Tissue in the lungs

For air to reach the lungs, it must travel through the 3 main airways: Trachea, Bronchi, and Bronchioles.

The following requirements determine efficiency:

• Larger airways must be exactly that, larger, so that the required volume of air can flow without obstruction
•  These airways must divide into smaller airways to deliver air to alveoli
• Must be strong enough so that when the pressure drops during inhalation, they don't collapse.
• Must be flexible, to allow movement
• Must be able to stretch and recoil.

Have a similar structure. Different sizes (Bronchi narrower than Trachea).

Thick Walls - consist of several layers of tissue

• Majority of wall is Cartilage( in form of incomplete rings/C-rings in Trachea, less regular in Bronchi)

• Inside Surface of Cartiladge is a layer of Glandular Tissue, Connective Tissue, Elastic Fibres, Smooth Muscle and Blood Vessels. Often called 'Loose Tissue'

• Inner Lining is an Epithelial layer: Majority (Cilliated Epithelial Cells), others Goblet Cells.

• Narrower than Bronchi,

• Cartilage may be found in larger Bronchioles, none in smaller.

• Walls made of mostly smooth muscle and elastic fibres

• Smallest Bronchioles have alveoli at their ends

Cartilage

• Structure (supports Trachea+Bronchi and prevents collapsing)
• Incomplete ring so some flexibility -allows movement without constriction of airways

Smooth Muscle

•  Contracts and narrows lumen (in bronchiole can restrict flow to&from alveoli*)
• *Important if harmful substances are in air (not voulntary e.g asthma)

Elastic Fibres

• when smooth muscle contracts, airway constricts-deforms elastic fibres-, as smooth muscle relaxes -elastic fibres recoil-. Helps to dilate (widen) airway

Goblet Cells and Glandular Tissue

• Secrete Mucas
• Mucas traps tiny particles in the air e.g pollen, bacteria.
• Removing reduces risk of Infection

Cilliated Epithelium

• Epithelium consists of ciliated cells
• Cilia- small hair like structures waft in synch to move Mucus to back of throat
• Mucus swallowed- Stomach acid kills bateria