Cardiovascular Physiology Lecture 6
Objective 1
- Understand how CO is distributed to various organs and how this process is regulated.
Distribution of blood in the body at rest
CO: 5.0 L/min (left)
Distributed based on needs of oxygen
At rest: 50% goes to Liver + digestive tract & kidneys
100% CO (Right) means all of the blood pumped from the heart is used
Blood flow through 4 identical vessels (A-D) is equal. Total flow into vessels equals total flow out.
If one of the vessels increases resistance, decrease flow, flow is diverted from that vessels and divided among the lower resistance vessels.
Regulation of Cardiovascular Function
Cardiovascular Control Center (CVCC): Goal: ensure adequate perfusion of the brain and hear by maintaining sufficient mean arterial pressure
Baroreceptor Reflex: baroreceptors in the carotid arteries and aorta continuously monitor pressure blood flowing to brain (carotid) and rest of body (aorta)
Objective 2
Understand how the autonomic nervous system regulates organ blood flow
Increase firing of baroreceptors in carotid arteries and aorta
Activates PNS to release ACh
Which decreases signal rate at SA node
Stimulates SNS to inactivate
Sensory neurons
Increase BP
CVCC n medulla oblongata
Decrease Sympathetic output (less NE)
Increase Parasympathetic output
B1 receptor: Ventricular myocardium
B1 receptor: SA node
a-receptor: Arteriolar smooth muscle
Vasodilation
Decrease Force of contraction
Decrease HR
Decrease peripheral resistance
Decrease Blood pressure
Decrease CO
Decrease BP
Decrease CO
Decrease BP
More ACh on muscarinic receptor
SA node
Decrease HR
Decrease CO
Decrease BP
Objective 3
- Know how specific local factors modulate arteriolar resistance and how this process impacts organ blood flow
Integration of resistance changes and CO
If one arteriole constricts (increased resistance in the arteriole) and Increased total peripheral resistance (TPR)
Increase TPR x CO -> Increased MAP
Baroreceptors fire -> baroreceptor reflex
Decreased CO
INCREASE TPR & DECREASE CO = MAP restored to NORMAL
MAP is proportional to CO x TPR
3 sites of action:
CO via HR and SV
Peripheral Resistance via arteriolar diameter
Blood Distribution/Venous Return via venous constriction
Objective 4
- Understand the relationship between blood volume and BP
Blood Volume and BP
Changes in blood volume affect BP
-Increased blood volume= increased BP
-Decreased blood volume= decreased BP
Homeostatic compensation:
- Increase blood volume: vasodilation and decreased CO (rapid) ; kidneys excrete excess water (slow) -> maintains normal BP
- Decreased blood volume: kidneys conserve fluid but cannot replace lost fluid
Increase Blood Volume
Leads to Increase BP
Fast Response:
Compensation by CV system
Vasodilation
Decrease CO
Decrease BP to normal
Slow response:
Compensation by Kidneys
Excretion of fluid in urine, decrease blood volume
Decrease BP to normal