THE ARTERIAL DISTRIBUTION AND VENOUS COLLECTION SYSTEMS Flashcards
_______________ is the study of the physical laws of blood circulation. It therefore addresses the properties of both the “content” (i.e., blood) and the “container” (i.e., blood vessels).
Hemodynamics
True or False: The circulation is not a system of rigid tubes.
True
We can think of the _________ as a distribution system, the ______________ as a diffusion and filtration system, and the ______ as a collection system.
arteries
microcirculation
veins
The aorta branches out into billions of capillaries that ultimately regroup into a __________.
single vena cava
At each level of arborization of the peripheral circulation, the values of several key parameters vary dramatically:
- Number of vessels at each level of arborization
- Radius of a typical individual vessel
- Aggregate cross-sectional area of all vessels at that level
- Mean linear velocity of blood ow within an individual vessel
- Flow (i.e., volume/second) through a single vessel
At each level of arborization of the peripheral circulation, the values of several key parameters vary dramatically: (II)
- Relative blood volume (i.e., the fraction of the body’s total blood volume present in all vessels of a given level)
- Circulation (i.e., transit) time between two points of the circuit
- Pressure pro le along that portion of the circuit
- Structure of the vascular walls
- Elastic properties of the vascular walls
The _____________ at a particular level of arborization increases enormously from a single aorta to ∼104 small arteries, 107 arterioles, and finally ∼4 ×1010 capillaries.
number of vessels
However, only about __________ of all capillaries are normally open to ow at rest. Finally, all of the blood returns to a single vessel where the superior and inferior venae cavae join.
one fourth
The ____________ declines as a result of the arborization, decreasing from 1.1 cm in the aorta to a minimum of ∼3 μm in the smallest capillaries.
radius of an individual vessel
Because the cross-sectional area of an individual vessel is __________ to the square of the radius, this parameter decreases even more precipitously.
proportional
The ______________ at any level of branching is the sum of the single cross-sectional areas of all parallel vessels at that level of branching.
aggregate cross-sectional area
A fundamental law of vessel branching is that at each branch point, the combined cross-sectional area of daughter vessels ____________ the cross-sectional area of the parent vessel.
exceeds
In this process of bifurcation, the steepest increase in total cross-sectional area occurs in the _____________.
microcirculation
A _______________ in the smooth muscle and submucosa of the intestine encompasses a first-order arteriole, several orders of progressively smaller arterioles, capillaries, several orders of venules into which the capillaries empty, and eventually a first-order venule.
typical microcirculation
In humans, the maximum cross-sectional area occurs not at the level of the capillaries but at the “_______________” (i.e., fourth-order) venules.
postcapillary
Because of anastomoses among capillaries, capillaries only _____________ fourth-order venules, whereas the cross-sectional unit area of each venule is appreciably _______ than the area of a capillary.
Slightly outnumber
greater
Assuming that only a quarter of the capillaries are usually open, the peak aggregate cross-sectional area of these postcapillary venules can be ~______________ than the cross section of the parent artery (e.g., aorta).
1000-fold greater
The profile of the _________________ of flow (v) along a vascular circuit is roughly a mirror image of the profile of the total cross-sectional area.
Mean linear velocity
According to the _____________, which is an application of conversation of mass, TOTAL VOLUME FLOW of blood must be the same at any level of arborization.
Principle of continuity
As a consequence, v must be minimal in the postcapillary venules (~_______ cm/s) where A(total) is maximal.
0.03 cm/s
Conversely, v is maximal in the aorta (~__________ cm/s)
20 to 50 cm/s
Thus, both A(total) and v values range ~1000 fold from the aorta to the capillaries but are ___________ to one another.
Inversely related
The vena cava with a cross-sectional area ~50% larger than that of the aorta, has a mean linear velocity that is about __________.
One third less
___________, in contrast to total flow, varies by ~10 orders of magnitude.
Single-vessel flow
In the aorta, the flow is ______ the same as the cardiac output (~5 L/min).
~83 mL/s
When about ____ of the capillaries are open, a typical capillary has a mean linear velocity of 0.03 cm/s and a flow of 8x10-9 mL/s (8 pL/s) - 10 orders of magnitude less than the flow in the aorta.
25%
True or False: Within the microcirculation, single-vessel flow has considerable range.
True
Most of the blood volume resides in the _________.
Systemic veins
The body’s ______________ of about 5 L is not uniformly distributed along the x-axis.
Total blood volume (V)
At any level of branching, the __________ is the sum of the volumes of all parallel branches.
Total blood volume
Percentage of total blood volume.
Relative blood volumes
First, we can divide the blood volume into the systemic circulation (where ____ of blood resides), the pulmonary circulation (____) and the heart chambers (_____).
85%
10%
5%
________________ is quite adjustable (i.e, it can be much higher than 10%) and is carefully regulated.
Pulmonary blood volume
We can divide blood volume into what is contained in the high-pressure system (____), the low-pressure system (____) and the heart chambers (____).
15%
80%
5%
Of the 85% of the total blood volume that resides in the systemic circulation about three fourths ____% of the total- is on the venous side, particularly in the smaller veins.
65%
Thus the _________ acts as a volume reservoir.
Venous system
An abrupt increase in venous capacity causes pooling of blood in venous segments and may lead to ___________.
Syncope
We can also use a fourth approach for grouping of blood volumes - divide the blood into the _______________ (volumes of heart chambers and pulmonary circulation) versus the rest of circulation.
Central blood volume
This is very adjustable and it constitutes the filling reservoir for the left heart.
Central blood group
Can cause the normally careful regulation of the central blood volume to break down.
Left-sided heart failure
The _______________ is the time required for a bolus of blood to travel either across the entire length of the circulation or across a particular vascular bed.
Circulation time
Total circulation time is ____ minute.
1 minute
Circulatory time across a single vascular bed (i.e coronary circulation) may be as short as ___________.
10 seconds
Circulation times may be obtained in humans by injection of a substance such as _________ into an antecubital vein and measurement of the time to its appearance in the lung (___ to ____ seconds) or by injection of a bitter or sweet substance and measurement of the time to the perception of taste in the tongue (____ to ____ seconds).
Ether
4 to 8 seconds
10 to 18 seconds
Although in the past, circulation time was used clinically as an index of __________, the measurement has little physiological significance.
Cardiac output
The rationale for determination of ___________ was that a shortening of circulation time could signify an improvement of cardiac output.
Circulation time
However, the interpretation is more complicated because the _____________ is actually the ratio of blood volume to blood flow.
circulation time
True or False: Changes in circulation time may thus reflect no changes in volume as well as in flow.
False: Changes
The intravascular pressures along the systemic circuit are ______ than those along the pulmonary circuit.
Higher
Pressures are far ________ in the systemic than in the pulmonary circulation.
Higher
Although the cardiac output of the left and right hearts are the same in the steady state, the total resistance of the systemic circulation is far _____ than that of the pulmonary circulation.
Higher
This difference explains why the upstream driving pressure averages ___ mmHg in the systemic circulation but only ____ mmHg in the pulmonary circulation.
95 mmHg
15 mmHg
In both the systemic and pulmonary circulations, the systolic and diastolic pressures ________ downstream from the ventricles.
Decay
In addition, the systemic venous and pulmonary pressures vary with the respiratory cycle and venous pressure in the lower limbs varies with the contraction of _______________.
Skeletal muscle
The ___________ extends froms the left ventricle in the contracted state all the way to the systemic arterioles.
High pressure system
The ____________ extends from the systemic capillaries, through the rest of the systemic circuit into the right heart and then through the pulmonary circuit into the left heart in the relaxed state.
Low-pressure system
The ____________, unlike the systemic circuit is entirely a low pressure system; ___________ normally do not exceed 15 mmHg and the _________ do not rise above 10 mmHg.
Pulmonary circuit
Mean arterial pressure
Capillary pressures
Under normal conditions, the steepest pressure drop in the sytemic circulation occurs in __________, the site of greatest vascular resistance.
Arterioles
It is the ___________ of each vascular segment that determines the profile of pressure fall between the upstream arterial and downstream venous ends of the circulation.
resistance
In particular, the pressure difference between two points along the axis of the vessel depends on the _______ and ___________.
Flow and resistance
According to ___________, the resistance (Ri) of an individual, unbranched vascular segment is inversely proportional to the fourth power of the radius,
Poiseuille’s law
Thus the pressure drop between any two points along the circuit depends critically on the ____________ between these two points.
Diameter of the vessels
The steepest pressure drop does not occur along the capillaries where vessel diameters are smallest but rather along the _______________.
Precapillary arterioles
The _______________ contributed by vessels of a particular order of arborization depends not only on their average radius but also on the number of vessels in parallel.
Aggregate resistance
The more vessels in parallel, the ________ the aggregate resistance.
Smaller
True or False: Although the resistance of a single capillary exceeds that of a single arteriole, capillaries far outnumber arterioles.
True
The result is that aggregate resistance is larger in the arterioles and this is where the ____________ occurs.
Steepest 🔼P
________________ depends on the distribution of vascular resistance.
Local intravascular pressure
The major site of control of vascular resistance in the systemic circulation is the _____________ and ____________.
Terminal small arteries or feed arteries and arterioles
During ___________, the pressure drop between two points along the circuit is steep and concentrated at the arteriolar site.
Arteriolar constriction
During __________, the gradient is shallow and more spread out.
Arteriolar dilation
