Diving and Air Breathing Marine Mammals Flashcards
(35 cards)
What do the modifications of the aquatic mammals allow them to do?
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.
How does water pressure increase with depth?
It increases by 1 atmosphere every 10 metres.
What effects does increasing water pressure have?
1) Direct mechanical compression.
2) Any increase in external water pressure must be matched by an increases in air pressure supply.
Where does mechanical pressure have major effects? How have aquatic mammals in general evolved to deal with this?
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.
How have cetaceans evolved to deal with mechanical compression?
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.
How have sea turtles evolved to deal with mechanical compression?
They have a flexible plastron to allow lung collapse.
What are the overriding characteristics of ALL aquatic mammals?
As they secondarily returned to the water, they have all retained lungs and breathe air, but with some modifications.
What are the problems with hyperventilation?
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.
How do diving mammals deal with shallow water blackout?
They have a high tolerance of anoxia in the brain.
What is the alternative to apnoea (holding breath)?
Air supplies. However, the pressure of the supplied air must match the external water pressure, and breathing at increased pressure causes physiological problems.
What is decompression sickness and what is it caused by?
‘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.
What damage does decompression sickness do?
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.
What are the three problems of diving to deeper waters?
Nitrogen narcosis, oxygen toxicity and high pressure nervous syndrome.
What is nitrogen narcosis?
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.
Why does nitrogen narcosis happen?
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.
What is oxygen toxicity?
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.
What is the current gas mixed used for diving? How far can you dive with it?
Oxy-helium mixtures, allow diving to beyond 150 metres.
What is high pressure nervous syndrome (HPNS)?
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.
How can HPNS be avoided?
Slow compression in oxy-helium to these depths does not produce HPNS.
What are the three main approaches to animal adaptations?
Reduction of oxygen usage, tolerance of the effects of apnoea, and greater efficiency of gas exchange and limited non-gaseous storage of oxygen.
How do aquatic animals reduce oxygen usage?
Streamlining to minimise energy used in swimming, reduction of heat loss, reduced heart rate and shunting.
How do aquatic animals reduce their heat loss?
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.
How much do organisms slow their heart rates during immersion?
Seals 120bpm is reduced to 4 or 5 bpm. Green sea turtles down to 1bpm. Humans reduced to 20-50% of normal.
How is blood pressure maintained during episodes of bradycardia?
Increased resistance in the peripheral vascular tissue.
