Short Term Control of Blood Pressure

Question 1

Why is it important to regulate mean arterial pressure?

Answer 1

• MAP is the driving force pushing blood through the circulation
• Too low → fainting (syncope)
• Too high → hypertension

Question 2

Explain the relationship between TPR, MAP and CO

Answer 2

MAP = Cardiac Output x Total Pressure Resistance

Question 3

What is the arterial baroreceptor reflex?

Answer 3

Arterial baroreceptor reflex is a short term response to sudden changes in blood pressure

Question 4

Identify other inputs to the medullary cardiovascular centres

Answer 4

• Cardiopulmonary baroreceptors
  
  • Sensing central blood volume
• Central chemoreceptors
  
  • Sensing arterial pCO2 and pO2
• Chemoreceptors in muscle
  
  • Sensing metabolite concentrations
• Joint receptors
  
  • Sensing joint movement
• Higher centres
  
  • Hypothalamus and cerebral cortex

Question 5

Explain the effect of the Valsalva manoeuvre on the cardiovascular system

Answer 5

= FORCED EXPIRATION AGAINST A CLOSED GLOTTIS

1. increased thoracic pressure is transmitted through to aorta
2. Increased thoracic pressure reduces the filling pressure from the veins, therefore decrease in VR, EDV, SV, CO, MAP
   - The reduced MAP is detected by baroreceptors which initiate a reflex increase in CO and TPR
3. At end of the manoeuvre, the decrease in thoracic pressure is transmitted through to the aorta
4. VR is resorted so SV increases, but reflex effects have not worn off
   EVENTUALLY BACK TO NORMAL

Question 6

What happens when blood pressure increases in relation to the arterial baroreceptor reflex

Answer 6

• Baroreceptors release action potentials at a higher than normal rate to NTS (in brain stem)
• NTS activates parasympathetic system and inhibits the sympathetic system (causing vasodilation of blood vessels)
• Decreases heart rate by releasing ACh which acts on pacemaker cells of SA nodes

Question 7

What happens when blood pressure drops (when you stand up too fast) in relation to the arterial baroreceptor reflex

Answer 7

• Baroreceptors fire at a lower than normal rate to NTS (in brain stem)
• NTS inhibits parasympathetic NS and activates sympathetic NS
• Sympathetic NS releases norepinephrine which increases heart rate