Control of Tissue Blood Flow Flashcards
Most tissues have the ability to control their own blood flow in proportion to
their own specific metabolic needs
What are the specific needs of tissues? (6)
- Delivery of ____ to tissues
- Delivery of ____ to tissues (such as?)
- Removal of ___ from tissues
- Removal of ___ from tissues
- Maintaining proper what?
- Transportation of what?
- Delivery of O2 to tissues
- Delivery of nutrients (glucose, amino acids, fatty acids)
- Removal of CO2 from tissues
- Removal of H+ ions from tissues
- Maintaining proper concentrations of ions in tissues
- Transport hormones and other substances to different tissues
Acute control of blood flow occurs within (time frame)
seconds to minutes
Long term control of blood flow occurs within
days, weeks or even months
Acute control includes rapid changes in local vasodilation or vasoconstriction of _____, meta-_____ and pre-capillary _____
arterioles, meta-arterioles, pre-capillary sphincters
Angiogenesis
new vessel formation
Long term control includes ____ controlled changes that result from an increase or decrease in physical ____ and numbers of blood vessels supplying the ____
slow
size
tissues
Effect of Oxygen availability examples (3)
- High Altitude
- Pneumonia
- Carbon Monoxide Poisoning
Vasodilator Theory includes either
less available o2 OR greater rate of metabolism, which leads to the greater rate of formation of vasodilator substances in tissue cells
What intense vasodilator is important for the body?
Adenosine
Substances will diffuse through the tissues to cause
vasodilation
Nutrient (Oxygen) Theory states that O2 and other nutrients are required to cause
vascular muscle contraction
In the absence of O2, blood vessels will
dilate and relax
Increasing metabolism will result in increase of ____, which would decrease the availability of O2 to the smooth muscle fibers in local blood vessels causing ____
O2; vasodilation
The # of precapillary sphincters that are open at any given time is roughly proportional to the
requirements of tissue for nutrition
Opening and closing of the precapillary sphincters is cyclical depending on the (also known as…)
metabolic needs of the tissue (Vasomotion)
Oxygen is a requirement for what muscle type to remain contracted?
smooth
Strength of the contraction of the sphincters increases with`
O2 concentration
Sphincters remain closed until the cells…
consume excess O2
When O2 is gone, or the O2 concentration falls low enough, the sphincters would
open once more to being cycle again
Reactive Hyperemia is the
occlusion of blood flow for a few seconds or longer
When blood flow is restored, it increases immediately to
4-7x the normal
Active Hyperemia is
any tissue becomes highly active
increase in metabolism causes cells to consume tissue fluid nutrients rapidly and release large quantities of vasodilator substances
blood flow increases immediately as much as 20-fold during intense exercise
A rapid increase in arterial pressure causes an immediate rise in
blood flow
A compensatory mechanism occurs within less than a minute and blood flow returns to almost normal levels even though arterial pressure is kept elevated. This is known as…
autoregulation
Metabolic Theory of Autoregulation states
too much O2 causes vasoconstriction
Myogenic Theory of Autoregulation states
stretch of small blood vessels causes smooth muscle of vessel wall to contract
Endothelial-derived relaxing factor
substances derived from endothelial cell lining blood vessels; major one is Nitric Oxide (NO)
NO is a
lipophilic gas released from endothelial cells in response to stimuli
NO causes
blood vessels to relax
Damage to the endothelial cells can lead to
hypertension or artherosclerosis
Impairing NO synthesis contributes to excess
vasoconstriction (think: tight chest pain, angina)
Nitroglycerin and nitrate derivatives treat angina because they increase
coronary blood flow via vasodilation
Which powerful vasoconstrictor prevents bleeding out and greatly increases when vessels are injured?
Endothelin
Drugs that block endothelin receptors have been used to treat what?
pulmonary hypertension because you want to vasodilate & decrease BP
Humoral control of the circulation means
control by substances secreted or absorbed into the body fluids such as hormones and locally produced factors
A powerful vasoconstrictor that is released when the sympathetic nervous system is stressed or exercising is
Norepinephrine (noradrenalin)
Excited the heart, contracts veins and arteries
A less powerful vasoconstrictor that can cause mild vasodilation (such as decreasing an allergic reaction via Epi-Pen) is
Epinephrine
A powerful vasoconstrictor hormone that constricts the small arterioles and increases blood pressure dramatically is
Angiotensin II
Angiotensin II increases BP dramatically by (2)
increasing total peripheral resistance
decreasing sodium and water excretion by kidneys
An even more powerful vasoconstrictor than Angiotensin II that helps to control body fluid volume by increasing water reabsorption from renal tubules back into the blood is
Vasopressin (ADH)
A powerful vasodilatory only activated for a few minutes that causes powerful arteriolar dilation, increased capillary permeability, local edema and has a special role in regulating flow and fluids in inflamed tissue
Bradykinin
Derived from mast cells and released in every tissue of the body if it is damaged/inflamed/allergically reacting is known as
Histamine
also a powerful arteriolar dilator, increases capillary permeability and plays large role in edema
What increases in both number and size within a few weeks to match the needs of tissues?
Arterioles & Capillary Vessels
If metabolism in tissue is increased for a prolonged period, what increases?
its vascularity
If metabolism in tissue is decreased for a prolonged period, what decreases?
its vascularity
Where atmospheric oxygen is LOW such as in high altitudes, what increases?
vascularity
example: mountain goats have a high vascularity due to the formation of angiogenic growth factors aiding in the increased need for O2
Why do premature babies tend to have eye issues?
Increased O2 in the NICU causes retinopathy
Formation of new blood vessels is known as
angiogenesis
Deficiency of tissue oxygen or other nutrients leads to formation of what factors?
angiogenic
What are 4 main angiogenic factors?
- VEGF - vascular endothelial growth factor
- Fibroblast growth factor
- PDGF - platelet derived growth factor
- Angiogenin
What are 2 main angiogenesis inhibitors?
- Angiostatin - fragment of protein plasminogen
- Endostatin - derived from breakdown of collagen type XVII
can impair the rapid growth of cancerous tumors
4 main application to know in regards to Vascularity
- Chronic Exercise Training
- Development of Collateral Circulation
- Hypertension
- Bypass Graft Procedures
In chronic exercise training, vascularity of trained muscles _____ to accommodate their higher blood flow
increases
Development of collateral circulation is when a blockage of a vein or artery will facilitate a
new vascular channel to develop around the blockage to allow partial resupply of blood to affected tissues
HTN causes what kind of remodeling? What does it do?
Hypertrophic Remodeling
Occurs in large arteries to increase the size of smooth muscle cells and stimulate formation of the extracellular matrix proteins in order to reinforce the strength of the vascular wall
**MAKES THE LARGE BLOOD VESSELS STIFFER
Bypass Graft Procedures usually take which vein from the leg to sew into the aorta and connect to a coronary artery?
Saphenous
Take Homes of Control of Tissue Blood Flow (5)
- Less O2 OR increased metabolism will increase vasodilator substances in tissue cells
- Active Hyperemia/Reactive Hyperemia increase blood flow acutely
- Endothelial Nitric oxide synthase will synthesize NO and thus dilate larger blood vessels
- Powerful humoral vasoconstrictors include Norepinephrine, Vasopressin and Angiotensin II (acutely)
- Increase in metabolism or decrease in O2 over a prolonged period of time causes increase in vascularity (angiogenesis) which contributes to long-term blood flow regulation
