Overview Flashcards
What is the main site of TPR?
arterioles
What contains most blood under resting conditions?
veins
What is another way MAP can be calculated (other than 2xdiastolic+systolic/3)?
MAP = DBP + 1/3 difference between SBP and DBP
What does vasoconstriction do to TPR and MAP?
increase
What is resistance to blood flow directly proportional to?
blood viscosity and length of blood vessel
How is resistance to blood flow related to radius of blood vessel?
inversely to the power of 4
Are vascular smooth muscles controlled by extrinsic or intrinsic factors?
Both
What is it called when the vascular smooth muscles are partially constricted at rest?
vasomotor tone
What is vasomotor tone caused by?
by tonic discharge of sympathetic nerves resulting in continuous release of noradernaline
What will increased sympathetic discharge do?
it will increase the vasomotor tone resulting in vasoconstriction
“There is no significant parasympathetic innervation of arterial smooth muscles” - what are the exceptions to this?
exceptions are penis and clitoris
What hormone is involved in exstrinsic control of vascular smooth muscle?
adrenaline
Adrenaline acting on what receptors causes vasoconstriction?
alpha
Adrenaline acting on what receptors causes vasodilation?
beta
Where are alpha receptors predominant?
skin, gut, kidney arterioles
Where are beta receptors predominant?
cardiac and skeletal muscle arterioles
What helps with strategic redistribution of blood e.g. during exercise?
Extrinsic stimulation of vascular smooth muscle by adrenaline
What other hormones affect vascular smooth muscle?
Angiotensin II: causes vasoconstriction Antidiuretic hormone (vasopressin): causes vasoconstriction
Which type, intrinsic or extrinsic, can override the control of the other?
instrinsic
Which metabolic changes cause vasodilation?
Decreased local PO2
Increased local PCO2
Increased local [H+] (decreased pH)
Increased extra-cellular [K+]
Increased osmolality of ECF
Adenosine release (from ATP)
Which local chemical (humural agents) cause vasodilation?
Histamine
Prostaglandins
Bradykinin
Nitric Oxide (NO)
Which chemical agent is continuously released by endothelial cells of arteries and arterioles from the amino acid L-arginine?
Nitric Oxide
Does NO have a short or long half life?
short (a few seconds)
What causes activation of nitric oxide synthase?
increased FLOW and release of calcium in vascular endothelial cells
where does nitric oxide diffuse and what does it do there?
from the vascular endothelium into the adjacent smooth muscle cells where it activates the formation of cGMP that serves as a second messenger for signalling smooth muscle relaxation
Which humoral agents cause vasoconstriction?
Serotonin
Thromboxane A2
Leukotrienes
Endothelin
What stimulates production of endothelin?
angiotensin II and vasopressin
Does the cold cause vasoconstriction or vasodilation?
Vasoconstriction
What is the myogenic response to stress and what tissues is it important in?
If MAP rises resistance vessels automatically constrict to limit flow
If MAP falls resistance vessels automatically dilate to increase flow
Important in tissues like brain and kidneys
What does “shear stress” response mean?
Dilatation of arterioles causes sheer stress in the arteries upstream to make them dilate. This increases blood flow to metabolically active tissues
What does increased venomotor tone do to venous return?
increases
What does contraction of muscles aid?
venous return
Does sympathetic stimulation cause slop of pacemaker cells to increase or decrease?
increase
What does sympathetic nerve contraction do to Frank Starling Curve?
shifted to LEFT
