Regulation of Organ Blood Flow
Mark T Ziolo, PhD, FAHA
Associate Professor, Physiology & Cell Biology
019 Hamilton Hall
614-688-7905
ziolo.1@osu.edu
Objectives
• Describe the regulation of organ blood flow by myogenic
regulation and autoregulation (intrinsic tone, neuronal
influence, local or metabolic influence, hormonal
influence)
• Describe active and reactive hyperemia
Detailed Objectives
 Understand the myogenic regulation and the
autoregulation of blood flow
 Know the mechanism of myogenic regulation
 Know how the different factors (intrinsic tone, neuronal
influence, local (metabolic) influence, and hormonal
influence) responsible for autoregulation regulate blood
flow
 Understand the role of active and reactive hyperemia
 Understand how control of flow is different between
organs with strong local (metabolic) control of arterial
tone and organs with strong neuronal control of arterial
tone
References
• Mohrman DE, Heller LJ. Cardiovascular Physiology
Seventh Edition. Lange Medical Books/McGraw-Hill
Publishers, 2010.
• Berne RM, Levy MN. Cardiovascular Physiology Sixth
Edition. Mosby-Year Book, Inc., 2010.
• MediaPhys 3.0. An Introduction to Human Physiology.
The McGraw-Hill Publishers, 2010.
Myogenic Regulation
Myogenic Regulation
Vital Organ
Myogenic Regulation
Vital Organ
Pressure
Myogenic Regulation
Vital Organ
Pressure
Myogenic Regulation
Autoregulation
Myogenic Regulation
 Smooth muscle contracts in response to an increase in
transmural pressure
 Smooth muscle relaxes in response to a decrease in
transmural pressure
Autoregulation- with ↑ metabolic demand
Muscle
Autoregulation- with ↑ metabolic demand
Muscle
Working
Autoregulation- with ↑ metabolic demand
Muscle
Working
Autoregulation
 Factors Responsible:




Intrinsic tone
Neuronal Influences
Local Influences
Hormonal Influences
Intrinsic Tone
 Arterioles remain partially constricted even when all
external influences are removed
 This baseline is what external influences adjust
Neuronal Influences
 Fibers innervate arterioles in ALL systemic
organs
 These fibers release NE proportionally to their
electrical activity

Acts via a-adrenergic receptors
 Increases vascular tone

Via decrease membrane potential & increase in AP
frequency
 Parasympathetic may act on the external
genitalia for vasodilation
Local (metabolic) Influences
 Smooth muscle is exposed to the chemical composition
of the interstitial fluid of the organ
 These substances reflect the balance of the organ’s
metabolic activity and blood supply


O2*, CO2, H+, K+, lactic acid, phosphate
adenosine
* Pulmonary circulation
Local (metabolic) Influences
Release proportional to
tissue metabolism
Tissue
Cells
Vasodilator factors
Removal rate proportional
to blood flow
Blood Flow
Other Local Influences
 Influences from Endothelial cells

Nitric oxide, endothelin
 Other influences

Prostaglandins (COX pathway)


Histamine


Some vasodilate, others vasoconstrict
Vasodilation and increases permeability (swelling)
Bradykinin

Vasodilation via nitric oxide
Hyperemia
Active Hyperemia
• Increased blood flow caused by enhanced tissue activity
• Metabolic (local) influence
Reactive Hyperemia
• Increased blood flow after removal of occlusion
• Metabolic (local) influence AND myogenic regulation
• Reduced intravascular pressure
• Decreased stretch
Reactive Hyperemia
Metabolic vs Neuronal Control
Hormonal Influences
 Under normal circumstances play a minor role in
regulating blood flow
 Following hormones are vasoconstrictors



NE and E (hemorrhagic shock)
ADH (hemorrhage)
Angiotensin II (hypertension?)
Summary
 Myogenic regulation maintains a constant organ blood flow (at constant
levels of tissue metabolism) with changes in perfusion pressure.
 Changes in transmural pressure will change smooth muscle contraction
 Autoregulation is maintaining constant organ blood flow which occurs
via myogenic regulation
 Intrinsic tone is the remaining constriction of the arterioles when all
external influences are removed. This is what the other influences adjust
 Neuronal tone is activation of the sympathetic fibers increasing vascular
tone (i.e., vasoconstriction)
 Local influence is the degree of smooth muscle contraction dependent
upon the chemical composition of the interstitial fluid of the organ
 Hormonal influence plays a minor role in regulating blood flow except
under various physiological (e.g., exercise) and/or pathological stresses
Summary, cont
 Active hyperemia is increased blood flow caused by
enhanced tissue activity due to local (metabolic)
influence
 Reactive hyperemia is increased blood flow after removal
of occlusion due to local (metabolic) influence and
myogenic regulation
 Blood flow to some organs such as heart and skeletal
muscle has a higher responsiveness to metabolic than
neuronal control. Blood flow to other organs such as GI
tract, spleen, pancreas, and liver has a higher
responsiveness to neuronal than metabolic control
Quiz Questions
 Provide 3-5 multiple choice questions w/ feedback to
each answer (correct or incorrect).
Thank you for completing this module
Questions- mark.ziolo@osumc.edu
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