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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.
2
Osmoregulation by Birds
Eldon J. BraunDepartment of PhysiologyUniversity of Arizona
(14-18)
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Name that student:3
Cody_Diehl
Insulin Resistanceand MuscleMetabolismResearch
Derek_Dindal
MCB...
Krystal_Rotty
Marine BioInterests?
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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.
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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)
1
2
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5
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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?
13(14-17)
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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
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Knut Schmidt_Nielsen 1997
12
3
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Nephron Anatomy
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Knut Schmidt_Nielsen 1997
Vasa recta
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Countercurrentexchange
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(14-21)
1. FILTRATIONblood --> filtrate
2. REABSORPTION filtrate --> blood
3. SECRETION blood --> filtrate
All 3 involved in finalUrine Composition
Kidney Processes- overview19
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Knut Schmidt_Nielsen 1997
Filtration plus secretionU/PMosm = x1000
20
+
Dipodomys
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(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
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(14-22)
1.StarvationImplications?
2.Kidney StoneImplications?
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Bowman’s capsule
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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
12
3
4
5
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301. FILTRATION
blood --> filtrate
2. REABSORPTION filtrate --> blood
3. SECRETION blood --> filtrate
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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
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Gradients established and used:
(14-12)
active
passive
Mammalian Kidney
33b
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Gradients established and used:
(14-13)
passive
passive
active
Mammalian Kidney
Sympo
rters
33c
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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
34
Knut Schmidt_Nielsen 1997
Countercurrentmultiplier
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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.
35
Another driver ofconcentrating
mechanism of nephron
(14-18)
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(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
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(14-28)
ADH acts instippled region ofcollecting duct
Urine can be 100-1200 mOsmin humans (plasma about 300)
Urine concentrating ability42
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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
48(14-17)
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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+
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-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)
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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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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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