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RESPIRATORY SYSTEM. Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City. Compare and contrast the advantages/ disadvantages of counter current and concurrent types of ventilation on vertebrate respiration.

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Mrs. Ofelia Solano Saludar

Department of Natural Sciences University of St. La Salle Bacolod City


Compare and contrast the advantages/ disadvantages of counter current and concurrent types of ventilation on vertebrate respiration.

Describe the functional anatomy of gills, lungs.

List the requirements that a fish must undergo to become a terrestrial vertebrate.

Discuss how the swim bladder is structurally and functionally related to the lungs.

Discuss the phylogeny and attendant modifications of the respiratory tract of the following groups:

a. fishes

b. amphibians

c. reptiles

d. birds

e. mammals


RESPIRATION- the process of obtaining oxygen from the external environment & eliminating CO2.

Respiratory System Principles

  • Movement of an O2-containing medium so it contacts a moist membrane overlying blood vessels.
  • Diffusion of O2 from the medium into the blood.
  • Transport of O2 to the tissues and cells of the body.
  • Diffusion of O2 from the blood into cells.
  • CO2 follows a reverse path.

External respiration- O2 and CO2 exchanged between the external environment & the body cells by diffusion; takes place via highly vascular membranes with thin, moist epithelia

  • Internal respiration- gas exchange between blood & cells; cells use oxygen for ATP production & produce CO2 as waste product
    • Ventilation – bringing gas in contact with respiratory exchange surfaces, e.g. water through gills, or air in & out of lungs of vertebrates, tracheoles of insects
    • Afferent & efferent blood vessels conduct blood to and from sites of respiratory exchange





  • Primary organs in adult vertebrates are external &  internal gills, swim bladders or lungs, skin, &the buccopharyngealmucosa
  • Less common respiratory devices include filamentous outgrowths of the posterior trunk & thigh (African hairy frog), lining of the cloaca, & lining of esophagus


  • Respiration through the skin can take place in air, water, or both
  • Most important among amphibians (especially the family Plethodontidae)


  • External gills
  • Outgrowths from the external surface of 1 or more gill arches
  • Filamentous extensions of internal gills that project through gill slits
  • Gill slits & external gills occur in amphibian larvae & adult urodeles
  • Amnioteembryos have gill slits with no traces of gills

Internal gills – wall of pharynx is pierced by typically 6 gill slits between skeletal gill arches; gill pouch is the passage between external & internal slits; the tissue between gill pouches is the gill bar; bars bear internal gill with filaments.



Gill arch

Gill pouch

Gill filaments


Larval gills

  • May be external or internal
  • External in dipnoans, a few actinopterygians, amphibians
  • Filamentous internal gills in a few teleosts and larval elasmobranchs


  • Maintain salt homeostasis
  • Excretion of nitrogenous wastes and CO2

Opercular gills

  • Little or no septum because operculum covers and protects gills
  • Ventilation is similar to shark


Gill arch


Gill filaments

Gill structure
  • Gill septae or interbranchial septum is between gills
  • Gill bar extends to body surface for more support
  • Gill filaments have rakers: inner surface of gills which keeps food out of gills

Gill filaments:

  • Holobranch– gill filaments on both sides of gill
  • Hemibranch – gill filaments on one side of gill
  • Pseudobranch– false gill, faces into spiracle and monitors oxygen requirements to eye

In fishes, the arches are supplied with respiratory branchial muscles & aortic blood vessels

  • In amniotes, the tympanic cavity & auditory tube connecting it with the pharynx develop as an outgrowth from the 1st gill pouch.
  • The external auditory meatus is a depression in the position of the 1st gill slit.
  • The entodermal lining of the gill pouches persists as tonsils, thymus, parathyroids & epithelial bodies
  • The thyroid gland persists as an evagination of the pharyngeal floor between the 2nd gill arches.

External nares:

  • Extant jawed fishes- lead to blind olfactory sacs
  • Dipnoans & tetrapods- connected with oropharyngeal cavity or pharynx via nasal canals; respiratory use only in tetrapods

Internal nares:

  • Opens further caudad if secondary palate is present


  • 5-15 pouched gills; branchial basket support
  • External & internal branchial pores
  • Pulsations of branchial muscles move water in and out of same openings, as mouth is attached to prey
  • Pouches connected to pharynx by afferent branchial ducts & to exterior by efferent branchial ducts


  • 5 ‘naked’ gill slits with apertures protected by flaplike valve
  • Septae support septal gills which look like a set of stacked plates
  • Spiracle is modified first gill pouch for water intake
  • Posterior wall of last (5th) chamber has no demibranch.


  • 5 gill slits           
  • Operculum projects backward over gill chambers
  • Interbranchialsepta are very short or absent
  • Most do not have spiracle
  • A branchiostegal membrane is attached to the operculum, supported by gular bones or branchiostegal rays.


  • Pneumatics sacs arising as paired or unpaired endodermaloutpocketing of embryonic foregut.
  • Similarities between swim bladders & lungs indicate they are homologous organs.
  • Swim bladder dorsal, lungs ventral
  • Serve primarily as a hydrostatic organ (regulates a fish's specific gravity)
  • Vertebrates without swim bladders or lungs include cyclostomes, cartilaginous fish, and a few teleosts.

Have a pneumatic duct that connects to the esophagus.

  • The duct remains open (physostomous) in bowfins and lungfish, but closes off (physoclistous) in most teleosts.

Gain gas by way of a 'red body' (red gland)

  • Gas is resorbed via the oval body on posterior part of bladder via retemirabile, a network of blood vessels
  • Countercurrent blood flow

Swim bladders also play important roles in:

Respiration- the swim bladder of lungfish has a number subdivisions or septa (to increase surface area); O2 and CO2 is exchanged between the bladder & the blood

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.

Hearing- some fresh water teleosts(catfish, goldfish, carp) 'hear' by way of pressure waves transmitted via the swim bladder and small bones called Weberianossicles



  • Gills are efficient in water but on land, gills will collapse and will lose water quickly. Terrestrial organisms had to evolve respiratory surfaces within the body cavity to reduce water loss.
  • A “lung fish” has LUNGS for adaptations to living on oxygen-poor water or to spending time exposed to air.


  • Lungs are 2 small, simple sacs that do not provide a large surface
  • Occupy the pleuroperitoneal cavity
  • Internal lining may be smooth or have simple sacculations or pockets

In Urodeles, lungs are often of minor importance; respiration is often through external gills and skin

  • In Anurans, the larynx is the cartilaginous entry into trachea; the opening of larynx is the glottis
  • Internal nares are functional for first time in evolutionary history
  • Air is exchanged via positive-pressure ventilation; involves gulping (pulse pump)

Amphibians force air into their lungs by creating a greater-than-atmospheric pressure (positive pressure) in the air outside their lungs. They do this by filling their buccal cavity with air, closing their mouth and nostrils, and then elevating the floor of their oral cavity. This pushes air into their lungs in the same way that a pressurized tank of air is used to fill balloons. This is called positive pressure breathing; in humans, it would be analogous to forcing air into a victim’s lungs by performing mouth-to-mouth resuscitation.



  • Similar to amphibians in anatomy
  • Air is exchanged via positive- pressure ventilation; suction effect
  • Inspiration involves creating negative pressure inside chest cavity via intercostaland abdominal muscles
  • Expiration is passive
  • Each lung occupies a pleural cavity; a fibrous oblique septa separate pleural cavities from the rest of the coelom

Lizards, crocodilians, & turtles – highly compartmentalized

  • Some turtles supplement lung breathing with gas exchange across moist epithelial surfaces in their mouth and anus.


  • Modified from those of reptiles
  • Trachea delivers air to bronchi
  • The primary bronchi are divided into: ventrobronchi, dorsobronchi, and thousands of parabronchi in between

Highly vascularized: capillaries are open ended in the walls of parabronchi; form a honeycomb appearance

  • Inhaled air flows nonstop through the lungs and into air sacs, returns to the lungs via recurrent bronchi, flows through open-ended capillaries, and then vented.

Air sacs: 2 abdominal; 2 posterior thoracic; 2 anterior thoracic; 2 cervical; 1 interclavicular



Cervical air sac

Interclavicular air sac

Anterior thoracic air sac

Abdominal air sac

Posterior thoracic air sac



  • Air sacs act as bellows to allow continuous ventilation
  • Unidirectional air flow through lungs and air sacs result to extremely efficient ventilation
  • High vascularity allows for efficient diffusion between air sacs and blood capillaries
  • Penetrate some bones making them lighter
  • Thermoregulatory
  • Buoyancy in water fowl
Very unique respiratory system:
  • Inhaled air flows through lungs & into air sacs which extend into viscera and hollow bones
  • No dead- end passages of air ducts (cross- current)

Syrinx- vocal apparatus in interclavicular air sac region

  • Furcula- flight muscles acts as a pressure pump that allows expansion and contraction of air air sacs during flight


  • Multichambered& usually divided into lobes; highly spongy
  • Diaphragmseparates pleural cavity; mediastinum separates each pleural cavity
  • Bidirectional air flow: Trachea <-> 10 bronchi <-> 20 bronchi <-> 30 bronchi <-> bronchioles <-> alveoli

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


Deep-seas divers: some elephant seals can dive for 1500 m and stay for 2 hours!

  • WeddelSeal routinely plunges 200-500 m for 20 – 60 min!
  • Storage of oxygen in blood and muscle: 2x as much the volume of blood compared to humans
  • Most oxygen in blood (70%) vs lungs (5%); in humans: blood (51%) and lungs (36%)


  • Tetrapodsbesides mammals- 2 pair of cartilages: arytenoid& 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


Stalk of bifurcated lung outgrowth; supported by cartilaginous rings

Leads to bronchi (forms the bird syrinx at that point)

Usually about as long as a vertebrates neck (except in a few birds such as cranes)


Quiz next meeting

Next topic… Circulatory System