Respiration is the process of obtaining oxygen from the external environment & eliminating CO2.

• External respiration - oxygen and carbon dioxide exchanged between the external environment & the body cells
• Internal respiration - cells use oxygen for ATP production (& produce carbon dioxide in the process)

Adaptations for external respiration:

    1 - Primary organs in adult vertebrates are external &  internal gills, swim bladders or lungs, skin, & the buccopharyngeal mucosa

    2 - Less common respiratory devices include filamentous outgrowths of the posterior trunk & thigh (African hairy frog), lining of the cloaca, & lining of esophagus

Respiratory organs:

• Cutaneous respiration
• respiration through the skin can take place in air, water, or both
• most important among amphibians (especially the family Plethodontidae)
• Gills (see Respiration in Fishes)
• Cartilaginous fishes:
• 5 ‘naked’ gill slits
• Anterior & posterior walls of the 1st 4 gill chambers have a gill surface (demibranch). Posterior wall of last (5th) chamber has no demibranch.
• Interbranchial septum lies between 2 demibranchs of a gill arch
• Gill rakers protrude from gill cartilage & ‘guard’ entrance into gill chamber
• 2 demibranchs + septum & associated cartilage, blood vessels, muscles, & nerves = holobranch

• Bony fishes (teleosts):      (See 'Ventilation in Teleost Fishes')

• usually have 5 gill slits
• operculum projects backward over gill chambers
• interbranchial septa are very short or absent

• Agnathans:
• 6 - 15 pairs of gill pouches
• pouches connected to pharynx by afferent branchial (or gill) ducts & to exterior by efferent branchial (or gill) ducts

•  Larval gills:
• External gills
• outgrowths from the external surface of 1 or more gill arches
• found in lungfish & amphibians
• Filamentous extensions of internal gills
• project through gill slits
• occur in early stages of development of elasmobranchs
• Internal gills - hidden behind larval operculum of late anuran tadpoles

Swim bladder & origin of lungs - most vertebrates develop an outpocketing of pharynx or esophagus that becomes one or a pair of sacs (swim bladders or lungs) filled with gases derived directly or indirectly from the atmosphere. Similarities between swim bladders & lungs indicate they are the same organs.

Vertebrates without swim bladders or lungs include cyclostomes, cartilaginous fish, and a few teleosts (e.g., flounders and other bottom-dwellers).

Swim bladders:

• may be paired or unpaired (see diagram above)
• have, during development, a pneumatic duct that usually connects to the esophagus. The duct remains open (physostomous) in bowfins and lungfish, but closes off (physoclistous) in most teleosts.
• serve primarily as a hydrostatic organ (regulating a fish's specific gravity)
• gain gas by way of a 'red body' (or red gland); gas is resorbed via the oval body on posterior part of bladder

• may also play important roles in:
• hearing - some freshwater teleosts (e.g., catfish, goldfish, & carp) 'hear' by way of pressure waves transmitted via the swim bladder and small bones called Weberian ossicles (see diagram below)
• sound production - muscles attached to the swim bladder contract to move air between 'sub-chambers' of the bladder. The resulting vibration creates sound in fish such as croakers, grunters, & midshipman fish.
• respiration - the swim bladder of lungfish has number subdivisions or septa (to increase surface area) & oxygen and carbon dioxide is exchanged between the bladder & the blood

Source: http://www.notcatfish.com/ichthyology/weberian_apperatus.htm

Lungs & associated structures

• Larynx
• Tetrapods besides mammals - 2 pair of cartilages: artytenoid & cricoid
• Mammals - paired arytenoids + cricoid + thyroid + several other small cartilages including the epiglottis (closes glottis when swallowing)
• Amphibians, some lizards, & most mammals - also have vocal cords stretched across the laryngeal chamber

Source: http://www.worldzone.net/music/singingvoice/images/glottis.gif

•  Trachea & syrinx
• Trachea
• usually about as long as a vertebrates neck (except in a few birds such as cranes)
• reinforced by cartilaginous rings (or c-rings)
• splits into 2 primary bronchi &, in birds only, forms the syrinx at that point

•  Lungs
• Amphibian lungs
• 2 simple sacs
• internal lining may be smooth or have simple sacculations or pockets
• air exchanged via positive-pressure ventilation

• Reptilian lungs
• simple sacs in Sphenodon & snakes
• Lizards, crocodilians, & turtles - lining is septate, with lots of chambers & subchambers
• air exchanged via positive-pressure ventilation

• Avian lungs - modified from those of reptiles:
• air sacs (diverticula of lungs) extensively distributed throughout most of the body
• arrangement of air ducts in lungs ----> no passageway is a dead-end
• air flow through lungs (parabronchi) is unidirectional

• Mammalian lungs:
• multichambered & usually divided into lobes
• air flow is bidirectional:

• air exchanged via negative pressure ventilation, with pressures changing due to contraction & relaxation of diaphragm & intercostal muscles

Related links:

Chordate Respiratory Organs and Functions

Back to BIO 342 syllabus