9/ short term control of blood pressure

Question 1

what is MAP? why is it important?

Answer 1

• mean arterial pressure, the driving force pushing blood through the circulation - has to be regulated as too low may lead to syncope (fainting) and too high leads to hypertension

Question 2

where are the main arterial baroreflex? where do they send their signal to?

Answer 2

• on the aortic arch (aortic arch baroreceptor)
• on the carotid sinus of the internal carotid arteries (carotid sinus baroreceptors)
• signals from baroreceptors are sent to the brain

Question 3

which nerve receives the signal from the aortic arch baroreceptor?

Answer 3

vagus nerve

Question 4

which nerve receives the signal from the carotid sinus baroreceptors?

Answer 4

glossopharyngeal nerve

Question 5

where in the brain are these signals sent?

Answer 5

medullary cardiovascular centres

Question 6

which nerve leads the response signal from medullary CV centres to right heart?

Answer 6

parasympathetic of vagus nerve

Question 7

which nerve leads the response signal from medullary CV centres to left heart?

Answer 7

sympathetic nerves (stops at the adrenal medulla to get the adrenaline)

Question 8

what are the possible responses from the sympathetic system?

Answer 8

increases contraction, venoconstriction and arteriolar constriction (in the systemic circulation)

Question 9

what are the possible response from the parasympathetic system?

Answer 9

increased or decreased contraction into the respiratory circulation

Question 10

what other inputs are there to the medullary CV centres?

Answer 10

• cardiopulmonary baroreceptors
• central chemoreceptors
• chemoreceptors in muscle
• joint receptors
• higher centres

Question 11

what are the major inputs for the long term regulation of blood pressure?

Answer 11

• cannot be arterial baroreceptors (they would eventually re-program to higher threshold)
• revolves around blood volume
• main sensors are the cardio-pulmonary baroreceptors
• effects tend to be hormonal and tend to act on blood vessels and kidneys

Question 12

what are the different inputs for hormonal long term regulation of blood pressure?

Answer 12

• renin, angiotensin, aldosterone system:
• vasopressin (= antidiuretic hormone)
• atrial natriuretic peptide & brain natriuretic peptide

Question 13

characteristics of renin - angiotensin - aldosterone system

Answer 13

• angiotensin II causes arteriolar constriction and increase in TPR
• aldosterone increases Na+ reabsorption, and increases plasma volume

Question 14

characteristics of vasopressin (= antidiuretic hormone)

Answer 14

• vasopressin causes arteriolar constriction, increase in TPR, increase in water permeability of collecting duct and increase in plasma volume

Question 15

characteristics of atrial natriuretic peptide & brain natriuretic peptide

Answer 15

• causes arteriolar dilation and decrease in TPR

- increase Na+ excretion (natriuresis) and decrease in blood volume

Question 16

what do the effects of standing have to do with venous pressure?

Answer 16

effects of standing: increased hydrostatic pressure causes pooling of blood in veins/ venules of feet/ legs

Question 17

how does the body deal with the effects of standing on venous pressure?

Answer 17

• decreased venous return, decreased EDV, decreased preload, decreased stroke volume, decreased cardiac output, decreased mean arterial pressure
• decreased baroreceptor firing rate

Question 18

how is the reflex response adapted to this?

Answer 18

• decreased vagal tone when standing (increased HR and CO)
• increased sympathetic tone (increased HR + CO, increased contractility (increased SV, CO) increase venoconstriction (increased VR, EDV, SV, CO), increased arteriolar constriction (increased TPR))

Question 19

what is the valsalva manoeuvre?

Answer 19

forced expiration against a closed glottis

Question 20

what is the effect of the valsalva manoeuvre on thoracic pressure (first part of the manoeuvre)?

Answer 20

increase in thoracic pressure

Question 21

what is the effect of increase in thoracic pressure?

Answer 21

decrease in VR, EDV, SV, CO, MAP

Question 22

what is triggered because of the decrease in MAP? what then?

Answer 22

baroreceptors initiates reflex to increase CO and TPR

Question 23

what is the effect of the valsalva manoeuvre on thoracic pressure (second part of the manoeuvre)?

Answer 23

decrease in thoracic pressure transmitted through the aorta

Question 24

what happens when thoracic pressure normalises?

Answer 24

VR is restored so SV increases, but the reflex effects have not worn off yet

then eventual back to normal

Question 25

what does long term control of MAP depend on?

Answer 25

blood volume