Regulation of blood pressure

Question 1

The main purpose of MAP

Answer 1

is to drive blood into Tissues

• i. e. blood flow to any given organ depends on:
  1. MAP (the driving pressure head)
  2. resistance of local arterioles (which overrides sympathetic effect)
• eg exercise - increase co2 , decrease 02
  3. vascularisation/open capillaries

Question 2

MAP must be closely monitored & regulated to ensure:

Answer 2

1. high enough for sufficient drive, despite local adjustments
2. low enough to avoid damage to heart & blood vessels

*Regulation occurs through the integration of elaborate mechanisms, involving various aspects of the body. The two determinants of MAP are:
MAP = CO x TPR

Question 3

If the arterioles in one organ dilate (to increase local flow), what would happen to MAP if nothing else changed?

Answer 3

MAP = CO x TPR

• it would initially decrease
• decrease TPR when dilating arterioles

Question 4

How can TPR be adjusted to compensate?

Answer 4

constriction

Question 5

How can CO be adjusted to compensate?

Answer 5

both maintain adequate driving pressure > for the dilated organ and the brain. CV variables are continuously juggled

Question 6

When MAP deviates from a normal ‘set-point’ numerous responses are initiated:

Answer 6

• Short-term: autonomic nervous system to heart, veins, & arterioles > CO & TPR
• Long-term: kidney & thirst responses to regulate total blood volume > CO

Question 7

Several factors can detect and/or influence MAP:

Answer 7

• Baroreceptors in the aortic arch & carotid sinus sensitive to pressure > short-term
• Left atrial volume receptors & hypothalamic osmoreceptors > long-term
• Chemoreceptors in carotid & aortic arteries sensitive to low O2 & high H+ > short-term
• Cerebral cortex-hypothalamic pathway sensitive to behaviour & emotion, which influence MAP
• Hypothalamus sensitive to body temperature, which affects cutaneous arterioles & overrides regulation of MAP

Question 8

Baroreceptor

Answer 8

• reflex regulates short-term responses in MAP

- are pressure sensors/mechanoreceptors that constantly monitor MAP

Question 9

Baroreceptor 2

Answer 9

• doesn’t require brain
• reflex arch has to have receptor, aff. pathway, integration, eff. pathway, effector organs
  – Baroreceptors fire action potentials in response to pressure in these arteries
  – Impulses are delivered via afferent neurons to the cardiovascular control centre in medulla of brain stem, where information is integrated
  – Sympathetic & parasympathetic outflow via efferent neurons are adjusted
  – Heart & blood vessels change their status to restore MAP

Question 10

firing rate in afferent neuron arising from carotid sinus baroreceptor

Answer 10

inc. MAP, inc. receptor potenial, inc, rate of firing in afferent neurons

Question 11

firing rate in afferent neuron arising from carotid sinus baroreceptor
- 2

Answer 11

dec. MAP, inc. receptor potenial, dec., rate of firing in afferent neurons

Question 12

summary

Answer 12

• Veins: volume reservoir
• Highly compliant & hold excess blood
• Low pressure but a maintained pressure gradient drives blood flow
• Factors that increase venous return to heart
• Regulation of blood pressure – baroreceptor reflex

Question 13

baroreceptor reflex 1

- short term

Answer 13

increase BP > inc. carotid sinus and aortic arch receptor potential > inc. firing rate of aff. neurons > CV center > decr. sympathetic and inc. parasympathetic > dec. HR, SV and arteriolar and venous resistance > decrease CO and TPR > Decrease BP

Question 14

baroreceptor reflex 2

- shorterm

Answer 14

dec BP > dec. carotid sinus and aortic arch receptor potential > dec.. firing rate of aff. neurons > CV center > inc.. sympathetic and dec. parasympathetic > inc.. HR, SV and arteriolar and venous resistance > inc. CO and TPR > inc. BP