Lecture 19

Question 1

Where do marine mammals store oxygen when they dive?

Answer 1

In the:
. Lungs (not a good place)
. Muscle
. Blood

Question 2

Why do marine mammals want to reduce their oxygen usage? How is this done?

Answer 2

So they can spend as much time as possible in their foraging area.
They stop oxygen using processes such as digestion, also the oxygen usage by the muscles that aren’t working (particularly important in birds because they may have two separate muscles blocks?). Can utilise anaerobic metabolism

Question 3

How much oxygen is stored in the lungs in diving marine mammals?

Answer 3

Very little

Question 4

How is oxygen stored in the blood?

Answer 4

Is attached to myoglobin

Question 5

How is oxygen attached in the blood?

Answer 5

Haemoglobin

Question 6

Where are most of the oxygen stores in diving marine mammals?

Answer 6

In the muscles and the blood

Question 7

What do deeper dives have more of?

Answer 7

Myoglobin (to increase their oxygen capacity)

They also tend to have bigger blood volumes

Question 8

What organ tends to be enlarged in marine mammals?

Answer 8

The spleen

Question 9

What is the sphincter and what does it do?

Answer 9

Is a muscle that goes around the venacava that can control the blood going into the heart

Question 10

What happens to the hepatic sinus and the spleen as an animal dives?

Answer 10

They increase in size as the dive duration increases

Spleen volume decreases as the animal dives

Question 11

What does the spleen store in marine mammals? What happens when the animal dives- explain this hypothesis

Answer 11

Oxygenated blood cells
When the animal dives the spleen contracts (splenic contraction) and pushes all of the oxygenated red blood cells into the blood system, goes into the sinus that would go straight into the system but the sphincter closes down and releases that blood gradually over the dive

Question 12

How do diving marine mammals decrease their metabolism?

Answer 12

. Increase their body size
. Swim efficiently, streamlining (shape)
. Hypometabolism (reduce metabolic rate)
- vasoconstriction and redistribution of blood (shutting down blood supply to areas of the body that don’t need it e.g. the intestines, the muscles that aren’t being used) so you aren’t pushing as much blood around so the heart can reduce the rate in which it contracts
- 50% of rearing metabolism costs due to organs
- increased tolerance to hypoxia (just means low levels of oxygen) so reduces urge to go and get more oxygen
- bradycardia (reduced heart rate)

Question 13

How does increased body size decrease metabolism in marine diving mammals? What does this allow?

Answer 13

Blood volume and tissue volume increase in proportion to your size so can be more efficient in utilising your oxygen store. Allows you to dive deeper because you can use oxygen at a lower rate

Question 14

What are the physical adjustments to forced submersion (e.g. in a lab)? Known as the diving response

Answer 14

. Peripheral vasoconstriction
. Reduction in cards in output (amount of blood that is pumped from the heart- mainly due to the lower breath rate)
. Bradycardia
. Reduced overall metabolic rate
. Increased reliance on anaerobic metabolism (increase in lactate levels and obviously oxygen is not reduced to the brain)
. Conserves oxygen

Question 15

When was the diving response thought to happen?

Answer 15

Whenever the animal dived or head it’s head stuck under water

Question 16

Is the diver response real? (Say the response to forced dives and natural dives)

Answer 16

. Forced dives

• no control over duration- doesn’t know how long it has to hold it’s breath for
• maximum response (fear)

. Natural dives

• animals control duration, effort, oxygen use
• graded response

Question 17

What is the aerobic dive limit (ADL)?

Answer 17

ADL is the maximum dive duration that an animal can sustain aerobic metabolism. After this point, an animal would have to rely exclusively on aerobic metabolism

Question 18

What are the two factors use to calculate ADL?

Answer 18

. The useable oxygen stores (some of the oxygen that is taken down with them is stuck in the non-respiratory tubes past 30m- so is there but isn’t useable. Red blood cells also won’t give up all their oxygen and will only give it up under certain levels of oxygen. So it’s hard to say how much is usable so we can only calculate the maximum)
. The metabolic rate of the animal during submersion (very few studies that have looked at this)

(The variables are rarely known but can have a significant bearing on the interpretation of the diving behaviour)

Question 19

What is the calculated ADL? Is it a sudden ‘switch’ or a gradual ‘switch’ from Aerobic to Anaerobic metabolism?

Answer 19

When all the oxygen has been used. But that is the point in which the brain has no oxygen, so the animal will die. So to avoid the animal dying it is likely to be a gradual ‘switch’, so there will be a gradual increase in anaerobic metabolism in those tissue that can support it e.g. the muscles- they can become anaerobic but the brain can’t. So they can extend the length of time they can stay under the water

Question 20

When is the ‘measured ADL’?

Answer 20

The point when the reliance of anaerobic metabolism begins to increase (only 3 studies that have got to the point/ where this has been measured) (the lactic acid is being produced but you don’t see it until the animal starts to breath again because it doesn’t get washed out until the blood flow starts again)

Question 21

What are options that diving marine mammals have when their O2 stores are depleted? What are the consequences?

Answer 21

. Oxidise lactate at the surface- increases recovery time
. Recycle lactate back to glucose at the surface- increased recovery time
. Oxidise lactate during subsequent dives- reduced dive duration
. Recycle lactate during dive- reduced dive duration

Question 22

What is the consequence of going past the ADL?

Answer 22

Recovery time is exponential which means if you have seen prey then you cannot go back down for it