Arterial vessels

Question 1

What is the driving pressure for blood flow?

Answer 1

ABP

Question 2

Where is ABP determined?

Answer 2

In the elastic arteries

Question 3

Why is it important to prevent a pulsatile pressure in the arteries?

Answer 3

Rhythmic ejection from the ventricle produces a pulsatile pressure in the aorta and large arteries. In smaller elastic arteries dampen down the pulsatile flow to a continuous flow to ensure BP in maintained during diastole.

Question 4

What features allow the aorta to be compliant?

Answer 4

Large amounts of elastin, smooth msucle and collagen allows the diameter to increase with volume.

Question 5

How is blood moved through an artery?

Answer 5

During systole, the elastic walls expand and store energy. In diastole as the wall recoils it releases its energy to propel the blood forward. Expansion and recoil creates the driving pressure that is continuous.

Question 6

What does compliance mean in terms of the aorta?

Answer 6

As a change in aortic pressure occurs, the change in aortic volume is equivalent.

Question 7

What affect does age have on compliance?

Answer 7

Reduces with age so vessels become stiffer with less recoil. To eject the same amount of SV, SP must increase and DP must decrease = PP increases with age

Question 8

What is resistance to flow determined by?

Answer 8

Vessel length (L)
Viscosity / haematocrit (n)
Radius (r)

Question 9

Why does a small change in radius create a big change in flow?

Answer 9

Resistance is proportional to:
n.L / r^4
The power of 4 is the influencing factor

Question 10

How does flow change with radius?

Answer 10

Flow increases with radius

Question 11

What is flow?

Answer 11

The pressure difference at arteriole end of a vessel compared to the venous end and its vessel resistance.
Flow = Change in pressure (Pa-Pv) / Resistance

Question 12

What is laminar blood flow?

Answer 12

Normal, highly efficient flow that occurs in most vessels. The fastest flow is at the centre of the volume.

Question 13

What is turbulent flow and what does it produce?

Answer 13

Occurs when there is a high velocity of flow causing inefficient flow. Creates a vibration which is heard as a MURMUR or Korotkoff sound

Question 14

What effect does a stenosed valve have on flow?

Answer 14

Stenosis causes a reduced diameter but as the heart is still ejecting the same SV, to pass through the valve velocity must be increased. Velocity is increased by force of contraction and SP = turbulent flow

Question 15

How is a Korotkoff sound produced?

Answer 15

When taking BP, the cuff stops the flow but on release the flow is pulsatile and turbulent creating a korotkoff sound. Once fully released the flow returns to laminar.
The sound intensity increases between SP and DP as the cuff is released as the flow gets more turbulent.

Question 16

What does systolic pressure give an indication of and why?

Answer 16

SV and what is happening in the heart because SP is determined by:

• SV = any factor changing SV, affects SP
• Arterial compliance
• Ejection velocity
• DP of previous beat

Question 17

What does diastolic pressure give an indication of and why?

Answer 17

What is happening in the vessels as it is determined by:

• HR = At a high HR the pressure doesn’t have time to fall so DP increases
• Arteriolar resistance = determined by diameter

Question 18

What affects arteriolar diameter?

Answer 18

Vasoconstriction, arteriosclerosis = Increases TPR, DP but reduces flow
Vasodilation = Reduced TPR, DP, flow but decreases ABP

Question 19

What is vasodilation/contraction under the control of and why are these factors important?

Answer 19

Endothelial factors, local, central neural and hormonal mechanisms.
Allows dilation/constriction to one organ at a time or to have the opposite affect at another

Question 20

Which endothelial factors cause dilation?

Answer 20

NO reduces Ca in muscle resulting in relaxation. NO synthesis must be continuous due to its short half life. Synthesis is stimulated by:
ACh, ATP, Thrombin, SUBSTANCE P, BRADYKININ, Stress, bacterial endotoxin

Dilation can also be caused by PGE, PGI2, EDHF directly.

Question 21

What endothelial factors cause vasoconstriction?

Answer 21

Endothelins that increase Ca in cells for contraction. Endothelins synthesis is caused by Ang-II and trauma.

Constriction also caused by PGF and thromboxane directly

Question 22

What is the effect of local factors in vessel diameter?

Answer 22

Tissues regulate their own metabolic need to produce factors through increased metabolism for dilation. Allows for autoregulation except in heart, kidney and brain.

Question 23

What is functional hyperemia?

Answer 23

A proportional increase in blood flow to metabolic function

Question 24

What is reactive hyperemia?

Answer 24

A greater increase in flow causing metabolite build up.

Question 25

What is the myogenic vasoconstriction response?

Answer 25

Vasoconstriction within tissues in response to intravascular pressure in order to maintain flow.

Question 26

What is the central neural influence on vessels?

Answer 26

Vascular smooth muscle has a tonic vasomotor tone due to continuous sympathetic activity. This slight contraction allows room for dilation.
NAd acts at alpha1 receptors in skeletal muscle and vessels for constriction.
Increase sym = Constriction
Decrease sym = Dilation
No parasympathetic influence

Question 27

What NAd receptors are present in skeletal muscle?

Answer 27

Both alpha1 for constriction and beta1 for dilation but alpha dominates

Question 28

What is the hormonal influence over vessel diameter?

Answer 28

Circulating Ad binds weakly to alpha1 for constriction but is overcome by Ad binding to beta2 for dilation to increase flow.
ADH = vasoconstriciton when blood volume falls to maintain flow and increase water reabsorption.
AngII = vasoconstriction to increase BP and produces aldosterone for Na retention