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* Diet, mostly fruits and vegetables, is the major source of potassium for the body. | * Diet, mostly fruits and vegetables, is the major source of potassium for the body. | ||
* Potassium is the principal [[intracellular]] [[cation]], with a concentration of about 145 mEq/L, as compared with a normal value of 3.5 - 5.0 mEq/L in [[extracellular]] fluid, including blood. | * Potassium is the principal [[intracellular]] [[cation]], with a concentration of about 145 mEq/L, as compared with a normal value of 3.5 - 5.0 mEq/L in [[extracellular]] fluid, including blood. | ||
* More than 98% of the body's potassium is [[intracellular]]; measuring it from a blood sample is relatively insensitive, with small fluctuations in the blood corresponding to substantial changes in the total bodily reservoir of [[potassium]]. | * More than 98% of the body's potassium is [[intracellular]]; measuring it from a blood sample is relatively insensitive, with small fluctuations in the blood corresponding to substantial changes in the total bodily reservoir of [[potassium]].<ref name="pmid23674806">{{cite journal| author=Weaver CM| title=Potassium and health. | journal=Adv Nutr | year= 2013 | volume= 4 | issue= 3 | pages= 368S-77S | pmid=23674806 | doi=10.3945/an.112.003533 | pmc=3650509 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23674806 }} </ref> | ||
=== The Cellular Effect of Hypokalemia === | === The Cellular Effect of Hypokalemia === | ||
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Aida Javanbakht, M.D. Aditya Govindavarjhulla, M.B.B.S. [3] ; Assistant Editor(s)-In-Chief: Jack Khouri
Synonyms and keywords: Hypokalaemia; potassium levels low (plasma or serum); potassium - low; low blood potassium; potassium depletion
Overview
Pathophysiology
Potassium is the principal intracellular cation, with a concentration of about 145 mEq/L, as compared with a normal value of 3.5 - 5.0 mEq/L in extracellular fluid, including blood. Any disorder of potassium serum levels can disturb the transmembrane potential and renders excitable cells (nerve and muscle) hyperpolarized and less sensitive. However, cardiac cells don't obey this rule and become hyperexcitable. Potassium regulation is essential to maintain a normal activity in cells. Any impairment in potassium serum levels will have severe consequences on several organs especially the heart and the nervous system. Typically, total potassium excretion in the stool is low and most ingested potassium is absorbed. The kidney is the primary regulator of potassium balance through excretion (the kidney excretes 90-95% of dietary potassium); the gut excretes a minimal amount of dietary potassium (approximately 10%).
Historical Perspective
Pathophysiology
Hypokalemia can result from several conditions:
- Trans-cellular shifts of potassium inside the cells (most common)
- Renal loss of potassium
- Increased distal Na delivery
- Increased urine flow
- Metabolic alkalosis
- Increased aldosterone level
- Gastrointestinal (GI) loss of potassium
- Increased hematopoiesis (increased cellular use of potassium)
- Decreased intake of potassium (least common)
Shown below is a table summarizing the different pathophysiological processes that can lead to hypokalemia.[1] [2] [3] [4]
| Trans-cellular shifts | Renal loss | GI loss | Increased hematopoiesis | Decreased intake of potassium | |
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Subject is normo or hypotensive Associated with alkalosis
Variable acid/base status |
Subject is hypertensive
Secondary hyperaldosteronism
Non aldosterone increase in mineralcorticoid
|
Associated with metabolic acidosis Associated with metabolic alkalosis
|
|
|
The Role of the Kidney
- The Kidneys play an important role in keeping the balance of potassium.
- At the glomerulus, potassium is freely filtered and reabsorbed mainly in the proximal tubule and thick ascending loop of Henle (>60 % of filtered potassium).
- The cortical collecting duct receives 10–15% of filtered potassium and constitutes the kidney’s primary site of potassium excretion.
- Potassium excretion at the cortical collecting duct depends on the amount of sodium delivered there and the activity of aldosterone.
- The absorption of sodium by the principal cells of the cortical collecting ducts is mediated by the apical epithelial sodium channels (ENaC); when the amount of sodium delivered to the cortical collecting duct is very high, the absorption of sodium increases without concomitant absorption of the accompanying anions (e.g., bicarbonates and chloride ions) which are not easy to absorb. This physiologic process causes the formation of a negative charge within the cortical collecting duct lumen, causing potassium and proton secretion.
- Aldosterone increases sodium absorption at the cortical collecting duct by means of enhancing the activity of Na-K-ATPase pumps and augmenting the number of the ENaC channels.
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Factors Increasing Kidney Potassium Excretion
- Increased aldosterone
- High urine flow rate
- High distal sodium delivery
- Metabolic alkalosis
- High extracellular fluid K+ concentration
Some Factors Affecting Potassium Distribution Between the Cells and the Extracellular Fluid
- Na/K ATPase
- Insulin
- Catecholamines
- Plasma potassium concentration
- Extracellular pH
- Hyperosmolarity [5]
The Physiologic Role of Potassium
- Potassium is essential during numerous body functions, particularly for excitable cells such as muscle and nerve cells.
- Diet, mostly fruits and vegetables, is the major source of potassium for the body.
- Potassium is the principal intracellular cation, with a concentration of about 145 mEq/L, as compared with a normal value of 3.5 - 5.0 mEq/L in extracellular fluid, including blood.
- More than 98% of the body's potassium is intracellular; measuring it from a blood sample is relatively insensitive, with small fluctuations in the blood corresponding to substantial changes in the total bodily reservoir of potassium.[6]
The Cellular Effect of Hypokalemia
The normal ratio of intracellular to extracellular potassium in the body is vital for the generation of action potential and results in appropriate cardiac and neuromuscular cells performance. By decreasing the potassium concentration in extracellular space, the amount of the potassium gradient across the cell membrane is risen and results in hyperpolarization. This alteration moves the resting membrane potential from the threshold to a higher level; hence, a bigger than standard stimulus is necessary to generate an action potential. Consequently, reduced excitability in the neurons and muscle cells would appear and cause flaccid muscle paralysis, rhabdomyolysis (in severe hypokalemia), and paralytic ileus.[7]
Pathophysiology of Hypokalemic Heart Arrhythmias
- Hypokalemia in neurons and muscle cells reduces the membrane responsiveness and causes hyperpolarization. But in cardiac cells, specifically in the conducting system, depolarization is observed. The main reason is the alteration of ion selectivity of TWIK-1 K+ channels, which in standard situation leak potassium. During pathological hypokalemia, these channels transport sodium inward the cells, leading to paradoxical depolarization and may result in cardiac arrhythmias.
- Decreased extracellular potassium also suppresses the activity of some potassium channels conductance, and in turn, it delays ventricular repolarization. Prolonged repolarization could also predispose re-entrant arrhythmias.
- Moreover, Hypokalemia can inhibit Na+-K+ ATPase activity, leading to intracellular Na+ And Ca2+ increase. The accumulation of intracellular ca2+ activates calmodulin kinase and, in turn, induces late Na+ and Ca2+ currents and causes a further reduction in repolarization reserve. This would result in early after-depolarization (EAD)–mediated arrhythmias.[8] [9]
Pathophysiology of Hypokalemic in GI system:
- A low level of potassium causes dysfunctional gastrointestinal smooth muscle performance, the slow movement of the GI system, constipation, and paralytic ileus. The primary rationale behind them is the impairment of normal action potential in the muscle cell membrane, which disturbs favorable contraction and cellular depolarization. [10] [7]
Causes
Differentiating Hypokalemia from other Diseases
Epidemiology and Demographics
Risk Factors
Natural History, Complications and Prognosis
Diagnosis
Diagnostic Algorithm | History and Symptoms | Physical Examination | Laboratory Findings | Electrocardiogram | Other Diagnostic Studies
Treatment
Medical Therapy | Primary Prevention | Secondary Prevention | Cost-Effectiveness of Therapy | Future or Investigational Therapies
Case Studies
Related Chapters
- ↑ Daly K, Farrington E (2013). "Hypokalemia and hyperkalemia in infants and children: pathophysiology and treatment". J Pediatr Health Care. 27 (6): 486–96, quiz 497–8. doi:10.1016/j.pedhc.2013.08.003. PMID 24139581.
- ↑ Unwin RJ, Luft FC, Shirley DG (February 2011). "Pathophysiology and management of hypokalemia: a clinical perspective". Nat Rev Nephrol. 7 (2): 75–84. doi:10.1038/nrneph.2010.175. PMID 21278718.
- ↑ Cheungpasitporn W, Suksaranjit P, Chanprasert S (February 2012). "Pathophysiology of vomiting-induced hypokalemia and diagnostic approach". Am J Emerg Med. 30 (2): 384. doi:10.1016/j.ajem.2011.10.005. PMID 22169581.
- ↑ Bisogni V, Rossi GP, Calò LA (June 2014). "Apparent mineralcorticoid excess syndrome, an often forgotten or unrecognized cause of hypokalemia and hypertension: case report and appraisal of the pathophysiology". Blood Press. 23 (3): 189–92. doi:10.3109/08037051.2013.832967. PMID 24053336.
- ↑ Hall, John (2016). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Elsevier. ISBN 978-1-4557-7005-2.
- ↑ Weaver CM (2013). "Potassium and health". Adv Nutr. 4 (3): 368S–77S. doi:10.3945/an.112.003533. PMC 3650509. PMID 23674806.
- ↑ 7.0 7.1 Palmer, Biff F.; Clegg, Deborah J. (2016). "Physiology and pathophysiology of potassium homeostasis". Advances in Physiology Education. 40 (4): 480–490. doi:10.1152/advan.00121.2016. ISSN 1043-4046.
- ↑ Ma, L.; Zhang, X.; Chen, H. (2011). "TWIK-1 Two-Pore Domain Potassium Channels Change Ion Selectivity and Conduct Inward Leak Sodium Currents in Hypokalemia". Science Signaling. 4 (176): ra37–ra37. doi:10.1126/scisignal.2001726. ISSN 1945-0877.
- ↑ Weiss, James N.; Qu, Zhilin; Shivkumar, Kalyanam (2017). "Electrophysiology of Hypokalemia and Hyperkalemia". Circulation: Arrhythmia and Electrophysiology. 10 (3). doi:10.1161/CIRCEP.116.004667. ISSN 1941-3149.
- ↑ Streeten, D. H. P.; Williams, E. M. Vaughan (1952). "Loss of cellular potassium as a cause of intestinal paralysis in dogs". The Journal of Physiology. 118 (2): 149–170. doi:10.1113/jphysiol.1952.sp004782. ISSN 0022-3751.