1. Unit Four: The Circulation
Chapter 17: Local and Humoral Control of Tissue Blood Flow
Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Local Control in Response to Tissue Needs
Delivery of oxygen to the tissues
Delivery of other nutrients, such as glucose, amino acids, and fatty acids
Removal of carbon dioxide from the tissues
Removal of hydrogen ions from the tissues
Maintenance of proper concentrations of other ions in the tissues
Transport of various hormones and other substances to the different tissues

3. 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
Bone 5
250 3
Skin 6
300
Thyroid gland 1
160
Adrenal glands
0.5
Other tissues
3.5
175
1.3
Total
100.0
5000
Table Blood flow to different organs and tissues under basal conditions

4. 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

5. Blood Flow Control (cont.)
Acute Control
Effect of tissue metabolism on local blood flow
Fig Effect of increasing rate of metabolism on tissue blood flow

6. Blood Flow Control (cont.)
Acute Control
b. Regulation when oxygen availability changes
Fig Effect of decreasing arterial oxygen saturation on blood flow

7. Blood Flow Control (cont.)
Acute Control
Two theories for when either (a) or (b) occurs
Vasodilator theory
Oxygen lack theory

8. Blood Flow Control (cont.)
Vasodilator Theory
The greater the rate of metabolism or the less oxygen
available, the greater the rate of formation of
vasodilators
Examples: adenosine, carbon dioxide, adenosine
phosphate, histamine, potassium ions, hydrogen ions

9. Blood Flow Control (cont.)
Oxygen Lack Theory
In the absence of oxygen or other nutrients, the blood
vessels simply relax and therefore naturally dilate
Fig Diagram of a tissue unit area for explanation of acute local control
of blood flow.

10. Blood Flow Control (cont.)
Special Examples of Acute “Metabolic” Control
Reactive hyperemia: increase flow after a temporary
block
b. Active hyperemia: increase flow due to activity

11. Blood Flow Control (cont.)
Autoregulation
Metabolic theory
Myogenic theory
Fig Effect of different levels of arterial pressure on
blood flow through a muscle.

12. Blood Flow Control (cont.)
Special Mechanisms
Kidneys: tubuloglomerular feedback
Brain: concentrations of carbon dioxide and hydrogen ions
Skin: closely linked to the regulation of body temperature

13. Blood Flow Control (cont.)
Endothelial-Derived Relaxing or Constricting Factors
Nitric oxide-vasodilator from healthy endothelial cells
Endothelin-vasoconstrictor from damaged endothelial cells

14. Blood Flow Control (cont.)
Long Term Regulation
Changes in tissue vascularity (i.e. angiogenesis)
Role of oxygen
Role of vascular endothelial growth factor
Vascularity is Determined by Maximum Blood Flow, Not
by Average Need
Development of Collateral Circulation

15. Humoral Control of the Circulation
Vasoconstrictor Agents
Norepinephrine and epinephrine
Angiotensin II
Vasopressin

16. Humoral Control of the Circulation
Vasodilator Agents
Bradykinin
Histamine

17. Humoral Control of the Circulation
Vascular Control by Ions and Other Chemical Factors
Vasoconstriction: increase in Ca ion concentration,
carbon dioxide concentration increase in the brain, slight
decrease in H ions
Vasodilation: increases in K ion, Mg ion concentrations,
anions (acetate and citrate), H ions on arterioles