1. Hyposecretion of anterior pituitary hormones Flashcards
(35 cards)
What is hypopituitarism?
Decreased production of all anterior pituitary hormones (panhypopituitarism) or of specific hormones
Give examples of causes of panhypopituitarism
- Congenital defects (rare)
* Gene mutations (very rare) e.g. PROP1 - transcription factor involved in development of pit. gland
In who does panhypopituitarism usually develop?
- Adults
* Presents with progressive loss of pituitary secretion
In what order does the loss of secretion usually happen in panhypopituitarism?
• Gonadotrophins (LH and FSH) • GH • Thyrotrophin • Corticotrophin (• Prolactin deficiency is uncommon)
What are the 3 main types of panhypopituitarism?
- Simmond’s Disease
- Sheehan’s Syndrome
- Pituitary Apoplexy
What are the causes of Simmond’s Disease?
• Infiltrative processes • Pituitary adenomas • Craniopharyngiomas • Cranial injury • Surgery (• Insidious onset - develops very slowly)
What are the symptoms of Simmond’s Disease?
(• Mainly due to decreased thyroidal, adrenal and gonadal function) • Secondary amenorrhoea or oligomenorrhoea • Impotence • Loss of libido • Tiredness • Waxy skin • Loss of body hair • Hypotension
Outline the development of Sheehan’s Syndrome
• Specific in women
• Develops acutely following post-partum heamorrhage which leads to pituitary infarction
- blood loss => vasoconstrictor spasm of hypophysial arteries
- ischaemia of pituitary
- necrosis of pituitary
• Very fast development
Outline the development of Pituitary Apoplexy
• Similar to Sheehan’s but not specific to women
• Intra-pituitary infarction or haemorrhage
• Rapid presentation
- especially in patients with pre-existing pituitary tumours which suddenly infarct
Why is more than one measurement needed to diagnose hypopituitarism?
- Hypothalamus mostly releases in pulses
* More than one measurement needed
What types of hormones are measured to diagnose hypopituitarism?
- Hypothalamic hormones can’t be measured
* Measure basal plasma values of pituitary or target endocrine gland hormones instead
What tests can be done to diagnose hypopituitarism?
• Stimulation (or provocation) test - find out if hormone is produced at normal level
- done using a combine function test (administration of various releasing hormones)
- hormones administered IV
- one releasing hormone if testing for a specific hypothyroidism
• Insulin-induced hypoglycaemia test for GH
A deficiency in a single adenohypophysial hormone can result in which secondary endocrine gland failures?
Deficiency of:
• Gonadotrophins - Hypogonadism
• Thyrotrophin - Hypothyroidism
• Corticotrophin - Hypoadrenocorticalism
What are the effect of a lack of Somatotrophin in children and adults?
- Children - pituitary dwarfism
* Adults - uncertain
What are causes of short stature in children?
- Genetic
- Malnutrition
- Emotional deprivation
- Endocrine disorders (e.g. lack of T3 and T4)
What are the congenital causes of GH deficiency in children?
- Deficiency of hypothalamic GHRH (largest endocrine cause)
- Mutations of GH gene
- Development abnormalities (e.g. aplasia or hypoplasia of the pituitary gland)
What are the acquired causes of GH deficiency in children?
- Tumours of the hypothalamus of pituitary
- Other nearby intracranial tumours e.g. optic nerve glioma
- Irradiation can affect somatotrophs
- Head injuries
- Infection or inflammation
- Severe psychosocial deprivation
What is growth hormone controlled by at a hypothalamic level?
- GHRH (mainly)
* Somatostatin
Which protein in the liver does growth hormone stimulate the production of?
- Insulin-like Growth Factor I (IGF I)
- Also produced by many other tissues in the body
- Mediates growth effects
What is Laron Dwarfism?
- GH receptor defect
* Therefore, low IGF I
Which people can be considered when identifying the importance of IGF I?
• Pygmies in Africa
- short stature
- have IGF I but doesn’t work normally
- lack growth that we normally associate with IGF I
What is Tertiary Hypopituitarism?
- Diminished secretion of pituitary hormones caused by…
- Specific hypothalamic hormone defects
- e.g. Gonadotrophin-releasing hormone (GnRH) deficiency
Describe 2 examples of tertiary hypopituitarism
Kallmann’s Syndrome
• Hypogonadism
• Associated with anosmia (loss of sense of smell)
• Genetic defect - neurones in embryo to produce GnRH (and develop sense of smell) don’t migrate to hypothalamus
Prader-Willi Syndrome
• Hypogonadism is one of the aspects of this disorder
• Problem at the level of the hypothalamus
What are the different GH Provocation tests
• Use IV GHRH to stimulate GH production (alternatives being used as GHRH is hard to get)
• Gold standard - Insulin-induced Hypoglycaemia
- hypoglycaemia is a potent stimulus for GH release
• Arginine (IV) - stimulates GH release
• Glucagon (IM) - usually causes hyperglycaemia, but stimulates GH release in people who lack GH (could be a direct stimulatory effect on somatotrophs)
• Exercise - e.g. 10 mins step climbing
• Measure GH before and after the tests
