What is the Davenport diagram and why it is useful?
-describes Acid-Base status in biological systems (blood, cells, etc)
A-B status: pCO2, pH and [HCO3-]
-for an air-breathing animal, the range of pCO2 and [HCO3-] values is relatively high, and the range of pH values is relatively low
What are the four essential components of the Davenport diagram?
- Non-bicarbonate buffering (NBB) line
- top (isopleths)= PCO2 (notice it goes from high to low)
- Y-axis= [HCO3-]
- X-axis= pH
Which fish will have a higher non-bicarbonate buffering (NBB) capacity in its white muscle, a blue fin tuna or a flounder? Why?
- blue fin tuna
- does more anaerobic respiration and needs to buffer the acid in its blood more
The hemolymph of squid can carry 5 ml O2 / 100 mL, and the hemolymph of octopus can carry 1 mL O2 / 100 mL. Which animal do you think will have a higher hemolymph NBB capacity, and why?
- the octopus
- the organism that can carry less oxygen is likely doing anaerobic respiration more
- this indicates a greater need to buffer their hemolymph and a higher NBB capacity (steeper slope)
Describe the three most common types of blood A/B stress experienced by aquatic animals, and how they compensate them
- Respiratory acidosis: caused by elevated pCO2 (e.g. hypercapnia)
- -gills secrete H+ and retain HCO3-
- -pH is compensated
- -CO2 remains elevated
- Metabolic acidosis: caused by addition of H+ (e.g. anaerobic metabolism)
- -Gills excrete H+ and retain HCO3-
- -Restores pH
- -Everything goes back to normal
- Metabolic alkalosis: caused by addition of HCO3- (e.g. post-feeding)
- -Gills excrete HCO3- and retain H+
- -Restores pH
- -Everything goes back to normal
How will the Davenport diagram would look like for the painted turtle and the Crucian carp during the winter?
- painted turtle breathes air while crucian carp does not, so numbers on axes are much larger
- painted turtle has steeper slope
Draw Davenport diagrams for a high performance fish (e.g. a tuna) after 5 and 10 minutes of very intense swimming while it chases a prey. What type of acid-base disturbance took place? How does the tuna compensate?
- metabolic acidosis
- 10 minutes of intense swimming will result in a greater change from the origin
- Gills excrete H+ and retain HCO3- to compensate
Now let’s consider two different aquaculture facilities. One holds 20 seabass, and the other holds 40. Draw the Davenport diagram for one seabass from each facility.
The facility with 40 seabass will have a greater reduction of pH along the NBB line. The compensated final position will be at the same pH for the two, but it will be at a higher HCO3- for the tank with more fish because of the greater amount of compensation.
Draw two Davenport diagrams, one for a shark after eating a 1 kg fish, and another for the same shark after eating a 2 kg fish (~2 and 4 pounds, respectively). What type of acid-base disturbance took place? How does the shark compensate?
- metabolic alkalosis
- the larger fish will cause a greater increase in HCO3- concentration
- the gills will excrete HCO3- and retain H+ to rebalance the pH
How do you think the python will compensate blood alkalosis after a large meal? (e.g. after eating a deer)
- the kidneys could secrete HCO3- to restore the pH
- the lungs could hypoventilate and accumulate CO2 to compensate the pH but the HCO3- concentration would still be higher than before and slightly increased from the extra CO2
