Cardiac Physiology Flashcards
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Explain how the heart stimulates a heart beat, and the path taken by current.
The heart generates its own intrinsic electrical activity
The AP originates in the SA node
It is conducted through the atrio-ventricular node, after a delay
It is then carried down into the ventricles by the bundles of His.
Heart muscle is a syncytium.
How do the sympathetic and parasympathetic systems regulate the heart?
Parasympathetic innervated by the vagus nerve.
PS releases ACh which acts via muscarinic receptors to slow heart rate (negative chronotropism)
Sympathetic releases NA which acts via Beta receptors to increase heart rate (positive chronotropism)
Discuss the Contraction of the heart muscle, which comparison to skeletal muscle.
Same molecular mechanism as skeletal muscle (sliding filament)
Is triggered by a rise in intracellular calcium, same as skeletal muscle
The calcium comes largely from internal stores
The calcium release from the stores is caused by calcium influx into the cell (unlike skeletal)
How does the body control ventricle stroke volume (1)
Sympathetic stimulation = NA/ A acts at beta-receptors
Beta-receptors increase cAMP
cAMP stimulates a kinase
The kinase phosphorylates calcium channels
Calcium influx increases, so contraction force increases
How does the body control ventricle stroke volume (2)
Frank - Starling law
The output of the heart has to match the “input” and the two sides have to match each other.
The frank-starling law states that the force of contraction of the heart (blood pumped out) increases when the end-diastolic pressure and volume is increase (ie. muscle is stretched)
Graph for Frank - Starling Model and Heart Failure
Overview of Cardiac Output
What are the Atrioventricular valves
Right and Left AV valves are positioned between atrium and ventricles on right and left sides
Prevent backflow of blood from ventricles into atria during ventricular emptying
Right AV valve: also called tricuspid valve
Left AV valve: also called biscuspid valve or mitral valve
What are Chordae Tendinae
Fibrous cords which prevent valves from being everted
Papillary muscles
What are the semilunar valves?
Aortic and pulmonary valves
Lie at juncture where major arteries leave ventricles
Prevented from everting by anatomic structure and positioning of cusps
Why are there no valves between atria and veins?
Atrial pressures usually are not much higher than venous pressures
Sites where venae cavae enter atria are partially compressed during atrial contraction
What are the pressures for both ventricles?
Left ventricle (120/ 80 mmHg)
Right ventricle (40/10 mmHg)
What can go wrong in the coronary arteries?
Partial blockage (left): leads to ischaemia (produces angina)
Total blockage (right): leads to infarction (cell death) - MI
