The Circulatory System 5 Flashcards
what is the efficiency + work of the heart as a pump measured as?
cardiac output
what is cardiac output?
vol of blood heart pumps out every min (ml/min or L/min)
what is cardiac output determined by?
- stroke vol
- heart rate
formula to find CO?
CO = SV x HR
what is stroke volume?
vol of blood ejected by the left ventricle with each heart beat (ml/beat)
what are the determinants of heart rate?
ANS/autonomic tone on heart
- inc in SNS/sympathetic tone INC heart rate
- inc in PNS/parasympathetic tone DEC heart rate
what are the determinants of stroke volume?
- preload
- afterload
- cardiac contractility
what is preload?
workload imposed on heart before contraction begins
what does preload =
end-diastolic vol / pressure
what is EDV/EDP?
vol of blood/pressure in ventricle prior to contraction (i.e at end of diastole)
what does EDV =
venous return (VR)
what is Frank-Starlings law of the heart?
SV = directly proportional to preload (or VR)
what does an inc in preload lead to?
- inc in stretch of cardiac muscle fibres
- inc in contraction
- inc in SV
what is afterload?
pressure heart must generate/overcome in order to eject blood into aorta
what does afterload =
aortic pressure = systemic arterial BP
what is afterload determined by?
systemic/total peripheral resistance (TPR)
what is SV inversely proportional to?
afterload (or TPR)
what does an increase in afterload lead to?
decrease in SV
what is contractility?
ability of heart to change its force of contraction without changing rest of muscle length
what does contractility =
strength of contraction at any given EDV
what does contractility depend on?
availability of intracellular ca2+ to participate in contractile process
what is SV directly proportional to?
cardiac contractility
what does an inc in [Ca2+]i lead to?
- inc in actin-myosin crossbridge formation
- inc in contractility
- inc in SV
what is cardiac contractility inc by?
SNS activation
- inc in SV
control of cardiac output
- inc in symp activity (+ epinephrine) inc heart rate and SV —> inc cardiac output (via EXTRINSIC control)
- inc in end-diastolic vol inc SV —> inc CO (via INTRINSIC control)
- inc in venous return —> inc SV —> CO (via INTRINSIC control)
what is systolic BP?
force exerted by blood on arterial walls during systole
what is diastolic BP?
force exerted by blood on arterial walls during diastole
what is the mean arterial BP?
average pressure responsible for driving blood forward into tissues
formula to find pulse pressure?
systolic BP - diastolic BP
formula to find mean BP?
diastolic BP + (1/3 x pulse pressure)
what is BP determined by?
- cardiac output
- total peripheral resistance (TPR)
formula to find BP?
CO x TPR
what is TPR determined by?
- sympathetic tone: vascular alpha 1 + beta 2 adrenoreceptors
- circulating hormones - Ang II + catecholamines
- local hormones - NO, ETs, PGs + adenosine
cardiac output is determined by HR and SV.
give further examples within these 2 points
HR- autonomic tone, catecholamines
SV- cardiac contractility, venous return
the mean BP is closely regulated + kept within narrow physiological range.
give the 2 reasons why?
- must = high enough to ensure adequate perfusion of organs + tissues
- must not be so high that places undue strain on heart + risks damaging blood vessels
homeostatic control involved 2 mechanisms
give the 2 mechanisms?
- short-term control mechanism: via baroreceptors
- long-term control mechanisms: via kidneys
short term control adjustments
- happens in seconds
- involves alterations in CO + TPR
- mediated via autonomic nervous system influences on heart, arterioles + veins
long term control adjustments
- needs minutes to days
- involves renal mechanisms of normal salt + water balance —> adjustments in total blood vol
short term BP control mechanism (parasympathetic output)
- inc in BP
- inc in firing of baroreceptors in carotid arteries + aorta
- sensory neurones
- medulla oblongata
- inc in parasympathetic output
- more ACh on muscarinic receptor
- SA node
- dec heart rate
- dec CO
- dec BP
short term BP control mechanism
sympathetic output
- inc in BP
- less NE released
- alpha receptor —> arteriolar smooth muscle —> vasodilation
- dec peripheral resistance
- beta receptor —> ventricular myocardium —> dec force of contraction. —> dec CO
- dec BP
what kind of mechanism is the short control BP control mechanism?
negative feedback
long term BP control mechanism
kidneys
- dec in extracellular fluid
- dec in arterial BP
- renin released
- convertes angiotensinogen to angiotensin I
- angiotensin I converted into angiotensin II
- goes to adrenal cortex + arterioles
- adrenal cortex rel aldosterone —> Na+ reabsorption by kidney
- —> inc in vascular vol
- arterioles vasoconstrict
- —> inc in arterial BP
long term BP control mechanism
hypothalamic neuron
- hypothalamic osmoreceptors stimulate hypothalamic neurons
- inc thirst
- —> water intake
- —> inc in plasma bol and plasma osmolarity
- —> relieves inc in osmolarity
- —> relieves dec in ECF vol + arterial blood pressure
- stimulates left atrial volume receptors
- stim hypothalamic neurones
- inc in vasopressin
- —> water permeability of DCT and PCT
- —> inc in water reabsorption
- dec in urine output
- inc in plasma vol
integrated BP control mechanism
- inc in blood vol
- —> inc BP
- triggers compensation by cardiovascular system (FAST**) + compensation by kidneys (SLOW*)
- ** —> vasodilation + dec CO —> dec BP to normal
- —> excretion of fluid in urine dec blood vol
- —> dec BP
