Endocrine lecture notes Flashcards
endocrine vs exocrine
endocrine - glands secrete into bloodstream
exocrine - glands secrete through a duct to site of action
describe water soluble hormones in terms of: transport cell interaction half-life clearance examples when are they syntehsised/stored?
transport: unbound
cell interaction: bind to surface receptor
half-life: short
clearance: fast
eg peptides, monoamines
- stored in vesicles and secreted when needed
describe fat soluble hormones in terms of: transport cell interaction half-life clearance eg when are they synthesised?
transport: protein bound cell interaction: diffuse into cell half-life: long clearance: slow eg. thyroid hormone, steroids - synthesised on demand
What are some roles of thyroid hormone?
- increased food metabolism
- increased protein synthesis
- stimulates carb metabolism
- enhances fat metabolism
- increased CO and HR so increased BP
- increased ventilation rate
- increased growth rate
- brain development. foetal and post natal
What are some roles of cortisol?
- bone development
- BP
- anti-inflammatory, immune system
- skin: texture of collagen
- released as a reaction to stress
what are the results of too much cortisol?
protein breakdown, put on weight, increased blood sugar
How is the balance between energy expenditure and energy intake maintained normally in the body?
By hormones of the…
- GI tract: eg CCK
- brain: eg vagus nerve stimulated by gastric stretch to stop appetite
- adipose tissue
What are the components of the satiety cascade?
- internal physiological drive
- feeling prompts thought of food - psychological
- time of day
Where is the centre of appetite regulation? whithin this, where us the hunger centre compared with the satiety centre?
Appetite regulation occurs in the hypothalamus.
Hunger = lateral hypothalamus
Satiety = ventromedial hypothalamic nucleus
what role does the arcuate nucleus of the hypothalamus have in apetite regulation?
Has fenestrated blood brain barrier so can sample peripheral hormones.
Secretes leptin hormone, which switches off appetite and is immunostimulatory.
Blood levels increase after a meal and decrease after fasting.
What stimulates an individual to want to eat?
- Ghrelin hormone, expressed in the stomach, stimulates GH release and appetite
- olfactory, gustatory, cognitive and visual stimuli
Describe the Pituitary - thyroid axis
Hypothalamus releases TRH which stimulates pituitary to release TSH. TSH stimulates production of T4 and T3 from the thyroid, which has a negative feedback effect on both TRH and TSH secretion.
How would removal of the thyroid, vs an overactive thyroid, affect TSH levels?
Can levels of this hormone therefore be used in screening for thyroid problems?
What about in screening for pituitary disease?
Removal: increased TSH
Overactive: decreased TSH
Levels are used to screen for thyroid problems but NOT for pituitary disease
Why is prolactin unusual as a hormone released from the anterior pituitary?
Which drugs may be relevant in affecting prolactin levels?
Its axis
Prolactin is under negative control by dopamine from the hypothalamus.
Drugs such as anti-psychotics which inhibit the release of dopamine can cause increased prolactin levels
How is benign pituitary adenoma usually picked up?
Usually accidentally on MRI. It is relatively common.
Describe the 3 different presentations of a pituitary tumour
- Pressure on local structure, e.g optic nerve causing bitemporal hemianopia
- Pressure on normal pituitary (hypopituitarism)
- Functioning tumour (of hormone releasing cells)
What is the effect of hypopituitarism caused by pressure on the normal pituitary due to a tumour?
Slow onset
If child: poor growth
Adult: pale, no body hair, central obesity… Need steroid replacement, often wear bracelet explaining this in case of emergency
Describe 3 examples of functioning pituitary tumours. Which hormones are over produced?
Prolactinoma - prolactin
Cushing’s - ACTH
Acromegaly - GH
why is important to be aware of acromegaly?
Uncommon, but its slow progression means it can go undiagnosed for years and co-morbidities can cause significant harm.
Describe briefly the pathogenesis of acromegaly
Too much GH
GH stimulates the production of IGF-1 from the liver.
IGF- 1 targets other organs in the body leading to clinical signs.
What are common co-morbidities of acromegaly?
Arthritis (due to bone overgrowth), cerebrovascular events, headache, sleep apnea, diabetes (GH has antagonistic effects to insulin), hypertension, heart disease.
It is important to treat these co-morbidities alongside the acromegaly.
What are 2 ways, other than looking at clinical features, of diagnosing acromegaly?
- Normally, GH secretion is pulsatile, stimulated by GHRH from hypothalamus. In acromegaly the pulses are disrupted so GH secretion will be dysregulated. Levels will also never by completely gone, as with normal inividuals.
- Normally, glucose promptly supresses GH, but not with acromegaly. Therefore a glucose tolerance test is an important diagnostic tool.
3 modes of treatment of acromegaly?
- pituitary surgery
- medical therapy (dopamine agonist, somatostatin analogues, GH receptor antagonist)
- radiotherapy (interrupts vascular supply, prevents DNA division)
What is a key principle of endocrinology in terms of the pathway for diagnosing an endocrine issue?
Clinical suspicion –> biochemistry –> scan
In that order.
This is because scan may show accidental findings.
Why is recognising prolactinoma important?
Common: 10 in 100000
Easily treated.
Causes infertility.
Define prolactinoma
lactotroph call tumour of the pituitary
OR
non-functioning: interruption of pituitary stalk means dopamine can’t reach the pituitary so prolactin levels increase uninhibited
What effect does dopamine have on a prolactinoma?
Tumour cells are not under inhibition by dopamine
Describe the clinical features of someone which may indicate that they have a prolactinoma
Galactorrhoea (milk in the breast)
Amenorrhoea, infertility, loss libido, visual defect, hypogonadism.
More common in women
What is the treatment for prolactinoma? How does this differ from other pituitary treatment?
Management is medical, not surgery.
Dopamine agonists used.
Adrenal insufficiency - what are the primary, secondary and tertiary causes?
Primary: autoimmune, Addison’s
Secondary: hypopituitarism
Tertiary: suppressed HPA
what is the HPA axis?
Hypothalamus stimulates ACTH prod. from the anterior pituitary, which stimulates the adrenal cortex to secrete cortisol, which has a negative feedback effect on both the hypothalamus and ant. pituitary.
Principles of endocrinology:
What test when looking for a deficiency?
What test when looking for an excess?
Deficiency = stimulatory test Excess = suppression test
Acute administration of what can save someone in adrenal crisis? how?
Hydrocortisone.
Treatment for adrenal insufficiency?
Hydrocortison 2/3 times daily in attempt to mimic cortisol levels throughout the day.
However, hard to replace mid night cortisol spike.
Examples of thyroid autoimmunity?
Post partum thyroiditis (after pregnancy) Graves disease (immune system antibodies stimulate the thyroid) - MOST COMMON CAUSE OF HYPERTHYROIDISM
What are factors that predispose to thyroid autoimmunity?
- female (onset common post partum)
- genetic: HLA-DR3 and other immunoregulatory genes
- environmental: stress, high iodine intake, smoking
Describe autoimmune hypothyroidism
- immune system (cytotoxic T cell mediated) attacks thyroid, follicles break down and there is an invasion of lymphocytes and a build up of fibrotic
describe Graves disease
symptoms?
Most common type of hyperthyroidism, 70-80% cases.
Thyroid stimulating antibodies stimulate the thyroid.
This causes thickening of the cells and overproduction of thyroid hormone.
Affects other systems
Symptoms: periorbital oedema, weight loss, enlarged thyroid, tachycardia, hyperphagia, anxiety, tremor, heat intolerance, sweating, diarrhoea, lid lag and stare, menstrual disturbance
What is goitre?
Palpable and visible thyroid enlargment.
Commonest endocrine disorder, has a variety of causes.
What investigations will reveal primary hyperthyroidism? What about secondary hyperthyroidism?
Primary: increased free T4 and T3, suppressed TSH
Secondary: increased free T4 and T3, inappropriately high TSH
What is primary hyperthyroidism? Secondary?
Primary: abnormal functioning of the thyroid gland itself. 80% occurs due to single benign adenoma.
Secondary: dysfunction is caused by factors extrinsic to the thyroid gland (i.e., not due to a disorder in the gland).
What is primary hypothyroidism? Secondary?
primary - dysfunction of the thyroid gland
secondary/tertiary - pituitary/hypothalamic dysfunction
Treatment for hypothyroidism?
synthetic thyroxine
1.6mg/kg body weirgh
treatment for hyperthyroidism?
antithyroid drugs
radioiodine
surgery