Respiratory

• What is the earliest form of respiration in vertebrates and what does it involve?

  1. Pharyngeal slits
  2. water movement by cilia
• Velar folds or velum 


  these are pumps that produce the feeding-ventilation currents in Ammocoete larvae
• Ammocoete larva (Agnatha) has 7 pharyngeal slits which are small and round
• In Agnatha: One-way flow from the pharyngeal cavity to outside because they need a way to prevent the backflow of deoxygenated water.
• Gill components of Ammocoete larva:

  1. interbranchial septum
  2. primary gill filaments/lamellae
  3. secondary lamella
• Adult lampreys can have a parasitic lifestyle. While sucking, they respirate through their gill slits. Their gill slits have a bidirectional flow of water (same water entry and exit)
• Hagfishes: their branchial apparatus does not have major expansions or contractions
• Hagfishes: because they do not have major expansions in branchial apparatus, they have branchial pouches instead that act as pumps and inverted T-shaped velum, that produce currents of water from the nostril
• Hagfishes have a muscle layer around the lamellae allowing them to contract and expand to some degree
• Gill orientation comparison:

  • Lamprey: medial to branchial arch
  • Elasmobranch: lateral to branchial arch
• Elasmobranch:

  • gills present on both sides: holobranch
  • gills present on one side: hemibranch
• Components of the Elasmobranch (shark) gill:

  1. interbranchial septum: have banks of lamellae supported by gills rays and a medial branchial arch
  2. Primary lamellae
  3. secondary lamella
  4. Gill ray
• Respiratory unit: facing gill lamellae from adjacent gills
• In Elasmobranch: the first-gill slit is reduced to an opening (spiracle) with reduced hemibranch (spiracular pseudobranch).
• Dual pump mechanism of Elasmobranch (sharks)

  1. Suction pump: for inspiration; expansion of the buccal cavity creates a negative pressure which allows water entry into the mouth.
  2. Force pump: for expiration; contraction of the buccal cavity creates positive pressure which allows water to exit through the parabranchial chambers
• Countercurrent exchange: performed by Elasmobranchs; efficient gas exchange because it is less energy consumption. CO2 is being released and oxygen is being absorbed at the same time.
• In bony fishes: the operculum is bony or cartilaginous
• Operculum (in bony fishes): provides a protective cover over the branchial arches and gills they support.
• Bony fishes have tiny adductor muscles that cross between filaments to control the arrangement of adjacent gills that govern the flow of water across the secondary lamellae.
• Countercurrent exchange: both performed by Elasmobranchs and bony fishes.
• Bony fishes ventilate through a gas bladder by gulping and forcing fresh air through the pneumatic duct.
• Gill rakers in bony fishes function in feeding and gives insight on the diet and their feeding ecology.
• In bony fishes: Gills

  • Dual pump: most common ventilation device serving gill irrigation
  • the branchial arches and associated muscles are components of this pump. As these are also involved in feeding, the design of the branchial apparatus is a compromise between the demands of feeding and ventilation.
• Bony fishes: Lungs

  • have respiratory and hydrostatic functions
  • Australian Protopterus: single lung
  • African Protopterus: paired lungs
• Bony fishes: Lungs are subdivided into vascularized chambers

  • Faveoli: for non-mammalian
  • Alveoli: for mammalian
• Bony fishes: Swim bladder

  • hydrostatic organ for buoyancy as their calcified bones make them denser than water.
  • these are absent in bottom-dwelling fishes and fishes of open water such as tuna and mackerel that swim continuously.
  • Physostomous: swim bladder in primitive teleosts, connected to the digestive tract via pneumatic duct.
  • Physoclistous: swim bladder in advanced teleosts, the connection is lost; a closed bag of gases; gas glands secrete, oval resorbs.
• Secondary function of swim bladders

  • hearing and sound production
• What are the four shark characteristics that make them buoyant even without swim bladders?

  1. Cartilaginous skeleton
  2. Heterocercal tail
  3. Pectoral fin: stabilizes the shark when swimming
  4. Liver: has squalene (oil) which makes them more buoyant
• Lissamphibia's main respiratory organ is its skin. It is moist, has a thin layer, and vascularized.
• Lungs are present in most amphibians but not all.

  • they are developed anteriorly
  • septal surface: partitions form and subdivide to increase the surface area exposed to the incoming air.
  • vascularized faveoli: open into the central chamber within each lung
• Faveoli: in non-mammals; they are not found at the end of a highly branched tracheal system. They are internal subdivisions of the lung wall that open into a common central chamber.
• Larval amphibians possess external gills that are:

  1. vascularized
  2. passive or active irrigation
• Frog larvae employ buccal and pharyngeal force pumps to produce a unidirectional flow of water across the gills and generate a food-bearing current.
• The buccal and pharyngeal cavities of frog larvae are separated by a valve called the velum.

  • The buccal cavity is separated from the mouth by the oral valve; and from the nares by an internal narial valve
• Gills are lost in adult amphibians after metamorphosis, while cutaneous respiration continues to play respiratory demands in the adult stage.
• Lungs, if present in adult amphibians, are ventilated by the buccal pump.
• The buccal pump and buccal cavity in adult amphibians are also used in vocalizations