Endocrinology Flashcards
What hormones are released by the anterior pituitary gland?
TSH
FSH/LH
Prolactin
GH
ACTH
What hormones are released by the posterior pituitary?
Oxytocin
ADH
Describe the thyroid axis
Hypothalamus releases thyrotropin releasing hormone (TRH) -> Anterior pituitary releases TSH -> Thyroid gland releases T3 and T4
T3 and T4 have negative feedback on both anterior pituitary and hypothalamus
Describe the adrenal axis
Hypothalamus releases corticotrophin-releasing hormone (CRH) -> anterior pituitary releases ACTH -> Adrenal glands release cortisol (negative feedback)
What is the role of cortisol?
Increase alertness
Inhibit immune system
Inhibit bone formation
Raise blood glucose
Increase metabolism
Describe the parathyroid axis
Parathyroid hormone (PTH) released from parathyroid glands in response to low calcium
PTH increases activity and number of osteoclasts in bone, increases calcium reabsorption in the kidney and stimulated kidney to convert D3 to calcitriol to increase intestinal absorption
Describe the growth hormone axis
Hypothalamus releases GHRH -> anterior pituitary releases GH which stimulates release of IGF-1 from liver
Describe the Renin-Angiotensin-Aldosterone system
Renin secreted by Juxtaglomerular cells in afferent arterioles -> sense blood pressure and secrete more renin if BP low
Renin converts angiotensinogen-> angiotensin I -> angiotensin II in lungs with the help of ACE
Angiotensin II causes vasoconstriction and stimulates aldosterone
aldosterone causes cardiac remodelling, increases Na reabsorption, increase K secretion and hydrogen secretion
What are 4 causes of primary hyperthyroidism
Graves disease
Inflammation (thyroiditis)
Solitary toxic thyroid nodule
Toxic multinodular goitre
What are 3 causes of primary hypothyroidism
Hashimoto’s thyroiditis
Iodine deficiency
Treatment for hyperthyroidism
What can radioisotope scans be used for and what would they show
- Diffuse high uptake in Grave’s disease
- Focal high uptake in toxic multinodular goitre and adenomas
- Cold areas in thyroid cancer
What are the TSH, T3 and T4 levels in primary hyperthyroidism
TSH = low
T3 + T4 = high
What are the TSH, T3 and T4 levels in secondary hyperthyroidism
TSH = high
T3 and T4 = high
What are the TSH, T3 and T4 levels in primary hypothyroidism
TSH = high
T3 + 4 = low
What are the TSH, T3 and T4 levels in secondary hypothyroidism
TSH = low
T3 + 4 = low
what causes secondary hyperthyroidism
pathology in hypothalamus or pituitary
What is subclinical hyperthyroidism
Thyroid hormones (T3 and T4) are normal and thyroid-stimulating hormone (TSH) is suppressed (low). There may be absent or mild symptoms.
What is the pathophysiology of Grave’s disease
autoimmune, TSH receptor antibodies stimulate TSH receptors on the thyroid causing primary hyperthyroidism
What is a toxic multinodular goitre? (Plummer’s disease)
nodules develop on the thyroid gland, which are unregulated by the thyroid axis and continuously produce excessive thyroid hormones. It is most common in patients over 50 years.
What are 4 types of thyroiditis
De Quervain’s thyroiditis
Hashimoto’s thyroiditis
Postpartum thyroiditis
Drug-induced thyroiditis
How can hyperthyroidism present
- anxiety and irritability
- sweating and heat intolerance
- tachycardia
- weight loss
- fatigue
- insomnia
- frequent loose stools
- sexual dysfunction
- brisk reflexes
What are some specific features of Graves relating to presence of TSH receptor antibodies
- Diffuse goitre
- Graves’ eye disease (incl. exophthalmos)
- Pretibial myxoedema
- thyroid acropachy (hand swelling and finger clubbing)
What are the 3 phases of De Quervain’s thyroiditis?
- Thyrotoxicosis
- Hypothyroidism
- return to normal
What are some features of thyrotoxicosis
Excessive thyroid hormones
Thyroid swelling and tenderness
Flu-like illness
Raised inflammatory markers
What is the treatment for De Quervain’s thyroiditis
supportive
- NSAIDS (pain and inflammation)
- Beta blockers (symptoms of hyperthyroidism)
- Levothyroxine (symptoms of hypothyroidism)
Features of a thyroid storm (thyrotoxic crisis)
Fever, tachycardia, delirium
Management of thyroid storm
admission and monitoring
may need fluid resuscitation, anti-arrhythmic medications, beta blockers
What is the 1st line drug for hyperthyroidism
Carbimazole
What is the 2nd line drug for hyperthyroidism
Propylthiouracil
What are some cautions for radioactive iodine therapy
- pregnant or breast feeding women, women must not get pregnant within 6m of treatment
- men must not father children within 4m of treatment
- limit contact with people after dose (esp children and pregnant women)
What is the first choice medication for the adrenalin-related symptoms of hyperthyroidism
Propranolol
What are 4 causes of primary hypothyroidism
Hashimoto’s thyroiditis
Iodine deficiency
Treatments for hyperthyroidism e.g. Carbimazole
Medications e.g. lithium, amiodarone
What is the most common cause of hypothyroidism in the developed world
Hashimoto’s thyroiditis
What is the most common cause of hypothyroidism in the developing world?
Iodine deficiency
Name 2 antibodies associated with Hashimoto’s thyroiditis
anti-thyroid peroxidase (anti-TPO)
anti-thyroglobulin (anti-Tg)
What are some causes of secondary hypothyroidism
Tumours (pituitary adenomas)
Surgery to the pituitary
Radiotherapy
Sheehan’s syndrome
Trauma
what are some features of hypothyroidism
Weight gain
Fatigue
Dry skin
Coarse hair and hair loss
Fluid retention (incl. oedema, pleural effusions and ascites)
Heavy or irregular periods
Constipation
What types of hypothyroidism cause a goitre
Iodine deficiency
Hashimoto’s can initially cause a goitre after which there is atrophy of the thyroid gland
What is the management of hypothyroidism
Oral Levothyroxine
What is Cushing’s syndrome
prolonged high levels of glucocorticoids e.g. cortisol
What causes Cushing’s disease
pituitary adenoma secreting excessive adrenocorticotrophic hormone (ACTH) stimulating excess cortisol release from the adrenal glands
What are some features of Cushing’s syndrome
round face
central obesity
abdominal striae
enlarged fat pad on upper back (buffalo hump)
proximal limb muscle wasting
hirsutism
easy bruising and poor skin healing
hyperpigmentation (in Cushing’s disease due to high ACTH)
What are some metabolic effects of Cushing’s syndrome
Hypertension
Cardiac hypertrophy
Type 2 diabetes
Dyslipidaemia
Osteoporosis
What are some mental health effects of Cushing’s syndrome
Anxiety
Depression
Insomnia
Psychosis
What are the causes of Cushing’s syndrome
Cushing’s disease - pituitary adenoma releases excessive ACTH
Adrenal adenoma - adrenal tumour secreting excess cortisol
Paraneoplastic syndrome
Exogenous steroids
What investigations are used to diagnose Cushing’s syndrome
dexamethasone suppression tests
What would dexamethasone suppression tests show for a patient with an adrenal adenoma
low dose test cortisol = not suppressed
high dose = not suppressed
ACTH = low
What would dexamethasone suppression tests show for a patient with a pituitary adenoma
low dose test cortisol = not suppressed
high dose = low
ACTH = high
What would dexamethasone suppression tests show for a patient with an ectopic ACTH e.g. small cell lung cancer
Low dose test cortisol = not suppressed
high dose = not suppressed
ACTH = high
What is an alternative test to dexamethasone suppression test for Cushing’s syndrome
24-hour urinary free cortisol
What is the treatment of Cushing’s disease
Trans-sphenoidal removal of pituitary adenoma
What is Nelson’s syndrome
the development of an ACTH-producing pituitary tumour after the surgical removal of both adrenal glands due to a lack of cortisol and negative feedback. It causes skin pigmentation (high ACTH), bitemporal hemianopia and a lack of other pituitary hormones.
What is Conn’s syndrome
an adrenal adenoma producing too much aldosterone
what is primary hyperaldosteronism
adrenal glands are directly responsible for producing too much aldosterone