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Flashcards in Tubular processing of glomerular filtrate Deck (105)
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What are the 3 basic renal processes that represent all the substances in the urine?

- glomerular filtration
- tubular reabsorption
- tubular secretion


Is tubular reabsorption passive or selective?

Highly selective!!


The glomerular filtrate that is presented to the tubules is basically ______

Plasma, without the protein or anything bound to protein
- need to consider when administering drugs that are bound to protein


Calcium is bound to ____

- filtrate should contain half the concentration of total calcium or the same amount as ionized/unbound calcium


Carrier mediated reabsorption process

Too many solutes presented to be reabsorbed will cause carrier proteins to become saturated and any more solute will pass on and fail to be reabsorbed


What are 4 main substances that are usually reabsorbed 100%?

- glucose
- amino acids
- protein
- bicarb (>99.9%)


What is 1 substance that is never reabsorbed?



Why is urea reabsorbed 50% of the time if it is a waste product?

To increase tonicity of the medulla to allow for reabsorption of water


Route of transport for tubular reabsorption

- across tubular epithelial membranes
- into renal interstitial fluid
- through the peritubular capillary membrane back into the blood


How are water and solutes transported?

- transcellular: thought the cell membrane
- paracellular: through spaces between the cell junctions


Substances are diffused through the peritubular capillary walls into the blood by what 3 forces?

- hydrostatic
- colloidal
- osmotic
*Starlings forces*


Active transport

Moves a solute against an electrochemical gradient and requires energy derived from metabolism


Primary active transport

Transport that is coupled directly to an energy source
- ex: sodium-potassium ATPase pump


Secondary active transport

Transport that is coupled indirectly to an energy source
- ex: reabsorption of glucose due to an ion gradient



Reabsorption of water by a passive physical mechanism, from a region of low solute concentration to high solute concentration


In the proximal tubules, water passage is relatively ______

- compare to controlled passage in the distal tubules and collecting ducts


What are the 4 primary known active pumps?

- Na K ATPase (provides electrochemical gradient for secondary active facilitated uptake of other substances)
- Ca ATPase
- H ATPase
- H K ATPase



Bulk flow
- passive method of transporting solutes thru the peritubular capillary walls into the blood
- mediated by hydrostatic and colloid osmotic forces


Is reabsorption of sodium primary or secondary active transport?

- utilizes an electrochemical gradient (Na-K ATPase)


Where is the Na-K ATPase pump located within the cell?

On the basolateral side
- uses released energy from hydrolysis of ATP to transport sodium ions out of the cell and into the interstitum


Where does sodium diffuse to once it is in the interstitium?

Could go into the peritubular capillary and into the blood, or it could diffuse back into the tubular lumen


Why would sodium move back into the tubular lumen?

Ensures that there is always sodium available to provide substrate for the cotransport of molecules and prevents excessive sodium resorption in times of excessive sodium consumption


There is a ____ concentration of sodium and a ____ concentration of potassium inside the cell

Low; high
- creates a negative charge of -70 millivolts


What is located on the apical side of the proximal tubular epithelial cells to facilitate diffusion?

- brush border
- channels
- molecules/ligands to bind both sodium and another solute (glucose, amino acids, etc)


What are the 3 steps of sodium transport from the tubular lumen into the blood?

- Na diffuses across apical membrane into cell DOWN an electrochemical gradient
- Na is transported across basolateral membrane AGAINST an electrochemical gradient
- Na, water, etc are reabsorbed from intestinal fluid into peritubular capillaries by ultrafiltration


How are proteins reabsorbed due to their large size?

Attach to specific receptor molecules on tubular epithelial cell membrane and are invaginated internally into the cell
--> pinocytosis


What are the requirements of pinocytosis?

- tubulin polymerization
- small changes in cytoskeleton
*both require energy, so pinocytosis is another form of active transport!!*


In secondary active transport _____ interacts with _____ and are transported together across the membrane

2 (or more) substances; specific membrane protein (carrier)
- requires a specialized carrier molecule designed to fit both transported molecules
- BOTH molecules need to be present and bound to carrier for it to work


Does secondary active transport require energy directly from ATP?

No, utilizes electrochemical gradient created by simultaneous facilitated diffusion of another transported substance (usually sodium)


Glucose and amino acids are transported into the cell ______ the electrochemical gradient and are diffused across the basolateral membrane by _______

Against; facilitated diffusion due to concentration gradient inside the cell