Respiratory

• Respiratory System Function

  • deliver air for gas exchange
  • protect deep alveolar tissues from damage
  • vocalization
  • where appropriate contain olfactory receptors
• • marine mammals conserve water and expired air contains much less moisture than terrestrial mammalsex. dolphins expire air at 70% less saturated than land mammals
• seals have structure in anterior nasal cavity composed bone with dense mesh → captures moisture during exhalation
• basal structures

  • nasal tract
  • larynx
  • trachea
  • lungs
  • bronchi
  • bronchioles
  • alveoli
• Terrestrial:

  Upper Airway

  • nasal and oral cavity connected to some degree, can chew and breathe at the same time
  • can’t breathe and swallow at the same time
  • have an epiglottis which flips open to breathe, associated muscles close the esophagus
  • to swallow it flips closed, open esophagus and closes off trachea
• Blowhole

  • to conserve energy they open them contracting skeletal muscle, passive relaxation to keep blowhole closed
  • cetaceans have blowhole on top of the head except for Sperm whales which are more anterior and slightly to the left
  • mysticetes have 2 odontocetes have 1
• Nares

  • Sirenians have 2 valved nostril system
  • during dive they are passively closed by anterior hinged valves
  • Pinnipeds open by contraction of muscles, relaxing this closes the openings
  • polar bears and sea otters have annular muscles surrounding nares
• • air from nares pass through a nasal cavity to the larynx
  • composed of an elongated epiglottis, cartilage, muscles
  • serves to keep air separate from food going down the esophagus
• in terrestrial, sea otter and polar bears→ epiglottis flips open to block oral cavity while breathing occurs and flips closed to block trachea when swallowing
• in pinnipeds → to keep water out of trachea have the epiglottis as well as 2 large throat cartilages, arytenoids lie close together and touch the posterior part of the epiglottis and powerful muscles
• in Odontocetes→ below air sacs there is bony septum which divides the nasal passage into 2
• Odontocete

  • left and right internal nares open into the nasopharynx
  • larynx has 2 elongated cartilages between trachea and blowhole → often called goosebeak
  • supported by large thyroid cartilage and extends through a small opening in the esophagus into the vertical nares passage which allows food to pass on either side
  • allows air from the blowhole passage to enter the trachea directly
• • in Mysticetes→ larynx- similar to other marine and land mammals but shifted orientation and extra soft tissue
  • larynx is largest of any marine mammal to support the upper airway, thyroid cartilages large
• Hyoid Bones in Humans

  • Functions
  • hold up the tongue which sits above it
  • holds up larynx which is below it
  • transmits the force of muscle that help open the jaw
• Hyoid Bones In pinnipeds

  • in sea lion some places are fused, shape is different
  • in harbour seals it is more separate parts, more horseshoe shape
• • Mysticeti Hyoid Bone
  • well developed in connection to the tongue muscles, very large in U shape ish
• • odontoceti Hyoid bone
  • divisible into basal portion and suspensory portion, many different bones
  • muscles that retract the hyoid apparatus or control the tongue are enlarged and suggested hat they may be important in suction feeding in some species
• Hyoid Bones in Manatee

  • Epihyoid in two positions and two basilhyoid bone in to positions
• In pinnipeds to keep water out of the trachea

  • 2 throat cartilages (arytenoids) lie closely together and touch posterior part of the epiglottis at beginning of trachea
  • larynx has powerful muscles to keep water out
• Most marine mammals have tracheas composed of cartilaginous rings that completely or partially encircle it which is an adaptation for diving
• • Human trachea
  • 16-20 rings C shaped
• • Pinniped trachea
  • complete or incomplete circles and overlap dorsally
• • cetacean trachea
  • short and consists of several cartilaginous rings, generally O shaped
  • 5-7 in Belugas and Sperm whales
  • 13-15 in Fin whales
• • Dugong trachea
  • 4 rings
• • Manatee trachea
  • longer with 8-12 rings
• Diaphragm Musculature in Pig vs Sea Otter

  • in sea otter central tendon is reduced and muscles are larger and more dense, want to ensure they have complete exhalation
• • Manatee diaphragm
  • left lateral schematic representations of the development of the diaphragm of the manatee
  • transverse septum persists in separating the heart and the liver but is not part of the diaphragm does not attach tot he sternum and thus is not pre-hepatic
• • 2 bronchi
  • tube leading to lung lobes which separate into 2 tubes and secondary and tertiary bronchi
  • bronchioles
  • smaller branching of bronchi
  • alveoli
  • microscopic compartments where gas exchange occurs
• Marine mammal lungs are not larger when adjusted to body mass but have important differences
• deeper diving so need flexible chest walls and other structures to allow for more complete emptying of air from alveoli during dive
• Cetaceans

  • lungs have no lobes
  • right lung is usually larger, longer and heavier → results in heart being pushed over towards the left side
  • lungs are more rigid and elastic due to having more cartilaginous support
  • mysticete lung is smaller than odontocete
  • relatively lower lung volume than terrestrial
  • small residual lung volumes → less air left in lungs after exhalation
• • advantages of cetacean respiratory system is based on its efficiency
  • large tidal volume allows exchange nearly all of the depleted air in its lung with each exhalation
  • in land mammals tidal volume ranges from 10-15%, land mammals it is 75% and max of 90%
  • increased tidal volume is better than larger lungs because larger lungs would need more energy to counteract the increased buoyancy
  • tidal volume is both spatially and energetically advantageous
• Cetacean lungs

  • primary bronchi runs almost whole length of the lung
  • few secondary bronchi, turn into small tubes that end in respiratory vesicles which are found along the length of the bronchioles and not at their ends like land mammals
• Sirenians

  • very long and extend almost as far back as the kidneys
  • primary bronchi run almost entire length, very few secondary
  • arrangement of alveoli is unique to their species
  • bronchioles are very muscular and can control where air is moving from one respiratory vesicle to another
  • allows lung volume and air density to be compressed and be used to control buoyancy without flippers or caudal fins
  • lungs are similar to scuba tank in humans
• Pinnipeds

  • both are approx equal in size
  • both have 3 lobes except right lungs has a small additional lobe
  • trachea divided into 2 bronchi, almost immediately as it enters chest which run parallel
  • then bronchi divide into bronchioles and eventually end in alveoli
• Human alveoli -> no cartilage

  Phocid -> bronchiole reinforced completely with muscle and partially with cartilage, muscle extends full length

  Otariidae -> bronchiole reinforced with cartilage mainly, extends to mouth of alveolar sacs, muscle does not extend much

  Odobenid -> bronchiole reinforced completely with muscle and partially with cartilage, muscle extends full length, alveoli originates from cartilaginous airways, offshoot on muscle coat, laterally as alveolated ending
• Sea otters

  • large thoracic cavity for body size
  • right lung has 4 lobes
  • left lung has 2 lobes
  • lungs are large in relation to body size (2.5 times larger than in other mammals of similar size)
  • lungs are used to control buoyancy rather than store oxygen for diving