Gas exchange in humans

Describe the movement of gas in the human exchange system

- Air flows into the mouth then down into the trachea. This splits into two bronchi which branch off further into smaller tubes called bronchioles and then into the alveoli

Describe the function of pleural fluid

- Lubricates the lungs and helps the lungs adhere to the walls of the thoracic cavity by water cohesion

Describe the function and location of cartillage

- Found in the trachea and bronchus.

- Provides strength to the trachea and bronchus

- Holds the airway open and prevents the airway from collapsing when air pressure falls

Describe the function and location of surfactant

- Coats the surface of the lungs

- Phospholipid layer which maintains moisture but reduces surface tension to stop alveoli collapsing when air pressure falls

Describe the function and location of the smooth muscle

- Lining the trachea and bronchioles

- Can contract to constrict the airways

Describe the function and location of the goblet cells

- Lining the trachea and bronchioles

- Secrete mucus which traps particles of dust and bacteria which are breathed into the lungs

Describe the function and location of the Ciliated epithelial cells

- Lining the trachea and bronchioles

- Beat regularly to move mucus upwards towards the mouth to be removed. Helps keep the airway clear and prevent infections.

- Contain lots of mitochondria to provide energy required to move cells.

Describe the function and the location of the elastin

- Lining all of the airways of the alveoli

- Allows lung tissue to stretch when breathing in and filling up the lungs, recoils when breathing out to help force air out of the lungs.

- Allows alveoli to return to original shape after exhaling

Describe the function and location of the squamous epithelium

- Lining the alveoli

- Gives a short diffusion pathway for oxygen and carbon dioxide in the alveoli, cell layer only 0.05-0.3 micrometres wide

Describe the adaptations of alveoli

● Alveolar epithelium and capillary endothekium are very thin- This shortens the diffusion distance of gases

Large number of alveoli- Increases surface area for gas exchange

Capillaries around the alveoli are very narrow- Red blood cells are slowed down increasing the time for diffusion

Large number of capillaries around the alveoli- Maintains a steeo concentration gradient because oxygenated blood is constantly removed

● Constant ventilation of air in and out of lungs- Maintains a steep concentration gradient

Describe the process of inspiration

● Diaphragm contracts(moves down)

● External intercostal muscles contract and the ribcage moves up and out

● Increases volume of the thoracic cavity which reduces the air pressure because there is more space

● Air moves into the trachea down the pressure gradient

● Active process- requires energy

Describe the process of expiration

● Diaphragm relaxes(moves up)

● External intercostal muscles relax, ribcage moves in and down

● Decreases volume of the thoracic cavity which increases the air pressure because there is less space

● Air moves out of the trachea down the pressure gradient

● Normal expiration is a passive process.

Describe how air gets to the blood

● Trachea, Bronchitis, bronchiolitis, alveoli, alveolar epithelium, capillary epithelium, blood