Flashcards in Human Lungs Deck (146):
What is external respiration?
The process by which oxygen is absorbed from the atmosphere to the blood in the pulmonary capillaries, and carbon dioxide is excreted.
Occurs in the lungs
What is internal respiration?
The exchange of gases between blood in the systemic capillaries and the cells surrounding them
What is cellular respiration?
The process occurring within individual cells where they gain energy by breaking down molecule such as glucose
It occurs in the mitochondria, consuming oxygen and generating carbon dioxide
What is pulmonary ventilation?
The bulk movement of air into and out of the lungs.
What is the ventilatory pump?
Consists of the rib cage and associated muscles, and the diaphragm
What are the functional classifications of the respiratory system?
What is the conducting part of the respiratory system?
Series of thick-walled tubes conducting air from the nose to the lungs, which condition the air.
Includes: Nasal cavities, pharynx, larynx, trachea, bronchi and bronchioles
What is the respiratory part of the respiratory system?
Series of tiny, thin-walled airways where casses are exchanged between air and blood.
Includes: Respiratory bronchioles, alveolar ducts and sacs, and alveoli.
What are the structural classifications of the respiratory system?
Upper and lower respiratory tract
What structures form the upper respiratory tract?
Nasal cavities through to pharynx
What structures form the lower respiratory tract?
Larynx through to alveoli.
What is conditioning?
Making the air:
1. Warm (37 degrees)
2. Filtering air
3. Humidifying air to 100%
Why should air be warm?
It increases the Ek of the air, making it move more for faster gas exchange
Why should the air be filtered?
Prevent impairment of gas exchange and disease causing organisms
Why should the air be humid?
Having air in liquid form aids the solubility of the gasses,
What is laminar flow and why is it important?
It means air goes in a straight line to aid quick entry to the lungs.
What is the structure of the nasal cavity?
Air enters through the nares (nostrils) and passes the nasal hairs. It then reaches the conchi, which are projecting bones either side of the nasal septum.
They are lined with respiratory epithelium.
Paranasal sinuses also open into the nasal cavity.
What is respiratory epithelium?
pseudostratified columnar epithelium with cilia and goblet cells
Where is olfactory epithelium located?
On the superior conchus.
What is the function of the conchi?
They slow air flow down, causing it to swirl around to throw large particles onto the sticky mucous.
It increases the surface area and air mixing for heating, humidifying and filtering the air, as it contains a rich capillary network underneath it.
(This is important for warming the air as it is so close to the blood)
What is the function of goblet cells in the respiratory epithelium?
They secrete seromucus, a wet and sticky secretion. Its stickiness traps large particles while its wetness means that the air is humidified
Why are respiratory epithelia ciliated?
They beat in unison and very fast to move the carpet of mucus towards the pharynx. This is called the mucociliary escalator.
What is the process of moving mucus to the pharyx and why is it important?
The cilia beat to move the mucus towards the pharynx, which allows it to be swallowed and thus removed. They have a powerstroke followed by a flat, scooping sweep underneath the mucus
The lower respiratory epithelia also have cilia beating in the opposite direction, so that all mucus is removed from the tract.
This is important for protection from infection, as if pathogens become stuck in mucus, macrophages may destroy it as they gather, damaging the respiratory tract.
What happens in smokers' respiratory tracts?
The mucociliary escalator is slowed down, although it still beats. This means there is a high risk of infection, as particle-latden mucus hangs around longer.
Therefore, they often have to move the mucus mechanically by coughing. Smoking also causes more and thicker mucus, further increasing the risk of infection.
What are the paranasal sinuses and what do they do?
They are lined with respiratory epithelium and goblet cells, and open into the nasal cavity.
They make the face lighter, and add resonance to the voice
What is sinusitis?
Occurs when the paranasal sinuses fill with mucus- it's difficult to treat and painful.
What is the cribiform plate?
The uppermost layer of bone above the nasal cavity, through which axons of olfactory neurons extend.
What are the three components of the pharynx?
Oropharynx (from oral cavity)
Which system does the pharynx belong to?
Partly respiratory, but mainly gastrointestinal
It connects the nasal cavity to the trachea
How does food get swallowed into the oesophagus instead of the windpipe?
The food bolus pushes the epiglottis downward, to cover the entrance to the trachea.
How does choking occur?
When the timing of epiglottal closure is inaccurate, and it doesn't fold over in time.
Food enters the trachea, causing a coughing reflex.
In what order does the respiratory system divide?
Main stem bronchi
What happens when a respiratory tube divides?
Its diameter becomes smaller and it forms 2 new tubes.
Which bronchi section off the lobes of the lung?
Which bronchi section of segments of the lung?
What is the trachea?
A tube approx. 12cm, with incomplete C shaped rings of cartilage connected vertically by fibrous CT.
Free ends of cartilage are connected by a dorsal trachealis muscle (smooth muscle). Its contraction narrows the diameter of the trachea, but this may not be functionally significant
What is the trachea lined with and why is this important?
It is lined with ciliated epithelium (pseudostratified columnar)
This is important for transporting mucus to the nasopharynx.
What is the function of the trachea?
It filters the air, takes it to the lungs and maintains the conditioning done by the nasal cavities
Cartilage holds it open, which is important when the pressure in the lungs drops below that of the atmosphere.
What are the layers in the wall of a bronchus?
Respiratory eptithelium: Pseudostratified ciliated columnar cells with goblet cells (mucus for humidifying and filtering
Smooth muscle for limited contraction
Mucus glands- secondary source of mucus with connections to the lumen
Cartilage plates- get smaller distally. Hold bronchi patent to prevent collapse and reduce pressure & energy needed for subsequent breaths
NB they are surrounded by alveoli- not part of the bronchus, but they exist wherever there is space.
What are the layers of a bronchiole?
Smaller diameter and simpler than a bronchus
Contain simple columnar ciliated epithelium with club cells to secrete a watery mucus
Smooth muscle to control its diameter
Alveoli outside it
Why do bronchioles need to secrete watery mucus? Why not regular mucus?
It keeps the air and cells moist, but doesn't need to filter the air as this has been done previously
Why is smooth muscle important for bronchioles?
Not all the lung is ventilated at rest, in order to conserve energy at lower O2 demands. Sympathetic stimulation dilates the bronchioles for greater airflow: increased air volume due to decreased resistance
In hypoxia, bronchioles constrict to give more priority to better ventilated areas of the lung.
How does asthma occur?
The smooth muscle in bronchioles (and to some extent in bronchi) constricts during attacks. As you have many more bronchioles than bronchi, it's more effective this way.
To reverse it you need a bronchodilator
How does the conducting zone of the respiratory system move to the respiratory zone?
Terminal bronchioles are the last conducting brochioles.
They split off into respiratory bronchioles, identifiable by their alveoli branching off them- they can now undergo gas exchange. They contain cuboidal epithelia.
Corridors of alveoli connected to a tube branch off these, called the alveolar ducts
Alveolar sacs are bunches of alveoli, not occurring in a tube, but not singly. These appear randomly.
What is the layout of the alveoli?
Have very dense capillary networks wrapped around individuals, allowing for a high surface area for efficient respiration.
What is the structure of the alveolar wall?
Inside: air space
Contains Type I alveolar cells/ squamous pneumatocytes. These are very thin cells with long cytoplasms wrapping around the alveolus
Type II cells: produce surfactant. This keeps the alveolus moist and stops them collapsing during expiration by reducing surface tension. The allows it to reinflate under less pressure
Alveolar macrophages: consume any and all particles reaching this level. They form a last line of defense and move around between alveoli.
Capillaries surround it that contain red blood cells
What forms the diffusion barrier?
Basement membranes of sqam. pneu and capillary endothelium- fused to reduce the diffusion barrier
Where do cartilage/mucus glands stop?
They do not continue past the smallest bronchi
Where does the smooth muscle coat end?
It gets larger relative to thickness as you progress down the conducting zone, but stops after the smallest bronchioles
How does the makeup of the epithelium change as you go down the resp. system?
Gets thinner and secretory change.
How many primary bronchi are there?
How many secondary (lobar) bronchi are there in each lung?
2 on the left, 3 on the right
How many tertiary (segmental) bronchi are there in each lung?
8 on the left, 10 on the right
What does each lung segment have and why is this important?
Each has their own bronchus, blood lymph and nerve supply.
This allows any treatment to be localized to a single segment, preventing damage to the lung overall.
What are the pleurae?
A smooth membrane lining the lungs (visceral) and the thoracic cavity (parietal). They are continuous with the hilum and separated by a very thin film of serous fluid
Why is the serous fluid crucial for the lungs?
- Prevent friction between lungs and rib cage
- Prevent membranes from becoming separated using surface tension, causing the lungs to follow when the ribs expand or contract
How do the ribs contribute to quiet breathing?
External intercostal muscles contract, causing the ribs to lift up and out. This drags the lungs along with them, causing inhalation
(ribs responsible for 25% of air movement)
The ribs then return to resting position due to elasticity of lungs, pulling them along with it due to surface tension. (passive process)
How do the ribs contribute to panting?
Both external and internal intercostals are involved.
Ribs pivot around their joints with the vertebral column due to external intercostal contraction, lifting the ribs and increasing thoracic volume
During exhalation, the internal intercostal muscles (at right angles to the externals) contract, dragging the ribs down and in, forcing air out
How does the diaphragm contribute to breathing?
When it contracts it flattens, pulling the central dome down and increasing thoracic volume
It relaxes passively, allowing the thoracic volume to decrease
Its movement is responsible for 75% of quiet breathing, but a smaller proportion of panting.
What is the structure of the diaphragm?
Its central dome is made of CT (an aponeurosis) called the central tendon. Lateral muscles are fast acting skeletal muscle, innervated by the phrenic nerve (spinal)
It forms the floor of the thorax and the roof of the abdomen
What are units for volume?
L or mL
What are units for pressure?
kPa or mmHg or cmH2O (common for lungs)
What are units for content of gas in blood?
What are units for compliance?
Why is human respiration tidal?
We use the same structures for inhalation as we do for exhalation
What is residual volume?
The amount of air left in the respiratory structures after a maximal expiration.
It exists as it is impossible to fully expel all the air from our lungs.
How much is residual volume?
What is functional residual capacity?
The amount of air remaining in the lungs at the end of a normal expiration.
It's called 'functional' as it can serve as a source of O2 between breaths
What is tidal volume?
The volume of air in a normal breath.
How much is functional residual capacity?
How much is tidal volume?
What is total lung capacity?
Lung volume achieved by maximum inspiration
How much is total lung capacity?
How does pressure result in breath?
Air enters the lungs when alveolar pressure (PA) is less than atmospheric pressure (PB) and leaves when PB is less than PA
(provided the glottis is open)
What does V. prop to (PB - PA) mean?
Bulk rate of air flow is proportional to the diff. between PB and PA
The rate of lung expansion/deflation is reduced by factors increasing resistance to air flow, allowing
V. = (PB - PA) / R
What force is the lung vs. the ribcage exerting and what impact does this have on the chest?
The lungs are highly elastic and attempt to recoil inwards, pulling the lungs in. Additionally, remaining surface tension in the alveoli tries to collapse them, pulling the lungs further. However, the chest wall experiences an outward pulling force, trying to expand the ribcage.
This reduces intrapleural pressure below atmospheric pressure.
Where is a balance between the inward recoil of the lungs and the outward stretch of the chest wall acheived?
At functional residual capacity (provided airway pressure is 0)
What is pneumothorax and why does it occur?
It is air in the intrapleural space.
It occurs when the chest wall is penetrated, creating a connection between the intrapleural space and the atmosphere
The adhesion of the affected lung to the parietal pleura is prevented, causing the lung to recoil inwards all the way and shrink, while the chest wall is able to expand.
How does intrapleural pressure change during breathing and why?
- During inspiration, it decreases from approx. 3mmHg to approx. 6mmHg. This reverses during expiration
- This id due to the fact that inspiration pulls the membranes apart, while expiration pushes them closer together
How does alveolar pressure change during breathing and why?
During inspiration, it decreases from 0 to -1mmHg and then curves up again to meet atmospheric pressure. During expiration, it increases to about 1mmHg, and then back down to atmospheric (0).
- This is because the lungs expand, creating a vacuum until the recoil causes them to return to atmospheric pressure. During exhalation, the collapsing of the chest puts more pressure on the lungs, increasing their pressure above atmospheric. When the air has mainly gone, pressure cannot be sustained at this level, so it drps back
How does air flow change during breathing and why?
During inspiration, .5L air flows inwards, causing a -5 value (negatives show inward movement). This eventually drops off until there is no movement. Then, .5L air flows outward, a positive value. However, this rate also drops off, returning to 0. (FRC)
How does tidal volume change during breathing and why?
(Using FRC as our 0 value)
During inspiration, it increases to about .45L, and during expiration this decreases to 0 again
How does air flow of .5 L in and .5L out get reconciled with tidal volume?
Look at the time scale- Average air flow is about .25L/sec, which is the same tidal volume.
What is rate of ventilation?
Breaths per minute x Tidal volume
What is the process of inspiration?
Inspiratory muscles contract, enlarging thoracic cavity
Intrapleural pressure becomes more subatmospheric, pulling the visceral pleura and lungs outward
Pressure in alveoli is subatmospheric, air rushes inward
What is the process of expiration?
Alveolar pressure returns to atmospheric pressure
Diaphragm relaxes, intrapleural pressure rises and lungs recoil
Gasses in alveoli compressed, forcing them from the lungs.
What affects the exchange of air?
- Muscular effort (more effort = greater flow)
- Lung compliance (change of V per change in P)
- Resistance (Change in P per change in Flow)
- Dead space
How do you calculate compliance?
Compliance = change in V / Change in P
How does compliance affect air flow?
Lower compliance means air is more able to enter the lung, increasing inspiratory air flow
However, if compliance increases too much, recoil may be negatively affected, causing decreased outflow of air
What is the relationship between the pressure of inhalation and the percent the lung will fill?
It takes a large amount of pressure to inflate the lungs to FRC- about 8mmHg. After this pressure, any change in pressure will result in a fairly substantial change in volume until it plateaus towards 100%
Is it easier to inflate the lungs if they are full of saline or air and why?
Easier with saline, as it means there is no surface tension to overcome- lungs open up really easily and reach maximum volume with very little pressure change.
How does resistance affect air flow?
At higher resistance, less air is able to enter the lungs
This is because it increases the intrapulmonary pressure, allowing less of a gradient for air flow.
How is resistance measured in the lung?
By total cross sectional area
This means that the smaller alveoli have less resistance than the bronchi, even though their lumens are smaller.
What is anatomic dead space?
The volume of the conducting airways- it's a consequence of tidal ventilation as some fresh air never reaches the respiratory zone. In addition, some alveolar air remains in the lungs, diluting the fresh air coming in.
It comprises about 1/3 of tidal volume- 150 mL (3% of total lung capacity) However, this proportion gets smaller as we take larger breaths.
How does dead space influence air flow?
The smaller the breaths we take, the larger the proportion is dead space.
How does diffusion affect air flow?
The diffusion of Co2 and O2 between alveoli and pulmonary capillaries is described by fick's law:
Volume of gas transported across a membrane per unit time is directly related to:
Driving partial pressure of gas
Area of membrane.
Inversely related to:
Square root of mol. weight of Gas
What is RDS?
Respiratory distress syndrome:
To inflate the alveoli, their surface tension and recoil must be overcome.
Surfactant secreted by type II alveolar cells reduces this surface tension.
In premature babies it can be absent, meaning much more effort is required to generate sufficient intrapulmonary pressure
What is emphysema?
Destruction of alveolar and peribronchial elastic tissue, resulting in collapse of lungs during exhalation, trapping air downstream
This increases functional residual capacity (causing a barrel chest), disadvantaging inspiratory muscles is you have to exert more and more force to inhale sufficient air
What is asthma?
Characterised by constriction of bronchioles, increasing resistance.
It requires increased pressure to achieve tidal volume and therefore increased muscular effort.
What is pulmonary edema?
It is characterised by an increased diffusion distance- can be cardiogenic (increased capillary pressure causing increased IF) or caused by increased mucus secretion within the alveoli.
This reduces gas exchange and is usually caused by pneumonia.
What is Dalton's law?
The total pressure of a gas is equal to the sum of the pressure exerted by each individual constituent (partial pressure)
What is henry's law?
The concentration of a dissolved gas is relative to its partial pressure and solubility in the particular solvent.
What is partial pressure?
The amount of force needing to be exerted on a dissolved gas to prevent its escape from solution.
What are the components and proportionalities of 'air'?
Carbon Dioxide (.04%)
H2O (differs depending on location and weather)
What is solubility?
A physico-chemical property of a given solution (gas and solvent)
What is the oxygen content of blood?
The amount of O2 carried in whole blood
- 150g of Hb in erythrocytes, which holds 1.34mL O2 or up to 200mL of O2 per L blood
Only about 3mL of O2 is dissolved in plasma as it is very insoluble
What is Hb saturation?
The amount of O2 actually bonded to Hb relative to max. it can bind- anywhere between 0 and 4 molecules of O2.
How do O2 and Hb bind cooperatively?
It is difficult to get the first O2 molecule bonded, but it gets easier progressively. This leads to a sigmoidal-shaped O2-PO2 relationship
What does the sigmoidal relationship between PO2 and hemoglobin saturation mean?
PO2 can be decreased to almost half its normal value and saturation can remain nearly full.
What is the common PO2 in the alveoli vs. the tissues?
About 100 vs. 40 mmHg
How does Hb saturation differ with pH?
At low pHs, with lots of acidity, saturation is lower per PO2. At high pHs, saturation is higher per PO2.
What is the application of low pH and low O2 saturation?
During exercise which produces lactic acid, more O2 will be unloaded into the tissues, without needing to decrease the PO2 a large amount, which is necessary to keep high to create a steeper diffusion gradient.
How does partial pressure of O2 change as we exercise?
Our tissues use more of the O2 offloaded to them, which decreases the PO2 in the tissues. Therefore, more Oxygen is released from the Hb as the diffusion gradient is steeper.
How much O2 is released from the Hb at resting state?
Only about 25-30%- much of the Oxygen remains bonded to the Hb
How does Hb saturation differ with different CO2 concentration and why?
CO2 forms a much stronger bond with Hb than O2 does, so rising levels of CO2 result in lower O2 saturation and vice versa
This is useful as when tissues are more active they need more O2 and produce more CO2.
How does HB saturation differ with temperature?
At higher temperatures, saturation is lower and vice versa
How is CO2 transported through the blood?
About 9% in plasma as it is more soluble than blood
13% attached to Hb
78% as HCO3-, as it reacts with H2o and then loses a proton
Some as H2CO3
How is CO2 expelled?
Excreted by the blood as CO2 from the lungs, and as HCO3- by the kidneys
Excreted from the body via exhalation and urination
How does CO poisoning affect Oxygen saturation?
Binding of O2 to hemoglobin is blocked by CO, which forms a much stronger bond. This reduces the saturation of hemoglobin to about half its usual value
How does anemia affect Oxygen saturation?
The amount of Hemoglobin (which requires iron) is reduced. Although saturation of remaining hemoglobin will still be high, there will be less of it, and so much less oxygen in the blood.
How do amount of CO2 and O2 in the blood differ?
O2 content is about a third of CO2- 200mL//L vs. 600mL/L respectively, depending on their partial pressures
How does the amount of O2 in the blood affect the concentration of CO2?
Higher oxygen levels decrease the amount of HbCO2, and vice versa.
What are the reactions of O2 and CO2 transport occurring, from inhalation to exhalation and overall?
1. Lungs: Hb + nO2 --> Hb(O2)n
2. Tissues: Hb(O2)n --> Hb + nO2
3. O2 + fuel --> CO2 + H2O
4. CO2 + Hb ---> HbCO2
5. Lungs: HbCO2 ---> Hb + CO2
Overall: HbCO2 + O2 HbO2 + CO2
How does PO2 change as it moves through the body?
Alveolar gas: 104
Blood: 95 vs. 37 (venous)
Cells: Approx. 40, decreasing to final pressure
How does PCO2 change as it moves through the body?
Alveolar gas: 38
Blood: 38 vs. 44 (venous)
What is alveolar ventilation?
It is the exchange of oxygen and carbon dioxide in the alveoli
Why is alveolar ventilation important and regulated?
It maintains the partial pressures of O2 and CO2 in arterial blood- matching pulmonary O2 intake with tissue O2 consumption and CO2 exhalation with tissue CO2 production
It is regulated to achieve this
What happens during hypo-ventilation?to
The tissues still produce CO2 at concentrations of 200mL/minute, so at lower resp. rate, there is an increase of PCO2 in both the arteries and the alveoli.
The tissues also still consume O2 at a rate of 250mL/min, so there is a lower-than-normal PO2 in both the alveoli and the arteries.
The increased CO2 is associated with a decrease in pH, which eventually leads to acidotic coma.
What happens during hyperventilation?
Oxygen is still consumed by tissues at a rate of 250mL/min and CO2 produced at 200mL/min.
Therefore there is low PCO2 in both the alveoli and the arteries, and high PO2.
The decreased CO2 is associated with increased pH, eventually leading to alkalotic coma.
What is the equation for alveolar ventilation and what does it mean?
V.A = fR x (VT-VD)
Rate at which alveolar volume is ventilated is proportioal to the alveolar volume (tidal volume less dead space) multiplied by the frequency of breathing.
What is the body's response to decreasing levels of Oxygen in inhaled air?
As Oxygen percentage decreases, respiration only really increased past 10% Oxygen- about half what is normally in air.
Some people didn't even react.
Pulse rate increased slightly, but there is a range of responses
Oxygen saturation decreased as concentration in air decreased.
What happens to respiratory minute volume as %O2 decreases?
It has little change until about 10-8% threshold is reached; then it increases
What happens to respiratory minute volume as pH decreases?
Little change until about 7.2, then it increases quickly but quickly tapers off as you start to enter a coma
What happens to respiratory minute volume when CO2 concentration increases?
after about 3% is reached, it suddenly and steeply increases to levels not even normal during exercise, proving we are most sensitive to CO2 content of air
What is the part of the brain responsible for respiration?
The dorsal and ventral respiratory groups in the medulla oblongata.
Dorsal is responsible for inspiration, while ventral does some in inspiration, some in active exhalation.
How does feedback from airways and lungs regulate respiration?
Slow stretch receptors in bronchi/oles send signals via vagus nerves to respiratory centres.
Their activation terminates inspiration
Irritant sensors in airways respond to mechanical and chemical stimuli, histamine, prostaglandins and hyperinflation to reflexively constrict the bronchioles, causing rapid shallow breathing, coughing and increased mucous secretion
How do peripheral and central chemoreceptors send signals to the brain?
- Peripheral sensors in carotid and aortic bodies detect PO2 and PCO2 in the arteries, informing resp. centers if more ventilation is needed or not.
- Carotid bodies respond to arterial PO2 decreases and PCO2 increases, sending info along the glossopharygeal nerve
- Aortic bodies send this info via the vagus nerve
- Central chemoreceptors are on the ventral surface of the medulla and are sensitive to CSF pH
How do central chemoreceptors monitor pH of CSF as H+ can't cross the blood-brain barrier?
CO2 is soluble in CSF, where it reacts with H2O to form HCO2- and H+. This H+ is able to be sensed by central chemoreceptors.
What happens to ventilation rate when O2 decreases and CO2 is not held constant?
PO2 can decrease to about 50mmHg before ventilation rate increases slightly, and pACO2 decreases as a result
What happens to ventilation rate when O2 decreases and CO2 is held constant?
After PAO2 decreases to about 80mmHg, there is a very steep increase in ventilation rate.
This proves that we are very sensitive to PO2 provided PCO2 is constant.
However, our sensitivity to PCO2 is much higher, which ensures that ventilation rate is never too high.
What happens to ventilation rate at a constant low vs. high PAO2?
Ventilation rate increases steeply for low PAO2 as PACO2 is increased, but less steeply at a higher PO2
What is voluntary vs. involuntary in terms of respiration types?
Sighing (done to open closed alveoli)
Singing, whistling, yodelling, speaking
Parturition (control of respiration in labour)
Demonstrates self importance
Defacation and urination
How do the respiratory centers receive feedforward?
They receive it from other brain regions like sleep-wake, swallowing, speaking, emotion, temp and breath-holding.
What do the respiratory centers give input to?
Feed impulses to:
Thoracic and abdominal muscles
Feed impulses to:
Laryngeal and pharyngeal muscles
How does ventilation provide feedback?
Ventilation and metabolism control PaO2, PaCO2 and pH. PaO2 affects the peripheral chemoreceptors, and PaCO2 and pH affects peripheral and central chemoreceptors which they send impulses to the respiratory centres.