7.2 Mammalian GE Systems Flashcards
Where is the Human Gaseous Exchange System and is it a small or large SA:V ratio
Small SA:V ratio because they’re large organisms
High metabolic rate because they are active and have to regulate their temp independently of their environment
Need lots of O2 for respiration
Takes place in the lungs
What is the order of the Pathway of air
O2 into nose/mouth
Down trachea
Down bronchus
Splits into 2 bronchioles
Goes into tiny alveoli sacs that expand to fill with O2.
GE takes place where O2 goes into capillaries and CO2 diffuses back into alveoli to be exhaled out
Key structure: Nasal cavity
Large SA with good blood supply which warms air to body temp
Hairy lining which secretes mucus to trap dust and bacteria
Moist surfaces to increase humidity of incoming air, reducing evaporation from exchange surfaces
Key structure: trachea
Main airway
Wide tube supported by rings of cartilage to prevent collapsing (rings are incomplete so food can move easily behind the trachea in the oesophagus
Trachea and it’s branches lined with ciliated epithelium with goblet cells between and below epithelial cells.
(Goblet cells= secrete mucus onto trachea lining)
Cilia beat trapped dust and bacteria away from lungs, most is then swallowed and digested.
Negative effect of smoking is that it stops cilia beating
Key structure: bronchus
Similar in structure to trachea and split into 2 (right going to right lung and left going to left lung)
Also have sake supporting cartilage rings but are smaller
Key structure: bronchioles
Bronchi divides into many small branches called bronchioles. The smaller bronchioles are 1mm or less and have no rings of cartilage but the walls do contain smooth muscle.
When smooth muscle contracts the bronchioles constrict; when it relaxes they dilate. Bronchioles are lined with a thin layer of flattened epithelium making a small amount of GE possible.
Key structure: alveoli
Tiny air sacs which are main GE surfaces of the body. Unique to mammalian lungs.
Each one has a diameter of around 200-300 micrometers and consists of a layer of thin flattened epithelial cells, along with some collagen and elastic fibres (composed of elastin).
These elastic tissues allow alveoli to stretch as air is drawn in.
When they return to their resting size they help squeeze air out (known as elastic recoil)
What are Adaptations of alveoli
For effective gaseous exchange:
Large SA - around 300-500 million alveoli per adult lung. The alveolar surface area for GE in the 2 lungs combined is around 50-75m^2
Thin layers - only one epithelial cells thick so diffusion is efficient
Good blood supply - all alveoli are covered in capillaries so there is easy access to the bloodstream for oxygen to diffuse into.
Good ventilation - breathing moves air which helps maintain a steep diffusion gradients for oxygen and CO2.
Lung surfactant - inner surface of alveoli are covered in a solution of water, salts and lung surfactant which keeps alveolus inflated.
How does the body ventilate the lungs
Air is moved in and out of the lungs due to pressure changes the thorax (chest cavity) bought about by breathing movements.
Movement of air is called ventilation
Rib cage provides a semi-rigid case within which pressure can lowered compared to the air outside it.
Diaphragm is a broad, domed sheet of muscle which forms the floor of the thorax.
External and internal intercostal muscles are between ribs
Thorax is lined by the pleural membranes which surround the lungs. The pleural cavity (space between the membranes) is lubricated so membranes move easily
What are the features of Inspiration
Energy-using process.
Diaphragm contracts, moves down and flattens.
External intercostal muscles contract moving robs up and outwards.
Volume of thorax increases, decreasing the pressure of the thorax.
It is now lower than the atmospheric air pressure so air is drawn in
(Which equalised pressures inside and outside)
What are the features of Expiration
Passive process.
Diaphragm relaxes, rises and curves.
External intercostal muscles relax bringing ribs in and downwards.
Elastic fibres in the alveoli of lungs return to normal length.
Effect of this decreases volume of thorax, increasing pressure.
Pressure is now greater than atmospheric air pressure so air is pushed out.
You can exhale forcefully using energy. To do this the internal intercostal muscles contract, pulling ribs down faster; abdominal muscles contract forcing diaphragm up to increase pressure of lungs rapidly.
