Gas Exchange in Humans 3A Flashcards
Describe the structure air passes through as it passes into the lungs.
Nose/Mouth –> Trachea –> Bronchi –> Bronchioles –> Alveoli
Describe the role of surfactant in the alveoli
Maintains moisture but reduces surface tension to stop alveoli collapsing when air pressure falls.
Describe the mechanism of inspiration.
Diaphragm contracts and external intercostal muscles contract. Increases the volume of the thoracic cavity which reduces the pressure. Air moves into the
trachea down the pressure gradient (high to low)
Why do alveoli walls contain elastic fibres?
Allows alveoli to stretch when breathing in and to recoil so that they return to
original shape after exhaling.
Which tissue type comprises alveoli walls?
Squamous (alveolar) epithelium
The trachea is lined with ciliated epithelial cells and goblet cells. Describe the roles of these.
Goblet cells produce mucus. Ciliated epithelial cells waft any mucus containing microorganisms up to the throat where they can be swallowed. This prevents infection. The epithelial cells contain lots of mitochondria to carry out aerobic respiration releasing ATP (energy) to move/waft the cilia.
The trachea and bronchi are lined with cartilage. Describe why.
Provides strength to trachea and bronchus; holds the airway open – prevents collapse of airway when air pressure falls
Describe the roles of the smooth muscle and elastic tissue in the airways.
Can contracts to constrict (narrow) the airways
Describe how alveoli are adapted to reduce diffusion distances.
Squamous (alveolar) epithelium are thin flat cells which give a short diffusion distance pathway for oxygen and carbon dioxide in the alveoli, cell layer only 0.05-0.3µm (1 cell thick).
Describe how air enters the lungs.
Diaphragm contracts (moves down and flattens), external intercostal muscle contracts (moves up and out). Increases volume of thoracic cavity, decreasing pressure. Air moves into the lungs down the pressure gradient.
Describe the process of exhalation.
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.
Why is inhalation an active process?
It requires energy as the muscles are contracting.
Describe the pathway of oxygen from air into the blood (do not describe ventilation).
Diffuses from the alveoli > alveolar (squamous) epithelium (1 cell thick) > capillary endothelium (1 cell thick) > blood down the concentration gradient. Diffuses through cell membrane as small and non-polar.
