrium
How is foramen ovale VALVE formed?
Upper part of septum primum gradually disappears / degenerates > remaining part becomes valve of oval foramen
How does foramen ovale shut tight at birth and cause complete separation of atria? (think lung circulation starting...)
lung circulation begins > Increased blood pressure in left atrium + Decreased pressure in right atrium
left atrial pressure > right
valve of oval foramen functionally closes against
separates right and left atria
How is atrial septal defect (ASD) caused in relation to primitive septum formation? (3)
Excessive cell death and
resorption (e.g. absence) of septum primum; and/or
Inadequate development/ abscence of septum secundum
Abscence of both septum
What does the AV canal initially only give access to?
Initially gives access only
to the primitive LEFT
What blocks blood from moving from LV to RV initially before septum formation?
Bulboventricular flange, AV canal lies to the left and doesnt supply RV
Separates RV (Bulbus cordis) from AV canal (which only access LV)
What 3 parts is the bulbus cordis (later forms RV) divided into?
Trabeculated part of RV > Conus Cordis > Truncus Arteriosus
What two structures change to allow Blood passing through both ventricles originally separated by Bulboventricular flange?
Bulboventricular flange regresses half way along base of superior endocardial cushion
AV canal enlargement to the right
What structure does RV arise from?
Proximal Bulbus Cordis
Which 2 endocardial cushions fuse to allow sealing of primitive interventricular foramen? When?
Posterior and Anterior endocardial cushion grows and fuse in middle of AV canal > form L/R AV canal
How does L/R AV canal shift?
Canal shifts toward middle:
Left AV canal lines up with left ventricle
Right AV canal lines up with right ventricle
Both ventricles now have blood flow towards outflow tract
What transient structure surrounds the atrioventricular cushion tissue and ventricular walls in each AV canal ?
mesenchymal myocardium tissue
What happens to the proliferated mesenchymal myocardium and the muscular chord durrounding the lumen of ventricle?
mesenchymal tissue CAVITATED (hollowed
and thinned) by bloodstream > form atrioventricular (AV) valve leaflets
Muscular chords degenerate and replaced by Chordae Tendinae (dense connective tissue)
How do AV valves leaflets attach to ventricles?
Leaflets > chordae tendinae > papillary muscles
What is a common ventricular septal defect?
How does tricuspid atresia arise?
Obliteration of Right AV Canal >
Absence or fusion of tricuspid valve, no connection between RA and RV
What are the physiological consequences of Tricuspid atresia?
Underdevelopment of right ventricles
Hypertrophy of left ventricle
No blood flow to lung tissue, pulmonary stenosis
What is the consequence of blood mixing in tricuspid atresia?
Blood passes through foramen ovale > mixing of deoxygenated and oxygenated blood > Low oxygen levels in blood
What are some symptoms of Tricuspid atresia?
bluish color to skin, shortness of breath, fatigue
What are the two components to the outflow tract?
What starts the partitioning of the outflow tract?
In truncus arteriosus > Pairs of OPPOSING SWELLINGS (right, left) appear
What do the opposing swellings of truncus arteriosus form?
Pairs of opposing swellings (right, left) appear > grow
toward aortic sac and twist around each other >
completely fuse (spiral closure) to form aorticopulmonary septum
What is the role of aorticopulmonary septum?
divides truncus into:
1. Aortic channel (aortic arch)
2. Pulmonary channel
How come pulmonary trunk ends up anterior to aorta?
Spiral closure of opposing swellings in truncus arteriosus in RIGHT-HANDED twist
What divides the conus cordis into separate outflow tracts of LV and RV? (think 2 truncoconal swellings grow and fuse)
Conus cordis swell along L/R ventral walls > Fuse and unite with truncus septum at Truncoconal transition > divide conus cordis into L/R outflow tracts
What do the L/R outflow tracts connect to?
Right: Pulmonary artery
What forms the primitive septum between ventricles?
Medial walls of expanding ventricles > apposed and merge > Muscular Interventricular Septum
The space between the top edge of muscular septum and endocardial cushions allow what? How is it sealed?
Allow flow between 2 ventricles
Aortico-pulmonary septum fuses with POSTERIOR Atrioventricular cushion to close gap in septum > form membranous septum
How are semilunar valves formed? (think tubercules, truncus arteriosus)
Main truncus arteriosus swelling > semilunar valves primordia become visible as 3 small tubercles > Tubercules hollowed out/ cavitated by blood in UPPER SURFACE > semilunar valves
Which is the most common congenital heart defect?
Which part of IV spetum deforms in majority of VSD?
What is the consequence and symptoms of VSD?
Mixing deoxy and oxy blood
Symptoms = fatigue, fat breathing, no appetite
What 4 defects does Tetralogy of Fallot Disease demonstrate? (start with VSD and Aorta displacement...)
1. Ventricular septal defects (VSDs)
2. Overriding / displacement of aorta over VSDs (not
to left ventricle)
3. Narrowing of pulmonary valve (pulmonic stenosis)
> restricts blood flow to lung, leading to…
4. …Thickening / hypertrophy of right ventricular wall
What symptoms for Tetralogy of Fallot?
Bluish tint to skin, fingertips, lips (cyanosis)
What is persistent/ common truncus arteriosus?
Failure in formation of conotruncal ridges = no septation of outflow tracts + interventricular septal defect