vertebrate physiology ecol 437 university of arizona fall...
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Lectures 21 and 22, 12 and 18 Nov 2003Chapter 14, Osmoregulation and Kidney Function
Vertebrate PhysiologyECOL 437
University of ArizonaFall 2003
instr: Kevin Boninet.a.: Bret Pasch
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Vertebrate Physiology 437
1. Osmoregulation Kidney Function (CH14)
2. Announcements… -Peer reviews due Thurs. -Eldon Braun Thurs.
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Osmoregulation by Birds
Eldon J. BraunDepartment of PhysiologyUniversity of Arizona
(14-18)
Name that student:3
Cody_Diehl
Insulin Resistanceand MuscleMetabolismResearch
Derek_Dindal
MCB...
Krystal_Rotty
Marine BioInterests?
Exam 3 next week!
4A reminder for all that this Friday (14th) at Doings we will be hearing from Brett Graham -- aDoctoral student in the lab of Rob Callister, Dept of Anatomy and Neuroscience, at TheUniversity of Newcastle, Australia. The title of Brett's talk is: Use of the patch-clamprecording technique in vivo. Hope you can all come to what promises to be yet another greatDoings. Gould Simpson 601 4pm.
Finding Nemo(marine adaptations and attempted trophic interactions)
VS.
Princess Bride(pain receptors and endocrine systems gone awry)
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Rubin and EdA complex tale about two republicans hell-bent on burying a frozen cat.
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How does ram ventilation work?
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Osmoregulatory MechanismsApical surface (faces lumen and outside world)Basal surface (faces body and extracellular fluid)
- Active movement of ions/salts requires ATP- Movement of water follows movement of ions/salts
(14-11)
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Gradients established and used…to move ions, water
(14-12)
active
passive
Mammalian Kidney
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Fish Gills Chloride cells involved in osmoregulation -(recall Pelis et al. paper on smolting) -lots of mitochondria to power ATPases -mechanism similar in nasal glands (birds and reptiles), and shark rectal gland
(14-14)
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2
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Kidney Functions:
-Osmoregulation-Blood volume regulation-Maintain proper ion concentrations-Dispose of metabolic waste products-pH regulation (at ~ 7.4)-Dispose of toxins and foreign substances
How does the kidney accomplish this?
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(14-17)Mammalian Kidney-Paired-1% body mass-20% blood flow
-from ureter to urinary bladder(smooth muscle, sphincter, inhibition)
-out via urethra during micturition
-urine contains: water metabolic byproducts (e.g., urea) excess salts etc.
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(14-17)
Mammalian Kidney Anatomy
FUNCTIONAL UNIT(~ 1 million)
Urine
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(14-18)
-numerous nephronsempty into collecting duct
-collecting ducts emptyinto renal pelvis
1 -Proximal tubule2 -Loop of Henle -descending -ascending3 -Distal tubule
16Nephron Anatomy
Knut Schmidt_Nielsen 1997
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Nephron Anatomy
Knut Schmidt_Nielsen 1997
Vasa recta
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Countercurrentexchange
(14-21)
1. FILTRATIONblood --> filtrate
2. REABSORPTION filtrate --> blood
3. SECRETION blood --> filtrate
All 3 involved in finalUrine Composition
Kidney Processes- overview19
Knut Schmidt_Nielsen 1997
Filtration plus secretionU/PMosm = x1000
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+
Dipodomys
(14-20)
Sympatheticinnervation tendsto constrict
Humans:125 ml/min
or180 L/day
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Filtration:
Bowman’s capsule3 layers1. Glomerular endothelial cells
-100x leakier than other capillary walls2. Basement membrane
-negatively charged glycoproteins-repel plasma proteins by charge
3. Epithelial cells-podocytes create slits
Glomerular Filtration Rate (GFR)Humans: 125 ml/min or 180 L/day (60x plasma vol.)
Filtrate = protein-free and cell-free plasma
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Bowman’s capsule
(14-23)
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(14-22)
proteins andlarger moleculesremain
About 20% of the plasmaand solutes that enterglomerulus end up in BC
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Bowman’s capsule
(14-22)
1.StarvationImplications?
2.Kidney StoneImplications?
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Bowman’s capsule
Filtration Regulation:
1. Myogenic props. of afferent arteriole resist stretch
2. Secretions from cells of juxtaglomerular apparatus(where distal tubule passes near bowman’s capsule)
-Macula densa cells (distal tubule)-monitor osmolarity and flow in distal tubule-paracrine hormonal activity on afferent arteriole
-Granular or juxtaglomerular cells (afferent arteriole)-release renin which alters blood pressure…
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(14-24)
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Filtration Regulation:
3. Sympathetic innervation (reduce GFR)-afferent vasoconstriction-decreased space between podocytes
Renin (from granular cells) released in response to-low renal BP,-low solute [ ] in distal tubule,-or sympathetic activation
Renin leads to activation of Angiotensin II whichcauses systemic vasoconstriction to inc. BPstimulates aldosterone from adrenal cortex
vasopressin (ADH) from post. pit.(these promote salt, water reabsorption)
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Renal Clearance:
Volume of plasma cleared of a substance by the kidney.
(Filtration, Reabsorption, Secretion)
Inulin (=GFR) b/c neither reabsorbed nor secreted
If clearance > GFR = secretionIf clearance < GFR = reabsorption
(More on page 603.)
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Knut Schmidt_Nielsen 1997
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301. FILTRATION
blood --> filtrate
2. REABSORPTION filtrate --> blood
3. SECRETION blood --> filtrate
Reabsorption:
of 180 L/day filtered, ~178.5 L reabsorbed in humans
Tight junctions not so tight inproximal tubule, so water canmove from filtrate to plasma
(14-19)
Lots of active transport ofsalts and other substances
Because of reabsorption(and secretion),Renal clearance doesNOT often equal GFR
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Reabsorption limit – Glucose example
(14-25)
Transportmaximum
Tm at 300 mg/min/100ml plasma
Carrier-mediatedtransport
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Reabsorption:
Proximal Tubule70% filtered Na+ actively reabsorbed
(by Na+/K+ATPase pump in basolateral membrane)Cl- and water follow
75% of filtrate is reabsorbedincluding glucose and amino acids (Na+ dependent)also, phosphates, Ca+, electrolytes as needed
Parathyroid hormone controls phosphate and Ca+ reabsorp.triggers calcitriol production (Vit. D) for Ca+
At end of proximal tubule filtrate is isoosmotic with plasma(~300mOsm)however, remaining substances are 4x concentrated
(14-27) 33a
Gradients established and used:
(14-12)
active
passive
Mammalian Kidney
33b
Gradients established and used:
(14-13)
passive
passive
active
Mammalian Kidney
Sympo
rters
33c
Reabsorption:
Loop of HenleDescending limb
-no active NaCl transport-low urea and NaCl permeability-permeable to water
Ascending thin limb-no active NaCl transport-but permeable to NaCl-low urea permeablity-low water permeability
Ascending thick limb-NaCl transported out of tubule-low water permeability
One driver ofconcentratingmechanism of
nephron
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Knut Schmidt_Nielsen 1997
Countercurrentmultiplier
Reabsorption:
Angiotensinogen Renin Ang. I ACE in lung Ang. II aldosterone from adrenal cortex
Distal Tubule-K+, H+, NH3 into tubule-under endocrine control-Na+, Cl-, HCO3
- back into body-water follows (Na+ reabsorption facilitated by aldosterone)
Collecting Duct-permeable to water-hormone control (ADH/vasopressin)-water (via aquaporins) follows osmotic gradient
-permeable to Urea in inner medulla
ADH from post. pit.
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Another driver ofconcentrating
mechanism of nephron
(14-18)
(p.279)
-ADH role in waterreabsorption/urine concentration
-Renin -> Ang. II -> ADH
-Baroreceptorinput (atrial andarterial)
-EtoH inhibitsADH release
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Atrial Natriuretic Peptide (ANP)-released by atrium cells in response to stretch
(elevated BP)
-opposite effect of renin-angiotensin system-decreases sodium reabsorption-therefore increased urine production-ANP inhibits release of ADH, renin, aldosterone
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(14-28)
ADH acts instippled region ofcollecting duct
Urine can be 100-1200 mOsmin humans (plasma about 300)
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Secretion:
From plasma into tubule of nephron
K+, H+, NH3, organic acids, organic bases
(14-30)
Organic anions (OA-):
Liver conjugatestoxins and wasteto glucuronic acid
Secreted intotubule lumen andexcreted
Na/K-ATPase
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Secretion:
-K+ secretion if, and only if, Na+ reabsorption (Na/K-ATPase)
-Can lead to unfavorably low levels of K+ ifaldosterone acting to reabsorb Na+
or
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-High K+ levels can affect heartfunction so excess stored in
tissue as result of insulin action
(14-28)
ADH acts instippled region ofcollecting duct
Urine can be 100-1200 mOsmin humans (plasma about 300)
Urine concentrating ability42
Knut Schmidt_Nielsen 1997
Same story,different picture
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Urine concentrating ability
(14-33)
1200 mOsm in humans9000 mOsm on kangaroo rats9600 mOsm in Perognathus (mouse)
-Length of loops of henle-Corticomedullary concentration gradient
sum
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(14-34)
Cortex andouter medulla
Inner medulla
-ActiveCountercurrentMultiplier
-Dynamic
Some urea“recycled”
-Vasa Recta
Urineconcentratingability
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-Vasa Recta
(14-18)
-Loops of Henle only inMammals and Birds ->Hyperosmotic Urine
-See Review ofUrine Formationon page 614
Urineconcentratingability
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Osmoregulatory Mechanisms-Similar mechanisms in nasal salt glands of birds andreptiles, mammalian kidney, rectal glands of sharks, gillsof marine fishes, etc.-Regulated by similar hormones as well.
(14-11)
(protons, Na+/K+, symporters)
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pH regulation
Proximal tubule and loop of henle: Na+/H+ antiporter (driven by Na/K-ATPase)
CO2 via lungs, H+ via kidneys (skin and gills can also play role)
Distal tubule and collecting duct:A-type cells with proton pump and anion exchanger
Acid Secretion
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protonpump
anionexchanger
(14-31)
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(14-32)
Ultrafiltrate buffered by bicarbonate, phosphates, andammonia allowing for more acid secretion
e.g., NH3 + H+ NH4+
if low onammonia,deaminateamino acids
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(14-31)
pH regulationBase Secretion (opposite A-type cells)
anionexchanger
protonpump
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Gradients established and used:
(14-13)
passive
active
Mammalian Kidney
Antiporterto get ridof protons(acid) andgain Na+
52-54
-Only birds also have loops of henle
Non-mammalian kidneys:
-Some marine fish without glomeruli orbowman’s capsule – urine formed by secretion,ammonia secreted by gills
-Freshwater fish with more and largerglomeruli to make lots of dilute urine
-Osmoregulation also via extrarenal organs…
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Salt Secretion:
(14-14)
active
Down electrochemical gradient(Paracellular)
recycle
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Salt Glands
Shark rectal glands to dispose of excess NaCl-blood hyperosmotic to seawater, but less salt-more urea and TMAO (trimethylamine oxide)-NaCl actively secreted
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Shark Rectal Salt Glands
Salt-secreting cells: -Na/K-ATPase pump in basolateral membrane -generates gradient for Na+ by which
Na+/2Cl-/K+ cotransporter drives up [Cl-] in cell -Cl- across apical membrane -Na+ follows paracellularly down electrochemical gradient (and H2O) -apical membrane impermeable to urea and TMAO -therefore iso-osmotic secretion with lots of NaCl
(14-36)
… slightly different in birds and lizards
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Salt Glands
Nasal/orbital salt glands of birds and reptiles -especially species in desert or marine environments.
Hypertonic NaCl secretions (2-3x plasma osmolarity)
Allows some birds to drink salt water and end up withosmotically free water
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Amblyrhynchus cristatus
(14-36)
Fish Gills Chloride cells involved in osmoregulation -(recall Pelis et al. paper on smolting) -lots of mitochondria to power ATPases -mechanism similar in nasal glands (birds and reptiles), and shark rectal gland
(14-14)
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Freshwater fish:The mechanism basically reversed to allow uptake ofsalt from water against concentration gradient
proton pump tocreate electricalgradient
Na/K-ATPaseto generateNa gradient
(14-31)
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Sea Freshwater
Switch between getting rid of excess salt inseawater and taking up salt in freshwater
Growth hormone and cortisol for sea(more active chloride cells with more
Na/K-ATPase activity)
(recall Pelis et al. paper on smolting)
Prolactin for freshwater
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END
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