Blood Pressure

Question 1

What is blood pressure?

Answer 1

pressure inside blood vessels or heart chambers, relative to atmospheric (unit: mmHg)

Question 2

How does your brain know what your blood pressure is and what does it do about it?

Answer 2

• blood pressure sensors (baroreceptors) communicate blood pressure level to brain (medulla) via afferent nerves
• brain (medulla) outputs blood pressure controllers (SNS and PSNS) via efferent nerves

Question 3

What are the SNS and PSNS responses to brain output?

Answer 3

change depending on what blood pressure is (if it decreased or increased)

Question 4

What are baroreceptors?

Answer 4

stretch-sensitive nerve endings that feedback information to brain

Question 5

Where are baroreceptors located?

Answer 5

• in carotid sinus – common carotid artery

- in aortic arch

Question 6

What is the afferent nerve that brings info to medulla from baroreceptor in carotid sinus?

Answer 6

glossopharyngeal nerve

Question 7

What is the afferent nerve that brings info to medulla from baroreceptor in aortic arch?

Answer 7

vagus nerve

Question 8

At rest, what is the brain input to SNS?

Answer 8

no sympathetic nerve activity

Question 9

At rest, what is the brain input to PSNS?

Answer 9

some parasympathetic nerve activity – explains why heart rate is lower than what intrinsic rate would be

Question 10

What happens if BP rises acutely?

Answer 10

↑ stretch of baroreceptors

↑ firing of afferent nerves

↑ stimulation of PSNS
- results in ↓ HR

↑ inhibition of SNS
- results in ↓ SVR and SV

BP = HR x SV x SVR therefore blood pressure is restored to normal

Question 11

What happens if BP falls acutely?

Answer 11

↓ stretch of baroreceptors

↓ firing of afferent nerves

↓ stimulation of PSNS
- results in ↑ HR

↓ inhibition of SNS
- results in ↑ SVR and SV

BP = HR x SV x SVR → blood pressure is restored to normal

Question 12

What does the brain do to SNS and AVP release normally at rest?

Answer 12

inhibits SNS and AVP release

Question 13

What happens when the SNS normally stimulates the kidney?

Answer 13

• results in renin release
• renin increases AII
• AII can affect SVR
• AII stimulates aldosterone
• aldosterone affects kidney Na+ reabsorption and water reabsorption

Question 14

What does the release of AVP usually do?

Answer 14

• has effect on SVR – which causes vasoconstriction

- stimulates kidney – which increases water reabsorption

Question 15

What does the brain do to SNS and AVP release if BP increases?

Answer 15

increases inhibition of SNS and AVP release

result:
- ↓ BV leads to ↓ CO
- ↓ SVR leads to ↓ BP

Question 16

What does the brain do to SNS and AVP release if BP decreases?

Answer 16

decreases inhibition of SNS and AVP release

result:
- ↑ BV leads to ↑ CO
- ↑ SVR leads to ↑ BP

Question 17

What are some cardiovascular adaptations to exercise? (6)

Answer 17

• ↑ left ventricle size and wall thickness (hypertrophy) –partly responsible for increase in SV
• ↑ SV (volume effect) – increase in BV, resulting in reflex increase in pumping via Frank Starling mechanism
• ↓ resting and submaximal HR
• ↑ BV
• BP does not change or slightly decrease
• CO better distributed to active muscles

Question 18

Describe the difference in stroke volume between trained and untrained individuals.

Answer 18

• higher in trained than untrained individuals

- larger increase during exercise in trained individuals

Question 19

Describe the difference in heart rate between trained and untrained individuals.

Answer 19

• higher in untrained than trained individuals

- trained and untrained individuals can reach close to same MHR

Question 20

Describe the difference in cardiac output between trained and untrained individuals.

Answer 20

cardiac output is similar between trained and untrained individuals

Question 21

What results in larger cardiac output?

Answer 21

• higher heart rate

- higher stroke volume

Question 22

What is ‘training-induced’ or ‘athletic’ bradycardia?

Answer 22

slower resting heart rate in athletes

Question 23

What are the mechanisms that cause training-induced or athletic bradycardia?

Answer 23

• increased vagal tone (controversial)
• passive, due to increased SV with no change in CO
• beta receptor desensitization (controversial)

Question 24

How does increased vagal tone reduce heart rate?

Answer 24

• more vagal input to heart reduces HR

- reduced SA node pacemaker activity

Question 25

Describe the ‘passive’ mechanism – due to increased SV with no change in CO.

Answer 25

even though HR drops, SV and CO increase at rest so CO is not altered when training vs. not training