Week 9 - Control of the CV System Flashcards
When the aortic valve become calcified, what can happen to the heart
Left ventricular hypertrophy leading to heart failure
What are korotkoff sounds
Sounds heard under the distal half of the sphygmomanometer cuff when between diastole and systole i.e when blood starts to flow into artery after being cut off
Stroke volume
Volume of blood ejected from the ventricle each beat
What is the stroke volume normally
Around 5L/min on both sides!
Describe the structure of purkinje fibres in the heart
They interdigitate with myocytes to spread the impulse across the ventricles
Tachycardia
Heart beats too fast
Bradycardia
Heart beats too slow
atrial/ventricular fibrillation
aberrant heartbeat due to problems with conduction of impulse across the heart
What does ECG measure
Changes in potential difference between two electrodes
Where are two electrodes on the heart
Heart surface
On limbs
Arrhythmias
Irregular heartbeat
What is P wave
Atrial depolarisation
What is QRS
Ventricular depolarisation
T wave
Ventricular repolarisation
P-R interval
Delay through the AV node
Which ion enters the SA node upon its depolarisation
Calcium
Which ion leave the SAN during repolarisation
Potassium
Drugs that increase heart rate affect SAN permeability in which way
Increased Ca permeability
Drugs that decrease heart rate affect SAN permeability in which way
Increased K permeability
How can drugs be used to treat heart failure
They increase intracellular calcium and/or increase myofilament sensitivity hence increasing contraction and input from failing heart
What does digoxin do and how does it work
slows the heart down and improves the filling of ventricles
It increases the intracellular calcium concentration
What is the main receptor type found on heart nodal tissue, conducting system and myocardium.
Adrenoreceptor B1
Effects of adrenoreceptor activation on heart
Positive intropy (strengthen the force of heartbeat)
Positive chronotropy (increase heart beat)
Positive lusitropy (causes heart to relax more quickly hence shortening heartbeat- greater efficiency)
Positive dromotropy (increases conduction through the AV node)
What are used as short-term support following cariogenic shock
Beta-agonists
Left vagus nerve terminates on which heart structure
AV node
Right vagus nerve terminates on which heart structure
SAN
How does acetylcholine reduce hr
Activates M2 receptors which increase k permeability
How does atropine (vagolytic drug) increase heart rate in bradycardic patients
Inhibits muscaranic receptor
Role of endothelial cells
Lines all vessels and inside heart chambers
Controls local blood pressure
Prevents platelet aggregation and blood clot formation
Releases nitric oxide
Angiogenesis and vessel remodelling
Permeability barrier for nutrients/fluid between plasma and interstitial fluid
Name of constrictor that endothelial cell can release
Thromboxane
Name of dilator that endothelial cells can release
Nitric oxide
How can endothelial cells affect LDL
Can release free radicals which oxidise LDL
Which vessels have vessels have vascular smooth muscle
All vessels apart from small capillaries
Why is compliance important in blood vessels
Prevents the pressure going to 0 as blood leaves the arteries
What happens to arterial compliance as we age
Compliance decreases
How does arterial calcification occur
Healing response to the presence of dead cells which reduces the elasticity of the vessels
How do we calculate mean arterial pressure
Diastolic BP + 1/3 pulse pressure (PP)
OR
CO x TPR
What is mean arterial pressure
The average pressuring pushing blood round the system
What type of artery is the carotid artery
Elastic artery
What structure dissipates the blood pressure from the arteries
The arterioles
Which structure contains most of the blood at low pressure (70%)
The venules, veins and vena cavae
What percentage of blood is help in the capillaries
5%
What happens to the colloid (osmotic pressure exerted by larger molecules) pressure between the arterial and venous end of the capillary
It stays the same
What happens to the hydrostatic pressure between the arterial and venous end of the capillary
It decreases as fluid is moves out
What is exceptional about pulmonary hydrostatic pressuress
Pulmonary hydrostatic pressures are much lower than systemic pressure which prevents pulmonary oedema
What can the result of capillary hydrostatic pressure increase be
Pitting oedema
Pulmonary oedema
Jugular vein distension
TPR (total peripheral resistance)/SVR (systemic vascular resistance)
Force exerted onto blood by vasculature of the body
Examples of alpha-1 selective adrenoceptor antagonists
prazosin
doxazosin
Examples of non-selective adrenoreceptor antagonists
Phentolamine
How do nasal decongestants work
Vasoconstrict the mucosal blood vessels
3 local controls of blood vessel tone
Active hyperaemia - changes in o2, co2, cellular metabolites can dilate arterioles causing this
Reactive hyperaemia - blockage of blood flow induces this
Factors which affect blood flow
Length of blood vessel
Viscosity of liquid flowing in the tube
Pressure gradient across the tube
Problems with the ‘French equation’
It assumes that:
flow is laminar, non-pulsatile and flows through a uniform, straight pipe.
Ways to reduce risk of viscous blood
Movement to encourage venous return
Hydration and reduce alcohol
Compression socks - create a pressure gradient which promotes flow
What is resistance proportional to
Diameter
What happens to resistance down the arterial tree
It increases and decreases flow
What percentage of total blood volume is contained in the veins
70%
What is the relative cross sectional area of veins
Large but pressure differential is small
What is return to the right ventricle called
Preload
What can increased preload cause
Heart failure
Angina
What drug can be used to decrease preload
Nitroglycerin causing venodilation
Which structures detect blood pressure
Aortic arch baroreceptor
Carotid sinus
Which baroreceptor is more important
Carotid sinus since more sensitive
Where does baroreceptor connect to
NTS (nucleus tractus solitarius) in brain
What can the peripheral effect be of arterial baroreceptors firing in response to low arterial pressure
Increase in sympathetic outflow to heart/arterioles and veins and decrease in parasympathetic outflow to the heart
Peripheral vs central control of BP
Peripheral - active/reactive/NO etc
Central - in the brain
Example of central control of high BP
NTS activates the parasympathetic nervous parasympathetic nervous system and inhibits the sympathetic nervous system
AND VICE VERSA
How does clonidine work
Alpha 2 agonist
Activates presynaptic receptors in brain to lower sympathetic output.
