Lung function & Structure Lung Structure Lung function & Structure

You should know The gross structure of the respiratory system The essential features of the alveolar epithelium as a surface over which gas exchange occurs The exchange of gases in the lungs The mechanism of breathing Pulmonary ventilation as the product of tidal volume and ventilation rate

Lung Structure Lungs are the interface for the exchange of gases and their function is affected by both pathogens and lifestyle. All aerobic organisms require a constant supply of oxygen in order to release energy in the form of ATP during respiration. The waste gas product carbon dioxide also has to be removed because the build up can be harmful.

Why have lungs? We need lungs to enable oxygenation of our blood system in order to circulate to the relatively large volume of living cells. Mammals have to maintain a high body temperature and therefore have high metabolic and respiratory rates. Air enters via the trachea and then into the left and right bronchus (plural bronchi). The bronchi lead into a pair of lobed structures called the lungs. Lungs consist of a series of highly branched tubules called bronchioles which end up in tiny air sacs called alveoli.

Why are a mammals lungs located within the body? Air is not dense enough to support and protect delicate structures They would cause loss of a great deal of water and dry out Because lungs are located internally, we need to have a means of moving the external medium (air) over the surface of our lungs. This movement is called ventilation.

Rib cage Rib cage is moved by muscles between ribs (intercostal muscles covered later) Causes ventilation by a tidal stream Means constant replenishment of air

Trachea Flexible and supported with cartilage Cartilage prevents trachea collapsing when air pressure falls Tracheal walls consist of muscle Lined with ciliated epithelium and goblet cells Goblet cells produce mucus to trap dirt particles and bacteria Cilia move mucus + dirt/bacteria up the throat into oesophagus to stomach

Bronchi Two divisions of the trachea – each leading to one lung Bronchi (plural) and left and right bronchus (singular) Similar cell structure as trachea – produce mucus and have cilia Larger bronchi have cartilage – cartilage reduced as bronchi get smaller

Bronchioles Series of branching subdivisions of the bronchi Walls made of muscle lined with epithelial cells Muscle permits constriction to control the flow of air in and out of the alveoli

Alveoli (plural); alveolus (singular) Alveoli are minute air sacs (about 100-300 μm) at the end of the bronchioles Contain collagen and elastic fibres Elastic fibres allow alveoli to stretch when breathing in When breath exits, elastic fibres spring/recoil back to aid expulsion of carbon dioxide Lined with squamous epithelium Alveoli membrane is the gas-exchange surface of the lungs Blood vessels line the alveoli to diffuse gases

List key structures of air travelling from the nostril to the blood vessels surrounding the alveoli? Nostril → nasal cavity → trachea → bronchi →bronchioles → alveoli → blood vessels

Mechanisms of Breathing Remember in Biology we DO NOT call the process of intake of air ‘Respiration’ (that is the process of ENERGY production), we call this process Ventilation. We must remember the HIGH → LOW rule again for particle movement This time we are talking about air pressure.

Breathing Inspiration External intercostal muscles pull ribs up and out. Diaphragm muscles flatten diaphragm Volume of thorax increases Air pressure within thorax drops Air enters lungs Expiration Internal intercostals muscles contract so ribs fall Diaphragm muscles relax so it becomes dome-shaped Volume of thorax decreases Air pressure within thorax increases Air leaves lungs

ACTIVE PROCESS – uses ENERY Largely PASSIVE PROCESS – requires little energy

Diaphragm A sheet of muscle between the thorax and abdomen The diaphragm is curved upward (domed position) when relaxed When diaphragm muscles contract, it flattens and moves down Causing an increase in thorax volume

During NORMAL quiet breathing, the recoil of the elastin within alveoli walls of the lungs is the MAIN cause of air being forced out (similar to balloons). Muscles become most important during strenuous condition such as exercise.

What is Pulmonary Ventilation? The total volume of air that is moved into the lungs during one minute To calculate this we need multiply two factors: TIDAL VOLUME = volume of air normally taken in at EACH breath when body is at REST (usually 0.5dm3) VENTILATION (Breathing) RATE = the number of breaths taken in one minute. (usually 12-20 breaths)

Pulmonary ventilation = tidal volume x ventilation rate (dm3 min-1) (dm3) (min-1)

Pulmonary ventilation is the product of tidal volume and ventilation rate.

Exchange of Gases in the Lungs Ventilation of gases within lungs is essential to provide a constant supply of oxygen to create a diffusion gradient within the alveolar surface.

What is the role of the alveoli in gas exchange?   We have about 300 million alveoli in EACH human lung. Their total surface area is 70m2 (half a tennis court) Each alveoli is lined with squamous epithelial cells (0.05μm to 0.3μm thick) AROUND each alveoli is a network of pulmonary capillaries Very narrow (7-10μm thick) so that red blood cells are flattened against the walls Also have a single very thin wall (0.04μm – 0.2μm)

Complete the following table identifying essential features of gas exchange surfaces: Characteristic Benefit to gas exchange Large surface area to volume ratio Speeds up gas exchange Squamous epithelial cells Very thin to keep diffusion distance small Partially permeable Selective materials permitted across Movement of environmental medium (air) Maintain diffusion gradient (O2 in & CO2 out) Movement of internal medium (blood) Moisture Aids optimal gas diffusion

Surface Area of exchange x Concentration Gradient Diffusion Distance Fick`s Law Rate of Diffusion is proportional to: Surface Area of exchange x Concentration Gradient Diffusion Distance

Fill in missing gaps with additional key words: Label the above diagram showing the key features with the appropriate number(s):

Summary Questions How does each of the following features contribute to gas exchange efficiency? The wall of each alveolus is not more than 0.3μm thick? Diffusion distance small – thus rapid movement There are 300 million alveoli in each lung? Collectively, very large surface area The surfaces of the alveoli are moist? Permits optimal gas exchange; gases are exchanged in solution. Each alveolus is covered by a dense network of pulmonary blood capillaries? Collectively, provide a VERY large surface interface with blood

Each pulmonary capillary is very narrow? Enables slowing down of blood (thus diffusion occurs faster) and blood cells pushed against capillary way to make diffusion distance smaller also

Explain the differences in air composition between the three samples.

Explain the differences in air composition between the three samples. Exhaled air has been mixed with residual air within the air passages (bronchioles, bronchi and trachea) so is closer to atmospheric air in composition than that in the alveolar lumen. Alveolar air has oxygen removed and carbon dioxide added.

Summary Lung function The gross structure of the human gas exchange system limited to the alveoli, bronchioles, bronchi, trachea and lungs. The essential features of the alveolar epithelium as a surface over which gas exchange takes place. The mechanism of breathing. Pulmonary ventilation as the product of tidal volume and ventilation rate. The exchange of gases in the lungs.