Flashcards in 7.2 Mammilian Gaseous Exchange System Deck (13):
What are the key features of the nasal cavity?
Large surface area with good blood supply, which warns the air to body temperature
Hairy lining, which secretes mucus to trap dust and bacteria, protecting delicate lung tissue from irritation and infection
Moist surfaces, which increase the humidity of the incoming air, reducing evaporation from the exchange surfaces
Describe, in detail, the structure of the trachea
Wide tube supported by incomplete rings of strong, flexible cartilage
Trachea and its branches are lined with a ciliated epithelium, with goblet cells between and below the goblet cells
Explain the purpose of the cartilage in the trachea
Stops the trachea from collapsing
Rings are incomplete so food can move easily down the oesophagus behind the trachea
Describe the roles of the goblet cells and epithelial cells in the trachea and branches
Goblet cells = secrete mucus to trap dust and micro organisms
Cilia = beat and move the mucus along with any trapped dirt and microorganism away from the lungs
Then it is either swallowed or coughed up
Describe the positioning and structure of the bronchus
In the chest cavity the trachea divides to form the left bronchus leading to the left lung and the right bronchus leading to the right lung.
Similar in structure to trachea with same supporting rings of cartilage, but smaller.
Describe the positioning and structure of the bronchioles
The bronchi divide to from many bronchioles.
These have no cartilage.
Diameter = 1 mm or less
Walls contain smooth muscle.
Bronchioles are lined with a thin layer of flattened epithelium, making some gaseous exchange possible.
How do bronchioles control how much air reaches the lungs
When the smooth muscle contracts, the bronchioles constrict.
When it relaxes, the bronchioles dilate.
This changes the amount of air reaching the lungs.
Describe the structure of alveoli
Tiny air sacs = main gas exchange surfaces of the body
Diameter = 200-300 um
Layer of thin, flattened epithelial cells
Has collagen and elastic fibres composed of elastin
Why is elastin important in alveoli?
They allow the alveoli to stretch as air is drawn in.
When the return to their resting size, they help to squeeze air out.
This is known as the elastic recoil of the lungs.
List and explain the main adaptations of the alveoli for effective gaseous exchange.
Large surface area - 300-500 million alveoli per adult lung. SA = 50-75m2
Thin layers - alveoli and capillaries that surround them have walls that are only a single epithelial cell thick = short diffusion distance
Good blood supply - network of 280 million capillaries. Constant flow brings CO2 and carries of O2 = steep concentration gradient
Good ventilation - moves air in and out of alveoli = steep diffusion gradient
What is lung surfactant ?
Makes it possible for the alveoli to remain inflated
What happens when you breathe out ( expire )?
External intercostal muscles relax
Ribs move down and onwards
Elastic fibres in the alveoli return to normal length
This decreases volume of thorax
Pressure inside is greater than pressure of atmosphere
Air moves out of the lungs until pressure inside and out is equal again