CVS S2 - The Heart as a Pump + Embryology S1 Flashcards
Where does each side of the heart pump blood to?
Left: systemic circulation
Right: pulmonary circulation
Name the compartments of the heart
Right atrium, left atrium, right ventricle, left ventricle
How long is the cardiac action potential?
~200-300ms
What controls contraction of the heart?
Pacemaker cells - normally the SAN (sino-atrial node) but if this isn’t working then the AVN (atrio-ventricular node) can perform the same function
What is systole?
When the ventricles of the heart are contracting
What is diastole?
When the ventricles are not contracting
Describe atrial contraction
Not very forceful
Small volume of blood moved
Occurs just before ventricular systole
Describe the first heart sound
Caused by the closure of the A-V valves
“Lub” sound
Occurs in ventricular systole
Describe the second heart sound
Caused by the closure of the semi lunar valves
“Dub” sound
Occurs in ventricular diastole
What do murmurs sound like and what causes them?
A “whooshing” noise
Caused by turbulent or disturbed flow eg through a narrowed valve
What is cardiac output?
Cardiac output = stroke volume x heart rate
This is the volume of blood pumped by the left ventricle per minute
When is the cardiogenic field formed?
Gastrulation
Where is the cardiogenic field just after formation and where and how does it move?
The cardiogenic field is initially at the cranial end of the embryo
Embryonic folding causes the field to move into the chest area
What is the cardiogenic field?
Embryonic tissue from which the heart, blood vessels and blood develop
When do the endocardial tubes form?
In the third week of development
What happens after the formation of the endocardial tubes?
The endocardial tubes are brought together in embryonic folding and fuse at the mid line to create the primitive heart tube
Describe the primitive heart tube
-Highly symmetrical
-Has four sections:
>Bulbus cordis
>Truncus arteriosus
>Primitive atrium
>Primitive ventricle
How does the primitive heart tube sit in the pericardial cavity?
Suspended by a membrane which subsequently degenerates
What does looping achieve?
Places both the inflow and outflow cranially with the inflow dorsal (behind/posterior) to the outflow
Places primordium of right ventricle nearest to outflow tract
Places primordium of left ventricle nearest to inflow tract
Formation of the transverse pericardial sinus
What will the primitive atrium become?
Contributes a SMALL component to the future atria
What will the bulbis cordis become?
It will go on to form part of the right ventricle
What will the primitive ventricle become?
The left ventricle
What will the truncus arteriosus become?
It will give rise to the roots and proximal portions of the aorta and pulmonary trunk
What does lateral/cephalocaudal folding achieve with respect to cardiac development?
Lateral folding causes formation of the primordial heart tube
Cephalocaudal folding brings the tube into the thoracic region
Describe blood flow in the primitive heart tube
Linear at first
Caudal-end inflow from sinus venosus
Cranial-end outflow through aortic roots
When does looping occur?
Between days ~23-28
How does looping of the primitive heart tube proceed?
Continued elongation of the tube results in bending
The cephalic, cranial end bends ventrally, caudally and to the right
The caudal portion bends dorsally, cranially and to the left
Describe communication between the atrium and ventricle after looping and what is the significance?
The communicate via the atrioventricular canal
This is the first division between the atrium and ventricle
What is the transverse pericardial sinus?
The space behind the cardiac outflow and in front of the inflow where a finger can be inserted
Describe the the sinus venosus and it’s development
All embryonic blood collects here Right and left horns are initially equal Venous return shifts to right hand side Left horn recedes Enlarging right atrium absorbs right sinus horn
Describe development of the right atrium
Develops mostly from the primitive atrium
Absorbs the right horn of the sinus venosus
Receives drainage from the body (venae cava) and heart (coronary sinus) after birth
Describe development of the left atrium
Develops from a small portion of the primitive atrium
Absorbs proximal parts of pulmonary veins
Receives oxygenated blood from the lungs after birth
Describe the oblique pericardial sinus and it’s development
A “cul-de-sac” or recess
Formed as left atrium expands by absorbing the pulmonary veins
Describe the general development of the aortic arches
Begins as bilaterally symmetrical system of arched vessels (1, 2, 3, 4, 6)
Undergo extensive remodelling
Most important arches are 4 and 6
Describe the development of the 4th arch of the aorta
The right arch forms the proximal part of the right subclavian artery
The left arch forms the arch of the aorta
Describe the development of the 6th arch of the aorta
Also known as the pulmonary arch
Right side forms right pulmonary artery
Left side forms left pulmonary artery and ductus arteriosus
Describe the path of the right and left recurrent laryngeal nerves compared to one another
The left laryngeal nerve is pulled down lower than the right by the ductus arteriosus and the the descent of the heart
