Gas Exchange in Humans Flashcards
What is the role of the gas exchange system?
To supply your blood with oxygen, and remove carbon dioxide from your body.
Why do humans need oxygen in the blood?
To take it to respiring cells.
What is the structure of the human gas exchange system?
- As you breathe in, air enters through the trachea.
- The trachea splits into two bronchi, one bronchus leading to each lung.
- Each bronchus then branches off into smaller tubes called bronchioles.
- The bronchioles end in small ‘air sacs’ called alveoli.
Where are gases exchanged in humans?
At the alveoli
What work together to move air in and out of the gas exchange system?
- Ribcage
- Intercostal muscles
- Diaphragm
Where are the intercostal muscles located?
Between the ribs.
What are the two types of intercostal muscles?
- Internal intercostal muscles
* External intercostal muscles
Where are the internal intercostal muscles found?
On the inside of the external intercostal muscles.
What is ventilation?
It consists of inspiration (breathing in) and expiration (breathing out).
What is ventilation controlled by?
The movements of the diaphragm, internal and external intercostal muscles and the ribcage.
What does the structure of the human gas exchange system look like?
image
What happens during inspiration?
- The external intercostal muscles and diaphragm contract.
- The ribcage moves upwards and outwards.
- The diaphragm flattens.
- Increasing the volume of thoracic cavity (the space where the lungs are).
- As the volume of thoracic cavity increases, the lung pressure decreases to below atmospheric pressure.
- Air flows down the trachea and into the lungs (as air always flows down the pressure gradient).
What type of process is inspiration?
Active (it requires energy).
What does inspiration look like?
image
What happens during expiration?
- The external intercostal muscles and diaphragm relax.
- The ribcage moves downwards and inwards.
- The diaphragm curves upwards again (becoming dome shaped).
- This decreases the volume of the thoracic cavity (the space where the lungs are).
- This causes the lung pressure to increase above atmospheric pressure.
- Air is forced down the pressure gradient and out of the lungs.
What does expiration look like?
image
What type of process is expiration?
Passive (it does not require energy).
What is forced expiration?
e.g. if you blow out the candles on your birthday cake.
What happens during forced expiration?
- The external intercostal muscles relax.
* The internal intercostal muscles contract, pulling the ribcage further down and in.
What is said about forced expiration?
That the movement of the two sets of intercostal muscles is said to be antagonistic (opposing).
How many alveoli do lungs contain?
Millions of microscopic alveoli, where gas exchange takes place.
What are the alveoli surrounded by?
A network of capillaries.
What is the structure of the alveoli?
The wall of each alveolus is made from a single layer of thin, flat cells called alveolar epithelium.
What do are the capillary walls that surround the alveoli made of?
Capillary endothelium.
What do these alveoli walls contain?
A protein called elastin (which is elastic).
What does elastin in the alveoli allow for?
It helps the alveoli return (recoil) to their normal shape after inhaling and exhaling air.
What does the alveoli structure look like?
image
How does oxygen move through the gas exchange system?
Air (containing oxygen) moves down the trachea, bronchi, bronchioles into the alveoli.
What allows oxygen to move through the gas exchange system?
Because it moves down a pressure gradient.
What happens to oxygen after it reaches the alveoli?
It moves into the blood, where it can be transported around the body.
What allows oxygen to move around the body in blood?
Because it moves down a diffusion gradient.
How does carbon dioxide move through the gas exchange system?
It moves down its own diffusion and pressure gradient, but in the opposite direction to oxygen, so that it can be breathed out.
What gas exchange occurs in the alveoli?
- Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into haemoglobin in the blood.
- Carbon dioxide diffuses into the alveoli from the blood.
What does alveolar gas exchange look like?
image
Summarise how oxygen moves through the gas exchange system and into the blood
Trachea - Bronchi - Bronchioles - Alveoli
DOWN A PRESSURE GRADIENT
- Alveolar epithelium - Capillary endothelium - Blood
DOWN A DIFFUSION GRADIENT
What do alveoli contain, which increase the rate of diffusion?
- A thin exchange surface (one cell thick = short diffusion pathway).
- A large surface area (millions of alveoli).
- A steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries.
How is the diffusion gradient of oxygen and carbon dioxide between the alveoli and the capillaries maintained?
By the flow of blood and ventilation.
What does blood and ventilation maintaining the concentration gradient look like?
image
