2.7.5 Human Gas Exchange System Flashcards
In humans what is the gas exchange surface
The lungs
All gas exchange surfaces have features in common which allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time, they include:
1. Large surface area to allow faster diffusion of gases across the surface
(Breathing Structures Table) Ribs Description
Bone structure that protects internal organs such as the lungs.
(Breathing Structures Table) Intercostal Muscle Description
Muscles between the ribs which control their movement causing inhalation and exhalation
(Breathing Structures Table) Diaphragm Description
Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation
(Breathing Structures Table) Trachea Description
Windpipe that connects the mouth and nose to the lungs
(Breathing Structures Table) Larynx Description
Also known as the voice box, when air passes across here we are able to make sounds
(Breathing Structures Table) Bronchi (pl) Description
Large tubes branching off the trachea with one bronchus (sin) for each lung
(Breathing Structures Table) Bronchioles Description
Bronchi split to form smaller tubes called bronchioles in the lungs connected to alveoli
(Breathing Structures Table) Alveoli Description
Tiny air sacs where gas exchange takes place
(Breathing Structures Table) Pleural Cavity Description
The fluid-filled space between the pleural membranes which reduces friction and allows the lungs to move freely
The passages down to the lungs are lined with, what?
ciliated epithelial cells
Describe the function of Cilia Cells
Cilia cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed
What is mucus made by
The mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet, or cup
What does the mucus do?
The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them from getting into the lungs and damaging the cells there
- Mucus traps particles, dust, and pathogens and cilia beat and push it up and away from the lungs
Exam Tip
You may notice that several of the features of alveoli that make them suited to their function are the same as those that make villi suited to their function or root hair cells suited to their function – the reason for this is because all of these structures are involved in transporting substances across their surfaces – by diffusion, active transport, osmosis or a combination.
So if you learn the features for one, you also know many of the features of the others!
How are alveoli highly specialized for gas exchange
1. There are many rounded alveolar sacs that give a very large surface area to volume ratio
Alveoli are specifically adapted to, do what?
maximize gas exchange
Muscles are only able to pull on bones, what can they not do?
not push on them
Because muscles cannot push on bones, there must be two sets of intercostal muscles to work antagonistically to facilitate breathing, what are they?
External intercostal muscles, pull the rib cage up
Internal intercostal muscles pull the ribcage down
Describe the process of Inhalation
The diaphragm contracts and flattens
The external set of intercostal muscles contract to pull the ribs up and out
This increases the volume of the chest cavity (thorax)
Leading to a decrease in air pressure inside the lungs relative to outside the body
Air is drawn in
Describe the process of exhalation
The diaphragm relaxes it moves upwards back into its domed shape
The external set of intercostal muscles relax so the ribs drop down and in
This decreases the volume of the chest cavity (thorax)
Leading to an increase in air pressure inside the lungs relative to outside the body
Air is forced out
Describe the process of breathing in
- External Intercostal Muscles contract
- Ribcage moves up and out
- Diaphragm contracts and flattens
- Volume of thorax increases
- Pressure inside Thorax decreases
- Air is drawn in
Describe the process of breathing out
- External Intercostal muscles relax
- Ribcage moves down and in
- Diaphragm relaxes and becomes dome-shaped
- Volume of thorax decreases
- Pressure inside thorax increases
- Air is forced out
Exam Tip
You may see the terms inhalation OR inspiration (breathing in), and exhalation OR expiration (breathing out). Both sets of terms mean exactly the same thing, so don’t let them confuse you!
This sequence of events is a common exam question and you should be able to explain in detail what is happening to the external and internal intercostal muscles, the rib cage, the diaphragm, the volume and the pressure-volume of the lungs when breathing in and out.
Remember, if you learn one, the other is almost exactly the opposite
The external and internal intercostal muscles work as, what?
antagonistic pairs (meaning they work in different directions to each other)
When we need to increase the rate of gas exchange (for example during strenuous activity) the internal intercostal muscles will also, do what?
work to pull the ribs down and in to decrease the volume of the thorax more, forcing air out more forcefully and quickly – this is called forced exhalation
What are the differences between inspired air and expired air during ventilation (Oxygen, Carbon Dio, Nitrogen)
Inspired Air (Oxygen): 21% Inspired Air (Carbon): 0.04% Inspired Air (Nitrogen): 78% Expired Air (Oxygen): 16% Expired Air (Carbon) 4% Expired Air (Nitrogen) 78%
