Na+ and H2O Balance Flashcards
Which hormone controls…
- Water balance
- Sodium balance?
- Water balance: anti-diuretic hormone (ADH)
- Sodium balance: steroids (released from the adrenals)
When is ADH released and from where?
When blood H2O is low (i.e., blood is too concentrated), ADH is released from the posterior pituitary gland
What is the effect of ADH release?
It acts on the kidneys to cause water to be reabsorbed from the renal tubules
This increases blood volume
High ADH = small/large volume of dilute/concentrated urine
?
High ADH = small volume of concentrated urine
Low ADH = small/large volume of dilute/concentrated urine
Low ADH = large volume of dilute urine
Urine concentration is measured as urine osmolality.
Concentrated urine = high osmolality. T/F?
True
Concentrated urine = high osmolality
Dilute urine = low osmolality
Which is the main steroid hormone involved in Na+ balance?
Aldosterone (a mineralocorticoid released from the zona glomerulosa)
The effect of steroids on Na+ balance is known as mineralocorticoid activity. Describe mineralocorticoid activity
MA = Na+ is reabsorbed in the renal tubules in exchange for K+/H+
In the body, too much mineralocorticoid activity results in a sodium loss. T/F?
False
Excess MA = sodium gain
Too little MA = sodium loss
What molecule follows Na+ that is reabsorbed in the renal tubules?
Water
What equation links H2O and Na+ balance?
Na+ conc. = the ratio of Na+ to water:
[Na+] = (mmol Na+) / (1L H2O)
Using the equation:
[Na+] = (mmol Na+) / (1L H2O)
Name 2 causes of hyponatraemia
Too little Na+
Too much H2O
Using the equation:
[Na+] = (mmol Na+) / (1L H2O)
Name 2 causes of hypernatraemia
Too much Na+
Too little H2O
Loss/gain of H2O is from/to…
a) Intracellular fluid
b) Extracellular fluid
c) All body compartments
c) All body compartments
Loss/gain of sodium is from/to…
a) Intracellular fluid
b) Extracellular fluid
c) All body compartments
b) Extracellular fluid
due to control by the Na+/K+ ATPase
Loss of Na+ from the ECF results in water loss from…
a) The ECF
b) All body compartments
a) The ECF
Changes in fluid compartment volumes are greater when caused by changes in... a) Na+ b) H2O ? Why?
a) Na+
This is because changes caused by Na+ are confined to the ECF and so the effect on that compartment is greater
Why does change in H2O volume have less effect than Na+?
Changes caused by H2O have less effect as they are shared across all body compartments
Hypernatraemia due to excess Na+ is common. T/F?
False
It is actually very rare
Hypernatraemia is usually caused by too little H2O e.g., in patients who are unable to eat or drink
Clinical signs of hyper or hyponatraemia are seen when Na+ imbalance is the cause. Why doesn’t H2O imbalance cause the same signs?
H2O imbalance is spread across all body compartments and so does not have enough of an effect to cause clinical signs
List some clinical signs of hyponatraemia (decreased ECF volume)
- Tachycardia
- Dry mucous membranes
- Decreased skin turgor
- Decreased consciousness
- Decreased urine output
- Postural hypotension
- Soft/sunken eyeballs
List some clinical signs of hypernatraemia (increased ECF volume)
- Abdominal swelling
- Peripheral oedema
- Pulmonary oedema
- Pleural effusion
- Coughing
- SOB
- Tiredness
- Increased pumping of heart
List some causes of hyponatraemia (caused by too little Na+ AND too much H2O)
Too little Na+:
- Loss from gut e.g., vomiting, diarrhoea
- Loss from skin e.g., sweating, burns
- Reduced food or drink intake
Too much H2O:
- SIADH (most common, causes reduced H2O excretion)
- Compulsive water drinking
List some causes of hypernatraemia (caused by too much Na+ AND too little H2O)
Too much Na+: (rare)
- Some IV meds
- Near drowning
Too little H2O:
- Diabetes insipidus
- Reduced food and drink intake e.g., young or elderly
List the workup to treating hyponatraemia
- Work out cause
- Treat too little Na+ by giving Na+ e.g., IV saline or oral Na+ salt
- Treat excess H2O by fluid restricting
List the workup to treating hypernatraemia
- Work out cause
- Treat excess Na+ by removing Na+ (using loop diuretics)
- Treat too little H2O by giving H2O as IV dextrose
IV saline increases the volume of all body compartments. T/F?
False
Dextrose increases fluid volume across all body compartments
Saline increases fluid volume in the ECF compartment only
