Blood pressure Flashcards
What is the normal BP for a dog/cat at rest?
120/80
How should blood pressure be calculated?
Take 3 readings and taken an average
- remember to take stress into account
What is the potential impact of a persistently high BP?
- Afterload on the ventricles is high
- More force is needed to overcomethe pressure in the arteries
- Increased heart workload
- Can lead to muscle thickening
- Backwards heart failure
- Damage to kidneys
- Eyes can be impacted
What is the potenital impact of a persistantly low BP?
- Leads to low perfusion of tissues
- Exercise intolerance and muscle wastage
- Reduced urine production
- Reduced filtration of blood
What is the equation for cardiac output?
SV x HR
What is the equation for aortic pressure (Pa)?
Pa = CO x TPR
What factors influence stroke volume?
EDVV and ESVV
What is the equation for SV?
SV = EDVV - ESVV
The volume of blood ejected into the circulation by one ‘stroke’ or contraction of the ventricle
What is the pathological effect of a high heart rate?
CO is reduced because EDVV is reduced so there isnt enough time for diastolic filling
What is the physiological effect of a high heart rate?
Sympathetic nervous system will shorten systole to allow more time for diastolic filling
- faster conduction of APs
What are the 2 main intrinsic mechanisms to control local blood flow?
- Metabolic autoregulation
- Paracrine control
What is metabolic autoregulation?
Increase in metabolic rate increases blood flow to tissues
- Increased production of CO2, K+, and lactic acid
- Causes vasodilation
What is paracrine control?
Locally acting hormones that lead to vasodilation e.g. nitric oxide
What are the 2 extrinsic mechanisms that preserve flow to essential tissues?
- Baroreflex
- RAAS
What is the baroreflex?
- First to kick in when theres decreased blood pressure
- Decreases CO and vasoconstriction to try and balance BP
- Doesn’t change overall volume of blood
What is the RAAS?
Can replace lost fluid volume
- Vasoconstriction
- ADH
- Thirst centres in hypothalamus
Where are baroreceptors located?
In the aortic arch and carotid sinuses
Where do baroreceptors send input and where does the output of that go?
To the CV centre in the medulla oblongata which sends outputs via the ANS
What are the main actions of the ANS in the baroreflex?
- Drop in BP = increased sympathetic NS
- Increased HR and contractility = increased SV
- Vasoconstriction of non-essential tissues
Which receptors are involved in the sympathetic NS, which response are they involved in?
Adrenergic - α1 α2 β1 β2
- fight or flight
Where are the different adrenergic receptors located in the body and what does stimulation of each of them cause?
α1 α2 = found in blood vessels, stimulation causes vasoconstriction
β1 = in cardiomyocytes and nodal tissue, stimulation causes increased contractility and HR
β2 = In the coronary arteries, stimulation causes vasodilation
Which receptors are a part of the rest and digest response?
Cholinergic = M2 and M3
Where are cholinergic receptors found and what does stimulation of each of them cause?
M2 = in cardiac tissue, causes decreased contractility and HR M3 = on blood vessels, leads to vasodilation
What is the role of nitric oxide in the control of blood flow?
- Released from endothelial cells when there is an increase in the speed of blood flow
- part of the parasympathetic NS
- causes vasodilation
What is first released in the RAAS and where is it released from?
Renin - from the liver in response to a decrease in BP
What is the effect on renin, within the RAAS?
- Causes angiotensinogen to be converted to angiotensin I
What then happens to angiotensin 1?
An enzyme in the lungs called ACE converts angiotensin I to angiotensin II
What is the role of angiotensin II?
- causes vasocontriction (increases BP) and release of aldosterone
What is the role of aldosterone?
- Causes the kidney to conserve sodium and water which increases the blood volume
- Increases thirst
How does angiotensin II also act on the pituitary gland?
Causes it to release antidiuretic hormone which causes the kidneys to conserve water, increasing blood volume and further vasoconstriction
Where is aldosterone produced?
Adrenal gland
Which organ is central to long term regulation of BP?
The Kidney
Which part of the kidney leads to activation of the RAAS?
The afferent arteriole detects changes in BP within the vessel, which leads to activation of the RAAS
What is pressure naatriuresis?
Kidney pressure changes affect sodium (and water) excretion
Which cells in DCT activate the RAAS?
Macula densa cells in the DCT sense reductions in sodium causing activation of the RAAS
Give the key points of how the ANS controls blood volume
Alpha 1/2 –> vasoconstriction & venoconstriction –> effectively increasing central blood volume & preload
How does a change in blood vessel diameter affect BP?
Causes a change in TPR, which affects the pressure of the atria, which changes the blood pressure
How do you increase heart rate and contractility at a cellular level?
β1 adrenoreceptor on nodal tissue and cardiac myocytes binds adrenaline/noradrenaline
- leads to formation of cAMP
What is the function of cAMP?
Activates PK-A which phosphorylates Ca channels causing an influx of Ca, which leads to contraction
How can vascular smooth muscle be made to contract - i.e. what are the stimuli?
- Stretch
- Electrical stimulus
- Chemical stimulus
How do these stimuli on vascular smooth muscle lead to contraction?
- Stimuli causes increased cellular calcium ions
- these activate myosin light chain kinase
- MLC phosphorylation causes cross bridge formation
- leads to muscle contraction
