Kalium (intrazellulär): the pathway in the body · Biomarker & Blood Analysis

Kalium (intrazellulär) is part of the pathway “Sodium and potassium”. This page shows the whole pathway; the station of Kalium (intrazellulär) is highlighted.

Where this laboratory value sits: Potassium in the cell — plentiful inside. Because of the pumping, almost all of the body’s potassium is inside the cells, above all in muscle cells. This store buffers the potassium in the blood. Source 1, 2

In brief

Sodium and potassium are charged minerals: sodium dominates outside cells, potassium inside. The sodium-potassium pump maintains this gradient, which carries nerve impulses and the transport of nutrients. Under aldosterone, the kidney sets how much of each stays.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Sodium and potassium → Uptake in the gut NHE3, channels Sodium enters the gut cells via channels and exchangers such as NHE3; water follows it. Potassium passes into the blood mainly between the cells. How much water the gut recovers depends on this sodium entry. Source 3, 2↑ supplies Sodium entry via NHE3 draws chloride and water after it: where sodium is absorbed from the gut, water follows osmotically. In this way sodium uptake helps determine how much water the small intestine recovers. established physiology Source 3
   ⚖ When the balance tips

   too much — If more sodium arrives in the gut, the exchangers absorb more of it, and more water follows the sodium from the gut contents into the tissue.

   too little — If sodium-proton exchange works more slowly, more sodium, and with it more water, stays in the gut contents.

   established physiology · Source 3

2. Uptake in the gut → In blood plasma In the space outside the cells, sodium is the most common positively charged particle. Potassium is present there only in small amounts. Even small shifts in potassium here act on nerves and muscles. Source 1, 2↑ supplies All cells draw their sodium and potassium from the plasma. The ratio of potassium inside to potassium outside sets the resting potential; this is why even a small shift in plasma potassium acts on nerves and muscles. established physiology Source 2, 1
   ⚖ When the balance tips

   too much — If potassium builds up outside the cells, the potassium gradient becomes flatter and the resting potential less negative. Excitable cells such as those of the heart respond to this in particular.

   too little — If there is little potassium outside the cells, the gradient becomes steeper and the resting potential more negative; nerve and muscle cells are then harder to excite.

   established physiology · Source 2

3. In blood plasma → Kidney · Aldosterone The kidney filters both ions and recovers most of the sodium; potassium is released in the collecting duct. The hormone aldosterone controls both processes. When it recovers sodium, it releases potassium in return. Source 2↑ supplies Under aldosterone the collecting duct recovers more sodium via channels; the charge this creates drives potassium into the urine. In this way the kidney keeps sodium in the body and releases potassium in return. established physiology Source 2
   ⚖ When the balance tips

   too much — If plenty of aldosterone is present, the kidney recovers more sodium and releases more potassium into the urine; if potassium rises in the blood, it itself stimulates aldosterone formation.

   too little — If little aldosterone is present or its receptor is occupied, more sodium stays in the urine and more potassium in the body.

   established physiology · Source 2, 5

4. Sodium-potassium pump → Potassium in the cell · ATP, Magnesium Because of the pumping, almost all of the body’s potassium is inside the cells, above all in muscle cells. This store buffers the potassium in the blood. Source 1, 2↑ supplies The potassium store in the cells is a buffer: if blood potassium rises after a meal, mainly the muscle cells absorb it; if it falls, they release potassium again. The high content inside is also the basis of the resting potential. established physiology Source 2, 1
   ⚖ When the balance tips

   too much — If insulin or adrenaline drive a lot of potassium into the cells, it falls in the blood, although the body as a whole does not contain less.

   too little — If the cells lose potassium, for instance when their interior becomes more acidic or little insulin acts, it moves into the blood; the level there rises although the total store does not grow.

   established physiology · Source 2

5. Sodium-potassium pump → Sodium outside Sodium is continuously moved to the outside. This maintains a gradient: much sodium outside, little inside. When sodium flows back, it can carry other substances with it. Source 1↑ supplies The sodium gradient is stored energy: when sodium flows back into the cell, it can carry sugars, amino acids or other ions with it. Because sodium stays outside, it draws no water into the cell; in this way the cell keeps its volume. established physiology Source 1, 4
   ⚖ When the balance tips

   too much — If sodium builds up outside the cells, it draws water out of them osmotically, and the cells shrink.

   too little — If the gradient becomes flatter because sodium flows back into the cell, water follows it, the cell swells, and transporters that rely on the gradient lose their drive.

   established physiology · Source 1, 4

6. Potassium in the cell → Resting potential Potassium channels Potassium slowly flows out through channels. Because this separates charge, the inside of the cell is negatively charged. This state is called the resting potential. Every excitation starts from it. Source 1↑ supplies The resting potential is the starting point of every excitation: only from it can sodium channels trigger an impulse. How negative it is depends mainly on the potassium gradient. established physiology Source 1, 2
   ⚖ When the balance tips

   too much — If the resting potential becomes more negative, for instance when there is little potassium outside, it lies further from the threshold, and nerves and muscles respond more sluggishly.

   too little — If it becomes less negative, for instance when potassium builds up outside, it first moves closer to the threshold; if this persists, sodium channels close and the cell becomes harder to excite.

   established physiology · Source 2

7. Resting potential → Excitation Sodium channels When sodium channels open, sodium rushes in and reverses the voltage. This is how nerve impulses and the trigger for muscle movement arise. Afterwards the potassium outflow restores the resting potential. Source 1↑ supplies The sodium influx sets nerve impulses in motion and gives muscle cells the signal to move. Afterwards the potassium outflow restores the resting potential, and the pump rebalances the shifted ions. established physiology Source 1
   ⚖ When the balance tips

   too much — If many impulses follow in quick succession, sodium collects in the cell and potassium outside; the pump then works faster to bring both back.

   too little — If the sodium gradient is flat, less sodium flows in when the channels open, and the impulse is weaker or does not occur.

   established physiology · Source 1

8. Sodium outside → Sodium co-transport SGLT and others The sodium gradient drives further transporters. SGLT pulls glucose into the cell together with sodium; other carriers move amino acids in the same way. Water follows sodium and glucose. Source 4↑ supplies SGLT uses the sodium gradient to bring glucose into gut and kidney cells, even against a gradient. Water follows sodium and glucose. established physiology Source 4
   ⚖ When the balance tips

   too much — If a lot of glucose arrives, the SGLT transporters run up to their full capacity; whatever exceeds it stays in the gut contents or, in the kidney, in the urine.

   too little — If the sodium gradient is flat, SGLT lacks its drive, and glucose is brought into the cell more slowly.

   established physiology · Source 4

Further stations

• Sodium and potassium — charged particles Sodium and potassium are charged particles known as ions. They come from food and are absorbed in the small and large intestine. From them the body builds the gradient across every cell membrane. Source 3, 2↑ supplies Food supplies both ions: the sodium that dominates outside the cells and the potassium that the cells store inside. From them the body builds the gradient across every cell membrane. established physiology Source 3, 2
  ⚖ When the balance tips

  too much — If a meal brings in a lot of potassium, the cells absorb it first; insulin drives the pump in the process. The kidney then releases the excess via the collecting duct.

  too little — If little potassium arrives, the kidney releases less of it, and the cells release potassium from their store into the blood.

  established physiology · Source 2

• Sodium-potassium pump — Na-K-ATPase This pump sits in the membrane of every cell. It splits ATP and in doing so moves three sodium ions out of the cell and two potassium ions in. The gradient formed in this way is stored energy. Source 1↑ supplies The pump builds the gradient on which the resting potential, excitation and sodium co-transport depend. It uses a large share of a cell's ATP to do so; the gradient is stored energy. established physiology Source 1
  ⚖ When the balance tips

  too much — If the pump works faster, for instance under insulin or adrenaline, potassium moves from the blood into the cells, and ATP consumption rises.

  too little — If little ATP or magnesium is available, the pump runs more slowly: sodium collects in the cell, water follows it, and the gradient becomes flatter.

  established physiology · Source 1, 2

Cofactors in this pathway

• ATP — Energy source of the sodium-potassium pump, which splits one ATP per cycle; with little ATP, the gradient flattens Source 1
• Magnesium — Forms the complex with ATP that the sodium-potassium pump uses; without it, the pump runs more slowly Source 1In the ORY catalogue as a laboratory value: Magnesium
• Chloride — Absorbed together with sodium in the small intestine via parallel exchangers; water follows both Source 3
• Bicarbonate — Exchanged for chloride in the small intestine, in parallel with sodium-proton exchange via NHE3; charge stays balanced Source 3
• Glucose — Carried into the cell together with sodium by the SGLT transporter; the sodium gradient provides the drive Source 4

What acts on this pathway

• Spironolactone — Spironolactone occupies the aldosterone receptor in the kidney. As a result, less sodium is recovered there and less potassium is released. The prescribing information describes this mechanism. Source 5

Sources

1. Clausen MV, Hilbers F, Poulsen H. The Structure and Function of the Na,K-ATPase Isoforms in Health and Disease. Front Physiol 2017 · PubMed 28634454
2. Palmer BF. Regulation of Potassium Homeostasis. Clin J Am Soc Nephrol 2015 · PubMed 24721891
3. Kato A, Romero MF. Regulation of electroneutral NaCl absorption by the small intestine. Annu Rev Physiol 2011 · PubMed 21054167
4. Wright EM, Loo DD, Hirayama BA. Biology of human sodium glucose transporters. Physiol Rev 2011 · PubMed 21527736
5. US prescribing information Aldactone (Spironolactone, DailyMed), section 12.1 Mechanism of Action · Prescribing information

Whole pathway: Sodium and potassium

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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