Lecture 16 - Respiratory Physiology I Volumes and pressures Flashcards Preview

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What is the main function of the respiratory system?


Provide oxygen and remove carbon dioxide



What are the steps in respiration ?


1.    Ventilation: Exchange of air

between atmosphere and alveoli

2.    Exchange of O2 and CO2 between alveolar air and blood in lung capillaries by diffusion

3.    Transport of O2 and CO2 through pulmonary and systemic circulation by bulk flow

4.    Exchange of O2 and CO2 between blood in tissue capillaries and cells in tissues by diffusion

5.    Cellular utilization of O2 and production of CO2




How many lobes do the lungs have ?



Right lung has 3 lobes and left lung has 2, each can function independently




What are the two groups of the respiratory tract, and which parts are in them?


Upper respiratory tract:

Nasal cavity





Lower respiratory tract:


Right main bronchus 

Right lung

Left main bronchus

Left lung





What are the functions of the upper respiratory tract



An important defence mechanism against infection with 10-15,000L of air passing through the nose/day.

Inhaled particles are trapped by hair and mucus in nasal passages.

Particles activate irritant receptors triggering sneezing reflex.

Excess mucus also passes back to pharynx to be removed by swallowing, or is expulsed through nose.

Conditioning of air

Air passing through nasal cavity is warmed and humidified. This is necessary for optimal gas exchange in the alveoli. Nasal passages have a rich blood supply for this purpose


Larynx contains vocal cords: two folds of elastic tissue stretched across its lumen. These vibrate as air flows across them, producing sound.





How much air passes through the nose each day?


10 - 15,000 L



What are the two zones of the lower respiratory tract and what are their functions ?


The lower respiratory tract is divided into the conducting zone and the respiratory zone.

Conducting zone:

Provides a low-resistance pathway for airflow. Resistance is physiologically regulated by changes in contraction of bronchiolar smooth muscle and by physical forces acting upon the airways.

Defends against microbes, toxic chemicals, and other foreign matter. Cilia, mucus, and macrophages perform this function.

Warms and moistens the air.

Phonates (vocal cords)


Trachea and bronchi:

Low resistance pathway for air flow.

C-shaped bands of rigid cartilage keep airways open.

Trachealis muscle spans gaps between ends of cartilage bands. Contracts to aid expulsion of blockages, eg. coughing reflex



No cartilage.

Smooth muscle bundles. Normally relaxed, allowing air to reach alveoli.

Contraction prevents irritants and particles from entering alveoli.


Respiratory zone: 

Respiratory bronchioles:

Minimal actual gaseous exchange. They branch into individual alveoli or alveolar ducts.


Alveolar ducts and alveolar sacs (~50 alveoli in each sac):

Site of gaseous exchange. Extensive blood supply, surrounded by capillaries.








What are the two types of pneumocytes(alveolar cells)?


Type I and Type II

Type I:

Flattened epithelium (gaseous exchange)

Type II:

Thicker cells (secrete surfactant)



Pores ?


gaps between alveoli. Allow entry of air even if duct is blocked and equalise pressure.



Lungs contain ~300x106 alveoli what are their diameter?




Very high surface area of ~85m2 and very thin walls of ~0.2µm, maximises gaseous exchange.



Summary of Functions of the Lungs?


Provides oxygen & removes carbon dioxide

Form speech sounds (phonation)

Protection from microbes & other foreign matter


Regulates blood hydrogen ion concentration (pH)


Removal of micro-thrombi arising in systemic veins


Removal or deactivation of circulating vasoactive hormones

5-hydroxytryptamine (serotonin)





Activation of angiotensin II:

Angiotensin converting enzyme (ACE) on surface of pulmonary endothelium converts angiotensin I into angiotensin II.

Angiotensin II = vasoconstrictor, triggers release of aldosterone from adrenal cortex




In normal steady quiet breathing, the volume of air inspired is

equal to the volume expired. What is this called and what is the volume?


It's called the Tidal volume (VT)

500 mL


Lung volumes vary between individuals: Influenced by age, gender and height.

Values quoted here are for an average young adult male



What is the maximum amount that lung volume can be increased above Vcalled? and what is the volume ?


Inspiratory Reserve Volume (IRV).

3000 mL


Lung volumes vary between individuals: Influenced by age, gender and height.

Values quoted here are for an average young adult male


After expiring VT, a further maximal exertion of the expiratory muscles a further volume can be expired. What is this called and what is the volume ?


This is the Expiratory Reserve Volume (ERV).



Lung volumes vary between individuals: Influenced by age, gender and height.

Values quoted here are for an average young adult male


Even after maximal expiratory effort, the lungs cannot be completely emptied, a sizeable volume always remains. What is this called and what is the volume?


This the Residual Volume (RV).

1200 mL


Lung volumes vary between individuals: Influenced by age, gender and height.

Values quoted here are for an average young adult male



What is the sum of Inspiratory Reserve Volume (IRV) and Tidal Volume (VT) called ?


Inspiratory Capacity (IC)




The sum of two or more ‘volumes’ are known as ??





What is the sum of The sum of IRV+VT+ERV called?


The Vital Capacity (VC).



What is the sum of ERV+RV called?


the Functional Residual Capacity (FRC).



What is the sum of all four volumes (IRV+VT+ERV+RV) called?


The Total Lung Capacity (TLC).





Inspiratory reserve volume





Tidal volume





Expiratory reserve volume 





Residual volume





Functional residual capacity





Vital capacity





Inspiratory capacity





Total lung capacity 



Exchange of air between atmosphere and the alveoli??





Total ventilation per minute?


Minute Ventilation (VE).  



Volume of fresh air reaching alveoli per minute?


Alveolar Ventilation (VA).




How is minute ventilation (VE) calculated?


If respiratory rate (R) = 12 breaths/min and tidal volume (V ) = 500ml.

Then: VE = 500 x 12 = 6000 ml/min, or 6.0 L/min.




Is VA different from VE?


Yes, because gaseous exchange occurs primarily in alveoli and minimally in respiratory bronchioles, while pharynx and conducting zone of lower respiratory tract do not contribute at all to this.


The volume from the top of the pharynx down to terminal bronchioles is known as the Anatomical Dead Space.




In adults this is fixed and is ~150 ml.



150 ml of air remains in conducting zone from previous breath.

Of the 500 ml tidal volume, 350 ml will reach the alveoli for gaseous exchange, while 150 ml will remain in the conducting zone and not be absorbed.

How do you calculate VA?


Alveolar vent. (VA) = minute vent. (VE) - dead space vent.

= (500 x 12) – (150 x 12) = 4200 ml/min




Although anatomical dead space is fixed, Physiological Dead Space is not, how does this work ?


In healthy lungs: Anatomical Dead Space = Physiological Dead Space.

However, If some alveoli are poorly perfused, then no gas exchange occurs in those areas.

This is the Alveolar Dead Space.

Physiological Dead Space = Anatomical Dead Space + Alveolar

Dead Space




How does ventilation occur ?


Air moves from a region of high pressure to a region of low pressure. This can be defined by the equation

Flow (F) = difference of pressure ∆P or P1-P2 / Resistance R (to the flow)

In ventilation, important pressures are atmospheric pressure (Patm) and alveolar pressure (Palv)

F = Palv – Patm / R

Movement of air into and out of lungs occurs when Palv becomes smaller or larger than Patm, respectively

So, in between breaths, when Palv is the same as Patm, there is no flow of air.




Boyles law?


The pressure (P) of a fixed amount of a gas (at a constant temperature) is inversely proportional to the volume (V) of the container in which it is placed.





At __________ (end of normal breath out), all respiratory muscles are relaxed and __________ is balanced by ________ of chest wall.


At Functional Residual Capacity (end of normal breath out), all respiratory muscles are relaxed and inward recoil of lungs is balanced by outward recoil of chest wall.



What is the difference between alveolar pressure and intrapleural pressure (PIP)?


Transpulmonary pressure (PTP).

PTP = Palv – PIP



Sequence of events in inspiration?


Nerves stimulate diaphragm and other inspiratory muscles to contract, expanding the chest wall


Intrapleural pressure falls – (becomes more negative -0.7 kPa)


Alveoli are expanded (due to increased PTP causing increased pressure gradient across alveoli)


Pressure in Alveoli falls (Boyles Law)


Air drawn into lungs (increased pressure gradient from mouth to alveoli)



Sequence of events in normal expiration?


Nerves decrease firing to diaphragm and intercostals, muscles relax


Expanded chest wall recoils inward


Intrapleural (PIP) pressure goes back towards pre-inspiration level

Transpulmonary pressure decreases to pre-inspiration level


Expanded lungs which have a greater elastic recoil, reduce in size


Air in alveoli gets compressed (Boyles Law)


Air flows out of lungs


In forced expiration or high ventilation: abdominal muscles increase recoil of diaphragm and speed shrinkage of chest wall and lungs. INTRAPLEURAL PRESSURE MAY BE POSITIVE.




Volume/pressure relationships during breathing?


1. Palv = Patm and there is no airflow

2. Mid-inspiration. Expanding chest wall lowers PIP, making PTP more positive (Palv - PIP). This expands the lung, making Palv negative and results in inward airflow

3. End of inspiration. Chest wall no longer expanding, but has yet to passively recoil. Palv = Patm and there is no airflow

4. Mid-expiration. Lung is collapsing, compressing alveolar gas. So Palv becomes positive relative to Patm, causing outward airflow

1 . Cycle starts over again




Dry air = mixture of gases, primarily N2 and O2. What are the fractional concentrations?


FN2 + inert gases = ~0.79 (79%)

FO2 = ~0.21 (21%)

FCO2 = <0.0004 (0.04%)


Humidified Air: presence of water vapour alters relative

concentrations of other gases



Pressure exerted by a gas is directly proportional to ??


Temperature + number of gas molecules in a given volume (concentration)





In dry air, if Patm = 101.3 kPa and FO2 is 0.21

what is PO2 ?


 PO2 = 101.3 x 0.21 = 21.2 kPa



In aerobic respiration, cells require O2 and produce CO2

O2 must be absorbed from the air and transported to cells

CO2 must transported from cells and released into the air

At rest:

250 ml O2 is consumed by tissues per min

so 250ml O2 is extracted from blood per min


200 ml CO2 is produced by tissues per min

so 200ml CO2 is expired in lungs per min


Why are the volumes different ??



Oxidation of organic fuel produces H2O as well as CO2

CO2 produced/O2 consumed = respiratory quotient = 0.8