Lecture #6

Question 1

Explain the “lip mechanism” used by the Tambaqui to increase O2 uptake, and the experiment that established its importance

Answer 1

• during exposure to hypoxia, the lower lip becomes very expanded and facilitates O2 uptake from the surface water by skimming
• fish swims along surface of the water to allow oxygen to diffuse into the highly vascularized lip
• measured blood oxygen content in normoxia, hypoxia with the fish surfacing, and hypoxia where the fish is not allowed to surface
• ~30% difference between allowed to surface or not, showing the lip skimming contributes significantly

Question 2

Explain the changes in oxygen uptake mechanisms experienced by Arapaima as it grows larger.

Answer 2

• as it grows, the skin gets thicker, then the gill lamellae get greatly reduced, then the Air Breathing Organ (ABO) develops
• oxygen can diffuse across the skin
• as it ages, the skin gets thicker (so this no longer works) but the fish can breathe using the gill lamellae
• then, as the oxygen demand continues to increase, the gills are not sufficient so the lamellae gets reduced and the ABO develops instead (some oxygen still from gills)

Question 3

Why is the Arapaima considered an obligate air breathing fish?

Answer 3

• it will drown after 10 minutes if it is denied access to air
• cannot take up enough oxygen using gills alone

Question 4

Painted turtle: why is there massive accumulation of lactate during anoxia? Where is lactate accumulated? What are the two mechanisms that prevent lethal acidification?

Answer 4

• lactate builds up because the turtle converts pyruvate to lactate in order to regenerate NAD+ and continue with fermentation to produce ATP
• uses Monocarboxylate transporter (MCT) to transport H+ and lactate from the cell to the blood
• the lactate accumulates in blood plasma and in the shell
• Mechanisms:
  1. calcium and carbonate from the shell are exported to neutralize the lactate and H+ (CO2+H20, CaLactate)
  2. lactate and H+ move into the shell and are stored there

Question 5

What happens to lactate during recovery from anoxia?

Answer 5

• lactate is oxidized into pyruvate, producing 15 ATP
• excess ATP used to convert pyruvate to glucose and store it as glycogen (gluconeogenesis)
• lactate levels go back to normal
• important energy stored in the bonds, so it would be wasteful to expel it during low-oxygen conditions just because it couldn’t be extracted yet

Question 6

What process produces H+ that can result in harmful acidification during oxygen limitation?

Answer 6

ATP hydrolysis