lecture 10 - CVS 6: control of blood pressure Flashcards
what does BP need to be maintained?
to ensure constant supply of blood to brain and heart
control mechanisms involved in regulating arterial BP
short term - fast response
long term - slow response
• involves kidneys and regulation of blood volume
baroreceptor reflex
short term control controlled by ANS and controls: • HR • SV • vessel diameter
where are baroreceptors found?
carotid sinus
aortic arch
properties of baroreceptors
- 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
what is orthostasis?
lying down to standing up
effect of orthostasis on BP
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
what does the reflex activation of baroreceptors do?
- 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
what is postural hypotension?
feel faint when standing up all the time
clinical problem
blood volume regulation
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
hormones involved in fluid loss/input
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
when do we get an increase in blood volume?
diet - too much salt intake - drives fluid intake
too much aldosterone
genetic disorders such as Middle syndrome
response to an increase in blood volume
1) stretch of atrium
2) increase in ANP
3) decrease in RAS and Aldo
4) decrease in ADH
5) increase in fluid loss
response to decrease in blood volume
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
examples where you get a decrease in blood volume
- haemorrhage
- vomitting and diarrhoea
- severe burns
- diabetes
- diuretics
cortico-hypothalamic influences
adaptive responses • playing dead • fight or flight • feeding • diving • temperature • sexual
response to extreme pain or emotional stress can lead to fainting (playing dead), how does this work?
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
what is vasovagal syncope?
HR and BP drop suddenly
modification of baroreceptor response during exercise
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
