Respiratory Physiology Flashcards
1
Q
What is respiratory physiology?
A
The study of how oxygen is brought into the lungs and delivered to the tissue and how carbon dioxide is removed
2
Q
What are the functions of the respiratory system?
A
Provides oxygen and eliminates carbon dioxide Protects against microbial infections Regulates blood pH Contributes to phonation Contributes to olfaction Is a reservoir for blood
3
Q
What are the structures in the upper airway?
A
Nasal and oral cavities
Pharynx
Larynx
4
Q
What is the structure of the trachea and primary bronchi?
A
C-shape cartilage anteriorly and smooth muscle posteriorly
5
Q
What is the structure of the bronchi?
A
Plates of cartilage and smooth muscle
6
Q
What is the structure of the bronchioles?
A
Smooth muscle only
7
Q
What is the conducting zone?
A
Leads gas to the gas exchanging region of the lungs
No alveoli
No gas exchange
8
Q
What is the respiratory zone?
A
Where gas exchange happens
Has alveoli
9
Q
What are terminal bronchioles?
A
The smallest airway without alveoli
10
Q
What are respiratory bronchioles?
A
Have occasional alveoli
11
Q
What are alveoli?
A
Tiny, thin-walled capillary rich sac in the lungs where the exchange of oxygen and carbon dioxide takes place
12
Q
What are type 1 alveolar cells?
A
Most of the surface of the alveolar walls are lined by a continuous monolayer of flat epithelial cells
Do not divide and are susceptible to inhaled or aspirated toxins
13
Q
What are type 2 alveolar cells?
A
7% of alveolar surface
Produce surfactant
Act as progenitor cells
14
Q
What is a surfactant?
A
A detergent-like substance made of lipoproteins
Reduces surface tension of the alveolar fluid
15
Q
What are progenitor cells?
A
When there is injury to type 1 cells, type 2 cells can multiply and eventually differentiate into type 1 cells
16
Q
How do O2 and CO2 transfer between alveolar air and blood?
A
Transfer of O2 and CO2 occurs by diffusion and through the respiratory membrane
17
Q
What are the steps of respiration?
A
Ventilation = exchange of air between atmosphere and alveoli by bulk flow
Exchange of O2 and CO2 between alveolar air and blood in lung capillaries by diffusion
Transport of O2 and CO2 through pulmonary and systemic circulation by bulk flow
Exchange of O2 and CO2 between blood in tissue capillaries and cells in tissues by diffusion
Cellular utilization of O2 and production of CO2
18
Q
How is ventilation produced?
A
CNS sends rhythmic excitatory drive to respiratory muscles
Respiratory muscles contract rhythmically and in a very organized pattern
Changes in volume and pressures at the level of the chest and lung occur
Air flows in and out
19
Q
What are the inspiratory pump muscles?
A
Diaphragm
External intercostals
Parasternal intercostals
20
Q
What are the expiratory pump muscles?
A
Internal intercostals
Abdominals
21
Q
What are the inspiratory airway muscles?
A
Tongue protruders
Alae nasi
Muscles around airways
22
Q
What are the expiratory airway muscles?
A
The muscles are the airways
23
Q
What are the inspiratory accessory muscles?
A
Sternocleidomastoid
Scalene
24
Q
What is the diaphragm?
A
A dome-shaped muscle which flattens during contraction (inspiration), abdominal contents are forced down and forward and rib case is widened
This increases the volume of the thorax
25
What are the external intercostal muscles?
Contact and pull ribs upward increasing the lateral volume of the thorax
26
What are the parasternal intercostal muscles?
Contract and pull sternum forward, increasing anterior posterior dimension of the rib cage
27
How do the abdominal muscles function in respiration?
Deeper, faster breathing requires active contraction of abdominal and internal intercostal muscles to return the lung to its resting position
28
How do the internal intercostal muscles function in respiration?
Relaxed at rest
| During exercise, internal intercostal muscles pull rib cage down, reducing thoracic volume
29
What do the scalenes do?
Elevate upper ribs
| Contract vigorously during exercise or forced respiration
30
What do the sternocleidomastoids do?
Raise the sternum
| Contract vigorously during exercise or forced respiration
31
What upper airway muscles contribute to opening the upper airways and reducing resistance?
Tongue protruders
Alae nasi
Pharyngeal and laryngeal dilators (inspiratory)
Pharyngeal and laryngeal constrictors (expiratory)
32
What is obstructive sleep apnea?
Reduction in upper airway patency during sleep
- reduction in muscle tone
- anatomical defects
33
What lines the conducting airways?
A superficial layer of epithelial cells which comprise mucus-producing (Goblet) cells and ciliated cells
-function in a coordinated fashion to entrap inhaled biological and inert particulates and remove them from the airways
34
How do ciliary cells help remove deposited particles in the tracheobronchial tree?
Produce periciliary fluid
| -low viscosity optimal for ciliary activity
35
How do Goblet cells help remove deposited particles in the tracheobronchial tree?
Produce mucus - thick GEL layer distributed in patches
- has high viscosity and high elastic properties
- traps inhaled materials
36
How do macrophages in the alveoli help with filtering action?
Macrophages are mostly present in the alveoli
Last defense to inhaled particles
-rapidly phagocytize foreign particles and substances as well as cellular debris
37
What do inhaling silica dust and asbestos lead to?
Pulmonary fibrosis
38
What is spirometry?
A pulmonary function test to determine the amount and the rate of inspired and expired air
39
What is a spirometer?
An apparatus used for measuring the volume of air inspired and expired air by the lungs
-it records the amount and the rate of air that you breathe in and out over a period of time
40
What is atelectasis?
Complete or partial collapse of a lung or a lobe of a lung
| Develops when alveoli become deflated/collapse
41
What is tidal volume?
The volume of air moved IN or OUT of the respiratory tract during each ventilatory cycle
42
What is the inspiratory reserve volume?
The additional volume of air that can be forcibly inhaled following a normal inspiration
It can be accessed by inspiring to the maximum possible inspiration
43
What is the expiratory reserve volume?
The additional volume of air that can be forcibly exhaled following a normal expiration
It can be accessed by expiring to the maximum voluntary expiration
44
What is residual volume?
The volume of air remaining in the lungs after a maximal expiration
It cannot be expired no matter how vigorous or long the effort
45
What is vital capacity?
The maximal volume of air that can be forcibly exhaled after a maximal inspiration
46
What is inspiratory capacity?
The maximal volume of air that can be forcibly inhaled
47
What is the functional residual capacity?
The volume of air remaining in the lungs at the end of a normal expiration
48
What is total lung capacity?
The volume of air in the lungs at the end of maximal inspiration
49
What is the average tidal volume?
The average volume of inspired air at each breath in 0.5 L
50
What is the total/minute ventilation?
The total amount of air moved into the respiratory system is about 7.5 L/min
51
What is alveolar ventilation?
The amount of air moved into the alveoli per minute
About 5.25 L/min
VA= ( VT - VD )x frequency
52
Is the depth of breathing or the rate of breathing more effective in increasing alveolar ventilation?
The depth of the breathing is more effective
53
What is the FEV1 Test?
Forced Expiratory Volume in 1 Second
| A healthy person can normally blow out most of the air from the lungs within one second
54
What is the FVC Test?
Forced Vital Capacity
The total amount of air that is blown out in one breath after max inspiration as fast as possible
Approx vital capacity
55
What are the three main patterns of a spirometry test?
Normal
An obstructive pattern
A restrictive pattern
56
What is the obstructive pattern?
People with obstructive lung disease have shortness of breath due to difficulty in exhaling all the air from their lungs
Because of damage to the lungs, exhaled air comes out more slowly than normal
At the end of a full exhalation, an abnormally high amount of air may still linger in the lungs
FEV1 is significantly reduced
FVC may be normal or reduced
57
What is the restrictive pattern?
Patients affected by restrictive lung disease cannot fully fill their lungs with air. Their lungs are restricted from fully expanding
Caused by stiffness in the lungs
Reduced vital capacity
FEV1 and FVC reduced
58
What is the helium dilution method?
Cann measure residual capacity
Helium is insoluble in blood, equilibrates after several breaths
Concentration is measured at the end of an expiratory effort
59
What are the static properties of the lung?
Mechanical properties when no air is flowing
Necessary to maintain lung and chest wall at a certain volume
-intrapleural pressure, transpulmonary pressure
-static compliance of the lung
-surface tension of the lung
60
What are the dynamic properties of the lung?
```
Mechanical properties when the lungs are changing volume and air is flowing in and out
Necessary to permit airflow
-alveolar pressure
-dynamic lung compliance
-airway and tissue resistance
```
61
What is ventilation?
Exchange of air between the atmosphere and the alveoli
62
What are the pleurae?
Thin double-layered envelope
63
What is the visceral pleura?
Covers the external surface of the lung
64
What is the parietal pleura?
Covers the thoracic wall and the superior face of the diaphragm
65
What is intrapleural fluid?
Reduces friction of lung against thoracic wall during breathing
Extremely thin
66
What is the elastic recoil of the lungs and chest wall?
The lungs have a tendency to collapse due to elastic recoil and the chest wall pulls the thoracic cage outward due to elastic recoil
Balances each other out
67
Where does interaction between the lungs and chest wall occur?
Through the intrapleural space between the visceral and parietal pleurae
68
What is intrapleural pressure?
Pressure in the pleural cavity
Acts as a relative vacuum
Fluctuates with breathing but it is always subatmospheric
If the intrapleural pressure equals the alveolar pressure then the lungs would collapse
69
What is alveolar pressure?
The pressure of the air inside the alveoli
When the glottis is open and no air flows into or out of the lungs, the pressures in all parts of the respiratory tree, including the alveoli are equal to atmospheric pressure
70
What is transpulmonary pressure?
The force responsible for keeping the alveoli open, expressed as the pressure gradient across the alveolar wall
Does not cause airflow but determines lung volume
71
What are the pressures during inspiration?
The diaphragm and intercostals contract, the thorax expands
Intrapleural pressure becomes more subatmospheric
Transpulmonary pressure increases
Lungs expand
Alveolar pressure becomes subatmospheric
Air flows into alveoli
72
What are the pressures during expiration?
Diaphragm and inspiratory intercostals stop contracting
Chest wall recoils inward
Intrapleural pressure moves back toward pre-inspiration value
Transpulmonary pressure moves back to pre-inspiration value
Lungs recoil toward pre-inspiration size
Air in the alveoli becomes compressed
Alveolar pressure becomes greater than atmospheric pressure
Air flows out of lungs
73
What are some airway resistive forces?
Inertia of the respiratory system
Friction of lung tissue going past itself during expansion
Friction of the lung and chest wall tissue surfaces gliding past each other
Frictional resistance to flow of air through the airways
74
What is laminar airflow?
The subject invests relatively little energy in airflow resistance; characteristic to the small airways that are distal to terminal bronchioles
75
What is transitional airflow?
It takes extra energy to produce vortices
The resistance increases
Airflow is transitional throughout most of the bronchial tree
76
What is turbulent airflow?
The effective resistance to airflow is the highest; in the large airways, where the airway radius is large and linear air velocities may be extremely high
77
What factor contributes most to resistance?
Radius
78
Why do smaller airways play a greater role in determining airflow resistance than large airways?
They are more easily occluded by:
- smooth muscle contraction in their walls
- edema occurring in the walls of the alveoli and bronchioles
- mucus collecting in the lumens of bronchioles
79
What is lung compliance?
A measure of the elastic properties of the lungs and a measure of how easily the lungs can expand
The magnitude of the change in lung volume produced y a given change in the transpulmonary pressure
The slope measured in the pressure-volume curve
80
What is static compliance of the lung?
Represents lung compliance during periods of no gas flow, such as during an inspiratory or expiratory pause
Determined by the P/V slope when measured at FRC
81
What is dynamic compliance of the lung?
Represents pulmonary compliance during periods of gas flow, such as during inspiration
It reflects not only lung stiffness but also the airway resistance, against which distending forces have to act
It is always less than or equal to static lung compliance
Falls when either lug stiffness or airway resistance increases
82
What is the pressure-volume relationship?
1. Stable VL = at low lung volumes it is difficult to pop open an almost completely collapsed airway
2. Opening of airways = the first increase in VL reflect the popping open of the proximal airways, followed by their expansion and recruitment of others
3. Linear expansion of open airways = when all the airways are open, making the intrapleural pressure more negative by chest wall expansion inflates the lungs and increases VL in a linear fashion
4. Limit of airway inflation = at high VL the lung compliance decreases
83
What is hysteresis?
The difference between the inflation and deflation compliance paths
Exists because a greater pressure difference is required to open a previously closed airway than to keep an open airway from closing
84
What is lung compliance determined by?
Elastic components of lungs and airway tissue
| Surface tension at the air-water interface within the alveoli
85
What are the elastic components of airways?
Localized in the alveolar walls and around blood vessels and bronchi
86
What is elastin?
Like a weak spring, low tensile strength, extensible
87
What is collagen?
Like a strong twine, high tensile strength, inextensible
88
What happens to elastin and collagen with age?
Increased lung compliance and the lungs are more floppy
89
What is emphysema?
Floppy lungs as a result of elastin destruction and alveolar wall destruction
Increased compliance
90
What is pulmonary fibrosis?
Collagen deposition in alveolar walls
| Reduction in lung compliance
91
What is alveolar surface tension?
Water molecules at the surface of a liquid-gas interface are attracted strongly to the water molecules within the liquid mass
92
What is surface tension?
A measure of the attracting forces acting to pull a liquid's surface molecules together at an air-liquid interface
93
What are factors that affect pressure-volume relation?
Surface tension is seen at all air-fluid boundaries and arises as a result of hydrogen bonding of water molecules
Important of surface tension is clear in P-V curve in which surface tension is eliminated with saline-filled lung
The effect of surface tension is to cause the surface to maintain as small an area as possible
No hysteresis and much lower inflation pressures
94
What type of cells produce alveolar surfactants?
Type 2 alveolar cells
95
What do alveolar surfactants do?
Lowers the surface tension of the lining fluid so that we can breathe without too much effort
Makes the alveoli stable against collapse
96
How does surfactant reduce surface tension?
It has hydrophobic and hydrophilic properties so it can get into the air-water interface and decreases the density of water molecules
This will increase the lung compliance and make it easier to breathe
97
How does surfactant stabilize the alveoli?
The thickness of the surfactant decreases with increased surface area
This causes T to increase with increasing alveolar diameter
This tends to equalize pressures between alveoli of different shapes which helps prevent collapse of small alveoli into larger alveoli
98
Surfactant in premature infants
Lack of surfactant decreases compliance and increases work of breathing
99
What are the regional differences in Pip?
The weight of the lungs increases pressure in regions near the bottom and therefore less pressure pulling it open then regions at the top of the lung
Alveoli at the bottom receive a larger portion of the inspired air because they start more deflated and can expand more
100
What is Dalton's Law?
In a mixture of gases, each gas operates independently
| The total pressure is the sum of the individual pressures
101
What is Fick's Law?
The rate of transfer of a gas through a sheet of tissue/unit time is proportional to the tissue area and the difference in gas partial pressure between the two sides, a diffusion constant, and inversely proportional to the tissue thickness
102
What is the Diffusion constant?
The amount of gas transferred between the alveoli and the blood/unit time is also proportional to the gas solubility in fluids or in tissue
103
Is CO2 or O2 solubility higher?
CO2 diffuses 20 more times rapidly than O2
104
What is Henry's Law?
The amount of as dissolved in a liquid is directly proportional to the partial pressure of gas in which the liquid is in equilibrium
105
What are 3 reasons why Po2 in the air is greater than the Po2 in alveoli
Warming and humidification of air in the respiratory tract decreases the partial pressure of oxygen
Loss of O2 to blood diffusion decreases the partial pressure of oxygen
Mixing of inspired air with functional residual volume decreases the partial pressure of oxygen
106
What are the 4 determinants of alveolar Po2?
Po2 in the atmosphere
Alveolar ventilation
Metabolic rate
Perfusion
107
What are the 4 determinants of alveolar Pco2?
Pco2 in the atmosphere
Alveolar ventilation
Metabolic rate
Perfusion
108
How does increasing alveolar ventilation affect alveolar PO2 and pCO2?
Alveolar Po2 will increase and alveolar Pco2 will decrease
109
How does increasing metabolic rate affect alveolar Po2 and Pco2
Alveolar Po2 will decrease and alveolar Pco2 will increase
110
Why is the pulmonary circulatory system a low-pressure system?
Needs to pump blood only to the top of the lung
| Important for avoiding rupture of respiratory membrane and edema formation
111
Why is the pulmonary circulatory system a low-resistance system?
It has shorter and wider vessels
112
How does the pulmonary circulatory system have high compliance vessels?
Higher number of arterioles with a low resting tone
Due to the thin walls and the paucity of smooth muscle can accept large amounts of blood
Can dilate in response to modest increases in arterial pressure
113
What is the ventilation-perfusion ratio?
The balance between the ventilation and the perfusion
| One of the major factors affecting the alveolar (and arterial) levels of O2 and CO2
114
The greater the ventilation...
The more closely alveolar Po2 and Pco2 approach their respective values in inspired air
115
The greater the perfusion...
The more closely the composition of local alveolar air approaches that of mixed venous blood
116
What does a high V/Q ratio mean?
That there is alveolar or physiologic dead space
117
What is alveolar Vd?
Regions of the lung with high V/Q ratios
Regions that are relatively over ventilated (under perfused) so that a portion of the fresh air reaching these alveoli cannot be taken up by the blood
118
What is anatomical Vd?
The volume of conducting airways that do not participate in gas exchange
119
What does a low V/Q ratio mean?
That there is an airway obstruction or shunt
120
What is a shunt?
A portion of venous blood doesn't get oxygenated and goes back to arterial blood
121
What are the regional differences in lung perfusion?
In an upright position, perfusion is greatest near the base of the lung and falls towards the apex
122
What does perfusion depend on?
Gravity
| Posture
123
What are homeostatic mechanisms?
Exist to limit the mismatch between ventilation and perfusion
Most important is the unique response of pulmonary capillaries to low O2 - pulmonary hypoxic vasoconstriction
124
What is the mismatch in ventilation and perfusion?
There is a low V/Q ratio at the bottom of the lungs and a high V/Q ratio at the top of the lungs
125
How is O2 carried in the blood?
Dissolved
| Combined with hemoglobin
126
Is O2 solubility low or high?
Low
127
What law does dissolved O2 follow?
Henry's Law
128
How much oxygen is carried to peripheral tissue in one minute?
1000 mL
129
What is the O2 capacity?
The maximum amount of O2 that can be combined with Hb
| Normally 20.8 mL O2 / 100 mL of blood
130
What is Hb saturation?
The percentage of available Hb binding sites that have O2 attached
131
What are the determinants of Hb saturation?
```
Arterial Po2 = most important
pH
Pco2
Temperature
Cooperative binding
```
132
What are the important features of a sigmoidal dissociation curve?
```
Flat portion (plateau) between 60-100 mmHg
The steep portion between 10-60 mmHg
```
133
What is the plateau portion of a sigmoidal dissociation curve?
Due to plateau, saturation stays high over wide range of alveolar Po2
Provides safety factor so that even a significant limitation of lung function still allows almost normal O2 saturation of Hb
134
What is the steep portion of a sigmoidal dissociation curve?
Unloads large amount of O2 with only a small decrease in Po2
135
Why is it important that Po2 remains relatively high in the capillary of peripheral tissue?
This pressure is necessary to drive diffusion of O2 from RBC, to blood to cells and mitochondria
136
How saturated is most Hb leaving peripheral tissues at rest?
75%
137
How does increases in metabolic rate affect tissue Po2?
Causes a further decrease in tissue Po2 which facilitates diffusion from plasma which leads to drop in plasma Po2, diffusion of O2 from RBC, drop in Po2in RBC, additional dissociation of O2 from Hb
138
What is anemia?
Reduction in the amount of Hb in the blood
139
How does anemia affect O2 concentration?
Decreases O2 concentration
140
What is polycythemia?
Increase of Hb amount in blood or reduction of blood volume that increases Hb concentration
141
How does polycythemia affect O2 concentration?
Increases O2 concentration
142
How does CO affect the O2-Hb dissociation curve?
Reduction in O2-Hb binding
| Shift to the left which leads to decreased unloading of O2 to tissues and a conformational change
143
How does oxygen move at the level of the respiratory membrane?
Before diffusion, the alveolar Po2 is much greater than the blood Po2
After diffusion alveolar Po2 = blood Po2
144
Does O2-Hb contribute to the Po2 value?
No
145
How does oxygen move in the peripheral tissue?
Before diffusion:
-blood Po2 > IF Po2 > cell Po2 > MIT Po2
Reduction of blood Po2 reduces the affinity of O2 for Hb and more O2 is released from the RBC
146
How does a shift to the right on a dissociation curve affect O2 affinity?
O2 affinity to Hb is decreased so there is more unloading
147
How does a shift to the left on a dissociation curve affect O2 affinity?
O2 affinity to Hb is increased so there is less unloading
148
How does DPG affect O2 affinity?
Shifts the curve to the right
| An increase in their end product of RBC metabolism results in chronic hypoxia
149
How is CO2 carried in the blood?
Dissolved
Bicarbonate
Carbamino compounds
150
Is CO2 solubility high or low?
High
151
How does the carbonate form leave the cells?
To maintain the electrical neutrality and allow for HCO3- to exit the cells, H+ will increase in venous blood
Decreases pH
152
What are carbamino compounds?
Combination of CO2 with amino group in blood proteins
| DeoxyHb has a higher affinity for CO2 so it will help to unload O2 from Hb in peripheral tissues
153
How does CO2 move in the peripheral tissue?
CO2 exits the cells and is dissolved in IF and diffuses to blood
CO2 can then:
-remain in plasma dissolved as CO2 (Pco2)
-enter the RBC and remain dissolved as CO2 and is bound to DeoxyHb
-react with water to produce HCO3- and H+
154
How does CO2 move at the level of the respiratory membrane?
Before diffusion alveolar Pco2 is less than blood Pco2
Dissolved CO2 in the blood diffuses into the alveoli
Lower Pco2 in plasma recalls dissolved CO2 from RBC and change the equilibrium for CO2/H2O and CO2/Hb reactions
155
How is H+ transported between tissues and lungs?
A large proportion of H+ is bound to Hb as DeoxyHb has a high affinity for H+
Physiological pH is preserved as Hb has a key role in buffering the production of H+ in the peripheral tissues
In the lungs, this equilibrium is reversed as H+ interacts with HCO3- and Hb is available for binding with O2
156
How is H+ made?
Produced during HCO3- production
157
What is respiratory acidosis?
Hypoventilation (more CO2 production than elimination)
| Pco2 and H+ concentration increases
158
What is respiratory alkalosis?
Hyperventilation (less CO2 production than elimination)
| Pco2 and H+ concentration decreases
159
What is metabolic acidosis?
Increase in blood H+ concentration independent from changes in Pco2
160
What is metabolic alkalosis?
Decrease in blood H+ concentration independent from changes in Pco2
161
Where is the rhythm of breathing established?
In the CNS
162
What initiates breathing?
The medulla by specialized neurons
163
How is breathing modified?
By higher structures of the CNS and inputs from central and peripheral chemoreceptors and mechanoreceptors in the lung and chest wall
164
What groups of respiratory neurons are located in the brainstem?
Pontine respiratory group, dorsal respiratory group, ventral respiratory group
165
What is the PreBotzinger (PreBotC) complex?
Group of neurons in the ventral respiratory group
| Generates excitatory inspiratory rhythmic activity that excites inspiratory muscles (via polysynaptic pathway)
166
What is the parafacial respiratory group (pFRG)?
Group of neurons in the ventral respiratory group
Important for generating rhythmic excitatory active expiratory rhythmic activity that excites expiratory muscles (via polysynaptic pathway)
167
Why does the rhythm of breathing change?
Neuronal networks must adjust the rhythm to accommodate changes in:
- metabolic demands
- varying mechanical conditions
- non-ventilatory behaviours
- pulmonary and non-pulmonary diseases
168
How is the rhythm of breathing generated?
Generated in the ventral respiratory group in the medulla
PreBotC and pFRG neurons drive activity in premotor neurons, which excite motorneurons that activate rhythmically respiratory muscles
Rhythmic activity is influenced by sensory and neuromodulatory inputs originating from different regions within and outside the CNS
169
What are the neuro-respiratory pathways of inspiration?
PreBotC innervates the INS premotorneuron in the rostral VRG which goes to the phrenic and thoracic motoneurons and innervates the diaphragm and ext. intercostal muscles respectively
PreBotC innervates the premotoneuron in the rostral VR and the parahypoglossal region which goes to cranial motoneurons which innervates the tongue and upper airway muscle
170
What are the neuro-respiratory pathways of active expiration?
pFRG innervates EXP premotoneurons in the caudal VRG which goes to thoracic and lumbar motoneurons which innervates the int. intercostal muscles and abdominal muscles respectively
171
What is chemical control of ventilation?
Hypoxia (low Po2), hypercapnia (high Pco2), and acidosis (low pH in the blood) all cause an increase in ventilation
Tends to raise Po2, lower Pco2, and raise pH
172
What key roles do chemoreceptors play in the chemical control of ventilation?
They are specialized structures that sense changes in Po2, Pco2, and pH
173
What are the two peripheral chemoreceptors?
Carotid and aortic bodies
174
What do peripheral chemoreceptors sense?
Primarily sense hypoxia (low Po2) but are also sensitive to pH
175
What are carotid bodies?
Extremely small, chemosensitive, highly vascularized, high metabolic rate
176
What are the two types of cells in the carotid bodies?
```
Type 1 (glomus cells) = the chemoreceptive cells
Type 2 (sustentacular cells) = act as support in the CB
```
177
What are glomus cells?
Has neuron-like characteristics
- variety of voltage-gated ion channels
- depolarization triggers APs
- have intracellular vesicles containing various neurotransmitters
- stimulation causes the release of these neurotransmitters and controls the firing of the sensory nerve endings
178
When do glomus cells fire>
Increase their firing rate with the lowering of Po2
| Also sensitive to changes in Pco2 and pH
179
What arterial Po2 stimulates peripheral chemoreceptors?
When it falls below 60 mmHg (60-120 is the normal range)
180
What is the response to hypoxia that is mediated by peripheral chemoreceptors?
Peripheral chemoreceptors activate dorsal and ventral respiratory group neurons in the medulla in order to control centrally the activity of the respiratory muscles by increasing the respiratory rate and the tidal volume
181
What are central chemoreceptors?
Specialized neurons located close to the ventral surface of the medulla (close contact with blood vessels and CSF)
Other thermosensitive sites are located in the medullary raphe and the hypothalamus
182
What do central chemoreceptors respond to?
Mostly hypercapnia (high Pco2)
183
What is the response to hypercapnia that is mediated by central chemoreceptors?
Mediated by effects at the level of the dorsal and ventral respiratory group that change ventilation
184
What is the respiratory response to metabolic acidosis?
H+ stimulates mostly peripheral chemoreceptors because H+ does not cross easily across the BBB
Hyperventilation is the response to low pH
