F211 - Exchange and Transport

Gaseuos exchange in the Lungs

• oxygen passes from the air in the alevoli to the blood
• carbon dioxide passes from the blood to the air in the alveoli  
• ...by diffusion

How are the lungs adapted for exchange?

• large surface area - more spcae for meolecules to pass through
• a barrier permebable to oxygen and carbon dioxide
• thin barrier to reduce diffusion pathway - alveolous one cell thick, capilary walls one cell thick
• good blood supply - maintains a diffusion gradient as blood brings carbon dioxide

Inspiration

• diaphram contracts and flattens puching the organs down
• the intercoastal muscles contract raising the ribs
• so the volume of the chest cavity increases
• the pressure in the chest capity drop below the atmopsheric pressure
• air moves into the lungs

Expiration

• diaphram relaxes and is pushed up by displaced organs underneath
• intercoastla muscles relax and the ribs fall
• so the volume of the chest cavity decreases
• the pressure in the chest cavity inccreases above atmospheric pressure
• air moves out of the lungs

What are the functions of the tissues in the lung cells?

Cartilage

• supports the trachea and bronchi by holding them open
• prevents collapse when air pressure is low in inspiration
• not a complete ring so there is some flexability so you can move your neck without restricting airways and so oesophagus can expand during swallowing

Smooth Muscle - can contract to restrict the airway to stop harmful substances entering alveoli

Elastic Fibres - when smooth muscle contracts the elastic fibres recoil to the original size to dilate the airways

Goblet cells and gladular tissue - secrete mucus to trap particles 

Ciliated epithilium - tiny hair like structures move to waft the muucus up the airway to the back of the throat