Electrolytes in body fluids Flashcards
Compare the electrolyte composition of blood plasma, interstitial fluid and ICF; discuss the functions and regulation of the 7 electrolytes
What are the seven essential electrolytes?
Ions of:
1. Sodium (Na⁺)
2. Chloride (Cl⁻)
3. Potassium (K⁺)
4. Bicarbonate (HCO₃⁻)
5. Calcium (Ca²⁺)
6. Phosphate (HPO₄²⁻)
7. Magnesium (Mg²⁺)
Are electrolytes usually confined to particular fluid compartments?
Yes
What are the four general functions of electrolytes?
- Control the osmosis of water between fluid compartments
- Help maintain acid-base balance
- Carry electrical current
- Serve as cofactors
Which three electrolytes are generally confined to ECF?
- Sodium, Na⁺
- Chloride, Cl⁻
- Calcium, Ca²⁺
Which three electrolytes are generally confined to ICF?
- Potassium, K⁺
- Magnesium, Mg²⁺
- Phosphate, HPO₄²⁻
What are the two primary functions of sodium ions (Na⁺)?
- Maintaining fluid and electrolyte balance
- Generation and conduction of action potentials in neurons and muscle fibres
Which three hormones control the Na⁺ level in blood?
- Aldosterone
- Antidiuretic hormone (ADH)
- Atrial natriuretic peptide (ANP)
What is the action of aldosterone in Na⁺ regulation?
Increases Na⁺ levels and blood volume by increasing renal Na⁺ and water reabsorption
What is the action of antidiuretic hormone (ADH) in Na⁺ regulation?
Increases Na⁺ concentration via reduced levels of ADH allowing greater excretion of water in urine
What is the action of atrial natriuretic peptide in Na⁺ regulation?
Reduces Na⁺ levels by increasing Na⁺ excretion and urine output by the kidneys
What are the three primary functions of chloride ions (Cl⁻)?
- Helps balance the level of anions in different fluid compartments
- Supports fluid balance between compartments
- Are part of hydrochloric acid secreted in to gastric juice
How is Cl⁻ balance in body fluids regulated?
By any processes that increase or decrease renal reabsorption of Na⁺ (they typically move in unison), and ADH (affects Cl concentration too)
What are the three main functions of potassium ions (K⁺)?
- Establishing resting membrane potential and repolarisation phase of action potentials
- Helps maintain normal ICF volume
- Helps regulate pH of body fluids (by swapping places with H⁺)
What is the main hormone which controls K⁺ levels?
Aldosterone, by encouraging excretion of K⁺ in the urine when concentration is high
How can abnormal K⁺ levels be fatal?
It is needed for the depolarisation phase of nerve impulses
Example effect: ventricular fibrillation
What are the two primary functions of bicarbonate ions (HCO₃⁻)?
- Helps maintain correct balance of anions in ECF by exchanging places with Cl⁻
- Acts as a weak acid in buffer systems to maintain acid-base balance
What two processes cause blood concentration of HCO₃⁻ to decrease?
- Exhalation of CO₂ by the lungs
- Excretion of excess by the kidneys
What two processes cause blood concentration of HCO₃⁻ to increase?
- The release of CO₂ in to the blood by metabolically active cells (CO₂ + H₂O > H₂CO₃ > H⁺ + HCO₃⁻)
- Formation in the kidneys if levels are too low
What are the four main functions of calcium ions (Ca²⁺)?
Roles in:
1. Blood clotting
2. Neurotransmitter release
3. Maintenance of muscle tone
4. Excitability of nervous and muscle tissue
Which hormone is the most important regulator of Ca²⁺ concentration in blood plasma?
Parathyroid hormone (PTH)
What are the three ways PTH affects Ca²⁺ concentration of the blood plasma?
- Stimulates osteoclasts to release calcium (bone resorption)
- Enhances reabsorption of Ca²⁺ by the kidneys
- Increases production of calcitriol (a form of vitamin D) which increases Ca²⁺ absorption from food
How does the body reduce Ca²⁺ concentration in the blood plasma, if needed?
Release of calcitonin (produced in the thyroid gland) which inhibits osteoclasts and accelerates Ca²⁺ deposition into bones
What are the three types of phosphate ions, and which is the most prevalent?
- HPO₄²⁻ (most prevalent)
- H₂PO₄⁻
- PO₄³⁻
What are the two main functions of phosphate ions?
- Most are covalently bonded to organic molecules e.g. phospholipids, ATP, nucleic acids
- Act as a buffer in acid-base balance
What are the main two hormones which regulate blood HPO₄²⁻ levels?
- Parathyroid hormone
- Calcitriol
How does PTH affect blood HPO₄²⁻ levels?
- Stimulates bone resorption to increase blood levels
- Inhibits resorption of HPO₄²⁻ by the kidneys to decrease blood levels
How does calcitriol affect HPO₄²⁻ levels?
Promotes absorption of phosphates in the digestive canal to increase blood levels
What other ‘local hormone’ (a polypeptide paracrine) also helps regulate HPO₄²⁻?
Fibroblast growth factor 23 (FGF 23)
How does FGF 23 affect HPO₄²⁻ levels and by what two methods?
Decreases blood levels by:
1. Increasing HPO₄²⁻ excretion by the kidneys
2. Decreasing absorption of HPO₄²⁻ by the digestive canal
What are the three main functions of magnesium ions (Mg²⁺)?
- Cofactor for the sodium-potassium pump and certain enzymes in carbohydrate and protein metabolism
- Neuromuscular activity, synaptic transmission and myocardial functioning
- Secretion of parathyroid hormone (PTH)
In what five body states will Mg²⁺ excretion by the kidneys increase?
- Hypercalcaemia
- Hypermagnasemia
- Increases in ECF volume
- Decreases in PTH
- Acidosis
In what five body states will Mg²⁺ excretion by the kidneys decrease?
- Hypocalcaemia
- Hypomagnasemia
- Decreases in ECF volume
- Increases in PTH
- Alkalosis
Which two pairs of electrolytes regularly swap places to support acid-base/pH balance?
- K⁺ with H⁺ to support acid base balance
- Cl⁻ with HCO₃⁻ via antiporters between blood cells (ICF) and blood plasma (ECF)
Which five medical interventions can increase risk of electrolyte imbalances?
- IV infusions
- Drainages or suctions
- Urinary catheters
- Diuretics
- Fluid restrictions
Which four population groups have increased risk of electrolyte imbalances?
- Dependent individuals e.g. infants, the elderly, people with altered levels of consciousness or impaired communication
- Athletes and military personnel in extremely hot environments
- Post-operative individuals
- People with severe burns or trauma
In which four long-term conditions are electrolyte imbalances more likely?
- Congestive heart failure
- Diabetes
- COPD
- Cancer
What are the names for deficiency and excess of Na⁺, respectively?
Hyponatraemia and hypernatraemia
What are the names for deficiency and excess of Cl⁻, respectively?
Hypochloraemia and hyperchloraemia
What are the names for deficiency and excess of K⁺, respectively?
Hypokalaemia and hyperkalaemia
What are the names for deficiency and excess of Ca²⁺, respectively?
Hypocalcaemia and hypercalcaemia
What are the names for deficiency and excess of HPO₄²⁻, respectively?
Hypophosphataemia and hyperphosphataemia
What are the names for deficiency and excess of Mg²⁺, respectively?
Hypomagnesaemia and hypermagnasaemia
What are the signs and symptoms of hypernatraemia?
- Intense thirst
- Hypertension
- Oedema
- Agitation and convulsions
What are the signs and symptoms of hyponatraemia?
- Muscular weakness
- Dizziness, headache, confusion, stupor and coma
- Hypotension
- Tachycardia and shock
What are some general signs of electrolyte deficiency?
- Tingling
- Spasms and cramps
- Mental confusion
- Muscular weakness
What are some general signs of electrolyte excess?
- Nausea and vomiting
- Anorexia
- Muscular weakness
- Lethargy
