Podcast
Questions and Answers
What substance is primarily released by the vascular endothelium in response to shear stress to cause vasodilation in upstream vessels?
What substance is primarily released by the vascular endothelium in response to shear stress to cause vasodilation in upstream vessels?
- Epinephrine
- Angiotensin II
- Nitric oxide (correct)
- Endothelin
Which factor is NOT listed as a possible reason for baseline tone in blood vessels?
Which factor is NOT listed as a possible reason for baseline tone in blood vessels?
- Presence of Ca++
- Presence of Mg++ (correct)
- Myogenic activity
- High oxygen content of arterial blood
Which of the following is a vasoconstrictor released from the posterior pituitary and contributes to neurohumoral control?
Which of the following is a vasoconstrictor released from the posterior pituitary and contributes to neurohumoral control?
- Angiotensin II
- Vasopressin (ADH) (correct)
- Norepinephrine
- Epinephrine
What substance is produced by damaged endothelial cells to induce local vasoconstriction and reduce bleeding?
What substance is produced by damaged endothelial cells to induce local vasoconstriction and reduce bleeding?
Which factor does NOT contribute to vasodilation in vascular smooth muscle?
Which factor does NOT contribute to vasodilation in vascular smooth muscle?
What range of blood pressures does long-term regulation of blood flow effectively manage?
What range of blood pressures does long-term regulation of blood flow effectively manage?
What happens when a blood vessel relaxes?
What happens when a blood vessel relaxes?
What is reactive hyperemia?
What is reactive hyperemia?
Which theory proposes that excess oxygen or other nutrients can lead to increased smooth muscle contraction and decreased blood flow?
Which theory proposes that excess oxygen or other nutrients can lead to increased smooth muscle contraction and decreased blood flow?
What is the Myogenic Theory of autoregulation independent of?
What is the Myogenic Theory of autoregulation independent of?
What does upstream regulation of vasodilation affect?
What does upstream regulation of vasodilation affect?
What effect does an increase in pressure initially have according to the Myogenic Mechanism of Autoregulation?
What effect does an increase in pressure initially have according to the Myogenic Mechanism of Autoregulation?
Variation of smooth muscle in the resistance vessels does NOT allow for?
Variation of smooth muscle in the resistance vessels does NOT allow for?
How does smooth muscle contraction in resistance vessels differ between smooth muscle and skeletal muscle?
How does smooth muscle contraction in resistance vessels differ between smooth muscle and skeletal muscle?
What is/are the core mechanism(s) of acute control of tissue blood flow?
What is/are the core mechanism(s) of acute control of tissue blood flow?
What happens in the absence of adequate oxygen according to the Oxygen Lack Theory of local blood flow regulation?
What happens in the absence of adequate oxygen according to the Oxygen Lack Theory of local blood flow regulation?
Bradykinin contributes to capillary leakage in inflammation.
Bradykinin contributes to capillary leakage in inflammation.
Histamine is a vasoconstrictor released from damaged endothelial cells.
Histamine is a vasoconstrictor released from damaged endothelial cells.
Acetate decreases vascular smooth muscle contractile state.
Acetate decreases vascular smooth muscle contractile state.
Study Notes
Mechanisms of Local and Humoral Control of Tissue Blood Flow
- Acute control occurs within seconds to minutes via local and neurohumoral mechanisms
- Long-term control occurs over days to months due to changes in size or number of blood vessels
Baseline Tone and Variation in Tissue Blood Flow
- Baseline tone: partial constriction of resistance vessels allowing for vasodilation and further vasoconstriction
- Variation in tissue blood flow: due to changes in metabolism, oxygen supply, and other nutrients
Smooth vs Skeletal Muscle
- Smooth muscle contraction:
- Develops slowly
- Develops high forces
- Maintains contraction for long periods
- Mechanisms of contraction:
- Electromechanical coupling: increased myoplasmic Ca++ via voltage-gated calcium channels
- Pharmacomechanical coupling: via receptor-mediated calcium channels, occurs in the absence of electrical excitation
Substances Involved in Pharmacomechanical Coupling
- Catecholamines
- Histamine
- Acetylcholine
- Serotonin
- Angiotensin
- Adenosine
- Nitric oxide
- CO2
- Potassium
- Prostaglandins
Theories of Local Blood Flow Regulation
- Vasodilator Theory: vasodilator substances produced and released due to increased metabolism or decreased oxygen supply
- Oxygen Lack Theory: smooth muscle relaxation in response to oxygen lack, leading to vasodilation
Acute Control of Local Blood Flow
- Reactive Hyperemia: increased blood flow following occlusion of blood supply
- Active Hyperemia: increased blood flow in highly active tissue, e.g., exercising skeletal muscle
Autoregulation of Blood Flow
- Maintenance of normal blood flow following changes in arterial pressure
- Two proposed mechanisms:
- Metabolic Theory: similar to oxygen lack theory
- Myogenic Theory: change in transmural pressure initiates contraction or relaxation of vascular smooth muscle
Upstream Regulation of Vasodilation
- Locally mediated vasodilation affects small arteries and arterioles, but not larger upstream arteries
- Increased flow through larger arteries upstream releases EDRF (primarily nitric oxide), causing vasodilation
Baseline Vascular Tone
- Independent of nervous system input
- Possibly due to myogenic activity, high oxygen content of arterial blood, presence of Ca++, or unknown plasma factor
Neurohumoral Control of Blood Flow
- Vasoconstrictors:
- Norepinephrine
- Epinephrine
- Angiotensin II
- Vasopressin (ADH)
- Endothelin
- Vasodilators:
- Bradykinin
- Histamine
Other Factors Affecting Vascular Smooth Muscle Contractile State
- Vasodilation:
- Increased K+
- Increased Mg++
- Increased H+
- Acetate
- Citrate
- Increased CO2 (cerebral)
- Vasoconstriction:
- Increased Ca++
- Decreased H+
- Increased CO2 (systemically via sympathetic nervous system)
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