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Tissues control blood flow in proportion to what 4 needs?
- Delivery of oxygen
- Delivery of nutrients
- Removal of CO2 and H+ and other metabolites
- Transport of various hormones and other substances to different tissues
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Flow is closely related to what?
Metabolic rate of tissues
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Acute control of local blood flow is determined by what structures?
- Arterioles
- Metarterioles
- Precapillary sphincters
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What 2 factors primarily alter tissue blood flow?
- 1) Tissue metabolism
- 2) Oxygen availability
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What are the 2 major theories for local blood flow?
- 1) The vasodilator theory
- 2) Oxygen demand theory
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How does increased tissue metabolism affect blood flow?
Increases flow
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How does decreased oxygen concentration affect blood flow?
Increases flow
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What law represents the relationship between pressure, flow, and resistance?
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Describe the Vasodilator Theory for blood flow control
Increase in metabolism/Decrease in oxygenation leads to release of vasodilators causing decreased resistance and increased flow
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Describe the Oxygen Demand Theory for blood flow control
Increase in metabolism/decrease in oxygenation leads to decrease tissue oxygen concentration causing decreased resistance and increased flow
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Define autoregulation
The ability of a tissue to maintain blood flow relatively constant over a wide range of arterial pressures
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List examples of vasodilators involved in the Vasodilator Theory for blood flow control
Adenosine, CO2, lactic acid, ADP compounds, histamine, K+ ions, H+ ions
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What is the Metabolic Theory of autoregulation?
Decreased arterial pressure leads to decreased oxygen and nutrient delivery which releases vasodilator(s)
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What is the Myogenic Theory of autoregulation?
As arterial pressure falls, arterioles have intrinsic property to dilate in response to the decrease in wall tension
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Explain LaPlace's Law as it relates to the Myogenic Theory of autoregulation.
- As pressure increases, the increase in tension will cause a decrease in vessel radius
- As pressure decreases, the decrease in wall tension will cause an increase in vessel radius
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Is long-term or short-term control of flow more effective?
Long-term
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How does long-term blood flow regulation occur?
By changing the size and number of vessels - angiogenesis
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How does high altitude affect angiogenesis?
Increased vascular growth in tissues in response to decreased oxygen levels
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What is the process of retrolental fibroplasia or retinopathy of prematurity?
High FiO2 decreases vessel growth or even causes degeneration. When the high oxygen concentration is removed, there is a proliferation of retinal vessels into the vitreous humor causing blindness
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What is the result of chronically overactive tissue with regards to blood flow/vessels?
Increase in both number and size of arterioles and capillaries to match needs of tissue
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Define angiogenesis
Growth of new blood vessels
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What 3 factors stimulate angiogenesis?
- Ischemic tissue
- Rapidly growing tissue
- Tissue with high metabolic rate (tumors)
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What are examples of angiogenic factors?
- Vascular endothelial cell growth factor (VEGF)
- Fibroblast growth factor (FGF)
- Angiogenin
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What are examples of vasoconstrictors involved in humoral regulation of blood flow?
- Norepinepherine
- Epinepherine
- Angiotensin II
- Vasopressin (ADH)
- Endothelin
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What are examples of vasodilators involved in humoral regulation of blood flow?
- Bradykinin
- Serotonin
- Histamine
- Prostaglandin
- Nitric oxide
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How do calcium ions affect blood flow?
Increased levels cause vasoconstriction through smooth muscle contraction
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How do potassium ions affect blood flow?
Increased levels cause vasodilation through smooth muscle inhibition
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How do magnesium ions affect blood flow?
Increased levels cause profound vasodilation through smooth muscle inhibition
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How do hydrogen ions affect blood flow?
- Increased levels cause vasodilation
- Decreased levels cause vasoconstriction
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How do anions like citrate and acetate affect blood flow?
Both cause mild vasodilation
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How does carbon dioxide concentration affect blood flow?
Increases cause moderate vasodilation in most tissues; profound vasodilation in the brain
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