16: Sodium Chloride

Where in the body is most of the sodium

ECF

Primary function of sodium

Controls water movement, primary cation of the ECF

Primary mechanism of transport for sodium

Na/K ATPase

What controls chloride movement

Where sodium is

Factors that change sodium levels in the body

• Sodium retention

• Hydration status

Factors that change sodium retention

Aldosterone and ANP

Stimulus for aldosterone release

Hypovolemia detected by the JGA

Stimulus for ANP release

Hypervolemia detected by atrial baroreceptors

Factors that change hydration

Thirst and ADH

Stimulus for thirst

Increased osmolarity sensed in the hypothalamus

Stimulus for ADH release

Increased osmolarity sensed in the hypothalamus

Most common cause of hypernatremia

Dehydration

More rare causes of hypernatremia

• Too much intake

• Contaminated water

• Iatrogenic (doctor induced)

Causes of hyponatremia

• Loss of sodium containing fluid

• Water retention

Types of fluid losses that would result in hyponatremia

• GI loss (V/D)

• Renal loss

• Sweating (horses)

Causes of water retention that would result in hyponatremia

• Bladder rupture

• Third space loss: ascites, effusion, etc.

• Hyperglycemia (osmotically active molecule!)

Effect of low Na/Cl on the kidneys

Medullary washout → no concentrating ability → dilute USG

Cause of renal azotemia that is not renal disease

Hypoadrenocorticism (no aldosterone!)

Primary function of chloride

Major ECF anion

Why do we usually not care a whole bunch about chloride

It just follows sodium

When do we actually care about chloride

If it isn’t moving with sodium

Equation that is used to evaluate if sodium and chloride are moving together

Strong ion difference: [Na] - [Cl]

If SID > 50, what is indicated

Primary chloride loss

If SID is <25, what is indicated

Primary chloride retention

What homeostatic function is chloride related to

Acid base balance

How does chloride participate in A/B balance

It moves opposite HCO₃^- to maintain electroneutrality