control of blood pressure L10 Flashcards
why does blood pressure need to be maintained
ensure a constant supply of blood to heart and brain
why does blood pressure need to be maintained
ensure a constant supply of blood to heart and brain
what are the two systems that control MABP
- short term (fast response involving baroreceptors)
- long term (slow response involving the kidneys and regulation of blood volume)
describe cortico- hypothalamic influences
higher brain centres
describe the role of baroreceptors and the pathway that follows
they detect stretching in the artery
1. send info via afferent pathways to medulla (control centre) via action potentials
2. the medulla sends signals via autonomic efferent pathways via action potentials to heart and blood vessels
- Baroreceptors, CV control centre & ANS form a simple ‘reflex’ arc that respond to changes in MABP
where are baroreceptors located
aortic arch & carotid sinuses
Nerve endings are found in adventitia layer of arteries
what are the afferent nerves attached to the baroreceptors at the aortic arch and carotid sinuses
- what do they do
AA: Carotid depressor
CS: Hering’s and IX glossopharyngeal
- send information via action potentials about MABP to the cardiovascular control centre in brainstem (medulla)
describe what happens when MABP increases
causes arteries to stretch which excites the nerve
causes receptors to fire more action potentials
how is baroreceptor action potential frequency related to MABP
if blood pressure is lower than 40mm/Hg, very few action potentials
if blood pressure is higher than 60mm/Hg, max frequency of action potential is met
- normal frequency is about half way between the two (the steep part of curve) allowing the action potentials to increase or decrease depending on whether you want to increase or decrease blood pressure
how is baroreceptor action potential frequency related to MABP
if blood pressure is lower than 40mm/Hg, very few action potentials
if blood pressure is higher than 60mm/Hg, max frequency of action potential is met
- normal frequency is about half way between the two (the steep part of curve) allowing the action potentials to increase or decrease depending on whether you want to increase or decrease blood pressure
what kind of pressure changes do baroreceptors respond better to
pulsatile pressure changes
what is action potential frequency like at low and high blood pressure
LOW: less frequent
HIGH: frequent
describe the pathway followed when MABP decreases
- less stretch of arteries detected by baroreceptors
- baroreceptors send less frequent action potentials
- the medulla decreases vagal tone to the heart (parasympathetic)
- medulla increases sympathetic supply to heart and blood vessels
- increases rate and contractilility of the heart - arterioles constrict increasing total peripheral resistance
- veins constrict increasing CVP
- adrenal medulla releases adrenaline
describe the pathway followed when MABP decreases
- less stretch of arteries detected by baroreceptors
- baroreceptors send less frequent action potentials
- the medulla decreases vagal tone to the heart (parasympathetic)
- medulla increases sympathetic supply to heart and blood vessels
- increases rate and contractilility of the heart - arterioles constrict increasing total peripheral resistance
- veins constrict increasing CVP
- adrenal medulla releases adrenaline
describe Postural Hypotension
- when you get up from lying down, blood is redistributed resulting in venous pooling
- ~ 500 ml of blood from the intrathoracic vessels into the veins of the lower limbs due to effect of gravity - results in
- venous return decreasing
- stroke volume decreases
- cardiac output falls
- Arterial blood pressure falls, and this may cause dizziness if MABP falls >20 mmHg
how do baroreceptors respond to postural hypotension
reflex tachycardia,
positive inotropic effects
vasoconstriction in skeletal, GI and renal beds ( TPR)
Restoration of MABP
how does blood volume affect blood pressure
it is a physical determinator
if volume drops, pressure drops
what detects changes in blood volume
Homeostatic mechanisms detect these changes in blood volume to try and maintain BP
this involves the intergration of kidney and CVS
what does long term response involve
- atrial pressure receptors
- sense stretching causing ANP, Renin-Angiotensin- Aldosterone System (RAAS) and ADH to be released - renal response
- controls fluid excretion and reabsorption
what does ANP (atrial natriuretic peptide) do
Increases Na+ & water excretion (loss) from kidney
what does Renin-Angiotensin- Aldosterone System (RAAS) do
Promotes Na+ & water re-absorption into body
what does ADH (vasopressin) do
Promotes water uptake into body
describe response to decrease in blood volume
- blood V decreases so blood pressure decreases
- detected by receptors in atria and carotid and aortic baroreceptors
- triggers homeostatic reflexes
- causes kidney to reserve water
- triggers thirst increases ICF and ECF volume
- increases cardiac output and vasocontraction
- increases blood pressure
what can cause decreased blood volume
Haemorrhage (hypovolaemic hypotension)
Vomiting and diarrhoea
Severe burns
Diabetes
Excessive use of diuretics
describe the role of ANP in volume increase
increased fluid causes atria to stretch which increases ANP
ANP directly effects kidneys causing it to loose fluid
also affects RAAS system- dampen downs its effects
dampens down ADH
- promotes fluid loss
what can cause an increase in volume
Diet – excessive salt intake
Too much aldosterone
Genetic diseases such as Liddle syndrome
what are Cortico-hypothalamic influences
Adaptive responses - ‘Higher centres’
Playing dead
Fight or flight
Defence reaction
Feeding
Diving
Thermo-regulatory
Sexual
what does stress cause
- Decrease in sympathetic supply to skeletal muscle. This relaxes smooth muscle in arterioles and leads to marked decrease in TPR
- Increase in parasympathetic output to heart. This causes a marked decrease in HR
Combined effect causes a very rapid decrease in BP and reduced flow to brain. Person loses consciousness
Vasovagal Syncope
what does feeding cause
increased blood pressure
increased supply to insteinal muscles and decrease to skeletal
what does defence behaviour cause
increased blood pressure
decrease supply to intestines
increased supply to muscles
