Hypothalamic-Pituitary Relationships Flashcards
Neural portion of the pituitary is the:
Posterior pituitary (neurohypophysis)
Epithelial portion of the pituitary is the:
Anterior pituitary (adenohypophysis)
Hypophysial stalk
Connects the hypothalamus to the pituitary
Where do cancers of the pituitary extend into?
The brain and against the optic n.
Location of the SON and PVN
Cell bodies are in the hypothalamus and their axons extend into the post pit.
What neuropeptides are secreted by the post pit and which nuclei produce them?
ADH (SON)
Oxytocin (PVN)
Which hormones are secreted by the ant pit? (6)
ACTH TSH FSH LH GH Prolactin
What vasculature connects the hypothalamus to the ant pit?
Hypothalamic-hypophysial portal vessels.
What are the 2 “important implications” of the hypothalamic-hypophysial portal vessels?
It allows hypothalamic hormones to the ant pit directly and in high conc.
Hypothalamic Hs do not appear in systemic circulation in high concs.
Primary endocrine d/o
Abn H levels due to problem with peripheral endocrine gland.
Secondary endocrine d/o
Abn H levels due to problem with pituitary gland.
Tertiary endocrine d/o
Abn H levels due to problem with hypothalamus.
Which Hs are secreted by the following cell types? Corticotroph Thyrotroph Gonadotroph Somatotroph Lactotroph
C - ACTH T - TSH G - FSH and LH S - GH L - prolactin
Acromegaly
Dz caused by prolonged secretion of GH as an adult.
Develops very gradually.
Excessive growth of soft tissues, cartilage, bones, face, hands, etc.
What gene transcription is stimulated by GH?
Somatomedin C (IGF-1) in the liver
Hypo —> pituitary target —> secretion TRH CRH GnRH GHRH, somatostatin TRH, PIF
TRH —> thyrotrophs —> TSH
CRH —> corticotrophs —> ACTH
GnRH —> gonadotrophs —> LH, FSH
GHRH (+), Somatostatin (-) —> somatootrophs —> GH
TRH (+), PIF (-) —> lactotrophs —> prolactin
How is a pituitary tumor treated? (2)
Initially, it is usually via transsphenoidal approach.
If tumor is >1 cm, radiation may be considered.
What are the targets for meds of acromegaly? (2)
Lower GH levels or block effects of GH.
3 meds for acromegaly
Somatostatin analog
GH receptor antagonist
DA receptor agonist
What effect can a DA receptor agonist have on GH secretion?
It may decrease GH secretion (effective in approx 25% of pts).
In which manner is GH secreted?
In a pulsatory manner from somatotrophs.
Pathophysiology of GH deficiency
Reduced secretion of GHRH (hypothalamic dysfunction) —> decreased GH secretion.
Cannot generate somatomedins —> GH or somatomedin resistance.
Pathophysiology of excess GH
Usually due to GH-secreting pituitary adenoma.
Can lead to gigantism before puberty OR acromegaly after puberty.
What are 3 metabolic functions of GH?
- Increases blood Glc —> insulin resistance and increased blood insulin levels (diabetogenic effect).
- Increased protein synthesis and organ growth. Increases uptake of AAs —> increased DNA/RNA/protein synthesis. Mediated by IGF-1.
- Increased linear growth —> increased metabolism of chondrocytes. Mediated by IGF-1.
Effects of fasting on GH, somatomedin and insulin
Increases GH
Decreases somatomedin
Decreases insulin
How does hyperprolactinemia suppress FSH and LH?
Prolactin inhibits the hypothalamus from secreting GnRH (GnRH would act on ant pit to secrete FSH/LH).
Hormone and its function: CRH DA GHRH GnRH Prolactin Somatostatin TRH
CRH: increase ACTH, MSH DA: decrease prolactin GHRH: increase GH GnRH: increase FSH, LH Prolactin: decrease GnRH Somatostatin: decrease GH, TSH TRH: increase TSH, prolactin
What are most pituitary tumors? How do they occur?
Pituitary adenomas. Spontaneously.
Microadenoma vs macroadenoma
Microadenoma < 1 cm
Macroadenoma > 1 cm
Pituitary tumors grow at which rate?
Slowly and a benign.
Functional pituitary adenomas
Secrete active H, usually in excess
Excess of ACTH causes which disease?
Cushing’s disease
Excess in GH causes which diseases?
Acromegaly
Gigantism
Excess prolactin causes which disease?
Prolactinoma
What are some causes of hypopituitarism?
Brain damage Tumors Non-pituitary tumors Infections Infarction Autoimmune d/o Pituitary plasma/hypoplasia Genetic dz
What is Sheehan’s syndrome?
Postpartum hypopiuitarism due to necrosis of pituitary gland.
What are presenting symptoms of Sheehan syndrome?
Most w/ agalactorrhea, trouble lactating, some w/ hypothyroid.
3 triggers of ADH secretion
Low BP (baroreceptors) Decreased arterial stretch (atrial stretch receptors) Increased Osmolality (hypothalamic osmoreceptors)
Secretion of ADH is most sensitive to?
Changes in Osmolality.
MOA of ADH in renal collecting duct (4)
- ADH binds to V2
- ATP binds adenylate cyclase —> + cAMP
- Activate PKA
- Upregulate aquaporins on luminal side of membrane.
Central DI
Unable to produce ADH from damage to pituitary/hypothalamus.
Treated w/ desmopressin.
Nephrogenic DI
Kidneys are unable to respond to ADH (increased plasma ADH).
Caused by drugs or chronic disorders.
DI results in what kind of urine?
High volume urine with low Osmolality.
SIADH
Excessive ADH secretion.
Excessive water retention.
Hypoosmalality cannot inhibit ADH release.
