Lecture 8: Controlling the Heart & BP

Question 1

What are the two major determinants of cardiac output?

What is cardiac output?

Answer 1

• Stroke volume
• heart rate
  CO = SV x HR
  cardiac output = stroke volume x HR
• blood flow leaving the heart L/min
• determined by SV and HR
• coordinated in the brainstem

Question 2

What is the stroke volume?

Is stroke volume equal ?

Answer 2

• The volume of blood ejected by a ventricle during a heart beat
• SV is equal in the left and right ventricle which are in series —-> blood flow is the same in the pulmonary and systemic circuit
  Flow out = systole , flow in = diastole

Question 3

Arterial pressure is tightly regulated within a narrow range, how is it regulated?

Answer 3

Regulation of blood pressure occurs through the control of the:

• heart = cardiac output
• blood vessels

Question 4

Describe the pathway taken to control arterial blood pressure?

Answer 4

1. Baroreceptors sense blood pressure and send afferent input to the brain
2. Efferent output is sent to the NS which controls blood pressure & HR either by the parasympathetic or nervous system

Question 5

What are baroreceptors ?

Answer 5

Are sensors which maintain BP

• are nerve endings
• found in the outside of the medial layer of the vascular wall

Question 6

What affect does the parasympathetic - BRAKE have on blood pressure & cardiac output?

Answer 6

• slows down HR, decreases blood arterial blood pressure, but has NO effect on SV
• cardiac vagus nerve innervates the San(pacemaker) & AVN

Question 7

What affect does the sympathetic - ACCELERATOR have on blood pressure & cardiac output?

Answer 7

• It increases HR, stroke volume and arterial pressure

- sympathetic cardiac nerves innervate the 2 nodes & ventricles.

Question 8

What is blood pressure regulated by?

Answer 8

• changes detected by baroreceptors
• control of pressure through changes to cardiac output
• changes in localised flow

Question 9

What effect does increased resistance have on arterial blood pressure/volume?

Answer 9

increased resistance —> decreased outflow —-> increase arterial blood volume and pressure ; due to high resistance, blood does not leave system

Question 10

What effect does decreased resistance have on arterial blood pressure/volume?

Answer 10

decreased resistance —-> increased outflow —> decreases arterial volume & pressure ; due to low resistance more blood flows out of system

Question 11

Where is cardiac output controlled?

Answer 11

Controlled by the cardiovascular centre in the brainstem