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Chemical Biochemistry > Salt And Water Balance > Flashcards

Salt And Water Balance Flashcards

1
Q

What is sodium important for

A

regulating body water

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2
Q

Where is sodium primarily held

A

In the extracellular fluid

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3
Q

What is the major determinant of plasma osmolality

A

Sodium

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4
Q

What does water diffuse from

A

High to low osmolality

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5
Q

Which 2 systems is sodium concentration regulated by

A
  1. ADH

2. RAAS

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6
Q

How is water volume regulated by ADH e.g when there is a rise in plasma osmolality

A
  1. Fluid depletion causes a rise in plasma osmolality
  2. This sends a message to the osmoreceptors in the hypothalamus
  3. This causes ADH release from the posterior pituitary gland
  4. ADH causes stimulation of thirst so you drink water
  5. ADH also acts on the collecting duct and DCT causes water re-absorption
  6. This increases the plasma osmolality
  7. A high plasma osmolalltiy inhibits the hypothalamus so you do not feel thirst and ADH is not released
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7
Q

How is the RAAS when there is fluid depletion

A
  1. Fluid depletion decreases ECF volume
  2. This is sensed by the arterial baroreceptors
  3. Sympathetic nervous system is activated to cause vasoconstriction
  4. Vasoconstriction is sensed by the juxtaglomerualr apparatus in the kidney as there is reduced arterial perfusion
  5. This causes renin release form the glomerulus
  6. Renin celaves angiotensin 1 to 2
  7. Angiotensin 2 increases aldosterone
  8. Aldosterone causes sodium reabsorption in the distal nephron
  9. Sodium is reteained so water is retained which increases the ECF volume
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8
Q

What are the categorical causes of hypernatraemia

A

Sodium retention in excess of water
Water loss in excess of sodium
Artefactual (sudden increase in plasma sodium concentration

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9
Q

What are the causes for sodium retention in excess of water

A

Low water intake- leads to activation od RAAS wich causes increased sodium conc
Primary hyperaldosteronism
Cushing disease

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10
Q

What are the causes of water loss

A

diabetes insipidus with inadequate drinking

Diarrhoea, vomiting, burns and haemorrhage

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11
Q

What is the cause for artefactual

A

Sample can be contaminated with iv saline

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12
Q

What is diabetes insipidus

A

Inability of the pituitary fland to produce ADH or the kidney to respond to ADH

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13
Q

What are the clinical symptoms of diabetes insipidus

A

Polyuria

Thirst

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14
Q

How do we test for diabetes insipidus

A

Water deprivation test: this will show hypernatraemia. You can give ADH, if it corrects then it suggests a pituitary problem, if it doesnt then the kidney is not repsondin to ADH which indicates nephrogenic diabetes insipidus

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15
Q

What is hyponatraemia

A

Low sodium

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16
Q

What are the categorical causes of hyponatraemia

A

Water retention in excess of sodium

Sodium loss is in excess of water

17
Q

What are the causes of water retention in excess of sodium

A

Oedematous state: nephrotic syndrome, heart failure, renal or liver failure
Syndrome of inappropriate ADH
Excessive drinking

18
Q

What are the causes of sodium loss in excess of water

A

Renal: osmotic diuresis, diuretic stage of renal failure, diuretic use, hypocortilosim
Non renal: diarrhoea, vomit, burns, fistula

19
Q

What is syndrome of inappropriate ADH (siadh)

A

When ADH is secreted out of its normal role to homeostasis, this causes renal water retention and hyponatraemia

20
Q

What are the causes of SIADH

A

CNS disease: infection or malignanct
Pulmonary disease
Drugs

21
Q

What is the clinical significance of sodium depletion

A 
Sodium determines brain volume when it is less than 120mmol it can be associated with:
Malasie
Confusion
Seizures
Coma
22
Q

What is the treatment of SIADH

A

Fluid restriction to correct sodium

23
Q

What are the ways of correcting hyponatraemia

A

Give iv saline slowly
Loop diuretics
Vasopressin antagonist

Chemical Biochemistry (5 decks)

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