Session 2 Lectures Flashcards
What are capacitance vessels?
Vessels that enable the system to vary the amount of blood pumped around body
Too much blood - blood stored here
Not enough blood - obtain from here
What are resistance vessels?
Vessels that restrict blood flow to drive supply to areas of the body that most need it
At rest where does the majority of our blood supply?
GI tract
When exercising where does the majority of our blood supply?
Muscles
What is systole?
The contraction and ejection of blood from ventricles
What is diastole?
The relaxation and filling of ventricles
Name the veins, arteries and valves in the right side of the heart
Veins = superior and inferior vena cava Arteries = pulmonary trunk supplying left and right pulmonary arteries Valves = tricuspid valve and pulmonary valve
Name the veins, arteries
and valves of the left side of the heart
Veins = pulmonary veins Arteries = ascending aorta (enters the arch of aorta with the brachiocephalic trunk, the left common carotid artery and the left subclavian vein) Valves = mitral valve and aortic valve
What is the typical pressure (mmhg) on right side of heart?
25 systole / 4 diastole
What is the typical pressure (mmhg) on left side of heart?
120 systole / 10 diastole
What is the stroke volume?
Amount of blood pumped per heartbeat
What is approximate stroke volume?
70ml per heartbeat
Over 1 minute this is roughly 5L blood
How are cardiac myocytes connected?
Via gap junctions
How are mitral and tricuspid valves attached to papillary muscles?
Via chordae tendineae
What are pacemaker cells and where are they?
Specialised myocytes that can conduct an action potential
Located in sinoatrial node
Why is there a delay in action potential spread at atrioventricular node?
To allow time for atrium to stop contracting before ventricles do
Where does action potential travel to from the AV node?
Down the Bundle of His (left and right bundle branches) to Purkinje fibres
As heart rate increases what changes - systole or diastole?
Diastole time decreases
Systole always remains the same
How many stages to the cardiac cycle are there and what stage do we begin at?
7 stages
Start at atrial contraction
What is phase 1 of the cardiac cycle?
Describe what you may see on the graph at this stage
Atrial contraction (part of diastole) The A wave = atrial pressure rises Small increases in LV volume = blood is being topped up as over 80% full from ventricle filling The P wave = in ECG is onset of atrial depolarisation
What is the end diastolic volume?
The maximal volume of the ventricles
What is phase 2 of the cardiac cycle?
Describe what you may see on the graph at this stage
Isovolumetric contraction (part of systole) Mitral valve closes when LV pressure is greater than LA pressure C wave = in atrial pressure Isovolumetric = no change in ventricular volume as mitral valve closed QRS complex in ECG = onset of LV depolarisation S1 on phonocardiogram = closing of mitral valve
What is phase 3 of the cardiac cycle?
Describe what you may see on the graph at this stage
Rapid ejection (part of systole)
Aortic valve opens when LV pressure is greater than LA
X descent (after C wave) on atrial pressure = where pressure decreases as LA is pulled down during LV contraction
Decrease in LV volume as blood ejected
At phase 3 of the cardiac cycle what valves are open and closed?
Aortic and pulmonary valves open
Mitral and tricuspid valves closed
What valves are open and closed during phase 1 of cardiac cycle?
Mitral and tricuspid open
Aortic and pulmonary closed
What valves are open and closed during phase 2 of cardiac cycle?
All valves closed (isovolumetric = no change in volume)
What is phase 4 of the cardiac cycle?
Describe what you may see on the graph at this stage
Reduced ejection (part of systole) Decline in LV pressure as LV repolarises V Wave in atrial pressure = atrial pressure gradually rises from venous return T wave of ECG = LV repolarisation
What valves are open and closed during Phase 4?
Aortic and pulmonary open
Mitral and tricuspid closed
What is phase 5 of the cardiac cycle?
Describe what you may see on the graph at this stage
Isovolumetric relaxation (part of diastole)
When LV pressure falls below aortic pressure aortic valve closes
S2 on phonocardiogram (sound 2)
Diacrotic notch in aortic pressure = increase as valve closes
Ventricular volume same = all valves closed
LV pressure rapid decline
Which valves are open and closed during phase 5 of cardiac cycle?
All valves closed (isovolumetric)
How do you calculate stroke volume?
End diastolic volume - end systolic volume
What is phase 6 of the cardiac cycle?
Describe what you may see on the graph at this stage
Rapid filling (part of diastole)
Y descent on atrial pressure = fall of pressure as mitral valve opens
When LV pressure falls below LA pressure the mitral valve opens
Increase in LV volume
When can S3 sometimes be heard and what does this mean?
During stage 6 = rapid filling
Sometimes S3 is heard during ventricular filling
Can often be heard in children but not in adults. In adults = sign of pathology e.g. heart failure
What is phase 7 of the cardiac cycle?
Describe what you may see on the graph at this stage
Reduced filling (part of diastole) Left ventricular volume only slowly rising as ventricle reaches maximum volume (end diastolic volume)
What valves and open and closed during phase 6 of cardiac cycle?
Mitral and tricuspid = open
Aortic and pulmonary = closed
What valves are open and closed during phase 7 of cardiac cycle?
Mitral and tricuspid = open
Aortic and pulmonary = closed
What side to most valve failures occur on?
Left
What is valve stenosis?
Valve doesn’t open enough = obstruction to blood flow
What is valve regurgitation?
Valve doesn’t close all the way = back leakage of blood
Give 3 possible causes of aortic stenosis
- Senile calcification/fibrosis (due to old age)
- Congenital = bicuspid valve rather than tricuspid
- Rheumatic fever
What is damage to RBCs called and how might it occur?
Shear stress
From aortic valve stenosis
What can aortic stenosis lead to?
LV hypertrophy (increased pressure) Left sided heart failure - can lead to angina (not enough blood to heart)
Give 2 causes of aortic valve regurgitation
- Aortic root dilation (leaflets pulled apart)
2. Rheumatic fever (damages valve)
Give 3 possible causes of mitral valve regurgitation
- Damage to papillary muscle after heart attack
- Left sided heart failure can stretch valve
- Rheumatic fever
What can cause preload to be increased?
Mitral valve regurgitation = more blood enters ventricle in next cycle
What is the main cause of mitral valve stenosis?
Rheumatic fever
Describe some of the effects of mitral valve regurgitation
- pulmonary oedema
- pulmonary hypertension
(both can lead to RV hypertrophy) - stretching of cardiac myocytes in LA can cause atrial fibrillation and oesophagus compression
What is the afterload?
What pressure is it equivalent to?
The load the heart must eject blood against - roughly equivalent to aortic pressure
What is preload?
Amount the ventricles are stretched during diastole
What is total peripheral resistance?
Resistance to blood flow by all systemic vasculature
Majority occurs in arterioles
What vessels offer greatest resistance?
What happens to pressure on each side of resistance?
Arterioles offer greatest resistance - the pressure drops as it flows through a resistance
Constriction of arterioles increases resistance = pressure increases on arterial side and pressure decreases on venous and capillary side
What happens to pressure in arteries and veins when:
TPR decreases
cardiac output the same
Arteries = pressure decreases Veins = pressure increases
What happens to pressure in arteries and veins when:
TPR increases
cardiac output same
Arteries = pressure increases Veins = pressure decreases
What happens to pressure in arteries and veins when:
CO increases
TPR same
Arteries = pressure increases Veins = pressure decreases
What happens to pressure in arteries and veins when:
CO decreases
TPR stays same
Arteries = pressure decreases Veins = pressure increases
If the tissues need more blood what happens to arterioles and capillary sphincters?
They dilate and TPR falls
This would result in artery pressure dropping - in order to prevent that the heart pumps more to balance the pressure
How do you calculate cardiac output?
Stoke volume x Heart rate
How do you calculate stroke volume?
End diastolic volume - end systolic volume
The ventricles fill during diastole until the pressure is equal to…?
the venous pressure
What happens to end diastolic volume when the pressure in the veins increase?
When the venous pressure increases the heart fills more during diastole so EDV increases
What is the frank starling law of the heart?
The more the heart fills (muscles are stretched) the harder it contracts
What is the normal left ventricle end diastolic pressure?
8 mm/hg
What is normal stroke volume?
Approx 70ml
What is contractility?
Force of contraction for a given fibre length
What extrinsic factors can increases contractility?
Sympathetic stimulation and circulating adrenaline
What happens to the left ventricular end diastolic volume when you increase and decrease contractility?
Increase contractility = increased stroke volume and decreased LVEDP
Decreased contractility = decreased stroke volume and increased LVEDP
What is the aortic impedance?
Pressure in the aorta
What happens to the TPR when metabolism increases?
How does this affect cardiac output?
When metabolism increases the TPR decreases to allow more blood to be supplied
When TPR decreases arterial pressure decreases and venous pressure increases
The heart reacts by pumping more = increases cardiac output so that the arterial pressure rises
