Lecture 15: Circulation Flashcards
Mean systemic arterial P depends on which 2 factors?
- Cardiac output
- Total peripheral resistance aka systemic vascular resistance (SVR)
MAP = CO * TPR
How do systolic P, diastolic P, and TPR affect each other?
Note the difference between systolic/diastolic P (aorta P), EDV/ESV (heart vol.), and atrial/ventricular P (heart P)
Greater TPR means less runoff from the aorta -> greater diastolic pressure -> more vol. in aorta @ systole start -> increased systolic P
Thus an increase in HR/TPR increase diastolic P which increases systolic P.
Changes in compliance
Sympathetic stim. increases venomotor tone, which decreases compliance (same ΔV at greater ΔP)
Compliance decreases w/ age (stiffer vessels)
Why does increased HR increase diastolic aortic P?
Increased heart rate means less runoff time before next systole starts.
Processes of arterial stiffening
Fibrosis and calcification due to aging, hypertension, or metabolic/CT diseases in arteries
Distensibility
Aka specific compliance; normalized compliance for volume. Defines % vol. change per unit pressure change.
Distensibility * volume = compliance
Control of venous return
Main factor for venous return is the ΔP by vis a tergo (push from behind)
Gravitational influence on lateral P
Gravitational potential energy (ρgh) can be exchanged for hydrostatic/lateral P energy (P); 1 cm above/below PE = 0 line -> lose/gain 1 cm H2O pressure
Effects of gravity on the veins
Because the veins are distensible tubes, blood pools in them due to gravity like when we stand up. This results in a temporary reduction of venous return
How does the body help maintain venous return despite changing volume?
-One-way valves
-Venomotor tone (symp. stim.)
-Sk. muscle pumps
-Respiratory pump (inspiration decreases thoracic P, increases abdominal P to increase VR)
