No description available.

No description available.

There is no abstract available for this thesis. / Department of Family and Consumer Sciences

The neurohormonal mechanisms underlying the regulation of extracellular osmolality are of critical physiological importance. These mechanisms act to maintain the osmolality of human plasma close to a “set-point” of about 290 milliosmoles per litre. The magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON), synthesize and secrete the neurohypophysial hormones vasopressin (VP) and oxytocin (OT). The primary hormonal regulator of osmolality is VP, which is released by the MNCs as a function of plasma osmolality and acts by controlling water reabsorption at the kidneys. MNCs decrease their volume and thus plasma membrane tension in response to acute increases in external osmolality and lack the compensatory mechanisms that limit volume changes in most cell types. This enables them to transduce changes in osmolality into changes in excitability via a mechanosensitive cation channel. It has been shown in vivo that sustained increases in plasma osmolality, however, cause marked hypertrophy of the MNCs that is part of a structural and functional adaptation that is thought to enable the MNCs to secrete large quantities of VP for prolonged periods. The mechanism of this important structural and functional adaptation of MNCs is difficult to address in an in vivo preparation and so an in vitro model of acutely isolated MNCs was used to pharmacologically assess the hypertrophy. It was observed that MNCs exposed to sustained hypertonic solutions, underwent an immediate shrinkage followed by a hypertrophy over 90 minutes and quickly recovered when reintroduced to isotonic conditions. This effect was found to depend on the size of the increase in osmolality, as smaller increases in osmolality resulted in smaller shrinkage and hypertrophy of the MNCs. Hypertrophy was shown to be independent of cell volume regulatory processes as inhibitors of the Na+-K+-Cl- cotransporter did not affect hypertrophy. Hypertrophy was also shown to be dependent on activation of phospholipase C (PLC) and protein kinase C (PKC), as adding inhibitors of these enzymes to the hypertonic solution prevented hypertrophy. Hypertrophy could occur in isotonic conditions by inducing cell depolarization, increasing intracellular calcium ([Ca2+]i) and by activating PKC, thus showing each of these processes are involved in hypertrophy. Recovery from hypertrophy depends upon dynamin-mediated endocytosis as blocking dynamin function prevented recovery. In addition, exposing the MNCs to hypotonic solution resulted in an immediate enlargement followed by a sustained decrease in cell size. Finally, exposing acutely isolated MNCs to hypertonic solution for two hours resulted in a 37% increase in the immunolabeling of the L-type Ca2+ channel CaV1.2 subunit. This increase in CaV1.2 immunolabeling does not depend on action potential firing as adding tetrodotoxin (TTX) to the hypertonic solution failed to prevent the increase. This project will help to elucidate the mechanisms underlying this interesting example of neuroendocrine adaptation and will help us to understand the regulation of body fluid balance during chronic challenges as seen in the elderly and chronically ill.

No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 68-73). Also available via the Internet.

No description available.

No description available.

We analyze output from a domain-filling forward trajectory model in order to better understand the annual cycle of water vapor entering the stratosphere. To do this, we determine the minimum water vapor saturation mixing ratio along each trajectory (the final dehydration point or FDP) and assume that the parcel carries that much water vapor into the stratosphere. In the annual average, the tropical Western Pacific, equatorial Africa and South America, and Southeast Asia are found to be the locations of the most frequent FDPs. Looking at individual seasons, we find that FDPs in the tropical western Pacific tend to occur in the summer hemisphere, with FDPs over South America and Africa occurring predominantly during the boreal winter. During boreal summer, a dehydration maximum occurs in the Asian monsoon region. In the annual average, FDP maxima occur at 99 and 84 hPa. Looking at individual seasons, we find that FDPs occur at higher altitudes (centered at 84 hPa) during boreal winter and at lower altitudes (99 hPa) during boreal summer. The annual cycle in FDP altitude combines with the annual cycle in tropical tropopause layer temperatures to generate the observed annual variations in water vapor entering the stratosphere.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The assessment of dehydration is an ever elusive golden standard, even given the plethora of hydration markers that exist to date. Many literature sources acknowledge the need for a portable device that can be used as an indicative tool for hydration. This project sought to find a solution for assessing dehydration on a micro level looking for an indication of hydration by investigating the levels of water concentration in the skin and water compartments of the body using bioelectrical impedance, stratum corneum impedance and infrared spectrometry. Two studies were conducted to evaluate the efficacy of these devices: an infield study to assess the efficacy of the devices for measuring dehydration brought on by exercise in adults and an infant study where the devices where used to assess its ability to measure dehydration in infants who have succumbed to diarrhoea. The studies showed that the devices are not applicable in measuring real time hydration in exercising subjects as sweat was a perturbing factor in the measurements. The infant study provided promising results with regards to the usage of the infrared device. It is believed that these results could spur further investigation into the field of using infrared spectrometry as a dehydration marker. Dehydration still remains to be an ever elusive standard but the importance of finding a solution to quantitatively assess hydration is a field which could benefit the general population and its importance should not be underestimated. / AFRIKAANSE OPSOMMING: Die assessering van dehidrasie is steeds 'n ontwykende goue standaard selfs gegewe die oorvloed van hidrasiemerkers wat bestaan tot op datum. Baie literatuurbronne erken egter die behoefte aan 'n draagbare toestel wat as 'n hulpmiddel kan dien vir die evaluering van die vlakke van dehidrasie. Hierdie projek streef daarna om ondersoek in te stel tot die assessering van dehidrasie op 'n mikrovlak deur die waterkonsentrasies te meet in die vel en die verskeie waterkompartemente in die liggaam via die gebruik van bio-elektriese impedansie analise, stratum corneum impedansie analise en infrarooi-spektrometrie. Twee studies is gedoen om die doeltreffendheid van die toestelle te evalueer: 'n inveldstudie wat die hidrasievlakke van volwassenes meet wat ly aan dehidrasie weens oefening en 'n studie wat dehidrasie meet in neonate wat ly aan dehidrasie weens diarree. Die studies het bewyse gelewer dat die toestelle nie effektief is met betrekking tot die meet van dehidrasie in aktiewe volwassenes nie, weens die rede dat sweet 'n verstorende faktor is. Die neonate studie het belowende resultate verskaf met betrekking tot die gebruik van die infrarooi toestel. Daar word geglo dat hierdie resultate verdere ondersoek in die veld met betrekking tot infrarooi spektrometrie as 'n hidrasie merker kan motiveer. Finale bevindinge wys dat die kwantifisering van dehidrasie steeds 'n ontwykende standaard is, maar die belangrikheid van 'n moontlike oplossing sal voordelig wees vir die wêreld se volke en moet dus nie onderskat word nie.