Biology 272a: Comparative Animal Physiology Diving mammals

Dive record of a male northern elephant seal Fig. 25.4

Dive durations of Weddell seals Fig. 25.1a

Problems with diving  Oxygen  Nitrogen  Waste products CO 2 Lactate

Forced diving  Led to an extreme diving response The seal didn’t know how long it would be underwater!

“Natural” Diving

Natural diving

The classical diving response  Apnoea  Bradycardia  Vasoconstriction and reduced blood flow

Oxygen  …or lack thereof Blood lactate Aerobic dive limit Fig 25.12

Oxygen stores Fig. 25.6

Conserving oxygen  Peripheral vasoconstriction  Hypoperfusion of viceral organs  Brain & retina remain normoxic

Body and heart-lung-brain become separate compartments Muscle O2 depleted Blood O2 remains high Fig a

Harbor seal breathing air 0.5 s 2 s6 s Fully perfused kidney and other viceral organs Fig a-c

Harbor seal in forced dive 0.5 s 2 s6 s No perfusion of kidney and other viceral organs Breathing Air Fig d-e

Waste products – CO 2  High blood buffering capacity Reduced changes in blood pH  Reduced ventilatory response to CO 2 Or increased threshold  Post-dive hyperventilation

Waste products - lactate Anaerobic metabolism is compartmentalised Fig b

Waste products - lactate Fig

“The Bends”  Workers in pressurised mine shafts and tunneling projects in 19 th C Caisson disease  PN 2 (lungs) > PN 2 (blood & tissue) results in increased N2 in tissues and fluids  Rapid decompression results in N 2 coming out of solution Bubbles of N 2 gas in joints cause “the bends” Other symptoms also due to bubbles and/or high [N 2 ]

Why don’t seals get the bends? Compressible thorax Fig Air is compressed out of gas exchange surfaces, so N2 cant diffuse into bloodstream … but nor can O2… Fig

Compressed alveoli… an oxygen supply for resurfacing? Decreasing depth and pressure More O2 becomes available during ascent

Gradations of the diving response Fig. 25.1Fig. 25.2

Gradations of the diving response Fig

The classical diving response  Apnoea  Bradycardia  Vasoconstriction and reduced blood flow

That’s it! See you Thursday for the review session “Fun” (ie: non-examinable) lecture about my research next Tuesday.