Cardiovascular: Blood Pressure L8 Flashcards
Define Cardiac Output.
The amount of blood the heart pumps per minute. It can be substituted for flow (Q), because the amount of blood that the heart pumps out is equal to the amount of blood that flows in the arteries.
Define Mean Arterial Blood Pressure (MABP). How does the change in BP occur in the arteries?
The average of the pressure in the arteries during a cardiac cycle. Pressure increases when the left ventricle contracts (Systole). As the blood flows back into the right atrium, pressure in arteries decrease.
Give five equations that relate to Mean arterial blood pressure.
MABP = CO x TPR CO = SV x HR SV = EDV - ESV MABP= DP + 1/3 PP PP = SP - DP
How does exercise affect cardiac output? What factors of cardiac output does it affect?
Both stroke volume and heart rate increase with exercise, therefore cardiac output increases from it’s resting 5L/min.
What is EDV, ESV and Stroke volume?
EDV (End-diastolic volume) = max blood in ventricles at end of ventricular diastole after filling complete.
ESV (End-systolic volume)= min blood in ventricles at end of ventricular systole after contraction complete.
SV = The difference between EDV and ESV because that is the amount of blood that got ejected in one heart beat.
At a biological level, how does stroke volume increase?
As contractility of heart increases (stronger beats), the amount of blood left in the ventricles after systole (ESV) will decrease, and SV will increase.
SV also increases from amount of blood in ventricles after diastole (EDV) increases (i.e when more blood returned to heart). when this happens, the cardiac muscle fibres in the ventricles stretch and become ‘prime for contraction’.
How is heart rate determined sympathetically and parasympathetically?
Determined by a combination of the pacemaker activity of the SAN, but also the parasympathetic and sympathetic nerve inputs.
Discuss the rapid negative feedback pathway for a decrease in mean arterial blood pressure. Include what the variable is, the sensor, the integration centre and effectors involved. How does this feedback maintain MABP?
An example of a situation where there is a sudden change in MABP is in posture, from lying down to standing up.
Controlled Variable - Gravity (Pools venous blood in legs), decreasing MABP.
Sensor - Baroreceptors, found in the carotid sinuses and aortic arch, have sensitive nerve endings that detect stretch in the arteries, meaning a change in blood pressure.
Integration centre - Information is sent to the Cardiovascular control centre in the medulla oblongata in the brainstem, will send efferent signals to heart and vessels to increase MABP back to set point.
Effectors - Increase heart rate.
Note: Venous pooling legs causes a decrease in ventricular filling, thus a decrease in stroke volume.
Maintenance - CO=SV x HR, because SV decreased from change in posture, heart rate increases to compensate, so there is little change in CO.
MABP = CO x TPR, little change in CO means little change in MABP.
Explain the role of the vagus nerve.
Parasympathetic, acts as a brake to slow down heart rate in rest and digest. Innervates sinoatrial node and the atrioventricular node, and stimulating them to spontaneously discharge at a slower rate.
Explain the role of the cardiac sympathetic nerves.
Sympathetic, accelerator of heart rate in fight or flight response, more innervation required. Nerves run down the thoracic spinal cord until they reach the level of the heart. They can then synapse in the sympathetic chain ganglia and run out to the sinoatrial node and the atrioventricular node. The cardiac sympathetic nerves stimulate them to discharge at a faster rate.
They also innervate the atria and ventricles.
How can heart rate in terms of nerves increase other than the cardiac sympathetic nerves?
By inhibition of the ‘brake’ vagus nerve activity on heart beat.
Do both vagus and cardiac sympathetic nerves normally work at same time in balance?
Yes.
How is stroke volume controlled? Sympathetic or Parasympathetic
Sympathetic. Sympathetic fibres densely innervate the contractile cells of the heart muscle. An increase in sympathetic activity will increase the force of contraction of these cells, increasing stroke volume.
