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BIOL-L 112: EXAM 2
osmoregulation
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general process by which animals control solute concentrations and balance water gain and loss
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osmolarity
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total solute concetration expressed at moles of solute/liter of solution
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osmolarity measurement
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milliOsmoles/liter or mOsm/L
1 mOsm/L = total solute concentration of 10^-3 M
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Osmolarity of Human Blood
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300 mOsms/L
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Osmolarity of seawater
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1000mOsm/L
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Salt Water bony fish
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Environment: hyperosmotic
Osmoregulation strategies: needs to conserve water, eliminate excess salts
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Fresh Water Bony Fish
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Environment: hypoosmotic
Osmoregulation strategies: needs to limit water uptake; conserves salts; absorb salts from the surrounding
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Osmoconformers
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internal osmolarity is isoosmotic with surrounding environment
-animals need to live in water with stable composition
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Osmoregulators
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controls internal osmolarity independent of its external environment
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Kangaroo Rat Water Balance
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Water Gain: .2 mL through ingested food; 1.8 mL through metabolism of food
Water Loss: Urine .45mL, Feces .09mL, Evaporation 1.46mL
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Human Water Balance
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Water gain: ingested food 750mL, ingested in liquid 1500mL, metabolism of food 250mL
Water Loss: Urine 1500mL, Feces 100mL, Evaporation 900mL
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Energetics of Osmoregulations
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Costly to maintain osmolarity differences between animal's body and the environment because physiological systems require solute gradients across cell and organelle membranes
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How do cells manipulate solute concentrations in the ECF?
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Active Transport Mechanisms
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Brine Shrimp
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-Osmoregulation of brine shrimp that lives in Utah's Great Salt Lakes uses 30% of resting metabolic rate
-It is so costly because the gradient between internal and external osmolarity is extremely high
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Excretion |
process that rids the body of nitrogenous metabolic waste products
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How is Ammonia made?
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-Proteins and Nucleic acids are metabolized or broken down and the product is very toxic NH3
-It is so toxic because ion (NH4+) interferes with oxidative phosphorylation
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Why are excretion and osmoregulation structurally and functionally linked?
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most metabolic waste must be dissolved in water to be excreted from the body
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Excretory process
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functions to dispose metabolic waste and control bod fluid composition
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Four key functions of excretory system
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Filtration, Reabsorption, Secretion, Excretion
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Components of Blood
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cells, proteins, large molecules, water, small solutes (salts, sugars, AA, nitrogenous waste)
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Which components move through the semipermeable membrane and by what mechanisms?
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small solutes via blood pressure
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Filtrate in Bowman's Capsule
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isoosmotic
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Cortical Nephron
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-present just in the cortex
-about 85% of the nephrons in the kidney are cortical
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Juxamedullary Nephron
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-crosses the cortex, outer, and inner medulla
-about 15% of nephrons in kidney are juxamedullary
-mammals and birds have jux. nephrons
-advantage: only jux can produce hyperosmotic urine
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How much blood flows through the kidney each day?
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1600L |
How much blood is filtered through the glomerulus?
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800L
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How much of the filtrate is voided as urine?
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1.5L
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Molecules Reabsorbed in the Proximal Tubule
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HCO3-, NaCl, H20, Nutrients, K+
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Molecules Secreted in the Proximal Tubule
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H+, NH3 (drugs, toxins)
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Molecules that move via Active Transport in Proximal Tubule
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NaCl, Glucose
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Molecules that move via Passive Transport in Proximal Tubule
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HCO3-, K+, AA
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Molecules that move via osmosis in Proximal Tubule
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water
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Osomolarity of filtrate at the end of PT
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300mOsm/L
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Volume of filtrate though PT
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volume has decreased as it passed through the PT
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Descending Loop of Henle
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-water is moved out (reabsorbed) via osmosis
-moves so quickly out because of the aquaporin channels
-osmolarity at the bottom of DLOF is 1200mOsm/L
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Ascending Loop of Henle
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-NaCl is moved out (reabsorbed) via passive transport in thin part and active transport in thick part via ion channels
-water does not move out because the ALOF is impermeable to water
-osmolarity at the top of the ALOF is 100mOsm/L
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Distal Tubule
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-NaCl, H20, HCO3- reabsorbed
-K+ and H+ secreted
-osmolarity at the end of the tube is 300mOsm/L
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Collecting Duct - when conserving water
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-Water moves out of the collecting duct in the renal cortex and medulla
-isoosmotic relative to interstitial fluid at the end of the CD
-filtrate is hyperosmotic
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Collecting Duct - when getting rid of excess water
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-NaCl moves out of the CD in the renal cortex and renal medulla
-filtrate is hypoosmotic relative to blood
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Where within the nephron is the greatest amount of energy consumed?
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thick portion of the ascending loop of henle
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What two solutes are the most important for affecting osmolarity within the nephron?
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NaCl and Urea
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ADH
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-Antidiuretic Hormone (vasopressin)
-made in the hypothalamus and stored in the posterior pituitary
-cannot work alone to overcome dehydration, must also drink water (osmoreceptors trigger thirst)
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What type of signal triggers the release of ADH?
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-Blood Osmolarity > 300 mOsm/L (dehydrated)
-effect: hyperosmotic urine
-not released if blood osmolarity <300mOsm/L (over hydrated)
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Name and Location of cell that monitors ADH signal
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Osmoreceptors in the hypothalamus
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Where does ADH react on the body and what is its function here?
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Collecting duct and distal tubule of the nephron to increase the reabsorption of water
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How does ADH exert its effects within the CD?
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ADH binds to receptor, stimulates production of cAMP, cAMP is a secondary messenger that functions to stimulate movement of aquaporin water channels to PM of CD. Once in membrane, H20 molecules can move much more quickly through the transport epithelium
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Alcohol and ADH
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Alcohol prevents the release of ADH therefore creating hypoosmotic urine because without aquaporin molecules in the transport epithelium cells of the CD, water could not be reabsorbed efficiently
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