Control of Blood Flow- Exam 1 Flashcards
What are the 4 components of maintaining tissue demand?
Delivery of oxygen and other nutrients
Removal of waste (co2 and hydrogen ions)
Maintain appropriate ion concentrations
Supply needed hormones
How is acute (metabolic control) response controlled?
Vasodilation/vasoconstriction of arterioles, metarterioles, precapillary sphincters
How is long term response controlled?
Increasing/decreasing physical size and number of blood vessels within tissue
Which type of response is finite?
Acute (metabolic control)
Which type of response is infinite?
Long-term response
How long does it take for an acute (metabolic) response to occur?
Response occurs within seconds (sudden change in metabolism; oxygen content; input pressure)
How long does it take for a long-term response to occur?
Takes days/weeks (more permanent changes in metabolism; oxygen content, input pressure)
An 8-fold increase in metabolism results in what increase in blood flow through tissue?
4-fold increase in blood flow
What are 4 examples of decrease in arterial oxygen sat resulting in increased blood flow?
- High altitude
- Pneumonia
- Carbon monoxide poisoning
- cyanide poisoning
What opens and closes multiple times each minute?
precapillary sphincters
What are the two theories for acute regulation?
Oxygen (nutrient) lack theory
Vasodilator theory
Oxygen (nutrient) lack theory
Oxygen & other nutrients needed for smooth muscle contraction
When nutrients not available - muscle relaxes/dilation
Metabolism increases local decrease in oxygen content results in vasodilation
Vasodilator Theory
Metabolism increases production/concentration of metabolic waste increases
Metabolic waste interacts with smooth muscle resulting in dilation
What do the theories for acute regulation affect?
Tone of smooth muscle mainly in metarterioles and precapillary sphincters with some affect on arterioles
What does the overall tone of arterioles depend on?
Tone of autonomic nervous system
What determines the overall concentration of vasodilator factors?
Equilibrium between metabolic rate and flow through tissue
Potential Vasoactive Substances
Adenosine Carbon dioxide Adenosine phosphate compounds Histamine Potassium ions Hydrogen ions
What releases adenosine?
Cardiac cells when coronary blood flow inadequate, oxygen concentration has decreased and stores of ATP has decreased
Tissue in response to decreased oxygen concentration
What is carbon dioxide and where is it most relevant?
Potent vasodilator especially in the brain
What do Adenosine Phosphate compounds result from?
Increased ATP degradation
What is histamine and where is it released?
Potent vasodilator released from mast cells and basophils
When are hydrogen ions released?
Released from tissue in form of lactic acid in response to decreased oxygen concentration
Active Hyperemia
Response to increased metabolic demand with a tissue
Ex. increased metabolic activity in skeletal muscle
Reactive Hyperemia
Response of tissue to no flow (ischemia)
What can flow get up to in reactive hyperemia?
Flow can increase 4-7x normal
Local control mechanisms are only functional as long as _______ doesn’t change.
MAP
What will be affected if MAP changes?
All tissue will be affected by a change in flow; all tissues would see some type of local control response
What are the two theories relating to ability to keep flow through tissue close to normal over autoregulatory range?
Myogenic theory
metabolic theory
Myogenic Theory
Sudden stretch of small blood vessels cause surrounding smooth muscle of vessel wall to contract
According to the myogenic theory, what does increased blood pressure result in?
Stretches small blood vessels triggering reactive constriction thus reducing blood flow
According to the myogenic theory, what does decreased blood pressure result in?
Decreased stretch of small blood vessels triggering reactive relaxation and increased blood flow
According to the myogenic theory, what changes are vessels responding to?
Changes in pressure, not changes in flow
Endothelial-Derived Control Factors
Release several substances that interact directly with the smooth muscle to cause relaxation or constriction
Ex. Nitric Oxide and endothelin
Nitric oxide
Importnat direct vasodilator; lipophilic gas
Endothelin
potent vasconstrictor; large amino acid peptide
What causes nitric oxide to be released?
Chemicals: Calcium & Angiotensin II
Physical stimuli: Shear stress due to increased flow
Where does nitric oxide mainly act?
Larger vessels upstream of metarterioles and precapillary sphincters
What happens when flow through capillary increases release of NO?
Causes corresponding dilation of the larger upstream vessels
What is a consequence of chronic hypertension or atherosclerosis?
Decreased NO release
What is the 1/2 life of NO?
6 seconds, moves into smooth muscle quickly
How is NO formed?
Arginine + Oxygen in the presence of nitric oxide synthase (NOS)
What does NO activate?
Soluble guanylate cyclase (SGC)
What does guanylate cyclase do?
Mediates conversion of cyclic guanosine triphosphate (cGTP) to cyclic guanosine monophosphate (cGMP)
What does cGMP activate?
cGMP-dependent protein kinase (PKG)
What does PKG ultimately lead to?
Relaxation of the smooth muscles
Where is endothelin present?
In all endothelial cells but concentration increases with vessel injury
Where is endothelin released?
Damaged cells
Endothelin can close arterial vessels as large as what diameter?
5mm
What happens if your pressure increases 100 to 150 mmHg (no change in metabolism)?
Quick increase in blood flow- 30 sec to 2 min
Local constriction, decrease in flow
When complete, flow still 10 to 15 % higher than needed
What would happen if you had a permanent increase in blood pressure?
Flow would slowly decrease over the next few weeks until flow back to original value
Short term changes in MAP attenuate changes in flow over what pressure range?
75 to 175 mmHg
Long-term changes able to keep flow normal over pressure range of what?
50 to 250 mmHg
Angiogenesis
increase in vascularity
Chronic increase in tissue metabolism/ chronic decrease in pressure produces what?
Angiogenesis
What changes as part of long term control?
Total number of arterioles and capillaries would increase
Size of existing arterioles and capillaries would increase
How long does it take for long-term vascularity changes to occur?
Days in younger patients
Weeks to months in older patients
What does the total change in vascularity depend on?
Maximum blood flow needed by tissue (allows tissue to response to exercise or other times when tissue flow has to increase to meet a short term need)
What are vascular endothelial growth factors
Small peptides that promote new vessel growth from existing vessels
What are some examples of endothelial growth factors?
Vascular endothelial growth factor (VEGF)
Fibroblast growth factor
Angiogenin
What are antiangiogenic substances?
Block the growth of new vessels
Ex. angiostatin, endostatin
potential anticancer agent
How do antiangiogenic substances act as anticancer agents?
cancer cells cannot grow into tumors unless they are able to develop an adequate blood supply, so they block the blood supply
Vasoconstrictor agnets
norepinephrine
epinephrine
angiotensin ii
vasopressin
Norepinephrine
potent constrictor, released via ANS and adrenal medullae
Epinphrine
vasoconstrictor, not as potent as norepi
Angiotensin II
vasoconstrictor; part of the overall regulation of blood pressure
How many grams of Angiotensin II can increase arterial pressure 50 mmHg?
1/1,000,000 gram
Vasopressin
ADH
More powerful than angiotensin ii
Where is vasopressin released?
posterior pituitary
What is the major role of vasopressin?
increase water reabsorption by the kidneys
What is the vasopressin role during acute hypovolemia?
Vasoactive role
What are the vasodilator agents?
Bradykinin
Histamine
What are kinins?
Small peptides split from alpha2-globulins by proteolytic enzymes
Kallikrein
proteolytic enzyme in the blood (inactive)
how is kallikrein activated?
damage to blood, inflammation
What does activated kallikrein interact with?
Alpha2-globulin to release kallidin
What is kallidin converted to?
Converted by tissue enzymes to bradykinin
Bradykinin
causes powerful vasodilation and increased capillary permeability; important responses during inflammation
Histamine is released by what?
Mast cells and basophils located in damaged or inflamed tissue
What is histamine?
potent vasodilator and increases capillary permeability; can result in edema, allergic rxns
What are some ions that act on smooth muscle?
Calcium potassium magnesium hydrogen acetate/citrate
Calcium
increased levels stimulate smooth muscle contraction leading to vasoconstriction
Potassium
increased levels inhibit smooth muscle contraction leading to vasodilation
Magnesium
increased levels cause significnat vasodilation by inhibiting smooth muscle contraction
How are potassium and magnesium acting?
Changing resting membrane potentials
Hydrogen
increased levels result in vasodilation; a slight decrease in hydrogen ions cause arterioles constriction
Acetate/citrate
increased levels cause mild vasodilation
