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Gas Exchange: Humans & Birds
Transcript of Gas Exchange: Humans & Birds
Why is Gas Exchange Needed?
A consequence of cellular respiration.
Cellular respiration creates a constant demand for oxygen and a need to eliminate carbon dioxide gas.
Gases need to be exchanged between the respiring cells and the environment.
How Does Gas Exchange Work?
As a steady flow of carbon dioxide is released from cellular respiration, a steady flow of oxygen is input and vice versa.
What is Gas Exchange?
For gas exchange to occur a gas exchange surface must be present.
Gas exchange surfaces provide a means for gases to enter and leave the body.
Some organisms use the surface of their body as the sole gas exchange surface while others have gas exchange structures.
Gas exchange surfaces must consist of a thin membrane, a large surface area, and be moist.
Fick's law describes the rate of diffusion across gas exchange surfaces.
Humans have a respiratory system which deals with gas exchange.
The respiratory system includes a pair of lungs, located in the thorax, that are connected to the outside of the body by way of the trachea, bronchi, and bronchioles.
Within the lungs, at the ends of the bronchioles, are the alveoli or air sacs.
These alveoli provide a large surface area for the exchange of respiratory gases between the alveoli and blood. Diffusion occurs across the respiratory membrane.
Lung capillaries surround the alveoli where blood transports oxygen via hemoglobin, a respiratory pigment.
How Does Homeostasis Relate to Gas Exchange?
Homeostasis: an organisms way of constantly maintaining an internal balance.
Homeostasis during gas exchange ensures enough oxygen flows throughout the body to release enough CO2.
Gas Exchange: Humans & Birds
3B AP Biology
January 15, 2015
What Happens When Gas Exchange Fails?
If gas exchange is not working correctly, there will not be enough oxygen to circulate through the body, or not enough CO2 to be released.
An excess of CO2 can lead to poisoning of the body, ultimately causing the body to fail.
Lack of oxygen will lead to fatigue; if continued cells will not be able to function or do work, causing cell death.
The air sacs do not necessarily contribute to gas exchange, but do aid in respiration
Air sacs store air allowing birds to constantly take in air, even during exhalation, preventing a lack of oxygen.
The respiratory system of birds is more efficient than that of mammals, transferring more oxygen with each breath.
Unfortunately, this means toxins in the air are also transferred more efficiently. This is one of the reasons why fumes from teflon are toxic to birds, but not to mammals at the same concentration
Birds are able to breathe at high elevations because their lung structure is more efficient.
Birds have lungs, but they also have air sacs. Depending upon the species, birds can have up to seven or nine air sacs.
In general oxygen moves through the trachea into the fist set of air sacs, then the lungs,and finally the last set of air sacs.
Lack of Oxygen
Blocked air ways
Breathing at high altitudes
Most carbon dioxide is carried in the blood as bicarbonate. It diffuses out of the red blood cells and into the plasma to contribute to the buffer capacity of blood.
When carbon dioxide levels are high, hemoglobin releases oxygen.
But what happens when there is an increase or decrease in the carbon dioxide concentration in the blood?
The bicarbonate buffer system helps regulate fluctuations in carbon dioxide.
Increase in CO2
Decrease in CO2
When CO2 concentration increases, the pH of blood decreases due to an increase in H+.
The most common challenges seen involving gas exchange include:
lack of oxygen: an insufficient amount of oxygen is available for organisms to do work.
an excess of CO2: can act as a poison to many organisms
blocked or obstructed air ways
When CO2 concentration decreases, the pH of blood increases due to a decrease in H+.
Increase in CO2
Excretion of excess H+.
Hyperventilation, which decreases CO2 and H+ concentrations.
An increase in bicarbonate production.
Decrease in CO2
Excretion of excess bicarbonate, which increases H+
Hypoventilation, which increases CO2 and H+ concentrations.
Although most birds have evolved to fly at different altitudes, how do birds at extreme altitudes fly without suffering from hypoxia?
Bar-headed geese have several adaptations that allow them to fly at high altitudes without suffering brain hypoxia:
enhanced hypoxic ventilatory system
effective breathing pattern
haemoglobin with a higher affinity for O2
further alterations to metabolic properties of skeletal and cardiac muscles
Due to an increased surface area and O2 affinity, and functional improvements of organs, tissues, and cells, these unique adaptations provide improved uptake, circulation, and efficient utilization of oxygen at high altitudes during hypoxia.
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Scott, G. (2011). Elevated performance: The unique physiology of birds that fly at high altitudes. The Journal of Experimental Biology, 214(15), 2455-2462. Retrieved January 15, 2015, from http://jeb.biologists.org/content/214/15/2455.full
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