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University of Toronto St. George
Chris Garside

Lecture 8 and 9 Osmoregulation Environment can be external for animal for cell or for enzymes. Mudpuppy: mucus: small compartment of water.  Epithelial: o Apical: outside o Basolateral: inside  Interstitial fluid: ¾ of ECF bathing a cell body Ion water balance: combination of tissues *Large animals: each cell is individually regulated *Small animals: ECF regulated Homeostasis:  Osmotic regulation: i. movement of solutes; ii. driving force for movement of water: Hydrostatic forces between plasma and interstitial  Ionic Regulation: in osmotic  Nitrogen Excretion Ionic and Osmotic Challenges: Salt Water Marine Gain Lose Fresh water Lose Gain Terrestrial lose Ionic Challenges:  Ionioconformer: little control over ions (marine) ECF  Ionioreguator: controls ion profile of ECF Osmotic Challenges:  Osmoconformer: similar osmolarity (marine)  Osmoregulators: constant osmolarity regardless of external environment Saline Challenges:  Stenohaline: narrow range  Euryhaline: wide range Sources of water: - Dietary 30% - Metabolic 10% - Drinking 60% Source of Solutes: Diet - K+ = intracellular - Na+ = Extracellular Classification of Solutes:  Perturbing: disrupts function of enzymes; NA+, K+,SO4+, CL-  Compatible: little effect on function. Polyols (glucose and glycerol) and uncharged amino acides  Counteracting: disrupts function alone. Counteracts other solutes. (TMAO and Urea) Cell Volume:  Osmotic Stresses: i. Swelling of structure ii. Metabolite concentration affected iii. Deformation of cytoskeleton  Water follows solutes  Animals regulate ECF composition to maintain volume Epithelial Tissue: *boundry between animal and environment *permeability depends on number of aquaporins. *mucus *structure Integument - Osmotic Barrier:  Mucus: - Traps water layer thus reducing cost of osmoregulation  Cuticle with Chitin: anthropods  Cornified Stratum Cornam: Keratin modified with kipids Cornification: cell dies but membrane remains Epithelial Tissue properties:  Asymmetrical distribution of membrane transporters: selective and directional  Somewhat impermeable due to tight junctions  Diverse cell composition  Abundant mitochondria (ATP supply) Ion movement:  Transcellular: through cell – tight junction  Paracellular: between cells – leaky membrane Transporters: o Na+/K+ ATPase o Ion channels o Electroneutral cotransporters o Electroneutral exchanger Example: Fish Gills o Lamellae: - Transport - Mitochondria rich o Chloride cells (mitochondria-rich) o Pavement cells (a subset of which are mitochondria-rich) Saltwater freshwater transition: Diadromous fish do this transition  Catadromous:freshwater migrate to salt (eels)  Anadromous: saltwater fish migrate to fresh (salmon) Smoltification (fresh water to salt water) - Upregulation of transporters : reverse NaCl transport, more Na+K+ATPase - Controlled by hormones: GH, thyroid, cortisol Salt Glands: - Near eye, drain into nostrils - Large amount of salt in a little water: i. Ion pumps ii. Counter current\\ Rectal Gland - Elasmobranchs: empties into digestive tract - Vasolactive intestinal peptide (VIP): chlorine out of apical, (-) gradient, Na+ moves Lecture 9 Osmoregulation\ Nitrogen Excretion Ammonia Uric Acid Urea Advantages - NH4+-NH3 - Few toxic -slightly toxic equilibrium effects - inexpensive - Little - Secreted in - 10x less water needed energetic cost small volume less than ammonia of water (x100 less) Disadvantages - Toxic - Expensive - Perturbing - Large volume - Cartilaginous of water to fish: urea used to store and increase tissue excrete osmolarity but counteracted by TMAO Examples Aquatic and larvae Amphibians and Terrestrial Terrestrial Kidney: Role: - Ion balance (Na+, K+) i. K+ too high: arythmia ii. K+ too low: weak muscles iii. Na+: high sodium in ECF - Osmotic balance - Blood pressure - pH balance (H+ and HCO3 work with respiratory) - excretion of metabolic waste and toxins - Hormone production (EPO and renin) Kidney structure: Nephron: functional unit  Renal tubule: - Lined with transport epithelium - Various segments - Processes blood filtrate  Vasculature - Delivers fluid and governs interstitia
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