Short Term Control of Blood Pressure

Question 1

Why is it important we maintain MAP?

Answer 1

Its the main driving force behind circulation, too high or low and we get ill

Question 2

What happens when MAP is too high?

Answer 2

Hypertension.

OVertime it damages capillary beds leading to stroke, heart attack etc.

Question 3

What happens when MAP is too low?

Answer 3

Hypotension
Syncope occurs (Fainting)

Question 4

How are MAP, Cardiac output and total peripheral resistance related?

Answer 4

MAP = CO x TPR

Question 5

What are baroreceptors and what do they respond to?

Answer 5

Stretch receptors in the walls of arteries that fire more when the arteries stretch under high pressure

Question 6

Where are the main baroreceptors found?

Answer 6

aortic arch & carotid sinus

Question 7

Where is the carotid sinus?

Answer 7

Where the internal & external carotid arteries split.

Question 8

How does the AP firing rate of baroreceptors change through the caridac cycle?

Answer 8

Its highest during systole and lowest during dystole

Question 9

Whats another name for cardiopulmonary baroreceptors?

Answer 9

Low pressure baroreceptors

Question 10

What happens to the baroreceptors firing rate during hyper/hypotension?

Answer 10

Increases in hypertension

Decreases in hypotension

Question 11

How are baroreceptor signals from the carotid sinus transferred tot he medullary CV centres?

Answer 11

Carotid Sinus -> Glossopharyngeal Nerve -> Medullary CV centres

Question 12

How are baroreceptor signals from the aortic arch transferred to the medullary CV centres?

Answer 12

Aortic Arch -> Vagus Nerve -> Medullary CV Centres

Question 13

What mechanisms reduce blood pressure in the baroreceptor reflex?

Answer 13

Decreased Symp. Tone reduces:
Veno/arteriolar constriction
Adrenaline production in adrenal medulla
Contractility
HR

Increased Vagal Tone lowers HR

Question 14

What mechanisms increase blood pressure in the baroreceptor reflex?

Answer 14

Decreased Vagal Tone increases HR

Increased Symp. Tone increases:

• Adrenaline production in adrenal medulla
• Veno & arteriolar constriction (increased venomotor tone)
• Contractility
• HR

Question 15

What carries signals durin the baroreceptor reflex from the medullary CV centres to the Sinoatrial Node?
(when reducing and increasing HR)

Answer 15

Vagus (parasympathetic fibres)

Sympathetic Nerves

Question 16

What carries signals durin the baroreceptor reflex from the medullary CV centres to the cardiac muscle?

Answer 16

Sympathetic Neves

Question 17

How do signals travel from the medullary CV centres to the veins/arteries smooth muscle?

Answer 17

Sympathetic Nerves

Question 18

What carries signals from the medullary CV centres to the adrenal medulla?

Answer 18

Sympathetic Nerves

Question 19

From which spinal levels do sympathetic fibres supplyin the heart arise?

Answer 19

T1-T4

Question 20

To what do central chemoreceptors respond?

Answer 20

Changes in the pH of the CSF brought on by changes in CO2 levels.
CSF is very closely related to blood

Question 21

How does activating central chemoreceptors affect MAP?

Answer 21

They activate at high CO2 levels causing increased HR & contractility -> increased CO -> increased MAP

Question 22

When do muscle chemoreceptors activate?

Answer 22

During exercise

Question 23

Why do muscle chemoreceptors cause a MAP increase?

Answer 23

They signal the heart to increase HR/contractility so CO increases and they get more blood. This increases MAP

Question 24

When are joint receptors activated?

Answer 24

During repeated movement, same reasoning as muscle chemoreceptors

Question 25

How do higher centres affect MAP when you know your about to do exercise?

Answer 25

Higher centres act as a feed forward mechanism.

They increase HR & contractility in anticipation of increased need for blood to certain muscles.

Question 26

Whats the importance of the arterial baroreceptor reflex when standing up?

Answer 26

Without it youd faint standing up as all the blood rushes to your lower limbs.

Question 27

How does standing effect MAP?

Answer 27

Blood pools in legs (venous distension) leading to lower VR

• > lower EDV
• > lower preload
• > lower SV
• > lower CO
• > lower MAP

Question 28

Define the valsalva manoeuvre?

Answer 28

Forced Expiration against a Closed Epiglottis.

Shitting, repressuriing on a plane etc.

Question 29

What does the forced expiration of the valsalva manoeuvre cause first?

Answer 29

An increased thoracic pressure

Question 30

How does increased thoracic pressure affect the aortic pressure?

Answer 30

Its transmitted through to the aorta where its added to the aortic pressure, hence MAP rises

Question 31

How does increased thoracic pressure affect venous return?

Answer 31

Increased thoracic pressure reduces venous return because it squashes the veins near the heart preventing blood flow.

Question 32

What is the bodies response to lowered MAP?

Answer 32

When MAP falls below normal (due to reduced VR) it triggers the baroreceptor reflex which makes MAP rise again

Question 33

When the valsalva manoeuvre ends the decreased thoracic pressure is transmitted to the aorta, what effect does this have on the MAP?

Answer 33

It reduces MAP, a large drop below resting level.

Question 34

How does normal venous return after ending the valsalva manoeuvre affect MAP?

Answer 34

After the valasalva manoeuvre thoracic pressure returns to normal so venous return does too.
This mean EDV returns to normal and MAP quickly rises again.
Since the baroreflex is still active MAP rises well above normal

Question 35

What happens after the baroreflex wears off after the valsalva manoeuvre?

Answer 35

BP returns to normal

Question 36

What is the risk of the valasalva manoeuvre in someone old& sedentary?

Answer 36

They’re CVS cant cope with the variations in MAP, particulary the sudden hypotension when thoracic pressure returns to normal and they have heart attacks.