Topic 8 B What happens in each segment Flashcards
Proximal Tubule % of filtered load of sodium & water reabsorbed
65%
Little less % for chloride
Quantity can be increased or decreased as needed
Proximal Tubule - mitochondria amount? why?
Contain large number of mitochondria
to support extensive active transport
activity
Proximal Tubule Ultrastructure Luminal border contains what?
extensive number of protein carrier molecules
Proximal Tubule Ultrastructure Co-transport of what?
amino acids and glucose
Proximal Tubule Ultrastructure Counter transport of what?
hydrogen ions (move a large quantity of hydrogen ions against small hydrogen ion gradient
Proximal Tubule Ultrastructure Basolateral border contains extensive amounts of what?
extensive amount of N-K ATPase
First half of Proximal tubule- co-transport of what ? what does it do to Na levels?
Extensive co-transport of sodium with glucose and amino acids
Sodium reabsorption carries glucose, bicarb, organic ions leaving chloride resulting in increasing [Cl-]
105 mEq/L increases to 140 mEq/L
Second half of Proximal Tubule –
Cl concentration ?
High chloride concentration favors chloride diffusion
Some movement may occur through specific chloride channels
Second half of Proximal Tubule –
Electrochemical gradient created by reabsorption how??
Most glucose & amino acids have been reabsorbed–sodium reabsorption drives chloride reabsorption
Electrochemical gradient
Many end products of metabolism are secreted by proximal tubule (4)
Bile salts
Oxalate
Urate
Various catecholamines
drugs & toxins secreted in proximal tubule (2)
Penicillin
Salicylates
Para-aminohippuric acid secreted in proximal tubule – what % used to determine what?
90% of PAH in renal blood flow is removed
Can be used to determine renal blood flow
Thin descending and ascending LOH segments characteristics ? (4)
Thin epithelial membrane
No brush border
Few mitochondria
Minimal metabolic level
Thin descending segment of LOH - permeability to H2O and solutes?
Highly permeable to water
Moderately permeable to most solute
Thin descending segment of LOH - diffusion?
Allows diffusion of water and solutes
Thin descending segment of LOH - reabsorption %?
No active reabsorption
20% of water reabsorption occurs in the loop of Henle
Thin ascending segment - H2O permeability?
impermeable to water
Part of mechanism for concentrating urine
Thick Ascending LOH - epithelial cells characteristics?
Thick epithelial cells with high concentration of mitochondria
Thick Ascending LOH - what % of sodium, chloride, & potassium reabsorbed is filtered load?
(Approx 25% of filtered load)
Thick Ascending LOH - water permeability ?
Fluid is what?
Impermeable to water
As solute reabsorb luminal solute concentrations drop especially since water NOT reabsorbed–Fluid very dilute
Sodium Reabsorption is driven by what in basolateral border of tubule cells?
N-K ATPase
Two transport mechanisms move sodium from tubular lumen (in LOH)
- 1 Na-2Cl-1K co-transport mechanism
- Na-H counter-transport mechanism
Primary transport means of moving sodium out of lumen into tubular cells (in LOH)
1 Na-2Cl-1K co-transport mechanism
Potassium reabsorbed AGAINST potassium concentration gradient
Cl-& K+ diffuse out of cell into renal interstitial fluid via specific ion channels
What loop diuretics inhibit the action of the 1Na-2Cl-1K co-transport mechanism out of lumen into tubular cells (in the LOH)
furosemide, ethacrynic acid, bumetanide
LOOP Diuretics - cause less sodium reabsorption does what to H2O and K
Less sodium reabsorption–less H2O reabsorption in later segments of the nephron
Less sodium reabsorption–less K reabsorption with potential loss of K
Na-Cl-K co-transport mechanism is what?
in LOH lumen
is isoelectric
BUT K able to diffuse back into lumen via potassium channels creating +8 mV positive charge in tubule lumen
Electrical gradient in LOH lumen and tubular cells drives diffusion of what?
Electrical gradient drives diffusion of Na+, K+, Mg++ & Ca++ into the renal interstitial space via the tight junctions (paracellular diffusion)
Macula densa is where??
first part of distal tubule
Part of juxtaglomerular complex
Macula densa provides what?
Provides feedback control for GFR and blood flow (for this nephron)
What is the segment after the macula densa in the distal tubule ? and reabsorption?
High convoluted Segment
Solute reabsorption–no water reabsorption
The High Convoluted Segment is also known as what segment of the distal tubule?
Diluting segment of distal tubule
In Early Distal Tubule what % of filtered load for sodium & chloride reabsorbed
5%
In Early Distal Tubule reabsorbed is driven by what?
Driven by Na-K ATPase in basolateral border of tubular cells
In Early Distal Tubule Na-Cl co-transport mechanism moves Na and Cl where?
mechanism moves Na+ and Cl-into cell down [Na+]
Chloride diffuses out of cell via chloride specific channels
Thiazide diuretics inhibit what mechanism? (in the early distal tubule)
Na-Cl co-transport mechanism
Reduces sodium and chloride reabsorption and ultimately water reabsorption in later segments of nephron
Late Distal Tubule & Cortical Collecting Tubule
Membranes permeability to urea?
impermeable to urea
All urea entering exits to collecting duct to be excreted
Some reabsorption of urea will occur in medullary collecting ducts
Late Distal Tubule & Cortical Collecting Tubule
Na and K secretion is controlled by what?
secretion controlled by various hormones but especially by aldosterone
Late Distal Tubule & Cortical Collecting Tubule
H+ ions secretion?
Able to secrete hydrogen ions against large concentration gradient (1000:1)
Proximal tubule moves hydrogen ions against small gradient (4 to 10:1)
Water permeability controlled by concentration of what?
antidiuretic hormone (ADH, aka vasopressin)
No ADH-no water permeability–excrete dilute urine
Increased conc of ADH increase permeability of water & decrease the volume of urine and increase the conc of the urine
Two types of cells in late distal and cortical collecting duct
Principal cells
Intercalated cells
Principal cells in late distal and cortical collecting duct do what?
Reabsorb sodium & water
Secrete potassium
Intercalated cells in late distal and cortical collecting ducts do what?
Reabsorb potassium
Secrete hydrogen
Principal Cells - what pump drives activity? what border is it on? which way does everything go?
Na-K ATPase in basolateral borders of tubule cells drives activity
Na follows concentration gradient–diffuses through sodium specific channels
K follows concentration gradient out of cell into tubular lumen via potassium specific channels
Aldosterone antagonists is what kind of diuretic ?
K sparing diuretic
Works in Late distal and cortical collecting duct
Aldosterone antagonists work on what receptors?
Mineralocorticoid receptor antagonists
Work in Late distal and cortical collecting duct
Aldosterone antagonists do what?
2 examples?
Compete with aldosterone receptor sites which inhibits Na reabsorption & K secretion
Spironolactone & eplerenone
Na channel blockers work how?
2 examples?
Inhibit entry of sodium into cell which reduces amount of sodium transported by Na-K ATPase
Also reduces secretion of potassium as action of Na-K ATPase decreases
Amiloride & triamterene
Na channel blockers are what kind of diuretic?
K sparing diuretic
ex: Amiloride and Triamterene
Work in Late distal and cortical collecting duct
Intercalated Cell Activity what is H+ ions secretion controlled by?
in Late distal and cortical collecting duct
Secretion controlled by H-ATPase transporter
In the Late distal and cortical collecting duct, Intercalated Cell Activity – the H-ATPase transporter must have have the presence of what for conversion of CO2 and H2O into H+ ions and HCO3?
Presence of carbonic anhydrase allows conversion of CO2 and H2O to hydrogen ions and bicarb ions
In the Late distal and cortical collecting duct, Intercalated Cell Activity – how is Chloride secreted ?
Chloride also secreted following electrochemical gradient
In the Late distal and cortical collecting duct, Intercalated Cell Activity - Bicarb is reabsorbed using what transport mechanism?
Bicarb reabsorbed using Cl-HCO3-counter-transport mechanism following the Cl-gradient into the cell
In the Late distal and cortical collecting duct, Intercalated Cell Activity what is moved freely between cell and interstitial fluid?
CO2 moved freely between cell and interstitial fluid
Meduallary Collecting Ducts reabsorb what % of filtered water and Na?
Reabsorb <10% of filtered water and sodium
Meduallary Collecting Ducts determines what?
Determine final concentration of solutes and urine concentration
Meduallary Collecting Ducts, Water permeability controlled by what?
ADH
Meduallary Collecting Ducts how is Urea reabsorbed?
Urea is reabsorbed via specific urea transporters which moves urea into the interstitial spaces thus affecting osmolarity
Meduallary Collecting Ducts secrete what ion?
Secretes hydrogen ions (like cortical collecting tubule)
Change in solute concentration depends
on what vs what?
rate of reabsorption (secretion) versus rate of water reabsorption
On the squiggly graph with all the different solutes – what does inulin’s line represent?
- what does a conc of 3 mean?
- what does a conc of 125 mean?
Inulin neither secreted or reabsorbed
provides indication of water reabsorption
Inulin conc of 3 means that 1/3 of water remains in tubule (2/3 has been reabsorbed)
Inulin conc of 125 means 1/125 of water remains while 124/125 has been reabsorbed
