The effects of fibrosis, asthma and emphysema on lung function.

Fibrosis
Scars in the lung tissue thicken the alveoli increasing the diffusion distance, decrease the volume in the lungs and reduce elasticity. This means that less air can be taken in, and oxygen diffuses more slowly decreasing the bodies supply.

• Shortness of breath- attempt to increase oxygen supply
• Cough- reflex to obstruction of the scars
• Pain- increased pressure
• Fatigue- lack of oxygen for respiration so less ATP (energy) is produced

Asthma

An allergic reaction causes white blood cells to release histamine, a chemical which inflames breathing pathways and constricts them (by contracting muscles)  and increases mucus.

• Difficulty breathing- constriction, inflammation and mucus
• Wheezing- constriction
• Tight feeling- lungs can't ventilate because of airway constriction
• Coughing- reflex to obstruction

Emphysema

Elastic tissue in the lungs looses its elastic properties due to smoking. The lungs can't recoil to push air out effectively, and so old air is not replenished and there is a reduced diffusion gradient. Alveoli break down so surface area and the walls thicken so the diffusion distance is increased. Due to these factors less oxygen can diffuse into the blood.

• Shortness of breath- attempt to increase oxygen supply
• Cough- reflex to obstruction of damaged tissue
• Blueish skin- low oxygen levels in the blood

The course of infection, symptoms and transmission of pulmonary tuberculosis.

Transmission

Mycobacterium tuberculosis and Mycobacterium bovis are bacteria that causes tuberculosis; it transmitted in aerosol (air born droplets) so can be transmitted by coughing, sneezing and spitting- providing some cells are breathed in. It can also be contracted from cows milk.

Risk of infection is increased by:

• Over crowded conditions
• Weak immune system
• Repeated contact with infect people

Course of infection

Primary infection:

• Bacteria enter the lungs and begin to multiply
• White blood cells go to attack them (engulfed by phagocytes) (encased in tubercle by macrophages)
• This inflames lymph nodes so they can't drain the lungs (causing cough)
• Often at this stage most bacteria are destroyed, but some may remain (dormant)

Post-primary infection:

• Years later the remaining bacteria cause a second infection (if immunosuppressed)
• They attack the epithelial cells- causing the infected person to cough it up damaged lung tissue
• The damage allows bacteria to enter the blood and spread to other organs
• The damage decreases the available surface area for gas exchange and makes the diffusion distance further, meaning sufferers will have reduced gas exchange

Symptoms

• Cough
• Fever
• Fatigue