Flashcards in Ramzi Ajjan's Intro to Endocrinology from IMS Deck (22):
What is the main functional difference between the anterior and posterior pituitary?
Anterior - produces hormones
Posterior - stores hormone
Which hormones are produces by the anterior pituitary?
Growth hormone (GH)
- For skeletal growth
Adrenocorticotrophic hormone (ACTH)
- Stimulates the adrenals to produce steroids
Gonadotrophins (FSH and LH)
- Stimulate the testicles or ovaries to produce sex hormones
Thyroid stimulating hormone or thyrotrophin (TSH)
- Stimulates the thyroid to produce thyroid hormones
- Stimulates breast milk production
Which hormones are stored in the posterior pituitary?
Those produced by the the hypothalamus:
Antidiuretic hormone (ADH)
- Stimulates water reabsorption by the kidneys
- Helps uterine contractions during labour
Which part of the brain controls the anterior pituitary?
What hormones are produced by the hypothalamus to control the anterior pituitary?
- Corticotrophin releasing hormone (CRH): stimulates ACTH secretion
- Growth hormone releasing hormone (GHRH): stimulates GH secretion
- Thyrotropin releasing hormone (TRH): stimulates TSH secretion
- Gonadotrophin releasing hormone (GnRH): stimulates FSH and LH secretion
- Prolactin releasing hormone does not exist and prolactin is under the inhibitory effect of the hypothalamus
How are pituitary hormones 'switched off'?
- Cortisol switches off ACTH and CRH
- Growth hormone, switches off GH and GHRH
- Thyroid hormones switch off TSH and TRH
- Sex hormones switch off FSH/LH and G
Which glands are not controlled by the pituitary?
- Produce adrenaline and noradrenaline
- Controls calcium levels
- Controls sugar levels
Describe the anatomy of the adrenal glands.
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)
Is catecholamine secretion controlled by the pituitary?
Catecholamine secretion is not controlled by the pituitary (related to blood pressure)
Is mineralcorticoid secretion controlled by the pituitary?
No - related to renin-angiotensin system, which controls the blood pressure.
What are the possible clinical abnormalities of endocrine glands\/
Tumour/nodules in the gland without affecting hormone secretion
What are static tests used for?
Can diagnose abnormalities of thyroid and sex glands. For example:
In those with primary hyperthyroidism (thyroid hormone overproduction), we can test for
- Thyroid hormones (T3 and T4)
If primary hyperthyroidism is present then T3 and/or T4 is elevated with suppressed (undetectable) TSH
What are stimulation tests used for?
For suspected hormonal under-secretion where a static test is not enough.
What is the synacthen test?
- Giving ACTH to test for adrenal insufficiency
- If an individual fails to respond to a stimulation test then gland failure is diagnosed
What is the insulin stress test?
- take 3 mL blood in plain tubes for GH, cortisol and 1 mL in fluoride tube for glucose and inject insulin iv.
- take 3 mL blood in plain tubes for GH, cortisol and 1 mL in fluoride tube for glucose.
Adequate hypoglycaemia ( 400 nmol/L may only need steroid cover for major illnesses or stresses.
- An adequate GH response occurs with an absolute response > 20 mU/L (7µg/L).
- There will be a rise of less than 170 nmol/L above the fluctuations of basal levels of cortisol.
What is the glucagon stimulation test?
0 min - take 2 mL blood into plain tube for cortisol & GH
immediately give Glucagon intra-muscularly.
150 min - take 2 mL blood into plain tube for cortisol & GH
180 min - take 2 mL blood into plain tube for cortisol & GH
An adequate cortisol response is defined as a rise of greater than 200 nmol/L to above 600 nmol/L.
What are suppression test used for?
- 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 kind of test would be used in the diagnosis of growth hormone oversecretion (gigantism, acromegaly)?
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.
What kind of test would be required to confirm a diagnosis of Cushing's disease (excess cortisol)?
Dexamethasone suppression test is used to confirm the failure to suppress endogenous cortisol production.
Is a static test enough to diagnose hyperthyroidism?
Thyroid blood test:
- Raised thyroid hormone
- Suppressed TSH
What tests may be used in the diagnosis of growth hormone deficiency?
- Glucagon stimulation test
- Insulin stress test