Post on 19-Jan-2015
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Gaseous Exchange
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
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?
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)
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.
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.
Gases and the Atmosphere
AIR – made up of many components
Nitrogen (N2)
Oxygen (O2)
other gases (e.g. CO2)
Water (H2O)
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.
Gases and the Atmosphere
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)
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
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
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
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
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.
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
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
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
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
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
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
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
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
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
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)
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.