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