RP4: Tubular Reabsorption and Secretion Flashcards
early distal tubule cell
alpha intercalated cell
early proximal tubule cell
Beta intercalated cell
principal cell
thick ascending limb cell
late proximal tubule
How can solutes go from the lumen into the tubular cells?
paracellular path
transcellular path
using active or passive (diffusion)
How can water go from the lumen into the tubular cells?
osmosis paracellularly or transcellularly
How do solutes and water go from the interstitial fluid (basolateral side) to the peritubular capillaries?
bulk flow
When something travels from the tubular cell to the capillary via interstial fluid what is the process called?
reabsorption
Which membrane of the tubular cell is apical?
facing the lumen
Which membrane of the tubular cell is basolateral?
facing the peritubular capillary
Once fluid is reabsorbed across the tubule epithelium into the interstitial fluid, it enters peritubular capillaries via…
Bulk Flow
The normal rate of Peritubular Capillary Reabsorption is…
124 ml/min
Does sodium reabsorption occur Transcellular or Paracellular?
BOTH
Sodium reabsorption is passive or active across the apical membrane?
passive
Sodium reabsorption is passive or active across the basolateral membrane?
active
Why is sodium reabsorption passive across the apical membrane?
the transepithelial potential difference (TEPD) between the tubular lumen and interstitial fluid is -3 mV
What is transport maximum?
Maximum rate some substances can be transported across the epithelium (absorption or secretion)
What is renal threshold?
plasma concentration that saturates the carrier (tubular load)
Reabsorption of water is strickly…
passive (where ever the solutes go the water will follow)
__________ highly permeable to H2O
Proximal tubule
PT Reabsorption of Na+, Cl-, Urea and H2O exhibit…
Gradient-Time Transport
Ascending limb of Loop of
Henle is permeable or not to water?
not permeable to H2O
If water is reabsorbed to a greater extent than the solute, the solute will become _____ concentrated in the tubule
more
ex: creatinine, inulin
If solute is reabsorbed to a greater extent than water, the solute will become ____ concentrated in the tubule
less
ex: amino acids, glucose
What is unique about the cells of the proximal tubule?
- high capacity for active/passive reabsorption
- large # of mitochondria
- large surface area
- high permeability to H2O
What does the proximal tubule reabsorb?
65% of…
Na+
Cl-
HCO3-
K+
all glucose
all amino acids
What does the proximal tubule secrete?
metabolic waste products like H+, bile salts, toxins, drugs, and PAH
What type of transport does the early proximal tubule use for Cl-?
paracellulary
What type of transport does the late proximal tubule use for Cl-?
- transcellular (apical - secondary active antiporter; basolateral - facilitated diffusion)
- paracellular
What type of transporters are in the early proximal tubule?
SGLT2
GLUT2
What type of transporters are in the late proximal tubule?
SGLT1
GLUT1
What type of transporters in the proximal tubule are in the apical membrane?
SGLT2 (early PT)
SGLT1 (late PT)
- secondary active
What type of transporters in the proximal tubule are in the basolateral membrane?
GLUT2 (early PT)
GLUT1 (late PT)
- facilitated diffusion
Where is 90% of the glucose reabsorbed?
early proximal tubule
Where is 10% of the glucose reabsorbed?
late proximal tubule
What is the affinity and capacity of the early proximal tubule transports (SGLT2 and GLUT2)?
low affinity
high capacity
What is the affinity and capacity of the late proximal tubule transports (SGLT1 and GLUT1)?
high affinity
low capacity
What transport inhibitor is used as a treatmetn for type 2 diabetes?
SGLT2 inhibitors (glifozins and invokana)
How does the tubular fluid conc of Na+ and H2O change as it goes through the proximal tubule?
does not change (isotonic)
How does the tubular fluid conc of glucose, amino acids, and HCO3- change as it goes through the proximal tubule?
decreases (reabsorbed into plasma)
How does the tubular fluid conc of Cl-, urea, and creatinine change as it goes through the proximal tubule?
increases
What percent of the filtrate is reabsorbed at the end of the proximal tubule?
70%
What are the features of the thin descending limb of the loop of henle?
- high H2O permeability
- NO active solute transport
- urea secretion via facilitated diffusion
What are the features of the thin ascending limb of the loop of henle?
- does not reabsorb anythign really
- impermeable to water
- urea secretion via facilitated diffusion
What are the features of the thick ascending limb of the loop of henle?
- impermeable to water and urea
- major site of Na+, K+, Cl- reabsorption
- H+ secretion
- forms a hyposmotic solution
- distal end forms the JG apparatus
By the end of the loop of henle what type of solution is formed?
hyposmotic
Where is the major site of Na+, K+, and Cl- reabsorption at?
thick ascending limb
Since the thick ascending limb is impermeable to H2O what happens to the luminal osmolarity when solutes are reabsorbed?
osmolarity decreases
What percent of the filtrate is reabsorbed by the end of the loop of henle?
20%
What is the main functions of the early distal tubule?
- absorbs solute without water
- impermeable to water and urea
- reabsorbs Na and Cl
- further dilutes the filtrate
What are the two cell types in the late distal/cortical collecting duct?
- principal cells
- intercalated cells
What is the function of the principal cells in the late distal/cortical collecting duct?
- aldosterone and ADH action
- reabsorb Na+ and water
- secrete K+
- impermeable to urea
What is the function of the alpha intercalated cells in the late distal/cortical collecting duct?
- important in acidosis
- secrete H+
- reabsorb K+ and HCO3-
- primary active transport of H+ across apical membrane
What is the function of the beta intercalated cells in the late distal/cortical collecting duct?
- important in alkalosis
- secrete K+ and HCO3-
- reabsorb H+
What is the function of hte medullary collecting duct?
- processes a small amount of Na+ and water (but important for regulation)
- aldosterone and ADH action
- urea reabsorbed via faciliated diffusion
- secretes H+
What percent of the filtrate is reabsorbed by the end of the collecting duct (final urine)?
9%
