Flashcards in Hemodynamics Deck (40):
1
Pressure generated is a result of...
Ventricle contraction
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Veins
Lower blood pressure tan arteries
Accommodate increased volume
Steady flow, opposite branching patters than arteries
Blood reservoirs
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Venules
Small veins collecting blood from capillaries
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Venous Sinuses
No smooth muscle
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Varicose Veins
Twisted, dilated, superficial veins
Caused by leaky venous valves
Allow back flow and pooling of blood
Deeper veins not susceptible because of surrounding muscles
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Portal System
Blood flows through two consecutive capillary networks before returning to the heart
Example: hepatic portal system between liver and intestines
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Anastomoses
Points where two blood vessels merge
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Arteriovenous Shunt
Artery flows directly into vein
Shunt changes direction of blood flow
Used to decrease heat loss in the cold
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Venous Anastomosis
Most common blockage
Less serious
Alternative drainage of organs
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Arterial Anastomosis
Collateral circulation (coronary)
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Blood Distribution
60% of blood volume at rest is in systemic veins and venules
15% of blood volume is in arteries and arterioles
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Venous Constriction
Constriction of veins during increased muscular activity or during hemorrhage
Increased Venoconstriction = Increased Preload, Stroke Volume, and Cardiac Output
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Capillary Exchange
Only occurs across capillary walls between blood and surrounding tissues
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Three Routes of Capillary Exchange
Intercellular clefts
Fenestrations
Through cytoplasm
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Mechanisms Involved in Capillary Exchange
Diffusion
Transcytosis
Filtration and reabsorption
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Filtration
Blood pressure drives fluid out of capillary
High on arterial end, low on venous end
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Reabsorption
Colloid osmotic pressure draws fluid into capillary
Same on both ends
Results from plasma proteins
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Oncotic Pressure
Net colloid osmotic pressure
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Dynamics of Capillary Exchange
Provides tissue with nutrients
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Net Filtration
At arterial end of capillaries is about 20l/day
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Net Reabsorption
At venous end of capillaries is about 17l/day
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Starling's Law of the Capillaries
Volume of the fluid and solutes reabsorbed is almost as large as the volume filtered
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Net Filtration Pressure
Determines whether fluids leave or enter capillaries
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Net Outward Pressure
10 mm Hg at arterial end
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Net Inward Pressure
9 mm Hg at venous end
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Edema
An abnormal increase in interstitial fluid if filtration exceeds reabsorption
Not noticeable until 30% above normal
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Result of Excess Filtration
Increased blood pressure
Increased permeability of capillaries allows plasma proteins to escape
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Result of Inadequate Reabsorption
Decreased concentration of plasma proteins lowers blood colloid osmotic pressure
Inadequate synthesis or loss from liver disease, burns, malnutrition, or kidney disease
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Causes of Edema
Poor venous return
Kidney failure
Histamine makes capillaries more permeable
Obstructed lymphatic drainage
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Consequences of Edema
Circulatory shock
Tissue necrosis
Pulmonary edema
Cerebral edema
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Vasoconstriction
Sympathetic stimulation of arterial alpha receptors
Decreases diameter
Increases blood pressure
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Vasodilation
Sympathetic stimulation of beta receptors
Increases diameter
Promotes blood flow
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Factors Affecting Circulation
Pressure differences that drive the blood flow
Resistance to flow
Venous return
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Blood Flow
Amount of blood flowing through a vessel in a given time (ml/min)
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Perfusion
Rate of blood flow per given mass of tissue (ml/min/g)
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Hemodynamics
Physical principles of blood flow based on pressure and resistance
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Flow Equation
DeltaP/R
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Resistance Equation
1/r^4
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Blood Flow Equation
r^4
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