6: Basic principles of endocrinology Flashcards
What the major endocrine glands of the body?
Pituitary
Hypothalamus
Pineal
Thyroid and parathyroids
Adrenals
Pancreas
Ovaries and testes
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
Which kinds of receptor have a role in the endocrine system?
G-protein coupled receptors
Tyrosine kinase receptors
Nuclear receptors
Mutations causing the loss of function of ___ receptors can cause endocrine disease.
G-protein coupled receptors
Where are
a) G-protein coupled receptors
b) Tyrosine kinase receptors
c) Steroid receptors
found?
a) Cell membrane
b) Cell membrane
c) Nucleus
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
Which axis regulates the activity of peripheral endocrine glands?
Hypothalamic - pituitary axis
Which hormones are secreted by the anterior pituitary?
All of them apart from ADH and oxytocin:
Growth hormone
FSH & LH
ACTH
TSH
PRL
Which hormones are produced by the posterior pituitary gland?
ADH
Oxytocin
What can be measured to diagnose and monitor endocrine diseases?
Hormone concentrations
What is the main determinant of hormone concentration?
Rate of secretion
What hormones are released from the hypothalamus and pituitary in the thyroid axis?
Hypothalamus - TRH
Anterior pituitary - TSH
In which diseases is TSH secretion
a) raised
b) suppressed?
a) Raised TSH secretion = hypothyroidism
b) Suppressed TSH secretion = hyperthyroidism
When may TSH not be a reliable indicator of thyroid status?
Anterior pituitary tumours
Pituitary dysfunction produces (primary / secondary) thyroid disease.
secondary thyroid disease
What anterior pituitary diseases can produce a secondary
a) hyperthyroidism
b) hypothyroidism?
a) hyperthyroidism - thyrotropinoma / TSHoma
b) hypothyroidism - anterior pituitary dysfunction
Why are thyroid hormone levels of limited value in acutely ill patients?
Fluctuate with disease
> Non-thyroid illness
Can throw your differential
What are two emergency conditions associated with
a) hyperthryoidism
b) hypothyroidism?
hyperthyroidism > Thyroid storm
hypothyroidism > Myxoedema coma
How is function of the pituitary gland assessed?
Hormone levels
MRI scan
Synacthen test
Which hormones are released from the hypothalamus and anterior pituitary in the adrenal axis?
Hypothalamus - corticotrophin-releasing hormone (CRH)
Anterior pituitary - adrenocorticotrophic hormone (ACTH)
Cortisol release by the adrenal glands is released in what kind of rhythm?
Circadian rhythm
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)
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
