2. Hypersecretion of anterior pituitary hormones Flashcards
What is hyperpituitarism?
Condition where the symptoms are associated with excess production of adenohypophysial hormones
What is the most likely cause of hyperpituitarism?
Isolated pituitary tumours (adenoma)
Explain bitemporal (heteronymous) hemianopia
- Light from the left visual field hits the right part of the retina and vice versa
- At the optic chiasm, fibres from the inner (nasal) part of both retinae cross
- Therefore, all light from the left visual field is detected by the right side of the brain
- All the light from the temporal fields cross at the optic chiasma for this to happen
- A pituitary tumour could protrude out of the sella turcica and disrupt the fibres coming from the nasal parts of the retinae
- This could lead to a loss of the temporal part of the visual field - bitemporal hemianopia
An excess of what 5 types of pituitary hormones can result what conditions?
- Corticotrophin (ACTH) => Cushing’s disease
- Thyrotrophin (TSH) => Thyrotoxicosis
- Gonadotrophins (LH and FSH) => Precocious puberty in children
- Prolactin => Hyperprolactinaemia
- Somatotrophin (GH) => Gigantism, Acromegaly
What is hyperprolactinaemia?
• Excess circulating prolactin when not due to a physiological cause e.g. pregnancy or breast-feeding
• Associated with pituitary tumours - prolactinoma
- most common type - microadenomas
What happens in hypoprolactinaemia?
- Not really a problem
* Absence of prolactin doesn’t really have any serious physiological consequences
What is the effect of hyperprolactinaemia due to prolactinoma in women?
• Galactorrhoea • Decreased LH and FSH levels leading to: - secondary amenorrhoea - loss of libido - infertility
What is the effect of hyperprolactinaemia due to prolactinoma in men?
• Galactorrhoea (uncommon) • Decreased LH and FSH levels leading to: - loss of libido - impotence - infertility
What does excess somatotrophin lead to in children and adults?
- Children - gigantism
* Adults - acromegaly (growth plates of long bones have fused so height doesn’t increase, but there are other effects)
Outline the onset and development of acromegaly?
- Insidious onset
- Signs and symptoms progress gradually over many years
- If untreated, associated with increased morbidity and mortality due to cardiovascular and respiratory complications
- Increased organ size - increased demand for oxygen - strain on CVS
What parts of the body grow in acromegaly?
- Periosteal bone
- Cartilage
- Fibrous tissue
- Connective tissue
- Internal organs e.g. hepatomegaly
- Prognathism (protrusion of mandible or maxilla)
- Enlarged supraorbital ridges
- Enlarged soft tissues
What are the metabolic effects of acromegaly?
- Increased endogenous glucose production
- Decreased muscle glucose uptake
- Increased insulin production => increased insulin resistance
- Impaired glucose tolerance
- Diabetes mellitus
Apart from growth, what are the other clinical manifestations of acromegaly?
- General coarseness of features
- Hyperhidrosis (excessive sweating)
- Carpal Tunnel Syndrome - increased cartilaginous growth creating pressure on nerve in wrist
- Joint pain
- Galactorrhoea
- Menstrual abnormalities, decreased libido and impotence
- Hypertension
What test is used to test pituitary hypersecretion?
Suppression test
Describe glucose-induced suppression of growth hormone secretion
• Normally, if glucose is given, GH release is inhibited, levels decrease then a there is a sudden rise • In acromegaly: - glucose given - paradoxical rise in GH - back down and levels out
