B3.1 Gas Exchange Flashcards
What are the three main functions of the respiratory system?
- Ventilation: The exchange of air between the atmosphere and the lungs – achieved by the physical act of breathing
- Gas Exchange: The exchange of oxygen and carbon dioxide between the alveoli and bloodstream across a membrane
- Cell Respiration: The release of ATP from organic molecules – it is enhanced by the presence of oxygen
OVERALL: it provides the body’s cells with the means of obtaining oxygen and eliminating carbon dioxide for our cells to produce ENERGY
what happens during gas exchange?
- Oxygen from the air is taken into the alveoli of the lungs
- Oxygen diffuses into the blood of the surrounding capillaries
- While (2) is happening, high concentrations of carbon dioxide in the blood of the capillaries diffuse into the alveoli to be expelled by the lungs
Diffusion and gas exchange also occurs in the tissues of the body with the blood
What is a gas exchange surface?
a specialized area within an organism where gases are exchanged between the body and the surrounding environment, typically through diffusion
- gas exchange surfaces in an organism are very different
–> different organisms have evolved different mechanisms for getting the gases to the gas exchange surface depending on size, where they live, etc
- All gas exchange surfaces have features in common
–> features allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time
what are some features of gas exchange surfaces?
- Large surface areato allow faster diffusion of gases across the surface
- Thin walls to ensure diffusion distances remain short
- Good ventilation with airso that diffusion gradients can be maintained
- Good blood supplyto maintain a high concentration gradient so diffusion occurs faster
how do you maximize the rate of diffusion for gas exchange?
- Membrane must be permeable
- Specialized respiratory surface must have a large surface area to volume ratio
- Specialized respiratory surface must be moist
- Specialized respiratory surface must be thin
- There must be a large concentration gradient across the respiratory surface
why is the membrane being permeable important in maximising the rate of diffusion for gas exchange?
It’s important because the cell membrane must allow substances (like oxygen and carbon dioxide) to pass through it
why is a large SA:V ratio important in maximising the rate of diffusion for gas exchange?
because with a higher SA:V ratio, there’s a large enough respiratory surface for diffusion to take place
it ensures that, per volume of air or water available, there’s plenty enough surface area for gas exchange to happen
why is the specialized respiratory surface being moist important in maximising the rate of diffusion for gas exchange?
For gas exchange to happen, oxygen and carbon dioxide must first dissolve in water or a solution before they can diffuse across a semipermeable membrane and enter / exit a cell
–> Because of this, a specialized respiratory surface must be moist with water, not dry, in order for ____
why is the specialized respiratory surface being thin important in maximising the rate of diffusion for gas exchange?
it has to be as thin as possible to make the distance the molecules have to travel as short as possible
–> a short diffusion distance means molecules can diffuse faster
why is a large concentration gradient important in maximising the rate of diffusion for gas exchange?
For a concentration gradient to be large, there must be a very high concentration of molecules on one side of the respiratory surface, and a very low concentration of the same molecule on the other side
–> the larger the concentration gradient, the higher the rate of diffusion
Diffusion of gases across gas exchange surfaces can only occur if ______
Diffusion of gases across gas exchange surfaces can only occur if there is a concentration gradient
Diffusion evens out concentration gradients until ______
Diffusion evens out concentration gradients until equilibrium is reached, which would stop gas exchange
–> in order for gasses to continue to diffuse, concentration gradients must be maintained
what maintains concentration gradients at the cellular level?
cell respiration!
- it continuously uses oxygen, so the concentration of O will remain lower inside the cell compared with outside the cell
- it continuously produces carbon dioxide, so the concentration of CO2 will remain higher inside the cell compared to the outside of the cell
what maintains concentration gradients at the tissue level?
the flow of blood!
- because it constantly circulates through capillaries, blood maintains a concentration difference between the blood and the tissue
how do single-celled organisms maintain concentration gradients?
(ex. Chlamydomonas)
Chlamydomonas= a single-celled organism that is found in fresh-water ponds
–> spherical in shape
–> has a diameter of 20μm
- Oxygen can diffuse across the cell wall and cell surface membrane of Chlamydomonas
- The maximum distance that oxygen molecules would have to diffuse to reach the centre of a Chlamydomonasis 10μm, this takes 100 milliseconds
how do root hair cells maintain concentration gradients? (unicellular)
- Root hair cells have aroot hairthat increases the surface area
–> so, the rate of water uptake by osmosis is greater
- The root hair is an extension of the cytoplasm, increasing the surface area of the cell in contact with the soil
–> this maximises the absorption of water and minerals
how does the extensive capillary network maintain concentration gradients?
- The walls of the capillaries are only one cell thick and these cells are flattened
–> keeps thediffusion distance short
- The constant flow of blood through the capillaries means that oxygenated blood is brought away from the alveoli and deoxygenated blood is brought to them
–> thismaintains the concentration gradientnecessary for gas exchange to occur
how do fish gills maintain concentration gradients?
Fish gills = adapted to directly extract oxygen from water as they have a large capillary network
–> the extensive capillary systemthat covers the gills ensures that the blood flow is in the opposite direction to the flow of water (acounter-current system)
- the counter-current system ensures the concentration gradient is maintained along thewhole lengthof the capillary
adaptations in mammalian lungs?
- its ventilation mechanism helps tomaintain a concentration gradientacross an exchange surface
–> ensures there isalways a higher concentration of oxygen in the alveoli than in the blood
- it maximizes surface area through the presence of large amounts of alveoli
–> means there are more sites for gas exchange to occur, therefore increasing the rate of diffusion
in regards to adaptations in mammalian lungs, what are type I pneumocytes and type II pneumocytes?
type I pneumocytes:
extremely thin alveolar cells that make up the alveoli walls, creating a small diffusion distance
type II pneumocytes:
cells within the alveoli that secrete a fluid called surfactant
–> surfactant consists of phospholipids and proteins that form a thin film on the surface of the alveoli
–> surfactant reduces surface tension, preventing the alveoli walls from sticking together and “collapsing” during expiration
what are alveol surrounded by?
The flow of blood through the capillaries maintains a _____
a dense network of capillaries
The flow of blood through the capillaries maintains a concentration gradient for diffusing gases
As soon as the diffusion occurs, the blood is quickly moved away in the blood stream, preventing equilibrium from being reached
Ventilation involves?
the physical movement of air into and out of the lungs
ventilation = breathing
Breathing / ventilation helps to?
maintain the concentration gradients in the alveoli of the lungs
it makes it so that oxygen can always diffuse down its concentration gradient from the air to the blood, while at the same time carbon dioxide can diffuse down its concentration gradient from the blood to the air
Inhalation replaces?
Exhalation removes?
Inhalation
replaces the diffused O2 maintaining a high oxygen concentration inside the alveoli
Exhalation
removes CO2 keeping carbon dioxide concentrations low
The volume of a fixed amount of gas is _______
The volume of a fixed amount of gas is inversely proportional to its pressure
–> so, as the volume of a gas decreases, its pressure increases
(and vice versa)
This explains the pressure changes in the lungs that result from the changes to the volume of the chest cavity during inspiration and expiration
gases move from ____ to _____
Gasses Move from High to Low Pressure
–> Gas molecules move randomly, but the net movement of a gas will be from areas of high pressure to areas of low pressure due to the higher number of molecules in the high-pressure region
This explains the movement of air into and out of the lungs:
- Inspiration: The volume of the chest cavity increases, causing the the pressure inside the lungs to decrease, which draws air into the lungs from the atmosphere
- Expiration: The volume of the chest cavity decreases, causing the pressure inside the lungs to increase, which forces air out of the lungs
What is Breathing?
the active movement of respiratory muscles that enables the passage of air into and out of the lungs
describe the process of breathing
- The contraction of respiratory muscles changes the volume of the thoracic cavity (the chest)
2. When the pressure in the chest is less than the atmospheric pressure, air will move into the lungs (inspiration)
- When the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs (expiration)
what are lungs?
large spongy organs encased by the ribs and diaphragm
- Diaphragm = the muscle that forms the floor of the chest cavity and aids in the breathing process
diaphram
–> when relaxed, it’s dome shaped and projects upward
–> when contracted, it’s flattened
- lungs have a double membrane
–> One layer covers lung while the outer layer is attached to the diaphragm and chest cavity allowing their movement to influence the pressure in the chest cavity
Muscles only do “work” when they?
contract and shorten creating a pulling force or tension causing movement in one direction
Muscles lengthen when they?
relax
–> this is often caused by the contraction of another “opposite” muscle
Muscles that work together in this “opposite” way are called ANTAGONISTIC MUSCLES
The internal and external intercostal muscles and the diaphragm and the abdominal muscles are?
antagonistic muscles used in ventilation
When one is contracted and doing work, the other is relaxed
Describe antagonistic muscle action
- The external and internal intercostal muscles work together antagonistically.
- The diaphragm and abdominal muscles are also antagonistic to each other. Antagonist muscles oppose a specific movement to help to control a motion
