Regulation of Blood Flow Flashcards
What is Ohm’s Law?
flow between any two points is determined by the pressure difference between the points/ divided by resistance
Q=delta(P)/R, q=flow
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)
- branch points
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?
- splanchnic/GI
- skeletal muscle
- kidneys
- brain (same upon exertion!)
Which organs receive the bulk of blood flow upon exertion?
- skeletal muscle
- skin
- 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
l=tube length
n=viscosity
r=radius
What is Reynolds number? Eqn?
Re = dvp(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)?
- local factors
- sympathetic NS
- 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
- vasodilation follows
- 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?
- adenosine
- ATP/ADP/AMP
- CO2
- lactic acid
- potassium ions
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?
- metabolic control
- myogenic control
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
What is the myogenic control of auto regulation?
stretch-activated calcium channels in the vessel smooth muscle cells will be activated from increased flow/pressure, calcium enters cells, leading to increased vascular tone and resistance
How does the CNS regulate blood flow?
innervation of blood vessels is mainly via sympathetic vasoconstrictor fibers, primarily NOR
- innervation varies among vessels and capillaries are not at all
Which vessels are highly sympathetically innervated?
- cutaneous
- renal
- GI
- skeletal muscle
Which vessels are sparsely sympathetically innervated?
- cerebral
- coronary vessels
most auto-regulated tissues
Describe the relationship between sympathetic activity (x) and vascular resistance (y).
sympathetic activity is never zero (tonic) on a vessel which allows the system to change quickly
this curve is concave down and asymptotically reaches a limit
What humoral factors regulate BF?
-Epi and Nor are released from adrenal medulla via sympathetic stimulation and interact with alpha and beta adrenergic receptors
What do alpha receptors do? beta?
alpha mediate vasoconstriction and beta mediate dilation
What is angiotensin II?
an oligopeptide that constricts both arteries and veins. Its involved in regulation of arterial pressure and plasma volume. It has a direct vasoconstrictor effect on blood vessels and it directs kidneys to decrease urine output
What is vasopressin?
an oligopeptide that regulates plasma volume by directing kidneys to decrease urine output. At high levels, it also constricts arteries and veins, particularly in the GI area
What effect do bradykinin and histamine have?
vasodilation and increase vascular permeability.
What effect do prostaglandins have?
PGI2 and PGE2 are vasodilators and TxA2 is a vasoconstrictor
What is atrial natriuretic peptide?
an oligopeptide that is released from atrial myocytes and that directs the kidneys to increase urine output
What is NO derived from and how does it regulate BF?
arginine; it decreases intracellular calcium levels and induces vasodilation in large vessels upstream of hyperemia tissue
What is rarefaction?
decreasing the number of blood vessels- long term mechanism like angiogenesis
T or F In humans, angiogenesis does not occur at a high level
T, except in neoplastic tumors
What is hyperopic vascular remodeling?
long term mechanism of regulating blood flow by increasing wall thickness and decreasing the vascular lumen
What things regulate coronary blood flow?
- NO
- NOR induces vasodilation via beta2-receptors in resistance arteries in the heart
- *-metabolic end products and/or altered oxygen (most important)**
How intense is the vasodilation caused by NOR in the heart?
it accounts for up to 25% of the exercise-induced vasodilation (not occurring at rest)
How is blood flow in the left ventricle different from other organs?
greatest blood flow occurs during diastole (essentially a reactive hyperemia) because contraction during systole compresses resistance arteries and increase vascular resistance. Similar but lesser effect in right heart
Why would the left side of the heart be highly susceptible to infarction?
because of perfusion problems- this problem is amplified if ventricular end-diastolic pressure is increased because cardiac perfusion will then be compromised even during diastole
T or F. During exercise, blood flow to skeletal muscle is mostly under local control
T.
At rest, blood flow to skeletal muscle is mostly under control from what?
the sympathetic nervous system will increase constriction if blood flow drops
What controls circulation in the brain?
some sympathetic an para innervation but mostly local control (strong auto- regulation)
active hyperemia common
What are the two circulatory systems of the liver?
1) portal system- provides 1,100 ml/min BF
2) arterial system- provides 350 ml/min go BF
T or F. The spleen plays the role of reservoir of RBCs and plasma volume
T, can be released during exercise or when BP drops
How is GI circulation controlled?
- active hyperemia (local metabolites and hormones released)
- extrinsic control (by the sympathetic nervous system)
- autoregulation
How does GI vascular resistance change after feeding (as a function of time)?
eating stimulates sympathetics (increasing resistance) then Gi begins to digest, and you see a big drop in resistance mediated by metabolites, etc. and then after digestion normalcy is reestablished (active hyperemia)
What controls circulation to the skin?
almost entirely controlled by CNS.
How does the skin react to heat?
When temp rises, blood flow increases to the skin to dissipate it
it opens anastomosing venous plexus in subcutaneous tissue leading to increased heat dissipation
How is renal blood flow regulated?
- high degree of auto regulation of both BF and GFR
- heavily invested with sympathetic fibers. Increased sympathetic activity overrides auto regulation and increases renal vascular resistance.
