Biochemistry Flashcards
Where is ADH released from?
POSTERIOR pituitary
What is the function of ADH?
Water reabsorption from the renal tubules
What effect does high ADH have on volume and osmolality of urine?
High ADH causes a small volume of concentrated urine (high osmolality)
What effect does low ADH have on volume and osmolality of urine?
Low ADH causes a large volume of dilute urine (low osmolality)
How do mineralocorticoid levels affect sodium levels?
Sodium balance is controlled by steroids
Too much mineralocorticoid means there will be sodium gain
Too little mineralocorticoid means there will be sodium loss
Which is the main steroid which controls sodium balance?
Aldosterone
Sodium is confined to which compartment?
Sodium is confined to the ECF. Sodium loss or gain is solely from and to the ECF
What are some of the possible causes/ mechanisms of low sodium?
Increased sodium loss
Decreased sodium intake
Decreased water excretion e.g SIADH
Increased water intake e.g compulsive drinking
What is Addison’s?
Autoimmune destruction of the adrenal cortex (primary adrenal insufficiency)
Why is addison’s associated with hyponatraemia?
Patients with addison’s have primary adrenal insufficiency which means they can’t make enough steroids so they can’t retain sodium
What are some of the signs and symptoms of Addison’s?
Anorexia and weight loss
Fatigue
Dizziness
Hypotension
Abdo pain and N&V
Hyperpigmentation of the skin
What biochemistry results is Addison’s associated with?
HYPERkalaemia
HYPOnatraemia
HYPOglycaemia
Increased renin to aldosterone ratio
What autoantibodies is Addison’s associated with?
Anti-adrenal autoantibodies
What is the management for Addison’s?
Hydrocortisone
Fludrocortisone
What are some of the possible causes/ mechanisms of high sodium?
Increased sodium intake (e.g IV meds and malicious causes - very rare)
Decreased sodium loss
Increased water loss (e.g diabetes insidious)
Decreased water intake
Why does Central Diabetes Insipidus result in hypernatraemia?
Central DI is a posterior pituitary problem
ADH Is not secreted from the posterior pituitary so there is no ADH to act on the kidneys to cause water to be reabsorbed. Water is therefore lost in the urine so sodium concentration is high reflecting the water deficit.
What are some of the causes of central diabetes insipidus?
Familial (DIDMOAD)
Trauma
Tumours
Infiltrative disease e.g sarcoidosis
What is the difference between central and nephrogenic diabetes insipidus?
Central DI is a posterior pituitary problem - ADH is not secreted
Nephrogenic DI is an issue with the kidneys being resistant to the action of ADH
What is the investigation for diabetes inspidus?
Water deprivation test
urine will remain dilute due to lack of ADH
What is the management of diabetes insipidus?
Desmospray/
Desmopressin
What is SIADH?
Syndrome of inappropriate ADH secretion. There is water retention which causes hyponatraemia due to the effects of dilution.
How does SIADH present clinically?
Hypotension
Pain
N&V
What ECG changes are associated with hyperkalaemia?
Peaked T waves
Flattened P waves
Prolonged QRS duration
What are the treatment options for hyperkalaemia? How do these work?
Calcium gluconate
(protects the myocardium)
Insulin (act rapid) and dextrose
Salbutamol
(move K+ back into cells)
Calcium resonium - NOT in the acute setting
(Prevents potassium absorption fro the GI tract)
What is Conn’s syndrome?
Primary hyperaldosteronism
What biochemistry results is primary hyperaldosteronism (Conn’s) associated with?
HYPOkalaemia
Alkalosis
Aldosterone excess
What investigations are done for primary hyperaldosteronism
Adrenal CT
Adrenal vein sampling
What are the causes of primary hyperaldosteronism?
Conn’s syndrome
Adrenal adenomas
Bilateral idiopathic adrenal hyperplasia
What is used to distinguish between central and nephrogenic diabetes insipidus?
DDAVP (synthetic analogue of AVP(ADH)) is used to distinguish between central and nephrogenic diabetes insipidus
What is used to distinguish between primary and secondary adrenal insufficiency?
Measurement of ACTH
Rehydration is always instituted early in the management of severe hypercalcaemia. Why is this?
Hypercalcaemia interferes with proximal tubular reabsorption of sodium and so causes loss of sodium and water, leaving patients dehydrated.
Once haemolysis and renal failure have been excluded, what is the next most likely cause of hyperkalaemia?
Antihypertensive drugs such as spironolactone
What is the most common cause of hyperkalaemia in hospital patients?
Potassium salts in intravenous drugs (e.g antibiotics)
Is SIADH usually associated with clinical evidence of water overload, e.g oedema?!
It is often not as the water is distributed across the whole body
What should you suspect when sodium appears really really low but the patient seems fine?
Pseudohyponatraemia
Is palmar pigmentation a feature of primary or secondary adrenal insufficiency?
Primary adrenal insufficiency
due to ACTH
When should potassium give to patients with DKA?
Potassium is usually required for patients with DKA. There is usually potassium depletion and even if levels look normal it is usually given anyway. It would only be if potassium levels were abnormally high that potassium replacement wouldn’t be given in DKA.
