Cardiovascular Development A Flashcards
Where does the cardiogenic crescent develop from and what does it become?
Lateral plate mesoderm forms on both sides of the embryonic disk and around the cranial end of the disc.
This discs fold ventrally and fuse at midline
In the cranial portion , a crescent of splanchnic mesoderm makes up the cardiogenic crescent that makes the heart
Lateral plate mesoderm folds ______ and joins at _______
______ enveloped inside (forms gut) with ______ around the gut (smooth muscle and connective tissue)
Lateral plate mesoderm folds ventrally and joins at midline
Endoderm enveloped inside (forms gut) with splanchnic mesoderm around the gut (smooth muscle and connective tissue)
All cavities form from the _________
Intraembryonic Coelom
What is the cardiac crescent?
Cardiac crescent/cardiogenic mesoderm
- A crescent of splanchnic mesoderm around the cranial end of the embryo is specified to become heart tissue
How is the primitive heart tube formed?
(1)
- Differentiation within splanchnic mesoderm at cardiac crescent: some of the sp. meso undergoes MET → differentiates as endocardium and assembles into endocardial tubes; rest becomes myocardium
- Creates bulge off gut tube → endocardial tubes on each side fuse → Primitive heart tube \ dorsal aortae also fuse to form a single descending aorta
MET = mesenchymal to epithelial transition
How is primitive heart tube formed (2) - following MET in splanchnic mesoderm:
- Differentiation within splanchnic mesoderm at cardiac crescent: some of the sp. meso undergoes MET → differentiates as endocardium and assembles into endocardial tubes; rest becomes myocardium
- Creates bulge off gut tube → endocardial tubes on each side fuse → Primitive heart tube \ dorsal aortae also fuse to form a single descending aorta
What are the three layers of the primitive heart tube?
- Endocardium - from MET of splanchnic mesoderm
- Cardiac Jelly (extracellular matrix secreted by cardiomyocytes)
- Myocardium (differentiating cardiomyocytes/sp meso)
After folding, there is a flap of splanchnic mesoderm (_________) anchoring the heart to the foregut
After folding, there is a flap of splanchnic mesoderm (Dorsal Mesocardium) anchoring the heart to the foregut
What happens to the dorsal mesocardium?
Dorsal Mesocardium = flap anchoring heart forming connection to gut
- Eventually disintegrates so heart will be anchored ONLY by incoming and outgoing vessels
- Loses connection between heart and gut
- Allows heart activity
Fusing of the endocardial tubes could be described as ________
Fusing of the endocardial tubes could be described as two tubes joining in the middle with openings at the top and bottom for bloodflow
How does the heart reposition with body folding?
Heart is moved from cranial disc inferiorly into the thorax because brain overgrows everything
The first aortic arch connects to the _______
dorsal aortae
What is the process that changes the endocardial tube?
Looping process changes tube
Label the diagram
First aortic arches - connect to dorsal aortae
Aortic Sac - expanded base leading into arteries
Left horn of sinus venosus - receives venous input
Label the diagram
Outflow Tract
Primitive Ventricle
Primitive atrium
What is the first step to making a mature heart from the primitive heart tube?
Cardiac looping
Formation of the cardiac loop:
Primitive heart tube folds and loops to bring ___________
At the same time, a series of _____ and _____ divide primary heart tube
Heart tube forms on day ____ and starts to beat on day ____ blood circulation begins by day _____
Formation of the cardiac loop:
Primitive heart tube folds and loops to bring the four presumptive chambers of the heart into correct spatial relation to each other
At the same time, a series of constrictions and expansions divide primary heart tube = give dif parts their own identities
Heart tube forms on day 21 and starts to beat on day 22 blood circulation begins by day 24 (wall of yolk sac gives early blood)
As a result of cardiac looping, the ventral midline shifts_______
As a result of cardiac looping, the ventral midline shifts -bends and twists to the right
What is the 1st morphological L-R patterning of the heart?
The tube bending and twisting to the right - primitive ventricle bulging to the right
Growth of primitive heart tube:
Heart tube grows through ______, but also by ________ from ______
Growth of primitive heart tube:
Heart tube grows through proliferation, but also by addition of cells from migrating into the tube at the arterial and venous poles
With heart looping, the heart tube bends into a ____ shape
Primitive atrium moves _____ and _____ (behind/posterior to _______)
Right ventricle comes from ________
With heart looping, the heart tube bends into a U shape
Primitive atrium moves superiorly and posteriorly (behind/posterior to outflow tract)
Right ventricle comes from migrating cells
When cardiac looping is complete the outflow tract is between the ______ with the _______ partly surrounding the outflow tract
When cardiac looping is complete the outflow tract is between the atria with the atrial appendages (auricles) partly surrounding the outflow tract
Label the heart tube in its C-shape bend:
As the atria moves superiorly, what happens to the sinus venosus (connected to the atria)
When atria move superiorly, so does the sinus venosus
- Sinus venosus leads into atria → pulled up and posterior
How do we get from atria posterior to OT to atria hugging OT?
Atrial appendages grow out and “hug” outflow tract
Lumen remodels and connection changes
SEPTATION OF HEART TUBE
_________ grow outward from walls of heart tube and constrict lumen of the ________
SEPTATION OF HEART TUBE
Endocardial cushions grow outward from walls of heart tube and constrict lumen of the atrioventricular canal
What are the endocardial cushions?
Cardiac jelly extracellular matrix (ECM) secreted by myocardium + cells derived from endocardium
- Secondary step: some endocardial cells undergo EMT to populate cushions (cells and ECM)
How does division of atrioventricular canal occur?
- Four tissue cushions grow in endocardium around atrioventricular canal
- Dorsal and ventral cushions fuse to form septum intermedium
- All four cushions will contribute to AV valves (tricuspid (Rt) and bicuspid (Lft))
Initially, the AV canals connects the right and left atria with only the _______
The AV valves are made by ___________
Initially, the AV canals connects the right and left atria with only the Left ventricle (Primitive atrium with septum forming = 2 atria both connected to LV)
The AV valves are made by remodeling of endocardial cushions (Dorsal endocardial cushion in image sculpted into valves)
What ventricular remodeling is required?
We have rv and lv stacked. Need to be flipped so they’re side by side = two circulations
- Align everything properly to allow two separate circuits of blood
Remodeling of ventricles:
- At the end of cardiac loop formation:
- _______ connect both atria to left ventricle
- Only ________ connects to outflow tract
- After remodeling:
- Right ventricle connects to _______ and _______
- Left ventricle connects to _____ and ______
Remodeling of ventricles:
- At the end of cardiac loop formation:
- AV canals connect both atria to left ventricle
- Only Right ventricle connects to outflow tract
- After remodeling:
- Right ventricle connects to right atrium and pulmonary trunk (pulmonary circulation)
- Left ventricle connects to left atrium and aorta (Systemic circulation)
Septation of atria:
- Adult interatrial septum formed by ________
Septation of atria:
- Adult interatrial septum formed by fusion of two embryonic partial septa
- Septum primum - thin and delicate (flap)
- Septum secundum - thick and muscular (wall)
- Together form a one way flap valve
- Both have large openings that allow blood to shunt from right to left atria
Why must fetal blood be shunted from right atrium to left atrium?
- Lungs are inactive during fetal development
- Oxygenated blood supplied by umbilical vein
- Little blood can flow through collapsed lungs → blood shunted away from lungs
- Pulmonary and systemic circulations do not become truly separate until birth
How does the atrial septum form?
First the thin, flexible septum primum grows down from posterior wall of primitive atria down towards septum intermedium - leaves a gap called the ostium primum
Second the thick, muscular septum secundum grows (again from posterior wall of primitive atria down towards septum intermedium)
When septum primum grows, at first it doesnt fully extend to the septum intermedium, leaving a (temporary) gap called the _______
Subsequently, cells in the superior portion of the septum primum will undergo apoptosis and create a new hole, the ________.
When septum primum grows, at first it doesnt fully extend to the septum intermedium, leaving a (temporary) gap called the Ostium primum
Subsequently, cells in the superior portion of the septum primum will undergo apoptosis and create a new hole, the Ostium Secundum - ostium primum will then close.
The septum secundum maintains an inferior hole, the _______
The septum secundum maintains an inferior hole, the foramen ovale
These holes SHOULD NOT overlap
The Atrial septum is made of ______ septa, each with a _______: _______ (top) and ______(bottom) = holes do not overlap (important for closing this shunt after birth)
The Atrial septum is made of 2 septa (Septum primum and septum secundum), each with a hole: Osteum secundum (top - on septum primum) and formamen ovale (bottom (Septum secundum)) = holes do not overlap (important for closing this shunt after birth)
What keeps the atrial septum open to allow blood to shunt from right atrium to left atrium?
- Higher pressure on right side of heart → septum primum can be pushed enough to let blood flow through the foramen
- Because the holes don’t overlap, when they are pushed together → forms complete wall → fuses overtime to form interatrial septum
Label the image
blue is aortic sac
How does the the atrial septum change after birth?
- Lungs inflate and blood flow from placenta is lost
- pressure changes (PR < PL)
- Septum primum will be pushed against the septum secundum → closing the interatrial wall
- Two will fuse to form the atrial septum (foramen ovale becomes fossa ovalis)
What are the two portions of the interventricular septum?
- Myocardium grows upward to form a partial separation
- Superior Membranous portion → endocardial cushions contribute to this portion
- Inferior Muscular portion → myocardium contributes to this portion
What separates the outflow tract into two?
Endocardial cushions → separate outflow tract into two and contribute to membranous portion of interventricular septum
What are the most common type of CHD (coronary heart disease)?
Ventricular septal defects (VSDs) - usually involve the membranous IV septum
How does the outflow tract change with fetal heart development?
- Outflow is initially through a common channel
- Outflow becomes divided into two by a septum to form aorta and pulmonary trunk
What type(s) of cells populate the Endocardial cushion ECM?
Endocardial cells and neural crest cells
How does septation of the outflow tract occur?
- Fusion of the septum begins in the middle and proceeds superiorly and inferiorly
- As the outflow tract is being divided it is also twisting
Label the image of the outflow tract
A. Trunococonal septae
B. Right auricle
C. Right ventricle
D. Superior endocardial cushion
E. Muscular ventricular septum
F. Left Ventricle
G. Right atrioventricular canal
H. Left atrioventricular canal
The inferior edge of the outflow tract fuses with the _______, contributing to ______
The inferior edge of the outflow tract fuses with the muscular ventricular septum, contributing to the membranous portion of the ventricular septum
The image shows:
- outflow tract stage?
- Ventricular stage?
- Connections?
- At this stage the outflow tract is divided and the ventricles are remodelled
- Right ventricle connects to pulmonary trunk
- Left ventricle to ascending aorta
The cardiac neural crest arises from _______
The cardiac neural crest arises from beside the hindbrain
Label the image
How do the semilunar valves form?
two additional endocardial cushions form on opposite walls of the outflow tract (these are the intercalated cushions)
Excavation of outflow tract cushions + intercalated cushions gives rise to semilunar valve leaflets
Label the image
Image shows semilunar valves after formation - formed by outflow tract cushions and intercalated cushions being excavated
Label the development of cardiac valves
The outer layer of the heart is an epithelium called the ________ (aka the ________)
The outer layer of the heart is an epithelium called the epicardium (aka the visceral pericardium)
The epicardium is derived from:
Epicardium is derived from cells that originate in proepicardial organ and migrate over the surface of the heart
Epicardial cells migrate over the heart as an _______
Some ______ and invade the _____ to contribute to various structures
Epicardial cells migrate over the heart as an epithelial sheet
Some delaminate and invade the heart to contribute to various structures
