Chapter 7 - Exchange Surfaces Flashcards
Why do we need specialized exchange surfaces?
Metabolic activity of a single cell is too low so O2 demand and CO2 production is low (in unicellular)
SA:V ratio in unicellular organisms is high
How do you calculate SA:V ratio?
ratio = surface area/volume
Volume is a sphere not a cube!
What are the features of an efficient exchange surface? Why?
Increased surface area - provides area needed for exchange
Thin layers - short diffusion distance, makes it faster
Good blood supply - steeper concentration gradient, substances are constantly delivered and received
Ventilation - maintain diffusion gradient
What are the key structures of the mammalian gas exchange system?
Nasal cavity
Trachea
Bronchus
Bronchioles
Alveoli
What are the features/functions of the nasal cavity?
Large surface area with good blood supply - warms air up to body temperature
Hairy lining - secretes mucus to trap dust and bacteria
Moist surface - reduces evaporation
What are the features/functions of the trachea?
Flexible rings of cartilage - stops the trachea from collapsing and incomplete for the oesophagus
Lined with ciliated epithelium with goblet cells - cilia brush dust and bacteria away from lungs, goblet cells secrete mucus
What are the features/functions of the bronchus?
Similar structure and functions as the trachea but smaller
What are the features/functions of the bronchioles?
Small bronchioles have no cartilage rings
Smooth muscle can contract and relax, this causes them to constrict and dilate allowing control of amount of air to reach lungs
Thin layer of flattened epithelium - some gas exchange possible
What are the features/functions of alveoli?
Tiny air sacs
Thin, flattened epithelial cells (some with collagen and elastic fibres, allowing them to stretch known as elastic recoil)
Large surface area - more space for exchange
Thin layers - short diffusion distance (1 cell thick)
Good blood supply - steep concentration gradient and constant supply of O2 and CO2
Good ventilation - steep concentration gradient
What is the mechanism of inspiration in mammals?
Taking air in
Diaphragm contracts and flattens
External intercostal muscles contracts
Ribs move upwards and outwards
Volume of thorax increases so pressure decreases and draws air in
What is the mechanism of expiration in mammals?
Breathing out air
Diaphragm relaxes and moves up
External intercostal muscles relax
Ribs move down and inwards
Volume of the thorax decreases and pressure increases so air moves out of the lungs
In forceful expiration internal intercostal muscles and abdominal muscles contract too to force the air out quicker
How can lung capacity be measured?
Peak flow meter
Vitalographs
Spirometer
What is tidal volume?
The volume of air that moves into and out of the lungs with each resting breath
What is vital capacity?
The volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible breath
What is inspiratory reserve volume?
The maximum volume of air you can breathe in over and above a normal inhalation
What is expiratory reserve volume?
The maximum volume you can force out of your lungs over and above the normal tidal volume of air you breathe out
What is residual volume?
The volume of air that is left in your lungs when you have exhaled as hard as possible. This cannot be measured directly.
What is total lung capacity?
The sum of the vital capacity and the residual volume
What is breathing rate?
Number of breaths taken per minute
What is ventilation rate?
Total volume of air inhaled in one minute
ventilation rate = tidal volume x breathing rate
How does gas exchange take place in insects?
Air enters in the spiracles
Goes into the tracheae and enters the tracheoles
At the end of the tracheoles is tracheal fluid which absorbs the oxygen from the air
What is a spiracle?
Small openings between the abdomen and thorax on an insect
Air enters and leaves through them however so does water, therefore they can be opened of closed by sphincters
The sphincters open as oxygen demand increases
What is a tracheae?
In insects
Lead away from the spiracles
Tubes are lined with chitin, which hold them open
Chitin is relatively impermeable to gases so little gas exchange takes place in the trachea
What are tracheoles?
Lead away from the tracheae
Each one is a greatly elongated cell with no chitin lining so they are freely permeable to gases so lots of gas exchange takes place here
What is tracheal fluid?
Found at the end of tracheoles
Absorbs oxygen which limits the penetration of air for diffusion
When oxygen demand builds up, lactic acid is produced and so water moves out of the tracheoles by osmosis so there is more surface area for gas exchange
What is mechanical ventilation?
Air is actively pumped into the system by muscular pumping of the thorax or abdomen
This draws air into or out of the spiracles due to changes of pressure
What is collapsible enlarged tracheae or air sacs?
Act as revivors of air
Increase volume of air moved through the gas exchange system
Can be inflated or deflated by ventilating movements of the thorax or abdomen
What is gas exchange for fish different to gas exchange for mammals?
Mammals live on land and inhale air into the lungs
Fish have no lungs and live in water which has lower concentrations of oxygen
What is gill lamellae?
Main site of gaseous exchange
Rich blood flow to maintain a steep concentration gradient
Large surface area to increase the area that oxygen can diffuse into
What are gill filaments?
Occur in large stacks
Need a flow of water to keep them apart to expose the large surface area needed for gas exchange
What is the operculum?
Bony flap covering the gill cavity
Maintains a flow of water over the gills
How does the fish opening it’s mouth affect gas exchange?
Increases the volume of the buccal cavity
Pressure lowers drawing water in
Opercular valve closes
Opercular cavity expands
What adaptations does the fish gas exchange system have to make it efficient?
Large surface area - lots of area for oxygen to be absorbed
Rich blood supply - Maintain steep concentration gradient
Thin layers - short diffusion distances
Tips of adjacent gill filaments overlap - creates resistance of water to slow it down and more oxygen can be absorbed
Counter current flow
What is counter current flow?
Water and blood are moving in opposite directions
Maintains a steep concentration gradient
Allows more gas exchange to take place as it can take more oxygen from the water without reaching equilibrium
