Chapter 17: Local and Humoral Control of
Tissue Blood Flow
Guyton and Hall, Textbook of Medical Physiology, 12 edition
Local Control in Response to Tissue Needs
1. Delivery of oxygen to the tissues
2. Delivery of other nutrients, such as glucose,
amino acids, and fatty acids
3. Removal of carbon dioxide from the tissues
4. Removal of hydrogen ions from the tissues
5. Maintenance of proper concentrations of
other ions in the tissues
6. Transport of various hormones and other
substances to the different tissues
Variations in Blood Flow in Different Tissues and Organs
Tissue or Organ
% of Cardiac
Output
ml/min
Ml/min per 100
grams tissue wt.
Brain
14
700
50
Heart
4
200
7
Bronchi
2
100
25
Kidneys
22
1100
360
Liver
27
1350
95
Muscle
15
750
4
Bone
5
250
3
Skin
6
300
3
Thyroid gland
1
50
160
Adrenal glands
0.5
25
300
Other tissues
3.5
175
1.3
100.0
5000
Total
Table 17.1 Blood flow to different organs and tissues under basal conditions
Mechanism of Blood Flow Control
• Acute Control- achieved by rapid changes in local
vasodilation or vasoconstriction of the arterioles,
metarterioles, precapillary sphincters; occurs in
seconds to minutes
• Long Term Control- slow, controlled changes that
occur over a period of days, weeks, or even
months; due to an increase or decrease in the
physical sizes or number of blood vessels
supplying the tissues
Blood Flow Control (cont.)
• Acute Control
a. Effect of tissue metabolism on local blood flow
Fig. 17.1 Effect of increasing rate of metabolism on tissue blood flow
Blood Flow Control (cont.)
• Acute Control
b. Regulation when oxygen availability changes
Fig. 17.2 Effect of decreasing arterial oxygen saturation on blood flow
Blood Flow Control (cont.)
• Acute Control
c. Two theories for when either (a) or (b) occurs
1. Vasodilator theory
2. Oxygen lack theory
Blood Flow Control (cont.)
• Vasodilator Theory
a. The greater the rate of metabolism or the less oxygen
available, the greater the rate of formation of
vasodilators
b. Examples: adenosine, carbon dioxide, adenosine
phosphate, histamine, potassium ions, hydrogen ions
Blood Flow Control (cont.)
• Oxygen Lack Theory
a. In the absence of oxygen or other nutrients, the blood
vessels simply relax and therefore naturally dilate
Fig. 17.3 Diagram of a tissue unit area for explanation of acute local control
of blood flow.
Blood Flow Control (cont.)
• Special Examples of Acute “Metabolic” Control
a. Reactive hyperemia: increase flow after a temporary
block
b. Active hyperemia: increase flow due to activity
Blood Flow Control (cont.)
• Autoregulation
a. Metabolic theory
b. Myogenic theory
Fig. 17.4 Effect of different levels of arterial pressure on
blood flow through a muscle.
Blood Flow Control (cont.)
• Special Mechanisms
a. Kidneys: tubuloglomerular feedback
b. Brain: concentrations of carbon dioxide and hydrogen ions
c. Skin: closely linked to the regulation of body temperature
Blood Flow Control (cont.)
• Endothelial-Derived Relaxing or Constricting Factors
a. Nitric oxide-vasodilator from healthy endothelial cells
b. Endothelin-vasoconstrictor from damaged endothelial cells
Blood Flow Control (cont.)
• Long Term Regulation
a. Changes in tissue vascularity (i.e. angiogenesis)
b. Role of oxygen
c. Role of vascular endothelial growth factor
•
Vascularity is Determined by Maximum Blood Flow, Not
by Average Need
•
Development of Collateral Circulation
Humoral Control of the Circulation
• Vasoconstrictor Agents
a. Norepinephrine and epinephrine
b. Angiotensin II
c. Vasopressin
Humoral Control of the Circulation
• Vasodilator Agents
a. Bradykinin
b. Histamine
Humoral Control of the Circulation
• Vascular Control by Ions and Other Chemical Factors
a. Vasoconstriction: increase in Ca ion concentration,
carbon dioxide concentration increase in the brain, slight
decrease in H ions
b. Vasodilation: increases in K ion, Mg ion concentrations,
anions (acetate and citrate), H ions on arterioles