Biology Unit 1, Lungs and Lung Disease

Mammals need to absorb large volumes of oxygen and remove large volumes of carbon dioxide, due to them having lots of cells and having to maintain a high body temp - high metabolic and respiratory rates.

Trachea - air enters and leaves via this, its supported by rings of cartilage, c-shaped rings to allow the osephogus to stretch. Walls made up of ciliated epithelium cells, and goblet cells - produce mucus that traps inhaled bacteria and dirt, cilia move the mucus up to the throat to be swallowed.

Bronchi - two divisions from trachea leading to a lung, also lined like the trachea to remover mucus.

Bronchioles - branch from the bronchi, can constrict to allow control of air in and out of alveoli.

Alveoli - end of the bronchioles, very minute.

Inspiration -

• intercostal muscles contract
• diaphragm contracts (flattens)
• increases volume of thorax
• decreased pressure in lungs
• atmospheric pressure higher then pulmonary pressure
• air moves into the lungs, down the pressure gradient.

Expiration -

• intercostal muscles relax
• diaphragm relaxes
• decreases volume of thorax
• increased pressure in lungs
• pulmonary pressure is higher then atmospheric pressure
• air moves out of the lungs, down the pressure gradient.

Pulmonary Ventilation = tidal volume x ventilation rate

(dm3min-1) (dm3) (min-1)

Pulmonary Ventilation - total volume of air moved into the lungs in one minute.

Tidal Volume - Volume of air usually taken in, in one breath.

Ventilation Rate - Number of breaths per minute.

Large Surface Area - their shape and very large number.

Short Diffusion Pathway - only two cell layers separate the blood and air, flattened epithelial cells on alveolar wall and endothelial cells on capillary walls.

Good Blood Supply - extensive network of blood capillaries surrounding each alveolus. Blood flow in capillaries maintains a constant concentration gradient for diffusion, ventilation of the lungs and action of the heart means that oxygen is being carried away and carbon dioxide is being brought continuously. Together they maintain a steep concentration gradient.

Capillaries are only wide enough to allow one blood cell through,they flatten themselves against the wall (also creates a larger surface area), therefore movement of blood cells is very slow, this provides enough time to allow diffusion to take place.

Infectious disease -can effect all of the body, first sight is usually the lungs.

Caused by bacteria, either mycobacterium tuberculosis or mycobacterium bovis.

Symptoms: persistant cough, tiredness and loss of appetite.

Transmission: air droplets relased into the air when infected cough, sneeze, talk or laugh.

M.Tuberculosis is resistant, it can survive for several weeks when droplets dry. Usually takes close contact to transmit bacterium - spread in families, friends, work, crowded or poorly ventilated areas.

M.Bovis infects cattle, it can be spread through milk, if it contains the bacterium. Milk is pasteurised by heating at high temps to denature bacterium.

Those at risk; living & sleeping in over crowded areas, working in long term care facilities, those with reduced immunity - young, old, homeless, those with AIDS (when they are less likely to resist disease), drug injectors and malnourished.

Course of Infection:

• inhaled by someone not immune
• bacteria grow and divide in upper lungs (plenty of oxygen)
• immune response - white blood cells ingest bacteria
• lymph nodes enlarge - drain lungs PRIMARY INFECTION
• few bacteria remain,few years later re-emerge POST PRIMARY TUBERCULOSIS
• body finds it difficult to control
• alveoli get infected and burst - cavities and inelastic scar tissue
• sufferer coughs up lung tissue - contains bacteria and blood

Vaccines All children in the UK are tested for immunity, those who are not are vaccinated. Attenuated (weakened) strain of M.Bovis (less likey to cause symptoms). Treatment with drugs lasts 6 - 9 months, four drugs as some bacterium do not respond. Some M. Tuberculosis become resistant to drugs, meaning they no longer respond.

Social & Economic Measures to Prevent Spread

• Better education about TB
• More and better housing (to reduce overcrowding and better ventilation systems)
• Improved health facilities and treatments
• Better nutrition - to prevent weakened immune systems that can make you more likely to catch TB

Pulmonary Fibrosis -

scars form on epithelium of lungs, becomes thickened. Oxygen can't diffuse into the blood efficiently due to lengthened pathway. Volume and elasticity of lungs also reduced - problem with breathing out as lungs cannot spring back.

Shortness of breath - loss of space in the lungs, taken up by fibrosis tissue - less oxygen taken in a one breath. Diffusion of oxygen into the blood is slow. Loss of elasticity makes ventilating difficult therefore hard to maintain conc gradient.

Chronic dry cough - fibrosis tissue blocks airways, reflex to cough it up.

Pain & Discomfort in Chest - pressure off damaged tissue, damage due to coughing.

Weakness - reduced intake of oxygen into the blood, less energy released by cells.

Asthma -

allergic reaction, white blood cells on lining of bronchi and bronchioles release histamine, causing lining of airwaves to become inflamed, epithelial cells secrete larger quantities of mucus, fluid leaves the cells and enters airways, muscle around bronchi contracts. Greater resistance of the flow of air in and out of the alveoli, making it difficult to ventilate lungs and maintain conc gradient.

Difficulty Breathing - constricted bronchi & bronchioles, infamed linings, excess mucus and fluids.

Wheezing Sound - ari passing through constricted bronchi & bronchioles.

Tight Feeling in Chest - not being able to ventilate lungs adequatley.

Coughing - reflex response to obstructed bronchi & bronchioles.

Emphysema - (irreversible damage)

Elastin in the lungs becomes permanently stretched, lungs can no longer force air out of the alveoli, surface area of the alveoli reduce and can end up bursting. There is little exchange of gasses due to damaged air sacs and stretched lungs.

Shortness of Breath - difficulty exhaling due to loss of elasticity, if the lungs cannot be emptied then it's difficult to inhale fresh air with oxygen in it.Smaller alvolur surface area leads to a reduced amount of blood moving into the lungs therefore the sufferer breathes more rapidly.

Chronic Cough - Cilia on the bronchi and bronchioles is damaged, therefore mucus & damaged tissue is not removed, the bodies reflex is to remove this by coughing.

Bluish Skin - low levels of oxygen in the blood as there is poor gas exchange in the lungs.