Diving anatomy and physiology. Week 3

Question 1

Intended learning outcomes

Answer 1

• Describe the main anatomical and physiological adaptations for diving, as well as different diving behaviours in cetaceans and pinnipeds

Question 2

Diving allows for using the ocean in 3D

Answer 2

– Foraging
– Mating
– Resting (sleeping)
– Predator avoidance

Question 3

How to adapt to high pressure, no oxygen and increasing CO2 and lactate?

Answer 3

– Anatomical and physiological adaptations aimed at oxygen uptake and storage in body
– Behavioural adaptations to conserve oxygen when diving

Question 4

Respiratory adaptations

Answer 4

• Respiration aimed at oxygen uptake
  – Lungs are elongated and tissue is elastic
  – Flexible rib cage and cartilaginous rings in trachea allowing lungs to empty and collapse during diving
  – Neutral buoyancy facilitate gliding during dive – Collapse of lungs avoid decompression sickness
• Active opening of nostrils/blow holes
• Rapid exhale and inhale (0.1s in small odontocetes)
• 90% of air is renewed in a single breath (10% in humans)
• 90% of oxygen diffuse to blood system (20% in humans)

Species differ in lung mass, total lung capacity (TLC) bronchiole structure, cartilage and myoelastic sphincters
* Phocoenid, delphinid and monodontid bronchioles contain cartilage to never collapse fully; allows for rapid breathing
* Ziphids, kogids and physeterids bronchioles contains muscles and collapse fully to allow for deep diving

Question 5

Circulatory adaptations

Answer 5

• Aimed at oxygen storage and conservation!
• Oxygen storage in blood
  – Increased blood volume (3-6 times)
  – Many red blood cells (and hemoglobin) per volume of blood (hematocrit levels: 40-60%)
  – Blood and oxygen storage in tissue with spiralled blood vessels (retia mirabilia)
• High myoglobin levels in muscle cells
• Glycogen stores in heart for anaerobic diving
• Blood and oxygen storage in the large spleen (phocids)

Question 6

The dive response

Answer 6

Regulation of blood flow
Reduced heart rate

Question 7

Regulation of blood flow (vasoconstriction)

Answer 7

– Restriction of blood flow to kidneys, liver and digestive system, as well as extremities (ischemia)
– Reduced body temperature (hypothermia)
– Reduced metabolism
– Cooling of brain to conserve oxygen

Question 8

Reduced heart rate (bradycardia)

Answer 8

– 5% of normal rate in some phocids
– 4 beats/min in Weddell seal
– Cognitive control of heart rate in porpoises …and perhaps all marine mammals?

Question 9

Aerobic dive limit (ADL)

Answer 9

• Dives within ADL–Aerobic metabolism
  – Reduction of heart rate (bradycardia)
  – Restriction of blood flow (ischemia)
  – Possible to make many dives, with little rest in between
• Dives exceeding ADL–Anaerobic metabolism
  – Anaerobic metabolism produce lactate and hydrogen
  – Switch over to anaerobic metabolism during activity bursts – Requires longer resting/recovery period between dives

Question 9

Aerobic dive limit (ADL)

Answer 9

• Dives within ADL–Aerobic metabolism
  – Reduction of heart rate (bradycardia)
  – Restriction of blood flow (ischemia)
  – Possible to make many dives, with little rest in between
• Dives exceeding ADL–Anaerobic metabolism
  – Anaerobic metabolism produce lactate and hydrogen
  – Switch over to anaerobic metabolism during activity bursts – Requires longer resting/recovery period between dives

Question 10

Diving behaviour

Answer 10

• Diving behaviour defined by
  – Prey availability, predator avoidance, etc
  – ADL (= physiological/anatomical adaptations)
• Rules of thumb:
  – Most dives within ADL; few dives exceed ADL
  – Animals seldom dives to max dive depth – Phocids dive deeper than otarids
  – Odontocetes dive deeper than mysticetes
  – …but very large variation!

Question 11

Diving behaviour

Answer 11

• Diving behaviour defined by
  – Prey availability, predator avoidance, etc
  – ADL (= physiological/anatomical adaptations)
• Rules of thumb:
  – Most dives within ADL; few dives exceed ADL
  – Animals seldom dives to max dive depth – Phocids dive deeper than otarids
  – Odontocetes dive deeper than mysticetes
  – …but very large variation!

Question 12

Example: Cuvier’s beaked whale

Answer 12

• Gliding during descent to conserve oxygen(green)
• Short burst activity during foraging and ascent (blue)
• Beaked whales make recovery dives to adjust gas levels and avoid decompression sickness
• Human activities (and predators) can disturb the dive…
• Behavioral aerobic dive limit (bADL) estimated from 23 tagged animals making a total of 3680 dives
• 95% of all dives are shorter than 77 min
  *When surfacing after a dive, they change direction to confuse orcas

Question 13

Mammal myoglobin

Answer 13

• Myoglobin (Mb) located in muscles
• Relatively short; consists of 153 amino acids
• Binds oxygen better than hemoglobin
• Little effect by pH and other allosteric effectors
• High charge of myoglobin (ZMb) increase O2 in muscles
• Convergent evolution in several mammalian lineages