Endocrine Flashcards
Features of water soluble hormones?
- transported unbound
- bind to cell surface receptors
- short half-life
- cleared fast
- stored in vesicles before secretion
Example of water-soluble hormones?
- peptides
- monoamines
Features of fat soluble hormones?
- transported bound to protein
- diffuse into cells
- long half-life
- cleared slowly
- synthesised on demand
Examples of fat-soluble hormones?
- thyroid hormone
- steroids
What is the main example of a peptide hormone?
Insulin
How are peptide hormones stored?
Stored in secretory granules.
How are peptide hormones released? (Timing)
Pulses / bursts
How are peptide hormones cleared?
Tissue enzymes / circulating enzymes.
How does insulin cause glucose uptake?
- binds to insulin receptors
- results in phosphorylation of the receptor
- this activates tyrosine kinase (secondary messenger)
- causing phosphorylation of signal cascade molecules
- results in glucose uptake (via GLUT4 channels)
Examples of amine hormones?
- dopamine
- adrenaline
- noradrenaline
What is the adrenaline (amine) synthesis pathway?
Phenylalanine > L-tyrosine > L-dopa > dopamine > noradrenaline > adrenaline
Which enzyme breaks down noradrenaline / adrenaline?
COMT (Catechol-O-methyl transferase)
What are the breakdown products of noradrenaline/ adrenaline?
Noradrenaline > normetanephrine
Adrenaline > metanephrine
What does binding of nor(adrenaline) to alpha receptors cause?
- vasoconstriction
- bowel muscle contraction
- sweating
- anxiety
What does binding of nor(adrenaline) to beta receptors cause?
- vasodilation
- increased HR
- increased force of contractility
- relaxation of bronchial smooth muscles
What are iodothyronines (T3/T4) bound to?
Thyroid-binding globulin (TBG)
Which is more active, T3 or T4?
T3
T4 is a reservoir for additional T3.
Which hormone is produced more, T3 or T4?
T4
How are T3/T4 synthesised?
- iodine binds to tyrosine on thyroglobulin
- this forms iodothyrosines (MIT / DIT)
- conjugation of MIT / DIT forms T3 / T4
How are T3 / T4 stored?
Stored in colloid of thyroid follicular cells (bound to thyroglobulin).
Thyroglobulin vs TBG?
Thyroglobulin binds T3/T4 in colloid of thyroid follicular cells.
TBG binds T3/T4 in the bloodstream.
What does TSH stimulate?
Movement of colloid into secretory cell, where T4 and T3 are cleaved from thyroglobulin.
Where does breakdown of T4 > T3 occur?
Outside the thyroid gland.
How does vitamin D act on a cell?
- enters cell directly (lipid soluble)
- binds to nucleus to stimulate mRNA production
How is vitamin D transported?
Vitamin D binding protein
Adrenal cortex vs adrenal medulla?
Adrenal cortex - GFR makes good sex.
Adrenal medulla - fight/flight (catecholamines, adrenaline)
How does oestrogen act on a cell?
Enters cell and acts directly on the nucleus.
How do cortisol, aldosterone, progesterone & testosterone act on a cell?
- enters cell and binds to cytoplasmic receptor
- receptor-hormone complex enters nucleus
- complex binds to glucocorticoid response element (GRE)
- binding initiates transcription
Which hormone receptors are located on the cell surface membrane?
Insulin
Which hormone receptors are located in the cytoplasm?
Steroids:
- glucocorticoids (cortisol)
- mineralocorticoids (aldosterone)
- androgens (testosterone)
- progesterone
Which hormone receptors are nuclear?
- thyroid hormones
- oestrogen
- vitamin D
Which hormones follow circadian rhythm?
- ACTH
- prolactin
- GH
- TSH
- cortisol
Which hormone inhibits prolactin?
Dopamine
Example of hormone receptor induction?
Induction of LH receptors by FSH.
What type of hormone are LH and FSH?
Peptide hormones.
Example of hormone synergism?
Glucagon + adrenaline.
Released when hypoglycaemic.
How are the hypothalamus and pituitary connected?
By the infundibulum (pituitary stalk).
Contains axons from hypothalamic neurones and small blood vessels.
Examples of hypophysiotropic hormones?
- CRH
- GHRH
- TRH
- GnRH
- dopamine
How does hypothalamus-anterior pituitary regulation work?
- hypothalamus is stimulated to release hypophysiotropic hormones by other areas of the CNS
- hormones reach the anterior pituitary via the hypothalamo-hypophyseal portal vessels
- hormones stimulate the release of hormones from the anterior pituitary
What is the blood supply to the anterior pituitary gland?
- no arterial supply
- portal venous circulation (hypothalamo-hypophyseal vessels)
What are the 6 hormones secreted by the pituitary?
- FSH
- LH
- ACTH
- TSH
- prolactin
- GH
Name of cells where FSH is produced?
Gonadotrophs
Name of cells where LH is produced?
Gonadotrophs
Name of cell where ACTH is produced?
Corticotrophs
Name of cell where TSH is produced?
Thyrotrophs
Name of cell where prolactin is produced?
Lactotrophs
Name of cell where GH is produced?
Somatotrophs
What is the function of FSH?
- stimulates germ cell development (ovum / sperm)
- stimulates oestrogen release (in females)
What does the release of oestrogen stimulate in the menstrual cycle?
Release of LH.
What is the function of LH?
- in females: stimulates the release of the egg, which stimulates progesterone release and causes thickening of the uterine wall
- in males: acts on leydig cells, stimulating testosterone release
What is the function of GH?
- stimulates gluconeogenesis and inhibits insulin (causing increased glucose)
- breaks down fat in adipose tissue
- acts on liver to increase protein synthesis
- stimulates IGF-1 which acts to increase cartilage proliferation
What is the function of ACTH?
- stimulates adrenal cortex to secrete cortisol (from zona fasiculata)
- stimulates androgen release (from zona reticularis)
- stimulates adrenaline release (from the adrenal medulla)
What is the function of cortisol?
- regulating & breaking down proteins, fats and carbohydrates
- anti-inflammatory effect (resulting in a lowered immune response)
- helps the body overcome stress (avoiding adrenal crisis)
What is the function of TSH?
- stimulates the release of thyroid hormone
What is the function of thyroid hormone?
- controls rate of metabolic reactions
- accelerates food metabolism
- increases protein synthesis
- stimulates carbohydrate metabolism
- enhances fat metabolism
- increases ventilation rate
- increases CO and HR
- brain development (foetal & post-natal)
- accelerates growth rate
What are the half lives of T3 and T4?
T3 - 1 day
T4 - 5-7 days
What is the function of prolactin?
- stimulates breasts to produce milk
- helps breast development
How does negative feedback work with prolactin?
Short-loop mechanism.
Prolactin acts on the hypothalamus to stimulate dopamine. Dopamine inhibits the secretion of prolactin.
What tissue type is the posterior pituitary?
- many glial-type cells present
- originates from neuronal tissue (extension of the hypothalamus)
What are glial cells?
Non-neuronal cells in the CNS that provide physical and metabolic support to neurons. (Like a Schwann cell but for the CNS).
Does the posterior pituitary synthesise hormones?
No, the hormones are synthesised in the hypothalamus and stored in the posterior pituitary.
Where is vasopressin synthesised?
Supraoptic nucleus.
Where is oxytocin synthesised?
Paraventricular nucleus.
How do vasopressin / oxytocin reach the posterior pituitary from the hypothalamus?
- axons of the supraoptic / paraventricular nuclei pass down the pituitary stalk and terminate in the posterior pituitary
- hormones move down the axons enclosed in vesicles and accumulate at the axon terminal in the posterior pituitary
What is the function of vasopressin?
- decreases water secretion in urine (helps maintain blood volume)
- acts on smooth muscle cells of blood vessels to cause vasoconstriction and increase BP (e.g. in response to low BP due to blood loss)
- stimulates ACTH release to increase aldosterone release
What stimulates vasopressin release?
- decreased blood volume
- trauma
- stress
- increased blood CO2 / decreased blood O2
- increased osmotic pressure of blood
What is the function of oxytocin?
- ejection of milk in response to mammary gland stimulation during breast feeding
- promotes the onset of labour and stimulates uterine smooth muscle contraction
What is the half life of vasopressin / oxytocin?
Very short, they are released on a minute to minute basis.
What receptors do all pituitary and hypothalamic hormones act on?
G-protein coupled receptors. (Cell-surface membrane receptors).
All are peptide hormones.
What are 6 main diseases of the pituitary?
- benign pituitary adenoma
- craniopharyngioma
- trauma
- Sheehan’s syndrome (pituitary infarction after labour)
- sarcoidosis (development of granulomas)
- TB
What are three main effects of pituitary tumours?
- pressure on local structures
- pressure on normal pituitary (hypopituitarism)
- functioning tumour (hyperpituitarism)
What might result from a tumour causing pressure on local structures?
- bitemporal hemianopia (pressure on optic chiasm)
- hydrocephalus (pressure on ventricles)
- CSF leak
What can result from a tumour causing pressure on the pituitary?
- cortisol deficiency - can be fatal
- presentation in males: pale, no body hair, central obesity, effeminate skin
- presentation in females: loose body hair, sallow complexion
What are the features of a prolactinoma?
- common in young women
- increased milk production in breast and galactorrhea)
- reduced fertility
- amenorrhoea
Treatment for prolactinoma?
Dopamine agonist to inhibit prolactin release. E.g. cabergoline.
What are some features of acromegaly?
- thick, greasy, sweaty skin
- large hands and feet
- enlarged organs (increased risk of heart disease)
- large brow and nose
What are some features of Cushing’s disease?
- central obesity
- bruising
- thin skin
- osteoporosis
- ulcers
- purple stretch marks
How does glucose uptake by the brain work?
- uptake independent of insulin
- brain cannot use FFAs as an energy source as they cannot cross the BBB
What happens during biphasic insulin release?
- initially there is a rapid release of stored insulin
- more insulin is synthesised and release if glucose levels remain high
What are some other counter-regulatory hormones of glucose (opposing insulin)?
- adrenaline, cortisol, GH
- increase glucose production in the liver
- reduce glucose utilisation in fat and muscle
Proinsulin vs insulin?
Proinsulin - contains alpha and beta insulin chains joined by C peptide.
Insulin - C peptide has been cleaved from alpha and beta chains.
Function of GLUT-1?
Enables basal, non-insulin stimulated glucose uptake into cells.
Function of GLUT-2?
- found in beta cells of pancreas (also renal tubules and hepatocytes)
- enables cells to sense glucose levels, by transporting glucose into the beta cell
- low affinity transporter: only allows glucose in when glucose concentration is high
Function of GLUT-3?
Enables non-insulin mediated glucose uptake into brain neurones and placenta.
Function of GLUT-4?
Channel in muscle and adipose
cell surface membranes for glucose uptake stimulated by insulin.
Examples of when diabetes is secondary to another condition?
- pancreatic pathology (total pancreatectomy, chronic pancreatitis, haemochromatosis)
- endocrine disease (acromegaly, Cushing’s disease)
- drug-induced (thiazide diuretics, corticosteroids)
- MODY
Where is the most common place for carcinoid tumours to metastasise to?
Liver
What are some side effects of metformin?
- GI disturbances
- peripheral neuropathy due to decreased absorption of B12
- lactic acidosis
What is the mechanism of action of metformin?
Decreases gluconeogenesis and encourages insulin sensitivity.
What is the risk of metformin in patients with renal impairment?
Lactic acidosis.
What is the mechanism of action of sulphonylureas?
Act on beta cells to promote insulin secretion.
Side effects of sulphonylureas?
- GI disturbances
- frequent hypoglycaemia
- weight gain
Mechanism of action of pioglitazone?
Reduces peripheral insulin resistance.
Side effects of pioglitazone?
- bone fractures
- weight gain
- bladder cancer
Mechanism of action of DPP-4 inhibitors?
Inhibition of DPP-4 increases insulin secretion and lowers glucagon secretion.
Side effects of DPP-4 inhibitors?
- headache
- acute pancreatitis
Mechanism of action of SGLT-2 inhibitors?
Inhibition of sodium-glucose co-transporter 2 results in reduced glucose reabsorption and increased urinary glucose excretion.
Side effects of SGLT-2 inhibitors?
- UTI
- genital pruritus
- DKA
What nerve roots are associated with carpal tunnel syndrome?
Median nerve (C5/6 - T1).
Diagnostic criteria for DKA?
- ketones >= 3.0 mmol/L
- glucose > 11.0 mmol/L
- pH < 7.3
What is the management of acromegaly?
- Transphenoidal surgery.
- Somatostatin analogue (ocreotide) +/- dopamine agonist.
- GH-receptor antagonist (pegvisomant).
- Radiotherapy
Non-diabetic HbA1c?
Less than 42 mmol/mol
Pre-diabetic HbA1c?
42 mmol/mol < HbA1c < 48 mmol/mol
Diabetic HbA1c?
> 48 mmol/mol
What is the cause of Cushing’s disease?
ACTH-secreting pituitary adenoma.
First line treatments for DKA?
IV fluids (0.9% sodium chloride). IV insulin +/- potassium.
Which arrhythmia is a consequence of untreated hyperkalaemia?
Ventricular tachycardia
Gold standard test for acromegaly?
Oral glucose tolerance test.
Treatment of hypercalcaemia?
- fluids
- bisphosphonates with calcitonin
Potassium in DKA?
Hyperkalaemia
Immediate management for carcinoid syndrome?
Somatostatin analogue (octreotide).
What is the definition of type 1 diabetes?
Autoimmune destruction of pancreatic beta cells leading to complete insulin deficiency.
What proportion of diabetes is type 1?
10%
Pathophysiology of T1D?
Autoantibodies attack beta cells in the islets of Langerhans, leading to insulin deficiency and hyperglycaemia. There is continuous breakdown of glycogen from the liver.
Risk factors for T1D?
- other autoimmune diseases
- HLA DR3-DQ2 or HLA DR4-DQ8
- northern european ancestry
Classic presentation of T1D?
- polydipsia
- polyuria
- weight loss
- ketosis
Usually short history of severe symptoms.
Diagnosis of T1D?
- random plasma glucose > 11 mmol/L
- fasting plasma glucose > 7 mmol/L
- HbA1c > 48 mmol/mol
Treatment of T1D?
Insulin therapy:
- quick-acting insulin given at mealtimes
- long-acting insulin given once or twice daily
Definition of type 2 diabetes?
Progressive disorder defined by deficits in insulin secretion and increased insulin resistance, leading to abnormal glucose metabolism and hyperglycaemia.
Secondary causes of type 2 diabetes?
- corticosteroid therapy (long term)
- Cushing’s disease
- chronic pancreatitis
Risk factors for T2D?
- obesity
- physical inactivity
- aged > 40
Signs and symptoms of T2D?
- polydipsia
- polyuria
- central obesity
- blurred vision
Investigations for T2D?
- fasting plasma glucose > 7 mmol/L
- random plasma glucose > 11 mmol/L
- HbA1c > 48 mmol/mol
T2D management summary?
- Lifestyle changes.
- Metformin
- Dual therapy with metformin + DPP4 inhibitor / sulphonylurea / pioglitiazone
- Triple therapy.
- Insulin therapy.
What is diabetic ketoacidosis?
Acute complication of T1D characterised by hyperglycaemia, ketonaemia and metabolic acidosis.
Causes of DKA?
- untreated T1D
- inadequate insulin therapy
- infection
- acute illness (MI, pancreatitis)
Pathophysiology of DKA?
- reduced insulin and increased insulin counter-regulatory hormones
- increased gluconeogenesis and glycogenolysis, with impaired glucose uptake in peripheral tissues
- this results in hyperglycaemia and hyperosmolality
- insulin deficiency leads to lipolysis and ketogenesis, resulting in metabolic acidosis
- osmotic diuresis results in severe dehydration and hypovolaemia
Why does hyperkalaemia occur in DKA?
- insulin normally drives potassium uptake into cells
- insulin deficiency increases serum potassium
- eventually total body potassium becomes low due to increased urinary excretion
What is the risk when correcting dehydration and hyperglycaemia in DKA?
Cerebral oedema - due to rapid shift in water from the extracellular space to the intracellular space in brain tissues.
Signs and symptoms of DKA?
- polydipsia and polyuria
- nausea & vomiting
- weight loss
- acetone smell on breath
- dehydration
- confusion / lethargy
- Kussmaul breathing (acidosis)
- tachycardia and hypotension
Investigations for DKA?
- random plasma glucose > 11 mmol/L
- plasma ketones > 3 mmol/L
- venous / arterial blood gas - pH < 7.35
- urine dipstick - glycosuria, ketouria
- raised urea and creatinine
- low total K+, elevated serum K+
Management of DKA?
ABCDE approach:
- IV fluids (0.9% saline) for rehydration
- IV insulin
- correct hypokalaemia
What is hyperosmolar hyperglycaemic state?
Serious complication of T2D - characterised by hyperglycaemia, hyperosmolality, and volume depletion in the absence of ketoacidosis.
Causes of HHS?
- infection (UTI, pneumonia)
- untreated T2D
- acute illness (MI, stroke)
Pathophysiology of HHS?
- relative insulin deficiency results in hyperglycaemia and hyperosmolality
- there may also be increased insulin counter regulatory hormones due to infection
- insulin concentration is sufficient to suppress lipolysis and ketogenesis, but insufficient to promoto glucose uptake and regulate gluconeogenesis and glycogenolysis
- osmotic diuresis results in hypovolaemia
What are insulin counter regulatory hormones?
- catecholamines (adrenaline)
- glucagon
- cortisol
- growth hormone
Signs and symptoms of HHS?
- nausea & vomiting
- weight loss
- polydipsia and polyuria
- dehydration
- confusion and lethargy
Investigations for HHS?
- random plasma glucose > 11 mmol/L
- urine dipstick - glycosuria
- plasma osmolality elevated
- raised creatinine
- raised serum K+, low total K+
Management of HHS?
- IV fluids (0.9% saline)
- IV insulin
- correct potassium
Causes of primary hyperthyroidism?
- Grave’s disease
- toxic multinodular goitre
Cause of secondary hyperthyroidism?
TSH-secreting pituitary adenoma
Most common cause of hyperthyroidism?
Grave’s disease
Pathophysiology of hyperthyroidism?
Increased thyroid hormone increases metabolic rate, cardiac output, bone resorption, and activates the sympathetic nervous system.
Signs and symptoms of hyperthyroidism?
- hot and sweaty
- diarrhoea
- weight loss
- palpitations
- tremor
- irritability
- anxiety
- oligomenorrhoea
- goitre
Pathophysiology of Grave’s disease?
TSH receptor autoantibodies cause thyroid hormone hyper-production, thyroid hypertrophy, and hyperplasia of thyroid follicular cells.
What causes extra-thyroidal manifestations of Grave’s disease?
TSH receptors are also found in retro-orbital and dermal tissue. Autoantibodies stimulate fibroblasts, resulting in retro-orbital tissue expansion.
Signs and symptoms of Grave’s disease?
- signs and symptoms of hyperthyroidism
- diffuse goitre
- orbitopathy (upper eyelid retraction, exophthalmos)
- pretibial myxoedema
- thyroid acropachy (digital clubbing)
Investigations for Grave’s disease?
- serum T3 and T4 - elevated
- serum TSH - low
- serum TSH-R autoantibodies
- ultrasound neck
- CT head and neck
Management of Grave’s disease?
- beta blockers to reduce sympathetic activity
- carbimazole / propylthiouracil in pregnancy
- radioiodine therapy
- thyroidectomy
Treatment of Grave’s dermopathy?
Topical corticosteroid
Treatment of Grave’s orbitopathy?
- eye drops
- high dose corticosteroids if sight-threatening
Complications of thyroidectomy?
- laryngeal nerve damage
- parathyroid damage
Complications of hyperthyroidism?
- AF
- congestive heart failure
- vision loss
What is Hashimoto’s thyroiditis?
Autoimmune-mediated inflammation of the thyroid, usually resulting in hypothyroidism due to destruction of thyroid cells.
Causes of primary hypothyroidism?
- Hashimoto’s thyroiditis
- primary atrophic hypothyroidism
- iodine deficiency
- post-thyroidectomy
Cause of secondary hypothyroidism?
Hypopituitarism
Signs and symptoms of hypothyroidism?
- fatigue & lethargy
- weight gain
- cold intolerance
- constipation
- depression
- menorrhagia
- goitre
Investigations for hypothyroidism?
- serum T3 and T4 - decreased
- TSH elevated if primary, decreased if secondary
- autoantibodies (thyroid peroxidase)
Treatment of hypothyroidism?
Thyroid replacement therapy with levothyroxine.
What is post-partum thyroiditis?
Autoimmune inflammation of the thyroid occurring within 12 months of delivery. May involve hyperthyroidism and / or hypothyroidism followed by a return to euthyroid.
What is the most common endocrine malignancy?
Thyroid cancer.
Risk factors for thyroid cancer?
- head and neck irradiation
- family Hx
Clinical presentation of thyroid cancer?
- palpable thyroid nodule
- hoarseness due to laryngeal nerve involvement
- dysphagia
- cervical lymphadenopathy
Gold standard investigation for thyroid cancer?
Thyroid biopsy
Investigations for thyroid cancer?
- biopsy
- ultrasound
Management of thyroid cancer?
- thyroidectomy
- radioactive iodine ablation
- chemotherapy / radiotherapy
What is Cushing’s syndrome?
The clinical manifestation of pathological hypercortisolism from any cause.
What is Cushing’s disease?
Pituitary adenoma secretes excessive ACTH, causing Cushing’s syndrome.
Causes of Cushing’s syndrome?
- exogenous corticosteroid exposure
- ACTH-secreting pituitary adenoma
- adrenal adenoma / carcinoma
- small cell lung cancer
Most common cause of Cushing’s syndrome?
Exogenous corticosteroid exposure.
Clinical manifestations of Cushing’s syndrome?
- facial rounding
- violaceous abdominal striae
- weight gain and central obesity
- acne
- depression
- proximal muscle wasting and weakness
- dorsal hump
- hypertension
- easy bruising
Which causes of Cushing’s syndrome are ACTH dependent?
- pituitary adenoma
- small cell lung cancer
Which causes of Cushing’s syndrome are not ACTH dependent?
- adrenal adenoma
- exogenous corticosteroid exposure
Gold standard investigation for Cushing’s syndrome?
Dexamethasone suppression test.
Initial investigation for Cushing’s syndrome?
Random plasma cortisol.
What do the results of the high-dose dexamethasone suppression test indicate?
Pituitary adenoma - high dose is sufficient to suppress cortisol.
Adrenal adenoma - high dose suppresses ACTH but not cortisol.
Small cell lung cancer - high dose does not suppress ACTH or cortisol.
Management of Cushing’s syndrome?
- stop corticosteroid medication if possible
- trans-sphenoidal removal of pituitary adenoma
- adrenalectomy for adrenal adenoma
Complications of Cushing’s syndrome?
- hypertension
- diabetes mellitus
- osteoporosis
- thrombosis
What is acromegaly?
Release of excess growth hormone, causing overgrowth of all systems.
Most common cause of acromegaly?
Pituitary adenoma.
Physiology of growth hormone?
- GH stimulates the release of IGF-1 from the liver
- IGF-1 causes widespread promotion of growth
- GH may also directly act on tissues to promote their growth
What hormone is a negative regulator of GH?
Somatostatin
Signs and symptoms of acromegaly?
- prominent forehead (frontal bossing)
- large protruding jaw (prognathism)
- large hands, nose, tongue, feet
- bitemporal hemianopia
- sweating
- lower pitch of voice
- obstructive sleep apnoea
- polydipsia and polyuria
- organomegaly
First line investigation for acromegaly?
Serum IGF-1 - elevated.
Gold standard investigation for acromegaly?
Oral glucose tolerance test.
Management of acromegaly?
- Trans-sphenoidal resection of pituitary adenoma.
- Somatostatin analogue (octreotide).
- GH receptor antagonist (pegvisomant).
- Dopamine agonist.
What is a prolactinoma?
Benign pituitary adenoma producing excess prolactin.
Signs and symptoms of prolactinoma?
- visual field defect (bitemporal hemianopia)
- headache
- menstrual irregularity
- infertility
- galactorrhoea
Why does a prolactinoma cause infertility?
Inhibition of FSH and LH.
Investigations for prolactinoma?
- pituitary MRI
- serum prolactin
Management of prolactinoma?
- Trans-sphenoidal resection of prolactinoma.
2. Dopamine agonists.
Dopamine agonist example?
Cabergoline
What is Conn’s syndrome?
Primary hyperaldosteronism (i.e. due to adrenal adenoma).
Pathophysiology of Conn’s syndrome?
Excess aldosterone production leads to:
- increased sodium and water retention
- increased renal potassium excretion
- hypertension
- metabolic acidosis
- low renin (negative feedback)
Signs and symptoms of Conn’s syndrome?
- hypertension
- hypokalaemia
- polyuria, polydipsia
- mood and concentration disturbance
- muscle cramps
- arrhythmia (AF)
What cells does aldosterone act on?
Principle cells (sodium-potassium transporters) in the DCT. Intercalated cells in the DCT (acid-base balance).
Investigations for Conn’s syndrome?
- aldosterone / renin ratio - increased
- serum potassium - low
Management of Conn’s syndrome?
- spironalactone
- laparoscopic adrenalectomy
What is Addison’s disease?
Primary adrenal insufficiency, resulting in impaired synthesis and secretion of all steroids (glucocorticoids and mineralocorticoids).
Causes of Addison’s disease?
- autoimmune
- infection (TB, pseudomonas, meningococcal)
- infiltrative disease (amyloidosis, sarcoidosis, haemochromatosis)
- metastasis
- bilateral adrenalectomy
- adrenal infarct
What causes skin hyperpigmentation in Addison’s disease?
Increased synthesis of ACTH precursor proopiomelanocortin, also a precursor of melanocyte-stimulating hormone.
Signs and symptoms of Addison’s disease?
- weight loss
- abdominal pain
- bronze hyperpigmentation
- fatigue
- postural hypotension
First line investigations for Addison’s disease?
- U&Es - hyponatraemia, hyperkalaemia
- blood glucose (hypoglycaemia)
Gold standard investigation for Addison’s disease?
Short synACTHen test.
Serum renin and aldosterone in Addison’s disease?
Renin - high
Aldosterone - low
Serum cortisol and ACTH in Addison’s disease?
Cortisol - low
ACTH - high
What autoantibodies may be seen in Addison’s disease?
21-hydroxylase antibodies
Summary of Addison’s disease investigations?
1. U&Es Gold standard - short synACTHen test. - serum renin & aldosterone - serum cortisol & ACTH - 21-hydroxylase antibodies - adrenal CT / MRI
Management of Addison’s disease?
- hydrocortisone to replace cortisol
- fludrocortisone to replace aldosterone
- treat underlying cause
- warn against suddenly stopping steroids (emergency ID tag)
What is Addisonian (adrenal) crisis?
Emergency presenting with hypotension and tachycardia due to lack of cortisol.
Management of adrenal crisis?
- IV fluids
- IV hydrocortisone
- correct hypoglycaemia
- correct electrolytes
Causes of secondary adrenal insufficiency?
- cessation of long term corticosteroid usage
- hypopituitarism
What is SIADH?
Syndrome of inappropriate ADH - characterised by hypotonic hyponatraemia, concentrated urine, and a euvolaemic state.
Causes of SIADH?
- small cell lung cancer
- CNS disorders (meningitis, encephalitis, trauma, multiple sclerosis, haemorrhage)
- anaesthesia and post-operative state
- nephrogenic (gain of function mutation in the vasopressin 2 receptor)
- medications (thiazide diuretics)
What is the most common cause of SIADH?
Medication (thiazide diuretics)
Signs and symptoms of SIADH?
- headache
- nausea
- fatigue
- muscle cramps
- confusion
Pathophysiology of SIADH?
- excessive ADH results in excessive water reabsorption in the collecting ducts
- water dilutes sodium in the blood, causing hyponatraemia
- increased extracellular volume results in RAA system suppression, and therefore increased naturesis
- euvolaemia as excessive water reabsorption is not enough to cause fluid overload
- high urine osmolality
Investigations for SIADH?
- hyponatraemia
- urine osmolality high
- urine sodium high
- exclude Addison’s (short synACTHen test)
Causes of hyponatraemia?
- SIADH
- Addison’s disease
- vomiting / diarrhoea
- diuretic use
- AKI / CKD
Management of SIADH?
- stop causative medication
- fluid restriction
- ADH receptor blocker (tolvaptan)
How should tolvaptan be used with caution?
ADH receptor blocker - don’t let sodium rise too quickly (aim for increase of less than 10 mmol in 24 hours). Risk of osmotic demyelination syndrome.
What potassium level is considered hyperkalaemia?
> 5.5 mmol/L
Causes of hyperkalaemia?
- AKI / CKD
- ACE inhibitors
- Addison’s disease
- decreased insulin
- IV K+ therapy
Signs and symptoms of hyperkalaemia?
- fatigue
- light-headedness
- chest pain
- palpitations (due to arrhythmia)
- reduced power and reflexes
- flaccid paralysis
Investigations for hyperkalaemia?
- ECG
- U&Es
- urine osmolality and electrolytes
Management of hyperkalaemia?
- cardiac monitoring and calcium gluconate to protect the myocardium
- insulin + dextrose
- nebulised salbutamol
- treat underlying cause
What potassium level is considered hypokalaemia?
< 3.5 mmol/L
Causes of hypokalaemia?
- thiazide and loop diuretics
- Conn’s syndrome
- diarrhoea and vomiting
- fasting
- salbutamol
Symptoms of hypokalaemia?
- fatigue
- light-headedness
- cramps
- palpitations (due to arrhythmia)
- constipation
- hypotonia and hyporeflexia
- muscle paralysis
Severe complication of hypokalaemia?
Rhabdomyolysis
ECG signs of hypokalaemia?
- prolonged PR
- ST depression
- flat T waves
- prominent U waves
ECG signs of hyperkalaemia?
- tall tented T waves
- small / absent p waves
- prolonged PR
- wide QRS
Investigations for hypokalaemia?
- ECG
- U&Es
- urine osmolality and electrolytes
Management of hypokalaemia?
- potassium replacement (oral or IV)
- treat underlying cause
What is diabetes insipidus?
Inadequate ADH secretion / inadequate renal response to ADH.
Subtypes of diabetes insipidus?
Central - abnormal ADH synthesis / secretion.
Nephrogenic - abnormal renal response to ADH.
Gestational - increased ADH metabolism.
Causes of central diabetes insipidus?
- brain tumours
- skull fracture
- surgical damage to hypothalamus / pituitary stalk
- CNS infection
- autoimmune disorders (Hashimoto’s / T1D)
Causes of nephrogenic diabetes insipidus?
Congenital - X-linked mutation of vasopressin 2 receptors.
Acquired - polycystic kidney disease, lithium.
Medication causing diabetes insipidus?
Lithium
Most common cause of nephrogenic diabetes insipidus?
Lithium
Where is vasopressin synthesised?
Supraoptic and paraventricular nuclei of the hypothalamus.
Signs and symptoms of DI?
- polyuria & polydipsia
- dehydration
- hypernatraemia (spasticity, hyper-reflexia, irritability)
Gold standard investigation for DI?
8 hour water deprivation test - no decrease in urine osmolality.
How is cranial DI distinguished from nephrogenic DI?
Desmopressin test following water deprivation test. If cranial, urine osmolality decreases. No decrease in urine osmolality if nephrogenic.
Management of DI?
- conservative management with rehydration in mild cases
- desmopressin to replace ADH in cranial DI
- bendroflumethiazide for nephrogenic DI if underlying cause cannot be resolved
What is primary hyperparathyroidism?
Parathyroid gland produces excess PTH.
What is secondary hyperparathyroidism?
Increased secretion of PTH to compensate for hypocalcaemia (e.g. due to kidney failure).
What is tertiary hyperparathyroidism?
Autonomous secretion of PTH even after correction of hypocalcaemia, due to CKD. Develops due to prolonged secondary hyperparathyroidism.
Causes of primary hyperparathyroidism?
- parathyroid adenoma (most common)
- parathyroid hyperplasia
Causes of secondary hyperparathyroidism?
- CKD
- low vitamin D
Signs and symptoms of hyperparathyroidism?
Hypercalcaemia
- bone pain
- renal stones
- psychiatric moans (depression)
- abdominal groans
Investigations for hyperparathyroidism?
- serum PTH
- bone profile (high calcium, low phosphate)
Serum PTH and calcium in primary hyperPTH?
- normal / high PTH
- high calcium
Serum PTH and calcium in secondary hyperPTH?
- low calcium
- high PTH
Serum PTH and calcium in tertiary hyperPTH?
- high calcium
- high PTH
Imaging for hyperPTH?
- DEXA scan
- X ray
- renal ultrasound for calculi
X ray signs in hyperPTH?
Salt and pepper degradation of bone.
Management of hyperPTH?
Mild - watchful waiting.
Primary: bisphosphonates, surgical removal of adenoma.
Secondary: correct calcium, treat underlying cause.
Tertiary: cinacalcet (calcium mimetic), parathyroidectomy.
Causes of primary hypoPTH?
- autoimmune destruction
- congenital (DiGeorge syndrome)
Causes of secondary hypoPTH?
- surgical removal of parathyroid glands
- damage during thyroidectomy
Pathophysiology of hypoPTH?
- hypocalcaemia and hyperphosphataemia
- neurons become more excitable
Signs and symptoms of hypoPTH?
Hypocalcaemia (CATS go numb) - convulsions - arrhythmias - tetany - spasm - numbness Chvostek and Trousseau's signs.
Investigations for hypoPTH?
- bone profile (low calcium, high phosphate, low PTH)
- ECG
ECG findings hypoPTH?
- prolonged QT
- prolonged ST
Management of hypoPTH?
- IV calcium
- AdCal D3
- synthetic PTH
Risk factors for neuroendocrine tumours?
- multiple endocrine neoplasia
- neurofibromatosis type 1
- von hippel-lindau
Where are neuroendocrine tumours commonly located?
- stomach
- intestine
- pancreas
- lungs
Examples of neuroendocrine tumours?
- insulinoma
- gastrinoma
- small cell lung cancer
What is carcinoid syndrome?
Symptoms occurring due to the release of serotonin (5-HT) and other vasoactive peptides into the systemic circulation from a carcinoid (neuroendocrine) tumour.
Signs and symptoms of carcinoid syndrome?
- diarrhoea
- flushing
- palpitations
- abdominal cramps
- telangiectasia
- wheeze
Investigations for carcinoid syndrome?
- urinary 5-hydroxyindoleacetic acid (serotonin metabolite)
- CT chest, abdomen, pelvis
- bronchoscopy / endoscopy
Management of carcinoid syndrome?
- somatostatin analogue (octreotide)
- surgical resection of tumour
What is a pheochromocytoma?
Tumour arising from catecholamine-producing chromaffin cells of the adrenal medulla.
Hereditary risk factors for pheochromocytoma?
- multiple endocrine neoplasia type 2
- von hippel-lindau
- neurofibromatosis type 1
Pathophysiology of pheochromocytoma?
- excess secretion of catecholamines
- activation of alpha and beta adrenergic receptors
- alpha receptors: increased BP, increased cardiac contractility
- beta receptors: increased HR and cardiac contractility
Pattern of symptoms in pheochromocytoma?
Usually paroxysmal (associated with periods when the tumour is secreting adrenaline). Can be persistent / asymptomatic.
Classic triad of symptoms in pheochromocytoma?
- episodic headache
- sweating
- tachycardia
Symptoms of hypertensive crisis?
- hypertension
- hyperthermia
- confusion
- end-organ dysfunction
- hypotension due to circulatory collapse
Complication of pheochromocytoma?
Hypertensive crisis
Investigations for pheochromocytoma?
- plasma free metanephrines (if high probability)
- urinary fractionated metanephrines (if low probability)
- CT / MRI
Complications of hypertensive crisis?
- stroke
- cardiac failure
- seizure
Management of pheochromocytoma?
- adrenalectomy
- alpha- and beta-blockers to control hypertension prior to surgery
Calcium in Addison’s disease?
Raised due to volume depletion and increased release into extracellular space.
Addison’s disease and blood volume?
Blood volume decreased due to naturesis.
Most common cause of Addisonian crisis?
Abrupt cessation of long term corticosteroid treatment.
Most important treatment for Addisonian crisis?
Hydrocortisone
What is pseudohypoPTH?
Peripheral resistance to PTH.