Gas Exchange in Humans Flashcards
What is the organ of gaseous exchange in humans (and other mammals)?
The lungs
Why is it important for the lungs to be efficient?
To allow mammals to be very active animals
What are the main components of the human gas exchange system?
Trachea, bronchi, bronchioles, alveoli
What is the alveoli?
The site of gaseous exchange
What are the trachea and bronchi held open by, why is this beneficial?
They are held open by bands of cartilage to prevent them from collapsing and to ensure constant air flow
What is the wall of an alveolus made up of?
A single layer of squamous epithelium
What is an advantage of squamous epithelial cells being very thin?
They are freely permeable to respiratory gases
How many cells this are the blood capillaries surrounding the alveoli?
One cell thick
Where does oxygen dissolve on the epithelium and where does it diffuse into?
Oxygen dissolves in the film of water on the surface of the epithelium and diffuses across into the blood capillary
What do the alveolar epithelium secrete?
A phospholipid surfactant
What is the role of the phospholipid surfactant secreted by the alveolar epithelium?
They decrease surface tension and so prevent alveoli from collapsing as they recoil after each breath
What is ventilation?
The exchange of air in the lungs with ambient air.
What does ventilation ensure?
A steep diffusion gradient is maintained across the alveoli
How is ventilation achieved?
By changes in the volume of the thoratic cavity and associated changes in pressure in the lungs
What happens to the external intercostal muscles in inspiration?
They contract
What happens to the internal intercostal muscles in inspiration?
They relax
How does the rib cage move in inspiration?
The rib cage moves up and out
What happens to the diaphragm muscle in inspiration?
It contracts and moves down
What happens to the volume of the thoratic cavity in inspiration?
It increases
What happens to pressure in the lungs in inspiration?
Pressure in the lungs decreases and becomes lower than atmospheric pressure
What happens to air flow in inspiration?
Air flows into the lungs down a pressure gradient
Describe the process of inspiration
External intercostal muscles contract
Internal intercostal muscles relax
Rib cage moves up and out
Diaphragm muscle contracts and moves down
Volume of thoratic cavity increases
Pressure in the lungs decreases and becomes lower than atmospheric pressure
Air flows into the lungs down a pressure gradient
What happens to the external intercostal muscles in expiration?
They relax
What happens to the internal intercostal muscles in expiration?
They contract
How does the rib cage move in expiration?
It moves down and inwards
What happens to the diaphragm muscle in expiration?
Relaxes and moves up
What happens to the volume of the thoratic cavity in expiration?
It decreases
What happens to pressure in the lungs in expiration?
Pressure in the lungs increases and becomes higher than atmospheric pressure
What happens to air flow in expiration?
Air flows out of the lungs down a pressure gradient
Describe the process of expiration
External intercostal muscles relax
Internal intercostal muscles contract
Rib cage moves down and inwards
Diaphragm muscle relaxes and moves up
Volume of thoratic cavity decreases
Pressure in lungs increases and becomes higher than atmospheric pressure
Air flows out of the lungs down a pressure gradient
