autoregulation of blood flow

Q1: Define the autoregulation of blood flow.
A1:

  • Intrinsic ability of an organ to maintain constant blood flow

  • Despite changes in perfusion pressure

  • Can be short term or long term

Q2: What is myogenic tone?
A2:

  • Vascular smooth muscle contracts when stretched

  • Sudden arterial pressure increase → Arterioles stretch and smooth muscle contracts

  • Results in vasoconstriction to maintain constant blood flow

  • Known as Bayliss Effect

Q3: Name two types of mediators released by the endothelium and their effects.
A3:

  • Vasoconstrictor: Endothelin

  • Vasodilator: NO, prostacyclins

Biosynthesis and Actions of Nitric Oxide

Q4: What is the substrate and enzyme involved in nitric oxide biosynthesis?
A4:

  • Substrate: L-Arginine

  • Enzyme: Endothelial Nitric Oxide Synthase (eNOS)

Q5: Describe the reaction catalyzed by eNOS.
A5:

  • eNOS converts L-arginine to nitric oxide (NO) and L-citrulline

  • Requires oxygen (O₂) and NADPH

Q6: How does nitric oxide diffuse and where does it go?
A6:

  • NO diffuses from endothelial cells

  • Moves to nearby vascular smooth muscle cells

Q7: What enzyme does nitric oxide activate in vascular smooth muscle cells?
A7:

  • Guanylyl cyclase

Q8: What is the result of guanylyl cyclase activation?
A8:

  • Converts GTP to cGMP (cyclic guanosine monophosphate)

Q9: How does cGMP affect vascular smooth muscle?
A9:

  • Triggers events leading to smooth muscle relaxation

  • Activates PKG

  • PKG phosphorylates target proteins

  • Decreases intracellular calcium levels

  • Reduces sensitivity of contractile proteins to calcium

Q10: What is the overall effect of nitric oxide on blood vessels?
A10:

  • Causes vasodilation

  • Decreases vascular resistance

  • Increases blood flow

Mechanisms of Hyperemia

Q11: What is active hyperemia?
A11:

  • Increased metabolic activity of a tissue

  • Produces vasodilators

  • High metabolic activity, high PCO2, low PO2, low pH induce vasodilator release

  • Increases blood flow

Q12: What is adenosine's role in vasodilation?
A12:

  • Breakdown product of ATP

  • Causes vasodilation

Q13: Define reactive hyperemia.
A13:

  • Decreased tissue blood flow due to occlusion

  • Release of metabolic vasodilators

Q14: Define inflammatory hyperemia and name some mediators.
A14:

  • Active process from increased arterial blood inflow

  • Due to inflammatory mediators

  • Mediators include histamine, bradykinin, prostanoids, neuropeptides

Triple Response of the Skin

Q15: Describe the first component of the triple response of the skin.
A15:

  • Red Line

  • Caused by vasodilation from histamine release

Q16: Describe the second component of the triple response of the skin.
A16:

  • Flare

  • Mediated by the axon reflex

  • Injury stimulates sensory nerve endings

  • Nerve endings release neuropeptides (substance P, CGRP)

  • Causes vasodilation in surrounding area

Q17: What is neurogenic inflammation?
A17:

  • Inflammation mediated by nerve-induced release of neuropeptides

  • Leads to vasodilation and redness spreading from the initial injury site

Q18: Describe the third component of the triple response of the skin.
A18:

  • Wheal

  • Localized swelling (edema)

  • Increased capillary and venule permeability

  • Fluid leakage into surrounding tissue

  • Caused by histamine and other inflammatory mediators