Respiratory System

Unit 1 - P6, M3 - Nathan Pilecki

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Structure of Respiratory System and how it works

Air is inspired through the nasal cavity, the tissue that covers the walls of the nose is full in blood vessels, the heat from the blood in the blood vessels help to heat the air as it passes through. The hairs and mucus in the walls of the nose trap and remove germs and dust particles as the air travels through the nasal cavity. Also, cells in the walls of your nose add small amounts of water to the air to help moisten the air as it travels through.

It then travels through the pharynx, this seperates the trachea and oesophagus so it sepeartes the path for food and air which will help prevent choking.

The air then goes through the Epiglottis, this is a small bit of cartliage which prevents food from entering the trachea and getting caught and preventing any damage that may be caused.

The air then travels through to the larynx (voice box) helps protect the trachea by producing a strong cough reflex if any solid objects pass through to remove these and prevent any solid objects getting caught.

The air then passes through the trachea (surrounded by 15-20 C shaped cartliage to protect and keep it open) which carries the air to the lungs. The trachea has cilia which catches particles of dust which trigger the hairs and this can then be removed by coughing.

The trachea then divides into left and right bronchi which lead into the left and right lung respectively (each lung is separated in lobes. three lobes on the right and two on the left lung where Visceral pleura sticks to the lung surface). The bronchus then divides into more smaller bronchus to create a network of bronchus in the lungs to allow more gaseous exchange to happen as it increases the amount of bronchioles and alveolar sacs so more gaseous exchange can happen.

In the lung, each lobe is surrounded by pleural cavity. In between the pleura is pleural fluid which is used as a lubricant for the lungs when they expand and contract to help the ease of breathing.

Then the air travels to the bronchioles which are bronchi which are divided. These are very narrow tubes, approximately around 1mm in diameter. There is no cartliage in these and leads to alveolar sacs.

The air finally ends up in the alveoli which are very small and thin which allows gaseous exchange with oxygen and carbon dioxide, they are small and thin to allow a higher amount of gaseous exhchange to happen and become more efficient when doing this and these then lead to a dense network of capillaries to allow carbon dioxide out the body.

The diaphragm is a broad band of muscle which is attached to the lower ribs, sternum and lumbar spine located under the lung. Contraction of diaphragm increases the volume of the chest and relaxation, it decreases.

Intercostal muscles are located inbetween the ribs and help form the chest wall and this are important in the mechanics of breathing as they help expand and shrink the capacity of chest cavity. The internal intercostal muscles contract and this allows the lungs and body to exhale and the external intercostal muscles contract and allows the lungs and body to inhale.

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Function of the Respiratory System

Gaseous Exchange - Gaseous exchange happens in the alveoli as they are small and thin. Their thin walls are moist to help the oxygen pass through the walls along with the carbon dioxide. Bunches of alveoli are surrounded by a dense network of capillaries (these have thin walls to allow the efficiency of oxygen and carbon dioxide in and out). The oxygen is diffused into the blood cells when oxygen goes into the alveoli, which then touches the capillaries, the oxygen passes through into the blood stream. Then the carbon dioxide is diffused into the alveoli so the oxygen goes out and the carbon dioxide goes in which then it is breathed out of the body into the air.

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Mechanics of Breathing

The process of the lungs expanding and breathing in air (respiratory cycle) is possible by inspiration and expiration.


  • External intercostal muscles between the ribs contract
  • Ribs and sternum actively move up and outwards
  • The width of the chest increases; allowing more air to enter the body
  • Diaphragm contracts which increases the depth of the chest
  • Capacity of thorax is increased and the elastic tissue of the lungs stretches and lungs expand to fill thoracic cavity
  • Air pressure decreases lower than the atmospheric pressure
  • Air is inspired and then gaseous exchange happens in the alveoli.


  • Internal intercostal muscles contract
  • Rib and sternum moves down and inwards
  • Width of chest decreases
  • Diaphragm relaxes and moves down and depth of chest decreases.
  • Capacity of thorax is decreased
  • Pressure between pleural surfaces increases
  • Elastic tissues of lungs rebound back
  • Air pressure in the alveoli increases to higher than atmospheric pressure
  • After gaseous exchange, air is expired.

Tidal Volume is the amount of air you inspire during normal inhalation when you are at rest.

Vital Capacity is the maximum amount of air a person can expire after he/she has taken in a maximum inspiration.

Residual Volume is the amount of air left in the persons lungs after maximum expiration, there will always be some air in the lungs to prevent them from collapsing.

Control of Breathing (neural and chemical)

Neural is when two neural mechanisms that conduct respiration one is for voluntary breathing and the other for automatic breathing. The voluntary impulse originates in the cerebral cortext layer of the brain and the automatic impulse originates in the medulla oblongata which controls things such as breathing and digestion.

Chemical is when the chemoreceptors in the brain and the heart that receive the amount of oxygen and carbon dioxide in the body and they adjust the rate of respiratory as a result of this to balance any of the changes in levels of the chemicals/oxygen levels. If there is little oxygen, the respiratory rate will increase and vice versa