Biochemistry Flashcards
Describe the RAAS system
- Juxtaglomerular cells sense low renal blood flow
- Kidneys produce renin
- Renin converts angiotensin to angiotensin I
- ACE converts angiotensin I to angiotensin II
- Angiotensin II vasocostricts and also stimulates the release of aldosterone from the adrenal cortex
- Aldosterone causes the renal tubules to increase the reabsorption of sodium and water and the excretion of potassium
If you lose sodium from the body, what happens to the water?
You lose the water because it follows sodium
What is syndrome of inappropriate ADH (SIADH)?
Excessive unsuppressible release of antidiuretic hormone (ADH) either from the posterior pituitary gland, or an abnormal non-pituitary source
How do the kidneys regulate blood volume?
Renal excretion of sodium
What is nephrogenic diabetes insipidus
Renal resistance to ADH
What is central diabetes insipidus
ADH deficiency originating in the posterior pituitary
What is Addison’s disease?
Primary adrenal insufficiency (usually autoimmune destruction) where the adrenal glands do not produce enough steroid hormones
What happens when you give a patient with renal insufficiency saline?
Patients with adrenal insufficiency are less able to retain infused saline (sodium) than normal subjects
What blood results might make you suspect Addison’s?
A hypotensive patient with low sodium and high potassium
What causes secondary adrenal insufficiency?
Adrenal hypofunction due to a lack of adrenocorticotropic hormone (ACTH)
What part of the kidney does autoimmune Addison’s attack?
Cortex
How do you diagnose Addison’s?
Synacthen test (ACTH stimulating test)
How do you diagnose Addison’s?
Synacthen test (ACTH stimulating test) - A basal cortisol of less than 100 is suspicious
What can distinguish between primary and secondary insufficiency?
Measurement of ACTH
Patients with malignancy-associated hypercalcaemia have high circulating concentrations of which hormone? (Hint - It’s similar to PTH)
PTHrP
What is primary hyperparathyroidism?
Overactivity of parathyroid gland (eg in parathyroid adenoma)
What is secondary hyperparathyroidism?
Physiological response to low calcium
What does PTH do?
Secreted from parathyroid glands in response to low blood serum calcium. It indirectly stimulates osteoclast activity
Why is primary hyperparathyroidism diagnosed earlier than it used to be?
Primary hyperparathyroidism is diagnosed much earlier than in the past because of hypercalcaemia; as a result, radiological changes like osteitis fibrosa cystica are rarely seen any more.
Why is rehydration always instituted early in the management of severe hypercalcaemia
Hypercalcaemia interferes with proximal
tubular reabsorption of sodium and so causes loss of sodium and water – patients are usually dehydrated
What is pseudohyperkalaemia?
Measured potassium levels is falsely elevated, due to mechanical trauma during blood drawing (potassium leakage out of the red blood cells due to haemolysis) etc
Once haemolysis and renal failure have been excluded, what is the most likely cause of hyperkalaemia?
Antihypertensive drugs e.g. spironolactone
Once haemolysis and renal failure have been excluded, what is the most likely cause of hyperkalaemia?
Antihypertensive drugs e.g. spironolactone, ACEI etc
What does the finding of gross hyperkalaemia and hypocalcaemia suggest?
The finding of gross hyperkalaemia and hypocalcaemia suggests contamination with potassium EDTA, the anticoagulant used in the FBC (‘purple-top’) bottle
What should happen to fluid intake in SIADH?
Fluid intake should be restricted
What happens to the urine osmolarity in SIADH?
High urine osmolarity (small amounts of very concentrated urine)
Why do you do a synacthen test if you suspect iatrogenic Cushing’s due to steroids?
It will show you that the kidneys are fine because they respond to the ACTH so it’s the pituitary axis that’s the problem
