Chapter 7 - Exchange Surfaces and Breathing Flashcards
What two factors allow diffusion alone to be enough to supply the needs of single-celled organisms?
- Low metabolic activity = low oxygen demand
- High SA:V ratio
What features do all effective exchange surfaces have?
- Large surface area
- Thin layers
- Good blood supply (to maintain steep concentration gradient)
Why do mammals have a high metabolic rate?
They are active and have to maintain their internal body temperature independent of the environment
What are 2 important features of the nasal cavity?
- Hairy lining which traps dust and bacteria from entering the lungs
- Moist and warm surface meaning the air entering the lungs is already of a similar temperature and humidity
What is the trachea?
The main large airway which carries air from the nose down the chest, leading into the bronchi
What is the structure of the trachea?
The trachea is a wide tube supported by incomplete rings of strong, flexible cartilage. These rings stop the trachea from collapsing
Why are the rings in the trachea incomplete?
So food can move down the oesophagus behind the trachea
What are the trachea and its branches lined with?
Ciliated epithelial cells and goblet cells
What do ciliated epithelial cells do in the trachea?
They have ‘hair-like’ structures called cilia on the surface, which move in a rhythmic way, beating mucus away from the lungs
What do goblet cells do in the trachea?
Secrete mucus to trap dust and microorganisms, stopping it from reaching the lungs
Where does the trachea divide, and into what?
In the chest cavity, the trachea splits to form the left bronchus, which leads to the left lung, and the right bronchus, which leads to the right lung
What is the structure of bronchi?
They are similar in structure to the trachea, with the same supporting rings of cartilage, but are smaller
Where do bronchi divide, and into what?
In the lungs the bronchi divide to form many small bronchioles
What is the structure of bronchioles?
The smaller bronchioles have no cartilage rings. They contain smooth muscle, which through constriction and relaxation can control the amount of air reaching the lungs
What are bronchioles lined with and what does this allow?
Bronchioles are lined with a thin layer of flattened epithelial cells, which allow some gaseous exchange to occur
What are alveoli?
Tiny air sacs that are the main gaseous exchange surfaces of the body
What are alveoli made up of?
A layer of thin flattened epithelial cells, along with some collagen and elastin
What do the elastic tissues in the alveoli cause?
Elastic recoil of the lungs
What is elastic recoil?
Where the elastic tissues in the alveoli stretch as air is drawn in, and when they return to the their resting size they help squeeze air back out
Where is lung surfactant found, and what does it do?
Lung surfactant is found on the inner walls of alveoli, and it makes it possible for alveoli to remain inflated, stopping them from collapsing and sticking together
What is the role of water on the inner lining of the alveoli?
Oxygen dissolves in the water before diffusing into the blood
How does inspiration and expiration work?
Air is moved in and out of the lungs due to changes in pressure in the thorax
Is inspiration an energy-using process?
Yes
What happens to the diaphragm during inspiration?
It contracts and lowers
Which intercostal muscles contract during inspiration?
The external intercostal muscles contract, moving the ribcage upwards and outwards, increasing the thoracic volume, decreasing the thoracic pressure.
What happens after the thoracic pressure in less than the pressure of atmospheric air?
Air is drawn in, equalising the pressures inside and outside the chest
Is expiration an energy-using process?
Most of the time, expiration is a passive process, however one can forcibly exhale, which uses energy
What happens to the diaphragm during passive expiration?
It relaxes and moves up
What happens to the external intercostal muscles during passive expiration?
They relax, moving the ribs down and inwards, decreasing thoracic volume and increasing thoracic pressure
What happens during forced exhalation?
The internal intercostal muscles contract, pulling the ribs down hard and fast, and the abdominal muscles contract, forcing the diaphragm up, rapidly increasing thoracic pressure, hence leading to rapid exhalation
Why do premature babies sometimes struggle to breathe, possibly leading to death?
Because the alveoli do not produce enough lung surfactant until week 30, meaning before this the babies alveoli may collapse and stick together, not allowing the baby to breathe
What do peak flow meters measure?
The rate at which air can be expelled from the lungs, and how much much air can be moved out of (and hence also into) the lungs
What do vitalographs measure?
These are a move sophisticated version of the peak flow meters. It produces a graph of the amount of air exhaled, and how quickly it is exhaled.
What do spirometers measure?
They measure many different aspects of lung volume, as well as breathing patterns
What is tidal volume?
The volume of air that moves in and out of the lungs with each resting breath
What is vital capacity?
The volume of air that can be inhaled when the strongest possible exhalation is followed by the strongest possible inhalation
What is inspiratory reserve volume?
The extra volume of air that can be forcibly inhaled after a normal tidal volume inhalation
What is expiratory reserve volume?
The extra volume of air that can be forced out after a normal tidal volume exhalation
What is residual volume?
The volume of air that is left in your lungs after you have exhaled as hard as possible; this cannot be directly measured
What is total lung capacity?
The sum of the vital capacity and the residual volume
What is the equation for ventilation rate?
Ventilation rate = Tidal volume x Breathing rate
What is breathing rate?
The number of breaths taken per minute
What is ventilation rate?
The total volume of air inhaled in one minute
Where does air enter through in insects?
Small opening along the abdomen of insects called spiracles
Why are spiracles closed most of the time?
Because when they are open, water is lost out through them, so they remain closed most of the time to minimise water loss
What controls the opening and closing of spiracles?
Sphincters
When do spiracles open?
When oxygen demand is raised or carbon dioxide levels build up
What takes oxygen from the spiracles to the tissues?
Tracheae
What are tracheae lined with?
Spirals of chitin, which keeps them open, as well as being relatively impermeable to gases, minimising gaseous exchange in the trachea
What does the tracheae branch to form?
Many tiny tracheoles
What is the structure of tracheoles?
Each tracheole is a single, greatly elongated cell with no chitin lining (so they are freely permeable to gases)
Where do tracheoles spread to?
They spread throughout the tissues of the insect, running between individual cells; this is where most of the gaseous exchange occurs
Where is tracheal fluid found?
At the ends of tracheoles in insects
What does tracheal fluid do?
It limits the surface area available for gaseous exchange
What happens to tracheal fluid when oxygen demand increases?
There is a build up of lactic acid in the tissues of the insect, causing the tracheal fluid to leave the tracheoles via osmosis, exposing more surface area to gaseous exchange
What other methods do insects have to increase the level of gaseous exchange?
- Mechanical ventilation
- Air sacs
In insects, how does mechanical ventilation increase the level of gaseous exchange?
Air is actively pumped into the system by muscular contractions of the thorax and/or abdomen, resulting in air being drawn in
In insects, how do air sacs work to increase the level of gaseous exchange?
They act as air reservoirs, and act to increase the amount of air moved through the gas exchange system
Why must bony fish have a specialised gaseous exchange system?
- Diffusion alone would not be enough to supply the oxygen they need
- They have a scaly outer covering which is not permeable enough to allow gaseous exchange
- The density, viscosity and lower oxygen content of water would make conventional diffusion impossible
In what way does gaseous exchange occur in a fish?
Through water flowing over the gills in a one way system
What make up the gills?
Gill lamellae and gill filaments
What are gill filaments?
Gill filaments are large stacks of gill plates and need a flow of water to keep them apart, exposing the large surface area needed for gaseous exchange. They contain gill lamellae
What are gill lamellae?
They are the main site of gaseous exchange in the fish
What is step one of water flowing over the gills?
The mouth is opened and the floor of the buccal cavity is lowered; this increases the volume and lowers the pressure of the buccal cavity, causing water to enter
What is step two of water flowing over the gills?
The opercular valve is closed and the opercular cavity containing the gills expands, lowering the pressure in the opercular cavity containing the gills.
What is step three of water flowing over the gills?
The floor of buccal cavity rises, causing the pressure of the buccal cavity to increase, meaning water moves form the buccal cavity to the opercular cavity, over the gills
What is step four of water flowing over the gills?
The opercular valve opens and the sides of the opercular cavity moves inwards. This increases the pressure in the opercular cavity, forcing water over the gills and out of the operculum
What two adaptions do bony fish have that ensure effective and efficient gaseous exchange?
- Tips of adjacent gill filaments overlap
- Water moving over the gills and blood in the gill filaments move in different directions
Why do the tips of adjacent gill filaments overlapping increases the efficiency of gaseous exchange?
It increases resistance to the flow of water, slowing it down and allowing more time for efficient gaseous exchange to occur
What is the name for the system of water and blood moving in different directions in fish?
Counter-current system
What is the effect of the counter current system in bony fish?
It means an oxygen concentration gradient is maintained between the blood and water along the entire gill, meaning more oxygen diffuses into the blood
What is the problem with a parallel system (blood and water moving in the same direction) in fish?
After an initial steep concentration gradient, the oxygen content in the blood and water would quickly reach equilibrium, meaning there would be no further net movement of oxygen
