Diving and Air Breathing Marine Mammals

Use table in notes

All aquatic mammals retained lungs and breathe air - modifications

Modifications take exisitng physiological attributes and develop them = diving forms

• Cope w/ physiological effects of water pressure and temporary anoxia

Water increase by 1atm every 10m

Increasing water pressure = increasing direct mechanical compression

• Increase in external water pressure matched by increase in air pressure supplu

Mechanical compression = effects gasous spaces e.g. lungs, middle ear, sinuses

• No sinuses
• Lungs able to withstand collapse
• Modified thorax - painless compression w/ short sternum and mobile/free ribs

Cetaceans - lungs collapse w/ residual air forced into reinforced bone/cartillage bronchi

• Remain open by impermable to hase
• Minimise hyperbaric O2/N2 toxicity
• Middle ear filled w/ waxy plug

Turtles - flexible plastron to allow lung collapse

Streamlining - minimises energy use

Reduction of heat loss = decrease respiration

• Large size, thick insulation
• Whale blubber <70cm thick
• ~1/3 weight blubber = polar pinnipeds
• Air trapped in dense seal fur

Bradycardia - reduced heartbeat during immersion

• Humans - reduces 20-50% heart rate
• Pinnipeds - 120bpm down to 4/5bpm
• Green sea turtles - 1bpm
• Normal blood pressure maintained by increased resistance in perpheral vasculat tissue

Pinnipeds - venous caval sphincter = contracts in diving to reduce blood to abdominal organs

Shunting - maintenacnce of blood flow to critical organs, reduction to digestive/reproductive tissue

Helps adjust whale's buoyancy

Before diving - cold water enters organ = solid wax

Increase in density - downward force of ~40kg = dive w/ less effort

Respiration in the hunt produces heat = melts spermaceti

Increases buoyancy = easy surfacing

Reduction in sensitivity of brain to hypoxia

Some freshwater turtles - respire anaerobically in hibernation/aestivation

• Marine chelonians least tolerant of hypoxia among reptiles

Seals only require 10+mmHg O2 (humans 19)

• Also tolerant of higher [CO2] and latic acid

Shallow divers e.g. reptiles, birds, sea otters

Not significantly affected by hyperbaric effects = use pulmonary stores of air

Cetaceans/pinnipeds - exhale all but 40-50% lung capacity

Reptiles - little difference in diving and non-diving species

• Exception - Leatherback - haemoglobin conc 50% higher than other reptiles (more like mammals)

Mammals - increase blood O2 carrying capacity by increasing blood volume and size of erythrocytes

• Viscocity limits increases in erythrocyte numbers
• Seals - large speels so can increase erythrocytes during diving periods

Enhanced Bohr shift = unloading of O2 to vital tissue can occur when blood O2 is low

Myglobin can unload O2 at very low PO2 - many marine mammals have high conc of this is blood

Simplest way to overcome apnoea = hyperventilate prior to diving

• Unwanted consequences = shallow water blackout
• Go deep on ascent but syncope (fainting) on descent
  • Drop in partial pressure of O2 in lungs
  • Diffusion gradient - oxygen diffuses from blood into lungs
  • Starves brain of oxygen

Free divers = no greater tolerance to anoxia but train to overcome stimulus to breathe caused by CO2 build up

Diving mammals - high tolerance to anoxia in brain

Alternative to apnoea for human divers = air supply 

• Pressure matches external water pressure
• Breathing increased pressure = phsyiological problems e.g. Caisson disease

The bends

Rapid reduction to surface air pressure = dissolved blood gases come out of solution

• Form bubbles usually 2-12 minutes after surfacing
• Less obvious damage = excessive clotting, loss of blood proteins, tissue/bone necrosis

Haldane produce decompression charts - caculate time needed to ascend so dissolved nitrogen could be exhaled

Diving technology = divers go deeper = higher pressures = new physiological problems

Nitrogen narcosis - divers working at compressed air >4atm (30m)

• Increasingly intoxicated and irresponsible = raptures of the deep
• Increased partial pressures = N2 dissolves into lipids e.g. CNS
  • Acts like anaesthetic gase
• Limits compressed air diving to 60m

Oxygen toxicity - supplying divers with pure oxygen

• Chronic exposure to hyperbaric oxygen is toxic 
• Lung damage and acute exposure

Nitrogen narcosis + oxygen toxicity = novel gas mixtures

Fossil mosasaur vertebrae = significant damage 

• Dysbaric osteonecrosis (nitrogen blockage in bone)

Sperm whale bones = pitting characteristic of the bends

Decompression avoidance could explain why some deep-diving mammals show periodic shallow-depth activity 

• Why gas emboli found in blubber of stranded cetaceans