1
Q
What is the main function of the Respiratory System?
A
= gas exchange between atmosphere and blood (so that cells can use oxygen and get rid of carbon dioxide)
2
Q
List the 4 steps of external respiration
A
- Ventilation or gas exchange between the atmosphere and alveoli in the lungs
- Exchange of oxygen and carbon dioxide between air in the alveoli and the blood in the pulmonary capillaries
- Transport of oxygen and carbon dioxide by the blood between the lungs and the tissues
- Exchange of oxygen and carbon dioxide between the blood in the systemic capillaries and the tissue cells
3
Q
Describe alveoli
A
- alveoli = respiratory air sacs
- singular = alveolus; plural = alveoli
- alveolar sac = cluster of alveoli
- covered in pulmonary capillaries
- site of gas exchange
4
Q
Describe the 3 types of alveoli cells
A
Type 1 Alveolar Cell = squamous cells lining the alveoli
Type 11 Alveolar Cell = produce surfactant
Alveolar Macrophages = phagocytose foreign material
5
Q
Describe alveoli gas exchange
A
- respiratory membrane = Type 1 Alveolar cell + endothelial cell + basement membrane
- gas exchange optimised by: factors affecting diffusion rate:
- large surface area
- short diffusion distance
6
Q
Describe the bronchial tree
A
- branching of airways in the lungs:
- trachea
- bronchi
- bronchioles (<1mm diameter)
- terminal bronchioles
- respiratory bronchioles
7
Q
Describe bronchial tree structural changes
A
- cartilage provides structural support in trachea (C-shaped rings) and bronchi (plates) -> keeps airways open
- smooth muscle in bronchioles allow small airways to dilate or constrict : bronchodilation, bronchoconstriction
8
Q
Describe lungs and the thoracic cavity
A
- lungs: right lungs has 3 lobes; left lungs has 2 lobes
- the lungs are highly elastic
- thoracic cavity:
- thoracic wall (rib cage)
- internal and external intercostal muscles
- diaphragm
- other components: heart, major blood vessels, oesophagus
9
Q
Discuss the pleural sac
A
- double walled closed sacs
- between lungs and thoracic wall
- filled with intrapleural fluid
- lubricates pleural surfaces
- “sticks” lungs to thoracic wall (surface tension)
10
Q
Describe pressure
A
- units: mmHg (millimetres of mercury)
- atmospheric pressure
- pressure exerted by weight of air on objects on earths surface
- decreases with height from sea level
- sea level = 760 mmHg
11
Q
List the 3 pressures influencing ventilation
A
- Atmospheric Pressure
- Intra-alveolar Pressure
- Intrapleural Pressure
12
Q
Describe Atmospheric Pressure
A
= the pressure exerted by the weight of the gas in the atmosphere on objects on Earth’s surface
- 760 mmHg at sea level
13
Q
Describe Intra-alveolar Pressure
A
= the pressure within the alveoli
- atmosphere and alveoli are linked by conducting airways -> intra-alveolar pressure quickly becomes the same as atmospheric pressure
- 760 mmHg when equilibrated with atmospheric pressure
14
Q
Describe Intrapleural Pressure
A
= the pressure within the pleural sac
- the pressure exerted outside the lungs within the thoracic cavity
- usually less than atmospheric pressure
- 756 mmHg (also expressed as -4 mmHg)
15
Q
List the 2 forces that the thoracic wall and lungs are held together by
A
- Surface tension of intrapleural fluid
2. Transmural pressure gradient
16
Q
Describe the transmural pressure gradient
A
trans = across ; mural = wall
- is the pressure difference between the lungs and the pleural cavity
- pushes lungs out towards the thoracic wall
17
Q
Describe gas pressure and volume
A
Boyle’s Law
- pressure of a gas in a container varies inversely with the volume of the gas
e.g. increasing the volume decreases the pressure
P1V1 = P2V2
18
Q
Describe Inspiration
A
- contraction of:
- diaphragm
- external intercostal muscles
- inspiration is muscle activity working AGAINST elastic recoil
19
Q
List the 4 step process of inspiration
A
- Diaphragm and external intercostal muscle contract
- Lung volume increases
- Slight drop in intra-alveolar pressure
- Air enters lungs
20
Q
Describe Expiration
A
- expiration is a passive process -> no contraction of muscles
- decreased lung volume caused by:
- relaxation of muscles (diaphragm and external intercostals)
- elastic recoil of lungs
21
Q
List the 4 step process of expiration
A
- Diaphragm and external intercostal muscles relax
- Lung volume decreases
- Slight rise in intra-alveolar pressure
- Air leaves lungs
22
Q
Describe forced breathing
A
- normal breathing = quite breathing
- forced breathing:
- exercise or disease
- requires extra muscles
23
Q
Describe Forced breathing - inspiration
A
- further contraction of external intercostals and diaphragm (as much as 10cm)
- contraction of accessory muscles in neck
**Inspiration is muscle activity working AGAINST elastic recoil
24
Q
Describe Forced breathing - expiration
A
- internal intercostals draw in ribs
- abdominal muscles contract and push the diaphragm upwards
- forced expiration is not passive
**Forced expiration is muscle activity working WITH elastic recoil
25
List 3 physical factors that influence ventilation
1. Airway Resistance
2. Alveolar Surface Tension
3. Lung Compliance and Elastic Recoil
26
Describe Airway Resistance
- airflow rate (F) depends on
* air pressure gradient (delta P): difference between atmospheric and intra-alveolar pressure
- airway resistance (R)
F = delta P/R
- airway resistance is very low in healthy individuals
- friction of air against walls of airways
- increased resistance = slower airforce
- main factor increasing resistance is reduced bronchiole radius
* bronchoconstriction
* mucous
* fluid
27
Describe Alveolar Surface Tension
- alveoli are lined with a layer of water
* creates surface tension
* water molecules attracted to each other, but not air
- can cause alveoli to collapse (expiration)
- resists inflation of alveoli (inspiration)
- surface tension inside an alveolus generates an inward-directed collapsing pressure
28
Describe Surface Tension
- Law of LaPlace: P=2T/r
* the magnitude of inward-directed pressure (P) is directly proportional to the surface tension (T) and inversely proportional to the radius (r) of the alveolus
* the collapsibility of an alveolus can be reduced by decreasing the surface tension
* for any given surface tension, small alveoli have a greater tendency to collapse
29
Describe Surfactant
- surfactant breaks the surface tension of water
* produced by type 11 alveolar cells
* mixture of proteins and lipids
- breaks hydrogen bonds between water molecules
* stops alveoli from collapsing
* easier to expand alveoli during inspiration
30
Describe Lung Compliance and Elastic Recoil
- compliance
*stretchability of the lungs during inspiration
*high compliance = easily stretched
*low compliance = hard to stretch
- factors reducing compliance
*high surface tension (reduced surfactant)
*scarring of lung tissues
- restrictive diseases
- elastic recoil
*ability of lungs to rebound (shrink)
*important during expiration
- elastic recoil influenced by 2 factors:
i) elastic fibres
ii) surface tension
Decreased surface tension = decreased elastic recoil
- emphysema
31
Define Inspiration Capacity (IC)
- maximum volume of air that can be inspired
| - TV + IRV
32
Define Vital Capacity (VC)
- maximum amount of air expired after maximum inspiration
| - TV + IRV + ERV
33
Define Functional Residual Capacity (RFC)
- volume of air in lungs after normal expiration
| - ERV + RV
34
Define Tidal Volume (TV)
- air inspired or expired during quiet breathing
| - 500 ml
35
Define Inspiratory Reserve Volume (IRV)
- extra air inspired during forced inspiration
36
Define Expiratory Reserve Volume (ERV)
- extra air expired during forced expiration
37
Define Residual Volume (RV)
- air left in the lungs after forced expiration
| - 1200 ml
38
Define Total Lung Capacity (TLC)
- maximum volume of air that the lungs can hold
| - VC + RV
39
Describe Pulmonary Ventilation
- also called minute ventilation
- volume of air breathed in and out per minute (ml/min)
Pulmonary Ventilation (ml/min) = Tidal Volume (ml/breath) x Respiratory Rate (breath/min)
40
Describe Anatomical Dead Space
- the volume of air available for gas exchange is less than the tidal volume
- why? Because some of the tidal volume never makes it into the alveoli -> anatomical dead space = air stuck in the airways
41
Describe the 4 steps of 'anatomical dead space' process
1. End of inspiration. Dead space filled with fresh air
2. Exhale 500ml (tidal volume). The first exhaled air comes out of the dead space. Only 350ml leaves the alveoli
3. At the end of expiration, the dead space is filled with "stale" air from the alveoli. Dead space is filled with stale air
4. Inhale 500ml of fresh air (tidal volume). Dead space is filled with fresh air. Only 350ml of fresh air reaches alveoli. The first 150ml of air into the alveoli is stale air from the dead space
42
Describe Alveolar Ventilation
- volume of air exchanged between the atmosphere and alveoli
* air available for gas exchange
* takes dead space into account
Alveolar Ventilation (ml/min) = (Tidal volume - Dead Space) (ml/breath) x Respiratory Rate (breath/min)
43
Describe Obstructive Lung Diseases
- difficulty with exhalation
- increased airway resistance
- examples:
* asthma
* emphysema
* chronic conditions
* cystic fibrosis
44
Describe Restrictive Lung Diseases
- difficult with inhalation
- impaired lung expansion
- examples:
* pleural effusion (fluid in the pleura)
* pleurisy (inflammation of the pleura)
* atelectasis (collapsed lungs)
* fibrosis
- impaired expansion of the lungs
* damage to lung tissue (e.g. fibrosis)
* disease of pleura/chest wall (e.g. scoliosis impacting on shape of thoracic cage)
* neuromuscular disease
45
Describe Pulmonary Fibrosis
- restrictive disease resulting in reduced lung compliance (less compliant = less ability to stretch)
- causes:
* exposure to irritants (e.g. asbestos, silica) -> these irritant fibres don't break down which causes scarring
- inflamed lung tissue becomes 'scarred'
- because lung tissue is scarred, the composition of lung tissue changes leading to reduced lung compliance
46
Describe Chronic Bronchitis
- hyper secretion of mucous and chronic productive cough for at least 3 months of the year, for at least 2 consecutive years
- chronic productive cough = including phlegm or fluids
- cause: cigarette smoking, air pollutants
47
Describe the Pathophysiology of Chronic Bronchitis
- chronic inflammation in lungs
- bronchial oedema (swelling) and increased mucous production
- impaired mucous clearance
- mucous accumulation in lungs and recurrent infections
48
Describe emphysema
- permanent enlargement of airways in the respiratory region (parts of the airways involved in gas exchange [alveoli and respiratory bronchioles])
- causes: cigarette smoking, pollutants and very rarely in 1-3% due to genetic causes
49
Describe the Pathophysiology of Emphysema
- increased enzymatic activity leading to breakdown of lung elastic fibres
- reduced elastic recoil
* lack/breakdown of elastic fibres
* decreased surface tension
- difficultly during expiration
- air trapping (increasing residual volume [air remaining in alveoli])
50
Describe the 5 step process regarding smoking/irritants and emphysema
1. Cigarette smoke
2. Increase neutrophils in alveoli
3. Increase in elastase activity (because cigarette smoke blocks alpha one-antitrypsin which neutralises elastase)
4. Destruction of elastic fibres
5. Alveolar tissue is destroyed
51
Describe the anatomical changes in emphysema
- in NORMAL LUNGS the alveolar walls are complete and the lung has a continuous network of elastic fibres
- with EMPHYSEMA the alveolar walls are broken and often large air sacs are present (elastic networks have been destroyed). Lungs can expand, but deflate poorly
52
Describe asthma
- periods of increased airway resistance due to three main changes in the bronchioles:
1. Inflammation (thickening of airway walls)
2. Increased mucous secretion
3. Airway hyper-responsiveness (bronchoconstriction)
- this leads to reduced airway radius in the bronchioles
- increased airway resistance
* triggered (e.g. pollen)
* reversible (spontaneous or treatment)
- types of asthma
* atopic asthma (allergic)
* non-atopic (non-allergic)
- stages
* early stage
* late stage
53
Describe Chronic Obstructive Pulmonary Disease symptoms
- obstruction
* bronchoconstriction/collapse
* excess mucous
- difficultly during expiration
* early small airway closure
* air trapping
- reduced gas exchange
* reduced surface area (emphysema)
* increased diffusion distance (chronic bronchitis)
- ventilation perfusion mismatch
* imbalance between air in the alveolus and blood in surrounding capillaries
54
Describe Normal Expiration
- resistance to airflow is low
- frictional loss of airway pressure is minimal
- airway pressure higher than intrapleural pressure
- airways remain open during normal quiet breathing
55
Describe Dynamic Airway Closure
- intrapleural and intra-alveolar pressures increase
- at low lung volume
* loss of pressure in the airways
- dynamic airway closure
* equal pressure in airways and pleural sac
* airways collapse
* remaining volume = residual volume
* only at low volumes in healthy people
56
Describe Early Small Airway Closure
- in obstructive diseases
*equal pressure point reached at higher lung volumes
*airways close before normal quantity of air is expired
- early small airway closure causes air trapping and increased residual volume
- early small airway closure is caused by:
*increased resistance to airflow
>decreased airway diameter
>asthma
*increased intrapleural pressure
>decreased elastic recoil
>emphysema
57
Describe tools for the diagnosis of respiratory diseases
- spirometry (lung function test)
- arterial blood gas analysis
- chest x-rays
58
Describe spirometry
- measures volume and flow of air
- two readouts:
* volume-time curve
* flow-volume loop
59
Describe the Volume-time curve
FVC= forced vital capacity
- maximum volume forcefully exhaled after maximum inspiration
FEV1= forced expiratory volume in 1 second
FEV1/FVC provides information about resistance to airflow
60
Describe the Flow Volume Loop
- maximum inspiration beforehand
- maximum fast expiration followed by maximum fast inspiration
- measures:
PEF= peak expiratory flow rate
FVC= forced vital capacity
PIF= peak inspiratory flow rate
61
Describe factors affecting lung function results
- in a healthy population:
* age
* height/build
* gender
- pathological factors:
* changes in airway resistance
* lung compliance
* early closure of the airways
62
Describe gas exchange
- exchange between:
* alveoli and pulmonary capillaries
* systemic capillaries and tissue cells
- gas exchange occurs down the pressure gradient
* high pressure to low pressure
- mixture of gases
* contribute partial pressure
* diffusion down partial pressure gradients
63
Describe partial pressures
- the total pressure of a mixed gas is the sum of the partial pressures from each gas
- partial pressure: % of total pressure caused by one gas type
- P= partial pressure
64
Describe alveolar partial pressures
- composition of air in alveoli is different to atmosphere
* alveolar air is mixed with water vapour and carbon dioxide
* both reduce partial pressure of alveolar oxygen
- alveolar partial presures
* P(oxygen) = 100 mmHg
* P(carbon dioxide) = 40 mmHg
65
Describe the 8 Step process of gas exchange
1. Alveolar P(oxygen) remains relatively high and alveolar P(carbon dioxide) remains relatively low because a portion of the alveolar air is exchanged for fresh atmospheric air with each breath
2. In contrast, the systemic venous blood entering the lungs is relatively low in oxygen and high in carbon dioxide, having given up oxygen and picked up carbon dioxide at the systemic capillary level
3. The partial pressure gradients established between the alveolar air and pulmonary capillary blood induce passive diffusion of oxygen into the blood and carbon dioxide out of the blood until the blood and alveolar partial pressures become equal
4. The blood leaving the lungs is thus relatively high in oxygen and low in carbon dioxide. It arrives at the tissues with the same blood-gas content as when it left the lungs
5. The partial pressure of oxygen is relatively low and that of carbon dioxide is relatively high in the oxygen-consuming, carbon dioxide-producing tissue cells
6. Consequently, partial pressure gradients for gas exchange at the tissue level favour the passive movement of oxygen out of the blood into cells to support their metabolic requirements and also favour the simultaneous transfer of carbon dioxide into the blood
7. Having equilibrated with the tissue cells, the blood leaving the tissues is relatively low in oxygen and high in carbon dioxide
8. The blood then returns to the lungs to once again fill up on oxygen and dump off carbon dioxide
66
Describe gas exchange at the lungs
- partial pressure gradients:
* Oxygen diffusion from alveoli to capillaries
* Carbon dioxide from capillaries to alveoli
67
Describe gas exchange at the tissues
- partial pressure gradients:
* Oxygen diffusion from capillaries to tissues
* Carbon dioxide diffusion from tissues to capillaries
68
Describe the method of transport in blood and percentage carried in this form of OXYGEN
1. Physically dissolved (1.5%)
| 2. Bound to haemoglobin (98.5%)
69
Describe the method of transport in blood and percentage carried in this form of CARBON DIOXIDE
1. Physically dissolved (10%)
2. Bound to haemoglobin (30%)
3. As bicarbonate (HCO3-) (60%)
70
Describe Haemoglobin
- found only in red blood cells (RBCs)
- two parts:
1. Globin
* protein: four subunits
2. Haeme
* non-protein: four haeme groups
* iron containing
* each iron atom binds to one oxygen molecule
- one haemoglobin molecule binds four oxygens
- one RBC contains 250 million haemoglobin molecules
71
Describe oxygen bound to haemoglobin
- Oxygen binding is reversible
Hb + O2 -> HbO2
- without oxygen binding = deoxyhaemoglobin
- with oxygen binding = oxyhemoglobin
72
Describe the Bohr Effect
= Carbon dioxide and H+ bind to protein part of haemoglobin and change shape of haemoglobin. This decreases oxygen affinity
73
Describe Carbon Dioxide Transport
- carbon dioxide is transported in blood three ways:
1. Dissolved in blood
2. Bound to haemoglobin
* globin portion
* forms carbamino haemoglobin (HbCO2)
3. As bicarbonate ion (HCO3-) [MOST COMMON]
74
Describe the process from Carbon Dioxide to HCO3-
- carbon dioxide is converted to HCO3- in RBCs
* carbonic anhydrase (enzyme) speeds up reaction
* CO2 + H20 -> H+ + HCO3-
- chloride shift
* HCO3- in RBC exchanged for Cl- outside cell
* facilitated diffusion through a carrier
- H+ (acid) binds to haemoglobin
* unbound H+ increases blood acidity
75
Describe the 3 things the control of breathing involves
1. Maintaining the rhythm of breathing (inspiration-expiration)
2. Regulating rate and depth of breathing
* matching breathing to body needs
3. Modifying respiratory activity
* e.g. speech, cough
76
Describe Respiratory Control Centres
- breathing is controlled through respiratory control centres
* brainstem (medulla and pons)
- medullary centres
* quiet breathing
* forced breathing
* respiratory rhythm
- pons centre
* smooth transition between inspiration and expiration
77
Describe Medullary Control Centres
- the rate and rhythm of breathing is controlled by the medullary control centres
- contains 3 main areas:
1. Dorsal Respiratory Group (DRG)
2. Ventral Respiratory Group (VRG)
3. Pre-Botzinger Complex
78
Describe the Dorsal Respiratory Group (DRG)
- inspiratory neurons
- contraction of inspiratory muscles
- quiet breathing
79
Describe the Ventral Respiratory Group (VRG)
- inspiratory and expiratory neurons
- contraction of inspiratory and expiratory muscles
- forced breathing
80
Describe Pre-Botzinger Complex
- auto-rhythmic cells
| - control rate of DRG inspiratory neurons
81
Describe chemical control of breathing
- rate and depth of breathing is adjusted to match the body's needs
- how do we detect the body's changing needs?
= chemoreceptors in major arteries and brain
*oxygen
*carbon dioxide
*H+
82
Describe control mechanisms
- we are more sensitive to changes in carbon dioxide than oxygen
83
Describe chemical control of oxygen
- P(oxygen) monitored by peripheral chemoreceptors
* carotid and aortic bodies
- arterial P(oxygen) needs to fall below 60 mmHg before respiratory centres respond
* severe disease state
* drop in atmospheric oxygen
84
Describe the PROCESS of chemical control of oxygen
```
Arterial P(oxygen) is less than 60mmHg
this stimulates
Peripheral Chemoreceptors
which sends action potentials to
Medullary Respiratory Centre
motor neurons then travel to respiratory muscles
Increased Ventilation
```
85
Describe chemical control of carbon dioxide and H+
- P(carbon dioxide) most important regulator of ventilation
- normal arterial P(carbon dioxide) = 40 mmHg +/- 3
- mostly controlled by central chemoreceptors
* medulla
* sensitive to increase H+ produced during carbon dioxide conversion to HCO3-
86
Describe the PROCESS of chemical control of carbon dioxide and H+
```
Increased arterial P(carbon dioxide)
Increased brain ECF carbon dioxide
Increased brain ECF H+
this stimulates
Central Chemoreceptors
which sends action potentials to
Medullary Respiratory Centre
motor neurons then travel to respiratory muscles
Increased Ventilation
```
