Tubular Reabsorption & Secretion(B)- Exam 3 Flashcards
What percent of filtered load of sodium and water is reabsorbed in the proximal tubule?
65% (little less percentage for chloride; quantity can be increased or decreased as needed)
What are the cells of the proximal tubule designed for?
High reabsorption capacity of sodium and water
What supports the extensive active transport activity in the proximal tubule?
Contains a large number of mitochondria
What provides a huge surface area for rapid diffusion in the proximal tubule?
Luminal (apical) brush border
What contains extensive number channels in between cells providing huge surface area?
Basolateral border
What contains extensive number of protein carrier molecules in the proximal tubule?
Luminal border
Why is there an extensive number of protein carrier molecules in the proximal tubule?
Co-transport of amino acids and glucose
Counter-transport of hydrogen ions (move a large quantity of hydrogen ions against small hydrogen ion gradient)
What contains an extensive amount of N/K ATPase in the proximal tubule?
Basolateral border
What is notable about the first half of the proximal tubule?
- Extensive co-transport of sodium with glucose and amino acids
- Sodium reabsorption carries glucose, bicarb, organic ions leaving chloride resulting in increasing [Cl-]
What is the change in [Cl-] in the early part of the proximal tubule?
105 mEq/L increases to 140 mEq/L
What is notable about the second half of the proximal tubule?
- High chloride concentration favors chloride diffusion (some movement thru Cl- channels)
- Most glucose and amino acids have been reabsorbed; sodium reabsorption drives chloride reabsorption (electrochemical gradient)
What changes (quantity/concentration) in the tubule throughout the reabsorption process?
Quantity of sodium in tubule changes, but concentration does not change because water reabsorption matches sodium reabsorption
Does osmolarity change during reabsorption?
No, water reabsorption matches sodium reabsorption
What happens to glucose and amino acid concentrations as they move through the tubules?
Decrease due to extensive reasborption
What happens to creatinine and urea concentrations as they move through the tubule?
they become more concentrated because they are not reabsorbed
Total amount of Na+, Cl-, HCO3-, glucose, amino acids in tubules ________(increase/decrease/does not change).
Decrease; but Cl- concentration goes up as were in the second half of the proximal tubule
Total amount of creatinine and urea in tubule _________(increase/decrease/does not change)
Does not change
What end products of metabolism are secreted by the proximal tubule?
Bile salts
Oxalate
Urate
Various catecholamines
What drugs and toxins are secreted?
Penicillin
Salicylates
What other acid is also secreted?
Para-aminohippuric acid (PAH)
What percent of PAH in the renal blood flow is removed?
90%
How can you use PAH to determine renal blood flow?
Knowing that 90% of PAH in renal blood flow is removed
What are the three functional segments of hte loop of henle?
Thin descending segment
Thin ascending segment
Thick ascending segment
What kind of membrane/characteristics does the thin descending and ascending segments have?
Thin epithelial membrane
(No brush border)
Few mitochondria (not a lot of active transport)
Minimal metabolic level
What is the only thing moving in the thin descending and ascending segments?
Water is the only thing that’s moving; and solutes through diffusion (no active transport)
What is the thin descending segment highly permeable to? Moderately permeable to?
Highly permeable: Water
Moderately permeable: Most solute
What percent of water reabsorption occurs in the loop of henle?
20%
What segment of the loop of henle is impermeable to water?
Thin ascending segment; part of mechanism for concentration urine
Describe the epithelial cells and mitochondria in the thick ascending segment.
Thick epithelial cells
High concentration of mitochondria
Why are there a lot of mitochondria in the thick ascending segment?
High level of metabolic activity
Thick ascending segment can absorb what percent of the filtered load?
25%; reabsorbs sodium, chloride, potassium.
Also absorbs: calcium, bicarb, magnesium
What is the thick ascending segments permeability to water?
Impermeable to water; as solute reabsorb luminal solute concentrations drop especially since water not reabsorbed (dilute fluid)
What drives sodium reabsorption?
N/K ATPase in basolateral border of tubule cells
What two transport mechanisms move sodium from the tubule lumen?
1 Na-2Cl-1K co-transport mechanism
Na-H Counter-transport mechanism
What is the primary means of moving sodium out of lumen into tubular cells?
1 Na-2Cl-1k co-transport mechanism
How does the 1Na-2Cl-1K co-transport mechanism affect electroneutrality?
It doesn’t affect it.
Potassium is reabsorbed _________(with/against) the potassium concentration gradient in the 1Na-2Cl-1K co-transport mechanism.
against
In the 1Na-2Cl-1K co-transport mechanism, what two ions diffuse out of the cell into renal interstitial fluid via specific ion channels?
Cl- and K+
What three diuretics inhibit the action of the 1Na-2Cl-1K co-transport mechanism?
Furosemide
Bumetanide
Ethacrynic acid
Less sodium reabsorption- ______(more/less) water reabsorption in later segments of the nephron.
Less
Less sodium reabsorption- ______(more/less) potassium reabsorption with potential loss of potassium.
Less
What co-transport mechanism is isoelectric?
Na-Cl-K co-transport
What is able to diffuse back into lumen via channels?
Potassium via potassium channels
What charge is created when K diffuses back into the lumen?
+8 charge in tubule lumen
Electrical gradient drives diffusion of what ions? How?
Na+, K+, Mg++ and Ca++ into renal interstitial space; via tight junctions (paracellular diffusion)
What forms the first part of the distal tubule?
Macula densa
What is the macula densa? What does it do?
Part of the juxtaglomerular complex
Provides feedback control for GFR and blood flow (for this nephron)
Describe the segment in the distal tubule past the macula densa.
Highly convoluted
What kind of reabsorption happens in the distal tubule past the macula densa?
Solute reabsorption
No water reabsorption
“diluting segment of the distal tubule”
In the early distal tubule, what percent of filtered load for sodium and chloride are reabsorbed?
5%
Reabsorption of sodium and chloride in the early distal tubule is driven by what?
Na-K ATPase in basolateral border of tubular cells
What co transport mechanism occurs in the early distal tubule?
Na-Cl co-transport mechanisms moves Na+ and Cl- into cell down [Na+]
How does chloride diffuse in the early distal tubule?
Out of cell via chloride specific channels
What inhibits Na-Cl co-transport mechanism in the early distal tubule? How?
Thiazide diuretics; reduces sodium and chloride reabsorption and ultimately water reabsorption in later segments of nephron
Late Distal Tubule and Cortical Collecting Tubule membranes are impermeable to what?
Urea; all urea entering exist to collecting duct to be excreted; some reabsorption will occur in the medullary collecting ducts
How is sodium reabsorption controlled in the late distal tubule and cortical collecting ducts?
Various hormones; but especially by aldosterone
How is potassium secretion controlled in late distal tubule and cortical collecting ducts?
Various hormones, especially by aldosterone
What happens with hydrogen in the late distal tubule and cortical collecting ducts?
Able to secrete hydrogen ions against a large concentration gradient (1000:1)
Proximal tubule moves hydrogen ions against what gradient?
(4 to 10) :1
What controls water permeability in the late distal tubule and cortical collecting ducts?
Concentration of ADH, aka vasopressin
What happens in late distal tubule and cortical collecting ducts if there’s no ADH?
No water permeability; excrete dilute urine
What happens in late distal tubule and cortical collecting ducts w/ increased ADH?
Increased permeability of water and decrease in volume of urine and increase the concentration of urine
What happens if aldosterone is increased?
Sodium reabsorption goes up
What are the two types of cells in the late distal tubule and cortical collecting ducts?
Principal cells
Intercalated cells
Principal cells reabsorb and secrete what
reabsorb sodium and water
secrete potassium
Intercalated cells reabsorb and secrete what
Reabsorb potassium
Secerete hydrogen
What drives the activity of principle cells?
Na-K ATPase in basolateral borders of tubule cells
Describe the gradients of Na and K in principle cells.
Sodium follows concentration gradient-diffuses through sodium specific channels
Potassium- follows concentration gradient out of cell into tubular lumen via potassium specific channels
Aldosterone antagonists are also called what?
Mineralcorticoid receptor antagonists
How do aldosterone antagonists work?
Compete with aldosterone receptor sites which inhibits sodium reabsorption and potassium secretion
What are some examples of aldosterone antagonists?
Spironolactone
Epleronone
What is a potassium sparing diuretic?
Sodium channel blockers; amiloride, triamterene
How do sodium channel blockers work?
Inhibit entry of sodium into cell which reduces amount of sodium transported by Na-K ATPase; reduces secretion of potassium as action of Na-K ATPase decreases
What ions have intercalated cell activity?
Hydrogen ions
Secretion of H+ are controlled by what?
H-ATPase transporter
Presence of what allows conversion of CO2 and H2O to hydrogen ions and bicarb?
Carbonic anhydrase
What is also secreted from cell with H+ ions?
Chloride; following electrochemical gradient
What happens to bicarb (intercalated cell activity)? What else has this same action?
Reabsorbed using Cl- HCO3- counter transport mechanism following the Cl- gradient into the cell
Potassium is also reabsorbed.
What happens with CO2?
Moves freely between cell and interstitial fluid
Medullary collecting ducts reabsorb what percent of filtered water and sodium?
<10%
What determines final concentration of solutes and urine concentration?
Medullary collecting ducts
Describe the epithelial cells and mitochondria in medullary collecting ducts.
Epithelial cells smooth with few mitochondria
What controls water permeability in medullary collecting duct?
ADH
How is urea reabsorbed in medullary collecting duct?
Specific urea transporters which moves urea into the interstitial space thus affecting osmolarity
What happens to hydrogen ions in the medullary collecting duct?
Secretes hydrogen ions (like cortical collecting tubule)
Change in solute concentration depends on what?
Rate of absorption (secretion) vs rate of water absorption
What happens to inulin? What does it indicate?
neither secreted or reabsorbed provides indication of water reabsorption
What does an inulin concentration of 3 mean?
1/3 of water remains in tubule (2/3 have been reabsorbed)
What does an inulin concentration of 125 mean?
1/125 of water remains in tubule 124/125 has been reabsorbed
