Part II: The Systemic Circulation Flashcards
Define transmural pressure
pressure tending to distend (or collapse) a vessel
Define mean arterial pressure
average pressure existing in the aorta and proximal arterial system during one cardiac cycle
What is the formula for mean arterial pressure?
diastolic pressure + 1/3 pulse pressure
Name the two physiological factors responsible for determining mean arterial pressure
1) cardiac output
2) peripheral resistance (responsible for pressurizing the system)
Name the two physical factors that determine mean arterial pressure
1) arterial blood volume
2) arterial compliance
Of the two physiological factors determining MAP, which primarily affects SYSTOLIC pressure?
cardiac output
regulated by autonomic nervous system
Of the two physiological factors determining MAP, which primarily affects DIASTOLIC pressure?
peripheral resistance
also regulated by ANS but local regulation can override nervous control
What is responsible for maintaining arterial blood pressure moment to moment via the ANS?
baroreceptor reflex
What happens to pulse pressure as you exercise and what is responsible for that change?
It widens because the systolic pressure increases and diastolic stays the same
What happens to mean arterial pressure as you exercise?
it increases
Name a few diseases that decrease blood pressure?
1) congestive heart failure
2) infarction
3) bradycardia
4) sepsis
What does arterial compliance affect? Systolic or diastolic pressure?
Both! Inversely related to systolic (decrease compliance, increase systolic) and directly related to diastolic
What factors can alter arterial compliance?
age, blood volume, sympathetic tone, pregnancy
Do highly compliant vessels have a larger or small pulse pressure?
SMALL
the lower the compliance, the higher the systolic so that generates a larger pulse pressure
What are the 3 mechanisms of local control on peripheral resistance?
1) Myogenic response
2) endothelium-mediated regulation (EDRF, NO, endothelin)
3) local metabolic changes (O2, CO2, metabolites)
What are the 3 global mechanisms of modulating peripheral resistance?
1) baroreceptor reflex
2) hormonal effects
3) sympathetic activity
What effect does the sympathetic system have on blood vessel diameter?
vasoconstrict
increasing venous return in the veins and total peripheral resistance in the arteries
What role does the sympathetic system play during exercise?
1) increases heart rate
2) increases contractility of the heart
OVERALL INCREASES CARDIAC OUTPUT
What three sections of the body are unaffected by sympathetic vasoconstriction?
1) cerebral
2) pulmonic
3) cardiac
there are no alpha receptors there to receive input
What molecules are involved in metabolic vasodilation?
1) K+
2) adenosine
3) CO2
4) H+
What is the importance of metabolic vasodilation?
It is what allows both skeletal muscle AND the heart to vasodilate during exercise. This lowers vascular resistance to these areas and increases blood flow 15-20 fold
How does metabolic vasodilation actually occur if there is sympathetic tone going on in the background, vasoconstricting arteries?
because local mechanisms ALWAYS override global, hormonal/neural input
How do the heart and skeletal muscle ensure increased oxygen flow during exercise?
Skeletal muscle can pull more O2 from hemoglobin (myoglobin has stronger affinity)
Heart can only get more O2 by increasing blood flow to it. It CANNOT increase O2 extraction during exercise
What happens to venous return during exercise?
It increases because of venoconstriction (want to get more blood back to the heart)
What happens to systolic pressure as you exercise?
It sharply goes up, primarily because of the increase in stroke volume
(also causes pulse pressure to increase)
