Circulatory 4 Flashcards
Precapillary resistance vessels
Arterioles, metarterioles, and precapillary sphincters
Exchange vessels
Capillaries
Postcapillary resistance vessels
Venules
Five characteristics of capillary blood flow
- Low velocity
- Vasomotion
- Pressure gradients
- Non-uniform
- Rouleaux formation
Transcapillary fluid exchange
Movement of fluid, exchange of nutrients, out of and into the capillary
Factors governing transcapillary fluid exchange
- Plasma oncotic pressure
- Capillary hydrostatic pressure
- Tissue oncotic pressure
- Interstitial hydrostatic pressure
Plasma oncotic pressure
An osmotic pressure exerted by substances found int he plasma, primarily plasma proteins
Capillary hydrostatic pressure
Mean capillary blood pressure
Tissue oncotic pressure
An osmotic pressure exerted by substances dissolved in the intersitium, such as proteins. Counterpart to plasma oncotic pressure
Interstitial hydrostatic pressure
Hydrostatic pressure caused by the volume of fluid within the interstitium
Determinants of plasma oncotic pressure
The key factor that holds fluid within the capillaries is the osmotic pressure of the plasma proteins
Most clinically relevant protein
Albumin
Why is that protein the most clinically relevant?
Albumin exerts a greater osmotic force than can be accounted for solely on the basis of the number of molecules dissolved in a unit volume of plasma (contributes a disproportionately large percentage of the plasma oncotic pressure)
With what does albumin interact?
Negatively charged ions, such as chloride, resulting in the retention of more sodium within the vascular space
Breakdown of proteins in plasma
Albumin - 51%
Globulin - 17%
Fibrinogen - 4%
Others - 28%
Determinants of capillary hydrostatic pressure: bathtub analogy
Amount of water filling a tub (capillary hydrostatic pressure) is determined by the resistance to water flow entering the tub through the faucet (precapillary resistance to arterial flow) and resistance to water flow leaving the tub through the drain (post-capillary resistance to venous flow)
What determinant plays the biggest part in capillary hydrostatic pressure?
Venous pressure; there is significant pre-capillary resistance on the arterial side, and little post-capillary resistance
Pre/post-capillary resistance ratio
Increase it: decrease capillary hydrostatic pressure
Decrease it: increase capillary hydrostatic pressure
Prostacyclins
Increase cAMP to phosphorylate myosin light chain kinase, inhibiting MLCK. Decreased phosphorylation of MLC, less actin-myosin interaction
VASODILATION
Endothelium-derived relaxing factor
Vasodilation, consisting of primarily nitric oxide
Nitric oxide
Acts via cGMP/PKG to phosphorylate MLCK, inhibiting MLCK, decreasing MLC phosphorylation and thereby decreasing actin-myosin interaction.
VASODILATION
Endothelin
ET receptors on vascular smooth muscle cells activate PLC to release IP3, which releases intracellular calcium
VASOCONSTRICTION
Metabolites
Adenosine, hydrogen ion, carbon dioxide, and potassium ion
Cause relaxation and vasodilation
Function of the lymphatic system
Collect and return interstitial fluid to the circulatory system
Structure of lymphatic vessels
Unidirectional flow of plasma and protein
Valvular, like veins, but have thinner walls
Non-fenestrated, no muscle
Where do lymphatic vessels eventually end up?
In large collecting vessels that return the lymphatic fluid to the subclavian veins
Three factors governing lymph flow
Amount of capillary filtration
Skeletal muscular activity
Lymphatic unidirectional valves
Edema
An accumulation of excess fluid within the interstitial space
Precipitating factors of peripheral edema
- Reduction in plasma protein concentration
- Increase in capillary hydrostatic pressure
- Increased permeability of capillary membrane
- Lymphatic obstruction
Possible causes of edema
- Congestive heart failure
- Mechanical obstruction of venous return
- Renal disease - loss of protein
- Liver disease - lack of protein
- Burn - increases capillary permeability
