Respiratory Physiology Flashcards
1
Q
What are the two zones of the respiratory system?
A
- conducting zone
- respiratory zone
2
Q
List the structures of both the conducting and respiratory zones of the respiratory system:
A
Conducting zone:
- Trachea
- Bronchi
- Bronchioles
- Terminal bronchioles
Respiratory zone:
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
3
Q
How many airway generations are there and at what generation does the respiratory zone begin?
(According to Weibel)
A
23 generations (respiratory zone begins at generation 17)
4
Q
What are the functions of the conducting zone?
A
- transport air into and out of the respiratory zone
- warm, humidify and filter air before it reaches the gas exchange region
5
Q
What is the function of the respiratory zone?
A
To participate in gas exchange
6
Q
What is the approx. tidal volume for an average sized person?
A
500 mL
7
Q
What inspiratory reserve volume?
A
The additional volume that can be inspired above tidal volume (approx. 3000 mL)
8
Q
What is expiratory reserve volume?
A
The additional volume that can be expired below tidal volume (approx. 1200 mL)
9
Q
What is residual volume?
A
Volume of gas remaining in the lungs after a maximal forced expiration (approx. 1200 mL)
10
Q
What is a lung capacity composed of?
A
Two or more lung volumes
11
Q
What is the value of inspiratory capacity (IC) and what is it composed of?
A
3500 mL
Tidal volume (500 mlL) plus the inspiratory reserve volume (3000 mL)
12
Q
What is the value of functional residual capacity and what is it composed of?
A
Approx. 2400 mL
Expiratory reserve volume (1200 mL) and residual volume (1200 mL)
13
Q
What is functional residual capacity?
A
It is the approx. amount of air remaining in the lungs following a normal tidal volume, thought as the equilibrium volume of the lungs
14
Q
The is the volume of vital capacity and what is it composed of?
A
4700 mL
Composed of inspiratory capacity (3500 mL) and expiratory reserve volume (1200 mL)
15
Q
What is vital capacity?
A
It is the volume that can be expired after maximal inspiration
16
Q
What factors can increase or decrease a person’s vital capacity?
A
Increase:
- body size
- male gender
- physical condition
Decrease:
- age
17
Q
What is the approx. value of total lung capacity and what is it composed of?
A
Approx. 5900 mL
Composed of vital capacity (4700 mL) and residual volume (1200 mL)
18
Q
What is the dead space of the lung?
A
Is the volume of the airways and lungs that does not participate in gas exchange, includes anatomic and physiologic dead space
Note: by definition physiologic dead space is the total volume of the lungs that does not participate in gas exchange (i.e. the anatomic dead space and the functional dead space of the alveoli)
19
Q
What is the volume of the anatomic dead space?
A
Approx. 150 mL
Note: it is the volume of the conducting airways (incl. nose/mouth, trachea, bronchi, bronchioles)
20
Q
What is functional dead space in the alveoli?
A
Can be thought as ventilated alveoli that do not participate in gas exchange
21
Q
What is minute ventilation?
A
Is the total rate of air movement into and out of the lungs
Minute ventilation = VT x Breaths/min
22
Q
What is alveolar ventilation?
A
Is minute ventilation corrected for the physiological dead space
Alveolar ventilation = (VT - VD) x Breaths/min
23
Q
What does the alveolar ventilation equation describe?
A
It describes the inverse relationship between alveolar ventilation and alveolar Pco2
24
Q
What does the alveolar gas equation predict? What is it based on?
A
Used to predict alveolar Po2, based on alveolar Pco2
25
What is **forced vital capacity (FVC)?**
Is the total volume of air that can be *forcibly* expired after a maximal inspiration
## Footnote
*Note: FEV c**an be expressed as the amount of air that can be expired in the first one, two or three seconds (FEVx), normally the entire vital capacity can be expired in 3 seconds, so there is no need for FEV4*
26
What are the three basic elements of respiratory control?
1. Sensors
* e.g. peripheral and central chemoreceptors, mechanoreceptors
2. Central control
* medulla and pons located in the brain stem, cerebral cortex (voluntary control)
3. Effectors
* respiratory muscles
27
What are the three main neuronal groups that generate and modify involuntary breathing?
1. Medullary respiratory centre
2. Apneustic centre
3. Pneumotaxic centre
28
Where is the medullary respiratory centre located?
Reticular formation of the medulla
29
What group of cells is responsible for generating a respiratory rhythm?
*Pre-Botzinger Complex*
30
What are the two centre's of the medullary respiratory centre? And where are they located?
1. Inspiratory centre - Dorsal Respiratory Group (DRG)
2. Expiratory centre - Ventral Respiratory Group (VRG)
31
What are the inputs for the inspiratory centre?
* Peripheral chemoreceptors via the glossopharyngeal nerve (CN IX) and vagus nerve (CN X)
* Mechanorecepotors via the vagus nerve (CN X)
32
What are the outputs of the inspiratory centre?
Motor output to the diaphragm via the vagus nerve (CN X)
33
What is the main role(s) of the inspiratory centre?
* Controls basic rhythm for breathing
* Sets frequency of inspiration
34
When is the expiratory centre activated?
* during active expiration (i.e. exercise)
## Footnote
*Note: as expiration is normally a passive process, the neurons in the expiratory centre are normally inactive during quite breathing*
35
What is the role of the apneustic centre?
Has an excitatory affect on the inspiratory centre
36
Where is the apneustic centre located?
Lower pons
37
What is the role of the *p**neumotaxic centre?*
* "Switches off" or inhibits the inspiratory centre
* therefore regulates inspiratory volume and secondary respiratory rate
* thought to be involved in "fine-tuning" of the respiratory rhythm
38
Where is the *pneumotaxic centre* located?
Upper pons
39
List the effectors of respiration:
* Diaphragm
* Intercostal muscles
* Abdominal muscles
* Accessory muscles (i.e. sternomastoids)
* Nasopharyngeal muscles
40
Where are the central chemoreceptors located?
Ventral surface of the medulla in the brain stem
## Footnote
*Note: are located near the DRG and the exit of CN IX/CN X*
41
What do the central chemoreceptors directly and indirectly respond to?
* *Directly* to changes in **pH**
* *Indirectly* to changes in **Pco2**
42
How will changes in pH detected by the central chemoreceptors modify ventilation?
* Decreased pH (increased H+) *→* **hyperventilation**
* increased pH (decreased H+) *→* **hypoventilation**
43
Where are the peripheral chemoreceptors located?
* carotid bodies (bifurcation of the common carotid arteries)
* aortic bodies (above and below the aortic arch)
44
How is informtation from the central chemoreceptors relayed to the inspiratory centre?
Direct communication
45
How is information relayed from the peripheral chemoreceptors to the inspiratory centre?
Via **CN IX** and **CN X**
46
An increase breathing rate is produced following what changes in arterial blood detected by the peripheral chemoreceptors?
* decreases in arterial Po2
* increases in arterail Pco2
* decreases in arterial pH
47
Are changes in arterial pH dected by the aortic bodies?
No changes in arterial pH are only detected by the **carotid bodies**
48
List other receptors in the body that influence respiratory rate:
* Lung receptors
* Pulmonary stretch receptors
* Irritant receptors
* Juxtacapillary (J) receptors
* Bronchial C fibres
* Joint and muscle receptors
* Respiratory muscles (muscle spindles/Gamma system)
* Nose and upper airway receptors
* Arterial baroreceptors
* Pain and temperature receptors
* Sympathetic nervous system
* Temperature
* Metabolic rate
* Exercise
* Pregnancy
* Pain and emotion
* Voluntary control
49
What is the Hering-Breuer reflex?
Slows respiratory frequency due to an increase in expiratory time
50
Do central chemoreceptors respond to changes in the pH of **arterial blood** or **CSF?**
Cerebrospinal fluid (CSF)
## Footnote
Note: CO2 is freely permeable across the blood-brain and brain-CSF barriers (H+ and HCO3- are not), CO2 enters the CSF which is converted to H+ and HCO3-, changes in H+ is dected by the central chemoreceptors
51
What receptors are responsible for the **Hering-Breuer Reflex?**
Pulmonary stretch receptors
52
What do pulmonary stretch receptors respond to and where are they located?
* Distention of the lung
* Located in smooth muscle of the airways
53
Where are the juxtacapillary (J) receptors located and what do they respond to?
* Located in the alveolar walls (i.e. near capillaries)
* Respond to engorgement of pulmonary capillaries and increased interstitial fluid volume (i.e. left heart failure)
54
Under normal conditions what is the most important factor in the control of ventilation?
Pco2
55
At what Po2 level in peripheral blood do peripheral chemoreceptors respond to increase ventilation?
Approx. Po2 of 50-60 mmHg
## Footnote
Note: a Po2 of between 60-100 mmHg results in a breathing rate that is virtually constant
56
Where is the Pre-Botzinger complex located?
Ventrolaterally in the medulla
57
List the muscles involved in inspiration:
* Diaphragm
* External intercostal muscles
* Accessory muscles
* Scalene muscles
* Sternomastoids
58
List the muscles involved in expiration:
* Abdominal muscles
* rectus abdominis
* internal and external obliques
* transversus abdominis
* Internal intercostal muscles
## Footnote
*Note:* expiration is generally a passive process during quiet breathing, these muscles become active during excercise and other states of hyperventilation
59
What is compliance of the lung?
How distensibile the lung is, describes the change in lung volume for a given change in pressure
60
What type of cells produce surfactant?
Type II alveolar cells
61
What is the most important constituent of surfactant?
Dipalmitoyl phosphatidylcholine (DPPC)
62
How does DPPC (main component of surfactant) reduce surface tension?
* Due to is amphipathic properties (i.e. hydrophobic on one end and hydrophilic on the other)
* The intermolecular forces of DPPC break up the attracting forces between the liquid molecules lining the alveoli (which is responsible for the high surface tension)
63
What are the functions of surfactant?
* Reduces surface tension, and therefore collapsing pressure allowing the alevoli to remain open
* Increases lung compliance, reducing the work required to expand the lungs during inspiration
* Keeps alveoli dry by reducing hydrostatic pressure in the tissue outside the capillaries, and therefore preventing transudation of fluid
* Reduces small alveoli emptying into large alveoli preventing areas of atelectasis
64
What are the consequences of a lack of surfactant?
* reduced lung compliance
* alveolar atelectasis
* tendency to pulmonary oedema
## Footnote
*Note:* this are the pathophysiological features of infant respiratory distress syndrome
65
Will airflow occur without a pressure gradient?
No - a *pressure gradient is the driving force of airflow*
I.e. at rest alveoli pressure equals atmospheric pressure and there is no airflow, during inspiration the diaphragm contracts, increasing lung volume, decreasing alveolar pressure and establishing a pressure gradient for airflow to occur
66
What factors produce a change in airway resistance?
* Autonomic nervous system
* Parasympathetic stimulation - constriction
* Sympathetic stimulation - relaxation
* Lung volume
* Viscosity of inspired air
67
How does lung volumes affect airway resistance?
* High lung volumes → provide greater traction, decreasing airway resistance
* Low lung volumes → less traction, resulting in increased airway resistance
68
What is **hysteresis?**
The phenomenon that the pressure-volume slopes of a lung are different on inspiration and expiration
69
On a pressure-volume curve of the lung, what does each slope represent?
**Compliance** of the lung on inspiration and expiration
70
In relation to the lung, what does the **law of Laplace** state?
States the pressure tending to collapse an alveolus (or pressure required to keep an alveolus open) is directly proportional to the surface tension generated by the molecules of liquid lining the alveolus and inversely proprotional to alveolar radius
71
What is the relationship between airflow, pressure and resistance?
Airflow (Q) is proportional to the pressure difference (between the mouth/nose and alveoli) and inversely proportional to the resistance of the airways (R)
72
What determines the resistance of an airway?
Resistance is determined by **Poiseuille's law**
73
Draw and explain the breathing cycle:
74
What is the general gas law?
States that the product of **pressure times volume** of a gas is equal to the **number of moles of the gas multiplied by the gas constant multiplied by the tempurate**
75
What is Boyle's Law?
States that at a given temperature, the product of pressure times volume for a gas is constant
P1V1 = P2V2
76
What is Dalton's Law of Partial Pressures?
States that the partial pressure of a gas in a mixture of gases is the pressure the gas would exert if it occupied the total volume of the mixture
77
What does Henry's Law deal with?
Gases dissolved in solution
## Footnote
Note; Henry's law can only calculate dissolved gas in a solution, it does not deal with gas in a solution that is bound (e.g. gas bound to haemoglobin or to plasma proteins)
78
What is Fick's Law?
States the rate of transfer by diffusion is **directly proportional** to the driving force, a diffusion coefficient and the surface area available for diffusion, and **inversely proportional** to the thickness of a membrane
79
What is the **lung diffusing capacity (DL)?**
Is the ability for a gas to diffuse across the alveolar, while also taking into account the ability for the gas to combine with proteins in the pulmonary capillary blood
80
What are the three forms of gases in solution?
1. Dissolved gas
* as determined by Henry's Law
2. Bound gas
* i.e. to haemoglobin and plasma proteins
3. Chemically modified gas
* Henderson-Hasselbalch equation (bicarbonate buffer system)
81
What is diffusion-limited gas exchange?
When the total amount of gas transported across the alveolar-capillary barrier is limited by the **diffusion process**
82
What is **perfusion-limited** gas exchange?
Means that the total amount of gas transported across the alveolar/capillary barrier is limited by **blood flow** (i.e. perfusion) through the pulmonary capillaries
83
How is O2 transported in blood?
* Dissolved
* Bound to Haemoglobin
84
What percentage of O2 in blood is dissolved and what percentage is reversibly bound to haemoglobin?
* Dissolved - approx. 2%
* Bound to haemoglobin - approx. 98%
85
In what state must the iron in the heme moieties exists to allow O2 to bind to the haemoglobin subunits?
Ferrous state (i.e. Fe2+)
86
What is methemoglobin and is it able to bind O2?
* is when the heme moieties are in the ferric (Fe3+) state
* *does not bind O2*
87
How many molecules of O2 can bind to one haemoglobin molecule?
Four
(one molecule to each subunit, bound to either the α and β chains)
88
What is haemoglobin F (fetal haemoglobin or HbF)?
It is when the two β chains are replaced with γ chains
89
What are the two primary determinants of O2 content in the blood?
1. Haemoglobin concentration
2. O2-binding capacity of available haemoglobin
90
What is the O2-binding capacity of blood?
20.1 mL O2/100 mL blood
| (15g/100 mL x 1.34 mL O2/g haemoglobin)
91
How much O2 can be bound by 1g of haemoglobin
1.34 mL
92
What is the normal concentration of haemoglobin in the blood?
15g/100 mL
93
What is the approx. O2 consumption required for a person at rest?
250 mL O2/min
94
How do you calculate the O2 content of blood?
95
How do you determine the O2 delivery to the tissues?
O2 delivery = Cardic output x O2 content of blood
where
= Cardic output x (Dissolved O2 + O2-haemoglobin)
96
What causes a **right shift** of the O2-haemoglobin dissociation curve?
* increased Pco2
* decreased pH (increased H+)
* increased temperature
* increased 2,3-DPG
97
What causes a **left shift** of the O2-haemoglobin dissociation curve?
* decreased Pco2
* increased pH (decreased H+)
* decreased temperature
* decreased 2,3-DPG
* Haemoglobin F
98
What is the significance of the P50 point on the O2-haemoglobin dissociation curve?
It is the point at which haemoglobin is 50% saturated (i.e. where two of the four heme groups are bound to O2)
99
What is the significance of a *shift to the right* of the O2-haemoglobin dissociation curve
* decreased affinity of haemoglobin for O2 (i.e. unloading of O2 in the tissues if facilitated)
* increased P50
100
What is the significance of a **lift shift** of the O2-haemoglobin dissociation curve?
* increased affinity (i.e. unloading of O2 in the tissues is more difficult, binding of O2 is tighter
* decreased P50
101
What is the **Bohr effect?**
It is the effect Pco2 and pH have on the O2-haemoglobin dissociation curve
102
What is 2,3-diphosphoglycerate (2,3-DPG)?
* it is a byproduct of glycolysis in red blood cells
* production increases in hypoxic conditions
103
What does 2,3-DPG bind to?
Binds to the β chains of deoxyhaemoglobin
104
What two effects does the higher affinity of carbon monoxide (CO) for haemoglobin have on O2 transport in blood?
* reducing O2-binding capacity
* increased affinity for O2
105
Breifly outline the steps involved in generating increased erythrocytes following hypoxia:
1. increased production of hypoxia-inducible factor 1α in response to hypoxia
2. hypoxia-inducible factor 1α acts on fibroblasts in the renal cortex and medulla to cause synthesis of the mRNA for eryhtropoietin (EPO)
3. mRN directs increased synthesis of EPO
4. EPO acts to cause differentiation of proerythroblasts
5. Proerythroblasts undergo further steps to form mature erythrocytes
106
How is CO2 transported in blood?
1. dissolved CO2
2. carbaminohaemoglobin (CO2 bound to haemoglobin)
3. bicarbonate (HCO3-)
107
Approx. what percentage of total CO2 is dissolved in blood?
Approx. 5%
108
Approx. what percent of total CO2 in the blood is bound to haemoglobin as carbaminohaemoglobin?
Approx. 3%
109
What is the **Haldane effect?**
It is the affect of when less O2 is bound to haemoglobin the affinity CO2 has for haemoglobin is increased
110
At what site of proteins (haemoglobin, plasma proteins) such CO2 bind?
Terminal amino groups
111
Approx. what percentage of total CO2 in the blood is chemically modified and transported as HCO3-?
Approx. 90%
112
Write the Henderson-Hasselbach equation:
113
Where is the highest concentration of carbonic anhydrase?
Red blood cells
114
Draw/describe the bicarbonate buffer system in red blood cells:
115
