Gas Exchange and Adaptations in Aquatic Animals

Lecture 7: Gas Exchange: Case Studies

• Coping with Hypoxia:
  • Adjusting Fick's principle
  • Oxygen storage
  • Altering ventilation
  • Modifying pigments
  • Refer to Box 24.2 (page 659), 728-734, 669-670 for more information

Gas Exchange: Bimodal Breathers

• Oxygen (O₂): Primarily absorbed from air via lungs
• Carbon Dioxide (CO₂): Mostly expelled into water via gills
• Blood routing is modified to support this dual method

Environmental Hypoxia

• Definition: Low oxygen levels in the environment
• Natural Causes
  • Air breathers, examples
  • Water breathers, examples

Cheat: Spatial Avoidance

• Aquatic surface respiration is a strategy employed by some species

Change X?

• Anatomical representation of X
• Selection pressure towards increasing/decreasing X
• Mathematical reasoning behind the change
• Summary of data in figure 23.8

Changing A: Adaptational

• Titicaca frog as example of adaptation
• Description of the lake and frog

Changing A: Adaptational

• Alternative surface areas for gas exchange (e.g., skin, buccal, or cloacal) that are not initially related to gas exchange, as seen in turtles
• These are secondary uses

Fitzroy River Turtle

• Specialized cloacal gill respiration enabling the turtle to stay submerged for extended periods
• The anatomy of the cloaca, and the muscles involved in the process
• Efficiency of oxygen extraction due to increased surface area and thin barrier between blood and water
• Indicates this species needs to surface less frequently to absorb oxygen

Changing A: Acclimation

• The "hairy" frog (Trichobatrachus robustus) is an example of species that can physiologically adjust to changing environments

Changing A: Acclimation (Carp gills)

• Hypoxia induces adaptive and reversible gill morphological changes in fish
• Carp gills can acclimate to hypoxia over 14 days, recovering in 7 additional days to normal function
• Gill morphology is measured at 0, 3, 7, 14 days during hypoxia and following recovery

Fish Gill Anatomy

• Detailed anatomy of fish gills
• Diagram of the gill arches, lamellae, blood flow and water flow

Changing A: Acclimation (Interlamellar cell mass)

• ILCM (interlamellar cell mass) comprises gill cells not involved in gas exchange
• Visual representation of the changes in gill anatomy due to varying durations of hypoxia and recovery

Changing A: Developmental

• Guinea pigs raised at different altitudes demonstrate differences in alveolar surface area
• Observations show increased alveolar growth and remodeling in higher altitude environments

Maintain P₁ - P₂: Ventilation

• Flexible bag analogy and relationship to pressure
• Dalton's Law implications regarding the effect of altering constituents

Changing Tidal Volume

• Details of lung volumes and capacities (e.g., tidal volume, inspiratory and expiratory reserve volumes, residual volume, vital capacity, total lung capacity, functional residual capacity)
• Visual representation of lung volumes/capacities during different phases of inspiration and expiration
• Definitions of pertinent terms

Modulating Breathing

• Definition of respiratory minute volume (RMV)
• Relationship between tidal volume, breath frequency, and RMV
• Factors influencing RMV

Changing Minute Ventilation

• Pre-Bötzinger complex initiating inhalation
• Stretch receptors halting inhalation
• Schematic of the nervous system's interaction with respiratory muscles

Does O₂ regulate breathing?

• Data on changes in % resting ventilation in relation to oxygen levels for different species

Changing Minute Ventilation

• Factors impacting V₁ or breathing frequency (f)
• Influence of chemical constituents (CO₂, O₂)
• Diagram to illustrate the neural pathways of breathing

Maintain P₁ - P₂: Ventilation

• Factors affecting ventilation in air-breathing and water-breathing animals
• Environmental hypoxia impacting the role of O₂
• Data charts comparing oxygen percentages and resulting breathing rates across species.