Control of Blood Flow by the Tissues: and Humoral Regulation Flashcards
local control of blood flow is in response to
tissue needs
function of the circulatory system
meet the metabolic needs of each tissue by controlling blood flow to the tissue
blood flow to tissue depends on the
metabolic rate of the tissue
needs of tissue
Delivery of oxygen to the tissues
Delivery of other nutrients
Removal of CO2 from the tissue
Maintenance of proper concentrations of ions
Transport of various hormones and other specific substances to the different tissue
greater metabolism in the organ
greater blood flow
local blood flow control can be divided into
Acute control (secs to minutes)
Long term control (days to weeks)
acute control of blood flow is achieved by
rapid changes in blood flow in local tissues by vasodilation or vasoconstriction of blood vessels within secs or minutes.
Local blood flow increases when:
Tissue metabolism increases
Oxygen availability decreases
long term control occurs
over days, weeks or months.
provides better control of flow in proportion to the needs of the tissues.
The changes are brought about by an increase or decrease in physical size and number of actual blood vessels supplying the tissues.
factors influencing O2 supply
High altitudes
Pneumonia
Carbon monoxide poisoning (poisons the ability of hemoglobin to transport oxygen)
Cyanide poisoning (poisons the ability of tissue to utilize oxygen)
how does cyanide work?
decreases oxygen usage by local tissues
what are the 2 theories for the regulation of local blood flow?
Vasodilator theory
The lack of oxygen/nutrient theory
define vasodilator theory
Increased tissue metabolism rate
Increased vasodilator formation rate
Vasodilators act at:
Precapillary sphincters
Arterioles
Metarterioles
vasodilator substances
Adenosine, Carbon dioxide, Lactic acid
Adenosine Phosphate compounds, Histamine
Potassium ion and Hydrogen ion
other possibility for the vasodilator theory: O2 deficiency may cause vasodilator formation due to
Decreasing oxygen availability does increase adenosine and lactic acid formation
Adenosine appears to be very important in control of coronary blood flow both in the active and failing heart.
The precapillary sphincters, arterioles and metarterioles exist in two states:
Open - sm. muscle relaxed
Closed - sm. muscle contracted
vasomotion
The rhythmical transition between the two states of open and closed muscle
oxygen glucose demand mechanism
When tissue oxygen level falls (increased metabolism due to system function) oxygen level in the sm. muscle falls, causing it to lose contractility (dilate, relax) and vice versa.
other nutrients that control blood flow
glucose
amino acids
fatty acids
vitamin B
thiamin
niacin
riboflavin
reactive hyperemia
When blood flow to a tissue bed is interrupted by occlusion for several minutes the oxygen debt that is repayed when the occlusion is released by an increase in blood flow above normal.
causes vasodilation
active hyperemia
The increase in local metabolism results in a rapid decrease in nutrients in the local tissue, which releases a large quantity of vasodilator substances. Increases blood flow to restore the local nutrient needs of the tissue
how does arterial pressure work?
When the arterial pressure to a tissue bed is increased or decreased the tissue vascular resistance will change in a direction that minimizes the change in blood flow.
autoregulation
An acute increase in arterial pressure causes an immediate rise in blood flow, within minutes the blood flow returns to normal even though the arterial pressure is kept elevated.
2 theories that explain autoregulation
Metabolic - vasodilator or nutrient demand
Myogenic - stretched muscle contracts
metabolic theory
When the arterial pressure is increased, there is increased blood flow which in turn brings too much oxygen and nutrients to the tissue. These nutrients then cause the blood vessels to constricts and the flow returns to nearly normal despite increased pressure.
