Flashcards in Lecture 9 Deck (43)
What are heart valves for?
-to ensure unidirectional flow of blood, open and close passively because of pressure differences
What are the three layers in the heart?
-myocardium (mainly that= muscle)
-endocardium(middle layer of cardiac muscle between an endothelial layer and the-
-epicardium (thin outer sheath)
What does the myocardium consist of?
-interlacing bundles of cardiac muscle fibres arranged spirally around the heart circumference
-when ventricular muscle contracts= chamber reduces in size
What's an intercalated disk?
-specialised cells joining adjacent muscle cells end to end
What are the two types of membrane junctions within an intercalated disk?
-desmosomes=type of adhering junction that mechanically holds cells together under high mechanical stress
-gap junctions=channels allowing AP to spread from one cardiac cell to the next
What initiates heart contraction?
-group of cells that can self excite
-myogenic= self excitable
Do pacemaker cells have a constant resting potential?
-the membrane potential slowly depolarises or drifts between APs until threshold is reached= AP
What are the three important changes in ion movement in terms of pacemaker potential?
1. an increased inwards Na+ leakage
2. decreased outwards K+ leakage
3. an increased inwards Ca2+ leakage
What is the pacemaker? Where is it?
sinoatrial node (SA) -the normal
atriventricular node (AV) - base of the right atrium just above the junction of the atria and ventricles
How is AP generated in the heart?
-close Na+/open Ca2+
-close Ca2+/open K+
Ca2+ from ECF and ICF
How does AP spread in the heart?
SAN- atria- AV=stops it for 0.1s to allow for the atria to be depolarised-ventricles (travels theer along Purkinje fibres)
Describe the action potential of cardiac muscle cells?
-close Na+/open Ca2+
-close Ca2+/open K+
-Ca2+ from ECF and INF
What is EEG?
-electrical currents generated by the cardiac muscle spread into surrounding tissue where it can be detected
-it therefore records only a portion of the electrical activity, just what gets to skin
What does the P wave represent?
What does the QRS complex represent?
What does the T wave represent?
What is the PR segment?
AV node delay
Why is there no wave for the SA node firing?
-not strong enough
Why is there no noticable wave for the atrial repolarisation?
-occurs simultaneously with the ventricular depolarisation and is masked by the QRS complex
Why is the P wave smaller than the QRS complex?
-because the atria have much smaller muscle mass than the ventricles and thus generate less electrical activity
What is systole?
AV valve closed- contraction of atria and ventricles-pulmonary and aortic valves open
What is diastole?
pulmonary aortic valve closed-ventricular filling
How to calculate stroke volume?
end diastolic volume - end systolic volume
What are the two heart sounds?
What happens in early ventricular diastole?
-atrium also in diastole
-the resting stage
-the atrial pressure is higher than ventricular (as there is inflow of blood to the atrium) so the AV valve is open and blood flows into the ventricle even before the atrial contraction
What happens in late ventricular diastole?
-the SA node reaches threshold and fires
-the depolarisation spreads through the atria (P wave) triggering atrial contraction
-contraction causes rise in atrial pressure
-blood coming into ventricle which also increases ventricular pressure
-atrial pressure still slightly higher so AV valve open during the contraction
What happens at the end of ventricular diastole?
-ends at the onset of ventricular contraction
-by this time, atrial contraction and ventricular filling are completed
-the volume of blood is known as = end diastolic volume
What happens during ventricular excitation and onset of ventricular systole?
-impulse passes through the AV node and Purkinje fibres to excite the ventricle (QRS complex)
-ventricular pressure increases shortly after QRS signaling the onset of ventricular systole
-as ventricular contraction begins= ventricular pressure exceeds the atrial and AV valve closes
What happens during isovolumetric ventricular contraction?
-volume in ventricle must increase till the before it can open the aortic valve so for a while the ventricle is a closed chamber with no blood entering and no blood leaving
-ventricular pressure increases
-volume remains constant
What happens during ventricular ejection?
-when ventricular pressure exceeds aortic pressure the aortic valve opens and ejection of blood begins
-aortic pressure rises as blood is forced into the aorta(faster than the blood draining into the smaller vessels at the end of it)
-ventricular volume decreases
ventricular systole is this and the isovolumetric ventriclar contraction
What happens at the end of ventricular systole?
-ventricle doesn't empty completely, about half of blood isn't pumped out till the next systole.
-stroke volume is what is pumped out of the ventricle
What happens at ventricular repolarisation and onset of ventricular diastole?
-T wave signifies ventricular repolarisation
-as the ventricle starts to relax the pressure falls below aortic pressure= aortic valve closes
-closure of the aortic valve causes dicrotic notch= disturbance on the aortic pressure curve
What happens during isovolumetric relaxation?
-when the aortic valve closes the AV valve is not open yet as ventricular pressure still exceeds atrial
-so all valves are closed for a brief period
-pressure falls and no blood flowing
WHat happens during ventricular filling?
-as ventricular pressure falls below atrial AV valve opens and ventricular filling occurs again
-ventricular diastole is this and the isovolumetric relaxation
-blood flowing from the pulmonary veins into the left atrium
-filling causes atrial pressure to go up and the AV valve opens and rapid filling of the ventricle
-when most blood delivered the pressure starts to fall
What is cardiac output?
the volume of blood per minute pumped by a heart to the body
=heart rate x stroke volume
How do large and small animals compare in heart beat and stroke volume?
-large animals have slower heartbeat and larger stroke volume
How does the parasympathetic system influence heart rate?
-slows it down, rest and digest= vagus nerve
-ACh makes it more permeable to K+ (more leaving) which hyperpolarises the SA node membrane= more difficult to achieve threshold
-ACh decreases excitability of the AV node, longer waiting there= longer AV delay
-reduced weakened atrial contractile strength, reduced Ca2+ leakage = the plateau phase is shortened= heart beat more leasurely
so heart rate is slower,longer time between atrial and ventricular contraction and atrial contraction is weaker
How does the sympathetic system influence heart rate?
-increases heart rate- cardiac output
-NE increases heart rate by increasing influx of Na+ and Ca2+
-higher Ca2+ permeability (in) =decreases the AV delay
-hypopolarised SA membrane so faster drift to threshold
-increases atrial and ventricular contractile strength
so:increase pumping by increasing heart rate , decrease in AV delay, increasing force of contraction
What are the extrinsic controls of the stroke volume?
-sympathetic nerves and andrenalin
-increase Ca2+ leakage
-decrease in end systolic volume
What are the intrinsic controls of the stroke volume?
-venous return= venous pressure x diastolic time
-increase in end diastolic volume
-optimal muscle fibre length
What does intrinsic control refer to?
heart's inherent ability to vary the stroke volume based on a direct correlation between end-diastolic volume and stroke volume
=more blood is returned to the heart, the more blood is pumped out
What influences the heart muscle fibre length?
-the degree of diastolic filling = more filling= more stretch= longer fibres