The Respiratory System

Inspiration - Intercostal muscles and diaphragm contract, causing ribcage to more upwards and outwards and the diaphragm flattens, increasing the volume in the thorax. As the volume of the thorax increases, lung pressure increases. This causes air to flow into the lungs. Inspiration is an active process (energy).
Expiration - Intercostal muscles and diaphragm muscles relax causing the ribcage to move down and inwards and diaphragm becomes curved again. Thorax volume decreases, causing the air pressure to increase so air is forced out of the lungs. Expiration is a passive process (no energy).
Alveoli - Huge number in the lungs so there is a huge surface area. They are surrounded by a network of capillaries. Oxygen diffuses out the alveoli, across the alveolar epithelium and into the capillary endothelium and into haemoglobin in the blood. Carbon dioxide diffuses into the alveoli from the blood and is breathed out.
Adapted for gas exchange - a thin exchange surface, one cell thick. Short diffusion pathway makes diffusion faster. A large surface area for faster diffusion.

Pulmonary Ventilation = Tidal Volume x Ventilation Rate

Tuberculosis - When you become infected by it, the immune system cells build a wall around the bacteria in the lungs. This forms small hard lumps called tubercles. Infected tissue within the tubercles dies and the gaseous exchange surface is damaged and so tidal volume is decreased. If the bacteria enters the bloodstream and they can spread to other parts of the body.
Symptoms - Persistent cough, coughing up blood and mucus, chest pain, shortness of breath and fatigue, fever, lose weight due to loss of appetite.
Transmission - By droplet infection, tends to spread where hygiene is poor and where people live in crowded conditions.
Tuberculosis can be treated by a BCG vaccine and antibiotics.

Fibrosis - formation of scar tissue in the lungs. Can  be the result of an infection or exposure to asbestos or dust. Scar tissue is thicker and more elastic so they are not able to expand as much and cannot hold as much air as normal so the tidal volume is reduced. It's also hard to force air out of the lungs because of the elasticity. This means there is a longer diffusion pathway and so a reduction in gas exchange rate so a slower diffusion. They have a faster breathing rate to get enough air into their lungs to oxygenate their blood.
Asthma - The airway becomes inflamed and irritated due to a reaction to dust or pollen. The smooth muscle lining the bronchioles contracts and a large amoount of mucus is produced. This cause constriction of the airways, making it difficult for the sufferer to breathe properly. Air flow in and out is severly reduced so less oxygen can enter the alveoli and into the blood. Inhalers cause the bronchioles to relax, opening up the airways.

Emphysema - Caused my smoking or long-term exposure to air pollution by the particles being trapped in the alveoli. This causes inflammation, which attracts phagocytes to the area. They produce an enzyme which breaks down the elastin. Elastin is elastic which helps the alveoli return to their normal shape after inhaling and exhaling air. Loss of elastin means the alveoli cannot recoil to expel air as well. It leads to destruction of the alveoli walls which reduces the surface area so the rate of gaseous exchange decreases.
Sufferers have an increased breathing rate as they try to increase the amount of air reaching the lungs.