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20
Mechanics of Breathing I
80
Pharmacology
Undergraduate 1
12/18/2016

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Term
Describe the respiration we do each day in numbers
Definition
Each day, we each take around 20,000 breaths, inhaling and exhaling around 10,000 litres of air.
Term
How long can you survive without air?
Definition
4 minutes
Term
What is the major function of pulmonary ventilation?
Definition
to exchange O2 and CO2 between the lung air spaces and the blood.

- O2 moves from the lung air space into the blood, into the internal environment.
- CO2 moves from the lung air space out of the blood, into the external environment.
Term
What are the secondary functions of the respiratory system? (6)
Definition
1. Acid – Base balance (via regulation of PaCO2)
2. Vocalisation (communication)
3. Defence against pathogens
4. An avenue for water and heat losses
5. Enhancing venous return (via the respiratory pump)
6. Activating some plasma proteins as the pass through the pulmonary circulation
Term
Define internal respiration
Definition
also known as cellular respiration; refers to the use of O2 to generate ATP within the mitochondria via oxidative phosphorylation
Term
Define external respiration
Definition
refers to the exchange of O2 and CO2 between the atmosphere and body tissues (this involves both the respiratory and circulatory systems)
Term
Give the 3 integrated steps of external respiration
Definition
1. Pulmonary ventilation: physically moves air into and out of the lungs.
2. Gas diffusion across the respiratory membrane: between the alveolar air spaces and alveolar capillaries, and across capillary walls between blood and other tissues.
3. Transport of O2 and CO2 between alveolar capillaries and capillary beds in other tissues.
Term
What makes up the upper airways?
Definition
air passages in the head and neck (nasal and oral cavities and the pharynx)
Term
What makes up the respiratory tract?
Definition
All airways leading from the pharynx to the lung (including those within the lungs themselves), starting with the larynx. It can be functionally divided into 2 components: the conducting zone and the respiratory zone
Term
What makes up the conducting zone?
Definition
The conducting airways include the passage of air in everything from the larynx to the terminal bronchioles.
Term
What does the trachea divide into?
Definition
2 primary bronchi
which then subdivide into successively smaller bronchi and bronchioles (23-30 orders of branching occur)
Term
What is the primary function of the conducting zone?
Definition
to provide a route for air to enter and leave the respiratory zone (where gas exchange occurs)
Term
What is the air in the conducting zone called?
Definition
dead space: the volume of inhaled air that does not take part in gas exchange because either it remains in the conducting airways, or reaches alveoli that are not or poorly perfused

150ml
Term
What happens to air in the conducting zone?
Definition
- warmed and humidified
- filtered (goblet cells secrete mucus, ciliated cells propel the mucus towards the glottis)
Term
What allows changes in bronchiolar diameter?
Definition
smooth muscle
Term
Why is PO2 in the air different to PO2 in the alveoli?
Definition
because air inhaled into the alveoli is partly air from the dead space, which contains less o2 and more co2 (diluting effect of dead space air)

also air is humidified so water vapour pressure is added to dry gas pressure. total pressure doesn't change so dry pressures must decrease
Term
What are the benefits of the conducting zone?
Definition
•CO2 is retained, making a bicarbonate-buffered blood and interstitium possible.
•Inspired air is brought to body temperature, increasing the affinity of haemoglobin for O2, improving O2 uptake.
•Particulate matter is trapped in the mucus that lines the conducting airways, allowing its removal by mucociliary transport. Defence!
•Inspired air is humidified, improving the quality of airway mucus.
Term
What is the function of the respiratory zone?
Definition
The function of alveolar air space is gas exchange! There are around 300million alveolar sacs with a combined maximal surface area of around 100m2.
Term
Define alveolar dead space
Definition
: the sum of the volumes of those alveoli which have little or no blood flowing through their adjacent pulmonary capillaries, i.e., alveoli that are ventilated but not perfused, and where, as a result, no gas exchange can occur.
Term
What factors increase the rate at which substances diffuse across a membrane?
Definition
membrane surface area increase
membrane thickness decrease
Term
How many alveolar are there and what is their total SA?
Definition
There are ~ 300 million alveoli, with a total SA of ~ 100m2
Term
What does the alveolar wall consist of?
Definition
a single layer of squamous epithelial cells, whose basement membrane is fused with that of the capillary endothelium. The total thickness of this barrier is only about 0.2 μm
Term
What muscles are responsible for breathing?
Definition
the diaphragm and the internal and external intercostals
Term
Describe the thoracic cavity
Definition
The lower end of the thoracic cavity is sealed off by the diaphragm, and the upper end by structures of the neck, so the compartment enclosing the lungs is airtight
Term
What surrounds each lung?
Definition
a membrane called the pleura
visceral - lines the exterior surface
parietal - lines the interior
Term
Whats lies between the pleura?
Definition
lies the intrapleural space, containing around 15 mL of intrapleural fluid (an aqueous solution)
Term
What is the function of the pleura?
Definition
The pleurae aid lung function: lubricated pleural fluid reduces mechanical resistance during ventilation, providing surface tension to attach the lungs to the chest walls. Pressure changes during ventilatory behaviour also occur.
Term
Explain bulk flow
Definition
air flow into or out of the lungs is an example of bulk flow, driven by a pressure gradient between the air in the alveoli and the atmosphere
Term
What must happen in order for inspiration to occur?
Definition
atmospheric pressure must exceed alveolar pressure (vice versa for expiration)
Term
What are the 4 pressures associated with ventilation?
Definition
Atmospheric pressure (Patm): taken to be 760 mmHg

Intra-alveolar pressure (Palv): 0 mmHg ‘at rest’

Intrapleural pressure (Pip): -4 mmHg ‘at rest’. This is the pressure within the pleural sac

Transpulmonary pressure ( = Palv – Pip). This is the distending pressure across the lung wall: at rest, this is around 4 mmHg, which is just enough to balance the elastic recoil forces within the lung and represents a state of equilibrium
Term
Which pressure is always less than another pressure during normal breathing?
Definition
Pip is always less then Palv and is always negative during normal breathing

Pip is always negative during normal breathing
Term
What is meant by the fact that the chest and lungs are both elastic structures?
Definition
they tend to recoil towards their natural positions when stretched or compressed
Term
Describe the lungs and chest wall at rest
Definition
chest: compressed and recoils outwards
lungs: stretched and recoils inwards

forces tend to move the lungs and chest wall apart
Term
Why don't the lungs and chest wall separate?
Definition
the surface tension of the intrapleural fluid prevents the visceral and parietal pleura from pulling apart, so a negative intrapleural pressure develops
Term
What state are breathing muscles in at rest?
Definition
relaxed
Term
What is the functional residual capacity (FRC)?
Definition
the volume of air within the lungs at rest
Term
What happens if the pleural sac is punctured?
Definition
- Pip equilibrated with Patm at 0mmHg
- the lungs recoil and collapse (chest wall recoils outwards)

pneumothorax
Term
If one lung is punctured, what happens to the other?
Definition
each lung is enclosed in its own pleural space, so the unaffected lung should continue to function
Term
When might a spontaneous pneumothorax occur?
Definition
if disease (e.g. pneumonia, emphysema) damages the visceral pleura so that air from the lung enters the intrapleural space
Term
What does Boyle's Law state?
Definition
gas pressure is inversely proportional to volume:

P α 1/V
Term
How does Boyle's Law relate to the lungs?
Definition
the pressure in the lungs changes when their volume changes
Term
What does flow equal?
Definition
pressure gradient divided by resistance:

Flow = (Patm – Palv) / R
Term
What is the driving force for air movements in and out of the lungs?
Definition
the driving force for air movements in and out of the lungs is the difference between Patm and Palv and since Patm is constant, changes in Palv determine the direction and rate of air movement
Term
What two factors determines intra-alveolar pressure?
Definition
- Quantity (moles) of air in the alveoli
- The volume of the alveoli
Term
Describe the events of inspiration
Definition
lungs expand
alveolar volume increases
Palv decreases
pressure gradient drives air into the lungs
Term
Describe the events of expiration
Definition
lungs recoil
alveolar volume decreases
Palv increases
pressure gradient drives air out of the lungs
Term
What are the major respiratory muscles for inspiration?
Definition
external intercostal muscles
diaphragm
Term
What are the major expiratory muscles for inspiration?
Definition
internal intercostal muscles
abdominal muscles
Term
How is inspiration caused?
Definition
1. diaphragm contracts, flattening and displacing downwards
2. external intercostal muscles contract, causing he ribs to pivot upwards and outwards
3. thoracic cavity volume increases
4. Pip decreases (becomes more negative)
5. transpulmonary pressure increases
6. lungs expand with the chest wall
7. Palv decreases to below Patm
8. Air flows into the lungs until Palv equals Patm
9. stronger contractions of the inspiratory muscles result in a greater lung expansion and a deeper inspiration
Term
Describe expiration in quiet breathing
Definition
passive
relaxing the inspiratory muscles allows the lungs and chest wall to recoil to their resting positions
Term
What happens are lung volume decreases?
Definition
Palv exceeds Patm and air flows out until lung volume equals FRC (equilibrium)
Term
What does more forceful expiration require?
Definition
contraction of the expiratory muscles: internal intercostals and some abdominal muscles

this causes a greater and more rapid decrease in thoracic volume, further increasing Palv and causing a greater and more rapid expiration
Term
What does the pressure gradient for ventilation (Patm - Palv) provide the force for?
Definition
moving air into and out the lungs
Term
What does the transpulmonary (Palv - Pip) provide the force for?
Definition
expansion of the lungs
Term
Define lung compliance
Definition
A measure of the ease with which the lungs can be inflated. The change in lung volume (ΔV) in response to a given change in transpulmonary pressure (ΔPalv – Pip)
Term
Is lung compliance good or bad?
Definition
In general, a large lung compliance is advantageous, as it reduces the work of breathing
Term
Define airway resistance
Definition
the resistance to air flow imposed by all the airways in the respiratory tract
Term
What is resistance most sensitive to?
Definition
airway radius
as radius decreases, airway resistance increases.
Term
What level of resistance is desirable?
Definition
In general, a low level of airway resistance is desirable; again, this reduces the work of breathing
Term
What does lung compliance depend on?
Definition
The structural elasticity of the lungs
The surface tension of the fluid lining the alveoli
Term
How does structural elasticity of the lungs affect lung compliance?
Definition
Due to the presence of elastic fibres in the connective tissue of the lung: forces in the elastic fibres oppose lung expansion

Lung stretches = fibres recoil
Term
How does surface tension of the fluid lining the alveoli of the lungs affect lung compliance?
Definition
The surface tension of a liquid is a measure of the work needed to increase its surface area by a given amount: the greater the surface tension, the more work needed.
Term
What causes surface tension in the lungs?
Definition
In the lungs, surface tension occurs as a result of the air-liquid interface formed by the thin layer of liquid lining the internal surface of the alveoli.

As the lung expands, so does the fluid layer in the alveoli. Therefore, during inspiration, the surface tension acts to decrease lung compliance
Term
What does type II alveolar cells secrete?
Definition
a detergent-like substance called pulmonary surfactant into the fluid lining the alveoli
Term
What is the function of pulmonary surfactant?
Definition
This phospholipid decreases surface tension by interfering with the hydrogen bonding between water molecules, thereby increasing lung compliance and decreasing the work of breathing
Term
What would happen in the absence of surfactant?
Definition
the smaller alveolus would indeed collapse, increasing the internal air pressure and moving air into the larger alveolus down the pressure gradient
Term
Describe infant respiratory distress syndrome
Definition
Surfactant production begins relative late during fetal development, and premature babies are often deficient, leading to potentially fatal breathing problems
Term
Why is airway resistance low in healthy lungs?
Definition
total cross sectional area of the airways at each order of branching is relatively high (and actually increases at the level of the bronchioles due to the extensive branching)

greater surface area = greater units in parallel therefore lower resistance
Term
What does lower resistance mean for the respiratory pressures gradient?
Definition
Palv does not need to differ from Patm to generate pressure gradient necessary for normal air flow

Darcy's Law = pressure gradient/resistance
Term
Give the Palv and Patm pressure gradient in quiet breathing
Definition
less than 2mmHg
Term
What happens if airway resistance increases?
Definition
a larger pressure gradient is required to produce a given rate of air flow
Term
What factors determine airway resistance? (3)
Definition
1. Passive forces exerted on the airways
2. Secretion of mucus into the airways
3. Contractile activity of bronchiolar smooth muscle
Term
What passive forces exert on the airways?
Definition
These include changes in transpulmonary pressure during the respiratory cycle, and tractive forces exerted on the airways by the tissues surrounding them
Term
Explain how passive forces exerted on the airways determine resistance
Definition
During inspiration, transpulmonary pressure increases, which pulls outwards on the airways causing them to distend
As surrounding tissue moves away from the airways during inspiration tractive forces exerted by the tissues increase, pulling the airways open and reducing resistance
Term
Explain how secretion of mucus into the airways determine resistance
Definition
Secretion of mucus into the airways by goblet cells is part of the air filtering and airway defence mechanisms, however excessive secretion or reduced clearance (often due to ciliary paralysis) may lead to accumulation of mucus, which increases airway resistance
Term
Explain how contractile activity of bronchiolar smooth muscles determine resistance
Definition
When this circular smooth muscle contracts, it decreases bronchiolar radius and increases resistance to air flow. The state of contraction is under both extrinsic (neural and hormonal) and intrinsic (local chemical mediator) control
Term
Explain neural control of bronchiolar smooth muscles
Definition
Sympathetic stimulation (and circulating adrenaline) cause bronchodilation; parasympathetic stimulation causes bronchoconstriction
Term
Explain hormonal control of bronchiolar smooth muscles
Definition
Histamine (released locally during allergic reactions) causes bronchoconstriction
Term
Explain intrinsic control of bronchiolar smooth muscles
Definition
An increase in local CO2 levels causes bronchodilation (important in ventilation : perfusion matching)
Term
Name 2 pathological conditions associated with increased airway resistance
Definition
asthma and chronic obstructive pulmonary diseases (COPDs)
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