endocrine system Flashcards
what are the main endocrine glands?
Hypothalamus/Pituitary Thyroid Parathyroid Pancreas Adrenal Ovaries/testicles
what are the two functional lobes of the pituitary and their general function?
Anterior pituitary
produces various hormones
Posterior pituitary
stores various hormones
which hormones do the anterior pituitary gland produce?
Growth hormone (GH) Adrenocorticotrophic hormone (ACTH) Gonadotrophins (FSH and LH) Thyroid stimulating hormone or thyrotrophin (TSH) Prolactin (PRL)
what does growth hormone do?
For skeletal growth
what does ACTH do?
Stimulates the adrenals to produce steroids
what do gonadotrophins do?
Stimulate the testicles or ovaries to produce sex hormones
what does TSH do?
Stimulates the thyroid to produce thyroid hormones
what does prolactin do?
Stimulates breast milk production
what does the posterior pituitary gland do?
stores the hormones produced in the hypothalamus
which hormones does the posterior pituitary produce?
Antidiuretic hormone (ADH) Oxytocin
what is the anterior pituitary controlled by?
the hypothalamus
what stimulates ACTH secretion?
corticotrophin releasing hormone
what stimulates GH secretion?
growth hormone releasing hormone
what stimulates TSH secretion?
thyotropin releasing hormone
what stimulates FSH and LH secretion?
gonadotrophin releasing hormone
how is prolactin controlled?
inhibitory effect from the hypothalamus
how are pituitary hormones switched off?
negative feedback from hormone
which glands are not controlled by the pituitary?
Adrenal medulla - Produce adrenaline and noradrenaline
Parathyroid - Controls calcium levels
Pancreas - Controls sugar levels
what is the thyroid composed of?
Midline isthmus (just below the cricoid cartilage)
Right lobe
Left lobe
how is the thyroid gland arranged?
Thyroid cells are arranged in follicles and produce thyroid hormones
The thyroid also contains C cells, which produce calcitonin (calcium metabolism)
what is calcium metabolism mainly controlled by?
4 parathryoid glands sitting behind the thyroid
which other organs are involved in the metabolism of calcium?
Kidneys
Calcium excretion and production of active vitamin D
Gut
Absorption of calcium
Bone
Storage of calcium
Thyroid
what are the two areas of the adrenal gland and what do they produce?
Adrenal cortex, 90% of the gland and produces:
Cortocosteroids (cortisol)
Androgens (male hormones)
Mineralocorticoid (aldosterone)
Adrenal medulla, 10% of the gland and produces:
Catecholamines (adrenaline, noradrenaline and dopamine)
which adrenal hormones are not controlled by the pituitary?
Catecholamine secretion is not controlled by the pituitary (related to blood pressure)
Mineralocorticoid secretion is not controlled by the pituitary (related to renin-angiotensin system, which controls the blood pressure)
what can a static test be used to diagnose?
abnormalities of thyroid and sex glands
what can stimulation tests be used to diagnose?
suspected hormonal under-secretion where a static test is not enough
what are suppression tests used to diagnose?
some hormonal over-secretion
Examples include:
Giving steroids and testing for endogenous steroid production (external steroids should switch off internal steroid production)
Giving glucose and testing GH secretion (glucose switches off GH secretion in normal individuals)
what is the clinical presentation of prolactin oversecretion and what is it normally due to?
Usually due to a pituitary tumour secreting prolactin (prolactinoma)
Clinical presentation
Galactorrhoea (breast milk production)
Amenorrohoea in women and sexual dysfunction in men
Headaches and visual field problems in large tumours
what can mildly raise prolactin levels?
Sexual intercourse Nipple stimulation Stress Large number of drugs Non-functioning pituitary tumour
how does GH oversecretion manifest in children?
Excessive growth spurt and increased size of feet and hands
If left untreated growth hormone excess leads to gigantism, the most serious consequence of the disease
how does GH oversecretion manifest in adults?
Acromegalic face
Wide and large hands/feet
Increased sweating (common complaint)
how do you diagnose GH oversecretion?
Suppression tests are necessary
Glucose is given, followed by GH measurements at different time points. In healthy individuals, glucose suppresses GH production and hence plasma levels of the hormones fall but not in those with oversecretion.
Imaging is necessary to confirm the presence of pituitary tumour
what can Cushings syndrome be caused by?
Pituitary secreting ACTH tumour (Cushing’s disease)
Adrenal tumours secreting cortisol
Cancers producing ACTH
how do you diagnose Cushings?
Static tests are not enough and suppression tests are required.
Dexamethasone suppression test is used to confirm the failure to suppress endogenous cortisol production.
what are the two types of hyperthyroidism?
Primary hyperthyroidism
Very common, RA sees 2 patients/week!
Secondary hyperthyroidism (pituitary TSH secretion) Rare; RA had seen 4 patients in his career so far!
what is hyperthyroidism caused by?
Graves’ disease (80%).
Autoimmune condition
Toxic nodule or toxic MNG (15%).
Thyroiditis (1%).
Drug induced (amiodarone)
clinical presentation of hyperthyroidism?
Hyperactivity, irritability, insomnia
Heat intolerance and increased sweating
Palpitations
Weight loss despite overeating
Menstrual problems
what are the signs of thyrotoxicosis?
Hand tremor
Inceased sweating
Fast pulse
what are extrathyroidal signs of hyperthyroidism?
Swelling round the eyes
Protrusion of the eye ball (proptosis)
Paralysis of eye muscles
can a static test be used for hyperthyroidism?
yes
how do you treat hyperthyroidism?
Anti-thyroid drugs: disease remission in 50% of patients after treatment for 6-18 months can suppress white cell production (very rare)
Radioactive iodine
Destroys the thyroid gland
Surgery
how does GH deficiency manifest?
Children
Failure of growth
Adults
Nothing
Tiredness
Depression
how do you test for GH deficiency?
Glucagon stimulation test
Insulin stress test (lowers blood glucose, stressing the body and forcing growth hormone secretion)
what may steroid under-secretion be due to?
Adrenal failure
Pituitary failure
how does steroid under-secretion present?
Failure to grow in children
Severe tiredness
Dizziness due to low blood pressure
Abdominal pain, vomiting an diarrhoea
how do you test for steroid under-secretion?
Synacthen test (giving ACTH) if primary adrenal failure is suspected
GST or IST if secondary adrenal insufficiency is suspected
what is primary hypothyroidism caused by?
thyroid failure and inability to produce thyroid hormones (common).
what is secondary hypothyroidism caused by?
failure to produce TSH (rare).