The Respiratory System RESPIRATORY SYSTEM
Primary functions
Major functional events
Pulmonary ventilation
Diffusion of O2 & CO2 between alveoli & blood
Transport of O2 & CO2 in blood and body fluids
Regulation of ventilation
2 Respiratory Gasses
What essential function does O2 serve?
How is CO2 produced and why do we need to get rid of it?
3 True or false: The oxygen you breathe in gets converted into carbon dioxide that you then breathe out.
A) True B) False
4 Review of Respiratory Structures
Upper vs. lower respiratory tracts
Thoracic cavity
Diaphragm
See Fig. 37-8
5 Review of Respiratory Structures
Respiratory tree
Trachea
Bronchi
Bronchioles
Alveolar sacs
Alveoli
6 See Fig. 37-8 Review of Respiratory Structures
Structural characteristics
Cartilage
Cilia
Mucus glands
Smooth muscle
See Fig. 37-8
7 Review of Respiratory Structures
Respiratory membrane
Blood-air barrier
Epithelial characteristics
Type I cells
Type II cells
Produce surfactant
8 See Fig. 37-8 Review of Respiratory Structures
Pleurae (membranes)
Parietal pleura
Visceral pleura
Pleural cavity
Serous fluid
Lungs “float” in pleural cavities
9 Fluids in the respiratory system have all of these functions except…
A) Reducing friction of lung against chest wall B) Reducing surface tension in the lung C) Allowing gasses to diffuse across epithelium D) Transporting metabolic fuels to body tissues
10 Mechanics of Breathing
Boyle’s Law
P1V1 = P2V2
The pressure of a gas varies inversely with its volume
volume, pressure = inhalation
volume, pressure = exhalation
Air moves from area of high pressure to area of low pressure
11 Mechanics of Breathing
Muscular events during inspiration
Diaphragm contracts & flattens inferiorly
External intercostals contract & elevate rib cage
thoracic volume
Fig. 37-1 12 Mechanics of Breathing
Muscular events during expiration
Diaphragm relaxes & moves superiorly
External intercostals relax, rib cage depressed
thoracic volume
Normal breath - recoil due to elasticity of lungs/thoracic cage
Fig. 37-1 13 Mechanics of Breathing
Heavy breathing
Inspiration
Raise rib cage
Exhalation
Compress rib cage
Fig. 37-1 14 Mechanics of Breathing
Thoracic pressures
Intrapulmonary pressure (alveolar pressure)
Pressure within alveoli
Equalizes with atmospheric pressure
15 Mechanics of Breathing
Thoracic pressures
Intrapulmonary pressure (alveolar pressure)
Pressure of fluid within pleural cavity
< alveolar pressure
Low pressure created by fluid draining into lymphatic capillaries
Fluid/pressure causes visceral pleura to “stick” to parietal pleura
as thoracic cavity expands, lungs expand
Elasticity of lungs causes recoil, aids expiration
Equalization with alveolar pressure = collapse 16 Mechanics of Breathing
Thoracic pressures
Intrapulmonary pressure (alveolar pressure)
Intrapleural pressure
Transpulmonary pressure
Difference between intrapulmonary and intrapleural pressures
Represents the elastic forces of the lungs
17 Thoracic Pressures
Fig. 37-1 18 Environmental pressure equalizes with which of the following pressures?
A) Transpulmonary pressure B) Pleural pressure C) Alveolar pressure D) All of the above
Relationship of lung expansion and transpulmonary pressure
Every 1 cm H2O increase in transpulmonary pressure results in 200 ml expansion in lung volume
Characteristics determined by elastic forces of lungs
Elasticity of lung tissue
Surface tension within alveoli
20 Lung Compliance
Tissue elasticity
High percentage of elastic fibers in connective tissue of lungs
Elastin & collagen
Stretched during expansion then recoil
21 Lung Compliance
Alveolar surface tension
Alveolar surfaces covered with fluid
Forms water-air surface
Increases rate of gas diffusion
Creates tension between water molecules
Cohesive forces of water
Surface tension
Surfactants decrease surface tension
Interfere with water cohesion
Degree of recoil reduced
22 Lung Compliance
Factors reducing lung compliance
Reduced tissue elasticity
Reduced surface tension
Increased airway resistance
Mucus buildup
Bronchial constriction
23 Lung compliance is affected by all of the following except…
A) Alveolar surface tension B) Elastic forces of lungs C) Airway resistance D) Size of alveoli
24 Pulmonary Volumes
Tidal volume (VT)
Normal inspiration/expiration Fig. 37-6 ~ 0.5 L
Inspiratory reserve volume (IRV)
Air forceably inspired
beyond VT
~ 3 L
25 Pulmonary Volumes
Expiratory reserve volume (ERV)
Air forcibly expired beyond V T Fig. 37-6 ~ 1.1 L
Residual volume (RV)
Air that cannot be forcibly expired
~ 1.2 L
26 Pulmonary Capacities
Inspiratory capacity (IC)
Max. air inspired after normal expiration Fig. 37-6 TV + IRV
~ 3.5 L
Functional residual capacity (FRC)
Air remaining in lungs after normal expiration
ERV + RV
~ 2.3 L
27 Pulmonary Capacities
Vital capacity (VC)
Max. air inspired after normal expiration Fig. 37-6 IRV + TV + ERV
~ 4.6 L
Total lung capacity (TLC)
VC + RV
~ 5.8 L
28 Other Respiratory Measurements
Minute respiratory volume
Amount of air moved into respiratory passages each minute
TV (ml) x respiratory rate (bpm)
Air filling respiratory passages but not reaching gas exchange areas
~ 0.15 L
29 The amount of air remaining in your lungs after a normal expiration is the…
A) Expiratory reserve volume B) Functional residual capacity C) Total lung capacity D) Residual volume
30 Determining Respiratory Volumes
Functional residual capacity (He dilution method)
Fill spirometer with known vol of air + known vol of He
Expire normally then breathe from spirometer
Air remaining in lungs = FRC Fig. 37-6
[He] diluted by FRC gasses
Calculate degree of dilution
31 Determining Respiratory Volumes
Residual volume and total lung capacity
Use FRC value
RV = FRC - ERV
TLC = FRC + IC or VC + RV Fig. 37-6
32 Determining Respiratory Volumes
Dead space
Breathe normally then take deep breath of pure O2
Exhale into nitrogen meter
First air expired = dead space all O2
[N2] as alveolar air is expired
[N2] plateaus as original alveolar concentration reached
Area to left of curve = dead air space
33 Fig. 37-7 Alveolar Ventilation
Rate at which “new” air reaches gas exchange area
Good index of effective ventilation
AVR (ml/min) = frequency x (VT - dead space)
E.g., AVR = 12 b/min x (500 ml/b - 150 ml/b) = 4200 ml/min
What this indicates…
Slow/deep breaths ventilation
E.g., AVR = 10 b/min x (700 ml/b - 150 ml/b) = 5500 ml/min
Rapid/shallow breaths ventilation
E.g., AVR = 15 b/min x (300 ml/b - 150 ml/b) = 2250 ml/min
34 If you want to increase the amount of new air in the lungs, you should…
A) Breathe more quickly B) Breathe more deeply
35 Gas Exchange Across Respiratory Membranes
Dalton’s Law of Partial Pressures
Total gas pressure = sum of partial pressures of gasses within the mixture
36 Gas Exchange Across Respiratory Membranes
Partial pressure of atmospheric gasses (sea level) mmHg %
N2 597.0 78.62
O2 159.0 20.84
CO2 0.3 0.04
H2O 3.7 0.50 Total 760.0 100.00
See Table 39-1 37 Gas Exchange Across Respiratory Membranes
Henry’s Law
When a gas mixture is in contact with a liquid, each gas will dissolve in proportion to its partial pressure and relative to its solubility in the liquid
conc. of dissolved gas partial pressure = solubility coefficient
solubility, more gas can dissolve without building up excess partial pressure
38 Gas Exchange Across Respiratory Membranes
Solubility coefficients of important respiratory gasses
PO2 0.024
PCO2 0.570 PCO 0.018
PN2 0.012 PHe 0.008
39 Gas Exchange Across Respiratory Membranes
Diffusion coefficient
Relative rates at which different gasses at same pressure levels will diffuse
Depends on molecular weight of the gas & solubility
O2 1.0
CO2 20.3 CO 0.81
N2 0.53 He 0.95
40 Gas Exchange Across Respiratory Membranes
Volume of gas that will diffuse through the membrane each minute at a partial pressure difference of 1 mmHg
41 Diffusing Capacity
O2 (at rest)
~ 21 ml/min/mmHg
Pressure difference across membrane ~ 11 mmHg
O2 diffusion = 11 x 21 = 230 ml/min (same as use rate)
42 Fig. 39-10 Diffusing Capacity
O2 (during exercise)
~ 65 ml/min/mmHg (max)
~ 3x increase due to…
Increased pulmonary circulation (dilation)
Increases diffusing capacity
Increased ventilation- perfusion ratio
43 Fig. 39-10 Diffusing Capacity
CO2
~ 400-450 ml/min/mmHg (at rest)
Theoretical
~20x O2
Pressure difference across membrane > 1 mmHg
Less pressure difference but higher solubility & diffusion coefficients
Fig. 39-10 44 The diffusing capacity of a membrane for a particular gas depends on all of these except:
A) diffusion coefficient of the gas B) pressure difference of the gas across membrane C) thickness of membrane D) absolute concentration of the gas in the blood
45 Alveolar Air
Composition differs from atmosphere
Humidified
Continual diffusion of CO2 into alveoli
Continual diffusion of O2 into blood
See Table 39-1 46 Alveolar Air
Only partially replaced
FRC ~2.3 L, only ~350 ml “fresh” air enters alveoli
Takes multiple breaths (16+) to completely replace
Slow replacement important to prevent sudden changes in gas concentration in the blood
Fig. 39-2 47 Alveolar air is replaced slowly, over the course of ~16 breaths, because…
A) the volume of air breathed in is small in relation to dead space B) the volume of air breathed in is small in relation to the functional reserve capacity C) the old air prevents new air from coming into the lung well D) the speed of air intake is insufficient to push old air out
48 Factors Influencing Rate of Diffusion Through Membrane
Membrane thickness
Averages ~0.6 m
thickness (i.e., edema), diffusion
Fig. 39-8 Fig. 39-9 49 Factors Influencing Rate of Diffusion Through Membrane
Membrane thickness
Averages ~0.6 m
thickness (i.e., edema), diffusion
Surface area 2 ~60-70 m
Partial pressure gradients
Gas solubilities
50 Diffusion of O2 & CO2 Across the Respiratory & Cellular Membranes
O2 CO2
Fig. 40-1 & 3 Fig. 40-6 & 5 51 Systemic PO2
Fig. 40-2
52 Carbon dioxide moves from alveolar capillaries into alveoli because…
A) Concentration of oxygen is higher in alveoli than in the blood B) Partial pressure of carbon dioxide is higher in alveoli than in the blood C) Concentration of carbon dioxide is higher in blood than in alveoli D) Partial pressure of carbon dioxide is higher in blood than in alveoli
53 Ventilation-Perfusion Coupling
Synchronization of blood flow with gas concentrations
Function
Redirect blood to where it is most needed for gas exchange
54 Ventilation-Perfusion Coupling
Alveolar capillaries
Respond to PO2
PO2 arterioles around reduced perfusion (inadequate alveoli constrict (blood flow) ventilation)
Less O2 reduce blood flow around affected alveoli
PO2 arterioles around increased perfusion (adequate alveoli dilate (blood flow) ventilation)
More O2 increase blood flow around affected alveoli
55 Ventilation-Perfusion Coupling
Bronchioles
Respond to PCO2
Alveoli Bronchioles
PCO2 Dilate (increase expiration volume)
PCO2 Constrict
56 Ventilation-Perfusion Ratio
Reflects respiratory exchange when alveolar
ventilation (VA) and blood flow (Q) are imbalanced
V-P ratio = VA/Q
VA = alveolar ventilation, Q = blood flow ratio compared to normal
Adequate blood flow but poor ventilation
Alveolus [O2/CO2] equilibrates with pulmonary capillary blood Blood shunted away from affected capillaries (physiologic shunt)
Reduced oxygenation of pulmonary venous blood 57 Ventilation-Perfusion Ratio
Reflects respiratory exchange when alveolar
ventilation (VA) and blood flow (Q) are imbalanced
ratio compared to normal
Adequate ventilation but poor blood flow
Alveolus [O2/CO2] equilibrates with inspired air
Physiologic dead space (wasted ventilation)
58 Ventilation-perfusion coupling imbalances may result in…
A) Increased physiological dead space B) Wasting of energy due to unnecessary ventilation C) Poor oxygenation of blood D) All of the above
59 Transport of O2 in Blood
Bound to hemoglobin
~97%
Dissolved in plasma
~3%
60 Hemoglobin (Hgb)
Hemoglobin
Tetramer
Globin polypeptides
& chains most common
1 heme / chain
Heme group
Porphyrin ring with Fe See Fig. 32-6 core
Pigment
61 Hemoglobin (Hgb)
O2 binding
1 O2 / heme group
4 heme groups / Hgb ( 4 O2 / Hgb)
62 Hemoglobin (Hgb)
O2 binding & pigment development
Causes conformational change in heme group
Oxyhemoglobin (HgbO2) = bright red
Deoxyhemoglobin (HHgb) = dark red
lungs + HHgb + O2 HgbO2 + H tissues
63 Hemoglobin (Hgb)
O2 binding & Hgb saturation st 1 O2 binds
Partial saturation
Conformational change increases uptake of
additional O2
Remaining 3 O2 bind
Full saturation
64 Oxygen binds to…
A) The alpha chain of hemoglobin B) The beta chain of hemoglobin C) The heme portion of hemoglobin D) All of the above
65 O2/Hgb Dissociation Curve
Reflects affinity of O2 for Hgb at different PO2
Observations to note
At PO2 of 40 (venous blood), Hgb is still ~70% saturated
Venous reserve
Fig. 40-8 66 O2/Hgb Dissociation Curve
Reflects affinity of O2 for Hgb at different PO2
Observations to note
Decreased alveolar PO2 can still allow adequate O2 binding ( elevation)
Fig. 40-8 67 O2/Hgb Dissociation Curve
Changes in metabolic factors can shift curve
& affect O2 loading/unloading
Shift to right → increase O2 unloading
Shift curve to left → increase O2 loading
loading
unloading
Fig. 40-8 68 Factors Influencing O2/Hgb Dissociation Curve
Any increase in the following factors shifts the curve to the right
Temperature + H
PCO2
BPG (2,3-bisphosphoglycerate)
Method
O2 affinity for Hgb
dissociation (unloading)
Fig. 40-10
69 Oxygen can be offloaded more easily when…
A) Carbon dioxide partial pressure is increased B) Blood is more alkaline C) Body temperature falls D) All of the above
70 Transport of CO2 in Blood
Dissolved in plasma
~7-10%
Bound to Hgb
~20-30%
Carbaminohemoglobin (HgbCO2)
Binds to globin doesn’t compete with O2 binding sites on heme
Binds most rapidly to HHgb than HgbO2
71 Transport of CO2 in Blood
Dissolved in plasma
~7-10%
Bound to Hgb
~20-30%
As bicarbonate ions in plasma
~60-70%
carbonic anhydrase - + CO2 + H2O H2CO3 HCO3 + H carbonic acid bicarbonate
72 Bicarbonate Buffering System
+ Dissociation of carbonic acid (H )
RBC + H + Hgb HHgb
Buffering
Weakens HgbO2 enhances O2 unloading
See Fig. 40-13 73 Bicarbonate Buffering System
- Dissociation of carbonic acid (HCO3 ) Chloride shift - Diffusion of HCO3 from RBC to plasma - Countered by influx of Cl from plasma into RBC Maintains charge balance Gradient favors anabolic action of carbonic anhydrase
See Fig. 40-13 74 Bicarbonate Buffering System
CO2 transport to lungs
PCO2 in blood
See Fig. 40-13 75 True or false: Carbonic anhydrase may catalyze opposite reactions depending on conditions.
A) True B) False
76 Bohr Effect
Effect of changes in pH and CO2 on the unloading / loading of O2 with hemoglobin Tissues
Uptake of CO2… + carbonic acid ( H )
O2-Hb curve shifts right O2 affinity for Hgb ( O2 unloading)
77 Bohr Effect
Effect of changes in pH and CO2 on the unloading / loading of O2 with hemoglobin Lungs
Removal of CO2… + carbonic acid ( H )
O2-Hb curve shifts left O2 affinity for Hgb ( O2 loading)
Effect of O2/Hgb binding on the displacement & uptake of CO2
Lungs + HgbO2 formation (O2 loading) releases H
tendency of Hgb to form HgbCO2
Drives catabolic action of carbonic anhydrase (CO2 formation)
79 Haldane Effect
Effect of O2/Hgb binding in the displacement & uptake of CO2
Tissues
HgbO2 dissociation (O2 unloading) frees Hgb
Favors HHgb & HgbCO2 formation + H utilization drives anabolic action of carbonic anhydrase
80 The ability of protons to influence O2 loading to hemoglobin is the…
A) Haldane effect B) Bohr effect
81 Regulation of Respiration
Respiratory centers in medulla oblongata & pons
Dorsal respiratory group (DRG)
Inspiratory center (sets respiratory rhythm)
Sensory input from vagus & glossopharyngeal nerves Fig. 41-1 Chemoreceptors
Baroreceptors
Sensory receptors within lungs
82 Regulation of Respiration
Respiratory centers in medulla oblongata & pons
Dorsal respiratory group (DRG)
Output to primary respiratory muscles (phrenic nerve)
“Ramp signal”
Gradually increases contraction
Steady increase in lung volume
Abrupt stop (expiration); recoil
83 Regulation of Respiration
Respiratory centers in medulla oblongata & pons
Ventral respiratory group (VRG)
Inspiration & expiration
Respiratory “overdrive”
Inactive during normal respiration
Activated with forced/increased breathing
Stimulate muscular activity of both inspiration & expiration 84 Regulation of Respiration
Respiratory centers in medulla oblongata & pons
Pneumotaxic center
Controls rate & pattern of breathing by limiting duration of inspiration
Controls DRG ramp “switch-off” point
Strong signal shortens ramp-up time
inspiration rate (30-40 bpm)
inspiration depth
85 Regulation of Respiration
Respiratory centers in medulla oblongata & pons
Pneumotaxic center
Controls rate & pattern of breathing by limiting duration of inspiration
Controls DRG ramp “switch-off” point
Strong signal lengthens ramp-up time
inspiration rate (3-5 bpm)
inspiration depth
86 Hering-Breuer Inflation Reflex
Response of lung inflation to limit respiration
Functions to protect against excess stretch
Inflation of lungs increases output signal from baroreceptors
Increased stimulus (vagal afferents) inhibits DRG
Terminates inspiration (ramp-off)
Sensory receptors within lungs
Deflation of lungs decreases output signal from baroreceptors
Decreased stimulus (vagal afferents), DRG not inhibited
Begins ramp-up 87 Which center in the medulla is primarily responsible for setting respiratory rate?
A) Dorsal respiratory group B) Pneumotaxic center C) Ventral respiratory group D) All of the above
88 Chemical Control of Respiration
Goal of respiration + Maintain O2, CO2, H concentrations in blood & tissues
Control of respiration + Response to changes in O2, CO2, H concentrations + CO2 & H act centrally on respiratory centers
O2 input from peripheral locations
89 CO2, Blood pH and Regulation of Breathing
Fig. 41-3 90 + CO2, H & Respiratory Control
Chemosensitive area of respiratory center
blood [CO2] provides indirect stimulation
CO2 diffuses into chemosensitive area
Reacts with H2O in tissues + blood PCO2 tissue PCO2 H
Effect
ventilation
91 Fig. 41-2 CO2, Blood pH and Regulation of Breathing
Carbonic acid-bicarbonate buffering system
- + CO2 + H2O H2CO3 HCO3 + H
pH drives equilibrium + pH ( H ) Drives equation left Rapid / deep breathing
Releases more CO2 raises pH (removes free H+) + pH ( H ) Drives equation right Slow / shallow breathing
Retains more CO2 lowers pH (increases free H+) 92
O2 & Respiratory Control
Peripheral chemoreceptors
Stimulated by arterial PO2 + Lesser extent by CO2 & H
Primarily carotid & aortic bodies
Carotid bodies
Afferents (Hering’s glossopharyngeal)
Synapse at DRG
Aortic bodies
Afferents (vagus)
Synapse at DRG
93 Fig. 41-4
O2 & Respiratory Control
Effect of arterial PO2
As PO2 decreases (< 100 mmHg)…
Impulse rate to respiratory centers increases
ventilation
Fig. 41-5 Fig. 41-6 94 True or false: Oxygen drives breathing rate more than carbon dioxide.
A) True B) False
95 Respiratory Insufficiency
Hypoxia
Inadequate delivery of O2 to tissues
Cyanosis
Skin, mucosa, nail beds turn “blue”
Depressed mental activity (may lead to coma)
Reduced muscle activity
Cell death
96 Respiratory Insufficiency
Asthma
Hypersensitivity (allergy) to airborne substances
Reaction
Immune response
Release of leukotrienes, bradykinin, histamine, etc.
Localized edema (walls of bronchioles)
Smooth muscle spasm (bronchioles)
Increased airway resistance (decreased ventilation)
Expiration difficulty
May cause dyspnea 97 Respiratory Insufficiency
Asthma
Common treatments
Simulate sympathetic response (bronchiole dilation)
Immediate relief
Corticosteroid aerosols
Long term therapy
Reduce frequency / intensity of attacks
98 Respiratory Insufficiency
Effect of CO
Competes with O2 for heme sites on Hb
~250x affinity for Hb
At PCO of 0.4 mmHg in alveoli, competes equally with O2 for Hb
Treatment
PO2 (pure O2)
Greater pressure differential displaces CO
PCO2
Increase ventilation
99 True or false: Oxygen drives breathing rate more than carbon dioxide.
A) True B) False
100