6: Basic principles of endocrinology Flashcards by Ross Wilson

What the major endocrine glands of the body?

Pituitary

Hypothalamus

Pineal

Thyroid and parathyroids

Adrenals

Pancreas

Ovaries and testes

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What are the three main classes of hormone and examples of each?

Peptide hormones - insulin, glucagon, prolactin, GH

Steroid hormones - cortisol, testosterone, oestrogen

Tyrosine derivatives - adrenaline, thyroid hormones

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Which kinds of receptor have a role in the endocrine system?

G-protein coupled receptors

Tyrosine kinase receptors

Nuclear receptors

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Mutations causing the loss of function of ___ receptors can cause endocrine disease.

G-protein coupled receptors

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Where are

a) G-protein coupled receptors
b) Tyrosine kinase receptors
c) Steroid receptors

found?

a) Cell membrane

b) Cell membrane

c) Nucleus

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What produces the cellular effect in

a) G-protein coupled receptors
b) Tyrosine kinase receptors
c) Steroid receptors?

a) Receptor activates signalling cascade (e.g cAMP)

b) Autophosphorylation of beta subunits

c) Hormone binds to DNA and alters gene transcription

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Which axis regulates the activity of peripheral endocrine glands?

Hypothalamic - pituitary axis

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Which hormones are secreted by the anterior pituitary?

All of them apart from ADH and oxytocin:

Growth hormone

FSH & LH

ACTH

TSH

PRL

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Which hormones are produced by the posterior pituitary gland?

ADH

Oxytocin

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What can be measured to diagnose and monitor endocrine diseases?

Hormone concentrations

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What is the main determinant of hormone concentration?

Rate of secretion

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What hormones are released from the hypothalamus and pituitary in the thyroid axis?

Hypothalamus - TRH

Anterior pituitary - TSH

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In which diseases is TSH secretion

a) raised
b) suppressed?

a) Raised TSH secretion = hypothyroidism

b) Suppressed TSH secretion = hyperthyroidism

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When may TSH not be a reliable indicator of thyroid status?

Anterior pituitary tumours

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Pituitary dysfunction produces (primary / secondary) thyroid disease.

secondary thyroid disease

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What anterior pituitary diseases can produce a secondary

a) hyperthyroidism
b) hypothyroidism?

a) hyperthyroidism - thyrotropinoma / TSHoma

b) hypothyroidism - anterior pituitary dysfunction

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Why are thyroid hormone levels of limited value in acutely ill patients?

Fluctuate with disease

> Non-thyroid illness

Can throw your differential

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What are two emergency conditions associated with

a) hyperthryoidism
b) hypothyroidism?

hyperthyroidism > Thyroid storm

hypothyroidism > Myxoedema coma

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How is function of the pituitary gland assessed?

Hormone levels

MRI scan

Synacthen test

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Which hormones are released from the hypothalamus and anterior pituitary in the adrenal axis?

Hypothalamus - corticotrophin-releasing hormone (CRH)

Anterior pituitary - adrenocorticotrophic hormone (ACTH)

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Cortisol release by the adrenal glands is released in what kind of rhythm?

Circadian rhythm

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When are cortisol levels supposed to be measured?

9am

What are the two hormones secreted by the hypothalamus to regulate growth hormone secretion by the anterior pituitary?

Somatostatin - inhibits growth hormone secretion

Growth hormone-releasing hormone (GHRH)

Which organ does GH act on?

Liver

Also adipose tissue

What is released by the liver in response to growth hormone?

**IGF-1** Insulin-like growth factor 1

GH must be measured through ___ testing.

**dynamic testing**

Which hormones are released from the hypothalamus and anterior pituitary in the gonadal axis?

**Hypothalamus** - gonadotrophin-releasing hormone (GnRH) **Anterior pituitary** - lutenising hormone (LH) , follicle-stimulating hormone (FSH)

When should testosterone levels be measured?

**9am**

When should female sex hormones be measured?

**Depends on timing of menstrual cycle**

Which hormone is released by **lactotroph cells** in the anterior pituitary?

**Prolactin**

Which hormone inhibits the release of prolactin?

**Dopamine**

What is the target tissue of prolactin?

**Breast**

When is hyperprolactinaemia physiological?

**Pregnancy** **Lactation** **Nipple stimulation**

Which medications cause hyperprolactinaemia?

**Dopamine antagonists** (remember they act to inhibit prolactin release)

Which gland secretes **ADH** and oxytocin?

**Posterior pituitary**

The secretion of ADH is important in controlling what?

**Blood pressure** (via control of fluid volume)

How does ADH increase blood pressure?

**a) Causes vasoconstriction**, increasing TPR **b) Stimulates increased fluid absorption by the kidneys**, increasing blood volume

Name three important steroid hormones.

**Cortisol** **Testosterone** **Aldosterone**

What are the dynamic tests done to diagnose a) hormone excess b) hormone deficiency?

**Hormone excess \> Suppression test** **Hormone deficiency \> Stimulation test**

What causes **cortisol deficiency**?

**Adrenal insufficiency** e.g Addison's disease (primary adrenal insufficiency) Pituitary gland disease

What causes **cortisol excess**?

**Cushing's syndrome** - overproduction of ACTH by anterior pituitary

What is the **stimulation test** used to investigate suspected Addison's disease?

**Synacthen test**

What is the dynamic test used to investigate suspected Cushing's syndrome?

**Dextromethasone suppression test**

What causes Cushing's syndrome?

**Excess ACTH production** (usually by anterior pituitary) ## Footnote **Cortisol excess**

What is the presentation of Cushing's syndrome?

**Hypertension** **Impaired glucose tolerance** **Moon face** **Acne** **Hirsutism** **Abdominal obesity and striae**

Apart from pituitary cell tumours, what else can cause Cushing's syndrome?

**Adrenal tumours** **Malignancy** **!!! Steroid use !!!**

Which type of tumour can produce ectopic ACTH and bring on Cushing's syndrome?

**Small cell carcinoma** of lungs

Why can steroid use cause Cushing's syndrome?

**Steroids have similar structure to cortisol**

Which causes of Cushing's syndrome are ACTH-related and ACTH-independent?

**ACTH-related** - pituitary tumour, ectopic ACTH **ACTH-independent** - adrenal tumour, steroids

Which suppression test is used to diagnose Cushing's syndrome?

Dextromethasone suppression test

If ACTH is low after a dextromethasone suppression test, the cause of Cushing's is related to what?

**Adrenal glands**

If ACTH is high after a dextromethasone suppression test, the cause of Cushing's disease could be what?

**Pituitary gland-related** **Ectopic ACTH-related**

How would you differentiate pituitary-related Cushing's from ectopic ACTH production?

**Do a CRH (corticotrophin releasing hormone) test** - ACTH and cortisol will be high