Endocrinology

Question 1

Thyroid Pathway

Answer 1

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

Question 2

TSH and T3/4 in Graves

Answer 2

This disease has autonomous thyroid hormone production

T3/4 will rise
TSH will be low due to negative feedback

Question 3

What is seen in secondary hyperthyroidism

Answer 3

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)

Question 4

Primary Hypothyroidism (Hashimotos) TSH and T3/4

Answer 4

Dysfunction of thyroid gland means low T3/4

TSH will be abnormally high (reduced -ve feedback)

Question 5

Sick Euthyroid

• What is
• TSH T3/4

Answer 5

This is abnormal thyroid function tests in someone with normal thyroid function but incurrent illness

Low TSH, Low T3/4 (secondary hypothyroid picture)

Question 6

Secondary Hypothyroid hormone levels

Answer 6

Tsh low and low T3/4 as a result (often due to destructive pituitary tumour)

Question 7

Relevance of TBG levels

Answer 7

A low free TBG indicates high binding e.g. in hyperthyroidism and vice versa.

Question 8

Glucocorticoid release pathway

Answer 8

(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

Question 9

Who gets exogenous cushing

Answer 9

Those receiving glucocorticoid therapy e.g. chronic severe asthma

Question 10

Causes of endogenous bushings (high cortisol)

Answer 10

Primary adrenal disease (adrenal tumour/Ca)

ACTH excess (from Pituitary gland, From ACTH producing tumour e.g. SC Lung Ca)

Question 11

How to measure cortisol

Answer 11

24 hour urine collection
OR
1mg over night dexamethasone suppression test (In Cushings, cortisol production will not be suppressed)

Question 12

Role of aldosterone

Answer 12

Aldosterone is released from RAAS to increase sodium and water retention

Question 13

Effect saline infusion should have on aldosterone

Answer 13

Saline infusion should reduce aldosterone unless the person has Conn’s

Question 14

What is Hypoadrenalism called

Pathophysiology

ACTH levels

Answer 14

Addisons

Defective Adrenal gland functioning

ACTH will be high due to reduction in negative feedback

Question 15

What test is used for Addisons and what will the result be

Answer 15

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)

Question 16

What is Phaeochromocytoma

Answer 16

Excess circulating catecholamines from adrenal medulla

Question 17

Phaeochromocytoma diagnosis

Answer 17

increased breakdown products in plasma (free metanephrines) or urine (fractional metanephrines)

If positive, visualise the tumour with MRI/CT or PET

Question 18

What causes Diabetes Insipidus

Answer 18

Problem with antidiuretic hormone (ADH acts to conserve water)
Patients become dehydrated and so drink to compensate for this

Question 19

Types of Diabetes Insipidus

How to differentiate between types

Answer 19

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

Question 20

What happens to urine and serum osmolality in water deprivation with Diabetes Insipidus

Answer 20

Urine osmolality will not rise (due to ADH defect)

Serum osmolality will rise (due to dehydration)

Question 21

What is SIADH

Serum and Urine concentration

Answer 21

Excess ADH production causing water retention

Dilute serum and concentrated urine

Question 22

Causes of SIADH

Answer 22

Thoracic - Infection, Tumour
Cranial - Infection, Tumour, Head injury
Drug - Carbemazepine, Antipsychotics

Question 23

Causes of high Prolactin

Answer 23

Prolactin secreting pituitary tumour (if very high)
Pregnancy and Lactation
Meds (Antipsychotics, Antiemetics)
PCOS

Question 24

Diabetes Symptoms

Answer 24

Polyuria
Polydipsia
Weight loss
Fatigue
Blurring vision
Other complications: UTI, cutaneous abscess

Question 25

What is Oral Glucose Tolerance Test used for

Answer 25

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

Question 26

Plasma glucose levels in Fasting and 2 hours following OGTT to be diagnostic of DM

Answer 26

7
11

like the shop!

Also diagnosed in any random blood glucose over 11 + symptoms

Question 27

HbA1c what is it and what levels are diagnostic

Answer 27

This is the Glycated Hb and gives better long term glucose control reading

48mmol/L OR 6.5% and over

Question 28

Causes of hypoglycaemia and usual levels

Answer 28

Imbalance between insulin and calorie intake in T1DM

Insulinoma

Liver failure

Alcohol

Less than 3.5mmol/L

Question 29

How to distinguish hypoglycaemia due to exogenous or endogenous insulin

Answer 29

C-Protein

This is cleaved of from endogenous pro-insulin to form insulin and so will be high in insulinoma

Question 30

cause of Acromegaly

What marker is measured
What is definitive test and what levels

Answer 30

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