Plasma carries wastes -- CO₂ released from respiratory organs; the rest is mostly nitrogenous wastes (ammonia [toxic], urea, uric acid) B gotten rid of using some other organ (Malpighian tubules, nephridia, kidneys, and even gills)

Excretion vs. Elimination B know the difference

1. Rid body of internally produced wastes
2. Regulate Salt/H₂O balance B osmoregulation

Aquatic Animals
     Excrete mostly ammonia B highly soluble; easily diffuses into surrounding water from gills; also excreted in some amount in the urine

    I.  Marine animals B salt/water balance
                many isotonic with sea (salt) water (life came from the sea)
        A.  cartilaginous fish (sharks/rays) : hypertonic body fluids B never drink; excrete dilute urine; 
                actively pick up salts across gills
        B.  bony fish: hypotonic B drink continuously; excrete small amounts of isotonic urine actively  
                excrete salt from gills
    II.  Freshwater B by definition, can=t be isotonic
                hypertonic (therefore, similar to sharks)

        Both marine and freshwater fish have water impermeable skin

Terrestrial Animals B most similar to marine bony fish, because these organisms face dehydration; skin also impermeable
        wastes B toxic ammonia converted into uric acid in egg-layers/urea in mammals

• Flatworms B tubular system with Aflame@ cells
• Earthworms B air of nephridia per segment
• Insects B Malpighian tubules

Vertebrate kidneys B  
        Cortex and medulla, pelvis.
        Nephrons: Bowman=s Capsule, proximal/distal convoluted tubule, Loop of Henle, collecting 
                tubule
        Associated Vessels: Renal arteries/veins, glomerulus (filtration; fenestrated capillaries) &
                Peritubular capillaries
        Rest of System B ureters, bladder, urethra

Urine Formation (Diuresis):  involves 

1. filtration (through glomerulus)
2. reabsorption (65 - 80% from proximal convoluted tubules, into peritubular capillaries)
3. secretion

Reabsorption and secretion help regulate the salt and water balance of the body.  Know differences between reabsorptive capabilities of different regions of the nephrons; and how this helps set up the salt gradient (discussed below)

Concentration of urine B necessary to conserve water. Accomplished by setting up a salt gradient in the tissue of the medulla; as urine Adescends@ through the medulla can reabsorb a significant amount of water from the urine.

Know effects of the hormones aldosterone/ADH (anti-diuretic hormone)