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 divingOxygenNitrogenWaste products

CO2

Lactate

Forced divingLed to an extreme diving

response The seal didn’t know how long it

would be underwater!

“Natural” Diving

Natural diving

The classical diving responseApnoeaBradycardiaVasoconstriction and reduced

blood flow

Oxygen …or lack thereof

Blo

od

lacta

te

Aerobic dive limit

Fig 25.12

Oxygen stores

Fig. 25.6

Conserving oxygenPeripheral vasoconstrictionHypoperfusion of viceral organsBrain & retina remain normoxic

Body and heart-lung-brain become separate compartments

Muscle O2 depleted

Blood O2 remains highFig. 25.10a

Harbor seal breathing air0.5 s 2 s 6 s

Fully perfused kidney and other viceral organsFig. 25.7 a-c

Harbor seal in forced dive0.5 s 2 s 6 s

No perfusion of kidney and other viceral organs

Bre

ath

ing

Air

Fig. 25.7 d-e

Waste products – CO2

High blood buffering capacity Reduced changes in blood pH

Reduced ventilatory response to CO2 Or increased threshold

Post-dive hyperventilation

Waste products - lactate

Anaerobic metabolism is compartmentalised

Fig. 25.10b

Waste products - lactate

Fig. 25.11

“The Bends” Workers in pressurised mine shafts

and tunneling projects in 19th C Caisson disease

PN2 (lungs) > PN2 (blood & tissue) results in increased N2 in tissues and

fluids Rapid decompression results in N2

coming out of solution Bubbles of N2 gas in joints cause “the

bends” Other symptoms also due to bubbles

and/or high [N2]

Why don’t seals get the bends?

Compressible thorax

Fig.

25.5

Air is compressed out of gas exchange surfaces, so N2 cant diffuse into bloodstream … but nor can O2…

Fig. 24.14

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. 25. 9

The classical diving responseApnoeaBradycardiaVasoconstriction and reduced

blood flow

That’s it!

See you Thursday for the review session

“Fun” (ie: non-examinable) lecture about my research

next Tuesday.