16. PHYSICS OF THE CIRCULATION SYSTEM (PART 1) Flashcards
1
Q
- What are the three components of the Cardiovascular system?
A
- Blood is the vehicle for transport
- The circulatory system is the distribution system
- it consists of a series of branches blood vessels
- blood represents about 7% of our body mass - The heart is a four-chambered pump
- it is composed mostly of cardiac muscles
- these enable the circulatory flow
- each section of the heart pumps about 80 mL with
each contraction
2
Q
- In Newtonian terms, what kind of fluid is blood?
A
- it is a Non-Newtonian fluid
3
Q
- What does the blood solution consist of?
A
- plasma
- red blood cells
- white blood cells
- platelets
4
Q
- What does Blood Viscosity increase with?
A
- it increases with hematocrits
HEMATOCRITS= the volume percentage of red blood cells in blood
5
Q
- What is the Rate of Deformation of a Newtonian Fluid?
A
- it is the velocity gradient
- it is proportional to the shear stress
VISCOSITY:
- the constant of proportionality
6
Q
- What can be said about the shear stress in solid substances?
A
- it is proportional to the deformation rate
7
Q
- What variation exists with regards to Newtonian and Non-Newtonian fluids?
A
- a variation in the shear stress with the rate of deformation
VISCOSITY:
- the slope of a curve at a point
- this is the apparent viscosity at that point
8
Q
- Blood is a Non-Newtonian fluid, however, we regards it as a Newtonian fluid within this section of studies.
Why is that?
A
- Blood behaves with an extreme similarity to a Newtonian Material
9
Q
- What is a Newtonian Fluid?
A
IT IS A FLUID WITH:
- a constant viscosity
- zero shear rate at zero shear stress
- the shear rate being directly proportional to the
shear stress
10
Q
- What is Blood Pressure?
A
- it is the pressure needed to push blood flow
11
Q
- What is the Oscillating pressure of blood as it leaves the aorta?
A
- it has pressures of between 80 mmHg and 120 mmHg
- this is reflected by the Oscillations in blood pressure
along the major arteries in systemic circulation
12
Q
- How long does systole last in one cycle?
A
- it lasts about ⅓ of the cycle
SYSTOLE = a phase of the heartbeat
= when the heart muscle contracts and pumps
blood from the chambers into the arteries
13
Q
- How do we calculate the weighted sum of blood pressure?
A
14
Q
- What is P pulse?
A
- this is the arterial pulse pressure
- it is the difference in pressure between systole and
diastole - this pressure difference is 40mmHg
DIASTOLE= a phase of the heartbeat
= this is when the heart muscle relaxes
= this allows the chambers to fill with blood
15
Q
- Where does much of the pressure drop within the arterial system?
A
- it drops within the arterioles
(the small arteries) - the capillaries
16
Q
- What can be said about the blood pressure in the veins?
A
- it is very low
17
Q
- What does the Pulmonary System mirror?
A
- systemic circulation
EXCEPT:
- all the pressures are lower
18
Q
- What happens when you stand upright?
(with regards to pressure)
A
- there is an additional pressure
- p.g.h
- h = the height relative to the heart
19
Q
- What is the approximate height in the upper arm where the blood measurements are made?
A
p = 1 060 kg/m³
g = 9.8 m/s²
h = 1m
P (pressure) = 10 400 Pa
= 79 mmHg
20
Q
- What can be said about the driving pressure difference from the arteries to the veins AT ANY GIVEN HEIGHT?
A
- it is unchanged
21
Q
- Why is it not important to consider the pressure change between the arteries and the veins WHEN looking at the pressure changes between the inside and the outside of a vessel?
A
- the p.g.h is added to both the inside and the outside of the vessel
- the effect of gravity is significant
22
Q
- How high does the blood pressure at the aorta have to be?
A
- it has to be high enough to pump the blood to the top of the brain
- this has a height of 40cm
- the pressure drop is about 30mmHg
23
Q
- What manifestation shows the effect of gravity?
A
- the potential of fainting when you stand
- the negative effects of standing on your head for long
periods of time - the veins in your head are not designed to pump blood
back to the heart - your feet would also stop receiving blood
- it is also why varicose veins are worse when you stand
upright - this is because blood needs to be pumped up
24
Q
- What happens when you stand up?
A
- the volume of blood in the veins in your legs increases
- the pressure in the veins decreases
(these veins pump blood back to the heart from the leg) - this decreases the cardiac output
- this decreases the flow of blood to the brain
HOWEVER:
- the reflex constriction of the leg veins makes sure that
the above mentioned rarely happens
25
Q
- What is the effect of the reflex arteriolar constriction of the veins in the legs?
A
- it limits the blood pool
- it increases the blood flow resistance
- this lessens the decrease in arterial blood pressure
26
Q
- What are the two types of conditions that the mechanical properties of blood vessels can be measured under?
A
- THE LENGTH OF THE GIVEN VESSEL IS KEPT
CONSTANT- the diameter is measured
- this is a result of the distending pressure
- THE DIAMETER OF THE GIVEN VESSEL IS KEPT
CONSTANT- the length is measured
- this is because it is stretched longitudinally
27
Q
- What affects the flow of blood in the arteries?
A
- the changes in the rate of the heart beat
- the volume of blood pumped per beat
(stroke volume) - changes in the arteries themselves
- they control their diameters
- they do this through chemical and neural mechanisms
28
Q
- Are blood vessels elastic or inelastic?
A
- they are elastic
- these tubes can change their diameter and area
- this is based on the pressure and the temperature they
are exposed to
29
Q
- What are the two physical attributes of blood vessels in a steady state?
A
- THEY HAVE A RESISTANCE TO BLOOD FLOW
- they need a pressure difference along the length of
the vessel - this will drive the blood flow
- they need a pressure difference along the length of
- THEY HAVE A COMPLIANCE
- this is in response to a distending pressure
- DISTENDING = swelling caused by pressure from the
inside
NB: without pressure fluid or tilting of the vessel
- no fluid will flow within the vessel
30
Q
- What is a Rigid Vessel?
A
- a rigid vessel has a constant volume (V)
- this is called a Resistance Vessel
- it has only friction present
- there is no compliance
- the flow rate of this vessel is affected by the pressure
drop inside the vessel
31
Q
- What is an Elastic Vessel?
A
- a vessel that has no noticeable resistance
- this is called a Compliance Vessel
- the volume of this vessel is affected by the pressure
difference between the inside and the outside of the
vessel
32
Q
- What can be said about real blood vessels?
A
- they have attributes of both Resistance and Compliance Vessels
33
Q
- What are three examples of vessels that are similar to Compliance Vessels?
A
- the Aorta
- Large Arteries
- Large Veins
- the pressure drops along these vessels are relatively
small
34
Q
- What are three examples of vessels that are similar to Resistance Vessels?
A
- Arterioles
- Capillaries
- Venules
35
Q
- Which vessel is the main site for pressure drops?
A
- arterioles
- this is why the heart needs to pump blood at such high pressures
36
Q
- How would we mathematically explain the relationship between the pressure inside and outside the blood vessel walls?
A
▵P = P - Pext
- the pressure inside the blood vessels walls (P)
is GREATER than the pressure outside (Pext)
37
Q
- What is the Law of Laplace for hallow cylinders?
A
T = ▵P x R
T = tension
▵P = change in pressure
R = the radius of curvature
