8. HPA & GH Flashcards
What is the embryological origin of the posterior pituitary?
Neuroectoderm - primitive brain tissue
What is the embryological origin of the anterior pituitary?
Oral ectoderm - primitive gut tissue
Which bone does the pituitary gland sit within?
Sella turcica
Which hormones are produced from the posterior pituitary?
ADH and oxytocin
Which hypothalamic nuclei produce ADH and oxytocin?
Supraoptic and paraventricular nuclei
Hormones synthesised in the hypothalamus are stored in the ______ ________ before release into the hypophyseal portal system.
Median eminence
What type of hormones are released from the hypothalamus to the anterior pituitary?
Tropic hormones - stimulate (or inhibit) endocrine cells in the anterior pituitary
What are the 6 tropic hormones produced by the hypothalamus?
TRH PIH CRH GnRH GHRH GHIH (somatostatin)
Why is the control of prolactin secretion unusual?
It is mainly inhibitory by PIH
What is PIH?
Dopamine
What are the 6 hormones produced by the anterior pituitary in response to the tropic hormones?
TSH PRL ACTH LH FSH GH
Which tropic hormones control the release of growth hormone from the anterior pituitary?
GHRH
GHIH (somatostatin)
What type of hormone is GH?
Protein
How are does GH exert most of it’s effect indirectly?
GH stimulates skeletal muscle and liver to produce IGF’s 1 and 2.
What is a major role of GH in childhood and teenage years?
Stimulates long bone growth, once epiphyseal plate closes, stimulates width growth.
What effect do IGF’s have on bone?
Stimulate bone and cartilage growth
What role does GH and IGFs have in adults?
Maintain muscle and bone mass
Promote healing and tissue repair
Modulate metabolism and body composition
How does sleep influence GH secretion?
Surge in GH after onset of deep sleep
REM sleep decreases GH secretion.
What conditions cause a rise in GH secretion?
Stress (trauma, fever)
Exercise
Fasting
Decrease in levels of glucose and FA
What conditions cause a decrease in GH secretion?
Obesity
Increase in levels of glucose or fatty acid
How is GH secretion regulated by long loop negative feedback?
Mediated by IGFs:
- Inhibit release of GHRH and stimulate release of somatostatin from hypothalamus.
- Inhibit release of GH from anterior pituitary
How is GH secretion regulated by short loop negative feedback?
GH itself stimulates somatostatin release
What is the condition caused by GH deficiency in childhood?
Pituitary dwarfism -proportionate
How can pituitary dwarfism be treated?
GH therapy
What is the condition caused by GH excess in children?
Gigantism
What is the condition caused by GH excess in adults?
Acromegaly
What are the signs of acromegaly?
Large extremities - hands, feet, lower jaw
What is the most common cause of GH excess?
Pituitary adenoma
How does GH exert its effect on cells?
Tyrosine receptor JAK kinases
What happens when GH binds to it’s tyrosine kinase receptor?
Cross phosphorylation of JAK, phosphorylation of receptor and activation of pathways leading to transcription of IGF.
Which IGF is mainly utilised for foetal growth?
IGF 2
What response does IGF binding to target cells generate?
Cell growth (hypertrophy)
Cell number (hyperplasia)
Increase rate of protein synthesis
Increase lipolysis
How do the actions of IGF and insulin differ?
Insulins effects are mainly metabolic
IGF mainly mitogenic
There is some cross-activation across receptors, especially at hybrid receptor.
What is the hybrid receptor comprised of?
one subunit from the insulin receptor and one subunit from the IGF1 receptor, so binds to both insulin and IGF1.
Which disease results from excess growth hormone secretion occuring after puberty after the epiphyseal plates have closed?
Acromegaly
Why might a patient with a pituitary adenoma develop visual field loss?
The pituitary is in close proximity to the optic chiasm so growth of the adenoma can compress the optic nerves
Which of the following is a symptom of hyperprolactinaemia in women?
Galactorrhoea - milky secretion from breasts
Which biochemical finding would you expect in a patient with acromegaly?
Plasma IGF-1 above the normal range
What is diabetes insipidus caused by?
Lack of ADH (vasopressin)
What is a typical clinical consequence of untreated diabetes insipidus?
Hypernatraemia
What is the pattern of cortisol concentration?
Cortisol is at its highest level in the morning and lowest level at midnight.
Which type of drug can be used to treat prolactinoma?
Dopamine receptor agonist
