LECTURE 12: Respiration in Animals

• Breathing - physical process
• Respiration - biochemical process
• Breathing - intake of fresh air and removal of stale air
• Echinoderms (e.g. sea stars)

  • acquire oxygen through diffusion across their body surface

  • oxygen from water is in contact with their tube feet and papulae

  or skin gills
• Tracheal System - system of tubules branching to all parts of the body
• Book Lung - found in air-breathing arachnids (spiders and scorpions)
• Mantle Lung - air enters through the pneumostome and flows inside the mantle cavity
• mantle is vascularised through which gas exchange occurs
• Gills

  • can extract over 80% of dissolved oxygen in the water passing over it

  • flow of water is opposite the flow of blood

  • bimodal respiration
• Lungs

  •used by land vertebrates to acquire oxygen in air

  •evolved from progenitor structure found in oldest bony fishes (Hoffman et al., 2016)

  •structure varies depending on the class of vertebrates
• Positive pressure mechanism - air is pushed into the lungs by pressure, in amphibians and some reptiles
• Negative pressure mechanism - air is inhaled by suction, in most reptiles, all birds and mammals
• Amphibians have simple saccular lungs because they can

  perform cutaneous respiration (or exchange of gases through the skin)
• Reptiles - have more complex lungs than amphibians
• Birds - because of high demand for oxygen and the need to dissipate heat, they have developed air sacs in addition to lungs
• Mammals - more complex and lobed lungs better equipped for gas exchange and maintenance of internal body temperature
• birds have small lungs and nine air sacs
• Avian Lungs

  • gas exchange occurs across the walls of the parabronchi in birds

  • unidirectional respiratory system
• In mammalian lungs, gas exchange occurs in sacscalled alveoli
• Mammalian Lungs - bidirectional respiratory system
• Bronchus - is a major airway that branches off from the trachea
• Bronchiole -is a smaller conducting airway with smooth muscles
• Alveoli or air sacs - site of gas exchange
• Inhalation (active process)

  • thoracic cage expands

  • intercostal muscles contract to pull the ribs up

  • diaphragm moves down

  • negative pressure is created inside the lungs

  • air rushes into the lungs
• Exhalation (passive process)

  • intercostal muscles relax bringing the ribs down

  • thoracic cage goes back to its normal size

  • diaphragm recoils to its normal position

  • the lungs are squeezed to release air out
• Carbon Dioxide - produced by cell metabolism and the amount produced depends on the rate of metabolism
• Carbonic acid - formed when CO2 combines with water
• Carbonic acid reaction is catalysed by carbonic anhydrase, which is found in many tissues and organs