The hypothalamus and pituitary Flashcards
How are the hypothalamus and the pituitary connected?
The pituitary stalk
What structure comes into close contact with the pituitary that can cause vision changes? Which vision changes are these?
The optic nerves in the optic chiasm
Pressure on these can cause bitemporal hemianopnea
Where does the pituitary gland sit?
In the pituitary fossa of the sphenoid bone (sella turcica).
How is the pituitary divided?
Into anterior adenohypophysis and posterior neurohypophysis
What synthesises posterior pituitary hormones?
Supraoptic and paraventricular nuclei in the hypothalamus.
Name the 5 releasing hormones from the hypothalamus
Growth hormone releasing hormone Prolactin releasing hormone Thyrotropin releasing hormone Corticotrophin releasing hormone Gonadotrophin releasing hormone
Name the 2 inhibitory hormones from the hypothalamus
Somatostatin
Dopamine
What does somatostatin do?
Suppresses release of growth hormone
What do all hypothalamic hormones have in common (other than dopamine)?
They are all peptides
Dopamine is an amine
Name the 6 hormones released from the anterior pituitary ?
Growth hormone Prolactin Lutinising hormone Follicle stimulating hormone Adrenocorticotrophic hormone Thyroid stimulating hormone
Name the 2 hormones released by the posterior pituitary
Oxytocin
Antidiuretic hormone
What effect does growth hormone have on the body?
It increases plasma glucose levels Increases protein synthesis Decreases fat storage Increases bone growth Increases soft tissue growth
How does growth hormone increase plasma glucose levels
By increasing liver gluconeogenesis and decreasing glucose uptake in cells.
What is IGF-1? And what does it do?
Produced by the liver in response to growth hormone.
Acts on the muscle to increase protein synthesis, increases soft tissue and bone growth.
Describe the symptoms and signs of excess growth hormone
Increase in hand and foot size Increased gap between the teeth Increased sweating (especially at night) Prominent supraorbital ridge Increase in jaw size Increase in tongue size Joint pain, lethargy, pain and tingling sensations Tongue and soft tissue enlargement may cause the patient to start to snore Polydipsia and polyuria
Why do patients with excess growth hormone get polyuria and polydipsia
The increase in glucose in the blood means that they can develop diabetes. The insulin at first accounts for it- however after a while the receptors become desensitised and type 2 diabetes ensues.
What are the complications of excess growth hormone?
Type 2 diabetes
High bp- increase in free fatty acids means patient is at higher risk of atherosclerosis
Carpal tunnel syndrome due to increase in growth of soft tissues.
What is the most likely cause of hyper secretion of growth hormone?
Pituitary adenoma
What is acromegaly?
Hypersecretion of growth hormone from the pituitary gland.
Could be due to a micro adenoma <1cm or a macro adenoma >1cm
What is gigantism?
Hypersecretion of growth hormone in children. In childhood- the epiphyseal growth plates haven’t fused yet so excess growth hormone release causes accelerated growth of long bones.
Why can’t gigantism occur in adults?
This can’t occur in adults due to the epiphyseal growth plates already being fused.
Symptoms of a pituitary tumour
Can cause local symptoms as well as those produced from excess release of hormone.
Headache
Bitemporal hemianopia
Hormone release- in 1/3rd of people it also causes hypersecretion of prolactin.
Suppress normal pituitary function- hypopituitism
Investigations into acromegaly
Oral glucose tolerance test IGF-1 test Visual field exam MRI Pituitary function tests Look at old photos and compare
Oral glucose tolerance test
Growth hormone causes an increase in plasma glucose levels. Therefore when plasma glucose levels are high- growth hormone becomes suppressed. This doesn’t happen in acromegaly- so by giving oral glucose at 9am and testing the patients growth hormone levels every half an hour for two hours you can see whether the growth hormone becomes suppressed.
Normal levels <1ug/L
Acromegaly levels>1ug/L
IGF-1 test
Gives an idea of the mean growth hormone secretion in the past 24 hours.
Normal levels of this and normal levels of growth hormone can rule out acromegaly.
What benefits come from doing an MRI on a patient with suspected acromegaly?
You can assess whether it is a micro adenoma or macro adenoma.
Why would you look at pituitary function tests in a patient with suspected acromegaly?
Other pituitary hormones may be suppressed because of the tumour.
Treatment of acromegaly
Trans-sphenoidal surgery
Radiotherapy
Medical therapy
Advantages of surgery
Generally first line treatment
Can cause remission in many cases
Advantages and disadvantages of radiotherapy
Advantage- success rate at 25% after 3 years
Can be used on its own or as add on therapy to surgery
Disadvantages- treatment only prevents growth of the tumour- may still get local symptoms
Also takes a LONG time- up to 10 years.
Patient may also suffer from hypopituitism as a result.
Name the medical therapies and describe them
Dopamine agonists- used to suppress the secretion of prolactin
Somatostatin receptor agonists- increase levels of somatostatin to deal with increased levels of growth hormone. Called octreotide or lanreotide
Growth hormone antagonists- act on growth hormone receptors around the body to de-sensitise them. Called Pegvisomant
