CVS Flashcards
What affects the rate of diffusion?
Area
Diffusion resistance - Nature of barrier, molecules and distance
Concentration gradient
What do we have a cardiovascular system?
Supplies cells in the body with metabolic needs because simple diffusion would be too slow
What must be kept at an appropriate rate to ensure concentration gradients during diffusion?
Flow of blood else gradients driving exchange will dissipate
How much blood does the cardiovascular system have to deliver?
Between 5 and 25 L/min
Which organs must the blood flow be maintained at a constant rate?
Brain and kidneys
What is the blood flow required to the brain and kidneys?
Brain - 0.75 L/min
Kidneys - 1.2 L/min
What are the components of the circulation?
Pump - heart
Distribution vessels - arteries
Flow control - resistance vessels (arteriolar, pre-capillary sphincters)
Capacitance - store of blood (veins)
What is the role of resistance vessels in the circulation?
Allows for restricted flow to parts of the body that are easily perfused and drives blood to parts that are not easily perfused
E.g. Arteriolar, pre-capillary sphincters
What is the role of capacitance vessels in circulation?
Ability to cope with changes in cardiac output. Stores blood which can be called upon to cope with temporary imbalances
E.g. Veins
What is the difference between elastic arteries and muscular arteries?
Elastic arteries - expand slightly with each heart beat (greater amount of elastic fibres)
Muscular arteries - regulate amount of blood reaching an organ/tissue, regulates blood pressure, branch into arterioles
Describe the flow of structures in the circulation system from heart to capillaries
I.e. The order in which they occur
Large elastic/conducting arteries —> medium muscular/distributing arteries —> arterioles —> metarterioles —> capillaries
Describe the flow of structures in the circulation system from capillaries to heart
I.e. The order in which they occur
Capillaries —> post capillary venules —> venules —> medium veins —> large veins
How is the diameter of arteries and arterioles controlled?
By autonomic nervous system
What are the two types of capillary walls?
Continuous & fenestrated
What can capillaries be surrounded by?
Pericytes - contractile cells
What are sinusoids and where are they found?
Capillaries that have a larger diameter and may contain special lining cells and incomplete basal lamina - increase permeability
Found in liver, spleen, bone marrow
What is the difference in restructure between vein and artery?
Similar structure except that wall is thinner and lumen wider and irregular
Veins contain semilunar paired valves - blood flow in 1 direction
What occurs to the veins if blood pressure is not maintained?
They collapse
What are the two factors that most effect blood flow in veins?
‘Muscle-pump’ action in the leg and pressure factors in the abdominal and thoracic cavities
What are the valves located in the left ventricle?
Tricuspid and pulmonary
What are the two values located in the right ventricle?
Mitral and aortic
What are the six properties of cardiac muscle allow heart to operate as a pump?
Striations Branching Centrally positioned nuclei Intercalated discs - electrical and mechanical coupling with adjacent cells Gap junctions T tubules inline with Z bands
How are action potentials generated in the heart?
Pacemaker cells (SA node) generate electrical activity which leads to activity in other cells
How long is cardiac contraction (systole)?
280ms
What is systole?
Period in which the myocardium is contracting
What is diastole?
Relaxation in-between contractions
How long does diastole last?
700ms
How does atrial systole occur?
SA node fibres an action potential - spreads over atria - atrial systole
What happens at the AV node?
Action potential is delayed for 120ms before spreading down septum
What causes the movement of blood from atrium to ventricle?
Intraventricular pressure falls below atrial pressure - rapid filling phase
How do the atrioventricular valves close?
Build of pressure exerted in ventricles causes slight back flow but blood seeps behind the valve flaps slamming them shut with pressure
How is the muscle in the ventricles organised to facilitate pumping of blood?
Organised into figure of 8 bands
What is the difference between the right and left side of the heart?
Left side has thicker myocardium
Right side has pacemaker cells
Describe isovolumetric contraction
When ventricles contract but there are no values open
What is isovolumetric relaxation?
When ventricles relax before atrioventricular valves open
When do the pulmonary/aortic valves open and close?
Open - when ventricular pressure exceeds diastolic pressure in pulmonary/aortic arteries - systole
Close - when arterial pressure is greater than ventricular pressure, slight back flow - end of systole
When do the tricuspid/mitral valves open and close
Open - atrial pressure greater than ventricular pressure - early diastole
Close - when ventricular pressure exceeds atrial pressure, slight back flow - ventricular systole
What are the origins of the heart sounds?
First sound - AV valves closing - lup
Second sound - semi-lunar valves closing (ventricular-arterial valves) - dup
What are the left coronary arteries?
Left anterior decending
Left marginal
Circumflex
What are the right coronary arteries?
Right marginal
Right anterior ventricular
In an ECG what signal does a depolarisation towards an electrode cause?
Upward signal
In an ECG what signal does a depolarisation moving away from an electrode cause?
Downward signal
In an ECG what signal does a repolarisation moving away from an electrode cause?
Upward signal
In an ECG what signal does a repolarisation moving towards an electrode cause?
Downward signal
What does the amplitude of an ECG signal depend on?
How much muscle is depolarising
How directly towards the electrode the excitation moves
When reading an ECG what do you look at?
Rate, rhythm, axis, P-wave, P-R segment, QRS complex, Q-T interval, T wave
What is the P-wave of an ECG?
Atrial depolarisation
What is the Q peak in an ECG?
Excitation spreads down halfway down septum and across axis of heart
What is the R peak of ECG?
Depolarisation spreads through ventricular muscle
What is the S peak of the ECG?
Depolarisation spreads upwards through ventricles
What is the T wave of an ECG?
Repolarisation on epicardium surface of ventricles
What are amplifiers in terms of an ECG?
One positive and one negative electrode - negative electrode takes signal and inverts it, adding it to positive input
What are the ECG changes of atrium fibrillation?
No P waves
Irregularly spaced QRS complex
What are the ECG changes consistent with first, second and third degree heart blocks?
First degree - prolonged P-R interval
Second degree - erratic P-R interval
Third degree - no relationship between P wave and QRS complex
What is the cause of axial deviation and what are the consistent ECG changes?
Caused by changes in amount of muscle
Moves normal rhythm out of lead II - alters axis
What are the changes consistent with bundle branch block?
Lengthens and changes shape of QRS complex
Rabbit ears
Damage to conducting pathways
What are the ECG changes consistent with myocardial infarction?
ST elevation
Inverted T waves
Pathological Q waves - caused by scar tissue
In which vessels is blood flow fastest?
Where total cross sectional area is least, e.g. aorta
Slowest in capillary beds
What are the layers of an artery?
Tunica intima Internal elastic lamina Tunica media External elastic lamina Tunica externa
What are the layers of a vein?
Tunica intima
Tunica media
Tunica externa
What are the layers of the pericardium?
Fibrous layer
Serous layer - divided into parietal and visceral layers
What is the sensory nerve supply to the pericardium?
Phrenic nerve (C3-C5)
What is valve stenosis?
Narrowing of the valve
What is valve incompetence and what does it result in?
Valve not closing properly causing regurgitation
What occurs during an ventricular action potential?
Opening of voltage gated Na channels - Na influx
Transient outflow of K+
Plateaux caused by opening of VOCC (L-type) - Ca influx
Ca channels inactive, voltage gated K+ open - K efflux
What occurs during an SA node action potential?
Gradual influx of Na through HCN channels (cAMP-dependent) - Funny current (If)
Opening of t-type voltage operated Ca channels - become inactive
Opening of voltage operated K channels cause depolarisation
Describe the mechanism by which the tone of blood vessels controlled?
Ca binds to calmodulin which binds to myosin light chain kinase (MLCK) which phosphorylates myosin head through conversion of ATP to ADP
How does sympathetic activity change the SA node action potential?
Increase cAMP causes increased gradient of If due to more channels open and more Na influx
Which nerve provides parasympathetic innervation of the SA node?
Vagus nerve
Where do sympathetic pre-ganglionic nerves synapse?
Paravertebral chain
What are the two exceptions to the usual ANS innervation?
Sweat glands - sympathetic innervation but release ACh to muscarinic receptors
Chromaffin cells in adrenal medulla - specialised postganglionic sympathetic neurones that release adrenaline into the bloodstream
Describe the mechanism of parasympathetic innervation of the SA node
M2 receptors - inhibit adenylyl cyclase - decreased cAMP - decreased opening of HCN channels, not main effect
Beta-gamma subunit increases open probability of K channels so causes hyperpolarisation so takes longer to reach threshold
Describe the mechanism of sympathetically led positive inotropy
Noradrenaline - B1 receptors - + adenylyl cyclase - increased cAMP - increased PKA
PKA phosphorylates L-type VOCC channels to increase open probability - increased Ca entry
Increased Ca induced Ca release from SR (ryanodine receptors)
Increased force of contraction
Describe the sympathetic drive of vasculature
Increased sympathetic drive - vasconstriction
Normal - vasomotor tone
Decreased sympathetic drive - vasodilation
Which receptors are involved in sympathetic innervation of vasculature?
Alpha 1 adrenoceptors
Describe the effect of metabolites on vasculature
Produced by active tissue (e.g. adenosine, K, H)
Strong vasodilatory effect
What controls sympathetic and parasympathetic drive of the heart?
Baroreceptors - sensitive to stretch therefore detect arterial pressure
Located in carotid sinus and aortic arch
Flow is determined by resistance but what is resistance determined by?
Nature of fluid and vessel
What is flow?
Volume of fluid passing a given point per unit of time
What is velocity?
Rate of movement of fluid particles along tube
At a given flow, velocity is inversely proportional to what?
Cross sectional area
Describe in laminar flow
Concentric rings of gradient of velocity (from middle to edge), highest in centre
What causes turbulent flow?
Increased mean velocity or narrowed
Increases flow resistance
Generates sound
What is viscocity of blood?
The extent to which adjacent layers resist sliding over one another due to laminar flow
What does Poiseulles law state?
Decreasing the radius by 1/2 will increase vessel resistance by 16 times
F proprotional to r4
What is special about the distensible tubes?
As vessel stretches, resistance falls
But as pressure drops, walls will eventually collapse - flow ceases before pressure falls to zero
What is the pressure and resistance of arteries?
Low resistance
High pressure - due to high resistance of arterioles
Distensible walls make flow less pusitile
What is TPR?
Total peripheral resistance - sum of all resistance from all vessels
What are the factors affecting systolic pressure?
How heart the heart pumps
Total peripheral resistance
Stretchiness of arteries
What are the factors affecting diastolic pressure?
Systolic pressure
TPR
What is TPR proportional too?
Inversely proportional to body’s need for blood
What does Starling’s Law of the Heart state?
The more the muscle is stretched the more is will contract (the bigger the stroke volume)
Therefore increased venous pressure will equal increased stroke volume
What occurs during ventricular filling?
Ventricle will fill until intra-ventricular pressure = venous pressure
*Ventricular compliance curve (venous pressure vs volume)
What does the Starling Curve show?
Stroke volume vs venous pressure (slope = contractility - ability of muscle to generate force for any given fibre length, caused by increased Ca)
Curve tapers off at high venous pressure because heart stretch is limited by pericardial sac and it will impinge on coronary arteries
What determines the force of contraction?
End diastolic volume (starling’s law)
Contractility (increase sympathetic activity)