(12) - Tubular Reabsorption Flashcards
(Importance)
- What is the single most critical function of the kidney?
- The success of all body systems depends on successful perfusion of all tissues with blood
- sodium reabsorption and maintntance of an “effective circulating volume”
(Key Points)
- The kidneys have separate mechanisms for regulating sodium and water
- Total body sodium content is regulated by what?
- The majority of Na is reabsorbed where?
- the kidneys
- proximal tubules ( with progressively smaller amounts in the loop of Henle, the distal tubules, and the collecting ducts)
(Key Pints)
- Resportbipn of Na is primarily what kind of process?
- Reabsorption of Cl- is active or passive?
- Reabsorption of water is by what and dependent on what?
- active, transcellular process (driven by Na-K-ATPase at the basolateral membrance)
- both - passive (paracellular) and active (transcellular) (but directly or indirectly coupled to reabsorption of Na)
- osmosis and dependent of reabsorption of solute
(Key Points)
- Reabsorption of most of the filtered water, anions, and osmotic concent is linked to what?
- active reabsorption of Na
(just read the thing)
(Goes with prior cards)
I guess we’ll get to this later
(Renal Sodium Handling)
(REabsorption of sodium is the most important function of the kidneys)
- most renal energy used to perform this task
- maintenance of sodium balance paramount
- ECF volume is sodium-dependent
B
because it will follow sodium - and sodium doesn’t cross ICF
he talked about this for awhile… at 1:08 or so
the answer might actually be D… eck
(ECF volume is sodium dependent)
- sodium restricted to certain fluid spaces (ECF)
- water follows sodium
(Body tonicity is tightly regulated to “set point”)
- do what to achieve this goal?
- what percent saline is isotonic?
- Sodium content determines the volume of the ECF (which determines tissue perfusion)
- Does sodium concent determine the plasma sodium concentration?
- add or subtract water
- 0.9%
- no
only one - one liter
(Sodium Reabsorption)
- vast majority of filtered Na is reabsorbed (most happens in proximal tubule)
- PCT?
- TAL?
- Early DCT?
- Late DCT and CD?
(Proximal Tubular Na Rebsorption)
(Differences between early and late PT)
- early?
- late?
- answer quesation
- reabsorbed with HCO3 and organic solutes
- reabsorbed with Cl; no organic solutes
(IMPORTANT CONCEPT - reabsorb most important stuff first)
- C (cause 67% of Na is reabsorbed and they are proportional)
PHARM
if you put something in the lumen - and it stays in the lumen - it will carry water with it for entire length of nephron (mannitol does this)
furosemide - loop diuretc - acts on loop of Henle
so ones that act early (carbonic anhyrase inhibitors) do leave Na in th elumen - but there are many opportunities to reabsor it as you go on so these aren’ta s powerful
he isn’t going to ask us what specific diuretic acts on which site
(By Midpoint of the PT)
- how much of filtered glucose is reabsorbed?
- what percent of filtered HCO3 is reabsorbed?
- How much of filtered phoshpate, lactate, and citrate hae been reabsorbed?
- what portion of Na reabsorbed?
- 100%
- 85%
- most
- large portion
(Late Proximal Tubule)
(Fluid entering late PT very different from glomerular filtrate)
- organic solutes present?
- high in what?
(Primarily reabsorption of NaCl)
- what is the driving force?
- has transcelluar and paracellular components
- mostly gone
- chlordide (Early PT, HCO3 reabsorbed preferentially over Cl – substantial removal of water in early PT)
- high chloride
(Glomerulotubular balance)
- Which is more important - control of GFR or regulation of tubular Na reabsorption?
- changes in GFR –> ?
- the percentage of filtered Na remains approximately constant
- regulation of tubular Na reabsorption
- proportional changes in reabsorption of Na by the proximal tubules
(Glomerulotubular Balance)
(Changes in PT reabsorption are appropriate!)
- does glomerulotubular balance mean that percentage reabsorbed does not change?
- When changes in percentage reabsorbed occur, they are caused by what?
- what is the goal?
- Mechanisms altering glomerultubular balance are entirely what?
- NO
- factors other than changes in GFR
- prevent large changes in Na excretion
- intrarenal
C
(Glomerular Balance: Mechanisms)
- GT balance secondary “line of defense” to prevent what?
2-3. Mechanism of GT balance depends on relationship between what two things?
- excessive urinary Na loss (autoregulation is first)
- filtration fraction
- Peritubular starling forces
(The loop of Henle)
(Thin descending limb)
- permeable to what?
(Thin ascebding limb)
- permeable to NaCl?
- permeable to water?
(Thick ascending limb)
- active reabsorption of what?
- load-dependent
- permeable to water?
- water and small solutes
- yes
- no
- Na
- nope
(collecting tubules are variably permeable to water due to insertion of aquaporin)
(Sodium and loop of Henle)
- passive exit from what?
(Active reabsorption of Na from thick ascending loop (TAL))
- load dependent?
- increased Na load enters TAL –> ?
- thin loops
- yep
- increased TAL reabsorption of Na+
(Distal Tubule and Collecting Duct)
- is sodium reabsorption load dependent?
(mechanisms of Na transport differ by location)
- early distal tubules
- late distal tubules and collecting ducts
- yes
(Cortical Diluting Segment)
(fluid entering the segment is already dilute)
- Passage through the cortical diluting segment does what to the tubular fluid?
(early distal tubule epithelium is impermeable to water)
- reabsorbs what?
- any water reabsorption?
- further dilutes
- water
- no
(Late Distal Tubule and Collecting Duct)
- what percentage of Na reabsorbed?
- fine adjustments to Na conc occur here
3-4. What are the two major cell types (plus their functions)?
- only 3%
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