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169 Cards in this Set
- Front
- Back
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Glycoprotein hormones of the adenohypophysis
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TSH, LH, and FSH
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Large polypeptide hormones of the adenohypophysis
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hGH and PRL
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Small peptide hormones of the adenohypophysis
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ACTH and melanocyte stimulating hormone (alpha-MSH)
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Th eglycoprotein pituitary hormones share
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TSH, LH and FSH are composed of two non-covalently-linked alpha dn dbeta subunits. The alpha subuniit is homologous with these and human chorionic gonadotropin
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What conferse biologicic and imunologic propterities to TSH, LH and FSH?
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beta subunits
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in glycoprotein pituitary hormones how are the subunits synthesized
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separately and are united before carbohydrate groups are attached.
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is the B subunit of glycoproteins related evolutionarily?
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yes It appears so b/c it is still closely related but specific
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Action of TSH
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1. Maintenance of thyroid size and vascularity 2. effects on height and activity of the follicular epithelium of the thyroid 3. control of the amount of thyroid colloid 4. effects on almost all reactions in thyroid hormone (thyroxine) biosyntheis) 5. simularion of thyroxine secretion
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what effects of TSH are mediated via an increase ni cAMP levels?
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3 Control of the amount of thyroid colloid, 4 effects on reaction in thyroid hormone (thyroxine) biosyntheis and 5 stimulation of thyroxine sectretion
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What secretes TRH?
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Hypothalamus neuroendocrine cell
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Where does TRH act upone?
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Thyrotroph's in the Adenohypophysis
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What secretes TSH?
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Thyrotorph's in response to TRH
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What inhibits TSH sectretion?
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T4
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What is the target of TSH?
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Epithelial follicular cells
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What do epithelial follicular cells release?
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t4
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What decreases TRH secretion?
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T4
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What is the aciton of t4
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decreases TSH secretion from thyrotroph and TRH secretion from the neuroendocrine cell in hypothalamus.
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Tests of TSH secretion
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Measure TSH directly or TRH stimulation tests
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What does a response to TRH indicate?
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Primary hypothalamic defect ast he cause of the hypothyroidism
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Consequence of hypersecretion of TSH
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not the usual cause for hyperhtyroidism but may cause an enlarged gland
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hyposecretion of TSH
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hypopituitarism, Isolated TSH deficiency is rare, the TRH test aids in diagnosis
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Hx of cold intolerance, constipation, tiredness, weakness and slowing of mental processes with an inability to concentrate. Physical exam shows bradycardia, hypothermia, prolonged relaxation of DTR's
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Hypothyroidism
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In males LH
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is responsible for differentiation and funciton of testosteron producing Leydig (interstitial) cells of the testis
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Leydig cells
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interstitial testosterone producing cells of the testis
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In femalse LH
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acts on the theca and interstitial cells of the ovary causing differntiation and steroid production
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What acts on mature granulosa cells controlling the vital process of ovulation and corpus luteum formation?
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LH
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In the theca cells of the ovary and leydig cells what specifically does LH do
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stimulates cholesterol side-chain cleavage and therefore androgen formation
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What stimulates progesterone formation by the corpus luteum
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LH
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What mediates LH action
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adenylate cyclase and cAMP
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What controls LH secretion
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GnRH in hypothalmus
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Which has greater secretory bursts LH or FSH
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LH
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What inhibits LH secretion
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Testosterone in men, progesterone in women
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What promotes LH secretion
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Low levels of estrogen in the preovulatory ovary
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Inhibins and Activins
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secreted by the granulosa cell, act on anterior pituitary. Inhibins inhibit LH secretion, activins promote
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What acts on both the anterior pituitary and the hypothalamus to regulate LH sectretion?
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Estrogens and progestins, Estrogens also act on the CNS
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FSH action in men
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acts primarily on the sertoli cells of the testis, working in concert with LH and testosterone to promote the development of the germinal epithelium and spermatogenesis
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In femalse FSH
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stimulates the primordial ovarian follicle to devlope causing proliferation and maturation of gransulosa cells.
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When do the granulosa cells of women become responsive to LH
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under the influence of FSH and estrogen
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Ho are estrogens formed
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via aromatization of androgens
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FSH acts mainly through which pathway
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activation of adenylate cyclase
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What brings about synthesis of addrogen binding protein and where?
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FSH activates synthesis, and it also stimulates aromatase activity in the sertoli cells of the testis
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what is the major source of inhibin in the testis
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sertoli cell
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what causes an imbalance in fsh and lh secretion, why should they be the same?
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GnRh stimulates FSH and LH so they should be the same, but inhibins regulates FSH
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Is gonadal steroid feedback positive or negative for FSH secretion
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either
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what is hGH similar to?
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Prolactin and human placental lactogen (chorionic somatommamotropin; hCS) in a few actions and in primary amino acid sequence
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hormones homologous to growth hormone
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PvGH and HCS1 and HCS2
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action of pvGH
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allows maternal metabolic adaptation to pregnancy, implicated in placental development via an autocrine or paracrine mechanism
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hCS1 and hCS@ actions
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placental lactogens that have affindity for the GH receptor that is 100 to 10000 fold less than GH of pvGH, principaly lactogenic
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what does the pitiuitary hGH gene give rise to?
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two alternatively spliced products that give rise the the 22kda GH whih is more abundant and the less abundant 20kDA GH with similar biologic activity
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where is hGH's prepro hormone synthesized
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rough er
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where is hGH's pro-hormone synthesized
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golgi
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when does differentiation between different types of hGH take place
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at splicing of intro/exon
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what type of growth hormones are active in man?
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only primate, although human GH is active in many animals
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what is the action of hGH?
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cause syntheis and release of insulin like growth factor (IGF-1) aka somatomedin C
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what is IGF-1?
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a growth promoting peptide with 3 disulfide bonds that acts directly on cartilage to promote bone grown, to increase protein synthesis and the synthesis of chondroitin sulfate
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what is GH's effect on stem cell differentiation
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it may stimulate the expression of IGF-1 which will in turn stimulate replication of that cell
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what is the action of growth hormone in adipose tissue?
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lipolysis
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since hGH causes lyposis, does it cause lipogenesis?
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yes it can cause lipogenesis b/c IGF-1 has insulin like effects stimlutating lipogenesis and increased glucose uptake by adipocytes
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can hGH function as an insulin antagonist?
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yes, and in acromegaly with high concentrations of hGH it can cause overt diabetes mellitus
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when are the largest and most protracted bursts of secretion of hGH?
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`within 2 hours of the onset of sleep
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does exercise increase GH secretion?
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yes
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what is the mediator of growht hormone
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GHRH aka somatocrinin
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where is GHRH secreted
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small neurons in arcuate nucleus
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how does GHRH act on somatotroph's
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cAMP PKA and entry of Ca2+
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what is the inhibitor of GH?
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somatostatin
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where is somatostatin synthesized
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paraventricular region of hypothalamus
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is the response to GHRH rapid or slow?
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rapid, in man GHRH is highly active and rapid
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IGF-1 is
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the mediator of growth hormone's action on the growth of cartilage
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IGF-1 regulator actions
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1 stimulates somatostatin secretion from periventricular nuclei, 2 inhibits GHRH secretion from the arcuate nucleus in the hypothalamus, 3 directly inhibits growth hormone sectiron by somatotrophs of the adenohypohysis
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In hypoglycemia GH secretion is
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increased
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where is the glucoreceptor that controls gh sectretion
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probably ventromedial nucleus
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do high protein meals or amino acids stimulate GH?
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yes
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do dopamine, NI and serotonin stimulate GH?
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yes even those these have little direct effect on the pituitary, must be through influencing GHRH from hypothalamus
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does GH inhitit GH secretion
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appears so
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Tests of Growth horomone secretion
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radio immuno assays of GH in plasma who are observed with basal and stimulatory conditions. The stimulatory conditions are l-dopa, insulin-induced hypoglycemia or arginine infusion and this is especially important in the diagnosis of impaired secretion of growth horomone as a cause of short stature
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hypersectrion of growth hormone in a child
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gigantism
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hypersecretion of growth hormone in a mature adult
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acromegaly
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what is the most common cause of hypersecretion of growth hormone
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acidophilic or "chromophobe" adenoma
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Why does acrogmegaly occur and not gigantism
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b/c after puberty significant linear growth of bones is no longer possible but marked periosteal overgrowth can lead to widening ofm any bones especially in the hands, feet an dmandible, also enlargment of abdominal viscera occurs
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how many pts with acromegaly develop DM?
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25%
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L-dopa in acromegaly
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for some reason causes a fall in GH secretion
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Hyposecretion of growth hormone
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causes hypopituitary dwarfism, although this is not the leading cuase of short stature. Usually in GH deficiency, other pituitary hormones may also be deficient especially ACTH and gonadotropins.
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Prolactin action
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lactogenic hormone promoting initiation of milk production of alveolar cells. PRL is also the primary homone responsible for maintaining milk production after it has been initiated
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Oxytocin action
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galactokinetitc hormone promoting contraction of myoepithelial cells and thus milk ejection
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How is prolaction secreted (timeframe)
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in bursts throughout the day and night with an increase occuring about an hour after the onset of sleep
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when is there the most dramatic increase in PRL secretion?
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pregnancy by the 8th week it's evident
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what causes the secretion of prl
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the increased estrogens associated with pregnancy cause hyperplasia of the pituitary mammotrophs and these respond after parturition with an acute release of PRL
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the control of prl sectirion by the hypothalamus is predominantly
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inhibitory
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cut pitiuitary stalk effect on PRL
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PRL secretion increases
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Transplatation of pituitiary to another body site leads to what with prolactin
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increased prolactin
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what inhibits prolactin
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DOPAMINE and also evidence for GnRH
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What are the first 12 amino acid residues in ACTH
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alpha melanocyte stimulating hormone (alpha-MSH)
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oOCTH is derived from
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proopiomelonocortin
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what is derived from proopiomelanocortin
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acth and lipotropin (LPH)
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LPH contains what
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b endorphin sequence
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N terminal region of POMC contains what
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POMC is proopiomelanocortin and its n-terminal sequence contains a gamma-MSH sequence and several biologically active peptides
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ACTH action
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stimulate secretion of glucocorticoids and androgens by the adrenal cortex.
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Other actions of ACTH
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effects sectrionof mineralocorticoids; increases the rate of cholesterol side chain cleavage increasing adrenal steroidgenesis;
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what mediatees ACTH
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an increase in cAMP
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What controls the growth of the adrenal cortex
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ACTH
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What happens to the adrenal cortex post hypophysectomy?
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it atrophies
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what is responsible for ACTH's melanotropic effects
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alpha MSH
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the secretion of ACTH is
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pulsatile (episodic) it has a pronounced circadian rhythm, driven by CRH (along with cortisol)
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circadian rhythm of ACTCH and Cortisol
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ACTH high just before waking, and afternoon, Cortisol hight in the AM, idps at noon and 4 and nighttime
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what secrestes CRH
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Neurons in PVN
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How does CRH cause release of ACTH?
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CRH binds to receptors in corticotrophs and activates adenylate cyclase leading to increased protein kinase a activity. There follows activation of L-type Ca2+ channels leading to increased CA concentration and a rapid release of ACTH
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What controls ACTH secretion
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3 factors, 1 sleep-activity cycle 2 reactions to stress 3 negative feedback of circulating glucocorticoids
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How long does an ACTH secreting burst last, what follows it
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ACTH secreting burst lasts for 10 minutes followed 10 minuts later by a rise in plasma cortisol
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Origin of ADH and Oxytocin
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both nonapeptides with a disulfide bond between two cyseins producing a ring with an arginine in the side chain hence arginine vasopressin
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what's the difference between oxt and adh?
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in the ring and one side chain
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What does each precursor of adh and OT have in common
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very large and has a characteristic nerophysin
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Prepropressophysin
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adh precursor
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preprooxyphysin
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ot precursor
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When are leader sequences removed in the synthesis of ADH?
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in the ER of cell bodies of neurons
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when does packaging into granules occur
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golgi appratus, granules are also called herring bodies
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how are granules of adh transported
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down axons by axoplasmic flow
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when does cleavage of prohormones of adh and ot occur?
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during transport to the neruohypophysis
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what do adhy storage granules contain
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both the free hormone and their corresponding neurophysin
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what triggers the released of adh?
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action potential triggers ca dependent exocytosis
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what does the release of adh and oxt from dendrites allow for
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them to function as both neurotransmitters and hormones
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what are oxt's targets?
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widespread including hypothalamus, amygdala, hippocampus, brainstem, heart, uterus and regions of the spinal cord that regulate the autonomic nervous system esp. the parasympathetic branch.
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what might be significant in austism
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oxt
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what controls adh secretion
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plasma osmolality
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what happens when osmolality is higher than 285mOsm/kg?
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there is increased ADH secretion
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ADH causes
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increased water reabsorption in the kidney and therefore and increase in plasma volume and lowering of plasma osmolality.
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ADH secrtion is increased by
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1. severe blood loss 2. nicotine 3. saline loading 4 dehydration
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ADH secretion is decreased by
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1. decrease in osmolality 2. increase in blood volume 3. ethanol 4. emotional stress 5 cold
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Primary action of ADH
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increased permeability of the distal nephron to water, in hgih doeses it can produces vasoconstriction hence AVP
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other actions of ADH
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stimulating renal mesangial cell contraction, inhibitin renin secretion, stimultatin gACTH secretion, and poossibly influencing behavior, learing and memory
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Renal actions of ADH
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ADH secretionis increased in hyperosmolar states and dramatically above 290MOsm/kg. Acts on V1 and V2 receptors, mainly through V2 with a G protein and an increase in cAMP to reabsorb water
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What is ADH's effect on permeability of the collecting ducts?
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It increases it
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In the absence of ADH waterpermeability of collectin gtubules and ducts is
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Low levels of estrogen in the preovulatory ovary
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ADH acts on collecting tubles by
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increasing cAMP which stimulates a microtubule dependent increase in the number of aqueos channels (aquaporins)
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ADH effect on urea permability
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increases
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in the presence of ADH urine flow
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decresases and urine osmolality approaches that of the medullary epithelium (about 1200 mOsm/kg).
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ADH absence and urine flow
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urine flow is increased and osmolality is decreased
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ADH and mesangial cells
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ADH increases mesangial cell contraction which lowers the filtration coefficienct of the glomerular membrane and therefore decreases the GFR which will further decrease the volume of urine flow
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At plasma osmolalities below 285mOsm/kg ADH levels are
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low
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low serum sodium with high urine sodume (>20 mM)
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increased ADH secretion
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Cardiovascular actions of ADH
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Stimulates arteriolar constriciton; smallveins are more sensitive to hcanges than large veins; skin and msucle are more sensitive;
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do large decreases in plasma volume override the plasma osmolality signal?
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yes
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is adh secretion more sensitive to osmolality or volume
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osmolality
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under normal everyday activity do you see large changes in overall bloodpressure
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no the caridovascular thershold for adh have not been reached
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avp and capillaries
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avp affects capillares decreasingnet absorption of fludi from the extracellular space increasing plasma volume
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Hypothalamic DI
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most commonly with hyopthalamic damage due to surgery or trauma. Will respond to exogenous AVP with a decrease in free water clearance
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Nephrogenic DI
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Plasma ADH levels are normal or high, but tubular insensitivity
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Psychogenic DI
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Compulsive water drinking no problem with AVP
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SIADH
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dilutional hyponatremia with a high urinary sodium
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what causes SIADH
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in 30% of patients with lung cancer, and other carcinomas at a smaller percentage. Also occurs from skull fractures,meningitis, encephalitis, pulmonary infections, PE,
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How does a PE cause SIADH
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same way a lung infection does, impedes blood return to the left atrium and activates or more apropriately inactivates the baroreceptors increasing vasopressin release
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targets of oxytocin
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breast and uterus
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Does oxytocin of maternal origin cause labor?
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no of fetal origin initiates labor, but maternal oxytocin may have several roles in labor after it's initiated
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When does the uterus become sensitive to oxytocin
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about 20 week of gestation, then there's an 80 fold increase in the number of OXT receptors, up to 200 fold during early labor
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How is maternal OXT released after labor starts?
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in bursts
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What does OXT bind to?
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Qaq-coupled receptors in the plasma membrane of uterine smooth muscle scells and breast myoepitheal cells tiggering the PLC cascade
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Effects of sucking
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1. Stimulates sensory nerves 2. neuronal input to hypothalamus inhibits DA release leading to an increase in PRL 3. Neronal input to supra optic and paraventricular nuclei of the hypothalamus tiggers release of oxytocin in the posteririo pituitary 4 in the preoptic area and arcuate nucleus the neuronal input inhibits GnRH release
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Suckling effect on arcuate nucles
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inhibits DA
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Suckling effect on supraoptic and paraventricular nuclei
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release oxytocin in the posterior pituitary
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suckling effect on GnRH
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inhibits secretion in the GnRH in the preoptic area and arcuate nucleus, inhibiting FSSH an dLH thus inhibitin the ovarian cycle
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what does the pineal gland secrete
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melatonin
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where does the pineal gland arise from
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roof of the 3rd fventricle under th eposterior end of the corpus callusum, connected to the posterior commissure and habenular commisure
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in young animals and infants the pineal gland is
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large
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is there direct nural connection to the pineal gland?
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no just sympathetic innervation via the superior cervical gangliion
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what is melatonin's precursors?
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tryptophan to 5-0h-TRP to serotonin (t-oh-tryptamin) to n--acetyle 5-oh-tryptamine to melatonin (N-acetyl-5-methoxytryptamine)
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when does melatonin synthesis occur
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during dorg perioud (low rate during daylight and hypoglythemia)
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what NT goes to Pineal
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NE from post ganglionics'
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bright lights and cancer?
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everything causes cancer
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decreased melatonin
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daytime sleepiness
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5mg daily of melatonin
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can maintain synchronization of the circadian rhythm to a 24 hour cycle in sighted persons living in conditions likely to induce a free running rhythm
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