The Respiratory System

Humans need to get oxygen into the body and carbon dioxide out of the body.

As you breathe in air enters the trachea.

The trachea splits into two bronchi - one bronchus leading to each lung.

Each bronchus then branches off into smaller tubes called bronchioles.

The brochioles end in small air sacs called alveoli.

The ribcage, intercostal muscles and diaphragm all work together to move air in and out.

Inspiration

The intercostal and diaphragm muscles contract.

This causes the ribcage to move upwards and outwards and the diaphragm to flatten. This increases the volume of the thorax.

As the volume of the thorax increases the lung pressure decreases to below atmospheric pressure.

This causes air to flow into the lungs.

Inspiration is an active process and requires energy.

Expiration

Intercostal and diaphragm muscles relax.

The ribcage moves downwards and inwards and the diaphragm becomes curved again.

The thorax volume decreases, causing the air pressure to increase to above atmospheric pressure.

Air is forced out of the lungs.

Expiration is a passive process and does not require energy.

Lungs contain millions of alveoli where gas exchange occurs.

Each alveolus is made from a single layer of thin, flat cells called alveolar epithelium.

They have a large surface area for the exchange of oxygen and carbon dioxide.

Alveoli are surrounded by a network of capillaries.

Oxygen diffuses out of the alveoli, across the alveolar epithelium and the cappilary endothelium.

Carbon dioxide diffuses into the alveoli from the blood and is breathed out.

Alveoli has a thin cell wall and therfore a short diffusion pathway.

The vast amount and the induvidual folds provide a large surface area.

Pulmonary Volume is the volume of air taken into the lungs in one minute.

Tidal Volume is the colume of air in each breath.

Ventilation Rate is the number of breaths per minute.

Pulmonary Ventilation = Tidal Volume x Ventilation Rate

When someone becomes infected with TB the immune system builds a wall around the bacteria in the lungs. This form small hard lumps known as tubercles.

Infected tissue within the tubercles dies and the gas exchange surface is damaged. This results in a decreased tidal volume. The bacteria can spread if it enters the bloodstream.

Symptoms:

Coughing up blood and mucus

Chest Pain and shortness of breath

TB is transmitted by droplet infection - where the droplets released when someone coughs or sneezes are breathed in by an uninfected person causing them to contract the infection.

Common in poor and crowded areas.

Can be prevented by the BCG vaccine and treated with antibiotics.

Fibrosis is the formation of scar tissue in the lungs which can be a result of infection or exposure to substances such as dust.

Scar tissue is thicker and has less elasticity than normal, healthy lung tissue.

This means the lungs are less able to expand and therefore the tidal volume is reduced. This also makes it harder to force air our of the lungs.

There's a reduction in the rate of gaseous exchange as diffusion is slower over a thicker, scarred membrane.

Symptoms include shortness of breath, a dry cough, chest pain and weakness.

Fibrosis sufferers have a higher breathing rate than normal to get enough air into the lungs and oxygenate the blood.

Asthma is a condition where the airways become inflamed and irritated. This is usually because of an alergy to substances such as pollen and dust.

During an asthma attck the smooth muscle lining the brochioles contacts and a large amount of mucus is produced.

This causes constriction of the airways making it more difficult to breathe. Air flow in and out of the lungs is serverly reduced.

Symptoms include wheezing, a tight chest and shortness of breath.

Attacks can be relieved by drugs that are usually in inhalers. This causes the muscle in the brochioles to relax therfore opening up the airways.

Emphysema is a disease caused by smoking or long term exposure to pollution where foreign particles become trapped in the alveoli.

This causes inflammation which attracts phagocytes to the area. The phagocytes produce an enzyme that breaks down elastin (a protein found in the walls of the alveoli).

Elastin is elastic - it halps the alveoli return to their original shape. Without this elastin the alveoli cannot return to its usual shape after inhaling and exhaling.

It also leads to the destruction of the alveoli walls which reduces the surface area so the rate of gaseous exchange is decreased.

Symptoms include shortness of breath and wheezing.

People with emphysema often have an increased breathing rate to try and get enough oxygen into thier lungs.