3A - Gas exchange in humans Flashcards
Describe the pathway of air in humans
Pharynx Larynx Trachea Bronchus Bronchioles Alveoli
What are the 2 types of intercostals we need to know about?
Internal and external
What is ventilation?
Breathing in and out.
What is the word for breathing in and out?
Ventilation
What is the word for breathing in?
Inspiration
What is the word for breathing out?
Expiration
Describe inspiration
External intercostals and diaphragm contract.
This causes the ribcage to move up and out and the diaphragm to flatten, increasing the volume of the thoracic cavity.
As the volume of the thoracic cavity increases, the lung pressure decreases (to below atmospheric pressure).
Air always flows from high pressure to low pressure, down a pressure gradient, so air flows down the trachea into the lungs.
Is inspiration active or passive?
Active
Describe expiration
External intercostals and diaphragm relax.
Ribcage moves down and in and diaphragm becomes curved again.
The internal intercostals contract, pulling the ribcage further down and in.
The volume of the thoracic cavity decreases, causing air pressure to increase (to above atmospheric pressure).
Air is forced out of the lungs, down the pressure gradient.
Is expiration passive or active?
Passive
What do the external and internal muscles make up?
An antagonistic pair.
Where does gas exchange in humans occur?
In the alveoli
What is each alveolus made from?
A single layer of thin, flat cells called alveolar epithelium.
How are alveoli adapted for gas exchange?
Huge number of them so large SA for exchange of carbon dioxide and oxygen.
Surrounded by a network of capillaries which maintain a concentration gradient.
Thin exchange surface so short diffusion pathway.
The alveoli are connected by a collagen cable which can contract to push air out of the alveoli.
Apart from the adaptations of the alveoli, what other adaptations are there for human gas exchange?
RBC slowed as they pass through narrow capillaries, increasing the time for diffusion to occur.
RBC flattened against capillary walls, decreasing the diffusion pathway.
Breathing movements keeps lungs ventilated, replacing the external medium.
Flow of blood maintains concentration gradients for exchange.
How does oxygen get into the blood?
Moves down the trachea, bronchi and bronchioles into the alveoli, down a pressure gradient. Once in the alveoli, the oxygen diffuses across the alveolar epithelium, down a diffusion gradient, then the capillary endothelium, ending up in the capillary itself.
What is the structure of the trachea&bronchi?
Has cartilage rings for support.
Walls are lined with goblet cells and epithelial cells.
What is the structure of the bronchioles?
Heavily branched.
Muscular walls to regulate air flow in and out of the alveoli by contraction of the pipes.
What is the structure of the alveoli?
100-300μm across.
At end of bronchioles.
Stretch to pull air in.
Collagen and elastic fibres help the alveoli.
What do the goblet and epithelial cells do in the trachea&bronchi?
Goblet cells produce mucus to stop pathogens entering the lungs.
Epithelial cells waft the mucus out of the lungs.
