Renal 3 Flashcards
How much fluid is excreted in the body
180L/day is filtered and less than 1% is actually excreted, Most of it reabsorbed
Purpose of Reabsorbtion
It allows kidneys to selectively regulate ions and water to the plasma to maintain homeostasis
Why do you filter 180L if only 1% is eliminated
Because many foreign substances filtered into tubules but not reabsorbed
Frequent filteration of ions and water into the tubules simplifies regulation and allows it to occur rapidly
Is reabsorbtion active or passive
Both
Steps of fluid reabsorbtion
Na + is reabsorbed by active transport
Anions follow due to the positive in ECF
Electrochemical gradient drives anion reabsorbtion
Water moves by osmosis, following solute reabsorbtion. Concentrations of other solutes increase as fluid volume in lumen decreases
Permeable solute are reabsorbed by diffusion through membrane transporters or by the paracellular pathway
Transepithelial Transport
Substances cross the apical and basolateral membrane of the tubule cells to enter the ECF
Paracellular Transport
Substances pass through the cell to cell junctions between 2 adjacent tubule cells
2 types of Active Transport Na+
- Basolateral Na+ Active Transport
- Secondary Active Transport: Symport with Na+
Basolateral Na+ Transport
- Moves through various membrane proteins and moves down its electrochemical gradient (Apical Side)
- Na + is pumped out the basolateral side of cell by the Na+ K+ ATPase
Secondary Active Transport: Symport with Na+
- Na+ moving down its concentration gradient
- Glucose diffuses out the basolateral side of the cell using the GLUT protein
- Na+ is pumped out by Na K+ ATPase
Passive Absorbtion
urea (Nitrogenous waste product)
Due to the movement of sodium into the ECF, the concentration of Urea in the filtrate goes up. Which creates a contration gradient for urea to move into the ECF
Endocytosis
very small plasma proteins or peptides using megalin
Example of Endocytosis in reabsorbtion
Receptor mediated endocytosis
Receptor binding plasma proteins known as megalin
- Once the cell the proteins are digested by lysomes
How are majority of the substances transported in the nephron
They use membrane proteins
Saturation
The maximum rate of transport that occurs when all available carriers are occupied
In an average individual you never reach saturation
How does saturation effect in filteration
Amount of glucose filtered depends on the plasma glucose
How does saturation effect in reabsorbtion
- The transport rate at saturation is the transport maximum
- Excess glucose filteres = more glucose than transporters and some glucose is excerted (diabetes)
Renal threshold
When solute starts to show up in urine
Occurs at transport maximum
When does renal threshold occur
occurs at Transport maximum
Amount Exerted
Amount filtered - amount reabsorbed + amount secreted
Glucose excreted
Glucose filtered - glucose absorbed
Glycosuria
- Glucose appearing in urine
- Occurs with elevated blood glucose
- Rare genetic disorder with reduced transporters
Which pressures favor reabsorbtion
Peritubular capillary pressures
What drives reabsorbtion
Sodium in the proximal tubule
Pathway of reabsorbtion
Proximal Tubule lumen - Epithelial cells of nephron - Extracellular fluid
Apical membrane
Faces the lumen of nephron
Basolateral membrane
Faces the extracellular fluid
Filtrate and plasma both
Are isosmotic
Same solute concentration
No concentration gradient
Where does active transport of sodium occur
At the Basolateral membrane using Sodium pottasium ATPase
ENac
Sodium transporters through just a simple concentration gradient (Fascilitated diffusion)
Glucose is low
In ECF and filterate
Where does secondary active sodium transport occur
Through symport using SGLT protein
Concentration of urea in ECF and filterate is
Equal
What kind of transport does urea use
Paracellular Transport
Majority of reabsorbtion happens due to the finite amount of
membrane proteins
The amount of glucose filtered depends on the
Plasma Concentration
As plasma glucose concentration goes up
Reabsorbtion goesup and Glucose transport into ECF goes up
Transport maximum
When saturation reached
More glucose than trasnporters
Lose glucose in urine (Diabetes)
hydrostatic pressure at peritubular cappilaries
10mmHg and its low
Second part of reabsorbtion
Peritibular pressure in 10 lower then oncotic pressure of 30
This creates a gradient for blood to travel into the peritubular capillaries
net pressure at peritubular pressure
20mmHg
Secretion
Transfer of molecules from ECF into the lumen of the nephron
Secretion depends on
Membrane transport proteins
What kind of transportation process does secretion use
Only Active process
Why does secretion occur
Homeostatic regulation of K+ and H+ (Distal)
Organic compoind removal
Amount Excreted =
Amount filtered - amount reabsorbed + amount secreted
Where does secretion occur
Proximal Tubule
Primary active transport during secretion
Happens at basolateral membrane to keep intracellular Na concentration low
Secondary Indirect Active Transport during secretion
Happens at apical membrane and basolateral membrane. Uses NaDC cotransporter
teritary active transport
Happens both at apical and basolateral membrane (OAT 1-3)
Excretion
Tells us what the body is eliminating
