Physiology Lab 3 - ANS

Question 1

What does SVR stand for, and what does SNS activation do to it?

Answer 1

Systemic vascular resistance. SVR is greatly increased by SNS stimulation, as a result of general vasoconstriction

Question 2

If stroke volume increases, will pulse pressure increase?

Answer 2

Yes, and vice versa

Question 3

Describe the changes in cardiac output (co) with SNS stimulation

Answer 3

CO will increase up to a point, but will then decrease as the time for ventricular filling reduces as heart rate continues to increase

Question 4

What are the main effects of PNS stimulation of the heart?

Answer 4

Suppression of heart rate, and therefore lowered cardiac output. PNS stim also reduces both diastolic and systolic blood pressure, also reducing pulse pressure.
Systemic vascular resistance (SVR) remains the same, because both cardiac output and blood pressure decrease

Question 5

What is the main determinant of stroke volume?

Answer 5

Mainly by how much time is available for the left ventricle to fill - so heart rate

Question 6

What are the main determinants of cardiac output?

Answer 6

Stroke volume, and heart rate

Question 7

What are the main determinants of arterial blood pressure?

Answer 7

Greater blood volume, so cardiac output, and vasocontraction (SNS stim)

Question 8

What are the autonomic responses to haemorrhage?

Answer 8

• Haemorrhage decreases blood volume, and therefore blood pressure. Baroreceptors detect this, and cause an increase in overall SNS: this increases heart rate, cardiac contractility and vasoconstriction, and so increases SVR.
• Cardiac output stays the same (ish), and diastolic blood pressure increases because SVR has increased as a result of vasoconstriction. There is less blood returning to the heart, so less blood is ejected, reducing Stroke volume. This also reduces the blood pressure per heart beat, reducing systolic blood pressure. With less venous return, right atrial pressure also decreases. Left ventricle end-diastolic pressure reduces as a result of SV reduction.

Question 9

What is the effect of an alpha-adrenergic antagonist on the heart?

Answer 9

These are only present on vascular smooth muscle, not the heart. An antagonist will block vasculature activation, causing a reduction in SVR, sBP and dBP, and pulse pressure. HR DOES NOT change