Gas Exchange in Animals Flashcards
Barometric pressure
Atmospheric pressure at sea level is 760 mm Hg.
Partial pressure
Partial pressure is the concentration of a particular gas in a mixture.
What is the partial pressure of O2
Partial pressure of O2 (PO2) is 160 mm Hg (21% of barometric pressure).
How does gas exchange relate to animal size?
The need to exchange respiratory gases limits the size and shape of many animals
What are some evolutionary adaptations for distributing gases?
Adaptations in species without internal system for distributing gases: small size, thin flat body; thin body wall around central body cavity
Fick’s law of diffusion
Fick’s law of diffusion applies to all gas exchange systems
Q = DA [(P1-P2)/L]
Q in Fick’s law
Q—the rate of diffusion.
D in Fick’s law
D—the diffusion coefficient: a characteristic of the diffusing substance, the medium, and the temperature. Expressed as mole/m2.s
A in Fick’s law
A—the area where diffusion occurs.
P1 and P2 in Fick’s law
P1 and P2—partial pressures of the gas at two locations.
L in Fick’s law
L—the diffusion path length between the locations.
(P1 – P2)/L in Fick’s law
(P1 – P2)/L is a partial pressure gradient (diffusion gradient).
What determines the concentration of gas in a liquid?
The concentration of gas in a liquid depends on the partial pressure of the gas in the air above the liquid and also on the solubility of gas in that liquid.
How does turbulence affect rate of diffusion?
Turbulence increases rate of diffusion until saturation is reached
why do we need oxygen?
to accept electrons that are created due to break down of food, which eventually forms water from H+ diffusing into mitochondrial matrix
Solubility of gases and temperature
The solubility of gases declines with temperature.
Metabolic cost of ventilation
it takes more energy to move water over gas exchange surface, compared to moving air over it.
Challenges of Water-Breathing for an Ectotherm
- In water, partial pressure of O2 is ~20 times lower than it is in air.
- Diffusion is slower in water than in air.
- The solubility of gases declines with temperature.
- Oxygen needs increase with temperature for an ecotherm.
- It takes more energy to ventilate
gas exchange surface with water than with air.
Why do animals require a specialized body surface for respiratory gas exchange and a system to transport O2 and CO2?
because the two processes require differently characterized cells; gas exchange requires a large surface area, whereas O2 and CO2 transport require large volume
Ventilation
the act of moving the gas exchange medium through gas exchange surfaces.
Is there more or less oxygen in cold water?
In cold water, there is more oxygen.
A denser fluid has a ___ metabolic cost to move.
A denser fluid has a greater metabolic cost to move.
Percentage of O2 in lakes
Lakes 1-2.5% O2
Percentage of O2 in sea water
Water .5-1% O2
What happens to oxygen availability as elevation increases?
Increase in altitude reduces available oxygen for air breathers due to lower partial pressure of oxygen at high altitudes
Does the overall percentage of oxygen in air change as altitude changes?
Partial pressure of oxygen declines with altitude, but the overall percentage of oxygen does not change
Overall atmospheric pressure ____ with altitude
The overall atmospheric pressure declines with altitude, as well as the pressure of all gases
Air at sea level: ___% O2
Air at sea level: 21% O2
Freshwater has ____ dissolved oxygen than saltwater does
Freshwater has more dissolved oxygen than saltwater does
CO2 is relatively ____ exchanged
CO2 is relatively easily exchanged
How does altitude affect the cocentration of CO2?
The concentration gradient of CO2 from air-breathers to the environment is always large; change with altitude is negligible
Is CO2 soluble in water?
CO2 is very soluble in water and is easy for aquatic animals to exchange
Content of CO2 in air
400ppm (0.04%)
Content of CO2 at water surface
~10ppm at water surface
~0.0001%
Adaptations that increase surface area for gas exchange
external gills, internal gills, lungs, tracheae
Why are external gills adaptive?
Increase surface area - also minimize the diffusion path length (L) of O2 and CO2 in water
Why are internal gills adaptive?
Protected from predators and damage
why are lungs adaptive?
internal cavities for respiratory gas exchange with air
What are tracheae
air-filled tubes in insects
Tracheal system in insects
Spiracles open into tracheae that branch to tracheoles, which end in air capillaries (actual gas exchange surfaces)
Spiracles in the abdomen open to allow gas exchange and close to limit water loss; air sacs serves as air reservoir
What force does gas exchange in the tracheal system rely on?
Relies mainly on diffusion; contraction of abdominal muscles helps in ventilation in some insects; note: no reliance on circulatory system
Air capillaries in the tracheal system
Terminal ends of the tracheoles are called air capillaries – this is where Q is maximized an the diffusion happens. The air capillaries are the true gas exchange surface.
How are alveoli adaptive for gas exchange?
- Increased surface area
- Thin film of liquid inside our alveoli and thin walls minimizes diffusion path length
- Minimize the diffusion that takes place in an aqueous medium
- Maximized partial pressure gradients
What is perfusion?
circulating blood over the gas exchange surfaces
What is ventilation?
active moving of the respiratory medium over the gas exchange surfaces
Partial pressure gradients increased by:
- Minimizing the diffusion path length (L) of O2 and CO2
- Perfusion
- Ventilation
Fish gills use _______ to maximize gas exchange
Fish gills use countercurrent flow to maximize gas exchange
In fish, how does taking water through the mouth and gills work, why is it adaptive?
Take in water through their mouth and then open their gills – Maximizes P1 to P2
In fish, what is the operculum?
operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body.
What is special about gas exchange in sharks?
Sharks – don’t have an operculum, so they move swiftly with their mouths open which create water currents that help water move unidirectionally through the gills.
Gill filament
Sheet of epithelium with capillaries inside
What are glls made up of?
Gills are made up of gill filaments that are covered by folds, or lamellae.
What are lamellae?
Lamellae are the site of gas exchange and minimize the diffusion path length (L) between blood and water.
In what direction does blood flow in the lamellae?
Blood flows through the lamellae in the direction opposite to the flow of water
What is the purpose of countercurrent flow?
The countercurrent flow optimizes the PO2 gradient
Because of countercurrent flow, a broad PO2 gradient is maintained over the full length of each gill lamella
Why are bird lungs so efficient?
Bird lungs use unidirectional air flow to maintain
a high PO2 gradient
After exhalation bird lungs have very little dead space (residual volume), why is this adaptive?
helps to maintain a high PO2 gradient.
What are air sacs in birds?
Birds have air sacs that receive inhaled air but are not sites of gas exchange.
Air pathway in birds
Air enters through the trachea, which divides into bronchi, then into parabronchi, and then into air capillaries
Air flows unidirectionally through the parabronchi
tidal ventilation
A type of breathing in which the lungs are inflated with air and then the chest muscles and diaphragm relax and recoil back to their original positions as an animal exhales.
What is the adaptive value of tidal ventilation?
Tidal ventilation in humans produces a residual volume (dead space) of poorly-mixed air that has lower oxygen levels than bulk air outside
Is inhalation passive or active?
active - requires contraction of the diapaphragm and external intercostal muscles.
Why does inhalation enable gas exchange?
Intrapleural pressure becomes more negative than atmospheric pressure
What happens during exhalation?
- Internal intercostal muscles not stretched
- Intrapleural pressure
less negative - Elastic recoil of lung tissue and diaphragm pulls thoracic cavity in; pushes air out
Why does pneumothorax (air in pleural cavity) cause shortness of breath?
pneumothorax is an abnormal collection of air or gas in the pleural space that causes an uncoupling of the lung from the chest wall.
How do respiratory tract secretions help ventilation in the lungs?
- The fluid covering inside of the alveoli has surface tension that makes the lungs elastic.
- A surfactant reduces the surface tension of a liquid.
- Lung surfactant is released by cells in the alveoli when they are stretched.
- It is critical for reducing the work needed to inflate the lungs.
How do lung surfactants relate to premature babies?
- Premature babies may not have developed the ability to make lung surfactant.
- Without it, they have great difficulty breathing and may die from exhaustion and lack of O2.
What are the advantages of using water as a respiratory media?
aquatic breathers can keep respiratory surfaces moist; aquatic breathers gain or lose ions and water via their respiratory surfaces
what are the disadvantages of using water as a respiratory media?
water contains much less oxygen than air, meaning they have to process much more water than the air processes by air breathers; water is denser and much more viscous than air, so aquatic breathers have to expend more energy to ventilate their respiratory surfaces than air breathers
what are the advantages of using air as a respiratory media?
contains much more oxygen than water; have to expend less energy to ventilate respiratory surfaces because air is relatively low in density and viscosity
what are the disadvantages of using air as a respiratory media?
air breathers have to prevent dessication of respiratory surfaces by keeping them moist
what happens to oxygen consumption of fish as water temperature increases?
fish consume more oxygen
why does high water temperature present a double challenge to water breathers?
because oxygen content of water decreases with increased temperature and water breathers consume more oxygen when water temp increases
what is the average % oxygen in air?
~21% at ALL altitudes
why does reduced partial pressure make it difficult for humans to breath?
because as the partial pressure of oxygen decreases, the pressure difference between the atm and inside the lungs diminishes, making it more difficult to inspire
what are the characteristics of gills that make them efficient for gas exchange?
have thin cells, a large surface area and partial pressure gradients via efficient circulation and countercurrent flow
what organisms are more efficient in extracting oxygen from air than mammals?
birds; because air flow in birds is unidirectional continuous and occurs in two cycles through parabronchi; however, this type of flow does not minimize evaporation
what is the low-altitude person typical response to high altitudes? why?
Increased respiration and increased heart rate because body needs to work harder to get oxygen from air
what is the most important feedback stimulus for air-breathing animals?
the level of CO2 in blood
