Investigating the endocrine system Flashcards
Endocrine systems
Thyroid, Gonads, Adrenal, Leptin from adipose tissue, Ghrelin from GI to regulate hunger
Types of hormones
- Peptide hormones from pituitary gland - ACTH, TSH
- Steroid hormones - testosterone, cortisol
- Tyrosine based hormones - T4 thyroxine, T3
Fundamental pathway for all endocrine systems
- hypothalamus produces hormone that acts on anterior pituitary to produce second hormone which acts on endocrine organ
- hormone ALWAYS inhibit the pathway, inhibits at pituitary and hypothalamus.
TSH low, ft4 low
Pituitary failure = secondary hypothyroidism
TSH high, fT4 low
- Unresponsive thyroid, no response to TSH = primary hyperthyroidism
TSH low, fT4 high
- Thyroid gland overproduction = primary hyperthyroidism
Both TSH + fT4 high
- Pituitary overproduction = secondary hyperthyroidism
Benefits of TSH frontline test
- Cheap
- Accounts for most diseases
- If TSH elevated measure fT4 to pick up hypothyroid patients
Negatives of TSH testing
- If low measure T3 and T4 to pick up hyperthyroid patients
- sometimes normal TSH patients are not followed up, they can have secondary hypothyroidism as they have low fT4 – 80% hypothyroid patients would be missed
Sick euthyroid syndrome
- show abnormality in thyroid function test but they are euthyroid (normal thyroid)
- Illness can supress TSH and also reduce the levels of TBG or modify its capacity to bind T3 and T4, hence increasing free thyroid hormone levels
Why is it futile to measure thyroid function in patients in hospital
- Mechanisms of acute illnesses influence the hypothalamic-pituitary-thyroid axis, producing thyroid test results - discordant, do not fit recognizable patterns, difficult to interpret
Frequency of tests during treatment
- Healthy = repeat 3 years
- Hyperthyroid = repeat 1-2 months after treatment
- Hypothyroid - Do not measure less than 2 months
- Thyroidectomy - serum TSH 6-8 weeks post op
Phaeochromocytoma
- tumour of neuroendocrine chromaffin cells – the majority in the adrenal medulla, tumour in adrenal medulla that produces catecholamine.
Phaeochromocytoma presentation
- Hypertension, sweating, pallor, panic attacks, headaches, abdominal pain or nothing as 50% found post-mortem
Phaeochromocytoma investigations
- Plasmametanephrines – metabolite of catecholamines; elevated more consistently across the day
- 24h urine fractionated metanephrines - no hypertensives 24h before
Phaeochromocytoma investigations follow up tests
- Plasma Chromogranin A – if negative it excludes Phaechromocytoma
- MRI/CT of adrenal glands
Definition of hypoglycaemia
- low plasma glucose, less than 3
- symptoms of hypoglycaemia
- Resolution if symptoms when you treat the low blood glucose
Causes of Hypoglycaemia
- Diabetes - overtreated with insulin
- Alcohol - co factor busy breaking down alcohol - needed for gluconeogenesis
Insulinoma
- Insulin mediated endogenous cause
- Insulin secreting tumour (islets)
- F>M, 40-60 years
How is Insulinoma diagnosed
- Simple fasting blood test
- Low blood sugar < 2.2
- High insulin 6 microunits or higher - Should be undetectable in hypoglycaemic patient = insulinoma
- High levels of C peptide
What is ectopic hormone production
- When hormones are being secreted by tissues that don’t usually secrete them - in a substantial enough quantity to cause clinical effects
Ectopic ACTH secreting tumour
- tumour outside of pituitary gland and makes lots of ACTH
- ACTH extremely higher than Cushing’s disease
ACTH releasing pituitary tumour
- pituitary ACTH acts on adrenal glands make lots of cortisol
- high ACTH. Disease is always due to pituitary ACTH secreting tumour whereas syndrome is any cause of Cushing’s
