Development of Heart Flashcards
First developmental system and organ
- First working unit in the developing embryo was circulatory system
- First functional organ was the heart
Why is the cardiovascular system the first to develop?
Embryo is growing and this process needs nutrients, oxygen, and removal or CO2 and metabolites
Circulatory system components
- Heart
- Arteries
- Veins
- Blood
Initial steps of cardiogenic field development
- Vertebrate heart arises from two areas of splanchnic or visceral mesoderm
- The progenitor cells in two small patches on either side of the epiblast enter the primitive streak
- Cells migrate in and then towards outer edge forming part of the new lateral plate mesoderm and therefore the heart field
**Migration results in the start of the specification of the heart field - The cells in the field are multipotent cardiac progenitor cells which separate into two regions on each side of the field
Region 1: will become the scaffold of heart tube and eventually the left ventricle of adult
Region 2: will add to both ends of heart tube and become right ventricle and inflow region of pulmonary vein and vena cava
Where do heart cell types come from?
All cell types of heart form from the two regions of the cardiogenic fields
What contributes to the septa that separates the aorta from the pulmonary tract?
The neural crest
Formation of the pericardial cavity
- Cardiogenic field is bent with embryonic folding. At the same time there is cell differentiation occurring independently on both the right and left sides of the embryo forming a horse-shoe shaped cardiac tube
- Folding results in in heart within pericardial cavity ventral to embryonic disc
What does the Horse-shoe shaped cardiac tube become?
Anterior extensions of horseshoe become 2 ventral aortae
- Posterior parts of the extension join with developing venous system
Dorsal parts of horseshoe become dorsal aortae
Lateral body folding then starts to bring the two developing tubes together in the midline of the embryo to eventually form primitive heart
Components formed by Differentiation of segmented tube
- Sinus venosus- all veins meet here
- Atrium
- Ventricle
- Bulbis cordis
- Truncus arteriosus- all arteries meet here
Outgrowing the pericardial cavity
- Growth of these indentations and dilatations leads to the heart tube trying to outgrow the pericardial cavity
- The sinus venosus and atrium are first not enclosed by pericardial cavity but with growth and bending they become enveloped (within 23 days of gestation)
Beating of heart tube
Set by pacemakers in the sinus venosus (at this time in early development)
Development of four chambered heart
Partitions form in the primitive heart to convert the pulsating heart tube into a 4 chambered organ
Formation of atrio-ventricular canal
- Septum intermedium- formed by mesenchymal endocardial cushions between endocardium and myocardium that move towards each other and fuse
- Creates left and right atrio-ventricular openings
Formation of left and right atrium
- Septum primum will arise from the dorsal wall of the common foetal atrium and move towards the endocardial cushions. A transitory foramen primum (present for access until foramen secundum is complete) is created and through apoptosis, a foramen secundum is created.
- A second membrane, the septum secundum develops from dorsal wall of right atrium
- There is an opening that remains between the free edge of the septum secundum and foramen secundum known as foramen ovale - Upper part of septum primum fuses with septum secundum while the rest becomes valve-like for foramen ovale. The bottom of the septum secundum fuses with septum intermedium.
Purpose of fusion of septum secundum and septum intermedium
Divides the blood flow returning to the heart from caudal vena cava into two streams
Foramen ovale
Allows for continuous flow and the potential to skip the right ventricle
Formation of left and right ventricles
Formed from Bulbus cordis
- Dilated part next to ventricle. Separated by interventricular septum
- Non-dilated part called Conus cordis continuous with truncus arteriosus. Separated by aorticopulmonary septum (formed from bulbar ridges in both regions fusing together)
Blood now flows into 2 separate channels resulting in separate outlets from right and left ventricles
Interventricular septum
Separation between dilated bulbus cordis and ventricle
Incorporation of the sinus venosus into right atrium
**Sinus venosus- all the veins come together
- Veins open into sinus venosis in order:
1. Vitelline veins
2. Umbilical veins
3. Cardinal veins - 3 pairs of veins in the sinus, forms left and right sinus horns
o Right merges with atrium. Where anterior part becomes cranial vena cava and posterior part becomes caudal vena cave
o Left becomes coronary sinus
Pulmonary veins
- Begin to open on left atrium
- First there is a single opening that drains 4 pulmonary veins
- Next, 4 separate openings for the pulmonary veins
Left auricle
The remains of the original left atrium
Smooth walled part of left atrium
Occurs from incorporated pulmonary veins
Atrioventricular valve development
- Edges of the right and left atrioventricular openings grow out and thicken and restructuring of ventricular walls (cavitation) also occurs
- Left side valves: bicuspid or mitral valve
- Right side: tricuspid
- Muscular cords attaching valves are replaced by connective tissue called chordae tendinae
- Rest of muscle becomes papillary muscles
Semilunar valve development
- Develop as swellings of sub-endothelial mesenchymal tissue of neural crest origin and become hollowed out into 3 valves in each of the aortic and pulmonary outlets
- Final formation will prevent backflow of blood into the left and right ventricles
Paired Vitelline veins and hepatic development
- Bring blood to the heart.
- Pass through umbilicus, run cranially on either side of the gut through the septum transversum and then enter the sinus venosus
- At the same time, the developing liver cords extend into the septum transversum
- The combination of the two forms a venous plexus and the vitelline vessels will become incorporated within the developing liver to form hepatic sinusoids
Left vitelline veins
- Atrophies
- Caudal part contributes to the formation of the portal vein in combination with rotation of stomach
Right vitelline veins
- Right cranial part will become part of caudal vena cava
- Also caudal part contributes to the formation of the portal vein in combination with rotation of stomach
Umbilical veins
- Bring blood from allantois and pass through umbilical cord, septum transversum and enter the sinus venosus
- As liver grows, middle part of umbilical veins are incorporated into the tissue and help form the sinusoids. Cranial portions atrophy. Caudal portions of right umbilical vein atrophy.
- Left umbilical vein enlarges to move oxygenated blood from placenta to embryonic liver
Ductus venosus
- A venous shunt that develops between left umbilical vein and cranial part of right vitelline vein which allows for blood movement through the liver and into the heart. Avoids getting caught up in sinusoids
- Persists up to birth in carnivores and ruminants
- Atrophies during gestation in horses and pigs
Paired cranial cardinal veins
Drain blood from head and neck
Paired caudal cardinal veins
Drain the body wall
Cardinal veins
The cranial and caudal veins on left and right side fuse to form the common cardinal veins that open into the sinus venosus
What forms the caudal vena cava?
- Parts of right vitelline vein
- Caudal cardinal veins
- Supracardinal veins
What does cranial cardinal veins become?
- Internal and external jugular veins
- Brachiocephalic veins
- Cranial vena cava
What does the caudal cardinal veins become?
- Paired supracardinal veins drain dorsal region of body walls
- Paired subcardinal veins drain the developing mesonephrons
Ectopia cordis
- Occurs in thoracic region when opposing sides of the ventral body wall fail to fuse together
- When severe, heart can be present outside the thoracic cavity
- Most common in cattle and heat can even be found in neck region under the skin
