Respiration

  1. General considerations
    1. Need oxygen for living processes
    2. Processes involved:
      1. Capture by diffusion
      2. Uptake by respiratory pigment: Hb to HbO2
      3. Transport to tissues
      4. Unloading of oxygen from pigment: acidification
      5. Movement into tissues by diffusion
    3. Properties of water
      1. Water is low in oxygen; 1/30 concentration of air above
      2. Water is dense; 800X air
      3. Water is viscous; 60X air
      4. Thus capturing oxygen from water might be tricky
      5. change with temperature, salt?
    4. Today, focus on structure and function of conventional water breathing in fishes
  2. Gross anatomy of gill cavity
    1. lamprey and hagfish (drawing and Fig. 5.3)
      1. gill tissue in multiple pouches, each with individual openings to pharynx inside
      2. Single or multiple to outside
      3. Water can flow into nostril and out gill opening, or go in and out gill opening
      4. Lamprey:
        1. branchial cartilage outside gills
        2. muscular contraction of cartilage pumps water out
        3. relaxation, expansion of branchial basket draws water in
    2. Sharks and rays (drawing)
      1. water flows into buccal chamber.
      2. water flows through multiple branchial (gill) chambers
      3. separated from others by septum
      4. so multiple gill slits. Usually 5 gill slits
      5. Gill arch supports gill lamellae and septa. Arch is medial (inside) gills
    3. bony fishes (Fig. 5.2, and drawing)
      1. buccal chamber
      2. 4 gill arches per side
      3. reduction or absence of septa (still see in lower bony fishes).
      4. lateral to gills, opercular chamber, covered by operculum, or gill cover.
      5. pseudobranch (fig 23-5, Bond)
        1. Inside gill cover
        2. remnant of gill on lost gill arch
        3. Receives only oxygenated blood; what does it do? see box 4.1.
      6. Parts of a bony fish gill (fig. 5.1 and drawing, use Campbell transparency)
        1. Arch
        2. primary lamellae
          1. lateral and medial set on each arch
          2. close contact between adjacent lamellae
          3. muscles hold together the tips of lateral lamellae against tips of medial lamellae from next anterior gill arch.
            1. Water must go past a curtain of gill tissue
        3. 2o lamellae
          1. These are like little fins projecting from surface of 1o lamellae, many per lamella, on top and underneath
          2. really close contact here: about 30 microns between these from adjacent filaments
        4. afferent (blood coming in) and efferent (blood leaving) arteries
  3. Flow of water and blood in bony fish
    1. Water flow
      1. Unidirectional flow over gills
        1. two valves, at mouth and operculum (branchiostegal rays)
        2. multiple steps
          1. mouth opens slightly. opercular valve closed
          2. buccal cavity expands, water flows in
          3. opercular cavity expands, water starts flow past gills
          4. mouth closes, opercular valve opens
          5. cavities contract, water expelled out gill opening
    2. Blood flow
        1. flow from heart into afferent branchial arteries, into lamellae, once leaves lamellae, exits via efferent branchial arteries (fig. 4.4)
        2. In lamellae (fig. 5.1): out along a 1o lamella, through 2o lamella, back along primary towards gill arch
        3. Flow in secondary lamella is in direction opposite to water.
        4. countercurrent exchanger: extraction efficiency up to 80%
  4. Breathing strategies
      1. Problem: cost of breathing
        1. high density and viscosity of water means that it takes energy to ventilate
        2. branchial pumping takes 10%-15% of total energy
        3. in humans, cost of breathing at rest is 2%
      2. Individual adjustments
        1. When oxygen demand increases, can
          1. breathe more often: increase ventilatory frequency
          2. take bigger gulps: increase stroke volume
            1. both of these steps increase the cost of pumping
          3. recruit more 2o lamellae
            1. lamellae at tips normally receive less water flow and blood flow
            2. as water flow increases over gills, tips receive more flow
            3. blood flow also increases to tips; higher blood pressure and dilation of afferent arterioles
        2. Another strategy: ram ventilation
          1. Open mouth and opercular cavity at same time, and swim
          2. Circumvents problem of high cost of breathing when active
          3. Transfers work of ventilation to locomotory muscles
          4. Seen in
            1. active fishes in rapidly-flowing water: salmonids
            2. active ocean fishes: mackerels, and some oceanic sharks, need to swim to breathe
          5. Actually improves swimming efficiency: better boundary layer along body
      3. Diversity among species
        1. active fishes have:
          1. reduced thickness of secondary lamellae

2. increased number of secondary lamellae per mm of primary lamella