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.
The Trachea and Bronchi
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
Role Of Tissues
- Structure (supports Trachea+Bronchi and prevents collapsing)
- Incomplete ring so some flexibility -allows movement without constriction of airways
- Contracts and narrows lumen (in bronchiole can restrict flow to&from alveoli*)
- *Important if harmful substances are in air (not voulntary e.g asthma)
- when smooth muscle contracts, airway constricts-deforms elastic fibres-, as smooth muscle relaxes -elastic fibres recoil-. Helps to dilate (widen) airway
Role Of Tissues ...Continued
Goblet Cells and Glandular Tissue
- Secrete Mucas
- Mucas traps tiny particles in the air e.g pollen, bacteria.
- Removing reduces risk of Infection
- 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