Microcirculation Flashcards
What blood vessel group is considered the “stopcocks” of circulation?
Arterioles
Which vessel group is considered storage vessels?
Veins
Which vessel group takes part in exchange of gases, water, and solutes?
Capillaries
Which vessels are in between arterioles and capillaries?
Metarterioles
What is the role of metarterioles?
Sphincters that regulate flow into the capillaries.
Which group of vessels has the greatest cross-sectional area and surface area?
Capillaries
How do precapillary sphincters regulate blood flow?
If one area within the capillary bed requires blood, the other areas will constrict their sphincters to redirect blood flow.
Is capillary distribution the same from tissue to tissue?
No; some areas have more dense capillary beds.
Do true capillaries have smooth muscle?
No; they are incapable of active constriction or relaxation.
Why can capillaries withstand high intravascular pressures?
The Law of LaPlace. Radius is directly proportional to wall tension
What are the four methods of exchange across the capillary endothelium?
- Diffusion.
- Bulk Flow.
- Vesicular transport.
- Active transport
What substances are exchanged across the endothelium via diffusion?
Oxygen.
Carbon dioxide.
Lipid-soluble substances.
(from high to low concentration)
What substances are exchanged across the endothelium via bulk flow?
Water, electrolytes, small molecules.
via intercellular clefts or “pores”
What substances are exchanged across the endothelium via vesicular transport?
Proteins
larger molecules
What substances are exchanged across the endothelium via active transport?
Ions, glucose, amino acids.
low to high/across chemical gradients, must use ATP
What is the normal distribution of fluid in the body by liter?
3L Plasma.
11L Interstitial Fluid.
28L Intracellular Fluid
How many liters of extracellular fluid?
14L
What three things does interstitial volume depend on?
- Rate of filtration.
- Rate of reabsorption.
- Lymph flow
Which substance is the major determinmant of oncotic pressure?
Proteins
What is capillary hydrostatic pressure (Pc)?
Pressure in the capillary that forces fluid OUTWARD through the capillary membrane
What is interstitial fluid hydrostatic pressure (Pif)?
Normally a negative pressure which creates an outward force (from capillary to interstitial) for fluid
What factor creates a negative interstitial fluid hydrostatic pressure?
Lymphatics create negative pressure via pumping action
What is the more abundant plasma protein?
Albumin
How are proteins similar to sodium in the body?
Proteins want to pull fluid to themselves. Similar to salt (water follows salt), fluid follow proteins as well
What is plasma colloid osmotic pressure (Pie-p)?
aka- Plasma oncotic pressure.
Tends to cause inward (into capillary) movement of fluid.
What is interstitial fluid osmotic pressure (Pie-if)?
aka- Interstitial fluid oncotic pressure.
Tends to cause outward (out of capillary) movement of fluid
What is the Gibbs-Donnon effect?
Albumin exerts a greater osmotic force than can be accounted for solely on the basis of the number of molecules dissolved in the plasma. (Albumin attracts Na+ which attracts Cl-, which ultimately increases osmotic force and pulls fluid towards them).
Which two ions does albumin naturally attract?
Sodium (Na+) and Chloride (Cl-)
Does the Gibbs-Donnan effect increase or decrease osmotic/oncotic pressure (pulling power)?
Increases
What is filtration the sum of?
The sum of the hydrostatic and osmotic forces favor the net movement of water from the capillary to the interstitial space.
Does filtration or reabsorption happen more on the arterial side? Venule side?
Filtration- Arterial side
Reabsorption- venule side
What is reabsorption the sum of?
The sum of the hydrostatic and osmotic forces favors the net movement of water from the interstitial space to the capillary
What is the net driving force of filtration?
Net driving force >0
What is the net driving force of reabsorption?
Net driving force<0
Over time, is there a net overage or deficit of filtration and how does the body compensate for this?
There is an overage over time.
This is all equaled out because of the lymphatic system
Describe dehydration in how it correlates to filtration/reabsoprtion?
Decrease capillary hydrostatic pressure
Increase oncotic pressure.
More fluid being pulled from interstital
What is the Starling Forces equation?
Net driving force= (Pc-Pif) - rc(Pie-c-Pie-if)
What does the Starling equation conclude?
That there is more fluid going out of the capillary than going in
What does muscular contraction do to lymphatics?
Distortion of and opening of spaces.
What is the cause for the negative pressure in the interstitial fluid space?
Lymphatics
How is plasma filtrate returned via the lymphatic circulation?
- Tissue pressure.
- Intermittent skeletal muscle activity.
- Lymphatic vessel contraction.
- System of one-way valves
What does the lymphatic system return to circulation?
Protein.
Bacteria.
Fat.
Excess fluid
What four things can cause edema?
- Increased capillary hydrostatic pressure.
- Decrease plasma oncotic pressure.
- Increased capillary permeability.
- Lymphatic obstruction
What is an example of something that increases capillary hydrostatic pressure?
Heart failure (High CVP) or venous obstruction
What is an example of something that decreases plasma oncotic pressure?
Hypoproteinemia from malnutrition.
Or low albumin in elderly
What is an example of something that increases capillary permeability?
Proinflammatory mediators-
- Histamine
- Bradykinin
Damage to structural integrity of kidneys-
- trauma
- burns
- severe inflammation
What is an example of lymphatic obstruction?
Filariasis
