Human gas exchange system - Lungs and Alveoli

Label the diagram

Describe the main structures of the human gas exchange

Name the 2 gas exchange tissues and their functions

• Cartilage is a strong and flexible tissue found along the trachea to help support and and ensure it stays open, while allowing it to move and flex while we breathe

• Ciliated epithelium is a specialised tissue found along the trachea down to the bronchi. Each cell has small projections of cilia which sweep mucus, dust and bacteria upwards and away from the lungs and the epithelium itself

Goblet cells and Mucus

• They’re found scattered throughout the ciliated epithelium in the trachea

• They’re mucus-producing cells that secrete viscous mucus which traps dust, bacteria and other microorganisms and prevents them from reaching the lungs

• The mucus is then swept along by the cilia of the ciliated epithelium upwards and is swallowed

• The mucus and any microorganisms will then be destroyed by the acid in the stomach

Why is ventilation so important

Ventilation ensures that the concentrations gradients of CO₂ and O₂ are maintained

Air moves down a pressure gradient in and out of the lungs

Tidal volume and ventilation rate

• Pulmonary ventilation rate: the total volume of air moved in and out of the lungs during 1 minute

• Tidal volume: the volume of air normally inspired at rest (0.5dm³)

• Ventilation rate: number of breaths in one minute (12-20)

  Pulmonary Ventilation (dm³min^-1) = tidal volume (dm³) x ventilation rate (breaths per min)

What type of epithelium cells do the alveoli have

Simple squamous

Alveolar structure

• Tiny air sacks

• Around 100-300μm in diameter

• Walls of the alveoli are mainly epithelial cells, contain collagen fibres and elastic fibres

• Elastic fibres allow walls to stretch when the alveoli are filled with air during inspiration and then to recoil and help force air out of the lungs during expiration

Capillary endothelium

• The wall of the capillary wrapped around the alveoli is also only 1 cell thick

• The lumen of the capillaries are very small

• RBCs pass through in single file, slowing them down long enough for diffusion of gases to take place

Adaptations of the alveoli and capillary

• Thin epithelium/ endothelium short diffusion pathway

• Inhale/ exhale air so air in alveoli is replenished to maintain steep concentration gradients

• Continuous blood flow to maintain a steep concentration gradient

• Large SA (highly folded membrane)

• Single file RBCs to allow time to exchange gases

• Layer of moisture called the surfactant prevents the walls of the alveoli from sticking to each other - reduces surface tension, prevents collapse of alveoli during exhalation