Week 4 - C - Week 3 - Sodium and Water Balance Flashcards
Does water follow sodium or does sodium follow water?
Water follows sodium everywhere
What controls the sodium levels in the body?
Mineralocorticoid activity
sodium retention in exchange for potassium and/or hydrogen ions What is this known as? When does sodium retention tend to occur?
Mineralocorticoid activity
When there is a drop in blood pressure
What does the kidneys release in response to detecting a low blood pressure? how does this process aim to correct blood pressure? (what in the correction process releases aldosterone)
The kidney releases renin, which cause anhiotensinogen to be converted to angiotensin 1 which is converted to angiotensin 2 via ACE
Angiotensin 2 causes the release of aldosterone from the adrenal cortex which promotes sodium reabsorption in the kidney tubules
What is the main mineralocorticoid?
Aldosterone
What does too little mineralocrticoid activity do sodium and what happens to water?
Too little causes increased sodium loss causing increased water loss (decreases BP)
What is diuresis?
Diuresis is increased production of urine
What is arginine vasopressin another name for?
ADH = AVP anti-diuretic hromone - arginine vasopressin
Where is ADH released from and what does it act on the kindey tubules to cause?
Released from the posterior pituitary and causes increased water reabsoprtion thus the antidiuretic effect
Is concentrated urine due to high or low ADH levels?
High ADH levels
When the the urine is described as having a high urine osmolality, is this concentrated or dilute urine?
Concentrated urine - high urine osmolality
Dilute urine - low urine osmolality
If the plasma volume is increased (meaning there is uptake of sodium and water), if the H2O plasma volume continues to increase howver the sodium levels decrease, what is a syndrome that can be a cause of this?
The syndrome of inappropriate antidiuretic hormone (ADH) secretion (SIADH)
In SIADH, what happens to the, osmolality of the serum (blood)? WHat happens to the urine osmolality?
Low serum osmolality due to other minerals being excreted in urine also
Urine osmolality is raised (>100mOsmol/kg, urine NA+ >20mmol/l)
Condition where the hyponatremia results from an excess of water rather than a deficiency of sodium?
SIADH
What is the best way to remember the causes of SIADH secretion? (3Cs)
Chest - pneumonia, TB, carcinoma
Cranial causes - head injury
Chlorpropamide (sulphonylurea) - no longer recommended for use
Which type of lung cancer can cause SIADH?
Small cell lung cancers can produce ectopic ADH and large amounts can lead to SIADH
Decreased [Na+] can be due to too much water or too little sodium
SIADH is a cause of the too much water
What disease cause too little sodium leading to a decreased [Na+]?
Addison’s disease
What are other causes of a decreased serum sodium concentration?
Vomiting and diarrhoea
Excessive sweating
Increased [Na] can be due to: too little water or to too much sodium
What disease can cause too little water?
Diabetes insipidus (problem with ADH secretion) (also a very little water intake)
What is a cause of too much sodium leading to an increased sodium concentration in the blood? (these are rare)
Some IV medications are given as sodium salts
High intake of salty foods in infants
A 24 year-old student presents with a six month history of malaise, tiredness, poor appetite and one stone weight loss. She has developed a craving for salty foods – crisps in particular. She has had a number of dizzy spells particularly while in warm places. She is thin. She has low BP which falls further on standing. You have the impression that she is tanned, and you find increased pigmentation in her mouth and hand creases. What is suspected diagnosis?
Addison’s disease
What is the other name for primary adrenal insufficiency? What is it?
Addison’s disease
Caused when something attacks the outer part of the adrenal gland - the adrenal cortex stopping it from producing aldosterone and cortisol properly
Due to the fact the body cannot produce enough steroid’s in addison’s disease, how does this cause the patient to be dehydrated?
Adrenal glands cannot produce aldosterone, leads to lack of reabsorption of sodium and water - therefore as sodium and water are lost through the urine patient is dehydrated
The patient in Addison’s is hypotensive due to a decreased ECF therefore experiences dizziness , why is there excess ACTH in Addison’s>
Due to the decreased cortisol levels, the hypothalamus senses a decrease and increases corticotrophin-releasing homrone production, this causes an increase in ACTH levels to try and correct the low cortisol levels
Why does the increased ACTH levels cause increased pigmentation of the skin?
The ACTH contains the sequence for the melanocyte stimulating hormone (MSH)
Eventually proteases breakdown the ACTH exposing the MSH which will lead to darkened patches of skin and easy tanning
What will the potassium and sodium levels show on blood tests?
Sodium levels will be low
Potassium levels will be high
In a patient presenting to hospital (usually for another illness), and they are found to have a low sodium, what should you check for? Volume status is usually unremarkable
Check for Addisons
If Addison’s comes back negative, what is usually thought to be the cause? Does a non-osmotic stimulus override an osmotic stimulus in this condition?
SIADH - syndrome of inappropriate ADH secretion
a non-osmotic stimulus overrides an osmotic stimulus in this condition
What are example’s of non-osmotic stimuli?
Hypovalaemia, hypotension, vomiting, diarrhoea and sweating
A 29 year-old man is admitted to ITU following a cycling accident in which he sustained a severe head injury. During his ITU stay his urine output is in excess of 12 litres daily; his IV fluid requirement is correspondingly large. Serum sodium is 167 mmol/L (high) on admission to ITU and slowly falls as fluid replacement ‘catches up’. He is in addition commenced on desmopressin (exogenous ADH) which produces a sharper fall in sodium. Diagnoses?
Diabetes insipidus
Why is it likely that the previous case shows diabtes insipidus?
Pituitary could potentially be damaged on injury, leading to posterior pituitary dysfunction decreasing ADH production which is causing the excess urine
Why in diabetes insipidus is the patients sodium high?
Sodium levels are high as due to the increased water loss, the ECF is decreasing and therefore there is increased sodium reabsorption
Does hypovalaemia imply water or sodium defecit?
Hypovolaemia implies water deficit.
If it is present when [Na] is low, then there must be an even bigger sodium deficit.
This is important: hypovolaemia in hyponatraemia → too little sodium.
What is the usual clinical finding for hypervolaemia?
Oedema
In heart failure, blood volume is usually decreased as it gathers in the feet/legs, what does this do to the compensatory mechanisms?
https://s3.amazonaws.com/classconnection/403/flashcards/11907403/jpg/picture1-159184401C646788B84.jpg
[Na] itself is helpful. If very low ( 155 mmol/L), then YES it is serious What symptoms can arise from low or high sodium meaning it is very serious?
altered consciousness, confusion, nausea
How should I treat it?
Too little sodium →
Too much water →
Too little water →
Too much sodium →
Too little sodium → give sodium
Too much water → fluid restrict
Too little water → give water
Too much sodium → get rid of excess sodium e.g. diuretics (furosemide) to induce natriuresis, and then replace just the water
