Water sodium and potassium

Question 1

How many Liters of intracellular fluid is in the body?

Answer 1

28L(66%)

Question 2

How manly liters of Extracellular fluid is in the body?

Answer 2

14L(33%)

3. 5L plasma water (8%)
4. 5L interstitial water (25%)

Question 3

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

Answer 3

1%

Question 4

How is the input regulated?

Answer 4

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

Question 5

How is the Output regulated?

Answer 5

Controlled by kidney and vasopressin hormone

Question 6

What is water retention?

Answer 6

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

Question 7

What is water loss(dehydration)?

Answer 7

Decrease in volume of ECF and ICF

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

Question 8

What are the 6 most important electrolytes for body function?

Answer 8

Sodium, 
potassium, 
chloride, 
bicarbonate,
 calcium and phosphate

Question 9

What are the roles of the electrolytes?

Answer 9

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

Question 10

Which ions contribute majorly to ECF

Answer 10

Sodium (cation), chloride (anion),

bicarbonate

Question 11

Which ions contribute majorly to ICF?

Answer 11

Sodium (cation), chloride (anion),

bicarbonate

Question 12

How do electrolytes enter the body?

Answer 12

Through the digestive tract

Question 13

How do ions leave the body?

Answer 13

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

Question 14

How is sodium maintained outside the cell?

Answer 14

Via sodium potassium ATPase pump

Question 15

what is the threshold level of sodium?

Answer 15

135-145mmol/L

Question 16

What is the role of sodium?

Answer 16

• Regulates the membrane potential of cells and important

for active transport of molecules across cell membranes

Question 17

What are the primary regulators of sodium?

Answer 17

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

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

Question 18

What are causes of sodium depletion (hyponatremia)

Answer 18

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

Question 19

What are causes of excess sodium(hypernatremia)

Answer 19

• Increased intake
Excessive parenteral administration
Absorption from saline

• Decreased excretion
Decreased glomerular filtration
Increased tubular reabsorption

Question 20

Explain Hyponatremia

Answer 20

• 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

Question 21

What is Pseudohyponatremia?

Answer 21

• 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

Question 22

What is Hypervolemic hyponatremia?

Answer 22

• 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

Question 23

What is Hypovolemic hyponatremia

Answer 23

• 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

Question 24

What is Euvolemic hyponatremia?

Answer 24

• 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

Question 25

What are the main causes of hypernatremia?

Answer 25

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) ```

Question 26

What is the treatment for hypernatremia?

Answer 26

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

Question 27

Who should have their plasma sodium concentration measured?

Answer 27

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

Question 28

What is the conventional method of investigating sodium disorders?

Answer 28

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

Question 29

What is the current method of investigating sodium disorders?

Answer 29

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

Question 30

What is the role of potassium?

Answer 30

• 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

Question 31

How is potassium regulated?

Answer 31

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)

Question 32

Explain Hypokalemia

Answer 32

• 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

Question 33

What are the symptoms of hypokalemia?

Answer 33

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

Question 34

What is the primary cause of Hypokalemia?

Answer 34

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

Question 35

Explain Hyperkalemia

Answer 35

• 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

Question 36

What are the clinical features of Hyperkalemia?

Answer 36

Cardiac arrest in asystole Slow ventricular fibrillation Muscle weakness Hyperventilation

Question 37

What is Pseudo hyperkalemia?

Answer 37

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