Circulation Flashcards
(6 cards)
Explain the physical principles, recall Poiseuille’s equation, explain the effect of gravity, explain the control of capillary blood flow, and explain the concept of vascular capacitance and compliance
Capacity of the veins can dilate and control the amount of blood more easily than arteries
Compliance; is the reltionship between the transmural pressure and the vessel volume and depends on vessel elasticity
therefore; venous compliance is 10 to 20 times greater than arterial complience at low pressures
Increasing smooth muscle contraction can help increase venous volume and increase venous pressure
Hydrostatic pressure increases in the legs as a result of gravity but not on the arms
The effect of gravity is on the distensible veins in the leg and the blood within them –> which may finaly lead to fainting
People that stand many hours still and have a high risk of fainting are told to move their toes which will promote muscle contraction which will help blood movement inside the veins ( veins also have valves to help with directional flow)
Respiratory pump; when you breath the diaphragm ccontracts and increases negative inter-thoracic pressure –> decreasing the the blood pressure and easing blood towards the heart
Incompetent valves; cause
varicose veins
Prolonged elevation of venous pressure may cause oedema
Explain the physical principles, structure and function of the circulation
key; pressure gradient–> generated by the heart bood flows high pressure point to low pressure point. ( blood pressure drives the circulation)
Circulation is responsible for;
- transport blood around the body
- regulate temperature
There are higly branched structure–> cappilaries need to be 10 μm from each cell ( one cell thick–> difffusion)
arteries–> arterioles–> cappillaries –> venules–> veins ( flow of blood)
ΔP= Q X R
Blood pressure (MAP)= Cardiac output (CO)- resistance (PVR)
The relation is an approximation because it assumes;
- Steady flow ( which is not the case due to the intermittent pumping of the heart)
- rigid vessels
- right atrial pressure is negligible
Physiologically regulation of flow is achieved by variation in resistance in the vessels while blood pressure remains relatively constant
–> pressure falls across the circulation due to viscous ( frictional ) pressure losses ( small artirioles are more resistance to flow)
—> Blood is distributed based on the importance of each organ
Rest; cardiac output = 5 L/ min
Exercise; cardiac output 20L/min
Resistance+ blood flow
How does blood flow ?
Laminar flow; Linear flow
- Velocity of the fluids is constant at any one point
- blood flows faster to the center of the lumen due to adhesive forces
Turbulent flow; ( less healthy)
- erratic flow of blood forming eddys ( prone to pooling)
- often associated with pathophysiological changes
shear rate; gradient of the velocity profile at any point
shear stress= shear rate x viscosity
–> important since it explains how endothelial ( govern laminar flow) cells work
Laminar shear stress;
- High shear stress ( healthy flow)
- promotes endothelial cell survival and quiescence
- cells are aligned in derection of flow
- seecretions are performed more easily helping with vasodilation and anticoagulation
Disturbed shear stress;
- Turbulent flow ( or low shear stress)
- Promotes endothelial proliferation
- promotes endothelial apoptosis and shape change
- Promotes vasocontriction, coagulation and platelet aggregation
- age related ( older more tuburlant flow )
Therefore, enothelial lining relies on high shear stress which relies on laminar flow
Blood pressure
Blood pressure is usually measured on upper arm
slow deflation of cuff causes turbulent flow which can be heard with a stethoscope.
Diastolic (DBP)+ systolic blood pressure (SBP)–> will see in labs
Pulse pressure (PP)= SBP-DBP
Mean artiriol pressure= DBP + 1/3 PP
Recall the Law of Laplace (vascular) and explain the relationship to blood flow
Vascular aneurysms increase radius of the vessels
this means the for the SAME internal pressure, the inward force exerted by the mascular wall must INCREASE
—> However because the muscle fibers are weakened the force cannot be produced and the aneurysm will continue to expand untill it RUPTURES
Treatment; mesh around aorta to maintain the same configuration
life threateninig
