Marine Mammal Diving Physiology

Physiological challenges for marine mammals

Pressure, oxygen storage, heart rate and cardiac output, environemental water tempertature, diving metabolism, lung collapse, aerobic dive limit

pascals law (fluid mechanics)

in a closed system, incresing pressure will be applied to all the fluid equally in all directions

boyles law

pressure is inversely proportional to volume so that gas pressure will decrease as volume increases in size

goose beak

trachea (main conducting tube at back of throat to lungs)

connects to blow hole for breathing

why is heart at angle?

due to the pressures of diving

main muscle types

slow or fast twitch - sporty

enhanced oxidative enzyme activity in areas of high force generation - allow high force generation when muscles used

aspects of mitochondria in muscles

high mitochondrial densities - high usage

interfibrillar and homogenously distributed - reduces diffusion distance

what happens under hypoxic conditions?

maintains aerobic metabolism - no lactate buildup

use flippers to descend then at 300m depth they glide which results in a near resting metabolic rate before ascending, breathing, then returning

thorax in shallow divers

intrathoracic abdominal cavity smaller - 25% of thorax

larger lungs

Thorax in deeper divers

intrathoracic abdominal cavity larger - 60% of thorax

smaller lungs

marine mammal dead space for respiratory system

• all in upper air way

blow hole

paranasal air sacs

sinuses (gaps within skull used for protection against brain implosion)

pharynx

larynx

trachea (with goose beak)

bronchi

what is managed in respiratory system while diving?

gas exchange

oxygen diffusion

ventillation rate

differences of marine respiratory anatomy to terrestrial

• more plates of cartilage (hyalin cartilage- formation)

• terminal and respiratory bronchioles (some gas exchange occurrs in them)

• vascular plexuses along trachea and bronchi (engorge while diving to help supprt, made of veins and arterioloes)

• reinforcement allows continued gas exchange while diving

• short trachea

• primary bronchi have little change in cross-sectional area as it goes down

• secondary bronchi are more numerous

• cross-sectional areas of quaternary bronchi is massive

what do phocids use for airway reinforcement?

oblique muscles in bronchial walls

waht do wallruses and sea otters have for respiratory reinforcement?

mix of cartilage and muscle elements but just distal airways

correlation between lung mass, body mass. and diving depth

lung mass decreases with body size and diving depth

what is the movement of air between lungs and trachea

when diving there is alveolar collapse that forces air from alveoli into trachea and in deeper diving cetaceans the air is moved into the larynx and nasal passages/sacs for echolocation

it is then returned to lungs at ascension and allows return of gas exchange

Differences of exhalation flow rate in cetaceans

maintains high flow rate at exhalation even at low volumes of air due to extent of air stored in trachea

differences in marine mammal lung volumes

in deep diving whales - small volume for body mass

in shallow diving - high volume for body mass

tidal volume

normal breathing rate at rest

cetacean tidal volumes

much larger tidal volume

so normal breathing is 80% of total lung capacity each breath

diving on inspiration animals

cetaceans and otariid pinnipeds

near total lung capacity

diving on exhalation species

phocid pinnipeds

reduce lung volume by 20-60% of total lung capacity

myglobin

single polypeptide chain

one oxygen molecule

found mainly in muscles - 1-2 O2 molec

hemoglobin

four polypeptide chain

four oxygen molecules

found in blood

oxygen storage locations and reasons for variations

respiratory

muscles

blood

varies:

• amongst species

• diving lung volume

• haemoglobin conc

• blood volume

• muscle mass

• myoglobin conc

reasons for oxygen storage and transport variants

• pH

  • Bohr effect

• organic phosphates in red blood cells

• temperature:

  • temp up = causes acidosis - Hb O2 affinity down (unloaded at tissues), higher Co2 conc, lower pH

  • temp down = alkalosis - O2 down, pH increases in blood, O2 staying on Hb

• cetaceans = higher Hb and Mb levels

types of globins (oxygen binding proteins)

hemoglobin (Hb) - transports oxygen

myoglobin (Mb) - stores oxygen in cardiac/skeletal muscles

Neuroglobin (Ngb) - lower conc

Cytoglobin (Cybg) - lower conc

Androglobin (Adgb) - lower conc

respiratory oxygen stores (FiO2) and amount in cetaceans

fraction of inspired oxygen - respiratory oxygen stores

• 15% in diving mammals

what can blood viscosity be affected by?

temperature

shear rate (how cells move past each other)

hematocrit

red blood cell characteristics

how do marine mammals optimize hemorheology while diving?

Hematocrit changes according to diving and viscosity of blood

red blood cell aggregation lower

viscosity is usually lower for diving

hematocrit

the ratio of the volume of red blood cells to the total volume of blood - viscosity

marine mammal heart adaptations

• heart is dorso-ventrally flattened

• angled

• right ventricle is enlarged and has thicker walls - halts compression with depth and helps push blood through

• increased pulmonary vascular resistance

arterial and venous system adaptations

• dense network of sympathetic nerves in proximal/distal arteries (might allow vasoconstriction during dives)

• venous capacitance - large hepatic sinus and posterior vena cava (holds 1/5 of blood volume)

spleen adaptations

• works as filter/storage for red blood cells

• when diving red blood cells get stored then released during dive

adaptations for thermoregulation

• counter current systems in fins and flippers

• veins have increased wall muscles at skin used for thermal stress

• thick blubber and muscle

• pinnipeds have arterial-venous anastomoses - shunts blood from artery to vein to conserve heat/bypasses capillary networks

windkessel effect and usage by phocids and whales

reduction of left ventricular pressure being pumped out by using contraction of elastic wall fibres which allows maintained blood flow to brain during diastole

• phocid seals

aortic arch dilated and leading to bulb

bulb reduces left ventricular pressure being pumped out by contraction of elastic wall fibres

• whales

same as phocid and found in carotid arteries

retia mirabilia

• found in thoracic/cervical/intercostal arteries

• network of blood vessels that supplies brain and spinal cord with blood all the time

• increases thoracic volume of blood

• extensive development sperm whales, dolphins

3 autonomic relfex behavoiurs of cardiovascular dive response

1. apnea

2. parasympathetic mediated bradycardia

3. sympathetic mediated peripheal vasocontriction

4. splenic contraction - releases red blood cells/ caused by low o2 high co2

aims to conserve brain and heart