Respiratory Physiology Flashcards
0
Q
What affects the type of respiratory system an animal can have?
A
The distance to which nutrients and oxygen have to be delivered and dehydration limits diffusion rate, therefore the size of an animal and the habitat of an animal affects the type of respiratory system it has.
1
Q
What is aerobic metabolism?
A
It is the conversion of food sources into ATP with oxygen present.
2
Q
What are the different lobes of the human lungs?
A
3 lobes in the right and 2 in the left lung.
Right lung - inferior lobe, middle love and superior lobe.
Left lung - inferior and superior lobe.
3
Q
What are the two main regions of the respiratory system?
A
The conducting zone (dead space) - not involved in respiratory gas exchange - includes nasal cavities, pharynx and larynx, trachea and primary bronchi.
The respiratory zone - responsible for gas exchange - includes respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.
4
Q
What are the components of the nasal cavities?
A
- Sweat glands
- Sebaceous glands
- Hair follicles - filters inhaled air.
They all protect the airways.
The nasal cavities are lined by mucosa which are epithelial cells (olfactory mucosa and respiratory mucosa).
Olfactory mucosa - sense of smell.
Respiratory mucosa - secretes antibacterial enzymes and mucus.
Ciliates cells sweep material to pharynx.
Surface area of epithelial is increased by scrolled nasal concha (to maximise heat exchange)
5
Q
What is the general function of the nasal cavities?
A
They warm, humidify and filter inhaled air.
6
Q
Why does the nasal cavity warm and humidify the air breathed in?
A
To make sure that cold, dry air does not get to the respiratory zone which may ‘ shock’ the body.
7
Q
What are the functions of the pharynx?
A
Pharynx (between nose and mouth) - involves the nasopharynx, oropharynx and laryngopharynx - it is part of the digestive system and respiratory system.
The epiglottis seals off the trachea during the swallowing reflex to separate the respiratory and digestive system by preventing food from passing to the trachea.
8
Q
What are the tonsils and what are their function(s)?
A
They are lymphoid tissues which surround the airways and defend it. They activate immune responses.
9
Q
What is the function of the larynx?
A
Larynx/voice box - involved in respiratory and speech. It contains two vocal cords which vibrate with breathing. Laryngeal muscles alter the tension/positioning folds to create different sounds
10
Q
What are the function(s) of the trachea?
A
It is a flattened tube connecting upper (nasal) lower (bronchial) airways There are rings of cartilage (c shape cartilage rings) on the trachea that prevent it from collapsing.
It also has submucosal tissue - produce mucus in trachea
Lamino propria - lymphocytes to provide immune response.
Pseudostratified ciliates epithelial cells
Cough reflex in trachea allows expulsion of foreign bodies.
11
Q
What are the function(s) of the bronchi?
A
Surrounded by muscle - to drive inspiration
They also have ciliates pseudostratified epithelial tissues.
They help defend the airways - via the mucociliary escalator :
1. Goblet cells produce sticky mucus to grow bacteria.
2. Bronchial epithelial cells - produce anti-microbial peptides to punch holes in bacteria and kill them.
3. Ciliates epithelial cells beat the mucus to the pharynx.
12
Q
What is the mucociliary escalatory?
A
This takes place in the bronchi.
Cilia, periciliary fluid and mucus raft on top of the cilia is required.
1. Sticky mucus (made of glycoproteins) traps inhaled particles and bacteria.
2. Cilia project into the periciliary fluid (a liquid layer secreted by epithelial cells).
3. The action of the ciliary beating moves the mucus raft to the back of the throat (where it can be swallowed or removed via the mouth).
13
Q
What is the difference between the epithelium in the airways of an individual with cystic fibrosis?
A
- There is an overproduction of thick mucus.
- There is no periciliary fluid for the cilia to ‘beat’ mucus into because the mucus is ‘dehydrated’.
- Dirt laden mucus is trapped and cannot get to the back of the throat and can therefore not be removed - the individual is more vulnerable to infections.
14
Q
What are alveolar ducts?
A
They are tiny ducts connecting respiratory bronchioles to alveolar sacs. They are surrounded by smooth muscle, elastin and collagen.
15
Q
What are alveolar sacs?
A
Each alveolar sac contains a bunch of alveoli.
16
Q
Where does the mucociliary escalator take place?
A
In the bronchi.
17
Q
Alveoli has type I and type II pneumocytes which are epithelial cells instead of pseudostratified epithelial cells. What are their functions?
A
Type I pneumocytes - responsible for gas exchange in alveoli - thin membrane which is close to the endothelium. They have tight junctions to create an impermeable barrier to foreign invaders (this is a function of epithelial cells).
Type II pneumocytes:
- involved in defence in alveoli. They are secretory cells produce surfactants which reduce surface tension to prevent the lugs from collapsing.
- they replenish damaged type II pneumocytes.
- they produce a(alpha)1-anti-trypsin which defend and protect the airways.
18
Q
What are alveolar macrophages?
A
They are monocytes that provide further protection/defence in the airways. They patrol the tissue for foreign material or dead/damaged cells that may interfere with lung function.
19
Q
What is the general function of the alveoli?
A
Type I pneumocytes - gas exchange.
Type II pneumocytes - repair, defence and regulation of surface tension to prevent lungs from collapsing.
Alveolar macrophages - defence.
33
Q
How is compliance measured clinically?
A
To measure compliance, changes in pressure and volume need to be measured. It is difficult to measure pressure changes (oesophageal balloon attached to a pressure transducers and different volumes of air are put into the balloon) but spirometry is used to measure volume changes.
34
Q
Give two conditions which increase and decrease lung compliance.
A
Emphysema (an obstructive lung disease) increases lung compliance - tissue damage - easier to inflate - lead to higher vital capacity - elastic recoil has been reduced - shifts compliance curve to the left.
Fibrosis (a restrictive lung disease) reduces compliance - increases elastic recoil - more pressure is required to increase volume - shifts compliance curve to the right.
35
Q
What is elastic recoil?
A
It is the inverse of compliance.
Stiff lungs have high elasticity but low compliance.
Elastic recoil of the lung is due to the elastic properties of the parenchyma (the functional parts of the lungs) which have elastin (more compliant) and collagen (less compliant).
An increase in collagen in parenchyma means less compliance and vice versa with elastin.
36
Q
What is alveolar surface tension?
A
Surface tension is what makes water form droplets (the cohesive forces between water molecules). The ability of the lungs to recoil (elastic recoil) is due to alveolar surface tension.
37
Why does alveolar surface tension arise?
Alveoli are not all the same size. Small alveoli tend to collapse - so alveoli will empty their air into adjacent alveoli.
38
What are the two factors that stabilise alveoli and prevent them from collapsing?
1. Structural interdependence of the alveoli - alveoli are held open by the chest wall pulling in the outer surface of the lung and they are dependent on each other. A collapsing alveolus causes stress on adjacent alveoli so they tend to hold each other open.
2. Pulmonary surfactant (released by type II pneumocytes) which reduces surface tension. It is made of lipids/phospholipids and proteins. It is recycled by type II pneumocytes.
SP-A and SP-D pulmonary surfactant are required for defence. SP-B is required to reduce surface tension.
39
Give example(s) where the lack of pulmonary surfactant affects the lungs.
Premature babies without functional surfactant have difficult inflating their lungs because elastic recoil is aided by alveolar surface tension - without the surfactant surface tension remains high and alveoli collapse - they can be given exogenous surfactant.
Hypoxia (where parts of the body have inadequate oxygen supply) may reduce surfactant production and can lead to ARDS (acute respiratory distress syndrome which leads to spontaneous lung collapse) - positive-pressure ventilation can be carried out so that alveolar pressure is greater than atmospheric to prevent spontaneous collage.
40
What is tidal volume?
The volume of air per breath - 500ml per breath for 70kg adults are eupnea (quite breathing).
41
What is the residual volume (RV)?
It is the volume of air remaining in the lungs after maximum forced expiration - 1.5L it is normally greater in emphysema - due to increased lung compliance which prevents elastic recoil of lungs.
It cannot be measured by spirometry.
42
What is the exploratory reserve volume (ERV)?
It is the volume expelled during maximum forced expiration starting at the end of normal tidal expiration - 1.5L.
It is also functional residual capacity - residual volume.
43
What is the inspiratory reserve volume (IRV)?
It is the volume inhaled during maximum forced inspiration starting at the end of normal tidal inspiration.
It is normally 2.5L.
44
What are lung capacities?
Hey are a sum of the lung volumes.
45
What is functional residual capacity (FRC)?
It is the volume remaining at the end of normal tidal expiration.
It is the residual volume + expiratory reserve volume. It is usually 3L.
46
What is the inspiration capacity (IC)?
It is the volume inhaled during maximum inspiratory effort at the end of normal tidal expiration.
It is vital capacity + inspiratory reserve volume. It is usually 3L.
47
What is the total lung capacity (TLC)?
It is the volume in the lungs after maximum inspiratory effort. It is residual volume + vital capacity + inspiratory reserve volume + expiratory reserve volume. It is about 6L.
48
What is vital capacity (VC)?
It is the volume expelled during maximum forced expiration after maximum forced inspiration. It is total lung capacity - residual volume. It is about 4.5L.
49
Apart from pathological states, what other factor(s) alters lung volume?
Physiology - for example when lying down or standing up - vital capacity is lower when lying down.
50
How can obstructive and restrictive diseases be diagnosed?
By measuring lung volumes.
51
What is a restrictive disease?
Restrictive diseases (alveolar fibrosis) leads to reduced compliance and increased elastic recoil.
FRC, TLC, VC, IRV and ERV will be reduced. The breathing rate of the individual will increase as they need to increase oxygen supply to tissues.
52
What is an obstructive disease?
Includes emphysema and chronic bronchitis.
There is increased resistance, increased compliance and decreased elastic recoil.
RV, FRC and TLC increase.
VC and ERV decrease.
Breathing rate decreases.
53
What is spirometry?
It is a simple way to measure gas volumes. The breathing pattern is traced on the rotating drum.
54
What are the limitations of spirometry?
Residual volume cannot be measured and functional residual capacity so the total lung capacity can also not be estimated. Spirometry can only be measured if the individual is conscious and cooperative.
55
How can we measure the other lung volumes that cannot be measured by spirometry?
1. Nitrogen wash out technique.
2. Helium-dilution technique.
3. Body plethysomography
They are used to measure function residual capacity which can be used to estimate residual volume and total lung capacity.
56
What is minute volume?
It is the volume of air entering and leaving the nose every minute - not the same as volume entering and leaving the alveoli - alveolar ventilation is less than the minute volume.
57
What is anatomical dead space?
It is the conducting airways - they are filled with air but are not involved in gas exchange.
58
What is alveolar dead space?
There are some alveoli that are not perfused (no capillaries surround them) so the volume of air in unperfused alveoli is the alveolar dead space - no gas exchange happens there.
59
What is the physiological dead space?
It is the anatomical dead space + alveolar dead space.
60
What does Boyle's law mean?
As the volume of the lungs increases, when an individual breathes in, pressure decreases, allowing air to flow into the lungs.
61
What does Dalton's law mean?
'The total pressure exerted by the mixture of non-reactive gases is equal to the sum of the pressure of individual gases.'
P(total) = P1+ P2 + P3 ..etc
Changes in the percentage of gas in the lung creates a driving force (pressure difference) to move gases in/out of the lungs.
62
What does Henry's law mean?
The amount of oxygen transported into the blood depends on the partial pressure - oxygen has to be transported in the blood as dissolved gas.
The amount of oxygen that dissolves in the gas depends on the pressure difference between the liquid and solid phase.
63
Describe the general gas exchange process between the tissues and the environment.
1. Air is breathed in and flows from conducting airways to the alveoli.
Inspiration is driven by respiratory muscles - this is controlled by the CNS.
2. The right ventricle pumps venous blood (deoxygenated blood) returning from tissues to the pulmonary capillaries in the lungs (high in carbon dioxide and low in oxygen) to be oxygenated.
3. The pulmonary capillaries allow exchange of carbon dioxide (in the alveoli) for oxygen so that blood leaving the lungs has high oxygen levels and low carbon dioxide levels.
4. Once the blood is oxygenated, it flows through the pulmonary veins into the left atrium and ventricle and the left ventricle pumps the oxygenated blood into the aorta and then to the systemic capillaries to be delivered to metabolising tissues.
64
What is the partial pressure of oxygen and carbon dioxide in oxygenated blood?
High partial pressure of oxygen and low partial pressure of carbon dioxide in oxygenated blood.
65
How is oxygen exchanged?
Oxygen is dissolved in the blood and combined to haemoglobin.
It enters the blood in the lungs, down it's partial pressure gradient (from a high partial pressure to low partial pressure). This is because inhaled air has higher oxygen concentration and therefore higher partial pressure than oxygen in venous blood.
Oxygen leaves the blood into tissues down its partial gradient - the oxygenated blood in the pulmonary veins has a higher concentration and therefore higher partial pressure than the tissues.
66
How is carbon dioxide exchanged?
Carbon dioxide enters the blood down from the tissues down its partial pressure gradient because tissues have a higher concentration of carbon dioxide and therefore higher partial pressure of carbon dioxide than the venous blood.
Carbon dioxide leaves the blood in the lungs down its partial pressure gradient because the arterial blood has a higher concentration of carbon dioxide than inhaled air.
67
How might the rate of gas exchange be reduced?
If the partial pressure gradient is reduced because gases diffuses according to partial pressure differences.
If the surface area of exchange is reduced - Fick's law says diffusion is directly proportional to surface area.
The diffusability of the gas also affects the rate of gas exchange (the diffusion coeffient) - depends in molecular weight of the gas and it's water solubility. The diffusion coefficient for carbon dioxide is much higher than for oxygen because carbon dioxide is much more soluble in water.
If the solubility of the gas is reduced - temperature dependent - oxygen is more soluble at low temperatures in fish.
If the distance for exchange is increased - e.g. In respiratory diseases like interstitial fibrosis.
68
Why does carbon dioxide diffuse much faster than oxygen during gas exchange?
Even though the partial pressure gradient of oxygen is much higher than carbon dioxide, the diffusion coefficient of carbon dioxide is much higher than oxygen.
69
Why can't we rely on dissolved oxygen only?
The amount of dissolved oxygen is too low to supply all the body's tissues.
70
How is the problem of 'inadequate supply of dissolved oxygen' solved?
Haemoglobin is also used along with dissolved oxygen to increase the oxygen carrying capacity of the blood. Each heme/haem group can bind to one molecule of oxygen. So each molecule of Hb (haemoglobin) can carry 4 molecules of oxygen.
71
What determines the proportion of oxyhaemoglobin in the blood?
It depends on the partial pressure of oxygen in the plasma.
72
What is % Hb saturation?
It is the percentage if haemoglobin that is carrying oxygen - oxygen bound to haemoglobin divided by oxygen capacity of haemoglobin x 100.
73
What does oxygen carrying capacity depend on?
It depends on the individual's haemoglobin content. Different people have different haemoglobin content. For example, anaemic patients have low haemoglobin content and so will have a lower oxygen carrying capacity.
74
How can we measure the haemoglobin content of an individual?
By producing a haematocrit which measures packed cell volume (PCV) about 46% of the blood must be blood cells. This figure is reduced in patients with anaemia/malaria and is increased in doping/EPO use.
However, a haematocrit does not tell us about the haemoglobin content, the red blood cells must be lysed to measure haemoglobin content.
75
What does an oxyhaemoglobin dissociation curve show?
The amount of oxygen bound to Hb relative to the partial pressure of oxygen.
76
At the high partial pressures of oxygen, is the affinity of haemoglobin to oxygen low or high?
At high partial pressures of oxygen, haemoglobin's affinity to oxygen is very high so loading of oxygen in the lungs is greater than unloading at the tissues.
77
At low partial pressures of oxygen, is the affinity of haemoglobin to oxygen high or low?
The affinity of haemoglobin to oxygen decreases, so there is more unloading of oxygen to tissues than loading.
78
What are the factors that affect oxygen carriage by haemoglobin?
1. pH - an increase in the concentration of protons/decrease in pH (due to anaerobic exercise) will increase UNLOADING of oxygen to metabolising tissues involved in the exercise and will shift the dissociation curve to the right and vice versa. This is the BOHR effect - lower pH reduces binding affinity of oxygen.
2. Partial pressure of carbon dioxide - BOHR effect (effect of proton and carbon dioxide on oxygen binding) if the partial pressure of carbon dioxide increases, unloading increases and if the partial pressure decreases, loading increases.
Increased partial pressure of carbon dioxide increases H2CO3 (carbonic acid) so the blood becomes more acidic. An increase in carbon dioxide levels may be caused by metabolising tissues.
3. Temperature - increase in temperature reduces affinity of haemoglobin to oxygen (more unloading), decrease in temperature, increases affinity of haemoglobin to oxygen (more loading) - an increase in temperature may be caused by metabolising/respiring tissues which is due to heat produced via respiration.
4. 2,3-DPG (2,3-diphosphoglycerate) which is a by product of red blood cell metabolism (2,3-DPG also increases in hypoxia) - increase in 2,3-DPG reduces affinity (unloading) and a decrease increases affinity (loading).
In hypoxia, 2,3-DPG is released, which will decreases affinity (increase in unloading of oxygen) and oxygen delivery to tissues will increase.
79
What is the difference between foetal haemoglobin and normal haemoglobin?
It has 2 alpha and rather than 2 beta protein subunits, it has 2 gamma subunits so foetal haemoglobin has a higher binding affinity to oxygen so the dissociation curve shifts to the left as loading of oxygen is increased.
Foetal blood can acquire oxygen from maternal, placental blood.
80
What is carboxyhaemoglobin?
It is haemoglobin that is bound to CARBON MONOXIDE. Haemoglobin has a much higher affinity to CO than oxygen and this reaction is less reversible than the binding of oxygen to haemoglobin.
The dissociation curve is shifted to the left because CO prevents oxygen from loading in the lungs and oxygen unloading in the tissues.
81
What environment and lifestyle factor(s) may increase carboxyhaemoglobin?
Smoking and urban pollution.
82
Why can't we only rely on dissolved carbon dioxide during gas exchange?
The carbon dioxide produced is too much to be dissolved in the blood. There are 3 ways by which carbon dioxide is carried/transported:
1. Dissolved in the blood (10%)
2. Bound to Hb (30%) - binds to the globin and not the haem groups.
3. As bicarbonate HCO3- (60%)
83
How is the bicarbonate ion (HCO3-) produced?
Carbon dioxide binds to water to form carbon acid (H2CO3) and then dissociates into H+ and HCO3-. Carbonic anhydrase (in red blood cells) catalyses this reaction so that carbon dioxide is straight away converted to H+ and HCO3-.
The bicarbonate ion is carried out of the red blood cells via facilitated diffusion via membrane carriers. The bicarbonate ion is more soluble in the plasma than carbon dioxide - easier transport.
The movement of the bicarbonate ion out of the red blood cells creates a proton gradient, as the proton is left behind, chloride ions are taken into the red blood cells to neutralise the fall in pH due to the protons left in the red blood cells (chloride shift).
84
What is the name of the product formed from carob dioxide and haemoglobin?
Carbaminohaemoglobin.
85
Which part of haemoglobin does carbon dioxide bind to?
The 'globin.'
86
Compare the affinity of carbaminohaemoglobin and oxyhaemoglobin to protons.
Carbaminohaemoglobin has a higher affinity for protons than oxyhaemoglobin.
87
What is the Haldane effect?
It says that deoxyhaemoglobin has a higher affinity for carbon dioxide and can unload more carbon dioxide at the lungs where there is more oxyhaemoglobin.
88
What is the difference between the Bohr effect and the Haldane effect?
The Bohr effect (effect of pH and partial pressure of carbon dioxide on affinity of haemoglobin for oxygen) explains that there will be unloading of oxygen and loading of carbon dioxide at the tissues.
The Haldane effect explains that oxyhaemoglobin has a lower affinity for carbon dioxide, so there is loading of oxygen at the lungs and unloading of carbon dioxide at the lungs where oxyhaemoglobin is found.
89
Name the components involved in the control of the respiratory system.
Sensors (receptors) - chemoreceptors
Central controller - medulla oblongata which receives information from the sensors (the peripheral and central chemoreceptors) - controls respiratory rhythm.
Effectors (respiratory muscles)
90
What is the other function of the respiratory system other than gas exchange?
Maintains normal levels of arterial partial pressure of oxygen (100mmHg)) and carbon dioxide (40mmHg).
91
What are allows the respiratory control system to carry out it's function?
It is automatic - maintenance of carbon dioxide and oxygen levels should not depend on levels of consciousness or alertness.
It must be adaptable - there are mechanisms to compensate for changes in oxygen uptake or carbon dioxide production.
It must be subject to voluntary control - there are mechanisms to voluntarily override the respiratory control mechanisms for brief periods of time.
92
The respiratory centre in the medulla controls the rhythmicity of breathing, what is this centre made up of?
1. Ventral respiratory group (VRG)
2. Dorsal respiratory group (DRG)
3. Pontine respiratory group (PRG)
They cooperate to regulate the depth, rate and pattern of breathing as an involuntary unconscious activity.
This respiratory centre also responds to the physiological needs of the body for oxygen and carbon dioxide exchange and for acid-base balance.
93
What is the function of the pontine respiratory group?
Involved in timing of inspiration, speech and sleep.
94
What is the function of the dorsal and ventral respiratory group?
Involved in the pattern of the respiratory cycle - DRG
Sets basic rhythm of ventilation - VRG - involved in the active expiration - contraction of internal intercostal muscles.
The firing of the VRG and DRG causes the respiratory muscles to contract or relax.
95
Where is the pre-Botzinger complex located?
It is located in the VRG. The pre-Botzinger complex contains the central pattern generator (CPG).
96
What is the central pattern generator?
A group of neurons that control breathing - there is no single pacemaker. There are different neurons involved in inspiratory activity and expiratory activity.
97
What are the six group of neurons involved in the CPG that control breathing?
Early inspiratory, inspiratory augmenting and late-inspiratory interneurones control inspiration.
Early expiratory decrement info expiratory augmenting and late expiratory pre-inspiratory neurons control expiration.
98
The respiratory cycle has 3 phases, describe the process.
1. Inspiratory phase:
- neuronal activity: onset of early inspiratory neurons followed by increase in inspiratory augmenting neurons.
- muscular effector function: inspiratory muscle contraction.
2. Post-inspiratory phase (expiratory phase 1):
- neuronal activity: reduced discharge from inspiratory augmenting neurons + early expiratory decrement in neurons are active.
- muscular effector function - reduced activity of inspiratory muscles - passive expiration.
3. Expiratory phase II:
- neuronal activity: expiratory augmenting neurons can be activated.
- muscular effector function: inspiratory muscles silent and expiratory muscle activity increases gradually.
99
What is the difference between quiet and active breathing?
Quiet breathing - expiration is almost completely passive.
Active. Restrung - (minut volume >40L/min) - expiration is mostly active - high activity of expiratory augmenting neurons.
100
What does the controls the diaphragm and the size of the rib cage?
The phrenic nerve controls the diaphragm.
| The intercostal muscles control the size of the rib cage.
101
What is the function of chemoreceptors?
They monitor the partial pressures of oxygen, carbon dioxide and the concentration of protons and they provide feedback to the breathing centres of the brain to modify breathing rate and tidal volume.
102
What are the two types of chemoreceptors?
Central and peripheral chemoreceptors.
103
What is the function of the central chemoreceptors?
Central chemoreceptors are found in the MEDULLA, they monitor the pH in the CSF as an indicator of what is going on in the plasma. They can't monitor pH directly so they respond to a change in the partial pressure of carbon dioxide because it is only CO2 (converted to H2CO3 and then H+ and HCO3-) that can diffuse across the blood brain barrier.
104
How does an increase in PCO2 increase respiratory rate?
An increase in PCO2 in CSF stimulates central chemoreceptors in medulla, which stimulates inspiratory muscles and respiratory rate increases to remove more carbon dioxide from the body, resulting in a decreased PCO2.
105
What is the function if peripheral chemoreceptors?
They monitor changes in the partial pressures of oxygen (if less than 60mmHg) and carbon dioxide from arterial blood. They are located in the carotid artery and aortic arch. The carotid body monitors oxygen delivery in the blood flowing to the brain.
106
How does the PCO2 and/or PO2 return back to the normal level?
Via negative feedback systems from the chemoreceptors to the effector respiratory muscles.
107
What is the difference between hypoventilation and hyperventilation?
Hypoventilation - less oxygen, more carbon dioxide - ventilation rate is increased to remove more carbon dioxide.
Hyperventilation - more oxygen, less carbon dioxide, ventilation rate is reduced.
108
What is the difference between peripheral and central chemoreceptors?
The peripheral chemoreceptors are only sensitive to PO2 below 60mmHg (the normal PO2 is 100mmHg) and are also sensitive to PCO2 but the central chemoreceptors are only sensitive to PCO2 (pH).
The peripheral chemoreceptors detect changes in arterial blood, central chemoreceptors detect changes in CSF.
They both send messages to the respiratory control centre in the medulla.
116
What is respiration?
```
Cellular respiration - biochemical reactions producing ATP.
External respiration (ventilation) - physiological process of oxygen and carbon dioxide uptake, transport and elimination.
```
117
Describe e process of external respiration (ventilation).
It involves transporting oxygen from the atmosphere to cells and transporting carbon dioxide from cells to the atmosphere.
118
What are the important factors involved in the process of breathing?
Inspiration, expiration, compliance, alveolar surface tension and pulmonary surfactant.
119
What is the importance of the pleural membranes (parietal pleura and visceral pleura)?
Parietal pleura is the lining inside the thoracic cavity.
The visceral pleura covers the lung.
The pleural membranes reduce friction and prevent damage of lung tissue. The pleural space contains pleural fluid, it is the fluid that reduces friction. The intrapleural pressure is negative (-3 to -5mmH2O) it is less than atmospheric pressure.
121
What is pneumothorax?
It is caused by damage to pleural cavity that equalises atmospheric and intrapleural pressure - so air enters the pleural space - breathing is altered and the lung collapses.
122
Describe the process of inspiration.
1. Thoracic cage lifts upwards and outwards
2. External intercostal muscles contract and pulls ribs together.
As the outward recoil of the chest increases, the intrapleural pressure increases (becomes more negative) because the pressure difference between the outward recoil of the chest and inward recoil or the lungs/alveoli increases.
3. Sternoclidomastoids and scalenus (accessory muscles) pull ribs upwards.
4. Diaphragm contracts (flattens) to increase the volume of the thorax - 75% of breathing is due to the contraction of the diaphragm.
5. Lungs expand - this lowers intra-alveolar pressure.
6. Pressure gradient causes air to flow into lungs/alveoli unit alveolar pressure equilibrates with atmospheric pressure.
123
What is transmural pressure difference?
It is the intrapleural pressure (outside) - alveolar pressure (inside)
So it is the pressure across the chest wall and lungs.
124
What is Boyle's law?
When transmural pressure difference (TPD) increases, alveolar pressure decreases so alveolar volume increases.
125
Describe the process of expiration.
It is a passive process.
1. External intercostal muscles, neck muscles (scalenus and sternocleidmastoid muscle) and diaphragm will relax.
2. Thoracic cage recoils passively back to inspiration position.
3. Air is forced out of the lungs until the pressure in the lungs is equal to atmosphere pressure.
126
What type of curves can be used to determine compliance?
Pressure-volume curves. The volume of the lungs is increased and the pressure of the lungs is measured. At lower volumes, a small change in pressure will lead to a higher change in volume. However at higher volumes, where the lungs are distended, a higher change in pressure is required for any change in volume.
127
What is compliance?
It is the measure of the ease of expansion of the lungs and thorax, which is determined by pulmonary volume and elasticity.
128
How is lung compliance measured?
Compliance = change in volume divided by the change in pressure. It is measured in L/cm2H2O
129
What causes intrapleural pressure?
It is caused by the elastic recoil forces of the lungs acting inwards and the recoil forces of the chest wall acting outwards.
