Endocrinology Flashcards
Thyroid Pathway
Hypothalamus releases TRH (thyrotropin releasing hormone) to Pituitary
Pituitary releases TSH (Thyroid stimulating hormone) to the thyroid
Thyroid releases Thyroxine (T4) and Triiodothyronine (T3)
- These are mostly bound to Thyroxine-binding globulin). Unbound forms = active
- T4 is converted by organs into T3 (the active form)
- Hormones give negative feedback to hypothalamus and pituitary
TSH and T3/4 in Graves
This disease has autonomous thyroid hormone production
T3/4 will rise
TSH will be low due to negative feedback
What is seen in secondary hyperthyroidism
This is due to pituitary tumour:
Levels of T3/4 will again be high and TSH will be inappropriately normal or high (no -ve feedback)
Primary Hypothyroidism (Hashimotos) TSH and T3/4
Dysfunction of thyroid gland means low T3/4
TSH will be abnormally high (reduced -ve feedback)
Sick Euthyroid
- What is
- TSH T3/4
This is abnormal thyroid function tests in someone with normal thyroid function but incurrent illness
Low TSH, Low T3/4 (secondary hypothyroid picture)
Secondary Hypothyroid hormone levels
Tsh low and low T3/4 as a result (often due to destructive pituitary tumour)
Relevance of TBG levels
A low free TBG indicates high binding e.g. in hyperthyroidism and vice versa.
Glucocorticoid release pathway
(CRH) Corticotropin releasing hormone from hypothalamus stimulates pituitary gland
Pituitary releases (ACTH) Adrenocorticotropic hormone which stimulate adrenal cortex
Cortical Glucocorticoids released and give negative feedback to H and P reducing CRH and ACTH
Who gets exogenous cushing
Those receiving glucocorticoid therapy e.g. chronic severe asthma
Causes of endogenous bushings (high cortisol)
Primary adrenal disease (adrenal tumour/Ca)
ACTH excess (from Pituitary gland, From ACTH producing tumour e.g. SC Lung Ca)
How to measure cortisol
24 hour urine collection
OR
1mg over night dexamethasone suppression test (In Cushings, cortisol production will not be suppressed)
Role of aldosterone
Aldosterone is released from RAAS to increase sodium and water retention
Effect saline infusion should have on aldosterone
Saline infusion should reduce aldosterone unless the person has Conn’s
What is Hypoadrenalism called
Pathophysiology
ACTH levels
Addisons
Defective Adrenal gland functioning
ACTH will be high due to reduction in negative feedback
What test is used for Addisons and what will the result be
Short Synacthen test
Synthetic ACTH is injected to stimulate adrenal gland
In addisons there will be no increase in circulating level of Cortisol
(cortisol under 600nmol/L 30 min after injection is diagnostic)
What is Phaeochromocytoma
Excess circulating catecholamines from adrenal medulla
Phaeochromocytoma diagnosis
increased breakdown products in plasma (free metanephrines) or urine (fractional metanephrines)
If positive, visualise the tumour with MRI/CT or PET
What causes Diabetes Insipidus
Problem with antidiuretic hormone (ADH acts to conserve water)
Patients become dehydrated and so drink to compensate for this
Types of Diabetes Insipidus
How to differentiate between types
Cranial - problem with ADH release from hypothalamus. low blood levels of ADH
Nephrogenic - ADH fails to exert its effects on the kidney
Giving Desmopression (synthetic ADH) will correct the problem in cranial DI but not in Nephrogenic
What happens to urine and serum osmolality in water deprivation with Diabetes Insipidus
Urine osmolality will not rise (due to ADH defect)
Serum osmolality will rise (due to dehydration)
What is SIADH
Serum and Urine concentration
Excess ADH production causing water retention
Dilute serum and concentrated urine
Causes of SIADH
Thoracic - Infection, Tumour
Cranial - Infection, Tumour, Head injury
Drug - Carbemazepine, Antipsychotics
Causes of high Prolactin
Prolactin secreting pituitary tumour (if very high)
Pregnancy and Lactation
Meds (Antipsychotics, Antiemetics)
PCOS
Diabetes Symptoms
Polyuria Polydipsia Weight loss Fatigue Blurring vision Other complications: UTI, cutaneous abscess
What is Oral Glucose Tolerance Test used for
Differentiating between various states of hyperglycaemia (Range from Normal, Impaired fasting glucose, Impaired glucose tolerance, DM / Gestational DM)
Involves testing plasma glucose level following 75g bolus Glucose
Plasma glucose levels in Fasting and 2 hours following OGTT to be diagnostic of DM
7
11
like the shop!
Also diagnosed in any random blood glucose over 11 + symptoms
HbA1c what is it and what levels are diagnostic
This is the Glycated Hb and gives better long term glucose control reading
48mmol/L OR 6.5% and over
Causes of hypoglycaemia and usual levels
Imbalance between insulin and calorie intake in T1DM
Insulinoma
Liver failure
Alcohol
Less than 3.5mmol/L
How to distinguish hypoglycaemia due to exogenous or endogenous insulin
C-Protein
This is cleaved of from endogenous pro-insulin to form insulin and so will be high in insulinoma
cause of Acromegaly
What marker is measured
What is definitive test and what levels
Elevated GH due to pituitary tumour
IGF-1 can be measured, if raised is suggestive
Glucose tolerance test and then measure GH. failure of GH to fall following glucose diagnoses Acromegaly
