Cardiovascular Physiology Lecture 6

Objective 1

  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

  1. 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

  1. 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:

  1. Increase blood volume: vasodilation and decreased CO (rapid) ; kidneys excrete excess water (slow) -> maintains normal BP
  2. 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