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Clinical Chemistry > Water sodium and potassium > Flashcards

Water sodium and potassium Flashcards

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1
Q

How many Liters of intracellular fluid is in the body?

A

28L(66%)

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2
Q

How manly liters of Extracellular fluid is in the body?

A

14L(33%)

  1. 5L plasma water (8%)
  2. 5L interstitial water (25%)
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3
Q

What is the normal day to day fluctuation of body water content?

A

1%

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4
Q

How is the input regulated?

A

Thirst is controlled by the hypothalamus thirst center. Its functioning is controlled by
ECF osmolality: Hypertonicity increases thirst
Blood volume: Deacreased volume increases thirst
Miscellaneous factors: Pain and stress increases thirst

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5
Q

How is the Output regulated?

A

Controlled by kidney and vasopressin hormone

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6
Q

What is water retention?

A

Increase in the volume of both ECF and ICF.
Caused by compulsive water drinking; excessive fluid administration, water absorption during bladder irrigation.

Decreased excretion (e.g renal failure, inappropriate or ectopic secretion of vasopressin; drugs stimulating vasopressin release

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7
Q

What is water loss(dehydration)?

A

Decrease in volume of ECF and ICF

From decreased intake or increased loss e.g loss from kidney skin and lungs

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8
Q

What are the 6 most important electrolytes for body function?

A 
Sodium, 
potassium, 
chloride, 
bicarbonate,
 calcium and phosphate
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9
Q

What are the roles of the electrolytes?

A

Transmission of electrical impulses

Stabilize protein structures

Aid in releasing hormones from endocrine glands

Contribute to the osmotic balance that controls the movement of water between cells and their environment

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10
Q

Which ions contribute majorly to ECF

A

Sodium (cation), chloride (anion),

bicarbonate

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11
Q

Which ions contribute majorly to ICF?

A

Sodium (cation), chloride (anion),

bicarbonate

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12
Q

How do electrolytes enter the body?

A

Through the digestive tract

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13
Q

How do ions leave the body?

A

Excretion occurs mainly through ions with small amounts lost in sweat and feces
Excessive sweating leads to Significant loss, especially of sodium and chloride

Severe vomiting or diarrhea leads to Loss of chloride and bicarbonate
ions

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14
Q

How is sodium maintained outside the cell?

A

Via sodium potassium ATPase pump

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15
Q

what is the threshold level of sodium?

A

135-145mmol/L

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16
Q

What is the role of sodium?

A

• Regulates the membrane potential of cells and important

for active transport of molecules across cell membranes

17
Q

What are the primary regulators of sodium?

A

Renin-angiotensin-aldosterone system (RAS): ↓[Na+] → activate RAS →
release aldosterone → increase sodium absorption from distal tubules and collecting
ducts → [Na+] ↑

  1. Natriuretic peptide hormones : ↓[Na+] → indirectly reduced effective atrial
    arterial pressure → inhibit atrial natriuretic peptide (ANP) release → reduce sodium
    loss from tubules
  2. Vasopressin (ADH): Regulates renal water loss and thus causes
    changes in the osmolality of body fluid compartments
18
Q

What are causes of sodium depletion (hyponatremia)

A 
Causes of sodium depletion 
(hyponatremia)
• Excessive loss
 From kidney
 Diuretic therapy; Cerebral salt-wasting

From skin
Burns; Cystic fibrosis; Massively
increased sweating

From gut
Vomiting and diarrhea; Intestinal
obstruction

19
Q

What are causes of excess sodium(hypernatremia)

A

• Increased intake
Excessive parenteral administration
Absorption from saline

• Decreased excretion
Decreased glomerular filtration
Increased tubular reabsorption

20
Q

Explain Hyponatremia

A

• Lower than normal sodium concentration

• Results in increased entry of water into cells
Causes swelling of the cells
Swelling of red blood cells Decreases their oxygen carrying efficiency and they become too large to fit through capillaries

Swelling of neurons leads to Neurological dysfunction causing
Nausea, malaise, headache, lethargy, reduced level of
consciousness

21
Q

What is Pseudohyponatremia?

A

• Artefactual low sodium result reported in patients with severe
hyperproteinaemia or hyperlipidaemia

• Increased amounts of protein or lipoprotein occupy more of the
plasma volume than usual, and the water less  low sodium amount

22
Q

What is Hypervolemic hyponatremia?

A

• Excess of total body water low sodium level
• Causes Congestive heart failure, hepatic cirrhosis, nephritic
syndrome, other edematous or ascites disorders
• Serum osmolality is low

23
Q

What is Hypovolemic hyponatremia

A

• Excess of total body water  low sodium level
• Causes  Congestive heart failure, hepatic cirrhosis, nephritic
syndrome, other edematous or ascites disorders
• Serum osmolality is low

24
Q

What is Euvolemic hyponatremia?

A

• Not associated with edema or volume depletion
• Causes Reduced salt intake, Excessive water intake in the presence
of Addison disease, hypothyroidism, or non-osmotic vasopressin
release (due to stress, post-operation and use of drugs)

• The syndrome of inappropriate secretion of antidiuretic hormone
(SIADH) inappropriate and continued secretion or action of vasopressin despite normal plasma volume impaired water excretion

25
Q

What are the main causes of hypernatremia?

A

Water loss from the blood loss
Impaired vasopressin secretion or action leads to failure to retain water

 Osmotic diuresis (Eg. diabetic ketoacidosis patient)  
Loss of both sodium and water 
 Excessive sodium intake, particularly from the use of intravenous solutions
 Primary hyperaldosteronism (Conn’s syndrome)
26
Q

What is the treatment for hypernatremia?

A

Administration of hypotonic fluids such as water (orally) or 5% dextrose
(parenterally)

Remove excess sodium

27
Q

Who should have their plasma sodium concentration measured?

A
  1. Patients with dehydration or excessive fluid loss,
    as a guide to appropriate replacement therapy
  2. Patients on parenteral fluid replacement who are
    unable to indicate or respond to thirst (Eg. the
    comatose, infants and the elderly)
  3. Patients with unexplained confusion, abnormal
    behavior or sign of CNS irritability
28
Q

What is the conventional method of investigating sodium disorders?

A

Flame photometry
 Relies on the fact that the sodium ion emits light at a
wavelength of 589 nm when excited in a gas flame
 Intensity of the light produced is proportional to the
concentration of the element

29
Q

What is the current method of investigating sodium disorders?

A

Ion-specific sodium electrodes

Measures the activity of sodium
Measures the number of atoms that act as true ions in a defined volume of water

30
Q

What is the role of potassium?

A

• Main intracellular cation
• Approximately 135-150mmol/l (~98%) is present intracellularly
• Daily requirement is about 1mmol/kg/day, which is absorbed
from the small intestine by diffusion (Almost all foods contain
potassium)
• Function  Helps establish the resting membrane potential in
neurons and muscle fibers after membrane depolarization and
action potentials
• Critical Values  Serum potassium concentration below
2.5mmol/L (hypokalemia) or above 6.0mmol/L (hyperkalemia) is
dangerous  Neuromuscular and cardiac muscle effects

31
Q

How is potassium regulated?

A

Mainly regulated by kidneys
filtered potassium is almost completely reabsorbed in proximal tubules
Its secretion takes place in the most distal part of the distal convoluted tubules(Passive process)
• Distal tubule An important site of sodium reabsorption
• When sodium is reabsorbed, the tubular lumen becomes
electronegative in relation to the adjacent cells, hence cations in the cell
(Eg. potassium, H+) move into the lumen to balance the charge
• The rate of potassium secretion into the lumen depends on Amount of sodium reabsorbed at the distal tubule (Under control of aldosterone
and Atrial Natriuretic Peptide)

Rate of urine flow (as the urine flow rate increases, potassium secretion
decreases)
 Concentration of potassium in the tubular cell
 Acid-base balance (potassium secretion is decreased when there is increased
hydrogen ion secretion. Eg. Acidotic patient)

32
Q

Explain Hypokalemia

A

• Occurs when output exceeds intake
• Classification
1. Hypokalemia with normal total body potassium 
Shift of potassium into the cell
2. Hypokalemia with a low total body potassium 
Increased potassium loss from the body (Eg.
Secondary to GI fluid loss such as vomiting, diarrhea
 Dehydration stimulates aldosterone production 
increases urinary potassium significantly

33
Q

What are the symptoms of hypokalemia?

A

Muscle weakness
Constipation (Eg. Paralytic ileus)
Cardiac dysrhythmias (could be fatal)

34
Q

What is the primary cause of Hypokalemia?

A

Urine Potassium
• In GI loss, urine potassium is raised but it is usually < 20 mmol/L
• In renal loss, urine potassium is raised and it is usually > 20 mmol/L

35
Q

Explain Hyperkalemia

A

• Excessive intake or decreased excretion
• Less common than hypokalemia, but more dangerous
• Lowers the resting membrane potential shortens
cardiac action potential increases speed of
repolarization

36
Q

What are the clinical features of Hyperkalemia?

A

Cardiac arrest in asystole
Slow ventricular fibrillation
Muscle weakness
Hyperventilation

37
Q

What is Pseudo hyperkalemia?

A

Most common high serum potassium concentration
laboratory findings
• Phlebotomy errors: Tight tourniquet; vigorous exercise of
the extremity during blood drawing; hemolysis due to
vigorous shaking of the test tube; delayed separation of the
serum (> 4 hours)
• Underlying disorders Thrombocytosis; Leukocytosis

Clinical Chemistry (5 decks)

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