Microcirculation

Question 1

Describe the range of size for arterioles vs meta-arterioles vs capillaries.

Answer 1

Arterioles: 5 - 100 micrometers

Meta-arterioles: 10 - 20 Micrometers

Capillaries: 5 - 10 micrometers

Question 2

What is responsible for the rhythmic oscillatory behavior seen in capillaries?

Answer 2

Contraction and relaxation of precapillary vessels

Question 3

How does transmural pressure affect vasomotion in capillaries?

Answer 3

• Increase in Transmural pressure causes contraction of terminal arterioles

Question 4

Compare contraction and vasomotion in Large arterioles and metarterioles vs terminal arterioles.

Answer 4

Lg Art + MetA —> Do not completely occlude blood flow when constricted

Terminal arterioles —> May arrest blood flow

Question 5

What is he role of PG12?

Answer 5

Prostacyclin: Relaxes vascular smooth muscles via increase in cAMP

Question 6

How is PG12 made?

Answer 6

• From Arachidonic acid

- PG12 Synthase

Question 7

How is PG12 released, and how does it work?

Answer 7

• Released by increase in shear stress caused by faster blood flow
• Inhibits platelet adherence to endothelium, platelet aggregation, and prevents intravascular clot formation
• relaxation in a secondary function

Question 8

Describe the function of NO and what causes it’s release.

Answer 8

• Released from endothelial cells stimulated by ACh, ATP, bradykinin, serotonin, substance P, histamine, or shear stress of blood flow
• Causes endothelium derived vasodilation
• No dilation in blood vessels lacking endothelium

Question 9

What is the functioning of Nitroprusside?

Answer 9

• Increases cGMP in vascular smooth muscle

* Not endothelium related

Question 10

What is the function of endothelin?

Answer 10

• Potential vasoconstrictor

- Affects Vascular the and BP

Question 11

What is Fick’s Law?

Answer 11

Describes diffusion of substances across a membrane

For Capillaries:

J = -PS(Co - Ci)

P = capillary permeability by the substance
S = capillary surface area
Co = concentration of the substance outside the capillary
Ci = concentration of the substance inside the capillary

Question 12

What is the actions of Bee stings?

Answer 12

Alters capillary permeability

Question 13

What 4 factors most influence capillary diffusion of O2?

Answer 13

1. Diffusion coefficient for O2
2. Capillary density and diffusion distances
3. Blood flow
4. Tissue O2 consumption: O
   2 supply of normal tissue at rest + during activity is not limited by diffusion or by the number of open capillaries

Question 14

How do capillaries in kidneys, intestines, and lover differ from others such a s skeletal?

Answer 14

Kidney/intestine: More porous and very permeable

Liver: Very porous and discontinuous endothelium (fenestrated)