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Cardiovascular Physiology 1 (Vasculature system (Pressure drop (Aorta…
Cardiovascular Physiology 1
Vasculature system
Microcirculation
Venous system
Low pressure system
One-way valves
Arterial system
High pressure system
More collagen: less compliant than veins
Blood vessels
Walls of arteries and veins have 3 layers
(Autoregulation)
Tunica intima
Longitudinal smooth muscles
Inner lining in direct contact with blood
Has an active role in vessel-related activities
Tunica media
Circular smooth muscle
Chiefly composed of smooth muscle that regulates the diameter of vessel lumen
Tunica externa
Single layer of endothelial cells
Helps anchor vessel to surrounding tissue through the use of elastic and collagen fibers
Blood
Functions
Transport (O2 and nutrients to tissue, remove CO2 and waste)
Homeostasis (distribution of water, solutes and heat)
Protection
Components
Cells
Erythrocytes (RBC)
Production of RBC regulated by erythropoietin
Leukocytes (WBC)
Granulocytes, lymphocytes, neutrophils, eosinophils and basophils
Platelets
Clotting effect
Blood coagulation
Platelet aggregation
Plasma
Water
Solutes
Proteins
Pressure drop
Aorta
Pulse dampening and distribution
Large arteries
Distribution of arterial blood
Small arteries
Distribution and resistance
Arterioles
Resistance (pressure & flow regulation)
Capillaries
Exchange
Venules
Exchange, collection, and capacitance
Veins
Capacitance function (blood volume)
Vena cava
Collection of venous blood
Hemodynamics
v = Q/A
For a tube of constant flow rate, velocity in the smaller diameter > velocity in the larger diameter
Conservation of mass
(ρVA)1 = (ρVA)2 = constant
Dynamic pressure
Pdyn = (ρv^2)/2
Static pressure
Pstat ∝ 1/v
At lower velocity (v), Pstat will be higher
Bernoulli's equation
Assumptions
Laminar
Incompressible fluid
Streamline
Steady flow
P + (1/2)ρv^2 + ρgh = C
Poiseuille's law
Q = (π (Pi-P0) r^4)/ 8μl
R = 8μl / πr^4
Turbulence flow in heart
Murmur
Physical basis for functional cardiac murmurs
(1) Reduced viscosity of blood in anemia
(2) High flow velocities associated with the high cardiac output that usually prevails in anemic patients
Can lead to shearing of blood
Formation of thrombi (blood clots)
Boundary layer
As long as there is
flow
along a
rigid body
Velocity gradient within B.L. due to larger speed at the top
No rotation outside B.L. but inside B.L. --> fluid particle in B.L. will shear
Shear stress on vessel wall
product of fluid viscosity and the velocity gradient
τ = 4μQ / πr^3
Shear stress is directly proportional to the flow rate and viscosity of the fluid
Influences
permeability of the vessel walls due to large molecules
synthetic activity of endothelial cells
Integrity of the formed elements in blood, and blood coagulation
effective stimulus for the release of nitrous oxide (NO) from vascular endothelial cells; NO is a potent vasodilator
Low shear stress
Large molecules e.g. lipids and monocytes will infiltrate
leads to occlusion of blood vessels
Flow separation
due to adverse pressure gradient
Recirculation bubble
Hemodynamics origin of cardiovascular disease
Flow separation --> low oscillatory ESS at recirculation bubble --> endothelial cells more permeable to lipid
Atherosclerosis
highly focal and occurs mainly at artery
bifurcations
, branch points and regions of
high curvature
that result in complex blood-flow patterns
site specific
at regions of low WSS e.g. coronary artery
chronic inflammatory
Endothelium are living cells that align themselves in direction of blood flow.
Elastin: Stretch
Collagen: Stiffness
Influence vessel compliance