4§ IntroductionThe “master gland”— controls three other endocrine glandsBetter to think of the pituitary gland as the relay center—Its function covers both endocrine target glands and nonendocrine target glands
6§ Pituitary Gland (Hypophysis) Suspended from hypothalamus by stalk (infundibulum)Location and sizehoused in sella turcica of sphenoid bone1.3 cm diameterAdenohypophysis (________ pituitary)arises from hypophyseal (Rathke’s) pouch (outgrowth of pharynx); Fig. 2.1 and xNeurohypophysis (________ pituitary)arises from brain;Magnocellular neurons– supraoptic and paraventricular nuclei; Nerve endings?17-6
13§ Hypothalamic-hypophyseal portal system--2 Advantages (of this portal system)—Almost all the blood supplied to the anterior pituitary must first drain through the __________________________Releasing/inhibiting hormones then can directly deliver to the anterior pituitary in what fashion ? ____________________________Therefore, only minute amounts of neural secretions are needed to achieve biologically effective concentrations in pituitary blood.
14Check Point Questions-- Besides hormones, give another way for intercellular communication.Give an example of a hormone. Why does your example qualify as a hormone? (hint: definition of hormone)Give an example of a hypothalamic hormone.What is the target tissue of a hypothalamic hormone secreted into the hypothalamic-hypophyseal portal system?
16§ Posterior Pituitary Hormones OT (oxytocin) and ADHproduced in hypothalamustransported by hypothalamo-hypophyseal tract to posterior lobe (stores/releases hormones)
17Hormone Actions: Posterior Lobe ADH (Antidiuretic Hormone)Target organ/tissue-- ? water retention, reduce urinealso functions as neurotransmitterOxytocinlabor contractions, lactation (milk ejection)possible role insperm transport . . .emotional bonding
18Regulation of Posterior Pituitary Posterior lobe control - neuroendocrine reflexeshormone release in response to nervous system signalssuckling infant stimulates nerve endings hypothalamus posterior lobe oxytocin milk ejectionhormone release in response to higher brain centersmilk ejection reflex can be triggered by a baby's cry
20§ Hormones secreted by anterior pituitary FSH (follicle stimulating hormone)LH (luteinizing hormone)The above two are called gonadotropinsTSH (thyroid stimulating hormone, thyrotropin)ACTH (adrenocorticotropic hormone)GH (growth hormone; somatotropin or somatotropic hormone)PRL (prolactin)Tropic (trophic) hormones-- target other endocrine glands to release their own hormones; which ones above? (Fig. x)
213 hormonal families of the anterior lobe: Table 2.1 (ALL proteins) 1.3.
22§ Glycoprotein hormone family– TSH, FSH, LH TSH– to stimulate the secretion of thyroid hormoneFSH & LH– important for the function of the testes and the ovariesFSH– growth of ovarian follicles and formation of spermLH (in women)– induce ovulation and the formation of the corpus luteum; stimulate the ovarian production of estrogen and progesteroneLH (in men)– stimulates the production of Testosterone; what cells?
23§ Glycoprotein hormone family (continued) 2 peptide subunits– alpha + betaThe three glycoprotein hormones and hCG (Human chorionic gonadotropin; a placental hormone) all share the same alpha subunit. Fig. 2.3Both subunits need to be present to be functional.Beta subunits are encoded in separate genes located on different chromosomes.
244 Glycoproteins– all of them share a common alpha subunit
25§ Growth hormone and prolactin (Fig. 2.4) Growth hormone (GH) is required for proper adult stature.Species specificity: primates for primate GHMetabolic effectsProlactin (PRL) is required for milk production in post-partum women.In men or nonlactating women-- not clear; however, evidence suggests it may has to do with the immune function.Human pracental lactogen (HPL) = human chorionic somatomammotropin
263 single-stranded peptides are similar in their structures and functions 2 GH & 3 human placental lactogen genes(lactogen)
27§ Adrenocorticotropin family (Fig. 2.5) ACTH (adrenal corticotropic hormone) regulates hormone secretion by the cortex of the adrenal glands.The gene produces ACTH is called POMC (pro-opiomelanocortin) in corticotropes and other cells by prohormone convertases.(Corticotropes) ACTH is the only one has an established physiological role in humans(melanocytes and keratinocytes)– pigmentation by MSH(Melanotrope in arcuate neurons)– food intake
28Pro-opiomelanocortin (POMC), a gene, products P. convertases1.2.3.Melanocyte-stimulating hormone (MSH)Corticotropin-like intermediate lobe peptide (CLIP)
31§ Development of the anterior pituitary Several transcription factors determine the different cellular lineages (Fig. 2.6)Corticotropes lineageGH, PRL, and TSH lineageGonadotropes lineageDisorders:Genetic absence of Pit-1 results in failure of the somatotropes, lactotropes, and thyrotropes to developAbsence of prop-1 results in deficiencies of these three hormones as well as deficiencies in gonadotropin production
33§ Regulation of anterior pituitary function Primarily by the CNS– All pituitary hormones except PRL would decline in the absence of the hypothalamusExperiment--Pituitary gland is removed and in vitro . . .By hormones produced in peripheral target glands—Example– inhibin secreted from gonadsAll anterior pituitary hormones secreted in a diurnal pattern.
38§ Thyrotropin-releasing hormone (TRH) TripeptideIs synthesized primarily in parvocellular neurons in the paraventricular nuclei of the hypothalamus, and stored in the nerve terminals in the median eminence.Function– regulate TSH secretion and thyroid function
39§ Gonadotropin releasing hormone (GnRH) A decapeptideIs synthesized primarily in the arcuate nucleus in the hypothalamus and secondary in the preoptic areaGnRH gene is also expressed in the placentaFunction– GnRH regulates FSH and LH secretionHow? Pulses of GnRH release determines the ratio of FSH and LH SecretedSecretions (Examples: Testosterone and inhibin) of the FSH/LH target organs regulate FSH/LH output
40§ Control of GH secretion By both Growth hormone releasing hormone (GHRH; from arcuate nuclei mainly); its gene is expressed in the GI tract and the pancreasand by somatostatin (Growth hormone release inhibiting hormone) (from preoptic periventricular and paraventricular nuclei); its gene is expressed in GI tract and the pancreasGhrelin (a peptide from the Arcuate Nuclei) also increase GH secretion via GHRHGhrelin is also synthesized in the stomach and is thought to signal feeding behavior
41§ Corticotropin releasing hormone (CRH) Containing 41 amino acidsSynthesized mainly in the paraventricular nuclei whose axons project to the median eminence. CRH-containing neurons in the CNS is wide distributed. What does this suggest?Also produced in the placentaCRH stimulates secretion of ACTH
42§ Dopamine and control of prolactin secretion Dopamin (an amine) is a prolactin inhibitory factor which can inhibit PRL secretionDopamine is synthesized in tuberohypophyseal neuronsPRL releasing hormone’s existence is unclear
43§ Secretion and actions of hypophysiotropic hormones (ONE to ONE) In general, the hypophysiotropic hormones affect the secretion of one or another pituitary hormone specifically; not always this wayExample: TRH increases PRL and TSH secretion; suckling at the breast increases both PRL and TSH secretionMany factors impact neurons that secrete hypophysiotropic hormones– internal and external environment(Action Mechanism on pituitary hormones)– all appear to act through G-protein
49§ Posterior Pituitary Hormones OT (oxytocin– rapid birth; mainly from paraventricular nuclei) and ADH (vasopressin– contraction of blood pressure- to _______ blood pressure; mainly from supraoptic nuclei)These two are from a single ancestral gene; both are nonapeptides and differ by only two amino acidsNeurophysins– cosecreted with AVP or oxytocin but no known hormonal actions.Fig. 2.9
50§ hormones of the neurohypophysis and their prohormone precursors.
51Hormone Actions: Posterior Lobe ADH (Antidiuretic Hormone; i.e. vasopressin)– through different G-proteinsReabsorption of water– through cAMPVascular muscular contraction– through inositol tris-phosphate/diacylglycerolOxytocinlabor contractions, lactation (milk ejection)Through a single class of G-protein– through the inositol trisphosphate/diaclglycerol