Term
| Renal handling of water, sodium, glucose, urea |
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Definition
- water- 99% reabsorbed
- sodium- 99.5% reabsorbed
- glucose- 100% reabsorbed, should never be present in urine**
- urea- 50% reabsorbed, amount excreted by the amount of urea produced per day*
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Term
| Transcellular vs. Paracellular movement |
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Definition
- transcellular- majority of solutes travel through the tubular epithelial cells
- paracellular- travel of solutes through the tight junctions b/w the cells
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Term
| 5 Basic Mechanisms for transcellular solute movement |
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Definition
Passive "downhill"
- simple diffusion- down electrochemical gradient via lipid bilayer/aqueous channels **NOT SATURATABLE**
- facilitated diffusion- down elctrochem gradient; specific carriers required
Active (Energy dependent)
- Primary active trans- against electochem grad, ATP hydrolysis provides E (ie. w/sodium transport)
- Secondary active trans- gradient of one substance provides the driving force for other substance (cotransport, countertransport)
- endocytosis- (protein reabsorption in the proximal tubule)
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Term
| Proximal tubular transport |
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Definition
- reabsorbs most of filtered water, sodium, potassium, bicarbonate, calcium, phosphate
- reabsorbs all filtered glucose & amino acids
- several organic anions & cations (including drugs, drug metabolites...) secreted in proximal tubule
** understand graph slide 12
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Term
| TF/P ration in Proximal Tubular Lumen: |
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Definition
- inulin- appears to rise, this is b/c concentration has increased 3 fold due to 2/3 water reabsorption
- glucose-falls to zero b/c it is absorbed w/the water
- PAH- secreted into the tubule & becomes more concentrated w/the 2/3 water reabsorption
- sodium- drives the water reabsorption & is usually coupled to transport of another solute **Powered by Na+, K+ ATPase in basolateral membrane
- Urea & Cl- become more concentrated in luminal fluid (2/3 water reabsorption) provides dring force for PARACELLULAR REABSORPTION
- water- carries dissolved solutes w/it into peritubular capillaires by bulk flow
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Term
| Sodium pumps linked to trancellular transport of other substances |
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Definition
- Na+, K+ ATPase- most important driving force for all other pumps (K+in, Na+ out)
- Na+ glucose- cotransport of glucose & sodium inside cell
- Na+ H+-counter cotransport, maintains pH
- Na+, K+, 2Cl- cotransport into cell
last 3 should be considered secondary active transport**
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Term
| Factors promoting fluid movement into peritubular capillaries |
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Definition
- high plasma colloid osmotic pressure (proteins)
- low hydrostatic pressure of blood in capillaries
** leads to amount of filtered fluid almost equal to reabsorbed amount
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Term
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Definition
- example is Mannitol- similar to glucose but is not absorbed and remains in lumen thus draws water and sodium back into lumen
- increases water & sodium excretion
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Term
| Basic Mechanism of tubular reabsorption |
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Definition
1. Secondary active transport (transcellular only)
2. uptake across luminal membrane:
- against concentration gradient
-coupled to Na+ entry
-ULTIMATELY DEPENDENT ON Na+ K+ ATPase
3. exits cell through basolateral membrane by facilitated diffusion |
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Term
| Glucose reabsorption is saturable |
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Definition
- limited # of Na+ glucose cotransporters in luminal membrane
- if filtered amount > critical rate:
- capacity of nephrons to reabsorb all filtered glucose is exceeded
gucose appears in urine (glucosuria)
- dz where saturation occurs- Diabetes
** Same principles apply to amino acid transport** |
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Term
Secretion of organic anions (ex: PAH) in PCT:
tertiary active transport |
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Definition
- Na, K ATPase estabhlish the Na electrochem grad across the membrane, driving force for...
- Na cotransport w/alpha-ketoglutarate (aKG) to concentrate aKG in cell to drive...
- exchange of aKG w/organic anion across basolateral membrane, this counter-transport concentrates organic anion in the cell which leads to...
- movement of organic anion across apical membrane into tubular lumen..
- and eventually voided from the body in urine
** PAH secretion is saturable** see slide 34
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Term
| Passive diffusion of organic acids & bases |
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Definition
- organic anions & cations are ionized forms of weak acids & bases
- charged forms are highly polar, hydrophilic (cannot diffuse through lipid bilayer)
- uncharged molecules: less polar, more lipid-soluble & therefore membrane-permeable
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Term
| Biochem of weak acids & bases |
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Definition
- Acidic sol'n- generate neutral forms of weak acids (A- + H+ = HA, neutral is protonated)
- Basic sol'n-generate neutral forms of weak bases (B + H+ = BH+, neutral is deprotonated)
** pH of luminal fluid determines what happens w/acids & bases
- acid (low pH) in tubular lumen favors reabsorption of organic acids; traps organic bases (thus they are excreted)
- Patient overdoses on aspirin (organic acid), how can yu promote urinary excretion of it from his body? --> administer a base (will cause the aspirin/acid to stay in lumen and be excreted)
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