Endocrinology Flashcards
Which hormones does the anterior pituitary gland produce?
Thyroid Stimulating Hormone (TSH) Adrenocorticotropic Hormone (ACTH) Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH) Growth Hormone (GH) Prolactin
Which hormones does the posterior pituitary gland produce?
Oxytocin Antidiuretic Hormone (ADH)
How is thyroid hormone regulated?
Hypothalamus –> TRH –> pituitary –> TSH –> thyroid gland –> T3 and T4 –> suppress hypothalamic and pituitary release of TRH and TSH (negative feedback).
How is cortisol regulated?
Hypothalamus –> CRH –> AP –> ACTH –> Adrenal glands –> cortisol –> suppresses hypothalamic and AP release of CRH and ACTH (negative feedback)
When is cortisol at its highest?
Early morning. Lower in evening.
Give 5 effects of cortisol.
Inhibits the immune system Inhibits bone formation Raises blood glucose Increases metabolism Increases alertness
How is growth hormone regulated?
Hypothalamus -> GHRH –> AP –> GH –> Liver –> IGF-1
Give 4 effects of growth hormone.
Stimulates muscle growth
Increases bone density and strength
Stimulates cell regeneration and reproduction
Stimulates growth of internal organs
How is serum calcium regulated?
Low serum Ca (or low Mg, or high phosphate) –> Parathyroid glands –> PTH –> increases serum Ca –> suppresses parathyroid release of PTH.
Give 3 ways in which PTH increases serum calcium.
- PTH increases the activity and number of osteoclasts in bone, causing reabsorption of calcium from the bone into the blood thereby increasing serum calcium concentration.
- PTH also stimulates an increase in calcium reabsorption in the kidneys meaning that less calcium is excreted in the urine.
- stimulates the kidneys to convert vitamin D3 into calcitriol, which is the active form of vitamin D that promotes calcium absorption from food in the small intestine.
How is blood pressure regulated using the renin-angiotensin system?
Low BP –> afferent arteriole of kidney –> juxtaglomerular cells –> renin –> liver –> angiotensinogen –> ATI –> ATII (via ACE in lungs) –> vasoconstriction, adrenals –> aldosterone –> retain Na –> retain water –> increase BP –> suppresses renin secretion from kidney.
What are 3 effects of aldosterone?
Mineralocorticoid hormone. Acts on nephrons to
1. increase sodium reabsorption from the distal tubule
2. increase potassium secretion from the distal tubule
3. increase hydrogen secretion from collecting ducts.
Water follow sodium by osmosis –> high intravascular volume –> higher blood pressure.
What is Cushing’s syndrome? Give 5 features.
Signs and symptoms of prolonged elevation of cortisol:
Central obesity, moon face, abdo striae (stretch marks), buffalo hump, proximal limb muscle wasting.
Cortisol –> htn, cardiac hypertrophy, hyperglycaemia (T2DM), depression, insomnia
Osteoporosis, easy bruising, poor skin healing
What is Cushing’s disease?
Elevated cortisol due to pituitary adenoma secreting ACTH. Causes a Cushing’s syndrome.
What causes Cushing’s syndrome?
- Exogenous steroids (in patients on long term high dose steroid medications)
- Cushing’s Disease (a pituitary adenoma releasing excessive ACTH)
- Adrenal Adenoma (a hormone secreting adrenal tumour)
- Paraneoplastic - ACTH is released from a cancer (ectopic ie not of the pituitary) and stimulates excessive cortisol release. Usually small cell lung cancer.
How is Cushing’s syndrome diagnosed? how does the test work?
Dexamethasone suppression test - dex is a steroid so in normal people should reduce CRH and ACTH from hypothalamus and pituitary, leading to reduced cortisol from the adrenals. Dex is given at 10pm and measured at 9am.
1. Low dose test - takes 1mg dex, see if hypothalamus responds by reducing the CRH output. If this is normal (cortisol level suppressed), Cushing’s is excluded. If abnormal (cortisol remains high), go on to (2)
2. High dose test - 8mg dex.
Cushings disease (Pituitary adenoma) - cortisol and ACTH suppressed by high dose
Adrenal adenoma - cortisol is not suppressed but ACTH is suppressed, because cortisol production is independent from the pituitary.
If ectopic ACTH eg SCLC, nothing is suppressed.
What bloods would you do in Cushing’s syndrome and what might they show?
FBC - raised WCC
U+E - low aldosterone –> low K+ - indicates adrenal adenoma
What causes low dose dexamethasone suppression test to show high cortisol, but the high dose test shows suppressed cortisol and ACTH? What investigation would help confirm the diagnosis?
Indicates Cushing’s disease. MRI brain for pituitary adenoma.
Low dose dex test: High cortisol
High dose dex test: high cortisol and ACTH
Diagnosis and next investigation?
Likely ectopic ACTH production, usually small cell lung cancer so chest CT.
Low dose dex test: High cortisol
High dose dex test: High cortisol, low ACTH
Diagnosis and next investigation?
Likely adrenal adenoma so abdo CT.
How is Cushing’s syndrome treated?
Remove underlying cause eg:
Trans-sphenoidal removal of pituitary adenoma
Surgical removal of adrenal tumour
Surgical removal of tumour producing ectopic ACTH.
Or remove adrenals and replace with steroids for life.
What is adrenal insufficiency?
Adrenal glands not producing enough steroid hormones, particularly cortisol and aldosterone. Life-threatening.
What is Addison’s disease?
Primary adrenal insufficiency - adrenal glands damaged, usually autoimmune.
What is secondary adrenal insufficiency?
Inadequate ACTH stimulating the adrenal glands, resulting in low cortisol release. Caused by pituitary excision, infection, ischemia, radiotherapy.
What is Sheehan’s syndrome?
Pituitary gland necrosis due to massive blood loss during childbirth.
What is tertiary adrenal insufficiency?
Inadequate CRH release by hypothalamus. Usually due to long term oral steroids (more than 3 weeks), suppress hypothalamus, withdrawal of steroids –> not enough endogenous steroids. Hence taper slowly
How does adrenal insufficiency present?
Fatigue, nausea, cramps, abdo pain, reduced libido
Bronze hyperpigmentation to skin (ACTH stimulates melanocytes), hypotension (particularly postural)
What investigations would you do for suspected adrenal insufficiency and what might they show?
Short synacthen test
U+Es - hyponatraemia, hyperkalaemia
Morning cortisol
Short synacthen test - cortisol fails to rise
ACTH - primary adrenal failure = high, secondary adrenal failure = low
Adrenal autoantibodies - adrenal cortex abs, 21-hydroxylase abs
CT/MRI adrenals if structural cause suspected (not for AI)
MRI pituitary if indicated
What is the short synacthen test?
Synacthen = SYNthetic ACTH. Give synacthen –> measure blood cortisol at baseline, 30 mins and 60 mins. If adrenals are working, they will be stimulated to produce cortisol. If the cortisol fails to rise to double the baseline, this indicates primary adrenal insufficiency (Addison’s disease).
Done in the morning.
What is Addisonian crisis?
Aka adrenal crisis
Acute severe primary adrenal insufficiency.
How does Addisonian crisis present?
Reduced consciousness, hypotension, hypoglycaemia, hyponatraemia, hyperkalaemia
What causes Addisonian crisis?
First presentation of Addison’s, infection, trauma, acute illness, sudden withdrawal of steroids.
How do you manage Addisonian crisis?
STEROIDS - IV hydrocortisone 100mg stat Intensive monitoring IV fluid resuscitation correct hypoglycaemia monitor electrolytes and fluid balance
What would TFTs show in hyperthyroidism?
Low TSH. Except pituitary adenoma which secretes TSH
Raised T3 and T4
What would TFTs show in hypothyroidism?
High TSH. Except secondary hypothyroidism when the low TSH is driving the hypothyroidism (pituitary/ hypothalamic cause)
Low T3 and T4
What do antithyroid peroxidase (anti-TPO) antibodies indicate?
Grave’s Disease
Hashimoto’s thyroiditis
What do antithyroglobulin antibodies indicate?
May be normal or present in Grave’s disease, Hashimoto’s thyroiditis or thyroid cancer.
What do TSH receptor antibodies indicate?
Grave’s disease.
What is the function of thyroid ultrasound?
Diagnose thyroid nodules
Distinguish between cystic (fluid-filled) and solid nodules
Guide thyroid lesion biopsy
What is the function of a radioisotope scan?
Investigation of hyperthyroidism and thyroid cancers.
Involves giving radioactive iodine PO/IV –> more iodine taken up if more active thyroid cells.
Gamma camera detects the gamma rays emitted from the iodine. More rays = more iodine = more activity.
What would be seen on radioisotope scan in Grave’s disease?
Diffuse high uptake.