Body fluids

Electrolytes

Electrolytes

• Electrolytes form IONS when in H2O (ions are electrically charged particles)

• (Non electrolytes are substances which do not split into ions, e.g. glucose)

CATIONS = Positively charged particles

(e.g. Na+, K+, Ca++)

ANIONS = Negatively charged particles (e.g. HCO3- Cl-)

E.g.

NaCl

Na+ + Cl-

Major body electrolytes• What are the body’s major electrolytes?

Sodium (Na+) Potassium (K+)Chloride (Cl-) Calcium (Ca+)Magnesium (Mg++) Bicarbonate (HCO3-)Phosphate (PO4--) Sulphate (SO4--)

(Urea and Creatinine are not electrolytes)

• You should be familiar with the chemical symbols: Na+, K+, Cl-, Ca+, Mg++, HCO3-

Importance of electrolyte balance

Electrolytes are critical for cellular reactions

They are found in all fluid compartments

Essential in:• Muscle co-ordination• Heart function• Fluid absorption and

excretion• Nerve function

Sodium (Na+)

Na+ is the main Extra-cellular fluid Cation

Normal range for Na+

= 135 – 145 mmol/L

The hormone that regulates Na+ levels?

= Aldosterone

Adrenal Cortex

Aldosterone

Nephron

reabsorption of Na+ = H20

Sodium (Na+)Functions of Na+

Maintaining volume and concentration of extra-cellular fluid

* Involved in nerve conduction

When is a sodium test requested?* Part of a routine laboratory evaluation

Na+

Na+

Na+

Na+Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Sodium (Na+)What is Hyponatraemia?

Low blood sodium levels (less than 135mmol/L)

May occur in:Excessive sweating

Symptoms of HyponatraemiaMuscle cramps & WeaknessFatigue & Nausea,Apathy & HeadacheConfusion Seizures

Treatment = Replacement therapy

Sodium (Na+)What is Hypernatraemia ?

High sodium in the blood (more than 145mmol/L)

Normally occurs because of inadequate fluid intake

Signs and symptoms includeIntense thirstDecreased urine output Confusion Seizures

Treatment =IV or oral water replacement

Potassium (K+)Potassium (K+)Primary intra-cellular cation

Necessary to maintainnerve conduction

Necessary for normal cardiac function

Normal range for Potassium (K+)

= 3.5 – 5.3 mmol/L

(K+)

(K+)

(K+)

(K+)

(K+)

(K+)

(K+)

(K+)

(K+)

Potassium (K+)What type of muscle isparticularly sensitive to K+levels?

Cardiac muscle

E.g. High K+ level Abnormal heart rhythm

Potassium testing* Routinely measured* Also specifically measured in diuretic therapy

Potassium (K+)Hypokalaemia = An abnormally low level of blood

potassium (less than 3.5mmol/L)Causes:

Inadequate intakeLoss of K+ from the body (e.g. diuretics or gastric losses)

Signs and symptoms Skeletal muscle weaknessECG changes

Treatment = Replacement - foods (e.g. bananas, spinach) or K+supplements

Potassium (K+)Hyperkalaemia = serum potassium concentration

greater than 5.5mmol/L

Caused by:

Decreased excretion of K+

Movement of K+ out of the cells in trauma

IV potassium infusion

Signs of hyperkalaemia:

Include ECG changes

Treatment

Depends on the blood K+ level

Calcium (Ca++)• 99% is stored in the skeleton

and teeth (huge reserve)

• 50% of blood calcium is ionized, the rest is protein bound.

* Only the ionized calcium is used in functions such as: muscle contraction cardiac nerve impulse

function transmission

Phosphate (PO4)• 85% of body’s total

phosphorus is contained in the bones,

• The remainder is in the cells.

• Phosphate is required for:

Generation of bony tissue, Metabolism,

Maintenance of acid base balance

Bicarbonate (HCO3-)

What is the normal range for Bicarbonate (HCO3-)

22 – 30 mmol/L

What is the ‘job’ of bicarbonate?

Prevents body getting too acidic

(i.e. acid-base balance)

Urea

Nitrogen containing waste product from metabolism (protein breakdown)

Excreted through the kidneys kidneys

Good indicator of renal function

Serum urea = 2.5 – 6.6 mmol/L

Creatinine• A metabolic waste product produced by

breakdown of muscle protein (creatine).

• Why is creatinine measured?To determine kidney function

• Serum Creatinine concentration is a more accurate indicator of renal function than urea

Laboratory ResultsIs an abnormal test always a sign of a real problem?

Not always, but should be further investigated

Are reference ranges specific to the laboratory that produces?

Yes

Final pointAll the above points are clinically relevant and it isimportant that you have a good understanding of fluidand electrolyte balance by the time you qualify.