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Dyck Lecture 13

QuestionAnswer
What is the driving force for blood flow? pressure
Relationship between flow resistance and pressure.
An increase in cardiac output leads too… An increase of volume of blood contained in the aorta and an increase in mean arterial pressure when TPR remains the same.
A constant cardiac output leads to... an increase in the volume of blood contained in the aorta and an increase in mean arterial pressure when TPR increases.
Characteristics of arteries Thick elastic arterial walls, Low compliance, Expand as blood enters arteries during systole, Recoil during diastole.
Arterial Blood Pressure varies with… Cardiac cycle
Systolic Blood Pressure= maximum pressure, When the ventricles contract, sending blood into the arteries
Diastolic blood pressure = minimum pressure, When the heart relaxes between beats - not zero due to elastic recoil of arterial wall
Korotkoff Sounds When cuff is completely inflated, artery is completely compressed= No sounds. When artery is opening and closing= Thudding sounds. When artery is completely open= No sounds.
Which blood pressure reading would concern you more? 150/75 or 120/105? 120/105 because heart has to overcome a higher pressure to pump again.
Arterioles are the prime controllers of… blood pressure – main site of TPR regulation
Arterioles serve as a gatekeeper to… the capillary beds
Vasoconstriction (smooth muscle contraction) Decrease radius à increase resistance
Vasodilation (smooth muscle relaxation) Increase radius à decrease resistance
Changes associated with increased metabolic activity generally cause… local vasodilation Ex. Carbon dioxide, Hydrogen ions, Adenosine (breakdown of ATP) – blocked by caffeine, Potassium
Changes associated with decreased metabolic activity generally cause… local vasoconstriction ex.Oxygen
Vasodilators due to inflammation Nitric oxide, Bradykinin (stimulates NO release), Histamine (stimulates NO release).
Effect of heat on arteriole diameter Increases blood flow
Effect of cold on arteriole diameter Decreases blood flow
When norepinephrine binds to a adrenergic receptors Produces vasoconstriction in most vascular beds, Increases TPR … and increases MAP.
When epinephrine binds to a and b2 receptors Vasoconstriction in most vascular beds (due to a2 ) Maintain/increase TPR à maintain blood pressure, Vasodilation in skeletal and cardiac muscle vascular beds (due to b2 ), Decrease TPR à decrease blood pressure, Increased by caffeine
Vasopression or ADH Secreted by posterior pituitary, Increases water reabsorption by kidneys, Retains water volume (minimizes loss),Vasoconstriction: therefore, ­ TPR
Endocrine control of arteriolar radius Angiotensin II Synthesized from angiotensinogen (precursor):
angiotensinogen renin angiotensin I ACE(ACE inhibitors are a common medication for treating hypertension) angiotensin II. Action: Vasoconstriction, Increases TPR
Baroreceptors (aortic arch, carotid body) – respond to stretch. Communicate with Cardiovascular Control Center (medula oblongata) to decrease SNS / increase PNS output.
So what happens if the normal responses to a decrease in MAP aren’t successful ? i.e. severe hypotension Blood flow to the brain decreases, and you faint … with the hopeful outcome of restoring cerebral blood flow!
Cardiac output increases how much during exercise 5x during exercise! Up to 8x in elite athletes!!
Regulation of blood flow and pressure during aerobic exercise Dilation of vessels to skeletal muscle and heart increases blood flow to muscles,Constriction of vessels to GI tract and kidneys decreases blood flow to these organs. Dilating vessels in the muscle decreases the TPR
Resistance exercise (e.g. weightlifting) can cause… dramatic increases in blood pressure. Reason? Holding your breath – increases intrathoracic pressure during the lift – called the “Valsalva maneover”
Created by: year1
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