Flashcards in Tubular Reabsorption Deck (60):
What is reabsorbed in proximal tubule?
All FREELY FILTERED substances: Na+, Cl-, K+, Ca2+, HCO3-, H20, glucose, amino acids, vitamins, urea, choline
What is reabsorbed in the descending limb of Loop of Henle?
descending limb = concentrating segment bec/ only permeable to water so water LEAVES
What is reabsorbed in the ascending limb of Loop of Henle?
Na+, Cl-, K+, Mg2+, Ca2+, NH4+ = all reabsorbed to create concentration gradient
ascending limb = diluting segment = solute LEAVES
Where does ADH act? What's the mechanism?
opens up aquaporin channels there,
ultimately this concentrates urine
What is secreted (and most of the time excreted!) in the proximal tubule?
H+, NH4+, Toxins, Drugs
What is reabsorbed in the distal tubule?
Ca2+, Na+, Cl-, H20
What is secreted (and excreted most of the time!) into distal tubule?
What is reabsorbed in the collecting duct?
Na+, K+, Cl-, Ca2+, HCO3-, H+, urea, H20
What's secreted in the collecting duct?
K+, H+, NH4+
Where does Aldosterone act?
What controls Aldosterone's regulation?
-Potassium (K+) High levels = triggers adrenal cortex cells to release aldosterone
-Blood pressure (low BP) triggers aldosterone
What transporters are found in the proximal tubule? And which side of the membrane are they found on?
1. Na+ glucose symporter on Apical side
2. MANY Na+-K+ ATPases (on ALL cells in body) on BasoLateral side (3Na+ out, 2K+ in)
3. Glut2 Transporter pumps out glucose into plasma (basolateral?)
4. H+ out, Na+ in antiporter (apical)
5. K+ channels (apical)
6. Cl-HCO3 Antiporter (basolateral) OR Na (out)-HCO3 (our) Symporter (basolateral)
What is Tmax for glucose?
320 mg/min (= filtered load of glucose)
What structure is found in both the proximal tubule and distal tubule?
microvilli (for reabsorption!)
Do organic substances (glucose, amino acids, acetate, Krebs cycle intermediates, water-soluble vitamins, lactate, acetoacetate) use 2ndary transport?
What are key characteristics of this transport?
-specific for stereochemistry (D or L configuration)
-can be inhibited by drugs, disease
What is the filtered load of Na+ normally?
We reabsorb at least 95% of all Na+ we take in daily!!
What transporters are in the Loop of Henle?
Ascending limb = has Na+-K+-2Cl- exchanger (apical membrane),
Ca2+ channels (apical?)
Ca2+ ATPase (basolateral)
K+ channels (apical + basolateral)
What are the 2 types of cells found in the distal tubule?
Principal cells (mainly in latter DT)
Intercalated cells (mainly in medullary collecting ducts)
*also macula densa cells have baroreceptors? so signal renin to secrete angiotensin?
What transporters are in the distal convoluted tubule?
1. Na+/Cl- symporter (Apical membrane)
2. Ca+ channels (Apical membrane)
3. Na+ channels (Apical membrane)
4. K+ channels (Apical membrane)
5. Na+K+ ATPase (Basolateral membrane)
6. Cl- channels (Basolateral membrane)
7. Ca+/3Na+ antiporter (Basolateral membrane)
8. Ca2+ ATPase (BL)
9. H+ into lumen/K+ into cell Antiporter (apical)
10. HCO3 (out of cell into blood) - Cl- Antiporter (basolateral) OR HCO3- Na symporter (BL)
Apical membrane is side of membrane closest to _______ vs. basolateral which is closest to __________?
Apical = closest to lumen of tubule
Basolateral = closest to blood
Where does Aldosterone act and what's its effect/does it do?
Distal tubule (remember mainly this for class), Collecting Duct
Effect: increases NaCl + H20 reabsorption, K+ Secretion
Where does ADH act?
Collecting ducts (mainly) and distal tubule to reabsorb water
*also proximal tubule to increase NaCl, water reabsorption, SECRETION of H+
Where does PTH act?
Proximal tubule, Thick ascending loop of henle, distal tubule by increasing Ca2+ reabsorption, PHOSPHATE SECRETION
Where does ANP/ANF act?
Distal Tubule, Collecting Duct to DECREASE NaCl reabsorption
Which type of pathway do ions use to cross the cell which involves many transporters?
2ndary active transport always relies on a _______ gradient?
Na+ gradient (created by Na+/K+ ATPase)
What are the secondary capillaries surrounding the proximal and distal tubule that can take substances directly into the blood stream?
Reabsorption moves solutes from _______ to ______?
tubular fluid/lumen into (cell then to interstitial fluid) then to plasma
What happens when a substance hits transport max - it is reabsorbed or secreted?
It's only secreted if the # of molecules filtered ABOVE transport max!
Which type of nephron has higher Tmax for glucose?
What is splay?
variability in body,
heterogeneity in nephrons (cortical= so e.g. glucose hits Tmax earlier in urine) vs. (juxtamedullary)
What are the 2 types of nephrons?
Cortical (80% of kidney) and juxtamedullary (20% of kidney)
What happens when substances filtered go above Tmax? Reabsorption or secretion?
Urea, uric acid, breakdown products of hormones, drugs etc. are ______?
secreted and excreted
All organic substances are freely filtered - how are they reabsorbed?
by 2ndary active transport so using transporters
=always less than Tmax
You can only reabsorb something if it has a __________ transporter in the body?
specific (configuration-specific e.g. D vs. L)
Where and how is Na+ reabsorbed?
1. PCT - 65-75% via Na+/Glucose Transporter (run by Na+/K+ ATPase creating gradient)
2. Loop of Henle - 15-20% = via Na+/K+/2Cl- exchanger (Na+, 2Cl- down its conc gradient, K+ up its conc gradient)
3. Distal tubule = 5% 2 ways:
a. Na+/Cl- symporter = SIMPLE way!
b. Aldosterone (steroid hormone) = complicated way: Na+ reabsorption by increasing Na+/K+ ATPases, Na+ channels, K+ channels to secrete K+
So at least 95% of Na+ filtered is going to be reabsorbed!
What's a normal GFR?
What's the normal filtered load of Na+?
25,200 mEq/day (*95% of Na's Filtered Load is reabsorbed)
What's the normal concentration of Na+ in the plasma?
How do we reabsorb Bicarb?
using Na+/H+ Antiporter (only antiporter in PCT!)
Are Na+ and Glucose reabsorbed the same way?
Yes! via the Na+/Glucose Symporter (cotransporter) via Na+/K+ creating gradient
*so this is 2ndary active transport and TRANSCELLULAR pathway
Every time Na+ is reabsorbed, what is also reabsorbed?
What's the major anion in the ECF?
Does Cl- use a Paracellular pathway? How is it reabsorbed?
by being dragged along with Na+ to ensure there's NO electrical gradient
Do most ions use the transcellular or paracellular pathway?
Is inulin filtered, reabsorbed and/or secreted?
Is glucose filtered, reabsorbed and/or secreted?
filtered and reabsorbed
How does the Na+/Cl+/K+ exchanger on Ascending limb of loop of henle work?
Na+ = down conc (out so into blood)
2 Cl- = down conc
K+ = up conc gradient
How do diuretics work?
Work on distal tubule mainly to increase volume of urine (so more Na+ and more water!):
1. Thiazide = Blocks Na+/Cl- channel so prevents reabsorption of Na+ and Cl- so more Na+, H20 so have more Na+ and H20 in urine
2. Amelioride Blocks Na+ channels that aldosterone opens so excrete more Na+ and H20 in urine
Is proximal convoluted tubule equally permeable to both water and solutes?
That's why its iso-osmotic
What's the concentration of filtrate by the time we get to distal tubule?
150 (bec/ lost solute but kept water in thick ascending limb)
Under normal conditions, do we have a net absorption or secretion of K+?
Secretion (occurs in distal tubule and collecting duct)
via Distal Tubule Principal cells via Na+/K+ ATPase, Na+ channel and K+ channel
Where and how do you reabsorb K+?
1. Proximal tubule by Bulk flow (K+ pulled along) = paracellular
2. LOH by Na+/K+/Cl- Transporter = transcellular & via bulk flow = paracellular
What controls K+ secretion?
Aldosterone (increases K+ secretion by decreasing K+ plasma levels!)
homeostatic control (negative feedback)
What affects aldosterone regulation?
1. K+ levels
2. blood volume/blood pressure
Most reabsorption of calcium occurs where?
How is Calcium regulated?
PCT - we don't know transporters
LOH via primary active transport increases Ca2+ channels (apical) and increases Ca2 + ATPases (but NOT 2ndary only PRIMARY active transport) and
Distal tubule (same as LOH)
PTH works mainly on the ____________?