Hypothalamic Pituitary Axis
ADRENOCORTICOTROPIC HORMONE • ACTH-secreting corticotrope cells constitute bout 20% of the pituitary cell population. • ACTH (39 ino cids) is derived from the POMC precursor protein (266 amino cids) that also generates sever l other peptides, including β-lipotropin, β- endorphin, met-enkephalin, α-melanocyte-stimulating hormone (α-MSH), and corticotropin-like intermediate lobe protein (CLIP). • Target gland: adrenals (induces steroid production) • Secretion agonists: CRH, AVP, proiniflammatory cytokines • Secretion antagonists: glucocorticoids (negative feedback)
GROWTH HORMONE • GH-secreting somatotrope cells constitute up to 50% of the total anterior pituitary cell population. • Target organs: liver (IGF-I production), bone (growth induction), other tissues (insulin antagonism). • Secretion agonists: GHRH, Ghrelin • Secretion antagonists: Somatostatin , IGF-I – via negative feedback.
PROLACTIN • PRL is synthesized in lactotropes, which constitute about 20% of anterior pituitary cells. • Target organ: breast (induces milk production). • Weak secretion agonists: Estrogen, TRH, VIP • Secretion antagonist: Dopamine
THYROID-STIMULATING HORMONE • TSH-secreting thyrotrope cells constitute 5% of the anterior pituitary cell population. • Target gland: thyroid (induces thyroid hormone synthesis). • Secretion agonist: TRH • Secretion antagonists: T3, T4, dopamine, somatostatin, glucocorticoids.
GONADOTROPINS: FSH AND LH • Gonadotrope cells constitute about 10% of anterior pituitary cells and produce two gonadotropin hormones— LH and FSH. • Target organs: ovary - FSH induces follicle growth and estrogen production, LH induces ovulation and maintenance of corpus lutheum; testis – LH induces Leydig cell testosterone synthesis and secretion, FSH stimulates seminiferous tubule development and regulates spermatogenesis. • Secretion agonists: GnRH, Estrogen. • Secretion antagonists: Sex steroids, inhibin (negative feedback).
Diagnostic Tests Stimulation Tests • i/v L- arginine, L-Dopa, GHRH and Insulin tolerance tests for GH stimulation • ITT, CRH, AVP and Metyrapone tests for ACTH stimulation Suppression Tests • OGTT for GH supression • 1 mg Dx test • High dose Dx Test
HYPOPITUITARISM Congenital • Transcription factor defect • Pituitary dysplasia/aplasia • Primary empty sella • Septo-optic dysplasia, • Prader-Willi syndrome, • Laurence-Moon-Biedl syndrome, • Kallmann syndrome Aquired • Traumatic (surgery, radiation, head injury).
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- Winter '20
- Jane Smith
- Pituitary adenoma