regulation of organ blood flow- ppt-2
TRANSCRIPT
Regulation of Organ Blood Flow
Mark T Ziolo, PhD, FAHAAssociate Professor, Physiology & Cell Biology019 Hamilton [email protected]
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
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