13. cardiac output ii Flashcards
what is contractility
the contractile ability of cardiac muscle at a given preload
positive inotropic
increases the contractility of the heart
are the sympathetic nervous system and adrenaline positively inotropic or negatively inotropic
positive inotropic
increases force of contraction and therefore storke volume
increases velocity of conduction of cardiac impulse
is the parasympathetic nervous system (acetylcholine) positively or negatively inotropic
negatively inotropic
decreases the contractility of the atria
when the heart rate is 150bpm with SNS tone the diastolic phase is longer than the systolic phase why
gives more time for the ventricles to fill, and then eject blood in the diastolic phase
what is afterload
the pressures that oppose the ejection of blood as it leaves the ventricles
how easily blood leaves the heart into arteries
what is afterload influenced by
blood vessel tone ie vasodilation/vasorelaxation
what is the capillary hydrostatic pressure
a minimum pressure needed to exchange fluids and substances across capillary networks- capillary exchange
what is hypotension and hypertension
hypotension blood pressure s too low
hypertension is when blood pressure is too high
what is blood pressure
the force placed on the walls of blood vessels by blood as it flows
what is blood pressure determined by
cardiac output x total peripheral resistance (arteriole radius)
autoregulation of blood pressure has both sort and long term regukatory mechanisms
short term mechanisms control heart rate, vasoconstriction, vasodilation
long term controls heart rate vasoconstriction vasodilation AND extracellular fluid volume regulation
what happens to blood flow to tissues in active tissues
tissue metabolism
increase in metabolites
arterioles dilate brings more blood flow to tissue
what are short term controls regulted by
baroreceptor and chemoreceptor
what are long term controls of blood pressure controlled by
hormones
how does the baroreceptor responf to an increase in blood pressure
baroreceptor is activated inhibits the cardioacceleratory centre and stimulates the cardioinhibitory centre, this will decrease the cardiac output and the heart rate ( release of acetylcholine by the PNS)baroreceptors also inhibit the vasomotor centres to cause vasodilation which will decrease the total peripheral resistance
this will decrease blood pressure
how does a baroreceptor respond to a low blood pressure
baroreceptor is inhibited
the cardioacceleratory centre is not inhibited so can increase the cardiac output and heart rate
the vasomotor centre is also not inhibited so vasoconstriction and increased total peripheral resistance (helps move blood)
role of peripheral chemoreceptors in the control of blood pressure
located in carotid body
detect changes on co2 pH and O2
if there was an increase in CO2 and a decrease in pH how would the peripheral chemoreceptor respond
would stimulate the cardioacceleratory and vasomotor centres and inhibit the cardioinhibitory centre
increases heart rate and cardiac output, and vasoconstriction
rule breaker how would a peripheral chemoreceptor respond to an increase in CO2 (and decrease in O2) in the pulmonary circulation
causes constriction the arterioles
what is the role of the brain/ central chemoreceptors in the control of blood to the brain
located in the medulla oblongata and is involved in respiratory function
detects an increase in CO2 / a decrease in pH
vasodilation of cerebral vessels
promotes blood flow to the brain
