1
Q
What are the systolic and diastolic pressures in the main pulmonary artery?
A
Systolic pressure: 25 mm Hg, Diastolic pressure: 8 mm Hg
The mean pressure in the pulmonary artery is about 15 mm Hg.
2
Q
What is the mean pressure in the pulmonary circulation?
A
About 15 mm Hg
This is roughly one-sixth of the typical mean pressure in the aorta, which is 100 mm Hg.
3
Q
What are the pressures in the right and left atriums?
A
Right atrium: about 2 mm Hg, Left atrium: about 5 mm Hg
These pressures are not very dissimilar.
4
Q
What is the pressure difference from inlet to outlet of the pulmonary system?
A
10 mm Hg
Calculated as (15 − 5) mm Hg.
5
Q
What is the pressure difference from inlet to outlet of the systemic system?
A
98 mm Hg
Calculated as (100 − 2) mm Hg.
6
Q
How does the pressure difference in the pulmonary system compare to that in the systemic system?
A
Pulmonary system has a pressure difference of 10 mm Hg, systemic system has 98 mm Hg
This shows a factor of 10 difference between the two systems.
7
Q
What are the characteristics of the walls of the pulmonary artery and its branches?
A
They are remarkably thin and contain relatively little smooth muscle
They can be easily mistaken for veins.
8
Q
How do the walls of systemic circulation arteries compare to those of the pulmonary circulation?
A
Systemic circulation arteries have thick walls and abundant smooth muscle
This is particularly true for arterioles.
9
Q
What is the primary function of the systemic circulation?
A
To regulate the supply of blood to various organs
This includes organs that may be far above the level of the heart, such as the brain.
10
Q
How does the lung’s function differ from that of the systemic circulation?
A
The lung accepts the whole of the cardiac output at all times
It is rarely concerned with directing blood from one region to another, except in response to localized alveolar hypoxia.
11
Q
What is the arterial pressure in the lungs primarily designed to do?
A
Keep it as low as necessary to lift blood to the top of the lung
This minimizes the work of the right heart for efficient gas exchange.
12
Q
Fill in the blank: The pulmonary artery walls are easily mistaken for _______.
A
veins
13
Q
True or False: The pulmonary circulation has high arterial pressure to facilitate blood flow.
A
False
14
Q
What is the pressure within the pulmonary capillaries compared to pulmonary arterial and venous pressure?
A
It lies about halfway between pulmonary arterial and venous pressure.
15
Q
Where does much of the pressure drop occur in the pulmonary circulation?
A
Within the capillary bed itself.
16
Q
How does the distribution of pressures along the pulmonary circulation compare to the systemic circulation?
A
It is far more symmetrical than in the systemic circulation.
17
Q
In the systemic circulation, where is most of the pressure drop located?
A
Just upstream of the capillaries.
18
Q
What causes the variability of pressure within the pulmonary capillaries throughout the lung?
A
Hydrostatic effects.
19
Q
True or False: The pressure within the pulmonary capillaries is constant throughout the lung.
A
False.
20
Q
What surrounds the pulmonary capillaries?
A
Gas
The pulmonary capillaries are virtually surrounded by gas.
21
Q
What type of cells line the alveoli?
A
Epithelial cells
There is a very thin layer of epithelial cells lining the alveoli.
22
Q
What can cause pulmonary capillaries to collapse or distend?
A
Pressures within and around them
The capillaries are liable to collapse or distend depending on these pressures.
23
Q
How does the pressure in the alveoli typically compare to atmospheric pressure?
A
Usually close
During breath-holding with the glottis open, alveolar pressure is identical to atmospheric pressure.
24
Q
What reduces the effective pressure around the capillaries under special conditions?
A
Surface tension of the fluid lining the alveoli
This reduction occurs under specific conditions.
25
What is the effective pressure around the capillaries usually equal to?
Alveolar pressure
## Footnote
Typically, the effective pressure is alveolar pressure.
26
What happens when alveolar pressure rises above capillary pressure?
Capillaries collapse
## Footnote
The pressure difference leads to the collapse of the capillaries.
27
What is the term for the pressure difference between the inside and outside of the capillaries?
Transmural pressure
## Footnote
This term describes the pressure difference affecting the capillaries.
28
What is the pressure around the pulmonary arteries and veins compared to alveolar pressure?
Considerably less than alveolar pressure
## Footnote
This indicates that the pressure surrounding the pulmonary arteries and veins decreases as the lung expands.
29
What effect does lung expansion have on the pulmonary blood vessels?
Pulled open by the radial traction of elastic lung parenchyma
## Footnote
The elastic lung tissue exerts a pulling force that helps expand the blood vessels.
30
What is the effective pressure around the pulmonary arteries and veins during lung expansion?
Low, potentially less than intrapleural pressure
## Footnote
This paradoxical situation arises from the mechanical advantage of surrounding expanding elastic material.
31
What mechanical advantage is observed with blood vessels surrounded by lung parenchyma?
Relatively rigid structure surrounded by rapidly expanding elastic material
## Footnote
This mechanical advantage explains the low effective pressure around the vessels.
32
What happens to the caliber of arteries and veins as the lung expands?
Increase in caliber
## Footnote
Both the pulmonary arteries and veins become wider as the lung expands.
33
What are the two categories of blood vessels in the lungs?
Alveolar vessels and extra-alveolar vessels
## Footnote
Alveolar vessels are exposed to alveolar pressure, while extra-alveolar vessels run through lung parenchyma.
34
What type of vessels are included in alveolar vessels?
Capillaries and slightly larger vessels in the corners of the alveolar walls
## Footnote
Alveolar vessels are directly influenced by alveolar pressure.
35
What determines the caliber of alveolar vessels?
The relationship between alveolar pressure and the pressure within them
## Footnote
This relationship directly impacts blood flow in the lungs.
36
What are extra-alveolar vessels?
All the arteries and veins that run through the lung parenchyma
## Footnote
Their caliber is influenced by lung volume.
37
What affects the caliber of extra-alveolar vessels?
Lung volume
## Footnote
Lung volume determines the expanding pull, or radial traction, of the parenchyma on their walls.
38
Where are the very large vessels near the hilum located?
Outside the lung substance
## Footnote
These vessels are exposed to intrapleural pressure.
39
True or False: Alveolar vessels are influenced by lung volume.
False
## Footnote
Alveolar vessels are influenced by alveolar pressure, not lung volume.
40
Fill in the blank: Alveolar vessels are exposed to _______.
alveolar pressure
41
Fill in the blank: Extra-alveolar vessels are influenced by _______ of the lung.
lung volume
42
How is lung vascular pressure calculated?
## Footnote
input pressure = pulmonary artery
output pressure = left atrium
bloodflow = cardiac output
43
What is the relationship between vascular resistance and blood flow?
The number for vascular resistance often depends on the magnitude of the blood flow
## Footnote
Vascular resistance is not a complete description of pressure-flow properties but allows for comparisons under different conditions.
44
What is the total pressure drop from the pulmonary artery to the left atrium in the pulmonary circulation?
About 10 mm Hg
## Footnote
This is significantly lower compared to the systemic circulation, which has a pressure drop of about 100 mm Hg.
45
How does the pulmonary vascular resistance compare to systemic vascular resistance?
Pulmonary vascular resistance is only one-tenth that of systemic vascular resistance
## Footnote
This is due to the similar blood flow rates in both circulations.
46
What is the pulmonary blood flow rate?
About 6 liters·min−1
## Footnote
This figure is used to calculate pulmonary vascular resistance.
47
Calculate the pulmonary vascular resistance using the given pressures and flow rate.
About 1.7 mm Hg·liter−1·min
## Footnote
Calculated from the formula (15 − 5)/6.
48
What largely causes the high resistance of the systemic circulation?
Very muscular arterioles
## Footnote
These arterioles regulate blood flow to various organs.
49
What type of vessels does the pulmonary circulation lack?
Muscular arterioles
## Footnote
This contributes to its low resistance.
50
The pulmonary circulation has low resistance to distribute blood in a thin film over a vast area in the _______.
alveolar walls
## Footnote
This is necessary for efficient gas exchange.
51
What is the normal state of pulmonary vascular resistance?
Extraordinarily small
## Footnote
This indicates that under typical conditions, the resistance in the pulmonary vasculature is minimal.
52
What happens to pulmonary vascular resistance when pulmonary arterial or venous pressure increases?
It falls
## Footnote
This relationship indicates that the pulmonary vascular system can adapt to changes in pressure.
53
What are the two mechanisms responsible for the fall in pulmonary vascular resistance?
Recruitment and increased blood flow
## Footnote
Recruitment refers to the opening of previously closed capillaries to allow blood flow.
54
What does the term 'recruitment' refer to in the context of pulmonary vascular resistance?
The opening of capillaries to conduct blood as pressure rises
## Footnote
This mechanism is crucial for reducing resistance when pulmonary artery pressure increases.
55
Why are some capillaries unperfused at low perfusing pressures?
Not fully understood; possibly due to random differences in geometry
## Footnote
These differences may create preferential channels for blood flow.
56
Fill in the blank: An increase in pulmonary arterial or venous pressure causes pulmonary vascular resistance to _______.
fall
57
True or False: The fall in pulmonary vascular resistance occurs only at low pulmonary artery pressures.
False
## Footnote
The fall in resistance is observed as pressure is raised from low levels.
58
What is the chief mechanism for the fall in pulmonary vascular resistance as the pulmonary artery pressure is raised?
Recruitment of capillaries
## Footnote
This mechanism plays a key role in accommodating increased blood flow.
59
How does pressure in the pulmonary vessels affect blood flow in capillaries?
Higher pressure opens closed capillaries, allowing blood flow
## Footnote
This change in flow contributes to the decrease in overall vascular resistance.
60
What happens to vascular resistance at large lung volumes?
Vascular resistance is low
## Footnote
The expansion of the lung pulls the extra-alveolar vessels open.
61
What occurs to vascular resistance at low lung volumes?
Resistance is high
## Footnote
Smooth muscle and elastic tissue in vessel walls resist distension.
62
What is the effect of smooth muscle tone when the lung is completely collapsed?
Pulmonary artery pressure must be raised above downstream pressure
## Footnote
This is necessary before any flow occurs.
63
What is defined as critical opening pressure?
The pressure required to initiate flow when the lung is collapsed
## Footnote
It reflects the effectiveness of smooth muscle tone in the vessels.
64
Fill in the blank: At large lung volumes, the extra-alveolar vessels experience _______.
low vascular resistance
65
Fill in the blank: The walls of extra-alveolar vessels contain _______ and _______ that resist distension.
smooth muscle, elastic tissue
66
What influences the vascular resistance of the capillaries?
Whether alveolar pressure changes with respect to capillary pressure.
67
What happens to capillary vessels when alveolar pressure rises with respect to capillary pressure?
The vessels tend to be squashed, and their resistance rises.
68
What typically occurs to pulmonary capillary pressure when a normal subject takes a deep inspiration?
Capillary pressure decreases and likely gets squashed.
due to vascular pressures falling since the heart is surrounded by intrapleural pressure, which falls on inspiration.
69
Do pressures in the pulmonary circulation remain steady after a deep inspiration?
No, they do not remain steady.
70
What happens to the caliber of capillaries at large lung volumes?
The caliber is reduced because of stretching across the walls.
71
Even if the transmural pressure of the capillaries is not changed with large lung inflations, what happens to their vascular resistance?
Their vascular resistance increases due to longitudinal stretching of the capillaries
## Footnote
A piece of thin-walled rubber tubing that is stretched across its diameter.
72
What role does smooth muscle play in pulmonary vascular resistance?
Smooth muscle determines the caliber of the extra-alveolar vessels, affecting pulmonary vascular resistance.
73
Which substances increase pulmonary vascular resistance?
* Serotonin
* Histamine
* Norepinephrine
* Endothelin
74
When are vasoconstrictors particularly effective in the pulmonary circulation?
When the lung volume is low and the expanding forces on the vessels are weak.
75
What substances can relax smooth muscle in the pulmonary circulation?
* Acetylcholine
* Calcium channel blockers
* Nitric oxide
* Phosphodiesterase-5 inhibitors
* Prostaglandin I2 (PGI2)
76
True or False: Hypoxia plays an important role in pulmonary vascular resistance.
True
77
What principle is used to calculate the volume of blood passing through the lungs each minute?
The Fick principle
Vo2 = Q (AVo2 diff)
Q = Vo2 / (Avo2 diff)
## Footnote
The Fick principle relates O2 consumption to the amount of O2 taken up by the blood in the lungs.
78
According to the Fick principle, what is the relationship between O2 consumption at the mouth and O2 uptake by blood in the lungs?
They are equal
## Footnote
O2 consumption per minute measured at the mouth equals the O2 taken up by the blood in the lungs.
79
How can the O2 concentration in expired gas be measured?
By collecting it in a large spirometer
## Footnote
The concentration is measured to calculate O2 consumption.
80
What modern systems are used to estimate O2 consumption?
Flow sensors and oxygen analyzers
## Footnote
These are connected to a mouthpiece to measure O2 consumed per breath.
81
Where is mixed venous blood obtained from?
From a catheter in the pulmonary artery
## Footnote
This is used for measuring O2 uptake in the lungs.
82
How is arterial blood typically obtained for measurements?
By puncture of the radial artery
## Footnote
This is necessary for comparing venous and arterial blood O2 levels.
83
Which dilution techniques can be used to determine pulmonary blood flow?
saline
dye
84
Describe the dye dilution technique for measuring pulmonary blood flow
To measure blood flow by injecting a dye or indicator
## Footnote
The concentration of the indicator in arterial blood is recorded.
85
Describe the saline dilution technique for measuring pulmonary blood flow
Infusing cold saline and measuring downstream temperature change
## Footnote
This method tracks how blood temperature changes in response to saline infusion.
86
How does blood flow in the upright human lung change from bottom to top?
Blood flow decreases almost linearly from bottom to top, reaching very low values at the apex.
## Footnote
This distribution is influenced by posture and exercise.
87
What happens to blood flow distribution when a subject lies supine?
Apical zone blood flow increases, while basal zone flow remains virtually unchanged, resulting in almost uniform distribution.
## Footnote
In this posture, blood flow in the posterior regions exceeds that in the anterior parts.
88
What is observed in subjects suspended upside down regarding blood flow?
Apical blood flow may exceed basal flow in this position.
## Footnote
This indicates that posture significantly affects blood flow distribution.
89
What effect does mild exercise have on regional blood flow in the lungs?
Both upper and lower zone blood flows increase, and regional differences become less pronounced.
## Footnote
This suggests that exercise helps to equalize blood flow across different lung regions.
90
What explains the uneven distribution of blood flow?
Hydrostatic pressure differences within the blood vessels
## Footnote
This concept is crucial for understanding blood flow dynamics in different body regions.
91
How does the height of the lung affect blood flow?
It creates a pressure difference due to hydrostatic forces
## Footnote
This principle illustrates how gravity influences circulation in upright positions.
92
What is zone 1 in the lung?
A region (usually near the top of the lung) where pulmonary arterial pressure falls below alveolar pressure, causing capillaries to be squashed flat and no flow to be possible.
## Footnote
This condition typically does not occur under normal circumstances.
93
Under what conditions can zone 1 occur?
When pulmonary arterial pressure is reduced or alveolar pressure is raised.
## Footnote
Examples include septic shock, hemorrhage, or positive pressure ventilation.
94
True or False: Zone 1 occurs under normal physiological conditions.
False
## Footnote
Normal pulmonary arterial pressure is sufficient to maintain blood flow to the top of the lung.
95
Fill in the blank: In zone 1, pulmonary arterial pressure falls below _______.
alveolar pressure
96
What happens to capillaries in zone 1?
They are squashed flat, preventing blood flow.
97
What effect does positive pressure ventilation have on the lung?
It can raise alveolar pressure, potentially leading to zone 1 conditions.
98
What physiological phenomenon does zone 1 create?
alveolar deadspace (regions have ventilation but no blood flow therefore no gas exchange)
99
What happens to pulmonary arterial pressure in zone 2 of the lung?
Pulmonary arterial pressure increases and exceeds alveolar pressure
## Footnote
This increase is due to the hydrostatic effect.
100
What is the relationship between venous pressure and alveolar pressure in zone 2?
Venous pressure is very low and less than alveolar pressure
## Footnote
capillaries get crushed by alveolar pressure
101
How is blood flow determined in zone 2 of the lung?
By the difference between arterial and alveolar pressures
## Footnote
This is unlike the usual arterial-venous pressure difference.
102
Under what condition does venous pressure influence blood flow?
When it exceeds alveolar pressure
## Footnote
Otherwise, venous pressure has no effect on flow.
103
What is the overall behavior of blood flow in the pulmonary capillary bed often referred to as?
The Starling resistor, sluice, or waterfall effect
## Footnote
This terminology reflects the unique flow characteristics in this region.
104
What is the pressure difference responsible for flow in zone 2?
The pressure difference increases due to increasing arterial pressure down the zone
## Footnote
Alveolar pressure remains constant throughout the lung.
105
What occurs in terms of capillary recruitment down zone 2?
Increasing recruitment of capillaries
## Footnote
This phenomenon contributes to the overall increase in blood flow.
106
What occurs in zone 3 regarding venous and alveolar pressure?
Venous pressure exceeds alveolar pressure, and flow is determined by the arterial-venous pressure difference.
107
What chiefly causes the increase in blood flow in zone 3?
Distension of the capillaries.
108
How does the pressure within capillaries change down zone 3?
The pressure within capillaries increases, while the alveolar pressure remains constant.
109
What happens to the transmural pressure of capillaries in zone 3?
The transmural pressure rises.
110
What is observed regarding the mean width of capillaries in zone 3?
Measurements show that their mean width increases.
111
What role does the recruitment of previously closed vessels play in zone 3?
It may contribute to the increase in blood flow down this zone.
112
At low lung volumes, what becomes important in determining blood flow?
The resistance of the extra-alveolar vessels.
113
Where does reduced regional blood flow start in the lungs?
At the base of the lung.
114
What is zone 4 characterized by?
A region of reduced blood flow due to narrowing of extra-alveolar vessels.
115
Why do extra-alveolar vessels narrow in zone 4?
Because the lung around them is poorly inflated.
116
What causes uneven blood flow in the lung? (aside from gravity)
Complex, partly random arrangement of blood vessels and capillaries
## Footnote
This arrangement leads to inequality of blood flow at any given level in the lung.
117
How does blood flow change along the acinus?
Blood flow decreases along the acinus, with peripheral parts less well supplied with blood
## Footnote
This indicates a gradient in blood supply from central to peripheral regions.
118
Which regions of the lung receive less blood flow? (barring gravitational effects)
Peripheral regions receive less blood flow than central regions
## Footnote
Measurements suggest a disparity in blood flow distribution within the lung.
119
What dominates the vascular resistance and flow distribution in the pulmonary circulation under normal conditions?
Passive factors
## Footnote
These factors include the physical properties of blood vessels and the effects of gravity.
120
What occurs when the Po2 of alveolar gas is reduced?
Hypoxic pulmonary vasoconstriction
## Footnote
This is a physiological response that involves the contraction of smooth muscle in small arterioles.
121
What is the mechanism behind hypoxic pulmonary vasoconstriction?
Contraction of smooth muscle in the walls of small arterioles
## Footnote
This contraction occurs specifically in hypoxic regions.
122
Does hypoxic pulmonary vasoconstriction depend on central nervous connections?
No
## Footnote
Excised segments of pulmonary artery can still constrict in a hypoxic environment.
123
What primarily determines the response in hypoxic pulmonary vasoconstriction?
The Po2 of the alveolar gas
## Footnote
This is distinct from the pulmonary arterial blood Po2.
124
What happens when a lung is perfused with blood of high Po2 while keeping the alveolar Po2 low?
hypoxic vasoconstriction still occurs
## Footnote
This indicates that the local action of hypoxia on the artery is crucial.
125
How do blood vessel walls "detect" and subsequently react to alveolar hypoxia?
* thin wall allows rapid diffussion over short distance
* vessel wall becomes hypoxic
* cause release of Ca2+
126
How does the proximity of alveoli affect small pulmonary arteries?
Small pulmonary arteries are very closely surrounded by alveoli.
## Footnote
This is in contrast to small pulmonary veins.
127
Describe the stimulus-response curve of hypoxia induced vasoconstriction.
The stimulus-response curve is very nonlinear.
## Footnote
This indicates varying responses at different levels of alveolar Po2.
128
What occurs to blood vessels when the alveolar Po2 is altered above 100 mm Hg?
Little change in vascular resistance is seen.
## Footnote
This suggests that high levels of alveolar Po2 do not significantly affect vascular behavior.
129
What happens to blood vessels when the alveolar Po2 is reduced below approximately 70 mm Hg?
Marked vasoconstriction may occur.
## Footnote
This is a critical threshold for initiating a significant vascular response.
130
What is the major trigger/mechanism for smooth muscle contraction in hypoxic pulmonary vasoconstriction?
An increase in cytoplasmic calcium ion concentration
## Footnote
This mechanism is still under extensive research.
131
Which channels are inhibited that contribute to the increase in cytoplasmic calcium ion concentrations? (Hypoxia induced vasoconstriction)
Voltage-gated potassium channels
## Footnote
Inhibition of these channels leads to membrane depolarization.
132
What physiological change occurs as a result of membrane depolarization in response to alveolar hypoxia?
Increased cytoplasmic calcium ion concentrations
## Footnote
This change is crucial for smooth muscle contraction.
133
True or False: The mechanism of hypoxic pulmonary vasoconstriction is fully understood.
False
## Footnote
It remains a subject of much research.
134
Fill in the blank: An increase in cytoplasmic calcium ion concentration is a major _______ for smooth muscle contraction.
trigger
135
How is nitric oxide usually formed?
L-arginine + endothelial nitric oxide synthase
136
describe the pathway that NO uses to cause vasodilation
* reacts with guanylate cyclase
* creates cGMP
* cGMP inhibits calcium ion channels
* no Ca2+ = no contraction
137
How does NO affect hypoxia induced vasoconstriction
* NO inhibitors increase HIVC
* low dose of inhaled NO (10-40 ppm) causes decreased HIVC
138
Given that vasoactive regulation is important for blood pressure modulation, what does inhibition of eNOS do?
induces pulmonary hypertension
139
Which vasoconstrictors do pulmonary vascular endothelial cells release?
endothelin-1 (ET-1) thromboxane A2 (TXA2)
## Footnote
These substances play a role in normal physiology and disease.
140
What is the role of endothelin receptor antagonists?
Part of treatment regimens for many patients with pulmonary hypertension
## Footnote
They are used to counteract the effects of endothelin-1.
141
True or False: Thromboxane A2 is a vasodilator.
False
## Footnote
Thromboxane A2 is a potent vasoconstrictor.
142
Fill in the blank: Endothelin-1 (ET-1) and thromboxane A2 (TXA2) are released by _______.
Pulmonary vascular endothelial cells
143
What is hypoxic vasoconstriction?
A mechanism that directs blood flow away from hypoxic regions of the lung.
144
What usually causes hypoxic regions in the lung?
Bronchial obstruction or alveolar filling.
145
What is the effect of hypoxic vasoconstriction on gas exchange?
Reduces deleterious effects on gas exchange by diverting blood flow away from dysfunctional alveoli
146
What happens to Po2 at high altitude?
It is reduced throughout the lung.
147
What occurs as a result of generalized pulmonary vasoconstriction at high altitude?
A rise in pulmonary arterial pressure.
148
When is hypoxic vasoconstriction most important?
At birth.
149
What is the pulmonary vascular resistance during fetal life?
Very high.
150
What percentage of cardiac output goes through the lungs during fetal life?
Approximately 15%.
151
What occurs when the first breath of a baby oxygenates the alveoli?
Vascular resistance falls dramatically.
152
What is the effect of relaxation of vascular smooth muscle after the first breath of a baby?
Pulmonary blood flow increases enormously.
153
What is the effect of low blood pH (acidemia) on vasoconstriction?
Causes vasoconstriction, especially when alveolar hypoxia is present
## Footnote
Acidemia is associated with reduced pH levels in the blood, leading to various physiological responses, including vasoconstriction.
154
How does severe hypothermia affect the vasoconstriction response to low blood pH?
Attenuates this response
## Footnote
Severe hypothermia can dampen the body's normal responses to acidemia and hypoxia.
155
What role does the autonomic nervous system play in vasoconstriction?
Exerts a weak control
## Footnote
The autonomic nervous system influences vascular tone but is not the primary regulator of vasoconstriction under these conditions.
156
What happens to the walls of the pulmonary arteries with increased sympathetic outflow?
Causes stiffening of the walls and vasoconstriction
## Footnote
Increased sympathetic activity leads to vascular changes that can affect blood flow and pressure.
157
What effect does iron deficiency have on vasoconstriction in response to alveolar hypoxia?
Causes increased vasoconstriction
## Footnote
Iron deficiency can enhance the body's response to low oxygen levels by promoting vasoconstriction.
158
What is the typical range of colloid osmotic pressure within the capillary?
25 to 28 mm Hg
## Footnote
This value is important for understanding fluid movement across capillary membranes.
159
Where is the capillary hydrostatic pressure higher?
At the bottom of the lung
## Footnote
This is significant for understanding fluid distribution in the lungs.
160
What is the colloid osmotic pressure of the interstitial fluid around lung lymph?
About 20 mm Hg
## Footnote
This value may differ from that in the interstitial fluid around the capillaries.
161
Is the interstitial hydrostatic pressure known?
Unknown
## Footnote
Some measurements indicate it is substantially below atmospheric pressure.
162
What is the probable net pressure according to the Starling equation?
Outward
## Footnote
This outward pressure contributes to lymph flow in normal conditions.
163
What is the estimated lymph flow in humans under normal conditions?
About 20 ml·h−1
## Footnote
This flow rate is indicative of fluid dynamics in the body.
164
Why is net fluid out typically not calculated in practice?
Due to ignorance of many values
## Footnote
This limits the application of theoretical equations in clinical settings.
165
Where does fluid go when it leaves the capillaries?
Fluid leaks into the interstitium of the alveolar wall and tracks through the interstitial space to the perivascular and peribronchial space within the lung.
166
What role do lymphatics play in fluid transport in the lungs?
Numerous lymphatics run in the perivascular spaces and help to transport the fluid to the hilar lymph nodes.
167
What is the pressure condition in the perivascular spaces?
The pressure in the perivascular spaces is low, forming a natural sump for the drainage of fluid.
168
What is interstitial edema?
The earliest form of pulmonary edema characterized by engorgement of the peribronchial and perivascular spaces.
169
What happens to the rate of lymph flow from the lung if capillary pressure is raised over a long period?
The rate of lymph flow from the lung increases considerably.
170
What happens in a later stage of pulmonary edema?
Fluid may cross the alveolar epithelium into the alveolar spaces.
171
What occurs when alveoli fill with fluid?
They become unventilated, preventing oxygenation of the blood passing through them.
172
What is the cause of fluid movement into the alveolar spaces?
It is not known, but may occur when the maximal drainage rate through the interstitial space is exceeded.
173
What is a potential consequence of high pressure in the interstitial space?
Fluid may begin to cross into the alveolar spaces.
174
How is fluid that reaches the alveolar spaces managed?
It is actively pumped out by a sodium-potassium ATPase pump in epithelial cells.
175
Why is alveolar edema more serious than interstitial edema?
Because it interferes with pulmonary gas exchange.
176
Fill in the blank: Alveolar edema is much more serious than _______ edema.
interstitial
177
True or False: Alveoli filled with fluid can still ventilate and oxygenate blood.
False
178
How does the lung reduce its pulmonary vascular resistance?
Through mechanisms of recruitment and distension.
179
What happens to pulmonary blood volume when vascular pressures are raised?
The lung can increase its blood volume with relatively small rises in pulmonary arterial or venous pressures.
180
What occurs when a subject lies down after standing?
Blood drains from the legs into the lung.
181
What is one function of the lung related to blood filtration?
Removing small blood thrombi from circulation.
182
What type of cells are trapped by the lung and later released?
Many white blood cells.
183
True or False: The value of trapping white blood cells in the lung is well understood.
False.
184
What organ, besides the heart, receives the whole circulation?
The lung
## Footnote
The lung has important metabolic functions in addition to gas exchange.
185
What is uniquely suited to modifying bloodborne substances?
The lung
## Footnote
The lung modifies a number of vasoactive substances.
186
What type of cells (related to metabolism) are substantially located in the lung?
Vascular endothelial cells
## Footnote
A substantial fraction of all vascular endothelial cells in the body are located in the lung.
187
In which ways do the lungs modify vasoactive substances?
activation
inactivation
metabolism
synthesis
188
What is the only known example of biological activation by passage through the pulmonary circulation?
The conversion of angiotensin I to angiotensin II
189
How much more active is angiotensin II compared to angiotensin I?
Up to 50 times more active
190
What effect does passage through the lung have on angiotensin II?
It is unaffected by passage through the lung
191
What enzyme catalyzes the conversion of angiotensin I to angiotensin II?
Angiotensin-converting enzyme (ACE)
192
Where is angiotensin-converting enzyme (ACE) located?
In small pits in the surface of the capillary endothelial cells
193
Which substances are inactivated by passage through the lungs?
bradykinin
serotonin
prostaglandins
norepinephrine
histamine (kind of)
194
What is the role of ACE in the inactivation of bradykinin?
ACE inactivates up to 80% of bradykinin
## Footnote
ACE stands for Angiotensin-Converting Enzyme, which plays a significant role in the renin-angiotensin system.
195
What is the major site of inactivation for serotonin?
The lung is the major site of inactivation of serotonin
## Footnote
Serotonin is also known as 5-hydroxytryptamine.
196
How is serotonin inactivated in the lungs?
By an uptake and storage process, not by enzymatic degradation
## Footnote
This process allows some serotonin to be transferred to platelets or stored for later release.
197
What happens to some of the serotonin in the lung during anaphylaxis?
Some serotonin may be transferred to platelets or stored and released
## Footnote
This mechanism highlights the lung's role in modulating immune responses.
198
Which prostaglandins are inactivated in the lung?
Prostaglandins E1, E2, and F2α
## Footnote
The lung contains enzymes responsible for the inactivation of these prostaglandins.
199
What percentage of norepinephrine is taken up by the lung?
Up to 30%
## Footnote
Norepinephrine is a neurotransmitter involved in the body's fight-or-flight response.
200
Is histamine affected by the intact lung?
No, histamine appears not to be affected by the intact lung
## Footnote
However, histamine is readily inactivated by lung slices.
201
Which substances are unaffected by passage through the lungs?
antiotensin II
vasopressin (ADH)
epinephrine
prostaglandin A1 and A2
202
What are vasoactive and bronchoactive substances metabolized in?
The lung
## Footnote
These substances may be released into the circulation under certain conditions.
203
What are important metabolites among vasoactive and bronchoactive substances?
Arachidonic acid metabolites
## Footnote
Arachidonic acid plays a significant role in various physiological processes.
204
How is arachidonic acid formed?
Through the action of phospholipase A2 on phospholipid bound to cell membranes
205
What are the two major synthetic pathways for arachidonic acid metabolites?
Lipoxygenase and cyclooxygenase pathways
## Footnote
These pathways involve different enzymes that catalyze the initial reactions.
206
What does the lipoxygenase pathway produce?
Leukotrienes
207
What is the slow-reacting substance of anaphylaxis (SRS-A)?
A mediator produced by leukotrienes
208
What effect do leukotrienes have on airways?
Cause airway constriction
209
What role do leukotrienes play in asthma?
They may have an important role in airway constriction and inflammation
210
What other function do leukotrienes serve besides causing airway constriction?
Involved in inflammatory responses
211
What are prostaglandins?
Potent vasoconstrictors or vasodilators
212
What role does prostaglandin E2 play in the fetus?
Helps to relax the patent ductus arteriosus
213
What is the role of prostaglandin I2?
Potent pulmonary vasodilator used in treatment of increased pulmonary artery pressure
214
In which other systems are prostaglandins active?
Kallikrein-kinin clotting cascade
215
What roles do prostaglandins have?
platelet aggregation
clotting cascade
asthma bronchoconstriction
216
What evidence suggests the lung plays a role in clotting?
Presence of mast cells containing heparin in the interstitium
217
What special immunoglobulin does the lung secrete in bronchial mucus?
IgA
218
What is the function of IgA in the lung?
Contributes to defenses against infection
219
True or False: Prostaglandins only act as vasodilators.
False
220
Fill in the blank: Prostaglandin I2 is used in the treatment of patients with increased _______.
pulmonary artery pressure
221
What are the synthetic functions of the lung?
Synthesis of phospholipids, protein synthesis, carbohydrate metabolism
222
What is dipalmitoyl phosphatidylcholine?
A component of pulmonary surfactant
223
Why is protein synthesis important in the lung?
Collagen and elastin form the structural framework of the lung
224
What may result from the breakdown of collagen and elastin in the lung?
Emphysema
225
What causes the breakdown of collagen and elastin under certain conditions?
Liberation of proteases from leukocytes
226
What is a significant area of carbohydrate metabolism in the lung?
Elaboration of mucopolysaccharides of bronchial mucus
227
Fill in the blank: The lung synthesizes phospholipids such as _______.
dipalmitoyl phosphatidylcholine
228
True or False: Collagen and elastin are not important for the structural integrity of the lung.
False
229
What structural components are formed by protein synthesis in the lung?
Collagen and elastin
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