Flashcards in Unit 6 - Introduction to Endocrinology Deck (27)
what does the fetal-placental unit secrete?
human chorionic gonadotrophin - peptide that stimulates corpus luteum to make estrogen and progesterone during early pregnancy
human plagental alctogen - peptide with GH and PRL-like actions
estrogens (mostly estriol) and progesterone
how do steroid and peptide-amine hormones differ in:
-interaction with cell membrane
-no pools (made on demand)
-diffusion thru cell membrane
-regulation of gene transcription (primarily)
-hours to days (primarily)
-binding to receptor on cell membrane
-on cell membrane
-signal transduction cascade(s) affect variety of cell processes
-seconds to minutes
what is pseudohypoparathyroidism? what can they increase risk for?
key defect is abnormality in stimulatory alpha subunit of heterotrimeric G PRO
-causes impairment of ability of PTH to regulate body Ca and P homeostasis
-low serum [Ca++] and high serum [PO3] (as if parathyroid glands removed)
-increased circulating [PTH], just can't act on target tissue
-increased risk of hypothyroidism and gonadal dysfunction
in what kind of fashion are hypothalamic and pituitary hormones released? (example with GH) what does this mean for hormonal treatment?
normally in cyclical fashion
-GH increases with strenuous exercise, and first few hours of deep sleep
-so can't give infusions all at once, but at different times with different amounts
what does the hypothalamic-pituitary axis do?
exerts central control over multiple endocrine organs
-pituitary gland (hypophysis) is highly vascularized and lies at base of brain in sella turcica
-secretion is regulated by hypothalamus via vascular (for anterior) and neural (for posterior) connections
how does the hypothalamus connect with the anterior pituitary?
adenohypophysis; receives venous blood carrying neuropeptides from hypothalamus and pituitary stalks to different cell types in gland
-axons from hypothalamic nuclei extend to median eminence to release hormones into hypophyseal portal circulation, which carry them directly to anterior pituitary to inhibit/stimulate release of different hormones (PRO or glycoPRO) into systemic blood
how does the hypothalamus connect with the posterior pituitary?
neurohypophysis; axons from hypothalamic nuclei extend to posterior pituitary, where oxytocin (from paraventricular nucleus) and vasopressin (from supraoptic nucleus) are stored until released into systemic bloodstream
-posterior pituitary gets arterial blood
-these hormones are smaller molecular mass peptides associated with neurophysins
what is release of anterior pituitary hormones controlled by?
hypothalamic releasing factors (except PRL) delivered via portal connection
-GH is under inhibitory control by somatostatin
-PRL is inhibited by dopamine
what are the releasing factors made in hypothalamus, the target cell, and hormone released by anterior pituitary?
-GHRH (inhibited by somatostatin) targets somatotrophs to release GH
-TRH targets thyrotrophs to release TSH
-CRH targets corticotrophs to release ACTH
-GnRH targets gonadotrophs to release both FSH and LH
-lactotrophs are constantly inhibited by dopamine and only are "active" during pregnancy to release prolactin
what are the targets of posterior pituitary hormones?
-AVP/ADH targets the collecting duct to increase water permeability
-OT (oxytocin) targets the uterus and breast for milk let down
what are the hormones and their target/effects of anterior pituitary?
-FSH - ovarian follicular cells to make estrogens and progestins; sertoli cells to initiate spermatogenesis
-LH - ovarian follicular cells to make estrogens and progestins; leydig cells to make testosterone
-ACTH - fasciculata and reticularis cells of adrenal cortex to make corticosteroids
-TSH - thyroid follicular cells to make thyroid hormone
-PRL - mammary glands to initiate and maintain milk production, promote breast development in puberty and pregnancy, and inhibit ovulation
-GH - multiple somatic tissues
are somatotropes and corticotropes acidophilic or basophilic?
somatotropes: acidophilic (30% of secreting cells)
corticotropes: basophilic (20% of secreting cells)
what is the kind of feedback of the endocrine system?
"closed-loop" can be simple or involve hierarchial control
-senses if it should increase or decrease activity
-"long-loop" feedback of hormones released from peripheral glands onto hypothalamic-pituitary axis
-"short-loop" feedback of anterior pituitary hormones feeding back on hypothalamus
what does it mean when cell types are "dynamic"?
their release depends on hormonal status
-lactotropes make and release PRL during pregnancy)
what makes PRL unique from other AP hormones? what happens if stalk is severed? what is its feedback loop?
under tonic inhibitory control by dopamine
-so instead of decreasing levels if pituitary stalk is severed, circulating PRL will increase
-TRH also stimulates PRL release
-short loop negative feedback by enhancing hypothalamic dopamine release
what do dopamine receptor antagonists and agonists do to PRL?
antagonists (D2 antipsychotic agents) will increase PRL (b/c decreased dopamine)
agonists (bromocriptine) inhibit PRL, and is used if have pyerprolactinemia
processing of posterior pituitary hormones
both made in cell bodies of hypothalamus
-prepropressophysin made in supraoptic nucleus
--cleaved and packaged into propressophysin
--cleaved to ADH in axon to posterior lobe of pituitary
-prepro-oxyphysin made in paraventricular nucleus
--cleaved and packaged into pro-oxyphysin
--cleaved to oxytocin in axon to posterior lobe of pituitary
both released with APs
what does oxytocin do?
-stimulates milk ejection/let-down in response to suckling
-uterine contractions during parturition in response to dilation of cervix
-secreted in response to sight, smell, sound of infant, and orgasm
what's the primary stimulation for ADH?
increased body fluid osmolarity
how does ADH regulate body fluid osmolarity?
secretion increases if increased serum osmolarity
-acts on specific cells/regions of kidney to promote water reabsorption involving a receptor V2
-contraction of vascular smooth muscle by stimulating V1 to increase total peripheral resistance
what is central diabetes insipidus?
failure of posterior pituitary to secrete ADH
-produce large volumes of dilute urine
-body fluids become concentrated
what is hypopituitarism? treatment?
inability of pituitary gland to produce hormones, or insufficiency of hypothalamic-releasing hormones
-multiple causes, and unspecific clinical symptoms
-can be life-threatening and lead to increased mortality
-patients with TBI or subarachnoid hemorrage are at high risk (may be more common reason than pituitary tumors)
-treat with hormone replacement therapy
what happens if you have corticotropin deficiency?
chronic: fatigue, pallor, anorexia, weight loss (hypoglycemia, hypotension, anemia, lymphocytosis, eosinophilia, hyponatremia)
acute: weakness, dizziness, nausea, vomiting, circulatory collapse, fever, shock
children: delayed puberty, failure to thrive
what happens if you have thyrotropin deficiency?
tiredness, cold intolerance, constipation, hair loss, dry skin, hoarseness, cognitive slowing (weight gain, bradycardia, hypotension)
children: growth retardation
what happens if you have gonadotropin deficiency?
women: amenorrhea, loss of libido, dyspareunia, infertility (osteoporosis)
men: loss of libido, impaired sexual function, mood impairment, loss of facial/scrotal/trunk hair (decreased muscle mass, osteoporosis, anemia)
children: delayed puberty
what happens if you have growth hormone deficiency/
decreased muscle mass/strength, visceral obesity, fatigue, decreased quality of life, impaired attention and memory (dyslipidemia, premature atherosclerosis)
children: growth retardation