Pressure and Flow in Arteries and Veins

Question 1

Define systolic pressure

Answer 1

the maximum blood pressure during contraction of the ventricles

Question 2

Define diastolic pressure

Answer 2

the minimum pressure recorded just prior to the next contraction

Question 3

Define pulse pressure

Answer 3

the difference between systolic and diastolic blood pressures

Question 4

Describe the mechanisms that prevent blood clotting in vessels

Answer 4

Stops blood contacting collagen
- No platelet aggregation
Produces prostacyclin and NO
- Both inhibit platelet aggregation

Produces tissue factor pathway inhibitor (TFPI)
- Stops thrombin production

Expresses thrombomodulin
- Binds thrombin and inactivates it

Expresses heparin
- Also inactivates thrombin
Secretes tissue plasminogen activator (t-PA)
- Plasminogen → plasmin and digests clot

Question 5

Indicate the factors affecting pressure and flow in veins

Answer 5

GRAVITY
- DOES NOT affect driving pressure from arteries to veins
- causes venous distension in legs
- ↓ CO, ↓ MAP
- Can be used to estimate central venous pressure

SKELETAL MUSCLE PUMP
- Rhythmic contraction increases venous return and EDV
- Significance:
~ Rhythmic vs. static exercise
~ Deep vein thrombosis

RESPIRATORY PUMP
- Increased respiratory rate and depth increase venous return and EDV

VENOMOTOR TONE
- Is the state of contraction of the smooth muscle surrounding the venules and veins
- Mobilises capacitance and increases EDV

SYSTEMIC FILLING PRESSURE
- Pressure created by ventricles and transmitted through vascular tree to the veins

Question 6

What is pressure wave affected by?

Answer 6

• Stroke volume
• Velocity of ejection
• Elasticity of arteries
• Total peripheral resistance

Question 7

Illustrate the changes in the aortic pressure wave as it passes through the vascular tree.

Answer 7

PRESSURE FALLS THROUGHOUT THE VASCULAR TREE
- Small drop through arteries = low resistance conduit
- Large drop through arterioles = resistance vessels

Question 8

Illustrate the changes in blood velocity and total cross-sectional area of the vessels
throughout the vasculature.

Answer 8

Velocity is related to total cross-sectional area
- Fastest in aorta and vena cava, slowest in capillaries

Question 9

Explain the origin of the Korotkoff sounds and their use

Answer 9

Arterial walls
Korotkoff sounds are generated when a blood pressure cuff changes the flow of blood through the artery.