Vascular Control - Nord Flashcards
What is difference in function of arterioles and veins when it comes to vascular control?
Arteriolar = distribute cardiac output among tissues with different needs Venous = Regulate the distribution of blood volume and cardiac filling
Differences between smooth msuce and skeletal/cardiac muscle?
- contract/relax more slowly
- can change activity based on AP’s or resting mem. potential
- can change contraction without mem. potential changes
- Maintains tension for long periods at low energy cost
- can be stretch-activated
Vascular smooth muscle still contracts by cross-bridges between actin/myosin, but there are some differences… What are a couple?
- Lack striations (because not arranged in regular repeating sarcomeres)
- No Z-lines, instead dense bodies
- Actin filaments are longer
Contractility of VSM (vasc. smooth musc.) is still Ca-mediated, but it’s a little wacky. Give a quick summary of how it uses Ca in a different way.
- Ca first complexes with calmodulin
- This activates MLCK(myosin light-chain kinase)
- MLC phosphorylated
- Enables cross-bridge formation and cycling
- VSM contractility depends on net MLC phosphorylation
The only 3 things you need to know about membrane potentials in VSM:
- Ca - is for depolarization
- K - is for repolarization
- Stretch sensitive
We now know that Ca is what mediates VSM contraction downstream, but what are the two ways that Ca is able to enter the cell in the 1st place?
1) Voltage-activated Ca-channels
2) Pharmacomechanical coupling
- g-prot.coupled receptor that affects both the Ca channel itself and the production of PL-C and release of more Ca from the sarco-retic.
Arteries have a continuos basal tone, but they respond to external influences. These can be local, neural, and hormonal.
Summarize how some of the local factors influence arteriolar tone:
LOCAL:
-Metabolic
Low O2, High CO2, H, K, and adenosine stimulate vasodilation
-Endothelial Cells
Produce NO to stimulate cGMP
Prostaglandins/Thromboxane can vasodilate or vasoconstrict
Leukotriens/Histamine/Bradykinin
-Transmural Pressure
Arterioles respond in the opposite direction to changes in transmural pressure
Arteries have a continuos basal tone, but they respond to external influences. These can be local, neural, and hormonal.
Summarize how some of the neural factors influence arteriolar tone:
NEURAL - The most important means of reflex control of vasculature
- Release NE in response to AP frequency
- Increased nerve activity = increased vasoconstriction
- Tonic firing can increase tone to be above basal tone
Arteries have a continuos basal tone, but they respond to external influences. These can be local, neural, and hormonal.
Summarize how some of the hormonal factors influence arteriolar tone:
(Include catecholamines and their receptors, vasopressin, and angiotensin II)
HORMONAL
- Epinephrine/Noreprinephrine released into blood when SNS is activated
- Beta-1 receptors increase HR/contractility
- Alpha-1 receptors cause vasoconstriction
- Vascular Beta-2 receptors are more sensitive to epinphrine than Alpha-1 ——> that means that with moderate epi levels there is vasodilation, but with high epi levels there is vasoconstriction
- Vasopressin - acts on renal collecting ducts to retain water in response to low volume or high fluid osmolarity - AND a potent vasoconstrictor
- Angiotensin II - regulates aldosterone release from the adrenal cortex to control Na balance - AND a potent vasoconstrictor
Please explain the major differences between venous tone and arteriolar tone:
Venous
- very little basal tone (usually very dilated)
- Thin walls make them more susceptible to external physical influences (skeletal muscle pump)
- Metabolites do not cause vasodilation
Please explain the major similarities between venous tone and arteriolar tone:
Their reflex influences are the same. Sympathetic constrictor nerves release NE to cause constriction
What is the most important influence on coronary blood flow?
Myocardial O2 consumption is most important - it trumps SNS
How is vascular control different in skeletal muscle between resting and active states?
Rest - somewhat by alterations in SNS
Exercise - local metabolite control is MOST important
How is vascular control changed in the brain?
- important to stay conscious, so we want blood to brain all the time
- Regulated almost entirely by local mechanisms
How is vascular control changed in the visceral organs? (splanchnic blood flow)
- Sympathetic neural activity is VERY important
- local metabolites play a role in GI motility, secretion, etc.
