Pressure and Flow in Arteries and Veins Flashcards
What is measurement of arteriolar pressure done by?
Auscultation of Karotkoff sounds using spygomanometer and stephoscope
What are the advantages of auscultation of Korotkoff sounds using sphygomomanometer and stephoscope?
Non-invasive
Cheap
What are disadvantages of auscultation of Korotkoff sounds using sphymomanometer and stephoscope?
Accuracy
Discontinuous
Needs care
What do elastic arteries act as?
Pressure reservoirs that damp down pressure variants
What is the pressure wave affected by?
Stroke volume
Velocity of ejection
Elasticity of arteries
Total peripheral resistance
What is normal arteriolar pressure?
120/80mmHg
How does normal arteriolar pressure change with age?
Increases
How does pressure and flow change from arteries to veins?
Pressure falls through the vascular tree:
Small drop through arteries (from about 95 to 90mmHg)
Large drop through arterioles (from about 90 to 40mmHg)
Pressure is already low when blood gets to capillaries
Leaves a small pressure difference pushing blood back through the veins (about 20 to 5mmHg)
Why is there only a small drop in pressure through arteries?
Low resistance conduit
Why is there a large drop through arterioles?
Resistance vessels
Why is it important that the blood pressure is low once it reaches capillaries?
They are thin walled
What is the small pressure difference that pushes blood back through the veins called?
Systemic filling pressure
What is the systemic filling pressure?
Small pressure pushing blood back through the veins
How does pulmonary circulation pressure compare to systemic?
1/5 the size
What is the velocity of blood flow related to?
Total cross section (fastest in aorta and vena cava, slowest in capillaries)
Where is blood flow the fastest?
Aorta and vena cava
Where is blood flow the slowest?
Capillaries
How does velocity of blood flow relate to total cross sectional area?
Greater the total cross sectional area the smaller the velocity
What can central venous pressure be estimated by?
Jugular collapse
How does the blood pressure drop as it goes through arteries?
Drops from 95 to 90mmHg
How does blood pressure drop as it goes through arterioles?
From 90 to 40mmHg
What is the value os systemic filling pressure?
20 to 5mmHg
What is the pressure like in veins?
Low so difference in pressure driving blood back to heart is low
What are the complications of veins being distensible and collapsible?
Flow is affected by external influences such as:
Gravity
Skeletal muscle pump
Respiratory pump
Venomotor tone
Systemic filling pressure
Why do external factors affect flow in veins?
They are distensible and collapsible
What are examples of external factors that affect flow in veins?
Gravity
Skeletal muscle pump
Respiratory pump
Venomotor tone
Systemic filling pressure
What can gravity cause in terms of flow through veins?
Venous distension in legs
Venous collapse in neck
What does venous distension in legs cause?
Decreases EDV
Decreases preload
Decreases stroke volume
Decreases cardiac output
Decreases mean arteriolar pressure
What can the venous collapse in the neck be used to estimate?
Central venous pressure
What are examples of skeletal muscle pump impacting venous flow?
Rhythmic vs static exercise
Hot guardsmen
Deep vein thrombosis
Varicose veins
What is venomotor tone?
State of contraction of the smooth muscles surrounding the venules and veins
What is the state of contraction of the smooth muscles surrounding the venules and veins valled?
Venomotor tone
How does gravity impact the flow of blood through veins?
Greater pressure at the bottom of the body
What does clotting involve?
Formation of a platelet plug
Formation of a fibrin clot
What is converted into fibrin?
Fibrinogen
What is fibrinogen converted into?
Fibrin
What catalyses the reaction of fibrinogen to fibrin?
Thrombin
What is blood in the capillaries in danger of due to travelling so slow?
Clotting
What works hard to prevent blood clotting through capillaries?
Epithelium
What are some anti-clotting mechanisms of the epithelium?
Stops blood contacting collagen
Produces prostacyclin and NO
Produces tissue factor pathway inhibitor (TFPI)
Expresses thrombomodulin
Expresses heparin
Secretes tissue plasminogen activator
How does stopping blood contacting collagen prevent clots?
No platelet aggregation
How does producing prostacyclin and NO prevent clots?
Both inhibit platelet aggregation
How does producing tissue factor pathway inhibitor prevent clots?
Stops thombin production
What does TFPI stand for?
Tissue factor pathway inhibitor
How does expressing thrombomodulin prevent clots?
Binds to thrombin and inactivates it
How does expressing heparin prevent clots?
Inactivates thrombin
How does secreting plasminogen activator prevent clots?
Catalyses the reaction of plasminogen to plasmin, and plasmin digests the clot
