regulation of organ blood flow- ppt-2

Regulation of Organ Blood Flow

Mark T Ziolo, PhD, FAHAAssociate Professor, Physiology & Cell Biology019 Hamilton Hall614-688-7905ziolo.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

Vital Organ

Myogenic Regulation

Vital OrganPressure

Myogenic Regulation

Vital OrganPressure

Myogenic Regulation

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

Muscle

Autoregulation- with ↑ metabolic demand

Muscle Working

Autoregulation- with ↑ metabolic demand

Muscle Working

Autoregulation- with ↑ metabolic demand

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 to that organ O2*, CO2, H+, K+, lactic acid, phosphate adenosine

* Pulmonary circulation

TissueCells

Blood Flow

Release proportional totissue metabolism

Vasodilator factorsRemoval rate proportional

to blood flow

Local (metabolic) Influences

Other Local Influences

Influences from Endothelial cells Nitric oxide, endothelin

Other influences Prostaglandins (COX pathway)

Some vasodilate, others vasoconstrict Histamine

Vasodilation and increases permeability (swelling) Bradykinin

Vasodilation via nitric oxide

Hyperemia

• Increased blood flow caused by enhanced tissue activity• Metabolic (local) influence

Active Hyperemia

• Increased blood flow after removal of occlusion• Metabolic (local) influence AND myogenic regulation

• Reduced intravascular pressure• Decreased stretch

Reactive Hyperemia

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

Questions- mark.ziolo@osumc.edu

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