[2] Lecture 10- Overview Of Circulatory System Flashcards
Systemic Arterial pressure, systolic and diastolic:
120 mmHg ; 80 mmHg
What is systemic pressure when it reaches the termination of the vena cava
0
Systemic capillary pressure:
35-10 mmHg
Pulmonary artery systolic pressure/ diastolic?
25 mmHg / 8 mm Hg
Blood pressure is:
Phasic
Why is Mean arterial pressure not an average?
More time is spent in diastole than systole…not an even average
Transport blood under high pressure
Arteries
Controls conduits of blood
Arterioles
Involved in exchange between blood and extracellular fluid
Capillaries
Blood pressure begins to drop @ what point?
As arteries branch into Arterioles and into capillaries-distribution of the forces
What percentage of blood is in the systemic circulation?
84%
What percentage of blood is in the heart and lungs?
16%
What percentage of blood is in the veins?
64%
What percentage of blood is in the arteries?
13%
What percentage of blood is in the systemic Arterioles and capillaries?
7%
What percentage of blood is in the heart?
7%
What percentage of blood is in the pulmonary circulation?
9%
Velocity of blood flow is inversely proportional to vascular cross-sectional area:
V= F/A
Norm aortic velocity:
33cm/s
Norm capillary velocity:
0.3 mm/s
Which vessel has the largest cross-sectional area?
CAPILLARY
What does it mean that capillaries have the largest cross-sectional area?
V =F/A
The blood flow velocity will be much slower for exchange to occur
3 principles that underlie all circulatory system functions:
1: rate of blood flow is precisely controlled r/t tissue need
2: CO is controlled by sum of all local tissue flows [w/ limits]
3: Arterial pressure regulation is generally independent of either blood flow control OR CO control
1-Flow control
2-CO control
3:Arterial pressure
What mainly controls Cardiac output?
The sum of all the local tissue flows-tissue demands
If the arterial pressure drops below 100 mm Hg:
- Increase F of heart pumping
- Constrict large venous reservoirs.
- Generally constrict most of the Arterioles throughout the body
- Kidneys may later play role
General underlying rule that guide 3 principles r/t circulatory system function?
It is Based on tissue needs/demands
2 main factors that control blood flow:
Pressure gradient: pressure difference btw 2 ends of vessel
Impediment to blood flow through the vessel [resistance]
*P gradient and resistance
Ohm’s law
Flow through a blood vessel
F= ∆P / R
Ohm’s law and relation to factors:
Directly proportional to pressure difference
Inversely proportional to resistance
Where can you apply poiseuille’s law? Vessel? Body?
You can apply to a single vessel, an organ, or an entire circuit
Blood flow of adult at rest:
5000ml/min
Laminar flow:
Streamline flow;
Flows at steady rate and in layers …vessel is long and smooth.
Not turbulent
Turbulent flow
Nonlayered flow,
Creates murmurs,
Produces more resistance than laminar flow
When does turbulent flow occur?
When flow is too great
When blood passes an obstruction or rough surface
When blood has to make sharp turn
When does blood flow with great resistance?
When eddy currents occur
Tendency for turbulent flow increases:
Direct proportion to velocity of blood flow, diameter of vessel, and density of blood
Inversely proportional to viscosity of blood
What can cause blood to be more dense?
higher # RBC’s
Higher density is directly proportional to increases in turbulent flow
Which aspect of blood flow ensures laminar flow:
Viscosity! Allows blood to be layered
Measure of the tendency for turbulence to occur
Reynolds number;
Re= (vdp) / viscosity
Turbulent flow will occur in SOME regions of a vessel
200-400
Turbulent flow will occur even in a straight vessel
> 2000
_____ is The force exerted by the blood against any unit area of the vessel wall.
Blood pressure
How can pressure be measured?
Manometers or electric transducers
Impediment to blood flow in a vessel
Must be indirectly calculated from measurements of blood flow and pressure
Resistance
Formula for resistance
R = (8viscosityL / πradius^4)
Three major variables that determine resistance:
Vessel radius
Blood viscosity
Vessel length
Arteries have low or high pressure drop d/t low or high resistance
Low pressure drop
Low resistance
Arterioles have low or high pressure drop d/t low or high resistance
High pressure drop
D/t highest resistance
The difference between systolic and diastolic pressure
Pulse pressure
This is highest arterial pressure during a cardiac cycle
Systolic pressure
When is systolic pressure measured? Diastolic pressure?
Systolic: after systole
Diastolic: during relaxation [diastole]
The lowest arterial pressure
Diastolic pressure
Range of systemic resistance:
0.2-4 PRU
How to calculate Resistance:
Pressure difference/ CO = R
Resistance of systemic circulation:
1 PRU
Normal CO
100 ml/s
Pulmonary vascular resistance:
0.14 PRU
In conditions where vessels are strongly constricted, Total peripheral resistance may rise to:
4 PRU
What conditions may cause the total peripheral resistance to drop significantly?
Vessel dilation
The measure of blood flow through a vessel for a given pressure difference
Conductance
Conductance units:
Ml/sec per ml Hg
Conductance is the exact reciprocal of:
Resistance
Conductance is directly proportional to:
Diameter
A minor change in what causes a vast increase in blood flow?
Diameter
Poiseuille’s law:
F = π∆Pr^4 / 8 viscosityL
IS resistance less in series or parallel?
Parallel
Why would blood vessels branch to form parallel circuits supplying blood to the many organs/tissues of the body?
Total resistance is far less than the resistance of any single blood vessel.
Total conductance for vessels =
The sum of the conductance of each parallel pathway
Ex of circulations in parallel:
Brain Kidney Muscle GI Skin Coronary circulation
When you decrease Resistance:
You increase conductance or flow
What effects are there to the body when limb is amputated or kidney removed?
This removes a parallel circuit.
- reduces total conductance
- reduces total blood flow
- increases total vascular resistance
A measure of the fluids internal resistance
Viscosity
Relate viscosity and resistance
Greater viscosity =greater resistance
What is the prime determinant of blood viscosity?
Hematocrit
Viscosity of water is one what is norm blood?
3
Average male Hct:
42
Average female hct:
38
Viscosity of blood at polycythemia:
10
Hct rises to 60-70:
Polycythemia
Viscosity of water is one. What is blood plasma?
1.5
F= π∆Pr^4 / 8nl
What are directly related and what is inversely related?
Viscosity and l inverse
P and radius directly related
Viscosity and anemia
Decreases viscosity
Polycythemia and viscosity
Increases
The ability of each tissue to adjust its vascular resistance and to maintain normal blood flow through changes in arterial pressure btw approx. 70 and 175 mm Hg
Blood flow autoregulation
Not enough pressure to maintain vessel
Critical closing pressure
Autoregulation occurs btw pressures of:
75 and 175 mm Hg
