Flashcards in Regulation of Blood Flow Deck (59)
What is Ohm's Law?
flow between any two points is determined by the pressure difference between the points/ divided by resistance
only applies to laminar flow
Where are some common points in vasculature for turbulence to develop?
- any time the cross sectional area decreases (velocity increases)
What is the equation for arterial pressure?
CO x TPR (total peripheral resistance)
Blood flow is often distributed among parallels routes in the body. What does this ensure?
1) biological fairness, meaning that each organ receives the same quality blood n terms of O2 and nutrients
2) total resistance is much lower (than if they were in series)
Which organs receive the bulk of blood flow at rest?
-brain (same upon exertion!)
Which organs receive the bulk of blood flow upon exertion?
-heart and brain
-kidneys and splanchnic (decrease to both)
What accounts for the increase or decrease of blood flow to the organs upon exertion?
sympathetic vasoconstriction decreases blood flow to some areas and other areas have mechanism to overcome the sympathetic constriction to increase blood flow-
The increased blood flow is an example of ACTIVE hyperemia
What the eqn for resistance in a vessel?
R= 8nl/(pi*r^4), where
What is Reynolds number? Eqn?
Re = d*v*p(density)/ n(viscosity)
Re above 400= turbulence in a branched/arched system
Re above 2000= turbulence in a linear system
What affects blood viscosity?
blood viscosity is greater than plasma because it contains erythrocytes. Thus, more red cells (HCT)= more viscosity= higher R
polycythemia= high R
anemia= low R
Changes in blood flow distribution is mainly attributed to changes in what?
Resistance. Thus, by changing the resistance in each individual organ, blood flow can be individually manipulated
all organs have the same delta(P) essentially
What things rapidly regulate vascular resistance (changes occur in seconds to minutes)?
-humoral (circulating) factors
What things slowly regulate vascular resistance (changes occur in weeks to months)?
reduction in blood vessel lumen size (hypertrophy) and/or change in number of blood vessels per tissue unit (aka vascularity)
What is hyperemia?
increased blood flow
What are the two types of hyperemia?
- active (functional) -increased blood flow that follows increased tissue activity
- reactive- increased blood flow above original resting level that follows reduction of blood flow to specific tissue
What is the eqn for work of the heart?
Pressure x Volume
T or F. The greater the metabolic needs of an organ, the greater the blood flow
T. BUT this relationship is not linear, it is concave up because most tissues have blood flow reserves so they can handle small jumps in metabolism without needing more flow
What organ has a linear relationship between need and blood flow?
Heart, no cardiac reserve here
What is the relationship between arterial oxygen saturation (x) and blood flow (y)?
same as for metabolism and blood flow, concave up
How does O2 regulate BF in active hyperemia?
-increased tissue activity causes increased metabolism
-leads to decreased O2 sat initially in tissue
- **vasodilation (radius increase) follows as a function/result of O2 levels**
- BF increases and O2 restored
What is the relationship of time of interruption of BF and intensity and duration of reactive hyperemia?
blood flow after blockage is actually higher than before the blockade and takes a while to normalize. The longer the ischemia persists, the longer and more intense the reactive hyperemia is.
How does O2 regulate BF in reactive hyperemia?
-decrease in blood flow
-decrease in O2 delivery
-blood flow increases
How does low oxygen influence vascular radius?
-low levels may decrease smooth muscle cell metabolism, thereby decreasing smooth muscle force generation, then leading to vascular relaxation
-oxygen sensing capacity in small arteries
What are some important vasodilator metabolites?
these are byproducts of metabolism which cause vasodilation to flush out the metabolites and restore normal levels
How do metabolites control blood flow in reactive hyperemia?
increase in metabolite accumulation causing vasodilation leading to increased blood flow
What is auto-regulation?
capacity of blood vessels to oppose changes in BF that are imposed by changes in BP. Occurs at the local level and doesn't include ANS
vessels will close at critical closing pressure because of tonic sympathetic activity so a huge increase in pressure won't increase BF beyond a certain point
T or F. Autoregulation also works to maintain BF to organs when arterial BP drops
T. The organ will decrease resistance in vessels in this case
What processes control auto-regulation?
What is the metabolic control of auto regulation?
increased pressure leads to increased flow, resulting in increased O2 or decreased metabolites, resulting in increased vascular resistance, and finally decreased flow