Week 3 Flashcards
(106 cards)
Where is the pituitary gland located?
Located at the base of the brain, just below the hypothalamus. The sphenoidal sinus is posterior to the pituitary gland, and it is in close proximity to the optic chiasm
What parts make up the pituitary gland?
Anterior and posterior parts
What hormones are secreted by the anterior pituitary, and what hypothalamic hormones stimulate their secretion?
Growth hormone (GHRH), FSH and LH (GnRH), adrenocorticotrophic hormone (CRH), TSH (TRH) and prolactin (dopamine)
What hormones are secreted by the posterior pituitary?
ADH and oxytocin
What system allows transport of hormones from the pituitary lobes into the blood?
Hypophyseal portal system
What is the posterior pituitary an extension of?
The central nervous system (neurohypophysis is a storage area for hypothalamic hormones)
What cells make hormones in the anterior pituitary?
Somatotrophs (GH), gonadotrophs (FSH/LH), corticotrophs (ACTH), thyrotrophs (TSH) and lactotrophes (prolactin)
What stimulates release of GHRH from the hypothalamus?
Stress, exercise, sleep and hypoglycaemia
What organs does GH affect?
Liver, directly, to produce IGF-1, and bone, adipose tissue and metabolism, either directly or through the action of IGF-1
How is GH production inhibited?
By negative feedback- GH inhibits GHRH secretion, and IGF-1 inhibits GH and GHRH secretion. Somatostatin released from the hypothalamus also inhibits anterior pituitary production of GH
Describe the HPA axis:
Time of day, illness and stress stimulate hypothalamus to release CRH, which stimulates anterior pituitary to secrete ACTH, stimulating cortisol and androgen production by adrenal cortex. Cortisol and androgens negatively affect production and secretion of CRH and ACTH
Describe the lactotroph axis:
Hypothalamus produces dopamine (decreases with stress), which acts on the anterior pituitary to inhibit secretion of prolactin. Oestrogen stimulates anterior pituitary production of prolactin
What is the action of prolactin?
Development of the mammary gland, and stimulation of lactation
Where are ADH and oxytocin produced?
Hypothalamic nuclei
What is oxytocin important for?
Labour and breast feeding- stimulates cervical dilatation and uterine contractions, as well as ‘let down’ reflex in mammary glands
What are the clinical disorders of the posterior pituitary?
Diabetes insipidus, and syndrome of inappropriate anti-diuretic hormone (SIADH)
What are the clinical disorders of the anterior pituitary?
Tumours (functioning or non-functioning), excess hormones (prolactin, GH, ACTH, TSH) and hypopituitarism
What does ADH action on the AVPR2 receptor cause?
Increased exocytosis of aquaporin channels (AQ2), and decreased endocytosis of AQ2, causing increased water uptake from the collecting duct
What are the clinical features of DI?
Polyuria- passage of >3 L/day of dilute urine, polydipsia, nocturia. Low urine osmolality and high plasma osmolality
What must be excluded before DI is tested for?
Hyperglycaemia and hypercalcaemia
What are the two classifications of DI aetiology?
Cranial and nephrogenic
Describe cranial DI:
Deficiency of ADH; can be idiopathic or genetic (mutation in ADH gene); more commonly caused by trauma, tumours, infections, inflammatory conditions of the posterior pituitary
Describe nephrogenic DI:
Resistance to ADH. Genetic (AVPR2 mutation), or secondary to drugs (lithium), metabolic upset, renal disease
How does the water deprivation test work?
Patients are deprived of fluid for 8 hours. Urea and electrolytes are taken every hour, and plasma and urine osmolality are measured every 2-4 hours. Synthetic ADH is then given, and urine osmolality reassessed