67: Tubular Reabsorption Flashcards
Reabsorption = ____ capillaries
Secretion = ______ fluid
Renal handling of solutes not synthesized by the kidney. Excreted = ___ + ____ - ______
Excretion & secretion units =
Filtered equation =
Excreted equation=
Reabsorption = peritubular capillaries
Secretion = tubular fluid
Renal handling of solutes not synthesized by the kidney. Excreted = Filtered + Secreted - Reabsorbed
Excretion = mMol/min
Filtered = P(mM) x GFR (ml/min)
Excreted = U(mM) x V (ml/min)
UV = PxGFR + mMol/min =
The concentration of filtered organic and inorganic solutes is the ___ in the plasma and in the tubular ultrafiltrate.
Most solute transport from the lumen to the peritubular space is active and is driven by energy released upon ATP hydrolysis via _____ active transport or by coupling to energy stored in transmembrane ion gradients via _____ active transport.
Water transport from the lumen to the peritubular space across the tubular epithelium is ____ and occurs via osmosis.
Transtubular, epithelial transport of solutes from the tubular fluid to the peritubular fluid causes an effect of _____ the water concentration in the tubular fluid and _____ the water concentration in the peritubular fluid. The gradient of water concentration created by trans-epithelial solute transport drives _____ transport of water _____ the water concentration gradient. Solute transport-dependent changes in osmolarity drive solute transport-dependent transport of water and illustrates the principle of osmosis where “water transport follows solute transport”.
The concentration of filtered organic and inorganic solutes is the same in the plasma and in the tubular ultrafiltrate.
Most solute transport from the lumen to the peritubular space is active and is driven by energy released upon ATP hydrolysis via primary active transport or by coupling to energy stored in transmembrane ion gradients via secondary active transport.
Water transport from the lumen to the peritubular space across the tubular epithelium is passive and occurs via osmosis.
Transtubular, epithelial transport of solutes from the tubular fluid to the peritubular fluid causes an effect of increasing the water concentration in the tubular fluid and decreasing the water concentration in the peritubular fluid. The gradient of water concentration created by trans-epithelial solute transport drives passive transport of water down the water concentration gradient. Solute transport-dependent changes in osmolarity drive solute transport-dependent transport of water and illustrates the principle of osmosis where “water transport follows solute transport”.
The transport pathway of solutes and water in the renal tubular epithelium can be either ______ or through the cell or _____ or between the junctions of cells. Both paracellular and transcellular can be involved in secretion or reabsorption.
The Na-K ATPase is only on the ______ membrane of all epithelial cells, where it maintains the concentration gradients of sodium and potassium and an inside ______ membrane potential difference.
The transport pathway of solutes and water in the renal tubular epithelium can be either transcellular or through the cell or paracellular or between the junctions of cells. Both paracellular and transcellular can be involved in secretion or reabsorption.
The Na-K ATPase is only on the basolateral membrane of all epithelial cells, where it maintains the concentration gradients of sodium and potassium and an inside negative membrane potential difference.
Primary active transport mechanisms capture and transduce the energy of ATP _____ to the energy stored in the formation of a solute electrochemical potential gradient. Primary active transport mechanisms include the ATP dependent “______”: Na+-K+ ATPase, H+ ATPase, H+-K+ ATPase.
Primary active transport mechanisms capture and transduce the energy of ATP hydrolysis to the energy stored in the formation of a solute electrochemical potential gradient. Primary active transport mechanisms include the ATP dependent “pumps”: Na+-K+ ATPase, H+ ATPase, H+-K+ ATPase.
Secondary active transport mechanisms transduce the energy of an ________ potential gradient of one solute into the energy stored in the formation of an ______ potential gradient of a second solute.
Secondary active co-transporters or symporters transport the driving and driven solute in the ______ direction across the membrane. The driving solute of most symporters is ______, which has a gradient going from ____ to _____ the cell.
Secondary active counter-transporters or antiporters or exchangers transport the driving and driven solute in _____ directions across the membrane. Exchangers transport in either direction across the membrane.
Secondary active transport mechanisms transduce the energy of an elecrochemical potential gradient of one solute into the energy stored in the formation of an electrochemical potential gradient of a second solute.
Secondary active co-transporters or symporters transport the driving and driven solute in the same direction across the membrane. The driving solute of most symporters is sodium, which has a gradient going from outside to inside the cell.
Secondary active counter-transporters or antiporters or exchangers transport the driving and driven solute in opposite directions across the membrane. Exchangers transport in either direction across the membrane.
Passive transport mechanisms done by carriers or channels mediate _____ diffusion of solute down their gradient across the membrane in either an inward or outward direction.
Passive transport mechanisms done by carriers or channels mediate facilitated diffusion of solute down their gradient across the membrane in either an inward or outward direction.
Paracellular transport is:
- _____ and driven by a transepithelial solute electrochemical potential gradient.
- Depends on the “_____” or solute-specific resistance to transport through of intercellular junctions. The ability of epithelia to maintain a transepithelial voltage difference or an osmotic gradient is determined by the cell-to-cell junctional resistance or “leakiness” of the epithelium to solute and water transport across the junction.
- Movement of water from the _____ lumen across the intercellular junctions to the _____ space occurs by osmosis and may entrain the movement of solute by a process of “solvent drag”, which contributes to transtubular solute reabsorption or secretion.
Paracellular transport is:
- Passive and driven by a transepithelial solute electrochemical potential gradient.
- Depends on the “tightness” or solute-specific resistance to transport through of intercellular junctions. The ability of epithelia to maintain a transepithelial voltage difference or an osmotic gradient is determined by the cell-to-cell junctional resistance or “leakiness” of the epithelium to solute and water transport across the junction.
- Movement of water from the tubular lumen across the intercellular junctions to the peritubular space occurs by osmosis and may entrain the movement of solute by a process of “solvent drag”, which contributes to transtubular solute reabsorption or secretion.
______ drag is when solutes in the ultrafiltrate are transported back from the renal tubule by the flow of water rather than specifically by ion pumps or other membrane transport proteins. It generally occurs in the paracellular pathway across the tubular cells.
Solvent drag is when solutes in the ultrafiltrate are transported back from the renal tubule by the flow of water rather than specifically by ion pumps or other membrane transport proteins. It generally occurs in the paracellular pathway across the tubular cells.
By definition, transport from the lumenal fluid across the cell to the peritubular fluid is ______.
By definition, transport from the peritubular fluid across the cell to the lumenal fluid is _____.
By definition, transport from the lumenal fluid across the cell to the peritubular fluid is reabsorption.
By definition, transport from the peritubular fluid across the cell to the lumenal fluid is secretion.
Tubular reabsorption of a solute may result from active transport uptake @ the ______ membrane and passive transport efflux @ the _____ membrane or passive transport uptake @ the _____ membrane and active transport efflux @ the _____ membrane.
Tubular secretion of a solute may result from active transport uptake @ the _____ membrane and passive transport efflux @ the _____ membrane or passive transport uptake @ the _____ membrane and active transport efflux @ the ______ membrane.
Transcellular reabsorption and secretion is saturable and a maximum rate called _____.
Transcellular reabsorption and secretion is inhibitable by drugs (diuretics) and citculating metabolites.
Diuretics block efflux & ______ the excretion of solute of water in the urine.
Diuretics are used to treat ______ to remove sodium & water.
Tubular reabsorption of a solute may result from active transport uptake @ the luminal membrane and passive transport efflux @ the basolateral membrane or passive transport uptake @ the luminal membrane and active transport efflux @ the basolateral membrane.
Tubular secretion of a solute may result from active transport uptake @ the basolateral membrane and passive transport efflux @ the lumenal membrane or passive transport uptake @ the basolateral membrane and active transport efflux @ the lumenal membrane.
Transcellular reabsorption and secretion is saturable and a maximum rate called Tmax.
Transcellular reabsorption and secretion is inhibitable by drugs (diuretics) and citculating metabolites.
Diuretics block efflux & increase the excretion of solute of water in the urine.
Diuretics are used to treat hypertenson to remove sodium & water.
The renal handling of glucose by the nephron includes filtration and reabsorption, but ____ secretion. The amount of glucose excreted in the urine is a function only of the amount filtered and the amount reabsorbed. Because the first tubular segment of the nephron, the _____, is the only segment of the nephron where glucose reabsorption occurs, all glucose escaping reabsorption in the proximal tubule will be excreted in the urine.
Excreted glucose = _______
Glucose is all reabsorbed from _____. After this, you saturate the ability of the proximal tubule to reabsorb glucose. The proximal tubule is the only place that reabsorbs glucose. In diabetes mellitus, glucose is not completely reabsorbed in the proximal tubule due to saturation so glucose will spill over into the ____ since the nephron segments beyond the proximal tubule do not have the capacity to transport glucose. See pg. 179.
The renal handling of glucose by the nephron includes filtration and reabsorption, but not secretion. The amount of glucose excreted in the urine is a function only of the amount filtered and the amount reabsorbed. Because the first tubular segment of the nephron, the proximal tubule, is the only segment of the nephron where glucose reabsorption occurs, all glucose escaping reabsorption in the proximal tubule will be excreted in the urine.
Excreted glucose = Filtered + Secreted (0) - Reabsorbed = Filtered - Reabsorbed
Glucose is all reabsorbed from 0 - 10 mM. After this, you saturate the ability of the proximal tubule to reabsorb glucose. The proximal tubule is the only place that reabsorbs glucose. In diabetes mellitus, glucose is not completely reabsorbed in the proximal tubule due to saturation so glucose will spill over into the urine since the nephron segments beyond the proximal tubule do not have the capacity to transport glucose. See pg. 179.
The clearance of glucose is zero at normal circulating levels of glucose and begins to increase at plasma levels of approximately 200 mg/dL (11 mM). This is a threshold plasma concentration at which glucose begins to appear in the urine. The role of the kidney in maintaining glucose homeostasis is to return filtered glucose to the circulation _____ when plasma glucose levels are excessively high, such as occurs in poorly controlled diabetes mellitus.
Tm is the tubular _____ maximum defining the maximum solute ______ rate (mMoles/min) or capacity for tubular solute _______. As plasma solute concentration increases and approaches the Tm the cell membrane transport mechanisms mediating transcellular solute reabsorption become saturated and solute begins to appear in the _____.
The clearance of glucose is zero at normal circulating levels of glucose and begins to increase at plasma levels of approximately 200 mg/dL (11 mM). This is a threshold plasma concentration at which glucose begins to appear in the urine. The role of the kidney in maintaining glucose homeostasis is to return filtered glucose to the circulation except when plasma glucose levels are excessively high, such as occurs in poorly controlled diabetes mellitus.
Tm is the tubular reabsorptive maximum defining the maximum solute reabsorptive rate (mMoles/min) or capacity for tubular solute reabsorption. As plasma solute concentration increases and approaches the Tm the cell membrane transport mechanisms mediating transcellular solute reabsorption become saturated and solute begins to appear in the urine.
______cellular glucose reabsorption across the proximal tubule:
Lumenal membrane:
• Na+ – Glucose cotransporter(s) mediate the concentrative accumulation of glucose ______ the cell driven by the inwardly directed Na + electrochemical potential gradient.
• The Na + to Glucose transport stoichiometry or coupling ratio is 1 or 2 to 1 resulting in net ______ charge transfer with each glucose transported. This property makes Na + – glucose cotransport ______ and sensitive to membrane potential as an additional driving force increasing concentrative glucose accumulation.
Basolateral membrane:
• ______ efflux of intracellular glucose mediated by facilitated diffusion (uniporter).
Transcellular glucose reabsorption across the proximal tubule:
Lumenal membrane:
• Na+ – Glucose cotransporter(s) mediate the concentrative accumulation of glucose inside the cell driven by the inwardly directed Na + electrochemical potential gradient.
• The Na + to Glucose transport stoichiometry or coupling ratio is 1 or 2 to 1 resulting in net positive charge transfer with each glucose transported. This property makes Na + – glucose cotransport electrogenic and sensitive to membrane potential as an additional driving force increasing concentrative glucose accumulation.
Basolateral membrane:
• Passive efflux of intracellular glucose mediated by facilitated diffusion (uniporter).
The filtered load or amount filtered ( PPO4 x GFR) of monobasic (H2PO4-) and dibasic phosphate (HPO42- ) is approximately 250 mMole/day, which is more than 10-fold the total extracellular pool of phosphates. Phosphate reabsorption occurs in the ____ where approximately 90% of the filtered load is returned to the circulation. As shown above, proximal tubular phosphate reabsorption increases with _____ filtered load of phosphate and approaches a tubular maximum of phosphate reabsorption where the process of transcellular phosphate transport becomes saturated and the rate of phosphate reabsorption becomes maximal and constant.
Note, like glucose, the renal handling of phosphate at normal physiological levels results in virtually _____ reabsorption of the filtered load of phosphate and a small, but important, amount of phosphate remains in the tubular fluid and is excreted in the urine.
The filtered load or amount filtered ( PPO4 x GFR) of monobasic (H2PO4-) and dibasic phosphate (HPO42- ) is approximately 250 mMole/day, which is more than 10-fold the total extracellular pool of phosphates. Phosphate reabsorption occurs in the proximal tubule where approximately 90% of the filtered load is returned to the circulation. As shown above, proximal tubular phosphate reabsorption increases with increasing filtered load of phosphate and approaches a tubular maximum of phosphate reabsorption where the process of transcellular phosphate transport becomes saturated and the rate of phosphate reabsorption becomes maximal and constant.
Note, like glucose, the renal handling of phosphate at normal physiological levels results in virtually complete reabsorption of the filtered load of phosphate and a small, but important, amount of phosphate remains in the tubular fluid and is excreted in the urine.
Phosphate reabsorption is _____ in the ____ tubule.
Na + – PO4 ______ mediate the concentrative accumulation of PO4 inside the cell driven the inwardly directed Na + electrochemical potential gradient @ the _____ membrane. The Na + to PO4 transport stoichiometry or coupling ratio is 2 or 3 to 1 resulting in net _____ charge transfer with each PO4 transported. This property makes Na + – PO4 cotransport electrogenically positive and sensitive to membrane potential as an additional driving force increasing concentrative, intracellular PO4 accumulation. Titration of dibasic to monobasic PO4 by increasing tubular fluid acidity inhibits PO4 transport by _____ the concentration of dibasic PO4 (pK – 7.2) and the transport of dibasic PO4.
_____ efflux of intracellular PO4 is mediated by facilitated diffusion @ the basolateral membrane.
Phosphate reabsorption is transcellular in the proximal tubule.
Na + – PO4 cotransporter(s) mediate the concentrative accumulation of PO4 inside the cell driven the inwardly directed Na + electrochemical potential gradient @ the lumenal membrane. The Na + to PO4 transport stoichiometry or coupling ratio is 2 or 3 to 1 resulting in net positive charge transfer with each PO4 transported. This property makes Na + – PO4 cotransport electrogenically positive and sensitive to membrane potential as an additional driving force increasing concentrative, intracellular PO4 accumulation. Titration of dibasic to monobasic PO4 by increasing tubular fluid acidity inhibits PO4 transport by decreasing the concentration of dibasic PO4 (pK – 7.2) and the transport of dibasic PO4.
Passive efflux of intracellular PO4 is mediated by facilitated diffusion @ the basolateral membrane.
