Cardiovascular system Lecture notes 3-7 Flashcards
why is the parallel arrangement important in systemic capillary beds?
each capillary bed receives arterial blood directly from the left ventricle
2 flow to different capillary beds can be altered selectively as situations demand: regulation of flow is determined by a resistance that precedes each capillary bed
where is the largest proportional pressure drop ?
the arterioles
whats the meaning of haemtaocrit ?
the ratio of the volume of red blood cells to the total volume of blood.
what affect does haemtocrit have an blood viscosity ?
increases
what is cardiac output ?
The flow through the systemic and pulmonary circulation is equal and is termed the cardiac output (Q).
what factors increase haematocrit ?
hypoxia (poor blood oxygenation) sickle cell anaemia which causes red blood cells die early
whats net effect does an increase in viscosity have on cardiac output ?
the heart has to do more work to maintain the same cardiac output.
ECG - p wave ?
atrial depolarisation
QRS complex ?
ventricular depolarisation
T wave ?
ventricular repolarisation
what is the PR interval determined by ?
P to Q the delay of the impulse at the a.v node. A longer time indicates heart block. 0.12-0.20
what is the QRS complex time represent ?
0.08 time for the depolarising wave to activate the ventricles. A longer time would indicate impaired Purkinje conduction ?
what does the QT interval represent ?
mean duration of the ventricular action potential
what does ST segment represent ?
s to a short segment after s - an isoelectric region on the ecg indicating no net current flow in the heart. The ST segment shows characteristic changes during certain cardiac diseases.
what do heart valves ensure ?
These ensure unidirectional flow in the heart from atrium, to ventricle, to outflow tract (aorta or pulmonary artery)
what innervates the heart ?
parasympathetic (vagus nerve) and sympathetic nerves
what is sinus arrhythmia ?
when respiratory activity alters heart rate
how long does a typical ventricular muscle action potential last ?
0.3 seconds
how long does one cycle i.e. from atrial systole to atrial systole last
0.8 seconds start again from alteration of cardiac output
what do you call capillary beds that are arranged in series ?
a portal system
give one example of an important portal system ?
the hepatic portal system
where is the mean velocity of blood flow the lowest ?
in the capillaries.. this along with a large surface area maximises conditions for exchange of nutrients
what is the formula of MABP ?
diastolic pressure + 1/3(pulse pressure)
formula for pulse pressure ?
systolic - diastolic pressure
convert 1 kPa to mmHg
7.50mmHg
convert 7.50mmHg to cmH20
10.2 cmH20
what is the definition of flow ?
volume per unit time cm3 per second
define velocity ?
it’s the speed at which a particle fluid moves cm per second . distance per unit time
whats the formula for systemic circulation pressure gradient ?
change in pressure equals mean arterial blood pressure minus right atrial pressure
whats formula for pulmonary circulation pressure gradient ?
mean pulmonary arterial BP - left atrial pressure
where in the heart is the action potential delayed ?
at the atrioventricular node
what comes before the purkinje fibres ?
the bundle of His
what is the formula for the fick principle ?
oxygen consumption divided by the oxygen conc out - conc in
what are the four ways to alter cardiac output ?
heart rate
preload
after load
myocardial contractility
what is the sino atrial node innervated by ?
by the autonomic nervous system
which neurotransmitter slows heart rate ?
vagus nerve.. acetylcholine
which neurotransmitter quickens heart rate ?
cardiac nerves.. noradrenaline
whats the definition of preload ?
preload is the tension in the walls of the ventricles at the end of diastole
define the term after load ?
after load is the pressure in aorta against which the heart must pump blood against
how do you increase myocardial contractility ?
add some adrenaline to the heart or excite the sympathetic nerves that supply the ventricle.. we can say that for the same preload cardiac function is increased when the sympathetic nerves are excited
how are heart rate and myocardial contractility regulated generally speaking ?
by neural and hormonal factors
what did ernest starling find ?
greater filling was measured as an increase of end-diastolic/pressure i.e preload resulting in increased strength of next cardiac contraction and stroke work. Thus the more blood there was in the ventricle at diastole, the greater was the stroke volume
what are the two important consequences of Starling’s law ?
- the input to the heart and the output from a ventricle are equal
- the output of the right ventricle and the left ventricle are equal
if after load increases what will decrease ?
stroke volume
what will increased resistance increase ?
after load
what determines heart rate ?
sion-atrial node
whats the main influence of heart rate ?
vagus (parasympathetic) nerve - increased activity of which slows heart rate. there are also sympathetic fibres that quicken the heart rate
what determines stroke work ?
myocardium contractility.. preload..afterload. the principal influence is from sympathetic fibres- increased activity of which exerts a positive inotropic effect
what determines the state of vascular smooth muscle ?
the principle influence is from sympathetic fibres - increased activity of which generates a vasoconstriction, decreased activity generates a vasodilation
do sympathetic fibres innervate smooth muscle in the veins and venules?
yes, increased activity will reduce the compliance of the venous system, facilitate venous return and so increase preload on the heart
what does the baroreceptor reflex sense and what does it act to do ?
baroreceptors in the carotid arteries and aorta sense increased blood pressure and ultimately act to decrease it by decreasing sympathetic stimulation of the smooth muscle fibres of the blood vessels and by increasing parasympathetic stimulation to the sino-atrial node hence reducing cardiac output and blood pressure
how is blood flow to tissues regulated ?
by the altering the resistance offered by the pre-capillary vessels, the arterioles
what are the two reasons why arteriolar resistance should be varied ?
- intrinsic mechanisms - to match blood flow to metabolic rate -
- extrinsic mechanisms. to preform homeostatic functions, such as the control of blood pressure or body temperature.
what effects do metabolic waste products have ?
a vasodilatory effect in general
what effect does ADH have blood vessels ?
vasoconstriction
what is the positive inotropic effect ?
increase of cardiac contraction strength increasing stroke volume
what is the positive chronotropic effect ?
increase of heart rate
what is auto regulation ?
this is a phenomenon whereby blood flow to a tissue stays relatively constant despite changes to arterial blood pressure - cerebral and renal circulations
what is the coronary circulation ?
denotes the arteries that supply the heart
when does the aortic valve close ?
at the end of ventricle contraction.. at the onset of ventricular relaxation
whats the function of cutaneous circulation ?
it supplies nutrient blood to the tissues
temperature regulation
protection against injury
