7 - Vascular physiology

Question 1

Propose a design for a medical device that can help compensate for a drop in blood pressure when moving from a lying to a standing position

Answer 1

• Passive stepping and Functional Electrical Stimulation (FES)
• Apply electrical current to cause muscle to contract, increase blood flow

Other ideas
(Stimulate muscle pump in the legs, Vasopressin, Epinephrine / sympathetic triggers, Blood volume, Compression stockings)

Question 2

What are the three main factors that affect blood flow?

Answer 2

• Pressure gradient
• Vascular resistance
• Blood vessel radius

Question 3

What are the reconditioning organs?

Answer 3

• Digestive organs
• Kidneys
• Skin

-> Adjust extra blood according to metabolic needs to achieve homeostasis

Question 4

What’s the equation for rate of blood flow?

Answer 4

The flow rate is directly proportional to pressure gradient and inversely proportional to vascular resistance

Question 5

What is pressure gradient?

Answer 5

Pressure diff between beginning and end of a vessel

Question 6

What is vascular resistance? What does is depend on

Answer 6

A measure of the opposition of blood flow through a vessel
Depends on:
- blood viscosity, vessel length, vessel radium

Vessel’s radius has biggest impact on resistance:

Question 7

What makes up the vascular tree?

Answer 7

• Arteries
• Arterioles (smaller branches of arteries)
• Capillaries (smaller branches of arterioles)
• Venules (smaller veins, formed when capillaries rejoin)
• Veins

Question 8

What are some structural differences between veins and arteries?

Answer 8

Arteries:
- Thick, highly elastic walls

Veins:
- Thin-walled

Similarities: Large radii, several hundred

Question 9

Arteries

What are the two functions of the arteries?

Answer 9

• Serve as rapid-transit passageways for blood from heart to organs (large radius = little resistance)
• Act as a pressure reservoir to provide driving force for blood when heart is relaxing
  (collagen and elastin fibres give strength and elasticity)

Question 10

Arteries -

What are the two kinds of arterial pressure?

Answer 10

1. Systolic pressure
   
   • Peak pressure exerted by ejected blood against vessel walls during cardiac systole (~120 mm Hg)
2. Diastolic pressure
   - Minimum pressure in arteries when blood is draining off into downstream vessles (~80 mm Hg)

Question 11

Arteries -

What is Pulse pressure?

Answer 11

The pressure diff between systolic and diastolic pressure

ex: if blood pressure is 120/80, pulse pressure is 40 mm Hg

Question 12

What is meant arterial pressure? How do you calculate mean arterial pressure?

Answer 12

• Average pressure driving blood forward into tissues throughout cardiac cycle
  
  • Mean arterial pressure = diastolic pressure + 1/3 pulse pressure

ex: 120/80:
80 mm Hg + 1/3(40) = 93 mm Hg

Question 13

How can you measure blood pressure?

Answer 13

• Using a sphygmomanometer or Korotkoff sounds

Question 14

Describe this diagram.

Answer 14

This is showing blood pressure within different blood vessels.
Left ventricle:
- 0 - 120 mm Hg
Large arteries: 
- 80 - 120 mm Hg

Pressure
Arterioles>Capillaries>Venules and veins

Question 15

Arterioles

What are the main role of the Arterioles?

Answer 15

• Distribute cardiac output among systemic organs, depending on body’s momentary needs
• Help regulate arterial blood pressure

Question 16

Arterioles

How do arterioles adjust arteriolar resistance?

Answer 16

1. Vasoconstriction: Narrowing of a vessel
2. Vasodilation: Enlargement in circumference and radius of vessel
   - > Results from relaxation of smooth muscle layer (decreases resistance and increases flow)

Smooth muscle has many sympathetic nerve fibres (sensitive to many chemical changes)

Question 17

What are the factors responsible for vascular tone?

Answer 17

(tone: degree of constriction)
1. Myogenic activity of smooth muscle (activity produced by muscle w/o any external stimulation)
2. Sympathetic stimulation

Question 18

What determines the amount of CO (cardiac output) that is delivered to each organ?

Answer 18

• The number and vascular tone of arterioles in that area

Question 19

What are the local chemical and physical influences on arteriolar radius?
(intrinsic controls)

Answer 19

Chemical:

• Metabolic change
• Histamine change

Physical:

• Local application of heat or cold
• Chemical response to shear stress
• Myogenic response to stretch

Question 20

What extrinsic controls affect arterioles radius?

Answer 20

• Sympathetic stimulation of smooth muscle adjusts the total peripheral resistance, vasoconstrictor effect
• Chemical:
  1. Vasopressin (maintains water balance by regulating amount of water retained by kidneys)
  2. Agiotensin II (part of renin-angiotensin-aldosterine system, regulates body salt balance, have vasoconstrictor effect)
  3. Epinephrine and norepinephrine (hormones that reinforce sympathetic nervous system)

**local controls override sympathetic vasoconstriction for organ-specific regulation

Question 21

What are the main factors affecting arteriolar radius?

Answer 21

1. Metabolic changes in Oxygen (Intrinsic control)

2. Sympathetic activity that affects vasoconstrictor effect (Extrinsic control)

Question 22

What is the role of the medullary cardiovascular control contre?

Answer 22

(Located in medulla of the brain stem)

• Influence of Epinephrine and Norepinephrine (sympathetic stimulation of adrenal medulla)
• Influence of vasopressin and agiotensin II (fluid balance)

Question 23

How does increased sympathetic activity affect blood pressure?

Answer 23

• Leads to arteriolar vasoconstriction
• When blood vessel volume is lowered, blood flow is also reduced. At the same time, the resistance or force of blood flow is raised. This causes higher blood pressure.