Flashcards in Renal 5 Deck (10)
what happens in the collecting duct if you have deplected k?
Transporters are different.
Intercalated (alpha) cell. (as opposed to a principle cell) - this region relies on a different cell. For reabsorption of potassium.
Apical: proton and potassium ATPase. H+ to lumen, Potassium into the cell
Exits basolateral membrane through potassium channel.
Reaborb it when we need to keep it!
- Decreases excretion from the body
describe how K is handled in the nephron? (summary)
- BULK k+ reabsorption happens in PT
- Paired with Na reabsorption in TAL
- Reguation of K+ transport occurs in CD
○ Normal: secretion
○ Low: reabsorption
Same at PCT
Paired at Thick ascending limb (NKCC that needs sodium to move potassium
End of Tubule and beginning of collecting duct (then things change with level of K+)
- Secretion or reabsorption (depends on how much potassium is there)
When depleted, continuation of reabosrption (see slides for a graph)
what is the henderson hasselback equation and how does bicarbonate relate to the renal system
ACID BASE (IM)BALANCE
Daily acid load (you eat more meat, more acid byproducts) - increased acid load
Acid base disturbance (high altitude/hyperventilating) - alterns pH of plasma. More ACUTE.
- Kidey regulates this.
Henderson Hasselbach equation (pH, bicarbonate and partial pressure of carbon dioxide)
pH can be modified with 2 different organs
- Phosphate buffer
- Hemoglobin buffer
Bicarbonate regulated by kidney
Partial pressure regulated through lungs by changing rate of respiration
What are typical sources of acid and how is this regulated?
1. Dietary intake
Meat acids > vegetable acids
2. Metabolic byproducts
Volitile acids (h2co3 carbonic acid, can be proken into bicarb and H+))
Non volitle acids (hso4 po4)
Organic acids (lactic, butyric, acetoacetic)
Kidneys maintain conditions in pH maintenence by
1. Handling bicarbonate
2. Excreting protons (H+)
Get rid of acid and make sure bicarb is available for buffering system.
(can also lose co2 through the lungs)
Kidneys maintain pH balance by…
1. Freely filtered at glomerulus (hco3) ALL of bicarbonate is reabsorbed into extracelllular fluid. Even tho we reabsorb all of it, we use a LOT of it. So kidneys need to produce more bicarbonate
2. Form titratable acids (h2po4) and excrete amonium
This produced bicarb goes into extracellualr fluid to buffer and to excrete hydrogens (in phosphate form or ammonium)
how is bicarbonate reabsorbed?
1st thing: reabsorption of filtered bicarbonate.
NHE (sodium proton exchanger)
SODium potassium ATPase (establishes sodium gradient)
Then sodium goes in and proton goes out.
- The proton is put in the lumen, joins with filtered bicarbonate (gone through glomerulus).
- These are converted into carbon dioxide and water.
○ Catalyzed by carbonic anhydrase. Found in tubule lumen tethered to the membrane.
- Both go back into proximal tubule cell.
- Then a different carbonic anhydrade converts co2 and water into a proton and bicarbonate.
- This is the bicarbonate that Is taken up by transporter into blood
- The two bicarbonates are not the same. I) filtered bicarbonate II) reclaimed bicarbonate
80% is reclaimed in the proximal tubule. (bicarbonate)
how is new bicarbonate generated?
Also need to make NEW bicarbonate so that we can buffer :)
Same transporters (NHE and sodiumpotassium atpase)
- Need this to form the titratable acid
Start with co2 and water (intracellularly) and carbonic anydrase - converts h20 and water to bicarbonate and proton.
- NEW bicarbonate
- Did not do transformations. Fresh bicarbonate
- Goes to be delivered to extracellular fluid so it can be added to bicarbonate buffer stores.
- Proton relies on nhe exhanger (exhange proton for sodium going down its gradient)
- This proton titrates phosphate and is excreted as titratable acid.
- Comes together with phosphase (NOT bicarbonate)
THE OTHER METHOD:
Break down glutamine
- Primary substrate for ammoniagenesis
1. Filtered at apical membrane
2. Within our blood and enters at basolateral membrane.
Once it enters cell, its broken into 2 ammonium (nh4) and 2 bicarbonate (hc02)
1. NHE exchanger: it ALSO transports ammonium INSTEAD OF a proton. (still have sodium going down the gradient) this moves ammonium into tubule lumen)
2. Breakdown into NH3 and proton (use proton pump for secretion) Once they're both out in the lumen, they combine again to form ammonium
3. Reabsorption relies on NBCe1 transporters
1 glutamine, 2 ammonium and 2 bicarb
Ammonium is secreted on apical side, bicarbonate is reabsorbed through NBce1 paired with sodium movement
Adds two new bicarbonates to buffer pool!
This makes more bicarbonate and secretes more acids.
This is good when we need to get rid of acids and add more buffer RAPIDLY.
how does the body respond to increased acid load?
Increased Acid Load
Diet: meat over vegetables
Starvation: alters body metabolism (favor lipid metabolism, increase in OH butyric and acetoaciteic acid)
Trauma, surgery, exercise (lactic acid), fever: catabolism, increased acid.
Normally, 1/3-1/2 is extreted in titratable acid, and remaining is ammonium
When increase in acid load: we need to excrete more acids. Titrtatable acid and ammonium are increased.
- Ammonium mechansim produces more bicarbonate and excretes more annomium, so it’s the most effective mechanism.
Graph: diet to increase acid load, and measured urine output. Ammonia went up MORE.
how are the kidneys and lungs related?
Coordinated function between 2 organs
- Kidney for bicarbonate levels
- Lungs for partial pressure of Co2 levels
- 2 ways to help maintain pH plasma at 7.4
If this is changed
- Bicarbonate: respond by altering CO2
- Carbon dioxide: respond by altering bicarbonate
As long as the ratio of bicarbonate to partial pressure of c02 maintained at 20, we can maintian blood pH at 7.4
describe the compensatory acid base disturbances flowchart?
1. What is blood pH?
2. Less than 7.4 is acidosis
a. Metabolic <24 mEq/L Bicarbonate(respiratory compensation) *ph is low because you don't have enough bicarbonate) decreasing carbon dioxite to < 40 mm Hg
b. Respiratory >40mmhg Carbon dioxite(renal compesation (because you have too much bicarbonate)
3. Greater then 7.4 is alkalosis
(and vise versa!!)
COMPENSATE USING THE OTHER MECHANSIM TO KEEP IT AT 20/1