Pump function and cardiac cycle Flashcards
What do neural controls of the peripheral system do?
Alter blood distribution to meet specific tissue demands and maintain adequate MAP by altering blood vessel diameter.
How do hormones affect blood pressure?
Chemicals, both endocrine and paracrine, influence blood pressure by acting on vascular smooth muscle or the vasomotor center.
Describe the cardiac cycle
right side
Vena cava-> right atrium-> tricuspid valve-> Right ventricle
Describe the cardiac cycle (left side)
Pulmonary vein-> Left atrium -> mitral valve-> left ventricle
Which side of the heart pumps blood at a higher pressure?
The left ventricle operates at 5x higher pressure than the right ventricle
What is the dicrotic notch?
When blood is forced into the major arteries, the walls are stretched
Where does most of the filling of the ventricle occur?
In the first third of the diastole which gives scope for increases in heart rate
What are the requirements of electrical conduction on the cardiac cycle?
Left and right atria must contract synchronously
Left and right ventricles must contract synchronously
Ventricles must contract atria
What is the origin of the heart beat?
Myogenic origin in the pacemaker cells of the sinuatrial node (SA) in the right atrium
What causes conduction of the heart?
Rudimentary conducting bundles project through the two atria to ensure rapid conduction of excitation and synchronous contraction
Why can the excitation not pass to the ventricles?
Due to insulating connective tissue except at the atrioventricular node (AV) node
Why is there a conduction delay at the AV node?
Due to the small diameter of the conducting cells, a conduction delay of 0.12 sec occurs
What happens once the excitation passes through the AV node?
It propagates very rapidly through the ventricles due to a conducting system made of large diameter conducting cells called Purkinje cells
Where are the Purkinje cells?
They are arranged in the septum into the bundle of His which then divides into right and left bundle branches
Where does the excitation spread from the conducting bundles?
Into the cardiac muscle cells (myoscytes), the membranes of which contain protein channels allowing communication between adjacent cells.
Where does contraction start?
At the septum and papillary muscles, then the apex and then moves towards the base
Where does relaxation occur?
At the septum and papillary muscles, then the apex and then moves towards the base
What are the effects of the autonomic nervous system on the heart rate?
Vagus nerves
Cardiac sympathetics and adrenaline
How can vagus nerves effect the heart rate?
Slow heart rate (bradycardia or negative chronotropic action) by action on SA node and slow conduction throught the AV nodes (negative dromotropic action) with minimal action on the ventricles
How can the cardiac sympathetics and adrenaline effect the heart rate?
Increase heart rate (tachycardia or positive chronotropic action) by action on SA node and increase conduction speed through the AV nodes (positive dromotropic action). Increased contractility of the ventricles (positiive inotropic action) with increased rate of relaxation (positive lusitropic action)
What does having a large mass of heart with numerous cardiac cells lying parallel mean?
That during excitation, a sizeable electrical field is generated
How can heart rate be measured
By electrocardiogram
How is electrocardiogram recorded?
By attaching recording leads to the left and right wrists and left ankle
What is the order of the cycle in an electrocardiogram?
P, QRS, T
