Diving and Air Breathing Marine Mammals

Question 1

What do the modifications of the aquatic mammals allow them to do?

Answer 1

Cope with the physiological effects of water pressure and temporary anoxia by taking existing physiological attributes and developing them, e.g. enhancement of oxygen carrying capacity and muscle respiratory pigments.

Question 2

How does water pressure increase with depth?

Answer 2

It increases by 1 atmosphere every 10 metres.

Question 3

What effects does increasing water pressure have?

Answer 3

1) Direct mechanical compression.

2) Any increase in external water pressure must be matched by an increases in air pressure supply.

Question 4

Where does mechanical pressure have major effects? How have aquatic mammals in general evolved to deal with this?

Answer 4

Mechanical compression effects the gaseous spaces in organisms, e.g. lungs, the middle ear and sinuses. Marine mammals have no sinuses, their lungs can withstand collapse and the thorax is modified to allow painless compression - short sternum and mobile/free ribs.

Question 5

How have cetaceans evolved to deal with mechanical compression?

Answer 5

Any residual air is forced into the bronchi that are reinforced by bone and cartilage, so they remain open but impermeable to gasses. Long collapse and short impermeable airways minimise hyperbaric oxygen and nitrogen toxicity. Their middle ear is filled with a waxy plug.

Question 6

How have sea turtles evolved to deal with mechanical compression?

Answer 6

They have a flexible plastron to allow lung collapse.

Question 7

What are the overriding characteristics of ALL aquatic mammals?

Answer 7

As they secondarily returned to the water, they have all retained lungs and breathe air, but with some modifications.

Question 8

What are the problems with hyperventilation?

Answer 8

Shallow water blackout - on ascent the syncope occurs, as the lungs expand. This causes a drop in the partial pressure of oxygen in the lungs, creating a diffusion gradient from blood –> lungs, starving the brain of O2.

Question 9

How do diving mammals deal with shallow water blackout?

Answer 9

They have a high tolerance of anoxia in the brain.

Question 10

What is the alternative to apnoea (holding breath)?

Answer 10

Air supplies. However, the pressure of the supplied air must match the external water pressure, and breathing at increased pressure causes physiological problems.

Question 11

What is decompression sickness and what is it caused by?

Answer 11

‘The bends’ is caused by rapid reduction to surface air pressure, so that gases dissolved in the blood and synovial fluid under pressure come out of solution and form bubbles - occuring 2-12 minutes after surfacing.

Question 12

What damage does decompression sickness do?

Answer 12

It causes air embolisms, blocking vessels and causing pain, paralysis and even death. Less obvious damage includes excessive clotting, loss of blood proteins and tissue damage. Even a single decompression episode can produce measurable bone necrosis - decreased osteoblasts and increased osteaclasts.

Question 13

What are the three problems of diving to deeper waters?

Answer 13

Nitrogen narcosis, oxygen toxicity and high pressure nervous syndrome.

Question 14

What is nitrogen narcosis?

Answer 14

Divers working w/ compressed air >4 atm became increasingly intoxicated & irresponsible. Governed by ‘Martini Law’ - 15 m = 1 martini, 30 m = 2, 45 = 3, 60 = 4.

Question 15

Why does nitrogen narcosis happen?

Answer 15

At increased partial pressures, nitrogen dissolves readily into lipids - particularly those of the CNS, where it acts in a similar way to other anaesthetic gases. This effectively limits compressed air diving to a max of 60 metres.

Question 16

What is oxygen toxicity?

Answer 16

Early attempts to avoid nitrogen narcosis by using pure oxygen showed that hyperbaric oxygen was toxic. Chronic exposure to oxygen above 0.6 atm produces lung damage and acute exposure, i.e. above 2atm produces involuntary spasms, particularly of facial muscles, which lead to fatal convulsions.

Question 17

What is the current gas mixed used for diving? How far can you dive with it?

Answer 17

Oxy-helium mixtures, allow diving to beyond 150 metres.

Question 18

What is high pressure nervous syndrome (HPNS)?

Answer 18

It causes complete disruption of the nervous system, but its causes remains unclear. Normal descent rates of ~30m/min produced symptoms in some @ 150m & all @ 250m. 350m dives were almost fatal.

Question 19

How can HPNS be avoided?

Answer 19

Slow compression in oxy-helium to these depths does not produce HPNS.

Question 20

What are the three main approaches to animal adaptations?

Answer 20

Reduction of oxygen usage, tolerance of the effects of apnoea, and greater efficiency of gas exchange and limited non-gaseous storage of oxygen.

Question 21

How do aquatic animals reduce oxygen usage?

Answer 21

Streamlining to minimise energy used in swimming, reduction of heat loss, reduced heart rate and shunting.

Question 22

How do aquatic animals reduce their heat loss?

Answer 22

They grow to large sizes, have rete mirable and insulate. Whale blubber can be 70cm thick and =~1/3 of the weight in polar pinnipeds. Air trapped in seal fur provides further insulation, with up to 18000 hairs per cm^2.

Question 23

How much do organisms slow their heart rates during immersion?

Answer 23

Seals 120bpm is reduced to 4 or 5 bpm. Green sea turtles down to 1bpm. Humans reduced to 20-50% of normal.

Question 24

How is blood pressure maintained during episodes of bradycardia?

Answer 24

Increased resistance in the peripheral vascular tissue.

Question 25

What is shunting?

Answer 25

Maintenance of blood flow to critical organs (brain, heart & adrenal glands) and reduced to less critical tissue (digestive & reproductive systems.)

Question 26

How do odontocete (toothed) cetaceans adjust buoyancy?

Answer 26

The spermaceti organ is saturated with cold water before diving, so the wax solidifies. The increase of specific density generates a down force of ~40kg & allows the whale to dive with less effort. During the hunt, O2 consumption produces heat & melts it, increasing buoyancy and allowing easy surfacing.

Question 27

How do air-breathers tolerate the effects of apnoea?

Answer 27

It’s mainly a reduction in the sensitivity of the brain to hypoxia. Some spp of f/w turtle can respire anaerobically during hibernation/aestivation. Humans require 2.5kPa of oxygen, where seals only require 1.3kPa.

Question 28

How do cetaceans increase their efficiency of gas exchange?

Answer 28

They have short airways to reduce ‘dead space’ and flushing is greatly increased by the pumping action of muscles in the walls of the alveoli. Air is retained longer and they can extract 90% of the available oxygen (non diving mammals extract 4-20%).

Question 29

How do shallow divers increase their carrying capacity?

Answer 29

Reptiles, birds and sea otters are not significantly affected by hyperbaric effects so can use pulmonary stores of air, whereas cetaceans and pinnipeds exhale all but 40-50% of lung capacity.

Question 30

How do aquatic reptiles change their haemoglobin storage?

Answer 30

There is little difference between diving and non diving species, apart from the leatherback sea turtle whose haemoglobin concentration is 50% higher than other reptiles and is comparable to mammals.

Question 31

How do mammals increase oxygen carrying capacity?

Answer 31

They increase blood volume (seals have 2x human blood vol per unit weight) and increasing the size of erythrocytes.

Question 32

How do diving mammals deal with the viscosity effects of an increase in erythrocytes?

Answer 32

Most diving mammals have about half the number of circulating erythrocytes. Seals have large spleens and are able to release erythrocytes when diving to increase their number.

Question 33

Why do diving mammals have an increased Bohr shift?

Answer 33

It allows the unloading of oxygen to vital tissues, even when the blood oxygen partial pressure is low.

Question 34

Do marine animals experience ‘the bends’?

Answer 34

Yes. Fossil mososaur vertebrae show significant damage interpreted as dysbaric osteonecrosis. Sperm whale bones also show pitting. Decompression avoidance may explain why some deep diving mammals show periodic shallow depth activity and why gas emboli are found in the blubber of stranded cetaceans.

Question 35

Give examples of animal physiological adaptations to apnoea?

Answer 35

Reduction of energy expenditure - insulation, bradycardia and shunting. Increased tolerance of reduced oxygen and increased carbon dioxide and lactic acid. Increased oxygen carrying capacity in the blood.