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Chemical pathology > C2&3 > Flashcards

C2&3 Flashcards

1
Q

What are the sources of water intake?

A

food, drink, metabolic water

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2
Q

What are the sources of water output?

A

kidneys, skin, lungs, GIT (stool)

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3
Q

What is the normal body water content?

A

60% of total body weight, decreases with age

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4
Q

How is total body water calculated (TBW)?

A

60% x total body weight

- e.g. 70kg x 60% = 42L TBW

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5
Q

What are the 2 fluid compartments that water is distributed between?

A
  • Intracellular fluid compartment (ICF)

- Extracellular fluid compartment (ECF)

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6
Q

How is water distributed between the 2 fluid compartments?

A
  • ECF: 45% of TBW

- ICF: 55% of TBW

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7
Q

What is the role of sodium in the body?

A
  • It is the predominant cation in the ECF, and influences distribution and movement of water between the ECF and ICF
  • Determines osmolality, ECF volume, blood volume, and blood pressure
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8
Q

How is sodium maintained?

A

By the the Na-K-ATPase pump, which keeps K in the ICF and Na in the ECF

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9
Q

What is the main source of sodium intake?

A

salt (NaCl): 100-200 mmol/day

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10
Q

How is sodium absorbed?

A

Most absorbed via GIT, via active transport

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11
Q

How is sodium excreted?

A

90% in the urine, stool, sweat

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12
Q

What are the mechanisms of water homeostasis?

A
  • ADH
  • ANP
  • RAAS system
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13
Q

Explain what happens when the water content in the blood drops below normal? (in terms of ADH)

A
  • Salt is eaten/sweating
  • Water content of blood becomes too low
  • osmoreceptors detect this, and pituitary releases ADH
  • High volume of water is reabsorbed by kidney and small volume of concentrated urine is passed to bladder
  • So, high volume of water is passed to the blood and the water content becomes normal again
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14
Q

Explain what happens when the water content in the blood rises above normal? (in terms of ADH)

A
  • Too much water drunk
  • Water content of blood becomes too high
  • osmoreceptors detect this, and pituitary releases little ADH
  • Low volume of water is reabsorbed by kidney and large volume of dilute urine is passed to bladder
  • So, low volume of water is passed to the blood and the water content becomes normal again
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15
Q

What does RAAS stand for?

A

Renin-angiotensin-aldosteron

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16
Q

When is the RAAS system activated?

A

dehydration, NA+ deficiency or heamorrhage

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17
Q

What is the goal of the RAAS system?

A

To decrease blood volume and blood pressure

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18
Q

Explain the mechanism of the RAAS system

A
  • Juxtoglomerular cells of kidneys detect (dehydration, NA+ deficiency, haemorrhage)
  • Kidneys secrete renin
  • Angiotensin I become angiotensin II
  • Angiotensin II acts on adrenal cortex to secrete aldosterone
  • Aldosterone acts on kidneys: increased Na+ and water reabsorption, increases K+ excretion in urine
  • Leads to an increase in blood volume and blood pressure to normal levels
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19
Q

What does ANP stand for?

A

Atrial natriuretic peptide

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20
Q

How is the homeostasis of the ECF disturbed?

A

ECF volume increases (fluid/salt)

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21
Q

What happens when the ECF homeostasis is disturbed?

A

Blood volume increases and atrial distension

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22
Q

What triggers and increases ANP release?

A

A disruption in the ECF homeostasis: blood volume increase and atrial distension

23
Q

What does and increased ANP release do?

A
  • decreases aldosterone
  • decreases ADH
  • decreased thirst
  • leads to increased water and Na+ loss
24
Q

What are the basic water disorders?

A
  • dehydration

- fluid overload

25
Q

What causes dehydration?

A
  • Water loss due to decreased intake or increased output

- Water and Na loss: extra-renal, renal

26
Q

Name disorders or conditions that cause an increased water output

A
  • Diabetes insipidus
  • Osmotic diuresis
  • Excess sweating
27
Q

Name renal causes of water and Na loss

A
  • Decreased aldosterone
  • Addison’s disease
  • Diuretics
28
Q

Name extra renal causes of water and Na loss

A
  • bleeding
  • diarrhoea
  • vomiting
  • burns
29
Q

What is Diabetes insipidus?

A
  • A disease that causes decreased ADH secretion or ADH resistance
  • This decreased absorption of water at collecting ducts
  • Large volumes of dilute urine - hypotonic fluid loss
30
Q

What is isotonic dehydration?

A

When water loss is equal to Na loss

31
Q

What is hypertonic dehydration?

A

When water loss if greater than Na loss

32
Q

What is hypotonic dehydration?

A

When isotonic fluid loss is replaced with pure water

33
Q

What causes fluid overload?

A
  • Water overload: increased water intake or decreased water output
  • Water and Na overload: iatrogenic or increased aldosterone
  • Na overload: increased intake, iatrogenic, develop hypernatraemia
34
Q

What causes a decreased output of water?

A
  • renal failure

- inappropriate ADH secretion (SIADH)

35
Q

Name a condition that causes water and Na overload

A

Oedema

36
Q

What is oedema a sign of?

A

cardiac failure, renal failure, liver cirrhosis

37
Q

How can your intake of Na become too high?

A

When sea water is consumed in near drowning

38
Q

What are iatrogenic causes of Na overload?

A

hypertonic saline IV

39
Q

What does SIADH stand for?

A

Syndrome of inappropriate ADH secretion

40
Q

What is SIADH?

A
  • When ADH is secreted in the presence of a decreased serum osmolality and hypervolaemia
  • Water is reabsorbed in collecting ducts: small volume of concentrated urine
  • The retained water is shared by the ECF and ICF
41
Q

What are causes of SIADH?

A

pulmonary disease, pneumonia, TB, intracranial head injury, meningitis, tumours secreting ADH ectopic production esp. in bronchial tumours, pain, trauma, and surgery

42
Q

What condition can SIADH cause?

A

cerebral oedema, which leads to decreased consiousness

43
Q

What is oedema?

A
  • When fluid leaks from the vascular compartment to the interstitial compartment
  • This decreased IV volume causes increased aldosterone secretion which causes Na and water retention
44
Q

What are the causes of oedema?

A
  • decreased vascular oncotic pressure (low albumin)

- increased vascular hydrostatic pressure

45
Q

What are the basic sodium disorders?

A
  • Hypernatraemia
  • Hypenatraemia
  • Pseudohyponatraemia
46
Q

What are the signs and symptoms of hypernatramia?

A

thirst, hypertension, pitting oedema, agitation, convulsions, dyspnoea, respiratory arrest

47
Q

What are the causes of hypernatraemia?

A

Water loss, Na and water loss, Na overload

48
Q

What are the consequences of hypernatraemia?

A

decreased ICF -> cells shrink -> brain haemorrhage

49
Q

What are the signs and symptoms of hyponatraemia?

A

muscle weakness, lethargy, confusion, hypotension, tachycardia

50
Q

What causes hyponatraemia?

A

water overload, water and Na overload, Na and water loss followed by water intake only, dilution due to glucose, pseudohyponatraemia

51
Q

What are the consequences of hyponatraemia?

A

increased ICF -> cells swell -> brain oedema

52
Q

What is pseudohyponatraemia?

A
  • False low Na measurement due to presence of increased lipids or proteins in specimen
  • Normally serum consists of 93% aqueous phase and 7% solid phase
  • Seen if using Indirect ISE method of measurement
  • Direct ISE method not affected (so more effective)
  • Identified by high osmolal gap
53
Q

What is the osmolal gap?

A

Difference between determined osmolality and calculated osmolality

54
Q

Why is the osmolal gap important?

A
  • When calculated and measured is not the same

- Osmolal gap will increase in presence of volatile substances in blood &alcohol or methanol poisoning

Chemical pathology (6 decks)

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