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48 Cards in this Set
- Front
- Back
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What is freely filtered by glomerular filtration?
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Water and low-molecular weight substances
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What isn't filtered by the glomerulus?
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Cells: RBC, WBC, platelets etc... too big to fit
Ptns: albumin, globulins Ptn-bound substances: 1/2 calcium ion, FA |
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What is the P in the glomerular capillaries?
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Positive
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What are the forces that favor filtraion?
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Glomerular capillar blood P (60m Hg)
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What are the forces that oppose filtration?
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Fluid P in Bowman's space: 15 mm Hg
Osmotic force due to ptn in plasma (oncotic P): 29 mm Hg ->Ptns are highly concentrated and they suck water from the Bowman's capsule |
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What is the net glomerular filtration P?
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PGC - PBS - пGC= 16 mm Hg
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What is the Glomerular filtration rate (GFR)?
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The volume of fluid filtered from the glomeruli into Bowman's space per unit time
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What regulates the GFR?
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Net filtration P
Mb permeability (different for each substance) Surface area available for filtration ->if these decrease, than the GFR decreases |
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What is the normal GFR of a 70kg person?
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180L/day
(125ml/min) (plasma volume of his person is 3.5L) |
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How many timesis the plasma filtered per day at the glomeruli?
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180/3.5
=51 times |
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When is there a decreased GFR?
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1) Constrict afferent arteriole (decreases Pgc, dec GFR)
2) Dilate efferent arteriole: decrease Pgc and GFR |
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When is GFR increased?
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1) EA is constricted
2) Afferent arteriole is dilated Both increase Pgc |
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What regulates dilation and constriction of arterioles?
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Hormones:
prostaglandin E1: vasodilation renin:vasoconstriction ->Balance between these 2 will define P |
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What is filtered load?
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Total amount of any freely filtered substance
Filtered load = GFR x Plasma concentration of the substance ex: filtered load of glucose =180L/day x 1g/L = 180g/day |
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When is there bet reabsorption?
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Filtered load > amount excreted in the urne
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When is there net secretion?
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Filtered load < amount excreted in the urine
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What does the GFR have to be to excrete waste products properly?
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GFR = verylarge
.: filtered volume of water and the filtered loads of all the nonwaste plasma solutes are also very large |
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What happens in the proximal tubule?
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Reabsorbs most of the filtered water and solutes
Major site of secretion for various solutes, except K+ |
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What happens to the filtrate in the Henle's loop?
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Absorbs relatively large quantities of the major ions (less water)
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What happens in the DCT/CD?
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Volume of water and masses of solutes here are small
Used for fine tuning Determines the final amount excreted in the urine by adjusting the rates of reabsorption and in a few cases, secretion Most homeostatic controls are exerted here |
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Where does most of the hormonal control take place?
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Takes place in the distal part of the nephron
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What is reabsorption?
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Mov't of substance from tubular lumen to peritubular capillary
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Where is the basolateral mb?
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In the blood side
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What is paracellular?
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In btw cells (water and substances through tight junctions)
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What is transcellular?
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Goes through the cell (enter and exit epithelial cells)
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Is the filtered load greater or less than the amount of substance in your body?
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Greater .: reabsorption is very important
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What are 4 important points about tubular reabsorption?
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1) Filtered loads are enormous, usually more than the amount of the substance in the body
2) Reabsorption of wase products is relatively incomplete (i.e. urea) 3) Reabsorption of most useful plasma components (i.e. water, inorganic ions and organic nutrients) is relatively complete 4)Reabsorption of some substances are not regulated (i.e. glucose, aa) while others are highly regulated (water, inorganic ions) |
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What are the 2 mechanism of reabsorption?
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Diffusion
Mediated transport |
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What is diffusion?
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Often across the tight junctions connecting the tubular epithelial cells
->urea reabsorption in the proxmal tubule: urea is freely filtered at glomerulus ->in the proximal tubule, water reabsorption occurs -> urea concentration in the tubular fluid becomes higher -> urea diffuses into the ISF and peritubular capillaries |
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What is medated transport?
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Occurs across tubular cells (transcellular epithelial transport)
Requires participation of transport ptns in the plasma mb of tubular cells Usually coupled to the reabsorption of sodium |
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What does the Na+/K+ ATPase do?
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Exchanger pump Na from cell to peritubular cap
[Na+] in cell is low, whereas lumen [Na+] is high .: it diffuses in cell |
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What are the differentways to classify solute transport?
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Passice: spontaneous, down an electrochemical gradient
->diffusion Facilitated diffusion: channels, uniport (glucose, aa), Coupled transport Solvent drag Active: against an electrochemical gradient (requires E) |
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What is the transmembrane maximum (Tm)?
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When mb transport ptns are saturated, the tubule can't reabsorb the substance any more (Tm)
->example: ppl with uncontrolled diabete mellitus, plasma [glucose] is high and filtered load of glucose exceeds the capacity of the tubules to reabsorb glucose (Tm is exceeded) -> glucose ends up in the urine |
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What is tubular secretion?
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Moves substance from peritubular cap ti tubular lumen (opposite of reabsorption)
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How is tubular secretion mediated?
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1) Diffusion
2) Transcellular mediated transport |
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What are the most important substances secreted by the tubules?
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Hydrogen ion
Potassium (K+) |
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What is tubular secretion usually coupled to?
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Coupled to reabsorption of sodium (antiport)
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***What is the concept of clearance?**
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Clearance: volume of plasma from which that substance is completely removed (cleared) fby the kidneys per unit time
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What is the equation for clearance of S?
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Clearance of S = Mass of S excreted per unit time (g/day)/ plasma concentration of S (g/L)
=L/day |
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What is the mass of S excreted per unit time?
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Urine concentraion of S (Us) x Urine volume per unit time (V)
.: Cs = UsxV/Ps |
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What is inulin?
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A polysac (produced and purified from beets)
Not produced by animals and administered intravenously |
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How can inulin clearance be measured?
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Inulin is freely filtered at the glomerulus but is NOT reabsorbed, secreted ot metabolized by the tubule
->Clearance of inulin (Cin) = volume of plasma originally filtered (GFR) -> Inulin is the most accurate marker of GFR |
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How can you calculate the GFR?
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Given: urine vol= 2.4L/day
[Inulin] in the urine = 300mg/L Amount of inulin excreted in the urine: 2.4 L/day x 300mg/L =720mg/day Cin= (720mg/day)/ (4mg/L) = 180L/day .: GFR =Cin = 180L/day |
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What is creatine clearance?
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Creatine= waster product produced by the muscle
Freely filtered at glomerulusand NOT reabsorbed ->Secreted at the tubule (but very small amount) ->NOT metabolized by the tubule .: creatine clearance is used as a clinical marker for GFR |
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Gow is creatine clearance measured?
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([Urine] of creatine x V)/ (Plasma concentration of creatine) ~= GFR
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Example: given urine vol= 2L/day
Urine concentration of creatine: 9.6mmol/L Plasma concentration of creatine= 0.3 mmol/L |
Creatine clearance = Ucr xV/ Pcr
=9.6 x 2/0.3 =64L/day -> This person has lost 2/3 of GFR |
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What happens if clearance of a substance > GFR?
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Secreted at the tubule
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What happens if the clearance of a substance < GFR?
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It is reabsorbed at the tubule
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