Water sodium and potassium Flashcards
How many Liters of intracellular fluid is in the body?
28L(66%)
How manly liters of Extracellular fluid is in the body?
14L(33%)
- 5L plasma water (8%)
- 5L interstitial water (25%)
What is the normal day to day fluctuation of body water content?
1%
How is the input regulated?
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
How is the Output regulated?
Controlled by kidney and vasopressin hormone
What is water retention?
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
What is water loss(dehydration)?
Decrease in volume of ECF and ICF
From decreased intake or increased loss e.g loss from kidney skin and lungs
What are the 6 most important electrolytes for body function?
Sodium, potassium, chloride, bicarbonate, calcium and phosphate
What are the roles of the electrolytes?
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
Which ions contribute majorly to ECF
Sodium (cation), chloride (anion),
bicarbonate
Which ions contribute majorly to ICF?
Sodium (cation), chloride (anion),
bicarbonate
How do electrolytes enter the body?
Through the digestive tract
How do ions leave the body?
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
How is sodium maintained outside the cell?
Via sodium potassium ATPase pump
what is the threshold level of sodium?
135-145mmol/L
What is the role of sodium?
• Regulates the membrane potential of cells and important
for active transport of molecules across cell membranes
What are the primary regulators of sodium?
Renin-angiotensin-aldosterone system (RAS): ↓[Na+] → activate RAS →
release aldosterone → increase sodium absorption from distal tubules and collecting
ducts → [Na+] ↑
- Natriuretic peptide hormones : ↓[Na+] → indirectly reduced effective atrial
arterial pressure → inhibit atrial natriuretic peptide (ANP) release → reduce sodium
loss from tubules - Vasopressin (ADH): Regulates renal water loss and thus causes
changes in the osmolality of body fluid compartments
What are causes of sodium depletion (hyponatremia)
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
What are causes of excess sodium(hypernatremia)
• Increased intake
Excessive parenteral administration
Absorption from saline
• Decreased excretion
Decreased glomerular filtration
Increased tubular reabsorption
Explain Hyponatremia
• 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
What is Pseudohyponatremia?
• 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
What is Hypervolemic hyponatremia?
• 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
What is Hypovolemic hyponatremia
• 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
What is Euvolemic hyponatremia?
• 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
What are the main causes of hypernatremia?
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)
What is the treatment for hypernatremia?
Administration of hypotonic fluids such as water (orally) or 5% dextrose
(parenterally)
Remove excess sodium
Who should have their plasma sodium concentration measured?
- Patients with dehydration or excessive fluid loss,
as a guide to appropriate replacement therapy - Patients on parenteral fluid replacement who are
unable to indicate or respond to thirst (Eg. the
comatose, infants and the elderly) - Patients with unexplained confusion, abnormal
behavior or sign of CNS irritability
What is the conventional method of investigating sodium disorders?
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
What is the current method of investigating sodium disorders?
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
What is the role of potassium?
• 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
How is potassium regulated?
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)
Explain Hypokalemia
• 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
What are the symptoms of hypokalemia?
Muscle weakness
Constipation (Eg. Paralytic ileus)
Cardiac dysrhythmias (could be fatal)
What is the primary cause of Hypokalemia?
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
Explain Hyperkalemia
• 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
What are the clinical features of Hyperkalemia?
Cardiac arrest in asystole
Slow ventricular fibrillation
Muscle weakness
Hyperventilation
What is Pseudo hyperkalemia?
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
