lecture 10 - CVS 6: control of blood pressure

Question 1

what does BP need to be maintained?

Answer 1

to ensure constant supply of blood to brain and heart

Question 2

control mechanisms involved in regulating arterial BP

Answer 2

short term - fast response

long term - slow response
• involves kidneys and regulation of blood volume

Question 3

baroreceptor reflex

Answer 3

short term control 
controlled by ANS and controls:
• HR 
• SV 
• vessel diameter

Question 4

where are baroreceptors found?

Answer 4

carotid sinus

aortic arch

Question 5

properties of baroreceptors

Answer 5

• high pressure sensory receptors
• active all the time
• respond to stretch of artery due to changes in BP
• increase in stretch causes more APs
• no response when BP < 40 mmHg

Question 6

what is orthostasis?

Answer 6

lying down to standing up

Question 7

effect of orthostasis on BP

Answer 7

get redistribution of 500ml blood from intrathoracic vessel into veins of the lower limbs due to gravity
• venus pooling - takes 15s

causes VR to decrease - not filling heart as well
• subsequent contraction reduced
• SV decreases so CO falls - starling mechanism
• MAP falls and may cause dizziness if below 20 mmHg

leads to reflex activation of baroreceptors

Question 8

what does the reflex activation of baroreceptors do?

Answer 8

• produces reflex tachycardia
• positive inotropic effects
• vasoconstriction in skeletal, GI and renal beds - increase TPR to restore BP

without baroreceptors you would faint when you stand up

Question 9

what is postural hypotension?

Answer 9

feel faint when standing up all the time

clinical problem

Question 10

blood volume regulation

Answer 10

long term regulation involves:
• atrial pressure receptors
• renal responses which control fluid excretion

thirst - control of fluid intake to increase blood volume

fluid loss/input involves signals from both heart and kidney

Question 11

hormones involved in fluid loss/input

Answer 11

ADH (vasopressin) - reduces water loss in urine

renin - stimulates aldosterone release and reduces Na+ and water excretion

ANP (atrial natriuretic peptide) - promotes Na+ and water excretion

Question 12

when do we get an increase in blood volume?

Answer 12

diet - too much salt intake - drives fluid intake

too much aldosterone

genetic disorders such as Middle syndrome

Question 13

response to an increase in blood volume

Answer 13

1) stretch of atrium
2) increase in ANP
3) decrease in RAS and Aldo
4) decrease in ADH
5) increase in fluid loss

Question 14

response to decrease in blood volume

Answer 14

decrease in blood pressure

detected by receptors in atria, carotid and aortic baroreceptors

triggers homeostatic reflexes:
• increased CO 
• vasoconstriction 
• thirst causes water intake 
• increase in ECF and ICF volume 
• increase in BP

Question 15

examples where you get a decrease in blood volume

Answer 15

• haemorrhage
• vomitting and diarrhoea
• severe burns
• diabetes
• diuretics

Question 16

cortico-hypothalamic influences

Answer 16

adaptive responses 
• playing dead 
• fight or flight 
• feeding 
• diving 
• temperature 
• sexual

Question 17

response to extreme pain or emotional stress can lead to fainting (playing dead), how does this work?

Answer 17

stress causes:
• intense increase in sympathetic cholinergic supply to skeletal muscles - decreases TPR
• intense increase in parasympathetic output to heart - marked decrease in HR

combined effect causes a very rapid decrease in BP and reduced flow to brain - person loses consciousness
• vasovagal syncope

Question 18

what is vasovagal syncope?

Answer 18

HR and BP drop suddenly

Question 19

modification of baroreceptor response during exercise

Answer 19

CNS overrides normal reflex

baroreflex wants to keep a constant arterial BP & so normal reflex would lead to reduced sympathetic supply – but in exercise BP does increase