Physiology of Circulation Flashcards
heart
pump
arteries
pressure reservoirs and conduits
aterioles
resistance vessels
capillaries
sites of exchange
veins
conduits and blood reservoirs
blood flow
- volume of blood flowing through a vessel, organ, or circulation system in a period of time
- blood flow remains fairly constant, and it is relatively equivalent to CO
blood pressure
- the force per unit area exerted on a vessel wall by the contained blood
- typically measured in the largest arteries near the heart
resistance
- opposite to flow, the amount of friction that blood encounters
- most friction is encountered well away from the heart (total peripheral resistance)
- sources of resistance: blood viscosity, vessel length, and vessel diameter
3 sources of friction
blood viscosity
blood vessel length
blood vessel diamater
blood viscosity
internal resistance to flow that exists in all fluids
- thickness of fluid
- greater viscosity = less movement
- blood viscosity is fairly constant - exception being the anemias and polycythemias
blood vessel length
longer vessel = greater resistances
blood vessel diameter
smaller diameter = greater resistance
Systolic pressure
blood is expelled into the aorta, the walls are stretched, aortic pressure peaks
120mmHg
Diastolic pressure
aortic walls recoil, aortic valves closes, and pressure drops
80mmHg
pulse pressure
difference in Systolic and diastolic pressure
MAP
the pressure that propels blood into the tissues - useful tool for determining tissue perfusion
- because diastole lasts longer than systole, MAP is not simply the halfway point between SBP and DBP
Why is it more difficult for blood to make its return trip to the heart via the veins?
Venous pressure is far less pulsatile – pressure gradients are less steep
Low venous pressure results from TPR – energy has been dissipated out
Despite valves, venous pressure is too low for adequate venous return
3 functional adaptations
- The muscular pump
- the respiratory pump
- the sympathetic vasoconstriction
The muscular pump
activity of the skeletal muscles surrounding the deep veins squeezes the veins and propels blood towards the heart
the respiratory pump
during breathing, pressure changes in the ventral body cavity propel blood towards the heart
Sympathetic vasoconstriction
during SNS firing, veins constrict, venous volume is reduced, and blood is pushed towards the heart
baroreceptors
pressure-sensitive mechanoreceptors that respond to changes in arterial pressure and stretch
inputs from baroreceptors are integrated into the cardiovascular center of the medulla oblongata
outputs travel via autonomic fibers to the heart and the vascular smooth muscle
slide 19-20
chemoreceptors slide 21
receptors that respond to changes in levels of CO 2+, H+, and O2 in the blood
slide 20-30
