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89 Cards in this Set
- Front
- Back
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4 basic process that determine the composition of urine:
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1. Filtration
2. Reabsorption 3. Secretion 4. Excretion |
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Excretion equals:
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-Filtered
plus -Secreted minus -Reabsorbed |
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What happens to most substances at nephrons?
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They are freely filtered and extensively reabsorbed by the renal tubules.
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How is the daily turnover of water and electrolytes regulated?
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By hormones which adjust the rate of tubular reabsorption.
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How much glucose is daily
-filtered -reabsorbed -excreted |
180 g filtered
180 g reabsorbed 0 excreted |
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What percent of the filtered load of bicarbonate is reabsorbed daily?
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99.9%
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What percent of the filtered load of sodium is reabsorbed daily?
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99.4%
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What percent of the filtered load of chloride is reabsorbed daily?
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99.1%
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What percent of the filtered load of potassium is reabsorbed daily?
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87.8%
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What percent of the filtered load of urea is reabsorbed daily?
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50%
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What percent of the filtered load of creatinine is reabsorbed daily?
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0
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How much creatinine is daily
-filtered -reabsorbed -excreted |
Filtered = 1.8 g/day
Reabsorbed = none Excreted = 1.8 g/day |
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In the beercan model for renal tubule epithelial organization, how are cells connected?
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By tight junctions at their apical sides.
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What are the 2 alternative routes across the renal tubule epithelium?
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1. Across the cells
2. Across the tight junctions |
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2 things that must occur for a substance to be reabsorbed:
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1. Transport across tubular epithelial membranes into renal interstitial fluid
2. Transport through the peritubular capillary membrane into the blood. |
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What mechanisms allow for transport of water and solutes across tubular epithelial cells?
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Passive and active, via transcellular or paracellular routes.
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What process allows substances to be transported from the renal interstitium to the peritubular capillary?
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Ultrafiltration mediated by starling's forces!
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What are the net forces like at the peritubular capillaries?
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Like the venous ends of systemic capillaries - net force is for movement of stuff INTO the capillaries.
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What sets up the driving force for passive and active transport of solutes across the tubule cells?
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Na/K ATPase
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By what process is water reabsorbed?
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By osmosis - it follows the solutes reabsorbed.
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What type of processes occur at
-The transcellular pathway? -The paracellular pathway? |
Transcellular = AT and PT
Paracellular = Passive diffusion only |
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What is achieved by the Na/K ATPase pump in the basolateral membranes of tubule cells?
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1. Sets up a concentration gradient for sodium to enter
2. Sets up a -70 mV electrical gradient that pulls pos charges on sodium in. |
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What are 3 types of 2ndary active transporters in tubule cells?
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1. Na/Glucose transporter
2. Na/Amino acid transporter 3. Sodium/H transporter |
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Which 2ndary active transporter is counter?
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Sodium/H
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How are the few proteins that do get into ultrafiltrate get reabsorbed?
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Via pinocytosis
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What is a Transport Maximum?
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The maximum rate at which a substance can be reabsorbed from renal tubules because its transporters are finite in number.
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What is the Threshold for excretion?
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The amt of a substance in the plasma above which excretion will begin to climb.
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What is the overall renal transport max for glucose?
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320 mg/min
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What gets reabsorbed in the Proximal tubule?
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-65% of the filtered load of Na, Cl, HCO3, K, and H2O.
-Almost all glucose and amino acids |
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What gets secreted in the Proximal tubule?
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H+, Organic acids, and bases
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What is the tonicity of the proximal tubule lumen?
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Isosmotic
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How many mechanisms are there for Sodium reabsorption in the proximal tubule?
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Three
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What are the three mechanisms of Sodium reabsorption in the Proximal Tubule?
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1. Na/H antiport
2. Na/Glu and Na/AA symport 3. Passive diffusion with Cl- |
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How does chloride drive its passive reabsorption w/ Na?
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As sodium gets reabsorbed by all its other mechanisms, Cl ends up being left by itself; as its concentration increases then its driving force for diffusion does.
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Where exactly do Cl- and Na diffuse into tubule cells?
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Across tight junctions in the LATE proximal tubule.
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How much Na/Cl and H2O get reabsorbed in the proximal tubule in total?
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65%
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How much of that 65% is transported by each mechanism?
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1/3 by each of the 3 mechanisms.
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Is chloride the only thing that gets passively reabsorbed?
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No; urea does too.
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What happens to the concentration of creatinine and urea as you go along the length of the proximal tubule?
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They increase rapidly because they aren't reabsorbed.
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What conc increases more; urea or creatinine?
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Creatinine - some urea is passively reabsorbed w/ Cl-
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What is reabsorbed most completely?
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Glu / Amino acids
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What is reabsorbed largely but less than Glu / AA?
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Bicarb
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How is water reabsorbed in the prox tubule?
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Via isosomtic reabsorption.
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What generates the force for Chloride passive reabsorption?
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The reabsorption of sodium bicarb and water, increasing [Cl] in their wake; also increases the neg potential in the lumen, retarding Cl-.
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What feature of peritubular capillaries allows bulk flow or reabsorbed substances?
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Their hydrostatic and oncotic pressures favor reabsorption.
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What is the oncotic pressure of the peritubular capillaries?
What is the hydrostatic pressure of the interstitial space? |
32 mm hg
6 mm Hg Net = 38 mm Hg pulling in. |
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What is the oncotic pressure of ISF around the peritubular capillaries?
Hydrostatic pressure? Net? |
15 mm Hg
13 mm hg Net = 28 mm Hg pulling out |
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What is the sum of Starling's forces at peritub capillaries?
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38 - 28 = 10 favoring reabsorption
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So what is the net filtration pressure at the peritubular capillaries?
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-10 mm Hg -> meaning it favors reabsorption from the renal interstitium!
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How are organic anions secreted at the proximal tubule?
How do the organic anions get into the tubule cells at all? |
-Via active transporters at the apical membrane of tubule cells.
-Via 2nd ATs in exchange for Na, DCA, and DCA in exch for Na. |
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6 endogenous organic anions:
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CHUBPO
-cAMP -hippurates -urate -bile salts -prostaglandins -oxalate |
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What is an important exogenous organic anion secreted in the proximal tubule?
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PAH
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How does the kidney handle PAH?
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-Freely filtered
-Secreted -Not reabsorbed -totally excreted |
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How are secreted substances similar to reabsorbed substances?
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Both have a transport maximum for their transporters
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What happens when a secretion transporter reaches its transport maximum?
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-Secretion plateaus
-Excretion rate rises less rapidly -Filtration continues to increase |
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What is an important endogenous cation secreted in the proximal tubule?
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Creatinine
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List 4 endogenous cations secreted in the prox tubule:
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-Creatinine
-Dopamine -Epinephrine -Norepinephrine |
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Exogenous cations secreted in the prox tubule:
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-Atropine
-Isoproterenol -Cimetidine -Morphine -Quinine -Amiloride |
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What do we use creatinine as an index for? Why?
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GFR - because it is freely filtered almost completely.
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Why is it bad that creatinine is slightly secreted?
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Measuring creatinine in the urine gives a bit of an overestimate of the GFR.
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What part of the renal tubule comes after the proximal tubule?
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The thin loop of Henle.
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What are the 3 functionally distinct segments of the Loop of Henle?
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-Thin descending
-Thin ascending -Thick ascending |
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What makes the thin desc and ascending limbs THIN?
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-Thin epithelial membranes
-No brush borders -Few mitochondria -Minimal levels of metabolic activity |
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What happens in the thin descending loop of Henle?
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Not much - reabsorption of water
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What causes the reabsorption of water in the thin descending loop of henle?
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The cortical-medullary osmotic gradient, which sets up the gradient for passive osmosis.
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What happens in the thin ascending limb of Henle's loop?
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It becomes impermeable to water!
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What gets reabsorbed at the thin ascending limb of Henle's loop? How?
What else happens here? |
-Na and Cl
-via passive diffusion -Urea gets secreted from blood to lumen to pass to late distal tubule for its cycling. |
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What happens to the tonicity of the lumen fluid in the ascending thin limb of henle's loop?
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It becomes DILUTE as Na/Cl are taken out but water is left behind.
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What is reabsorbed in the Thick Ascending limb of Henle's loop?
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25% of filtered Sodium
-Na/K/Ca/Mg |
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How is the 25% of sodium reabsorbed?
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Via Na/K/2Cl transport
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How are Na/K/Mg/Ca reabsorbed? What is the driving force?
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Via paracellular passive diffusion due to the positive potential in the lumen.
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What is secreted at the Thick ascending limb of henle's loop?
Via what transporter? |
Acid via the Na/H transporter.
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What happens to water at the thick ascending limb?
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Nothing - it is impermeable so the solution becomes more hyposmotic.
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What is the Na/K/2Cl transporter a target of?
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Loop diuretics like Lasix and furosemide
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What is reabsorbed in the early distal tubule?
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Na, Cl, Ca, and Mg
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What happens to water at the early distal tubule?
How does Na/Cl reabsorption change? |
Nothing; it is impermeable
Na/Cl transporter is now active |
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What is the Na/Cl transporter at the early distal tubule sensitive to?
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Thiazide diuretics
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What is the lumen electric potential at:
-Thick ascending limb of henle -Early distal tubule |
Thick asc limb = +8 mV
Early dist tubule = -10 mV |
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What is the late distal tubule similar to functionally?
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The cortical collecting tubule
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What are the 2 cell types that compose the late distal tubule and cortical collecting duct?
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-Principle cells
-Intercalated cells |
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What is reabsorbed in the Late distal tubule?
(either always or potentially) |
Sodium
Chloride Water Bicarb |
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What is secreted in the late distal tubule?
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K+ and H+
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What do Principle cells do?
under what control? |
Reabsorb sodium
Secrete potassium -Under the control of Aldosterone |
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What do Intercalated cells do?
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-Reabsorb K (when needed) and Bicarb
-Secrete Acid |
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What regulates the water permeability of the late distal tubule and cortical collecting duct?
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ADH
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What blocks the reabsorption of sodium and potassium secretion here?
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Aldosterone antagonists
(spironolactones) |
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What specific transporters do Aldosterone antagonists act on?
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The Na/K ATPase pumps on the basolateral membrane.
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What blocks the apical Na channels in late distal tubule principle cells?
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Amilioride and Triamterene
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What happens at the Medullary collecting duct?
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-Sodium reabsorption
-ADH-stimulated H2O reabsorption -Urea reabsorption |
