Ventilation Flashcards
Describe breathing and ventilation
this is the flow in and out of the respiratory system
what is the movement of air into the body due to
the movement of air in and out of the lungs occurs due to pressure differences
how are pressure differences created
- Pressure differences are created by changes in lung volume because air flows from a region of a high pressure to a region of low pressure
describe what drives inhalation
- driven by diaphragm which contracts and flattens leading to an increase in lung size and consequently air moves into the lungs
what drives exhalation
– diaphragm relaxes which leads to a decrease in lung size and therefore pressure increases and air moves out of the lungs
How do we measure lung function
spirometry
define tidal volume
amount of air you move into and out of your lungs during rest, not the sum of the two
define inspiratory capacity
total volume of air that you can breathe in at maximum lung capacity at rest
define expiratory capacity
total volume of air that you can breath out of the lungs at maximum lung capacity at rest
define forced vital capacity
maximum volume of air into and out of the lungs in a single respiratory cycle
define residual volume
volume of air that remains in the lungs even after maximal exhalation
How do you calculate the forced vital capacity
- Inspiratory reserve capacity+ tidal volume + expiratory reserve volume = forced vital capacity
what is FEV1/FVC
• FEVI/FVC is a ratio of Forced Expiratory Volume in 1 sec & Forced Vital Capacity
what is the normal FEV1/FVC ratio
values above 70-80% = normal. Age/gender adjusted
what causes the decrease of the FEV1/FVC
• Airflow limitation (e.g. Asthma)
what generates the pressure differences for breathing
it is the respiratory muscles that generate the pressure differences for breathing
what happens during inspiration of quiet breathing
- inspiration: active part of passive breathing
- Diaphragm and external intercostal muscles
what happens during inspiration in forced breathing
- Inspiration: diaphragm, external intercostal muscles and accessory muscles such as pectoralis major and minor and serratus anterior
what is the diaphragm innervated by
- it is innervated by the phrenic nerve
describe measurements of the diaphragm
- rest – 1-2cm
- forced breathing < 10cm
what are the two muscles that the external intercostal muscles do
- pump handle movements; anterior end of each rib is elevated
- bucket handle movements; dimeter of chest increases
what happens during expiration in quiet breathing
- expiration; largely passive as a result of elastic recoil of the lungs
what happen during expiration in forced breathing
- active
- involves accessory respiratory muscles
- E.g. Anterior abdominal muscles & quadratus lumborum
define alveolar ventilation
- Defined by portion of the total ventilation that reaches the alveoli and participates in gas exchange
How do gasses move between air and blood
move between air and blood by passive diffusion
- movement of gases is defined by partial pressure gradients
what is hypoventilation or hyperventilation a sign of
lung diseases
what decreases as you descend the airways
airway ventilation and perfusion decrease
what is dead space
• Volume of air in the mouth, pharynx, trachea and bronchi up to the terminal bronchioles
it is the volume of air that does not exchange in gas
how large is the anatomical dead space
150 ml does not exchange gas
what is the anatomical dead space made out of which structures
made up of upper respiratory tract, trachea, bronchi, bronchioles, terminal bronchioles
what is alveolar dead space
alveoli that have insufficient blood supply to act as effective respiratory membranes therefore do not take part in gas exchange
How do you work out physiological dead space
anatomical dead space and alveolar dead space
how do you work out the rate at which new air reaches the alveoli
(tidal volume - dead space) x respiratory rate
describe the example of how you work out the rate at which new air reaches the alveoli
tidal volume – dead space) x respiratory rate
- Tidal volume=500 mL
- Anatomic dead space=150 mL
- Fresh air entering the lungs=350 mL
- Respiratory rate=12 breaths/min
- Alveolar ventilation (ml/min)
- 12X350=4200 mL/min (4.2L/min)
- This is the effective ventilation that brings about the exchange of O2 and CO2.
describe alveolar ventilation and respiratory exchange
Room = Almost zero CO2 & alveolar gas = 5.5% giving an output of:
4.2 X (5.5-0/100)=0.231 L/min or 231 mL/min
Oxygen forms 21% of atmospheric air and alveolar gas contains about 14% giving an uptake of:
4.2 X (21-14/100)=0.294 L/min or 294 mL/min
How do you see the spirometers restyles
- look at flow volume loops on the graph, where the Y axis is and X axis is
- after the starting point the curve rapidly mounts to a peak (peak expiratory flow)
- after the PEF the curve descends = the flow decreases as more air is expired, a normal non pathological F/V loop will descend into a straight or a convex line form top PEF to bottom FVC
what is pulmonary ventilation breathing
- It is the process of air flow to the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation)
why does air flow occur
- Air flows because of pressure differences between the atmosphere and the gases inside the lungs
- muscular breathing and recoil of elastic tissues create the changes in pressure that results in ventilation
in what direction does airflow occur
air like other gases flows from a region with a high pressure to a region with lower pressure
what is the pressure at the beginning of the respiratory tract called
Patm
what is the pressure inside the lungs called
Pa
what happens if - If Patm and Pa are equal
- If Patm and Pa are equal than there is no airflow
what happens when Pa is smaller then Patm
- If Pa
what happens when Pa is larger than Patm
if Pa> Patm airflows out of the lungs
what is the law that defines the relationship between expansion and gas flow
Boyles law
Define Boyle’s Law
- If the volume of gas is made to increase the pressure exerted by the gas decreases
- As the alveoli are forced to expand the pressure inside them decreases and the gas in flows in from the conducting airways
lungs and there elastic properties
- lungs are elastic
- they return to there original shape fi a force that is distorting them is removed
- if you prevent the air escaping by blocking the lungs the recoil of the lungs will produce a recoil pressure
how do you generate inflation
- For an object to be distorted it must be subjected to a force for example pressure
- Inspiration = inflation and expiration – deflation
- Rather than blowing into the balloon: if the balloon = lungs, then they are inflated by reducing pressure outside (like a plunger in a syringe).
- Lowering the plunger (diaphragm) reduces the pressure around the balloon and generates inspiration
How do you work out inspiration
inflation and expiration - deflation
describe the elastic properties of the chest wall
- The thoracic cage is also elastic.
- Under normal conditions the chest wall has a tendency to pull outwards and the lung to pull inwards thus balancing themselves
why does the chest wall not collapse under normal circumstances
Under normal circumstances the chest wall does not collapse, this is because the lungs and chest wall are in close contract by the intrapleural fluid in the intrapleural space
This means that a pressure is created in that space
what is the sign for intrapleural pressure
Ppl
describe intrapleural space
intrapleural space has cohesive forces
- they are difficult to separate when they are adjoined to each other
- therefore as the chest wall expands during inspiration the lung follows therefore the two structures expand as a single unit
how is the intrapleural space generated
At the end of expiration when you are relaxed before you take your next breath there is a tension between the lungs whose elasticity is causing them to collapse and the chest wall whose elasticity is cause it to spring outwards this generates a pressure in the intrapleural space known as the intrapleural pressure Ppl
- Intrapleural pressure is negative with respect to atmosphere (and the air pressure in the alveoli which is connected to the atmosphere)
Describe the changes in the intrapleural pressure
- The normal pleural pressure the beginning of inspiration is negative
- During inspiration expansion of the chest cage pulls outward on the lungs and intrapleural pressure and becomes more negative
- Intrapleural pressure becomes less negative to lead to quiet expiration
describe what happens to the intrapleural pressure in a pneumothorax
- If the pleural cavity is damaged/ruptured air enters the pleural space (because the pleural pressure is less than atmosphere)
- The intrapleural pressure becomes equal to or exceeds the atmospheric pressure and the pressure surrounding the lungs will increase and may cause the lungs to collapse.
what is compliance
- Elasticity is a measure of how easily the lungs can be stretched and is conventionally expressed as compliance.
- Compliance is the ease at which the lungs expand under pressure
what is the compliance of the lungs changed by
- it is changed by most lung diseases
what is the equation of compliance
change in volume/change in pressure
how do you work out the total compliance
- Across the wall of the structure being investigated e.g. lungs (Cl) chest wall (Cw) or lungs and chest wall (Total compliance CTOT)
what happens to lung compliance at a high expanding pressure
- In normal range the lung is very complaint however at high expanding pressure the lung is stiffer and compliance is smaller
at any given pressure
- At any given pressure lung volume during inhalation is less than the lung volume during exhalation
what is airway closure
Even without any expanding pressure the lung always has some air in it. This is due to airway closure, where small airways close trapping gas in alveoli. Airway closure increases in certain conditions, such as age and lung disease
diseases that affect either the chest wall or lung structure will..
affect compliance
what causes a reduction in compliance
- Increase of fibrous tissue in the lung
- Collapse/closure of lung (atelectasis)
increase in pulmonary venous pressure
what causes an increase in compliance
- Age
- Emphysema
what is emphysema
- a lung disease which causes destruction of the normal lung architecture which includes the elastic fibres and collagen
what does emphysema cause to the structure of the lungs
- There is also impaired elastic recoil and lungs do not deflate as easily.
- The lung is more easily distended, and the compliance of the lung is increased (more compliant
what’s the differences between emphysema and fibrosis
Emphysema – same amount of pressure, easier to inflate
Fibrosis – same amount of pressure harder to inflate
what is the effect of kyphoscoliosis on the compliance of the chest wall
- Structural change in the thorax
- Kyphoscoliosis – a disorder characterised by progressive deformity of the spine will affect compliance
- However more usual that lung complacence is affected
what 2 main components generate the elastic properties of the lungs
1) elastic fibres and collagen
2) surface tension forces caused by the alveolar-liquid interface.
name the structure of the elastic fibres in the lungs
- Elastic fibres form the bulk of connective tissue present in the walls of the alveoli
- Elastin fibres act like stocking when stretched
filling a lung with …
fluid makes it easier to inflate
what happens in inflation to an air filled lung
- Inflation of the lung follows a different pressure/volume curve from deflation.
- This is known as hysteresis which literally means “to lag behind”.
- A greater pressure is required to reach a specific lung volume when you are inflating it rather than deflating it.
what happens to inflation in an saline filled lung
- Hysteresis is abolished.- no lagging behind
- Much easier (less pressure) to expand fluid filled lungs.
- In fluid filled lungs only the elastic forces are working - there must be another component that also contributes.
- In the fluid filled lungs the air-fluid interface has been abolished.
What is hysteresis
this is when the inflation of the lung follows a different pressure/volume curve from deflation
where is surface tension presence
in the alveoli
describe what surface tension does
- The cohesive forces between liquid molecules at the surface are responsible for the phenomenon known as surface tension.
- The molecules at the surface of the liquid do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface.
- This forms a surface “film” which makes it more difficult to move an object through the surface than to move it when it is completely submersed.
- the water molecules on the boundary have an especially strong attraction for one another and therefore as a result the water surface is always trying to contract
what is the surface tension elastic force
- On the inner surface of the alveoli the water surface is always trying to contract
- This results in the alveoli trying to collapse (forming air out through bronchi)
- The net effect is to generate an elastic contractile force throughout the entire lungs, this is known as the surface tension elastic force
what does Lapacales law relate to
relates pressure to surface tension and radius
what is the equation of Lapacales law
P = 2T/r
- P = pressure within the bubble
- T = surface tension
- R = radius
explain how Lapacles law works
- the smaller bubble the greater the internal pressure that is required to keep it inflated, the smaller the radius
How do the lungs compensate with problem of pressure differences arising from having alveoli of different sizes
- Surfactant this stabilises the alveoli
what do surfactants do on the alveoli
- Surfactants greatly reduce the surface tension and therefore reduce the surface tension elastic forces
what is the surfactant made up of
- Pulmonary surfactant is a complex mixture of lipids and proteins.
- A major component (approx. 50%) of surfactant is the phospholipid Dipalmitoylphosphatidylcholine (DPPtdCho)
describe the properties of the surfactant
- Amphipathic character (hydrophilic/water loving head groups and hydrophobic tails towards air) and resultant packing reduces surface tension.
what is surfactant secreted by
type II alveolar epithelial cells
describe how surfactant is formed
- Assembly of surfactant occurs in the lamellar bodies and is secreted into the alveolar fluid where it undergoes structural changes to form a meshwork known as tubular myelin before eventually forming a surfactant layer at air water interface
describe what happens in infant respiratory distress syndrome
- Caused by developmental insufficiency of surfactant production and structural immaturity in the lungs
• A baby normally begins producing surfactant between weeks 24 and 28 of pregnancy.
• Most babies produce enough surfactant to breathe normally by week 34.
• In babies born prematurely not enough surfactant produced and may lungs collapse
what is airway resistance
- Airway resistance Raw is defined as the resistance to the flow of gas within the airways of the lung
what happens in asthma
- Reduction of airway diameter due to contraction of smooth muscle or swelling due to inflammation and mucus production
- Contraction of bronchial smooth muscle narrows the airways and increases airway resistance
- Tone of the smooth muscle in the airways is under control of autonomic nervous system
what does the pattern of flow through tubes vary with
- varies with the velocity and physical properties of the fluid
what are the two types of flow
laminar and tuberlent
what is the difference between laminar and tuberlent flow
- In laminar flow the movement is orderly and streamlined whereas in turbulent flow movement is chaotic.
- In most circumstances flow can be considered laminar as a first approximation.
what is poiseullies law
relationship between driving pressure and flow
- smal changes in the dieter of airways leads to relatively big changes in flow
what type of flow is described by poiseuilles law
Laminar flow
do the example of working out the percentage increase
Airway radius of 4 units dilates to a radius of 5units.
• What is the percentage increase in the radius of the airway?
5-4/4)100=25%
• What is the percentage increase in the airflow?
• r=4, r4=256 and r=5, r4=625
• (625-256/256)100=144%
Relatively small changes in the diameter of airways ….
leads to big changes in flow
what are the sites of airway resistance
- upper respiratory tract
- lower respiratory tract
- small bronchi and bronchioles
describe airway resistance in the upper respiratory tract
- Almost half of resistance to airflow resides in the upper respiratory tract
- Significant resistance is nose such as inflammation and cold
- Reduced resistance when breathing through mouth e.g. shift during exercise
Describe airway resistance in the lower respiratory tract
- Half of resistance to airflow comes from the lower respiratory tract
- Assuming laminar flow poiseuille’s law would predicts that major resistance to airflow would occur in airways with smaller radius but this does not happen because the total cross sectional area increases as you go down the tracheobronchial tress although the diameter of each airway is small there is a larger number of them
describe airway resistance in the small bronchi and bronchioles
- The most important part of the bronchial tress in terms of physiological control of airway resistance are small bronchi and bronchioles
- Found at the level in bronchial tree where the increase in number of airways has not yet exerted its effects and the cross sectional area is small
- Virtually no cartilage but innervated smooth muscle
- Resistance of small bronchi and bronchioles is variable and under the influence of neuronal and hormonal factors.
- For example asthma is a spasm of the bronchial smooth muscle, which may be hyper responsive.
- Bronchodilators act to relax the muscle.
how does the parasympathetic system act on the bronchial smooth muscle
: postganglionic fibres release Ach which stimulate muscarinic receptors on smooth muscle causing them to contract.
how does the sympathetic system act on the bronchial smooth muscle
occurs mainly via circulating catecholamines. Adrenalin activates β2 receptors causing smooth muscle to relax.
what are the other factors that contribute to bornchomotor tone
- Non-adrenergic non cholinergic systems, NANC: includes bronchodilators (and possibly constrictors).
- Mediator release (e.g histamine etc): mast cell degranulation, neutrophils and eosinophils important in various stages of asthma
- Rapidly adapting pulmonary receptors: also known as irritant or cough receptors
- Slowly adapting/stretch pulmonary receptors: activity reduces bronchomotor tone
- Carbon dioxide: causes bronchodilation in underventilated areas where the gas builds up
what cause the work of breathing
- Resistance to airflow
2. Elastic recoil of the lungs
what is the equation for the work of breathing
- Energy measured in joules
- W = P . ∆V
what happens to work when disease happens in the lungs
- Normally respiration is very efficient and represents a small fraction of the total cost of metabolism; however this changes in disease.
- Changes in compliance and airway resistance may lead to increased work load.
what happens in COPD with energy requirements
severe COPD, energy requirements increase in order to breath. A situation may be reached in which the increased oxygen supplied from increasing ventilation is all consumed by respiratory muscles.
what is the thoracic skeleton composed of
12 thoracic vertebrae
12 pairs of ribs
sternum
what are the 3 types of ribs
True 1-7
false 8-10
floating 11-12
how do true ribs attach to the sternum
- they all have costal cartilages that attach directly to the sternum
How do the false ribs attach to the sternum
via a costal margin, forms a common cartilage that attaches to rib 7
- inferior border of costal joining to rib 7
floating ribs have no..
costal cartilages
What are Intercostal spaces and neurovascular structures named after
The rib above
What is the entrance and exit to the thoracic skeleton called
Thoracic inlet
thoracic outlet
where is the thoracic inlet
first rib of the sternum and T1 vertebrae
Describe the structure of the rib
- Made up of anterior and posterior parts, inferior and superior part
- Anterior part has cartilage joints
- Posterior - has facets and forms synovial joints
- The angle part of the rib is the weakest part and where it bends, this is the part where most rib fractures happen
- Head of the rib articulates with the vertebral body
- Articular facet articulates with the transverse process - synovial joints
- the synovial joint allows the ribs to elevate and depress
- articulate with the vertebrae posteriorly
- articulate with the sternum anteriorly
- tilit inferiorly therefore where they attach to the sternum is lower than the corresponding vertebrae
Describe the structure of the sternum
Made up of …
- Manubrium
- Body
- Xiphoid process
- Sternal angle is at rib 2 T4/T5
How do you know which way the rib is facing
the inferior part of the rib should have a costal groove this should be at the bottom
What is the first rib that you feel
2nd rib, 1st rib is under the sternum
What is between the sternoclavicular joint
In between the sternoclavicular joint is the jugular notch
describe what happens during inspiration
- During inspiration the sternum and ribs lower increasing the volume of the thorax and decreasing the pressure this causes air to move into the lungs
Describe what happens during expiration
- During expiration the ribs and sternum lower decreasing the volume of the thorax increasing the thoracic pressure, this causes air to move out of the lungs
What are the three intercostal muscles
external intercostal
internal intercostal
innermost intercostal
what is the role of the external intercostal muscles
involved in inspriation, travel downwards, they end anteriorly at the midcalvular line
What is the role of internal intercostal muscles
they are at a right angle to the external intercostal muscles – inovled in expiration and pulling your ribs down
What is the role of the innermost intercostal muscles
these are the same orientation as internal intercostal, they have the same function and are involved in forced expriation pulling the ribs down, these are deficinet posteriorly
How are the intercostal muscles innervated
- Intercostal nerves - these are the anterior rami of the thorax spinal nerve
what do you find in the costal groove
- this is in the inferior aspect of the rib
- in the groove there is the vein, artery and nerve
how is the intercostal muscles supplied with a blood supply
- Have intercostal arteries and veins
- posterior and anterior ones, there are 2 different sources for them, subclavian(starts at the anterior part of the thorax) and the descending aorta (starts at the posterior part of the thorax)
What does the anterior intercostal artery drain into
anteiror intercsotal vein
What does the posterior intercostal artery drain into
On the left hand side
- the posterior intercostal artery on the left hand side drains into the hemiazygous vein which drains into the azygous vein which drains into the superior vena cava
On the right hand side
- Posterior intercsotal atery drains on the rright hand side into the azygous vein which drains into the superior vena cava
What are the muscles making up the chest wall
- Serratus anterior – superiifical to the external intercsotal muscles, comes from scapula postierorly and wraps around the ribs anteirorly causes msucles to move upwards for, causes elevation affects respriation
- Pectoralis minor – scalup to ribs – goes from superior point to anterior point – causes elevation in the rib cage, affects repsiration
- Pectoralise major – elevates the ribs
- Sternocleidomastid – attached to sternum, clavicale and matiod procesed – can pull rib cage up and cause elevation
- Rectus abdominis – attaches to costal marign, pulls rib cage down, affects expiration and forces it
What are the muscles that cause inspiration
Quiet
- Diaphrgam
- External intercostals
Deep Accessory muscles of breathing - Scalene muscles - SCM - Pectrolais minor
What are the muscles that cause expiration
Expiration Quiet - Passive (recoil of repsiratory muscle) Forced - Internal intercsotal - Abdnominal muslces
what innverates the diaphragm
nnervated by phrenic nerve C3,C4,C5
why is the diaphragm higher on the right than on the left
liver is on the right
describe the structures that go through the diaphragm
- Vena cava T8
- Oesophagus T10
- Artic hiatus T12
Describe the pleura
- Continous double layered memrbane
- Surface which is contact with the cavity wall is the parietal layer attaches to the thoracic wall and superior surface of the diaphrgam
- Layer on the lung sruface is the visceral layer
- In between two layers of pleura is pleural fluid
Describe the nerve supply of the visceral pleura
gets innervation of the lung itself so autonomic nerves (sympahteitc and parasympathetic) nerve supply, cannot feel pain particulary well just feel stretch
Describe the nerve supply of the parietal pleura
- intercsotal nerves (T2-T12) these are somatic nerves – innervate parietal pleura, and make them sensitive to pain
- Medially phrenic nerve that innervates parietal pleura – this is a somatic nerve as well, senetiive to pain
what happens if you have a lung tumour in the visceral pleura
- In lung tumour in visceral pleura don’t feel it, if lung tumour is in parietal plerua you feel it
Describe the structure of the lungs
- Apex of the lung is 2cm above the clavicle
- Cardiac nothc at 4th rib
- The lungs can be found at T6, T8, T10
- Pleura boundaries (PARIETLA PLEURA) are at the 8, 10, 12, extend further than the lungs always 2 ribs lower so the lungs can expand
- The pleural sacs are larger than the lungs during quiet respiration, and inferiorly is a potential space, the costophrenic recess (space between visceral and parietal pleura)
Describe the structure of the left lung
- Left have a superior lobe and inferior lobe
- Oblique fissure
- Lingular – looks like a tongue comes down from superior lobe
Describe the structure of the right lung
- Superior lobe, middle lobe and inferior lobe
- Horizotnal fissure divides superior and middle lobe
- Oblique fissure divides the inferior and middle lobe
Name structures in the respiratory tree
- Trachea
- main bronchus
- lobular bronchi
- segmental bronchi
- conducting bronchioles
- terminal bronchioles
- respiratory bronchioles
- alveolar ducts
- alveolar sacs
Describe the anatomy of the respiratory tree
- Superiorly have the trchea – made up of C shaped rings of caritalge anteriorrly, posteriorly there is a layer of smooth muslce
- Trachea extends down splitting into the left and right angle, this happnes at the sternal angle
- When the traceha bifuricates there is the heart that sits underneath the left main bronchus therefore th eleft main bronchus travels horizotnally and the right main bronchis travels diagonally
- Lobulear bronchi is what the main bronchus split into, this goes the lobes in the lung, the lobular bronchi split into segmental bronchi in the lungs
whats the difference between bronchioles and bronchi
bronchi have cartilages and bronchioles do not have cartilage
describe the strucuture of the pat of the lung where stuff enters and leaves
- made up of the pulmonary artery, pulmonary veins and bronchus
- can distinguish has bronchus always has cartilage and the pulmonary artery is above the pulmonary vein
what are lungs divided into
functional areas called bronchopulmonary segments
describe what is in the bronchopulmonary segment
- Each segemtn has its on bronchus, artery, vein, lymph vessels
- Each segement is a functional area of the lung
What does the bronchopulmonary segment enable you to do
- can remove the segment that has damage into it without removing the whole lung
Describe the process of breathing
Intercostal and Phrenic nerves innervate External intercostal muscles and diaphragm
External intercostal and diaphragm contract
Rib cage increases in diameter and height
Pressure in the thorax decreases
Air moves in through the mouth or nose, though the pharynx, larynx and into the trachea.
The trachea bifurcates into the left and right main bronchi which divide into lobar then segmental bronchi
Segmental bronchi give rise to cartilage free bronchioles which lead into alveoli
External intercostal muscles and diaphragm relax, the rib cage decreases in size and air moves out
What is the main stimulus of breathing?
The increase of carbon dioxide in the blood
Where are the central chemoreceptors found?
In the Medulla
Where are the peripheral chemoreceptors found?
In the aorta and the carotid bodies
Where in the body does the central chemoreceptors detect and respond to the lowering of pH?
Central chemoreceptors respond to the lowering in the cerebral spinal fluid.
Because of the direct link between the concentration of CO2 level in the blood and the pH of the CSF; a rise in co2 does what to the pH?
It lowers the pH
What do the peripheral chemoreceptors detect?
It detects the rises is arterial C02, but also react to significant falls in the level of oxygen in the blood.
What is pulmonary ventilation?
This is the process by which gases are exchanged between lungs and atmosphere. This involves two key processes.
What two key process are involved in pulmonary ventiliation?
- External- Lungs
2. Internal - Capillaries
Describe Boyle’s Law.
This describes the relationship between pressure and volume. It states that as volume increases, pressure decreases.
Is Inspiration active or passive transport?
It is an active process during normal quiet breathing.
Is expiration active or passive transport?
It is a passive process during normal quiet breathing.
Describe the negative feedback mechanism involved in breathing.
Receptors-Controllers-Effectors
Co2 (too much)-Medulla/pons-Rate/depth
Name the areas of the medulla that are referred to as the medullary rhythmicity area? (4)
- Dorsal respiratory group
- Ventral respiratory group
- Apneustic centre
- Pneumotatic/ pontine respiratory group
Where are the Dorsal respiratory group located?
Medulla
Where is the Ventral respiratory group located?
Medulla
Where is the Apneustic centre located?
Pons
Where is the pneumatic located?
Pons
What is the function of the Dorsal respiratory group in medullary rhythmicity area?
It integrates chemoreceptors information and signals VRG
What is the function of Ventral respiratory group in medullary rhythmicity area?
It is the basic rhythm generator
What is the function of Apneustic centre in medullary rhythmicity area?
It helps regulate length/depth of inspiration
What is the function of Pneumotaxic in medullary rhythmicity area?
It is involved in regulation of apneustic centre and medullary rhymicity area.
What does the term compliance mean in breathing?
Stretchiness
What does the term lung compliance mean?
It is a measure of how easy the lungs inflate.
What would happen without surfactant?
The wet surfaces of the lungs would stick together and not be able to expand and take part in breathing.
What are the main muscles involved in normal quiet breathing in an adult?
Intercostal muscles and diaphragm
Name three major functions of the respiratory system.
- Gas exchange
- Filtration of particulate matter
- Thermoregulation
Explain the relationship between gas exchange and cellular metabolism.
Aerobic cellular respiration requires oxygen and releases carbon dioxide as a waste product. Gas exchange removes this unwanted CO2 from the cells and replaces it with O2 from the environment.
Specifically, O2 is required for the electron transport chain, while CO2 is produced mainly during the Krebs cycle.
Define:lung
The lung is the major organ in the respiratory system, acting to provide a site for gas exchange. Humans have two lungs that are connected to the outside environment via the respiratory tract.
The prefix “pulmo-“ and the root word “pleura” are often used to refer to the lungs and their associated structures.
Define:larynx
The larynx is a cartilagenous structure that contains the vocal cords. It sits directly below the pharynx and above the trachea.
Define:pulmonary alveoli
In the lungs, alveoli are small sacs at the ends of bronchioles. Each alveolus is enclosed by an epithelial lining and surrounded by pulmonary capillaries.
Alveoli are the site of gas exchange between the environment and the bloodstream. Oxygen moves from the alveoli to the capillaries, while carbon dioxide travels in the opposite direction.
In which pulmonary structure(s) is the activity of surface tension most relevant?
Surface tension, or the tendency of liquid molecules to associate with each other, is related to the alveoli.
Surface tension causes liquids to form spherical droplets, maximizing their contact with other liquid particles. Since the alveoli contain fluid, this property would tend to make alveoli collapse and is countered by the action of surfactant.
What substance serves to decrease surface tension in the alveoli?
Surfactant decreases surface tension and prevents the alveoli from collapsing.
Pulmonary surfactant is amphipathic, meaning that its molecules possess both hydrophobic and hydrophilic groups.
Premature infants often suffer from respiratory distress syndrome, a condition that involves insufficient surfactant production. What effect will this condition likely have on the alveoli?
It will cause the alveoli to collapse.
Surfactant serves to lower surface tension in the fluid associated with the alveolar lining. Without surfactant, this fluid will tend to minimize its own surface area, collapsing into the hollow interior of the alveolus and making inhalation very difficult.
The image below depicts a number of alveoli surrounded by pulmonary capillaries. What type of transport is used by gases to travel between these two structures?
The gases travel via diffusion.
Since gases are small and nonpolar, they are easily able to diffuse through cell membranes. Gas exchange is a passive process, meaning that oxygen and carbon dioxide move down their concentration gradients without using ATP.
Compare the partial pressure of carbon dioxide in the pulmonary capillaries to that in the alveoli.
The pulmonary capillaries have a higher partial pressure of CO2.
The pulmonary capillaries bring deoxygenated blood, which is CO2-rich, in close contact with the alveoli. If CO2 is to diffuse from the bloodstream to the alveolar interior, it must travel down its concentration gradient. The alveoli, then, must contain comparatively less carbon dioxide than the capillaries.
Place the following terms in order according to their oxygen partial pressures, from the lowest PO2 to the highest.
* Alveolar air
* Atmospheric air
* Blood from the pulmonary artery
Blood from the pulmonary artery < alveolar air < atmospheric air
The pulmonary artery carries deoxygenated blood from the heart to the lungs, so it contains a comparatively low amount of O2. It’s easy to assume that the alveoli contain only atmospheric air, but they also hold residual carbon dioxide from the previous respiration, resulting in a slightly lower oxygen partial pressure than that of atmospheric air.
What are the steps involved in inspiration?
- The diaphragm and external intercostal muscles contract, expanding the thoracic cavity.
- The lungs expand along with the surrounding cavity, lowering their internal pressure.
- Air flows from the comparatively high-pressure environment to the low-pressure lungs.
What is the significance of the term “negative pressure breathing?”
It describes the mechanism of inspiration. The pressure inside the lungs becomes lower than atmospheric pressure, causing air to flow inward.
Negative pressure also relates to MCAT physics. Remember that absolute pressure can never have a negative value. Instead, it is the gauge pressure that is negative, meaning simply that it is lower than ambient pressure.
Name the main muscles involved in inspiration.
Inspiration involves both the diaphragm and the external intercostals.
Both muscles contract to enlarge the thoracic cavity. The diaphragm flattens downward, while the external intercostals push outward.
The diaphragm is composed of which of the three types of muscle?
The diaphragm consists of skeletal muscle.
For the MCAT, skeletal muscle can usually be considered to be voluntary. The diaphragm is a notable exception, since it can be consciously contracted but is usually under involuntary control.
Name the main muscles involved in expiration.
Normal expiration is passive, requiring no muscular involvement. Expiration that is consciously forced involves the internal intercostals.
Other muscles aid in both expiration and inspiration, but they are not necessary to know for the MCAT.
During exhalation, the diaphragm must be in which state?
The diaphragm must be relaxed.
When relaxed, the diaphragm becomes rounded, pushing upward and decreasing the volume of the thoracic cavity. Lower volume results in increased pressure, forcing air outward.
What measurement describes the volume of air inhaled per breath during normal breathing?
Tidal volume
The tidal volume of an average human is approximately 500 mL.
What is the difference between inspiratory and expiratory reserve volume?
Inspiratory reserve volume (IRV) refers to the maximum volume of air that can be inhaled in addition to a normal inhalation, while expiratory reserve volume (ERV) refers to the maximum volume that can be exhaled in addition to a normal exhalation.
The sum of IRV, ERV, and tidal volume can be described by which lung measurement?
IRV, ERV, and tidal volume combine to form the lungs’ vital capacity.
Vital capacity is the largest volume that can possibly be inhaled or exhaled.
What measurement describes the volume of air that always remains in the lungs, regardless of the force of exhalation?
Residual volume
Since the residual volume never leaves the lungs, it cannot be directly measured, but must be calculated using the other lung volumes.
What is the difference between total lung capacity and vital capacity?
Total lung capacity (TLC) includes the entire volume of air that can be held in the lungs, while vital capacity (VC) only includes the volume that can be inhaled or exhaled.
TLC is equal to the sum of vital capacity and residual volume.
If inspiratory reserve volume and tidal volume are known, what additional measurements are needed to calculate residual volume?
Total lung capacity and expiratory reserve volume
ERV, IRV, and tidal volume can be added to find vital capacity. From there, residual volume can be found by subtracting vital capacity from total lung capacity.
Which substance, secreted by membranes in the nasal passages, helps protect the lungs from foreign particles?
The protective substance is mucus.
In the respiratory tract, mucus functions as part of the innate immune system. Mucous membranes also exist in the stomach.
Which organelle associated with respiratory epithelium would be seriously impaired by the inhibition of microtubule synthesis?
Cilia, small hairlike organelles that line much of the respiratory tract, are composed of microtubules. Cilia function to protect the lungs by moving mucus and particles toward the throat.
The MCAT often tests other microtubule-based structures, including the cytoskeleton and spindle apparatus.
Which type of immune cell is highly active in the alveoli of the lungs?
Macrophages
While macrophages exist throughout the body, specialized cells known as alveolar macrophages are present only in the lungs. If exposed to a pathogen, these cells can perform phagocytosis and release factors that activate other immune cells.
Define:hypoxia
Hypoxia refers to the condition of oxygen deprivation, usually due to low oxygen levels in the blood.
On the MCAT, prefixes and suffixes can often help in discerning a word’s significance. If this term were unfamiliar, the prefix “hypo-,” meaning “low” or “under,” could give away its meaning: low oxygen.
What homeostatic system relates to the equation below?H2O + CO2 ⇔ H2CO3 ⇔ H+ + HCO3-
The bicarbonate buffer functions according to this equation and is the main homeostatic method of maintaining constant pH in the blood.
The equation for the bicarbonate buffer is reversible, meaning that it can progress in either direction to reach an equilibrium. Most MCAT questions on this topic involve the use of Le Châtelier’s principle.
In the first step of the bicarbonate buffer, dissolved carbon dioxide reacts with water in the plasma. Which acid is produced by this reaction?
Water and carbon dioxide combine to form carbonic acid (H2CO3).
Carbonic acid is often confused with bicarbonate (HCO3-), since the “bi” prefix can be misunderstood to mean “two” protons. It’s important to remember that bicarbonate is actually the conjugate base of carbonic acid. The MCAT often tests this distinction.
How does the respiratory system respond to low blood pH levels?
Low pH, or acidity, in the blood results in an increased respiratory rate.
Consider the equilibria involved in the blood buffer:
H2O + CO2 ⇔ H2CO3 ⇔ H+ + HCO3-
Acidic blood has a high proton concentration, which will shift the reaction to the left to regain equilibrium. This will result in the production of water and carbon dioxide. To excrete this additional CO2, breathing rate must increase.
Rapid or excessive breathing, commonly known as hyperventilation, results in an abnormally high rate of CO2 exhalation. What condition can be caused by prolonged hyperventilation?
High blood pH, or alkalosis, can result.
More than any other factor, blood pH level depends on CO2 concentration. If respiratory rate is increased above normal levels, more CO2 will be exhaled than usual, and the bicarbonate buffer equilibrium will shift away from the production of hydrogen ions. With fewer protons, blood will become basic or alkaline.
If a normal individual suddenly began inhaling air with a significantly higher partial pressure of O2, what immediate effect would this have on her plasma pH?
Assume that her rates of respiration, carbon dioxide exhalation, and carbon dioxide production remain unchanged.
Plasma pH would be unaffected.
While blood pH depends directly on CO2 concentration, its relationship to O2 levels is much more indirect. Oxygen is not part of the bicarbonate buffer system, so if all else remained the same, it would have no immediate effect on pH.
Oxygen concentration in blood vessels is monitored by two clusters of peripheral receptors, shown below. What are the names of these two structures?
The aortic and carotid bodies are part of the peripheral nervous system. They function as chemoreceptors and signal the brain when O2 levels are low.
How will the aortic body respond if it senses low plasma O2 levels?
As part of the peripheral nervous system, the aortic body must first send an impulse to the brain, which can then increase respiratory rate.
Specifically, both the aortic and carotid bodies signal the medulla oblongata, which controls involuntary actions such as breathing.
What physiological value has the strongest effect on the brain’s control of respiratory rate?
Plasma CO2 levels (which determine plasma pH)
The brain contains its own chemoreceptors, but they monitor only blood pH and CO2 levels. These central receptors stimulate a stronger response than the peripheral bodies. For the MCAT, then, consider respiration to be more directly affected by CO2 than O2.
List the structures of the respiratory tract in order, beginning at the entrance for incoming air and ending at the site of gas exchange.
