Renal Physl 7 Flashcards
What percent of filtered fluid is reabsorbed?
99%
How many liters of urine is produced on average?
1.5L
Why does the kidney filter so much?
To allow the removal of wastes and control of fluid and electrolyte balance
What does the process of water and solute reabsorption from the filtrate to the renal interstitium heavily depend on?
Active transport mechanisms
What do tubular epithelial cells do in reabsorption?
They actively transport solutes out of the filtrate and into the renal interstitium
What does tubular epithelial cells actively transporting solute into the renal interstitium produce?
An electrochemical gradient
How does water get reabsobed?
It follows the solutes through osmosis
What creates a transepithelial electrochemical gradient?
The active transport of sodium ions into the renal interstitium to be reabsorbed
After sodium ions are reabsorbed to the renal interstitium, where is more negative?
The lumen is more negative the the interstitium
What happens as a result of the lumen being more negative and renal interstitium being more positive after sodium ions are actively transported out?
Anions follow the positively charged sodium ions into the interstitium to be reabsorbed
After all the solutes leave the tubule lumen what is the concentration of the filtrate?
The filtrate becomes more dilute compared to the interstium
What happens as a result of the filtrate being more dilute than the interstitium after the solutes enter the interstitium?
The water moves from the tubule lumen to the interstitium and this concentrates the remaining solutes in the tubule lumen
What happens once the filtrate is concentrated due to water moving to the interstitium?
Because the solutes in the lumen are so concentrated it moves down its concentration gradient to the interstitium
What kinds of transport does reabsorption involve?
Transport across tubular epithelial cells as well as paracellular transport
What is transcellular transport?
When solutes pass both the apical and basal lateral membrane of the epithelia cell to get to the renal interstitium
What occurs in the paracellular pathway?
Solutes pass between epithelial cells through cell junction
What does pattern of transport (transcellular or paracellular) depend on?
The permeability of the epithelial cells to each solute and the electrochemical gradient
Where does active reabsorption of sodium ions mostly take place?
At the proximal tubule
What happens since sodium concentration in the lumen is higher than in the cell interior?
Sodium can enter the epithelial cells passively going down its electrochemical gradient at the apical membrane
What kind of channels do sodium ions interact with when going from the lumen to the epithelial cells?
Symporters, antiports, and open leak channels
What channels contribute significantly to sodium reabsorption?
- Sodium hydrogen exchanger or NHE channels
* ENaC (apical epithelial sodium channel)
What transports sodium in the epithelial cell to the renal interstitium?
Sodium Potassium ATPase
What happens as a result of the sodium potassium ATPase actively transporting sodium out of the epithelial cell?
Potassium enters the cell but it can escape back out again through the basolateral potassium leak channels
What can the reabsorption of sodium be linked to?
The reabsorption of other substances through secondary active transport like amino acids, glucose, other ions and metabolites
How is glucose reabsorption linked to sodium reabsorption?
The apical membrane has a sodium glucose transporter SGLT
What keeps the intracellular levels of sodium in the epithelial cells low?
The basolateral membrane active transport of sodium out of epithelial cells
What happens as a result of the active transport of sodium out of epithelial cells?
Sodium can continue to move into the cells down its electrochemical gradient
What happens to glucose as a result of sodium being able to move down its electrical chemical gradient?
The energy can be used to power the apical sodium glucose transporter and facilitate the movement of glucose into the cell against its own concentration gradient
What happens as intracellular glucose concentration rises?
Its facilitated diffusion into the interstitium occurs via basal lateral glucose transporters
How can Urea be reabsorbed?
It can diffuse through epithelial cell junctions if there is a sufficient concentration gradient
What drives water reabsorption from the lumen?
Reabsorption of sodium and other solutes
Can proteins cross the glomerular capillaries?
Very small proteins and peptides can cross the filtration barrier
Where in the tubule are can reabsorption of proteins occur?
In the proximal tubule
How are proteins reabsorbed in the proximal tubule?
Receptor mediated endocytosis at the apical membrane brings them into the epithelial cell. The proteins are broken down by lysosomes into amino acids which are transported to the interstitium
What happens if all reabsorption transporters are occupied?
The transport maximum for a substance will be reached and the excess solute will be excreted in the final urine
What is a situation where reabsorption transporters will be satuarated?
In diabetic patients, circulating glucose maximizes occupation of apical sodium glucose transporters and glucose can’t be reabsorbed and is detected in the urine
What allows solutes and water to enter the peritubular capillaries after being in the interstitium?
The low hydrostatic pressure within the peritubular capillaries and higher colloid osmotic pressure due to a concentration of plasma proteins favors the movement of water and solutes from the interstitium into the capillaries by bulk flow
