integration of cardiovascular mechanisms (CVS 9&10) Flashcards
components of CVS/cardiovascular system
- heart = pump, CO must match needs
- arteries = passageways of blood from the heart to the tissue, pressure must be maintained, but not too high
- arterioles = major resistance vessels
- capillaries = site of exchange of gas, nutrients and water between blood and tissues
- veins = capacitance vessels (contain most of blood volume during rest), passageways of blood from tissues to heart, venous return must provide heard with sufficient blood to pump
heart
=pump of cardiovascular system
-CO must match needs
arteries
=passageways of blood from the heart to the tissue
-pressure must be maintained, but not too high
arterioles
=major resistance vessels of cardiovascular system
capillaries
=site of exchange of gas, nutrients and water between blood and tissues
veins
=capacitance vessels (contain most of blood volume during rest)
- passageways of blood from tissues to heart
- venous return must provide heard with sufficient blood to pump
regulation of heart rate (HR)
-mainly autonomic nervous system
regulation of stroke volume (SV)
-pre-load/myocardial contractibility/after-load
MAP =
- mean arterial blood pressure
- MAP = CO (cardiac output) x TPR (total peripheral resistance)
cardiac output (CO) =
HR x SV
regulation of MAP
-if we regulate HR, SR and TPR, we will regulate MAP
how is MAP approximated
MAP = DBP + 1/3 of the difference between SBP and DBP (pulse pressure)
eg. of approximation of MAP
-a blood pressure of 110/80mHg, indicates:
->systolic BP = 110mmHg
->diastolic BP = 80mmHg
->pulse pressure = 110 - 80 = 30mmHg
->MAP = DBP + 1/3 pulse pressure
= 80 + (1/3 30) = 80 + 10 = 90 mmHg
how is the total peripheral resistance (TPR) regulated
- TPR is regulated by vascular smooth muscles
- contraction of vascular smooth muscles causes vasoconstriction and increases TPR and MAP (ie.pressure upstream)
- relaxation of vascular smooth muscles causes vasodilation and decreases TPR and MAP
- > vascular smooth muscles are controlled by extrinsic and intrinsic mechanisms
main site of TPR (total peripheral resistance)
arterioles
components of total peripheral resistance (TPR)
- arteries (~20%)
- arterioles (~50%)
- capillaries (~20%)
- veins (~10%)
resistance to blood flow
- resistance to blood flow is directly proportional to blood viscosity and length of blood vessel, and inversely proportional to the radius of the blood vessel to the power of 4
- the resistance to blood flow is mainly controlled by vascular smooth muscles through the changes in the radius of arterioles
extrinsic control of vascular smooth muscles
-this involves nerves and hormones
nerves involved in the extrinsic control of vascular smooth muscles
- they are very important on blood pressure regulation (refer to baroreceptor reflex from previous lectures)
- the vascular smooth muscles are supplied by the sympathetic nerve fibres, the neurotransmitter is noradrenaline acting on alpha receptors
- increased sympathetic discharge will increase the vasomotor tone resulting in vasoconstriction
- decreased sympathetic discharge will decrease the vasomotor tone resulting in vasodilatation