Fluid, Electrolyte and Acid-Base Balance II

Composition of fluid compartments

Highest in Interstitial fluid compared to blood plasma in ECF

1. Bicarbonate

2. Chloride

3. Sodium

Highest in blood plasma compared to interstitial fluid

1. Calcium

2. Protein anions

Same amount in both blood plasma and interstitial fluid

1. Magnesium

2. Phosphate

3. Potassium

4. Sulfate

Highest in ICF compared to ECF

1. Magnesium

2. Phosphate

3. Potassium

4. Sulfate

5. Protein anions

Highest in ECF compared to ICF

1. Bicarbonate

2. Calcium

3. Chloride

4. Sodium

5. Protein anions

These levels of electrolytes are measured using blood serum (with cells and clotting proteins removed). Fluctuations in protein levels can interfere with the result.

1. Bicarbonate
•  carbonic acid-bicarbonate buffer
• regulated by kidneys by intercalated cells
2. Sodium
• fluid and electrolyte regulation & production of action potentials
• regulated by Renin-aldosterone-angiotensin mechanism, ADh and ANP
3. Chloride
• balance level of anion and HCl production
• regulated in the same way as Na+
4. Potassium
• production and propagation of nerve impulses along an axon
• regulate pH
• regulated by aldosterone. When K+ is too high in blood, aldosterone is secreted to stimulate principal cells along renal tubule to secrete more K+ to be released in urine
5. Magnesium
• Co-factor for many enzymes
• Needed for Neural and myocardial activity
• Secretion of parathyroid hormone
• Regulated by kidneys
6. Phosphate
• strengthen skeleton
• important pH buffer
• produce ATP
• Regulated by parathyroid hormone; when too low, parathyroid hormone released to promote release of phosphate from bone to blood. Calcitriol stimulates absorption from blood to bone from food; calcitonin vice versa
7. Calcium
• blood clotting
• neurotransmitter release
• muscle activity
• strengthen bone and teeth
• Regulated by parathyroid hormones
• When too low, parathyroid hormone is released to stimulate release of Calcium from bone to blood. When too high, parathyroid hormone 
• increases the reabsorption of Calcium from urine in renal tubules in the kidneys 
• stimulate the secretion of calcitriol, that increases the rate of calcium uptake from ingested food. 
• Calcitonin, produced by thyroid gland when calcium level is too high in blood, opposes effects of parathyroid hormone. It
• inhibits release of calcium from bone
• reduce reabsorption of calcium from kidneys
• inhibit calcium uptake from food
8. Sulfate
• maintenance of cell membrane
• regulated by kidneys (reabsorption)