Exam #2: Capillary Circulation

Question 1

What is the function of the capillaries?

Answer 1

Exchange of fluids, nutrients, electrolytes, hormones, and waste between blood & interstitial fluid

Question 2

Describe the structure of capillaries. What structural features of capillaries facilitate diffusion?

Answer 2

• V. thin walled structures with holes (pores) that allow for passage of water and small molecules
• High total surface area
• Slow flow velocity

Question 3

What is bulk flow?

Answer 3

Flux across the capillary membrane

Question 4

How is blood flow regulated through capillaries? What determines this regulation?

Answer 4

• Upstream contraction of meta-arterioles and precapillary sphincters regulates capillary blood flow.
• The primary controlling parameters are metabolites within the local environment

Note that precapillary sphincters can close completely, where arterioles will remain partially patent. Also, opening precapillary sphincters increases the total surface area of diffusion & decreases velocity of flow

Question 5

What is vasomotion?

Answer 5

Intermittent blood flow through capillaries due to contraction of meta-arterioles and pre-capillary sphincters

Question 6

What regulates blood flow in skeletal muscle? Which of these is primary?

Answer 6

Primarily oxygen, but also:

• CO2
• pH

Decreased O2, Increased CO2, decreased pH all cause vasodilation and increase flow

Question 7

What regulates blood flow in the brain? Which of these is primary?

Answer 7

Primarily, CO2, but also:

• O2
• Adenosine

Increased CO2, Decreased O2, and Increased adenoseine will all increase flow

Question 8

What regulates blood flow in the heart? Which of these is primary?

Answer 8

Primarily, adenosine, but also:

• O2
• CO2
• pH
• Decreased O2, Increased CO2, and decreased pH will increase flow

Question 9

What is the effect of epinephrine on circulation?

Answer 9

Vasoconstriction & Vasodilation

Question 10

What is the effect of NE on circulation?

Answer 10

Vasoconstriction via Alpha-1 receptors

Question 11

What is the effect of DA on circulation?

Answer 11

Vasoconstriction & Vasodilation

*Note that at low doses DA will cause a decrease in resistance & selective perfusion of the kidney. At higher doses, DA will activate Alpha-1 receptors and cause vasoconstriction.

Question 12

What is the effect of Histamine on circulation?

Answer 12

Vasodilation

Question 13

What is the effect of ACh on circulation?

Answer 13

Vasodilation

Question 14

What is the effect of Angiotensin II on circulation?

Answer 14

Vasoconstriction

Question 15

What is the effect of Kinins on circulation?

Answer 15

Vasodilation

Question 16

What is the effect of ADH/Vasopressin on circulation?

Answer 16

Vasoconstriction

Question 17

What is the effect of Adenosine, adenine, & nucleotides on circulation?

Answer 17

Vasoconstriction & Vasodilation

*Note that adenosine binds A2 receptors in the heart & other tissues, leading to vasodilation. In the kidney however, adenosine binds A1 receptors, leading to vasoconstriction.

Question 18

What is the effect of Hypoexmia on circulation?

Answer 18

Vasodilation

Question 19

What is the effect of increased H+ & K+ on circulation?

Answer 19

Vasodilation

Question 20

What is the effect of Hypercapnia on circulation?

Answer 20

Vasodilation

Question 21

What is the effect of Krebs cycle intermediates circulation?

Answer 21

Vasodilation

Question 22

What is the effect of Endothelin on circulation?

Answer 22

Vasoconstriction

Question 23

What is the effect of NO (EDRF) on circulation?

Answer 23

Vasodilation

Question 24

What factors affect the exchange of substances across a membrane

Answer 24

Diffusion

• Lipid-solubility
• Water-solubility
• Molecular size
• Permeability
• Concentration difference

Question 25

What is hydrostatic pressure?

Answer 25

Pressure exerted by the fluid itself

Question 26

What is the colloid osmotic fluid?

Answer 26

Pressure exerted by the “stuff” in the fluid

Question 27

What is capillary hydrostatic pressure (Pc)?

Answer 27

• Fluid pressure within capillaries

- tends to move fluid OUT

Question 28

What is tissue/ interstitial hydrostatic pressure (PIF)?

Answer 28

Fluid pressure exerted by the fluid in the tissue (should be lower than capillary hydrostatic pressure)

*Note that this is kept low by the function of the lymphatic system

Question 29

What is capillary oncotic pressure?

Answer 29

• The “pull” from the solutes within the capillary
• This is an inward pressure
• Increased solute concentration will move fluid into the capillary
• Conversely, increased solute concentration outside of the capillary will pull fluid out of the blood

Question 30

How is net pressure calculated? Write the equation.

Answer 30

N/A

Question 31

What happens when there is a decrease in plasma protein concentration?

Answer 31

Decreased capillary oncotic pressure, leading to an increase in filtration i.e. edema

This can be caused by a decrease in precapillary resistance, increasing the movement of solutes out of the circulation

Question 32

What happens when there is an increase in capillary hydrostatic pressure?

Answer 32

Net filtration

This can happen in a situation of venous blockage

Question 33

What is the challenge to decreased capillary hydrostatic pressure?

Answer 33

Oncotic pressure will increase, bringing fluid back into the circulation

Question 34

What can increase capillary hydrostatic pressure?

Answer 34

Standing
Heart failure
Venous thrombus

Question 35

What can decreased capilllary oncotic pressure?

Answer 35

Nephrotic Syndrome
Starvation
Pregnancy
Liver Disease (low serum protein production)