Local and Humoral Control of Blood Flow Flashcards
What do tissues need?
- Oxygen
- Nutrients
- Removal of CO2 and hydrogen and other metabolites
- Hormones
Flow is closely related to
Metabolic rate of tissues
Increase in metabolic rate=increase blood flow to tissue
Active hyperemia
Increase in blood flow (hyperemia) that’s associated with increased metabolic activity of an organ or tissue.
Mechanism of local control
Vasodilators released from cells during metabolism (adenosine, CO2, lactic acid, ADP compounds, histamine, K+, H+ ions)
Decrease in tissue oxygen levels directly causes increase in flow dilation of arterioles and precap sphincters
Vasoconstrictors
Angiotensin
Vasopressin
Humoral regulation (Circulating)
Vasodilator agents
Histamine
Nitric oxide
Humoral regulation (Circulating)
Angiotensin mechanism
Theres a decrease in arterial pressure
Renin (enzyme from kidney) interacts with circulating angiotensin (from liver) to make angiotensin I which is NOT biologically activated.
Angiotensin I interacts with angiotensin converting enzyme (ACE) to make angiotensin II which IS biologically active
Angiotensin II can constrict arterioles (increase Blood pressure).
ACE inhibitors decrease ability of angiotensin II frmo being made.
Vasopressin mechanism
Formed in hypothalmus and secreted into blood.
Released in response to decrease in arterial pressure or increase in plasma osmolarity (release inhibited by ROH)
Potent vasoconstrictor and increases renal absorption of water to make concentrated urine.
Histamine
Made from mast cells in tissues and basophils in blood
Released in response to tissue damage or inflammation or allergic rxn
Powerful vasodilator
Increases capillary permeability (excess interstitial fluid)
Histamine has global or local effect
Global- dilation everywhere, decreases blood pressure.
Nitric oxide
Gas
Produced in endothelial cells and diffuses to smooth muscle cells to cause dilation.
Local response
If endothelial cells are damaged what may happen?
Nitric oxide may not be made and enhances probability of clot formation because cells can’t dilate.
