1. General considerations
    1. We have talked about 2 systems that rely on or involve transport of oxygen:
      1. muscles use it
      2. gills provide it
      3. and we will soon discuss how swim bladder uses it
    2. Oxygen transported by blood. Here look at the transportation system
  2. General circulatory system
    1. General properties
      1. low blood volume: low metabolic rate. 1.5-3% body wt, vs. 6% for mammals
      2. turnover of blood may require 5 minutes: blood pressure drops about 50% at gills, flow sluggish through rest of body
      3. blood goes once through heart, out to system, back to heart. One pump, one circuit system
    2. The heart (handout: fig. 4.10, Moyle and Cech)
      1. Structure: four in-line chambers, just post. to gills
        1. Sinus venosus: collects blood
        2. Atrium: first acceleration
        3. Ventricle: most muscular, largest pressures
        4. Conus (chondrichthians and lungfish) or bulbus (teleosts) arteriosus.
          1. conus is muscular, and has valves to prevent backflow into heart as ventricle rebounds
          2. bulbus is nonmuscular, but elastic. Depulses flow
      2. Pericardium
      3. Heart is fairly small, 0.1%-0.2% body weight
    3. Major vessels (fig. 4.5 in Helfman et al., also handout fig. 23-2 Bond, also drawing)
      1. To and from gills
        1. Ventral aorta (single)
        2. to afferent branchial arteries (paired)
        3. Efferent branchial arteries
      2. Other arteries
        1. efferent branchial arteries to dorsal aorta
        2. paired anteriorly, where flow enters from gills
        3. directs flow to carotid arteries, to brain, etc.
        4. unpaired posteriorly, runs ventral to centra
        5. Other arteries give off from dorsal aorta, to guts and muscles
        6. at caudal vertebrae, dorsal aorta turns into caudal artery running through hemal arches
      3. Major veins
        1. Caudal vein, vent to caud artery in hemal arches, flow from muscles
        2. blood to kidneys from caudal vein and artery
        3. postcardinal vein, return from kidneys, gonads and muscles
        4. anterior cardinal vein, venous flow from head
        5. common cardinal vein, joining of anterior and postcardinal veins
        6. to sinus venosus
        7. separate return to sinus venosus from liver and gut via hepatic portal
  3. Blood structure and function
    1. Components of blood
      1. Plasma
        1. dissolved materials
      2. Blood cells
        1. leukocytes or white blood cells
          1. immune response, clotting, eating foreign particles
        2. erythrocytes, red blood cells
          1. carry hemoglobin for oxygen transport
          2. some fish don't have 'em: e.g. Antarctic fishes
    2. Hemoglobin structure
      1. Most fishes have tetrameric Hb
        1. four polypeptide chains, one heme
        2. structure similar to mammalian Hb
        3. agnathans: monomeric Hb
    3. Function: oxygen uptake and release
      1. oxygen dissociation curve (Fig. 5.5, Helfman et al., and drawing)
        1. amount of oxygen taken up by Hb increases with partial pressure of oxygen (the amount in solution in plasma)
        2. half-saturation point (P50): oxygen tension (partial pressure) at which blood is half-saturated.
        3. curve is typically sigmoid in shape; this is because of tetrameric molecular structure (see Box 5.2)
      2. Effect of pH change
        1. blood pH drops where there is higher carbon dioxide (areas of metabolic activity)
        2. conformation of Hb changes, and reduces affinity (lower half-saturation point): Bohr effect
        3. in some fishes, there is also lower oxygen capacity (reduction of asymptotic saturation): Root effect
        4. As results, Hb unloads oxygen in tissues where there is metabolic activity
      3. Diversity among fishes
        1. Effect of habitat
          1. fish in lower oxygen waters have lower P50 (fig. 5.5c)
        2. Activity level
          1. active fishes, higher Bohr shift