Blood pressure Flashcards
What is the equation for blood pressure/arterial pressure?
Pa = CO X TPR
What is blood pressure altered by?
CO and TPR
What is normal BP for a cat/dog? What do you have to take into account when measuring BP?
120/80
Higher when stressed - e.g. in practice
What is BP measured in? What does each number mean?
Millimetres of mercury (mmHg)
Systolic pressure/diastolic pressure
What affects stroke volume?
ESVV and EDVV - which in turn affects CO and BP
What is the consequence of a pathologically high HR?
CO is decreased due to decreased EDVV
What happens to systole during a physiologically high HR? What about vessel size?
Systole shortened to preserve diastole
Vasoconstriction
What are the consequences of a persistently low BP?
Prerenal failure - kidney working itself but decreased blood flow to kidney decreases function
Reduced GFR and urine production
Low tissue perfusion - fainting during exercise
Muscle atrophy
What are the consequences of a persistently high BP?
Increased afterload - ventricles have to work hard so stretch or thicken
Kidney damage
Retinal blood vessels wider and more tortuous than usual
Retinal detachment (end stage)
When are intrinsic controls of blood flow used? What are the 2 intrinsic controls of blood flow?
Within the tissue itself, local acting and within normal BP
Metabolic autoregulation and paracrine control
When are extrinsic controls of blood flow used? What are they (3) ?
When outside of normal BP
Preserve blood flow to essential tissue, baroreflex (acute), RAAS (chronic)
What is metabolic auto regulation?
Blood flow matches metabolic demand
What is paracrine control?
Vasoconstriction hormones and nitric oxide (vasodilator)
When is the baroreflex used to control blood flow? Does it alter blood volume?
Extrinsic mechanism, acute
No
When is the RAAS system used? Does it alter blood volume?
Extrinsic mechanism, chronic. Prolonged baroreflex stimulates RAAS
Yes
Where does the baroreflex send input info? The output info is via what nervous system?
CV centre in medulla oblongata
Output via ANS
What does baroreflex cause when BP is increased and decreased?
BP decreased = increase in sympathetic NS, decrease in parasympathetic NS
BP increased = decrease in sympathetic NS, decrease in parasympathetic NS
What are the adrenergic autonomic receptors? What nervous system are these mainly?
a1, a2, B1, B2
Sympathetic nervous system
What are the cholinergic autonomic receptors? What nervous system do these mainly use?
M2, M3
Parasympathetic NS
Where are a1 and a2 receptors located? What is their action?
Blood vessels
Vasoconstriction
Where are B1 receptors located? What is their action?
Cardiomyocytes and nodal tissue
Increase HR and contractility
Where are B2 receptors located? What is their action?
Blood vessels
Vasodilation during fight/flight
Where are M2 receptors located?
Cardiomyocytes and nodal tissue
Decrease HR and contractility
Where are M3 receptors located?
Blood vessels
Vasodilation during rest and digest
Nitric oxide is a vasodilator involved in the intrinsic control of blood flow. Where is it released? How does it work?
Endothelial cells and blood vessels
Cause relaxation of smooth muscle by activating cGMP which activates MLCP–> vasodilation
Which NS causes vasodilation via nitric oxide?
Parasympathetic
Which organ is the central regulation of BP? What do changes in BP cause a change in?
Kidneys
Increased BP –> Increased GFR and urine output
What part of the nephron monitors blood pressure? What happens when this detects a decrease in BP?
Afferent arterioles
Activates RAAS
What does renal artery perfusion regulate?
Sodium excretion - which itself alters water retention and BP
What part of the nephron detects sodium ions and what does this lead to?
Macula densa cells in DCT
Activates RAAS
High BP and kidney damage go hand in hand - it is hard to know which came first. Why does kidney disease often lead to high BP?
Can’t excrete sufficient Na
Water retention –> increased BP
Kidney not perfused properly –> sympathetic activation and activate RAAS
Changing blood volume is controlled how and by which nervous system?
Vasoconstriction by autonomic NS
Doesn’t actually alter volume but alters space to circulate
What are 3 ways blood volume can be changed?
Vasoconstriction (kind of)
RAAS
Kidneys (management of Na and ability to concentrate urine)
Changing blood volume leads to a change in…
CO which alters BP
Changing contractility leads to a change in….
CO which alters BP
Changing blood vessel diameter leads to a change in….
TPR which alters BP
B1 receptors change contractility at a cellular level. How do these receptors work?
Adrenaline/noradrenaline bind to B1 receptor
Leads to formation of cAMP
cAMP activates PKA
PKA phosphorylates Ca channels and causes a calcium influx
What does cardiac muscle have that smooth muscle does NOT have?
Troponin
Troponin not present in smooth muscle
How is smooth muscle activated?
Chemical, electrical or stretch stimuli
How does calcium cause smooth muscle to contract?
Increased cellular calcium activates MLCK
MLCK causes phosphorylation of MLC
Causes cross bridge formation and contraction
How does smooth muscle relax?
MLCP (myosin light chain phosphatase) dephosphorylates MLC
Increased cAMP and increased cGMP both cause vasodilation. How do cAMP and cGMP cause vasodilation?
cAMP inhibits MLCK –> relaxation and vasodilation
cGMP activates MLCP –> relaxation and vasodilation
What is PDE?
Enzyme in vascular smooth muscle that degrades intracellular cAMP
What is PDE III?
Heart specific PDE
What happens if PDE is inhibited?
cAMP increased and activated PKA phosphorylates Ca channels
Causes stronger contractions
