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Advanced Biochemistry > Water and Electrolyte Balance 5/11 > Flashcards

Water and Electrolyte Balance 5/11 Flashcards

1
Q

What are electrolytes?

A

Ions capable of carrying an electric charge

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2
Q

What are the two types of electrolytes?

A

anions and cations

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3
Q

What charge does an anion have?

A

negative charge

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4
Q

What charge does a cation have?

A

positive charge

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5
Q

What are the 4 processes that electrolytes are essential for?

A
  1. Volume and osmotic regulation (Na, Cl, K)
  2. Myocardial rhythm and contractility (K, Mg, Ca)
  3. Cofactors in enzyme activation (Mg, Ca, Zn)
  4. Blood coagulation (Ca, Mg)
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6
Q

Why does water in the body decline with age and obesity?

A

Due to less muscle mass (the more muscle mass = more water in the body)

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7
Q

Why do women have less body water % than men?

A

They have an increased body fat % and less muscle mass

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8
Q

What are the 2 body fluid compartments?

A 
Intracellular compartment (67% / 28L)
Extracellular compartment (interstitial space (25% / 11L) and plasma space (8% / 3L))
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9
Q

What is the major anion and cation in ICF?

A

K+ and HPO42-

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10
Q

What is the major anion and cation in ECF?

A

Na+ and Cl-

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11
Q

Why is ICF and ECF different in ionic composition?

A

Because of the Na/K pump

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12
Q

Why does interstitial fluid contain a lot less protein than plasma?

A

Because the capillary wall is only semi permeable to water and electrolytes, large molecules such as proteins are too big to pass through

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13
Q

What is the major difference between the composition of plasma and interstitial fluid?

A

Plasma has a large amount of protein

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14
Q

What 4 major ions are measured by electrolyte assays?

A

Na+
K+
Cl-
HCO3-

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15
Q

What is the calculation for anion gap?

A

[Na+] + [K+] - [Cl-] + [HCO3-]

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16
Q

Why does an anion gap have a positive value?

A

As there are unmeasured anions not included in the calculation eg sulphate, phosphate, protein

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17
Q

Why does an anion gap exist?

A

Due to the inability to routinely measure all ions present in the blood eg protein that carries significant number of charges or sulphate that is difficult to measure

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18
Q

What does an increase in anion gap mean?

A

Indicates an increase in one or more of the unmeasured anions

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19
Q

Why are proteins anions?

A

Because they are predominately negatively charged, they have a pI of between 5-6 which is below physiological pH of 7.4

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20
Q

What can cause an increase in anion gap?

A

Ketoacidosis, renal failure, glycol poisoning, error, lactic acidosis, hypernatremia

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21
Q

Define osmolality.

A

A physical property of a solution based on concentration of solute per kg of solvent

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22
Q

What makes up a large amount of osmolality?

A

Small molecules present in high concentrations eg Na+, Cl-, K+, HCO3-, glucose, urea

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23
Q

Why is glucose and urea contribution to osmolality normally small?

A

Because they are present in plasma at low concentrations

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24
Q

When would glucose contribution to osmolality become significant?

A

In diabetes

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25
Q

How do you measure osmolality and what is the principle behind it?

A

Osmometer (freezing point depression) - depression in the freezing point of water as solute concentration increases

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26
Q

What specimen would you use to measure osmolality?

A

Serum free of cells and heamolysis

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27
Q

Why would you not use plasma to measure osmolality?

A

Because anticoagulants interfere in solution

28
Q

How do you calculate osmolarity?

A

Calculated by clinicians using patient laboratory data

29
Q

What is the osmolarity calculation?

A

2[Na+] + [glucose mmol/L] + [urea mmol/L] or

2[Na+] + [glucose mg/dL]/18 + [urea mg/dL]/2.8

30
Q

What is the calculation for osmolar gap?

A

measured osmolality - calculated osmolarity

31
Q

What does the osmolar gap calculation help to identify?

A

The presence of unmeasured osmotically active substances in serum eg alcohols, sugars, lipids and proteins

32
Q

Why does an osmolar gap exist?

A

Due to the presence of osmotically active substances not included in calculation

33
Q

What is osmotic pressure?

A

The pressure that moves a substance from a dilute solution to a more concentrated one

34
Q

When does a solute not contribute to osmotic pressure?

A

When the membrane is permeable to that solute e.g Na/K dont contribute as they are permeable through passive movement but proteins do as they cant move freely

35
Q

What is colloid/oncotic pressure?

A

The osmotic pressure between plasma and ISF caused by protein concentration

36
Q

What would cause excessive fluid build up in tissues (edema)?

A

Low oncotic pressure due to conditions of reduced plasma proteins e.g malnutrition or proteinuria

37
Q

What is cell volume controlled by?

A

ICF and plasma osmolality

38
Q

What happens if ICF and plasma osmolality changes?

A

Water must move across the membrane to maintain osmotic equilibrium

39
Q

Define hypotonic.

A

Concentration of the solutes is greater inside the cell than outside the cell

40
Q

Define hypertonic

A

Concentration of the solutes is greater outside the cell than inside the cell

41
Q

What happens if the ECF becomes hypotonic?

A

Water will move from ECF to ICF causing the swells to cell (brain will most be affected due to rigid covering)

42
Q

What happens if the ECF becomes hypertonic?

A

Water will move from ICF to ECF causing the cell to shrink - damaging to brain tissue and often accompanied by blood vessel damage

43
Q

What regulates water input and output?

A

Thirst - regulates input

ADH (vasopressin) - regulates output

44
Q

What regulates sodium output?

A

RAAS and natriuretic peptides

45
Q

Define thirst.

A

Concious desire for water

46
Q

What does thirst respond to?

A

High osmolality and low plasma volume

47
Q

Where is ADH (vasopressin) released from?

A

Posterior pituitary

48
Q

What is ADH released in response to?

A

High osmolality and low blood volume

49
Q

What does ADH do to the kidney?

A

Increases permeability of kidney distal tubule - controls renal water excretion

50
Q

Low ADH does what to urine volume and osmolality?

A

High urine volume
Low urine osmolality
= diluted urine

51
Q

High ADH does what to urine volume and osmolality?

A

Low urine volume
High urine osmolality
= concentrated urine

52
Q

Describe how the RAAS regulates water and sodium?

A

Low renal perfusion or Na/loss restriction promotes renin release from the kidney
Renin converts angiotensinogen to angiotensin I, ACE enzyme converts AI to AII, AII acts on the adrenal gland to promote aldosterone release
Aldosterone acts in the proximal tubule to reabsorb sodium and excrete potassium

53
Q

Where are natriuretic peptides synthesized?

A

In the atrium of the heart and other tissues

54
Q

When are natriuretic peptides released?

A

When the atrium of the heart is distended by expansion of extracellular space eg overhydration

55
Q

What are the roles of natriuretic peptides (3)?

A
  1. Stimulate vasodilation thus reduce plasma volume and blood pressure
  2. Protect against salt induced hypertension and mitigate against congestive heart failure
  3. Increase salt and water excretion by the kidney by increasing GFR, increasing Na+ excretion and increasing water excretion
56
Q

What are the 2 disorders of sodium metabolism?

A

Hypernatremia >150mmol/L

Hyponatremia <136mmol/L

57
Q

What are the symptoms of hypernatremia?

A

Tremors, irritability, confusion, coma

58
Q

What are the causes of hypernatremia?

A

Ingestion of large amounts of salts
Administration of hypertonic NaCl or NaHCO3
Hyperaldosteronism
Excessive sweating
Diabetes insipidus (decreased ADH secretion or unresponsiveness to ADH)

59
Q

What are normal sodium levels?

A

135-145mmol/L

60
Q

What are the symptoms of hyponatremia?

A

Generalised weakness, nausea

61
Q

What are the causes of hyponatremia?

A 
GI losses eg vomiting, diarrhoea
Excessive sweating
Renal disease
Hypoaldosteronism
Diuretic therapy
Inappropriate ADH secretion
62
Q

What are the 2 disturbances of water metabolism?

A

Dehydration and overhydration

63
Q

What can dehydration be accompanied by?

A

Increased plasma Na = hypernatremic
Normal plasma Na = normonatremic
Low plasma Na = hyponatremic

64
Q

How is potassium excreted?

A

Kidney (major output), skin, gut

65
Q

Why will a small move of K+ from ICF to ECF cause a major plasma concentration change?

A

Because ICF K+ is so high

Advanced Biochemistry (18 decks)

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