Sodium

Question 1

Salt

Answer 1

A compound composed of a positive ion (other than H+) and a negative ion (other
than OH-) E.g. NaCl

Question 2

Electrolytes

Answer 2

salts that dissolve in water & dissociate into charged particles called ions
e.g. NaCl → Na+ Cl-

Question 3

Sodium

Answer 3

• Mineral and electrolyte (common salt NaCl)
• Principal cation (positively charged ion) of the
  extracellular fluid – Na+
• Maintaining the balance of fluid inside and outside
  cells is VITAL

Question 4

Sodium functions in the body

Answer 4

• Primary regulator of volume of
  extracellular fluid
• contributes to osmolarity of extracellular
  fluids
• Acid-base balance
• pH primarily determined by balance of
  Hydrogen (H+) and Bicarbonate (HCO3-)
• Na & Hydrogen excretion+ Cl- & HCO3-
  excretion are interlinke
• Balance of Na+ along with K+ & Cl-
  contributes to membrane potential of most
  cells
• Key role in action potentials of excitable
  cells
• Nerve impulse transmission & muscle
  contraction

Question 5

absorption

Answer 5

~ 95% of Na is absorbed by the intestinal tract by 3
mechanisms
1. Na+/Glucose co-transport – Small Intestine (SI)
2. Na+/Cl- exchange – SI & proximal large Intestine
3. Electrogenic Na absorption – Mainly large Intestine

Question 6

transport

Answer 6

Travels freely in the bloodstream

Question 7

excretion

Answer 7

Kidneys filter out sodium depending on body
requirements
* main output in urine
* variable output in sweat
* small output in faeces
* Interacts with Ca to ↑ Ca excretion in urine but ↓ Ca
excretion in faeces

Question 8

Sodium and Blood Pressure

Answer 8

• ↑ Na intake associated with ↑ blood
  pressure
• Role of kidneys includes maintaining Na
  balance by excreting excess Na in urine
• However some people are Salt Sensitive
• Excess Na → ↑ Water retention +
• Alterations of ion transport in smooth
  muscle → vessel contraction → ↑
  blood pressure
• The way individuals respond to Na varies
  considerably
• No good way of identifying who is and is not
  salt sensitive
• Risk factors include – family history of
  hypertension, chronic kidney disease,
  diabetes, ethnicity, age > 50 years, being
  overweight/obese

Question 9

Hyponatremia

Answer 9

• Hyponatremia - metabolic condition in which there is not enough sodium in the body fluids outside
  the cells
• Rare among general population
• Occurs in specific clinical conditions- vomiting, diarrhoea, heavy sweating, prolonged enteral-only feeding,
  Addison’s disease, burns, diuretics
• Hyponatremia in extreme sports

Question 10

Hyponatremia symptoms

Answer 10

• Symptoms- abnormal mental status, peripheral circulatory failure, dry mouth/tongue, skin lacking turgor,
  sunken eyes, weak pulse, low blood pressure, muscle weakness, vomiting, nausea
• Can be fatal, especially if rapidly developing
• The imbalance of water to Na in hyponatremia can be due to:
  1. Euvolemic hyponatremia – total body water increases, but the body’s sodium content stays the same
  2. Hypervolemic hyponatremia – both sodium and water content in the body increase, but the water gain
  is greater
  3. Hypovolemic hyponatremia – water and sodium are both lost from the body, but the sodium loss is
  greater

Question 11

Assessment of Na Status* Biochemistry
- Usual serum Na 137-147 mmol/L
* Can be influenced by factors influencing Na intake, absorption
and loss and factors influencing water intake, absorption and
loss
* Includes influence of gastrointestinal, endocrine, renal,
behavioural, cardiac and hepatic factors
- Urinary Na excretion
* All urine collected for 24 hours to measure Na excretion
* Reflects Na intake in healthy individuals
Dietary Intake
* Estimating Na intake using usual methods accurately very difficult
* Special questionnaires available to estimate Na intake