01 The Respiratory System

GAS EXCHANGEGAS EXCHANGE

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The gaseous exchange The gaseous exchange systemsystem

Cleans and warms air that enters during Cleans and warms air that enters during breathingbreathing

Maximises the surface area for diffusion of OMaximises the surface area for diffusion of O22 and COand CO22 between blood and atmosphere between blood and atmosphere

Minimises the distance for this diffusionMinimises the distance for this diffusion

Maintains adequate gradients for this Maintains adequate gradients for this diffusiondiffusion

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The Respiratory The Respiratory SystemSystemA flap of

elastic tissue that forms a lid over the opening of the trachea

Nasal cavity: air passing over the mucous membrane of the nasal cavity is moistened, warmed and filtered

Passage where the nose and mouth come together

Contains 2 ligaments (vocal cords) that produce sound when air move through them

LungsLungs Site of gaseous exchange between Site of gaseous exchange between

air and bloodair and blood

Presents a Presents a huge surface areahuge surface area to to the air that flows in and outthe air that flows in and out

In the In the thoracic (chest) cavitythoracic (chest) cavity surrounded by airtight space surrounded by airtight space containing fluid to allow friction-free containing fluid to allow friction-free movementmovement

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Alveoli Alveoli Have very Have very thin epithelial liningthin epithelial lining

Surrounded by many Surrounded by many blood blood capillariescapillaries

Alveolar walls contain Alveolar walls contain elastic fibreselastic fibres which stretch during breathing and which stretch during breathing and recoil during expiration to help force recoil during expiration to help force out air – allows alveoli to expandout air – allows alveoli to expand

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Alveoli (cont)Alveoli (cont)

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Gas exchange in alveoliGas exchange in alveoli

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BRAIN TEASERBRAIN TEASER

How many times must a molecule of How many times must a molecule of oxygen diffuse across a cell surface oxygen diffuse across a cell surface membrane in passing from the inside membrane in passing from the inside of an alveolus to haemoglobin?of an alveolus to haemoglobin?

How does the composition of How does the composition of inhaled air compare to that of inhaled air compare to that of

exhaled air?exhaled air?

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% Gas% Gas Atmospheric Atmospheric air (inhaled air (inhaled

air)air)

Alveolar air Alveolar air (exhaled air)(exhaled air)

NitrogenNitrogen 79.0%79.0% 79.0%79.0%

OxygenOxygen 20.9%20.9% 14.0%14.0%

Carbon Carbon dioxidedioxide

0.04%0.04% 5.6%5.6%

Water vapourWater vapour 1.0%1.0% 6.0%6.0%

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The ciliated epithelium

TRACHEA

The Lung Tissues

Bronchiole and Trachea in transverse Bronchiole and Trachea in transverse sectionsection

cartilage

Smooth muscleAnd elastic fibres

Ciliated epithelium and goblet cells

A transverse cross section view of the cartilaginous trachea

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CartilageCartilage Ciliated Ciliated epithelium epithelium

with with goblet goblet cellscells

Smooth Smooth musclemuscle

Connective Connective tissuetissue

TracheaTrachea √√ √√ √√ √√

Two Two bronchibronchi

√√ √√ √√ √√

BronchioleBronchiole Cartillage Cartillage gradually gradually

lostlost

No gobletNo goblet Gradually Gradually lostlost

√√

Alveolar Alveolar ductduct

No No cartilagecartilage

No ciliaNo cilia

No gobletNo gobletNoNo NoNo

Alveolar Alveolar sacsac

No No cartilagecartilage

No ciliaNo cilia

No gobletNo gobletNoNo NoNo

AlveoliAlveoli No No cartilagecartilage

No ciliaNo cilia

No gobletNo gobletNoNo NoNo

CartilageCartilage: prevents collapse of the tube : prevents collapse of the tube during inspiration.during inspiration.

CiliaCilia: beats rhythmically, gradually : beats rhythmically, gradually sweeping the mucus up towards the back sweeping the mucus up towards the back of the throat, where it is swallowed.of the throat, where it is swallowed.

Goblet cellsGoblet cells: secretes a protective : secretes a protective coating called mucus. Much of the dust coating called mucus. Much of the dust and microorganisms in the air which is and microorganisms in the air which is breathed in is trapped in this mucus.breathed in is trapped in this mucus.

Smooth muscleSmooth muscle: involuntary muscles. : involuntary muscles. When they contract, they narrow the When they contract, they narrow the airways.airways.

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Lung volumes and Lung volumes and capasitiescapasities

Tidal volumeTidal volume: the volume of gas : the volume of gas exchange during one breath in and out. exchange during one breath in and out. ~450 cm~450 cm33 during quiet breathing. After during quiet breathing. After exercise it rises to ~3 dmexercise it rises to ~3 dm33..

Vital capacityVital capacity: maximum volume of : maximum volume of air that a person can exhale after filling air that a person can exhale after filling the lungs to their maximum extent. the lungs to their maximum extent.

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TaskTask

1.1. State 3 ways in which the structure of the State 3 ways in which the structure of the lungs allows efficient gas exchange (4).lungs allows efficient gas exchange (4).

2.2. Explain why the barrier to diffusion must Explain why the barrier to diffusion must be as thin as possible (1).be as thin as possible (1).

3.3. Describe how a steep diffusion gradient is Describe how a steep diffusion gradient is achieved in the lungs (4).achieved in the lungs (4).

AnswersAnswers

1.1. State 3 ways in which the structure of the State 3 ways in which the structure of the lungs allows efficient gas exchange (4). lungs allows efficient gas exchange (4). Large surface area (1) provides more Large surface area (1) provides more space for molecules to pass through (1), space for molecules to pass through (1), plasma membranes surrounding the plasma membranes surrounding the cytoplasm create a permeable barrier cytoplasm create a permeable barrier allowing diffusion of oxygen and carbon allowing diffusion of oxygen and carbon dioxide (1), alveolus wall is one cell thick dioxide (1), alveolus wall is one cell thick creating a thin barrier for diffusion (1)creating a thin barrier for diffusion (1)

2. Explain why the barrier to diffusion must 2. Explain why the barrier to diffusion must be as thin as possible (1). be as thin as possible (1). It reduces the distance gases have to It reduces the distance gases have to diffuse (1)diffuse (1)

AnswersAnswers3.3. Describe how a steep diffusion gradient is achieved in Describe how a steep diffusion gradient is achieved in

the lungs (4). the lungs (4).

Blood brings carbon dioxide from the tissues to Blood brings carbon dioxide from the tissues to the lungs ensuring the the lungs ensuring the carbon dioxidecarbon dioxide concentration in the blood is concentration in the blood is higherhigher than that of than that of the air in the alveoli (1), it also carries oxygen the air in the alveoli (1), it also carries oxygen away from the lungs ensuring that the away from the lungs ensuring that the concentration of concentration of oxygenoxygen in the blood is kept in the blood is kept lowerlower than air inside the alveoli (1), the than air inside the alveoli (1), the movement of the lungs (ventilation) ensures movement of the lungs (ventilation) ensures there is a fresh supply of oxygen entering the there is a fresh supply of oxygen entering the lungs increasing the concentration of oxygen in lungs increasing the concentration of oxygen in the alveoli (1), carbon dioxide is also removed the alveoli (1), carbon dioxide is also removed by ventilation ensuring that the concentration in by ventilation ensuring that the concentration in the alveoli is lower than that of the blood (1)the alveoli is lower than that of the blood (1)

Mechanism of ventilationMechanism of ventilation

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External intercostal External intercostal muscles contract and the muscles contract and the internal intercostal muscle internal intercostal muscle relaxrelax

Pulls rib cage up and outPulls rib cage up and out

Diaphragm muscles Diaphragm muscles contract contract

This flattened the This flattened the diaphragmdiaphragm

Both actions increase the Both actions increase the volume of the thoraxvolume of the thorax

Pressure in the thorax, Pressure in the thorax, hence the lung, is reduced hence the lung, is reduced to less than atmospheric to less than atmospheric pressurepressure

Air enters the lungs, Air enters the lungs, inflating the alveoli, until inflating the alveoli, until the air pressure in the the air pressure in the lungs is equal to that of lungs is equal to that of the atmospherethe atmosphere

External intercostal External intercostal muscles relax and the muscles relax and the internal intercostal internal intercostal muscle contractmuscle contract

The rib cage drops, The rib cage drops, mainly due to its own mainly due to its own weightweight

Force the diaphragm Force the diaphragm into domed shape into domed shape

Diaphragm muscles Diaphragm muscles relaxrelax

Pressure in the thorax, Pressure in the thorax, hence the lung, is hence the lung, is increase, more than increase, more than atmospheric pressureatmospheric pressure

Air is forced out of the Air is forced out of the lungslungs