Exam #2: Capillary Circulation Flashcards
What is the function of the capillaries?
Exchange of fluids, nutrients, electrolytes, hormones, and waste between blood & interstitial fluid
Describe the structure of capillaries. What structural features of capillaries facilitate diffusion?
- V. thin walled structures with holes (pores) that allow for passage of water and small molecules
- High total surface area
- Slow flow velocity
What is bulk flow?
Flux across the capillary membrane
How is blood flow regulated through capillaries? What determines this regulation?
- 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
What is vasomotion?
Intermittent blood flow through capillaries due to contraction of meta-arterioles and pre-capillary sphincters
What regulates blood flow in skeletal muscle? Which of these is primary?
Primarily oxygen, but also:
- CO2
- pH
Decreased O2, Increased CO2, decreased pH all cause vasodilation and increase flow
What regulates blood flow in the brain? Which of these is primary?
Primarily, CO2, but also:
- O2
- Adenosine
Increased CO2, Decreased O2, and Increased adenoseine will all increase flow
What regulates blood flow in the heart? Which of these is primary?
Primarily, adenosine, but also:
- O2
- CO2
- pH
- Decreased O2, Increased CO2, and decreased pH will increase flow
What is the effect of epinephrine on circulation?
Vasoconstriction & Vasodilation
What is the effect of NE on circulation?
Vasoconstriction via Alpha-1 receptors
What is the effect of DA on circulation?
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.
What is the effect of Histamine on circulation?
Vasodilation
What is the effect of ACh on circulation?
Vasodilation
What is the effect of Angiotensin II on circulation?
Vasoconstriction
What is the effect of Kinins on circulation?
Vasodilation
What is the effect of ADH/Vasopressin on circulation?
Vasoconstriction
What is the effect of Adenosine, adenine, & nucleotides on circulation?
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.
What is the effect of Hypoexmia on circulation?
Vasodilation
What is the effect of increased H+ & K+ on circulation?
Vasodilation
What is the effect of Hypercapnia on circulation?
Vasodilation
What is the effect of Krebs cycle intermediates circulation?
Vasodilation
What is the effect of Endothelin on circulation?
Vasoconstriction
What is the effect of NO (EDRF) on circulation?
Vasodilation
What factors affect the exchange of substances across a membrane
Diffusion
- Lipid-solubility
- Water-solubility
- Molecular size
- Permeability
- Concentration difference
What is hydrostatic pressure?
Pressure exerted by the fluid itself
What is the colloid osmotic fluid?
Pressure exerted by the “stuff” in the fluid
What is capillary hydrostatic pressure (Pc)?
- Fluid pressure within capillaries
- tends to move fluid OUT
What is tissue/ interstitial hydrostatic pressure (PIF)?
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
What is capillary oncotic pressure?
- 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
How is net pressure calculated? Write the equation.
N/A
What happens when there is a decrease in plasma protein concentration?
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
What happens when there is an increase in capillary hydrostatic pressure?
Net filtration
This can happen in a situation of venous blockage
What is the challenge to decreased capillary hydrostatic pressure?
Oncotic pressure will increase, bringing fluid back into the circulation
What can increase capillary hydrostatic pressure?
Standing
Heart failure
Venous thrombus
What can decreased capilllary oncotic pressure?
Nephrotic Syndrome
Starvation
Pregnancy
Liver Disease (low serum protein production)
