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Lecture 5

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University of Waterloo
BIOL 370
Dinu Nesan

Lecture 5: Osmoregulatory Adaptations - Aqueous Environments: Freshwater (1-50 mOsm/L) & Seawater (1000mOsM/L) o E.g. Hagfish are isosmotic but can regulate some ions o E.g. Elasmobranchs are isosmotic/hyperosmotic but can regulate inorganic ions “ionoregulation”  Perturbing solute Urea vs. TMAO o E.g. Bony fish are hypoosmotic & ionoregulate major ions (Na , K & Cl) - - Freshwater Osmoregulation (Hyperosmotic body fluid - threat: Swelling) o Produce dilute urine o Salt is reabsorbed into the blood via Kidney tubules o Salt that are lost in the urine are replaced from ingested foods o Gill epithelial cells can actively transport salt from the external environment o Freshwater fish gills +  PNA- (Pavement cells): Transport Na from water to blood  CO + H O Carbonate anhydrase  HCO & H - + + 2 2 3 +  H moves to the basolateral side, acidifies the membrane to allow the intake of Na via Na /H exchanger - 2+  PNA+ (Chloride cells): Transport Cl & Ca from water to blood  CO 2 H O2 Carbonate anhydrase  HCO & H 3- + - - - - 2+  HCO t3avels to the bas2+ateral side, Cl is brought in via the Cl/HCO exc3anger, Ca can enters via the Ca channel - Seawater Osmoregulation (Hypoosmotic body fluid – threat: Shrinking) + + o Salt is absorbed at the gut (Apical NKCC & Basolateral Na /K ATPase) o Excessive salt is eliminated by  Active transport @ gill epithelium  Divalent cations & SO 42-are expelled through the anus  Urine is isotonic to blood but rich in divalent ions “not well transported via gills”  Gill and kidney conserves water & eliminates salt o Marine fish gills + -  Chloride cells: Transport Na & Cl from blood to water  Apical NKCC, Na leaves by Na /K ATPase & K leaves by K channel -  Cl is concentrated in the cell & leaves @ basolateral side  Na follows the electrochemical gradient paracellularly - Air-breathing Animals (Respiratory epithelia – threat: Dehydration) o Marine reptiles/birds: Drink seawater, kidney cannot produce concentrated urine so excess salt is excreted via salt gland o Marine mammals: No specialized salt glands, so don’t drinking seawater, water is obtained from food intake of water rich food (dietary water) & subsequent metabolism (metabolic water), has kidney  E.g. Elephant seal (Very efficient water conservation)  Loses only 88g of water per day  Hypertonic urine produced via Loop of Henle of the kidney  Reduces water loss via breathing (very large tidal volume)  Nasal countercurrent heat exchanger, reduces respiratory water loss  Slow metabolic rate (40 mins no breathing = 5 min of deep breathing) o Humans: Kidney can remove 6g Na /L via urine but seawater contains 12g Na /L + - Desert animals (Extreme heat & absence of freshwater – threat: Dehydration) o E.g. Kangaroo rat (very well adapted osmoregulator)  Avoid heat/exercise by remaining in burrows during daytime  Most efficient kidney known, highly concentrated urine, very advanced Loop of Henle  Nasal counter current mechanism, reduces respiratory water loss  Rectal absorption of water  dry fecal pellets  Water replenished from metabolic water  No net loss of water o E.g. Camel (thermoconformer, can avoid water loss in extreme conditions)  Body temperature rises during the day (same as T )  reduces evaporative water loss A  Produces very concentrated urine & dry feces  No urine is produced at low H 2 (Urea is sequestered in tissue)  Can rehydrate quickly by drinking 80L water in 10 minutes - Terrestrial anthropods (arachnids, ticks, mites) o Extract water vapor from the air @ low humidity, must have access to open air o Absorbs water via rectum from feces, feces then absorbs water from the air o Ticks can absorb water via tissues in the mouth, & then produce concentrated KCl solution from salivary gland - Invertebrates (2 methods for ion conservation) o Filtration-reabsorption (Molluscs & crustaceans – antennal gland of crayfish)  No distinct transporters needed but is energetically costly o Secretory-reabsorption (Insects – Locust malphigian tubules, hindgut)  Actively transport potassium, can reabsorb large amounts of water & ion & produce highly hypertonic urine  Net KCl uptake - +  Apical Cl
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