12.5 C Flashcards
What are the four major functions of microcirculation?
- filtration/reabsorption
- regulation of vascular smooth muscle activity
- production of endothelial-derive factors
- regulation of leukocyte trafficking
Which blood vessels don’t have a smooth muscle ring around them?
capillaries and post-capillary venules
When arterioles dilate, what happens to blood flow and pressure?
both increase
When arterioles dilate, what happens to filtration of fluid across the capillaries?
it increases
Arteriole tone plays a key role in regulating what two things?
organ blood flow and filtration
What are precapillary sphincters?
bands of smooth muscle at the beginning of capillaries which open or close to permit blood flow
Opening and closing of precapillary sphincters has what effect on vascular resistance within an organ?
negligible, resistance within an organ is dependent on arterioles
Post-capillary venules are an important site of what?
- leukocyte trafficking
- increased vascular permeability
What are arteriovenous shunts?
shunts for blood to flow from an arteriole directly to a venule, skipping the capillaries
Flow through AV shunts is important for what?
temperature control
How does local vasodilation of arterioles affect the amount of filtration?
it increases capillary flow and pressure, thus increasing filtration
Local dilation or constriction of arterioles within one organ does not usually change TPR or MAP with what exception?
skeletal muscle
Increased venous pressure does what to capillary pressure?
it increases capillary pressure
How does right sided heart failure lead to systemic edema?
it increases venous pressure, increasing capillary pressure, increasing the rate of filtration
What problems can lead to decreased oncotic pressure?
- liver disease impairs production of plasma proteins
- kidney disease leads to increased excretion of plasma proteins
- protein malnutrition impairs plasma protein production
When oncotic pressure is decreased, the clinical result is what?
edema
What are intercellular clefts?
gaps between endothelial cells, the width of which determines vascular permeability
How are intercellular clefts opened?
an increase in calcium (possibly due to histamine) causes contraction of actin/myosin in endothelial cells
What might trigger a calcium influx into endothelial cells?
histamine
Precapillary sphincters respond to changes in what?
oxygen levels
How do precapillary sphincters respond to changes in tissue oxygen levels?
they open in response to locally produced dilators which accumulate in tissue when blood flow is not sufficient to meet metabolic demand
Opening of precapillary sphincters has what effect on filtration?
increases total surface area for exchange and increases filtration
What is vasomotion?
the opening and closing of precapillary sphincters
What is bulk flow?
a mechanism using pressure differences for moving substance over longer distances than diffusion is efficient for
Why is edema problematic?
- it increases interstitial volume, increasing the distance nutrients must diffuse between capillaries and cells
- it also increases interstitial pressure, compressing venules, increasing venule resistance and decreasing blood flow
Calcium has what effect on vascular tone?
it causes vasoconstriction
Through what mechanism are cytosolic calcium concentrations decreased in endothelial cells?
Ca ATPase pumps
How does vascular smooth muscle contraction differ from skeletal muscle contraction?
the rate is slower allowing vascular smooth muscle to maintain sustained vascular tone
What accounts for the sustained tone of vascular smooth muscle?
a lower Ca ATPase activity
Changes in cytosolic calcium are more dependent on what source of calcium, intracellular stores or influx of extracellular ions?
extracellular ions
Why do calcium channel antagonists function to treat some forms of hypertension?
because they limit smooth muscle contraction by limiting the influx of extracellular calcium ions
How does NE action on vascular smooth muscle cause contraction?
it stimulates alpha-1 receptors which opens calcium channels and increases calcium influx
What is the effect and mechanism of effect of epinephrine on vascular smooth muscle in skeletal muscle?
- circulating epinephrine binds beta-2 receptors in skeletal muscle
- this increases activity of the calcium-ATPase pump
What experiment demonstrated that endothelial cells are more than a passive barrier?
- aortic rings with and without endothelial cells placed in a bath of ACh
- with endothelium, the smooth muscle had less contractile force
Endothelial-derived relaxing factor is another name for what compound?
nitric oxide
How does endothelial cell damage lead to ischemia?
damaged endothelial cells produce less NO, so vasoconstriction predominates leading to ischemia and tissue injury
NItric oxide synthase activity in endothelial cells is triggered by what?
calcium influx into endothelial cells
An increase in calcium levels in endothelial cells causes ____ while an increase in vascular smooth muscle cells causes _____.
vasodilation; vasoconstriction
What is L-NAME?
a competitive inhibitor of NO synthase that limits NO production by endothelial cells
How does NO protect endothelial cells?
by limiting leukocyte adhesion and thereby limiting leukocyte secretion of substances toxic to endothelial cells
L-NAME has what effects on vascular tone and vascular permeability?
since it inhibits NO production, it will increase vasoconstriction and leukocyte adhesion/permeability
How does NO function in the vascular system?
- vasodilator
- inhibit leukocyte and platelet adherence
- maintains normal low vascular permeability
- antioxidant
What two substance produced by endothelial cells inhibit aggregation of platelets?
NO and prostacyclin
Endothelin-1 production occurs in response to what?
in response to endothelial cell damage
What is the effect of endothelin-1?
increase calcium concentrations in smooth muscle causing sustained vasoconstriction
What is unique about the vasoconstriction caused by endothelin-1?
it is sustained for a very long time (hours)
A classic example of ischemia/reperfusion is what medical procedure?
organ transplant
The ROS created during ischemic reperfusion have what effects?
- direct damage to endothelial cells
- inactivation of NO
- increase formation of endothelin-1
What is the harm associated with giving an IV of NO?
it would vasodilate the whole system and causing a decrease in TPR and therefor shock
What is the harm associated with administering NO locally during an ischemic attack?
it would vasodilate the local arterioles, increasing pressure in the capillaries and cause edema
