3. gaseous exchange

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Transcript of 3. gaseous exchange

Page 1: 3. gaseous exchange
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Gaseous Exchange

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Lungs & Thoracic Cavity – Structure

Take a copy of a GCSE Lung structure diagram – can your students label it correctly?

OR

Using the white board get the students to add diagrams and labels to make up the complete Human Thorax – what detail is missing?

OR

Give your students an A level copy (click the web-link below) of the Human Thorax – can they identify the labels and structures not expressed at GCSE level?

For a detailed structure and how to make models of the lungs visit www.smm.org/heart/lessons/lesson7.htm

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Lungs & Thoracic Cavity – Structure

TASKS:

Create a Pathway for Air travel from the mouth to the Alveoli naming all the anatomical areas you pass.

AND

Why is the Double Pleural Membrane and the Pleural fluid so important to Lung Function?

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Lungs & Thoracic Cavity – Structure

To create a larger surface area for DIFFUSION to take place, the lungs contain many small air sacs called ALVEOLI. These air sacs have a thin wall to allow for the diffusion of Respiratory gases (02 & CO2) to take place. CAPPILATIES cover these thin walls to allow for efficient DIFFUSION to occur.

Capillary (less than 1 RBC wide so to distort cell as it travels through to increase its surface area aiding diffusion)

Alveolus (thin moist cell wall to assist with diffusion)

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DiffusionDIFFUSION is the movement of gases from one place

to another. Within the Gaseous exchange system this takes place in 2 areas;

1. The ALVEOLI (the lungs)

2. The WORKING MUSCLE

In both the above RESPIRATORY GASES are transported into the blood within the capillaries.

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DiffusionDIFFUSION OCCURS WHEN THERE IS A DIFFERENCE IN CONCENTRATION (the amount) OF A GAS BETWEEN ONE PLACE AND ANOTHER. This is called a DIFFUSION GRADIENT.

GASES ALWAYS TRAVEL FROM

HIGH CONCENTRATION LOW CONCENTRACTION

IMAGINE IF THE GAS WAS REPRESNTED BY FOOTBALLS PLACED HIGH AT THE TOP OF A HILL, THEY WOULD ALWAYS WANT TO

GO TO THE LOWEST POINT BY TRAVELLING DOWN.

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Gases and the Atmosphere

AIR – made up of many components

Nitrogen (N2)

Oxygen (O2)

other gases (e.g. CO2)

Water (H2O)

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Gases and the AtmosphereDue to atmospheric pressure AIR is thinner at altitude compared to at sea level.

This is because as you travel further away from the earth the area that the Air components has to fill is larger thus spreading out the molecules.

Place a bag of M & M’s in a small plastic box and see how many collisions they have with each other as you move the box. Now transfer the same M & M’s into a larger plastic box – notice that they have more

space to move and have less collisions.

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Gases and the Atmosphere

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Measurement & Accuracy

• AIR – as it is made up of many components it is easier and more accurate to compare the amount of each gas if we compare it to the other gases in terms of “pressure” rather than its %. How much pressure (the number of collisions each particle has with others) is called “partial pressure” (pp).

• Measured in Pascals (Pa), or mm of Mercury (Mg)

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Measurement & Accuracy

To find the pp of a gas we can use a simple equation.

pp of a gas = Barometric pressure X Fractional

of a gas Concentration

pp O2 = 760 X 21(dry atmospheric Air at sea level) 100

= 159.6mmHg ≈ 21 Kpa

Now find out the actual barometric pressure today by looking at the Met office website www.metoffice.gov.uk/weather/uk/uk_forecast_pressure.html

and work out the pp of O2 and CO2

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Breathing In - INSPIRATION

External Intercostals contract

Rib cage lifts up and out

Diaphragm contracts and flattens

Thoracic Cavity increases Volume

Pressure lower inside than out

Air rushes in

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Breathing In – Expiration (at rest)

External Intercostals relax

Rib cage drops down and in

Diaphragm relaxes and domes up

Thoracic Cavity decreases Volume

Pressure greater inside than out

Air pushes out

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Breathing In – Expiration (during exercise)

Often known as FORCED or ACTIVE Expiration

Internal Intercostals contract

Rib cage drops down and in

Diaphragm relaxes and domes up

Thoracic Cavity decreases Volume

Pressure greater inside than out

Air pushed out

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Breathing – Control of Movements

Happens by Nervous Control

– influenced by exercise

Breathing at rest – INVOLUNTARY, controlled by “Respiratory Control Centre” in Brain

DURING INSPIRATION DURING EXPIRATION

Inspiratory control centre Impulses stop and Muscles

Sends Motor Impulse to Relax.

external intercostals

& diaphragm.

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Breathing – Control of Movements

• Happens by Nervous Control – influenced by exercise• Breathing During Exercise – INVOLUNTARY, controlled by “Respiratory Control Centre” in Brain

DURING INSPIRATION DURING EXPIRATION

Inspiratory control centre Expiratory control centre

Sends Motor Impulse to Sends motor impulses to

external intercostals internal intercostals

& diaphragm.

RIBS = UP & OUT RIBS = DOWN & IN

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Breathing – Control of Movements

DECREASES IN BLOOD pH = INCREASES IN VENTILATION

Caused by - in LACTIC ACID & CO2 PRODUCTION

Ventilation – caused by rate (how often) and depth (how much) of breathing.

Start of Exercise – Ventilation increased due to

increasing DEPTH

Heavier Exercise – Ventilation increased due to

increased RATE & Depth

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Breathing – Control of Movements During INSPIRATION

Detected by specialised SENSORSY receptors.

BARORECEPTORS – Detect changes in Blood Pressure(Like a “Barometer “detects changes in air pressure)

CHEMORECEPTORS – Detect chemical changes in the

blood e.g. Increase in Acidity(Like “Chemotherapy” uses chemicals to treat illness and disease)

MUSCLE RECEPTORS – Detect movement and therefore

exercise is taking place

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Breathing – Control of Movements During EXPIRATION

During FORCED or Active EXPIRATION specialised SENSORY receptors known as STRETCH receptors are stimulated. These are found around the THORAX

These STRETCH receptors are stimulated to prevent over-inflation of the lungs.

Nerve impulses are sent from the STRETCH receptors to the EXPIRIATORY CONTROL CENTRE which stimulates the contraction of the INTERNAL Intercostals.

This is known as the HERING BREUER REFLEX

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Respiratory System – Volumes and Measurement

Accurate measurement of lung volumes and capacities are measured by a SPIROMETER.

The volumes measured are;

TV = Tidal Volume (at rest)

ERV = Expiratory Reserve Volume

VC = Vital Capacity

IRV = Inspiratory Reserve Volume

RV = Residual Volume

Total Lung Capacity

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Respiratory System – Volumes and Measurement

SPIROMETER TRACE - AVERAGE VOLUMES

TV ≈ 0.5l ERV ≈ >1.0l VC ≈ >4.5l

IRV ≈ >3.0l RV ≈ >1.0l Total Lung Capacity ≈ 6l

RESIDUAL VOLUME

IRV

ERV

TV VC

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Respiratory System – Volumes and Measurement

VC TV IRV ERV

Total Lung Capacity VC RV

Minute Ventilation volume of air inspired or

expired in 1 min

Commonly Used Equations

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Gaseous Exchange at the lungsRespiratory gases move from the air in the ALVEOLI into

the blood held in the CAPILLARIES and Visa Versa.In the ALVEOLI: pp of O2

pp of CO2

In the CAPILLARY: pp of O2

pp of CO2

(ATM AIR MIXED WITH ‘STALE’ AIR) Diffusion

Gradient Exists – O2 moves

into the CAPILLARY and CO2 moves into

the ALVEOLI

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Gaseous Exchange at the Working MusclesRespiratory gases move from the blood in the

CAPILLARIES to the MYOGLOBIN in the MUSCLE CELLS and Visa Versa.

In the CAPILLARY: pp of O2

pp of CO2

In the MUSCLE: pp of O2

pp of CO2

Diffusion Gradient Exists

– O2 moves into the

MUSCLE and CO2 moves into the CAPILLARY

MYOBLOBIN IS THE MUSCLES EQUIVELANT OF HEAMOGLOBIN,

AN OXYGEN CARRIER

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Oxygen Dissociation CurveOxygen is carried in the blood by the carrier HEAMOGLOBIN (Hb).

It can be loaded with O2 depending on how much O2 is available;

(> ppO2 = > Hb Saturation)

Hb can be fully loaded (SATURATED) with O2 at relatively low pp of O2 (≈ 13kPa)

MYOGLOBIN IS THE MUSCLE CELLS EQUIVELENT TO Hb however it has a GREATER AFFININTY FOR O2

(in other words it attracts it more)

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Oxygen Dissociation CurveSaturation of the HEAMOGLOBIN can be represented by

an ‘S’ shaped curve on a graph.

% Hb sat. with O2

pp O2 (mmHg)

= O2 Dissociation curve at rest = O2 curve during exercise when temp & acidity increases making it harder for O2 to attach to Hb. = Myoglobin Dissociation curve. Has greater affinity for O2 so can saturate easier.