J. Eric Jelovsek, MD
- Assistant Professor of Surgery, Associate Staff, Center of Urogynecology and
- Reconstructive Pelvic Surgery, Co-Site Director OB/GYN Residency, Department
- of Obstetrics and Gynecology, Obstetrics, Gynecology, and Women?
- Health Institute, Cleveland Clinic, Cleveland, Ohio
Nutrition including whether nutritional intake should be more closely matched to expenditure women's health exercise videos estrace 1 mg for sale. Early parenteral nutrition alone or parenteral nutrition in combination with enteral feedings is not recommended in patients who can be fed enterally womens health weight loss buy estrace master card. In patients who cannot be fed enterally menstrual wheel buy estrace 1mg low cost, parenteral nutrition alone or in combination with enteral feedings is not recommended over the first 7 days women's health magazine past issues cheap estrace 1mg otc. Monitoring of gastric residual volumes is not routinely recommended in critically ill patients with sepsis or septic shock women's health issues on thrombosis purchase estrace toronto. Only in patients with feeding intolerance or at high risk of aspiration should gastric residuals be measured and prokinetic agents considered (Rhodes 2017; McClave 2016) menstruation headache purchase estrace 1mg with visa. A small observational study used indirect calorimetry to measure the energy expenditure of patients during and after mechanical ventilation (Lee 2017). The principal finding of this study was that energy expenditure was higher during mechanical ventilation than afterward. Chemoprophylaxis should be considered for patients without a contraindication to therapy. Acute respiratory distress syndrome and higher positive end-expiratory pressure (10 vs. Another randomized clinical trial compared intravenous pantoprazole with placebo in mechanically ventilated patients (Alhazzani 2017). Gastrointestinal bleeding requiring endoscopic hemostasis, 30-day mortality, and incidence of C. A multicenter, parallel-group, blinded trial examined the effect of daily intravenous pantoprazole at a dose of 40 mg on various outcomes compared with placebo (Krag 2018). Around 20% of patients in each group had a coagulopathy, and around 80% of patients in each group required mechanical ventilation. These results did not significantly differ after adjustment for baseline characteristics. The authors concluded that pantoprazole did not significantly change patient outcomes. This been supported by several studies and reviews that show the benefit of pharmacist involvement in patient care. Of the 585 consultations performed for 130 patients, the most common consultations provided were dosing recommendations (53%) and optimizing the empiric antibiotic management (22%). Time to antibiotic administration was significantly shorter when a pharmacist was present than when a pharmacist was not present (0. A small retrospective study observed the successful selection of antimicrobial therapy before and after pharmacist intervention, time to administration of antimicrobial therapy, and time to appropriate antimicrobial administration in a cohort of patients with septic shock (Laine 2018). Results showed that the percentage of patients with successful selection of antimicrobial therapy significantly increased with pharmacist intervention from 66% to 80% (p=0. The study also showed significantly decreased time to appropriate antimicrobial therapy with pharmacist intervention in patients without initial successful selection of antimicrobial therapy. The authors concluded that pharmacist involvement can improve successful selection of antimicrobial therapy, facilitate rapid administration, and improve surrogate outcomes for mortality in septic shock. A review of pharmacist impact on various aspects of sepsis management when pharmacists were part of a multidisciplinary team ultimately showed decreased time to antibiotic administration, decreased mortality (by 4. Although not specific to pharmacy, a time-series analysis found bundle compliance before and after various interventions (Grek 2017). One such intervention was the implementation of a multidisciplinary sepsis and shock response team, which included a pharmacist. This team was called once patients were determined to have severe sepsis or septic shock and aimed to evaluate them within 15 minutes to ensure bundle compliance. The literature advocates developing and implementing multidisciplinary teams to manage complex disease states such as sepsis and septic shock. Each discipline can offer unique perspectives and benefits to patient care and outcomes. Pharmacists are a great resource in sepsis management with development of guidelines/protocols, appropriate identification/dosing, improved time to antibiotics/vasopressors, and antibiotic de-escalation. Withholding pantoprazole for stress ulcer prophylaxis in critically ill patients: a pilot randomized clinical trial and meta-analysis. Effectiveness and safety of procalcitonin evaluation for reducing mortality in adults with sepsis, severe sepsis or septic shock. Vasopressors for the treatment of septic shock: systemic review and meta-analysis. Effect of sodium selenite administration and procalcitonin-guided therapy on mortality in patients with severe sepsis and septic shock: a randomized clinical trial. Acetaminophen inhibits hemoprotein-catalyzed lipid peroxidation and attenuates rhabdomyolysis-induced renal failure. Predicting fluid responsiveness by passive leg raising: a systematic review and meta-analysis of 23 clinical trials. Because sepsis remains a major cause of morbidity and mortality and the incidence of sepsis is increasing, new literature is needed to more definitely outline best practices in this disease state. However, the new literature answers some of the clinical questions not directly addressed in the guidelines. Pharmacists continue to play a pivotal role in managing sepsis, not only by staying up to date on the literature but also by being involved in multidisciplinary teams. Efficacy and safety of procalcitonin guidance in reducing the duration of antibiotic treatment in critically ill patients: a randomised, controlled, open-label trial. Comparison of continuouswave doppler ultrasound monitor and echocardiography to assess cardiac output in intensive care patients. Enteral nutrition as stress ulcer prophylaxis in critically ill patients: a randomized controlled exploratory study. Empiric antibiotic treatment reduces mortality in severe sepsis and septic shock from the first hour: results from a guideline-based performance improvement program. Sepsis and shock response team: impact of a multidisciplinary approach to implementing Surviving Sepsis Campaign guidelines and surviving the process. Discontinuation of vasopressin before norepinephrine in the recovery phase of septic shock. Failure of chemical thromboprophylaxis in critically ill medical and surgical patients with sepsis. Effect of body weight on hemodynamic response in patients receiving fixeddose vasopressin for septic shock. Estimating ten-year trends in septic shock incidence and mortality in United States academic medical centers using clinical data. Skin necrosis after extravasation of low-dose vasopressin administered for septic shock. Effect of dexmedetomidine on mortality and ventilator-free days in patients requiring mechanical ventilation with sepsis: a randomized clinical trial. Clinical outcomes of weight-based norepinephrine dosing in underweight and morbidly obese patients: a propensitymatched analysis. Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock. Impact of pharmacist intervention on selection and timing of appropriate antimicrobial therapy in septic shock. Metabolic requirement of septic shock patients before and after liberation from mechanical ventilation. Impact of a combination antibiotic bag on compliance with Surviving Sepsis Campaign goals in emergency department patients with severe sepsis and septic shock. Early goal-directed therapy in severe sepsis and septic shock: a meta-analysis and trial sequential analysis of randomized controlled trials. Hydrocortisone, vitamin C, and thiamine for the treatment of severe sepsis and septic shock: a retrospective before-after study. Tolerability of enteral nutrition in mechanically ventilated patients with septic shock who require vasopressors. Volume overload: prevalence, risk factors, and functional outcome in survivors of septic shock. Passive leg raising for predicting fluid responsiveness: a systematic review and meta-analysis. The effect of propofol and dexmedetomidine sedation on norepinephrine requirements in septic shock patients: a crossover trial. Evaluating vasopressor discontinuation strategies in patients with septic shock on concomitant norepinephrine and vasopressin infusions. Comparative effectiveness of second vasoactive agents in septic shock refractory to norepinephrine. The effect of early goaldirected therapy for treatment of severe sepsis or septic shock: a systemic review and meta-analysis. Effect of acetaminophen on the prevention of acute kidney injury in patients with sepsis. Compliance with updated sepsis bundles to meet new sepsis core measure in a tertiary care hospital. Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock: 2016. Fluids in sepsis and septic shock group: fluid resuscitation in sepsis: a systematic review and network meta-analysis. Predictors of response to fixed-dose vasopressin in adult patients with septic shock. Hypotension risk based on vasoactive agent discontinuation order in patients in the recovery phase of septic shock. The third international consensus definitions for sepsis and septic shock (Sepsis-3). Systematic review and meta-analysis of antibiotic prophylaxis in severe acute pancreatitis. According to the Sepsis-3 guidelines, which one of the following best classifies Z. She is receiving norepinephrine at 25 mcg/ minute, which was initiated 2 hours ago. The attending physician asks for a recommendation on balanced versus unbalanced crystalloids for Z. Lactated Ringer solution is preferred to normal saline because of decreased ventilator-free days. No preference between balanced and unbalanced fluid because of no difference in clinical outcomes. Normal saline is preferred to lactated Ringer solution because of decreased hospital mortality. Another vasopressor should be added because lactate is still greater than 2 mmol/L. Norepinephrine continuous infusion can be tapered because lactate is trending downward D. The most recent lactate is less than 4 mmol/L; intravenous fluid should be changed to 5% albumin. A patient was admitted to the medical floor for a deep venous thrombosis 2 days ago. No complications or abnormal laboratory values were associated with this condition when she was admitted. Norepinephrine should be administered peripherally to avoid central line placement. Piperacillin/tazobactam and vancomycin Vitamin C, thiamine, and hydrocortisone Esmolol continuous infusion Hydrocortisone the recent literature, which one of the following is best to recommend for N. Which one of the following is best to recommend for this patient to improve heart rate and stroke volume without compromising tissue perfusion? Despite adequate fluid resuscitation, high-dose norepinephrine and fixed-dose vasopressin are not maintaining J. According to the recent literature, which one of the following is most likely to reduce J. Hydrocortisone plus fludrocortisone Methylprednisolone Hydrocortisone Dexamethasone 11. Which one of the following vasopressors is best to recommend initiating first for N. Currently, her vasoactive medications include norepinephrine 5 mcg/ minute and vasopressin 0. Sikorski Chemical and Functional Properties of Food Proteins Edited by Zdzislaw E. Sikorski Chemical and Functional Properties of Food Components, Second Edition Chemical and Functional Properties of Food Lipids Edited by Zdzislaw E. C44 2003 664-dc21 2003053186 this book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. The team of contributors to this volume presents modern developments in the field of food carbohydrates.
The causes for this mass extinction are not clear seven hills womens health center buy estrace 2 mg cheap, but the leading suspect is extended and widespread volcanic activity that led to a runaway global-warming event womens health blogs discount estrace online american express. Terrestrial tetrapod diversity took 30 million years to recover after the end-Permian extinction breast cancer mortality rate effective 2 mg estrace. The extinction event occurred just before the breakup of the supercontinent Pangaea breast cancer 8mm in size generic estrace 2 mg with amex, although recent scholarship suggests that the extinctions may have occurred more gradually throughout the Triassic menstrual vertigo generic estrace 1mg otc. The causes of the end-Cretaceous extinction event are the ones that are best understood menstrual 9gag cheap estrace online visa. It was during this extinction event about 65 million years ago that the dinosaurs, the dominant vertebrate group for millions of years, disappeared from the planet (with the exception of a theropod clade that gave rise to birds). This boundary marked the disappearance of the dinosaurs in fossils as well as many other taxa. The researchers who discovered the iridium spike interpreted it as a rapid influx of iridium from space to the atmosphere (in the form of a large asteroid) rather than a slowing in the deposition of sediments during that period. It was a radical explanation, but the report of an appropriately aged and sized impact crater in 1991 made the hypothesis more believable. Recovery times for biodiversity after the endCretaceous extinction are shorter, in geological time, than for the end-Permian extinction, on the order of 10 million years. The Pleistocene Extinction the Pleistocene Extinction is one of the lesser extinctions, and a recent one. It is well known that the North American, and to some degree Eurasian, megafauna, or large animals, disappeared toward the end of the last glaciation period. In North America, the losses were quite dramatic and included the woolly mammoths (last dated about 4,000 years ago in an isolated population), mastodon, giant beavers, giant ground sloths, saber-toothed cats, and the North American camel, just to name a few. The possibility that the rapid extinction of these large animals was caused by over-hunting was first suggested in the 1900s. It seems likely that over-hunting caused many pre-written history extinctions in many regions of the world. In general, the timing of the Pleistocene extinctions correlated with the arrival of humans and not with climate-change events, which is the main competing hypothesis for these extinctions. The extinctions began in Australia about 40,000 1406 Chapter 47 Conservation Biology and Biodiversity to 50,000 years ago, just after the arrival of humans in the area: a marsupial lion, a giant one-ton wombat, and several giant kangaroo species disappeared. Finally, on many remote oceanic islands, the extinctions of many species occurred coincident with human arrivals. Not all of the islands had large animals, but when there were large animals, they were lost. Madagascar was colonized about 2,000 years ago and the large mammals that lived there became extinct. Eurasia and Africa do not show this pattern, but they also did not experience a recent arrival of humans. Humans arrived in Eurasia hundreds of thousands of years ago after the origin of the species in Africa. It seems clear that even if climate played a role, in most cases human hunting precipitated the extinctions. Present-Time Extinctions the sixth, or Holocene, mass extinction appears to have begun earlier than previously believed and has mostly to do with the activities of Homo sapiens. Since the beginning of the Holocene period, there are numerous recent extinctions of individual species that are recorded in human writings. Most of these are coincident with the expansion of the European colonies since the 1500s. It was hunted for its meat by sailors and was easy prey because the dodo, which did not evolve with humans, would approach people without fear. Introduced pigs, rats, and dogs brought to the island by European ships also killed dodo young and eggs. This species had once darkened the skies of North America during its migrations, but it was hunted and suffered from habitat loss through the clearing of forests for farmland. This species was once common in the eastern United States, but it suffered from habitat loss. The species was also hunted because it ate orchard fruit when its native foods were destroyed to make way for farmland. The Japanese sea lion, which inhabited a broad area around Japan and the coast of Korea, became extinct in the 1950s due to fishermen. The Caribbean monk seal was distributed throughout the Caribbean Sea but was driven to extinction via hunting by 1952. Estimates of Present-Time Extinction Rates Estimates of extinction rates are hampered by the fact that most extinctions are probably happening without observation. The extinction of a bird or mammal is likely to be noticed by humans, especially if it has been hunted or used in some other way. But there are many organisms that are of less interest to humans (not necessarily of less value) and many that are undescribed. For example, assuming there are about ten million species in existence, the expectation is that ten species would become extinct each year (each year represents ten million species per year). One contemporary extinction rate estimate uses the extinctions in the written record since the year 1500. First, many species would not have been described until much later in the time period, so their loss would have gone unnoticed. Second, the number of recently extinct species is increasing because extinct species now are being described from skeletal remains. And third, some species are probably already extinct even though conservationists are reluctant to name them as such. A second approach to estimating present-time extinction rates is to correlate species loss with habitat loss by measuring forest-area loss and understanding species-area relationships. The species-area relationship is the rate at which new species are seen when the area surveyed is increased. Studies have shown that the number of species present increases as the size of the island increases. Turning this relationship around, if the habitat area is reduced, the number of species living there will also decline. Estimates of extinction rates based on habitat loss and species-area relationships have suggested that with about 90 percent habitat loss an expected 50 percent of species would become extinct. Species-area estimates have led to species extinction rate calculations of about 1000 E/ this OpenStax book is available for free at cnx. In general, actual observations do not show this amount of loss and suggestions have been made that there is a delay in extinction. Recent work has also called into question the applicability of the species-area relationship when estimating the loss of species. This work argues that the species-area relationship leads to an overestimate of extinction rates. When biodiversity loss is thought of as the extinction of the passenger pigeon, the dodo bird, and even the woolly mammoth, the loss may appear to be an emotional one. From the perspective of evolution and ecology, the loss of a particular individual species is unimportant (however, the loss of a keystone species can lead to ecological disaster). But the accelerated extinction rate means the loss of tens of thousands of species within our lifetimes, and it is likely to have dramatic effects on human welfare through the collapse of ecosystems and in added costs to maintain food production, clean air and water, and human health. Agriculture began after early hunter-gatherer societies first settled in one place and heavily modified their immediate environment. This cultural transition has made it difficult for humans to recognize their dependence on undomesticated living things on the planet. Biologists recognize the human species is embedded in ecosystems and is dependent on them, 1408 Chapter 47 Conservation Biology and Biodiversity just as every other species on the planet is dependent. Technology smoothes out the extremes of existence, but ultimately the human species cannot exist without its ecosystem. Human Health Contemporary societies that live close to the land often have a broad knowledge of the medicinal uses of plants growing in their area. Most plants produce secondary plant compounds, which are toxins used to protect the plant from insects and other animals that eat them, but some of which also work as medication. For centuries in Europe, older knowledge about the medical uses of plants was compiled in herbals-books that identified plants and their uses. Humans are not the only species to use plants for medicinal reasons: the great apes, orangutans, chimpanzees, bonobos, and gorillas have all been observed self-medicating with plants. Modern pharmaceutical science also recognizes the importance of these plant compounds. Examples of significant medicines derived from plant compounds include aspirin, codeine, digoxin, atropine, and vincristine (Figure 47. It is estimated that, at one time, 25 percent of modern drugs contained at least one plant extract. That number has probably decreased to about 10 percent as natural plant ingredients are replaced by synthetic versions. Antibiotics, which are responsible for extraordinary improvements in health and lifespans in developed countries, are compounds largely derived from fungi and bacteria. Among other uses, it is a source of vincristine, a drug used in the treatment of lymphomas. Another five drugs are undergoing clinical trials, and at least six drugs are being used in other countries. Other toxins under investigation come from mammals, snakes, lizards, various amphibians, fish, snails, octopuses, and scorpions. Pharmaceutical companies are actively looking for new compounds synthesized by living organisms that can function as medicine. It is estimated that 1/3 of pharmaceutical research and development is spent on natural compounds and that about 35 percent of new drugs brought to market between 1981 and 2002 were from natural compounds. The opportunities for new medications will be reduced in direct proportion to the disappearance of species. Agricultural Diversity Since the beginning of human agriculture more than 10,000 years ago, human groups have been breeding and selecting crop varieties. This crop diversity matched the cultural diversity of highly subdivided populations of humans. For example, potatoes were domesticated beginning around 7,000 years ago in the central Andes of Peru and Bolivia. The potatoes grown in that region belong to seven species and the number of varieties likely is in the thousands. Each variety has been bred to thrive at particular elevations and soil and climate conditions. The diversity is driven by the diverse demands of the topography, the limited movement of people, and the demands created by crop rotation for different varieties that will do well in different fields. Every plant, animal, and fungus that has been cultivated by humans has been bred from original wild ancestor species into diverse varieties arising from the demands for food value, adaptation to growing conditions, and resistance to pests. The potato demonstrates a well-known example of the risks of low crop diversity: the tragic Irish potato famine when the single variety grown in Ireland became susceptible to a potato blight, this OpenStax book is available for free at cnx. Resistance to disease is a chief benefit to maintaining crop biodiversity, and lack of diversity in contemporary crop species carries similar risks. Seed companies, which are the source of most crop varieties in developed countries, must continually breed new varieties to keep up with evolving pest organisms. These same seed companies, however, have participated in the decline of the number of varieties available as they focus on selling fewer varieties in more areas of the world. The ability to create new crop varieties relies on the diversity of varieties available and the accessibility of wild forms related to the crop plant. These wild forms are often the source of new gene variants that can be bred with existing varieties to create varieties with new attributes. Loss of wild species related to a crop will mean the loss of potential in crop improvement. Maintaining the genetic diversity of wild species related to domesticated species ensures our continued food supply. Since the 1920s, government agriculture departments have maintained seed banks of crop varieties as a way to maintain crop diversity. This system has flaws because, over time, seed banks are lost through accidents, and there is no way to replace them. If a regional seed bank stores varieties in Svalbard, losses can be replaced from Svalbard. Although some agricultural soils are rendered sterile using controversial cultivation and chemical treatments, most contain a huge diversity of organisms that maintain nutrient cycles-breaking down organic matter into nutrient compounds that crops need for growth. These organisms also maintain soil texture that affects water and oxygen dynamics in the soil that are necessary for plant growth. If farmers had to maintain arable soil using alternate means, the cost of food would be much higher than it is now. They occur within ecosystems, such as soil ecosystems, as a result of the diverse metabolic activities of the organisms living there, but they provide benefits to human food production, drinking water availability, and breathable air.
Furthermore menstrual migraine order estrace with visa, the half-lives of the proteins of these membranes vary quite widely breast cancer logo quality estrace 2 mg, some exhibiting short (hours) and others long (days) half-lives womens health retreats purchase estrace with american express. The biogenesis of membranes is thus a complex process about which much remains to be learned womens health fitness cheap estrace 1 mg on line. One indication of the complexity involved is to consider the number of posttranslational modifications that membrane proteins may be subjected to prior to attaining their mature state women's health fitness tips purchase estrace 2 mg with mastercard. No satisfactory scheme describing the assembly of any one of these membranes is available women's health clinic central coast 1 mg estrace free shipping. The transport of proteins, including membrane proteins, to various parts of the cell inside vesicles has also been described. Some disorders due to mutations in genes encoding proteins involved in intracellular membrane transport. Fusion of a vesicle with the plasma membrane preserves the orientation of any integral proteins embedded in the vesicle bilayer. After fusion, the amino terminal is on the exterior surface of the plasma membrane. Certain related conditions not listed here are also described in this publication. The majority of the disorders listed above affect lysosomal function; readers should consult a textbook of medicine for information on the clinical manifestations of these conditions. A number of other mutations affecting intracellular protein transport have been reported but are not included here. A major sorting decision is made when proteins are partitioned between cytosolic and membrane-bound polyribosomes by virtue of the absence or presence of a signal peptide. They are one class of glycoconjugate or complex carbohydrates-equivalent terms used to denote molecules containing one or more carbohydrate chains covalently linked to protein (to form glycoproteins or proteoglycans) or lipid (to form glycolipids). Many proteins of cellular membranes (Chapter 41) contain substantial amounts of carbohydrate. A major problem in cancer is metastasis, the phenomenon whereby cancer cells leave their tissue of origin (eg, the breast), migrate through the bloodstream to some distant site in the body (eg, the brain), and grow there in an unregulated manner, with catastrophic results for the affected individual. Many cancer researchers think that alterations in the structures of glycoproteins and other glycoconjugates on the surfaces of cancer cells are important in the phenomenon of metastasis. It is now established that certain oligosaccharide chains encode considerable biologic information and that this depends upon their constituent sugars, their sequences, and their linkages. For instance, mannose 6-phosphate residues target newly synthesized lysosomal enzymes to that organelle (see below). The conventional methods used to purify proteins and enzymes are also applicable to the purification of glycoproteins. Although linkage details are not stressed in this chapter, it is critical to appreciate that the precise natures of the linkages between the sugars of glycoproteins are of fundamental importance in determining the structures and functions of these molecules. Many viruses also contain glycoproteins, some of which have been much investigated, in part because they are very suitable for biosynthetic studies. Many studies have been conducted in an attempt to define the precise roles oligosaccharide chains play in the functions of glycoproteins. Method Use Periodic acid-Schiff reagent Detects glycoproteins as pink bands after electrophoretic separation. Incubation of cultured cells Leads to detection of a radiowith glycoproteins as active sugar after electrophoradioactive bands retic separation. Sepharose-lectin column chromatography To purify glycoproteins or glycopeptides that bind the particular lectin used. Mass spectrometry Provides information on molecular mass, composition, sequence, and sometimes branching of a glycan chain. Present during the biosynthesis of N-linked glycoproteins but not usually present in mature glycoproteins. Other types of sialic acid are also found, but NeuAc is the major species found in humans. The sugar attached to the polypeptide chain via Asn in N-linked glycoproteins; also found at other sites in the oligosaccharides of these proteins. Many of the glycosylation reactions involved in the biosynthesis of glycoproteins utilize these compounds (see below). The anhydro nature of the linkage between the phosphate group and the sugars is of the high-energy, high-group-transferpotential type (Chapter 10). This mechanism ensures an adequate concentration of each nucleotide sugar inside the Golgi apparatus. This procedure exposed subterminal Gal residues that were normally masked by terminal NeuAc residues. Neuraminidase-treated radioactive ceruloplasmin was found to disappear rapidly from the circulation, in contrast to the slow clearance of the untreated protein. Further studies demonstrated that liver cells contain a mammalian asialoglycoprotein receptor that recognizes the Gal moiety of many desialylated plasma proteins and leads to their endocytosis. This greatly strengthened the concept that oligosaccharide chains could contain biologic information. These enzymes act at either external (exoglycosidases) or internal (endoglycosidases) positions of oligosaccharide chains. Lectins contain at least two sugar-binding sites; proteins with a single sugar-binding site will not agglutinate cells or precipitate glycoconjugates. The specificity of a lectin is usually defined by the sugars that are best at inhibiting its ability to cause agglutination or precipitation. Lectins were first discovered in plants and microbes, but many lectins of 1 the enzymes are available from a variety of sources and are often specific for certain types of glycosidic linkages and also for their anomeric natures. F acts on both high-mannose and complex oligosaccharides, whereas H acts on the former. The number of oligosaccharide chains attached to one protein can vary from one to 30 or more, with the sugar chains ranging from one or two residues in length to much larger structures. Many proteins contain more than one type of linkage; for instance, glycophorin, an important red cell membrane glycoprotein (Chapter 52), contains both O- and N-linked oligosaccharides. The mammalian asialoglycoprotein receptor described above is an important example of an animal lectin. Much current research is centered on the roles of various animal lectins (eg, the selectins) in cell-cell interactions that occur in pathologic conditions such as inflammation and cancer metastasis (see below). Among many uses, lectins have been employed to purify specific glycoproteins, as tools for probing the glycoprotein profiles of cell surfaces, and as reagents for generating mutant cells deficient in certain enzymes involved in the biosynthesis of oligosaccharide chains. Structures of two O-linked oligosaccharides found in (A) submaxillary mucins and (B) fetuin and in the sialoglycoprotein of the membrane of human red blood cells. O-glycan chains are shown attached to the central region of the extended polypeptide chain and N-glycan chains to the carboxyl terminal region. The genes encoding the polypeptide backbones of a number of mucins derived from various tissues (eg, pancreas, small intestine, trachea and bronchi, stomach, and salivary glands) have been cloned and sequenced. These studies have revealed new information about the polypeptide backbones of mucins (size of tandem repeats, potential sites of N-glycosylation, etc) and ultimately should reveal aspects of their genetic control. The enzymes assembling O-linked chains are located in the Golgi apparatus, sequentially arranged in an assembly line with terminal reactions occurring in the trans-Golgi compartments. Secretory mucins generally have an oligomeric structure and thus often have a very high molecular mass. Intermolecular noncovalent interactions between various sugars on neighboring glycan chains contribute to gel formation. The high content of NeuAc and sulfate residues found in many mucins confers a negative charge on them. Membrane-bound mucins participate in various cell-cell interactions (eg, involving selectins; see below). The density of oligosaccharide chains makes it difficult for proteases to approach their polypeptide backbones, so that mucins are often resistant to their action. Mucins also carry cancer-specific peptide and carbohydrate epitopes (an epitope is a site on an antigen recognized by an antibody, also called an antigenic determinant). To form high-mannose chains, only the Glc residues plus certain of the peripheral Man residues are removed. To form an oligosaccharide chain of the complex type, the Glc residues and four of the Man residues are removed by glycosidases in the endoplasmic reticulum and Golgi. The phenomenon whereby the glycan chains of N-linked glycoproteins are first partially degraded and then in some cases rebuilt is referred to as oligosaccharide processing. Thus, the initial steps involved in the biosynthesis of the N-linked glycoproteins differ markedly from those involved in the biosynthesis of the O-linked glycoproteins. The former involves Dol-P-P-oligosaccharide; the latter, as described earlier, does not. The process of N-glycosylation can be broken down into two stages: (1) assembly of Dol-P-P-oligosaccharide and transfer of the oligosaccharide; and (2) processing of the oligosaccharide chain. The principal difference between this and the previous class, apart from the nature of the amino acid to which the oligosaccharide chain is attached (Asn versus Ser or Thr), concerns their biosynthesis. The oligosaccharide branches are often referred to as antennae, so that bi-, tri-, tetra-, and A. The boxed area encloses the pentasaccharide core common to all N-linked glycoproteins. Schematic diagram of the pentasaccharide core common to all N-linked glycoproteins and to which various outer chains of oligosaccharides may be attached. The phosphate in dolichol phosphate is attached to the primary alcohol group at the left-hand end of the molecule. The oligosaccharide linked to dolichol-P-P is transferred en bloc to form an N-glycosidic bond with one or more specific Asn residues of an acceptor protein emerging from the luminal surface of the membrane of the endoplasmic reticulum. The reaction is catalyzed by oligosaccharide:protein transferase, a membraneassociated enzyme complex. Glycosylation occurs at the Asn residue of an AsnX-Ser/Thr tripeptide sequence, where X is any amino acid except proline, aspartic acid, or glutamic acid. In the case of highmannose glycoproteins, the process may stop here, or up to four Man residues may also be removed. Late phase-To assemble a typical complex oligosaccharide chain, additional sugars must be added to the structure formed in reaction 7. Reactions 9, 10, and 11 involve the addition of Fuc, Gal, and NeuAc residues at the sites indicated, in reactions catalyzed by fucosyl, galactosyl, and sialyl transferases, respectively. Removal of the Glc and some of the peripheral Man residues also occurs in the endoplasmic reticulum. Vesicles containing glycoproteins appear to bud off in the endoplasmic reticulum and are transported to the cis Golgi. The thick arrows indicate various nucleotide sugars involved in the oveall scheme. Several Factors Regulate the Glycosylation of Glycoproteins It is evident that glycosylation of glycoproteins is a complex process involving a large number of enzymes. Multiple species of the other glycosyltransferases (eg, sialyltransferases) also exist. Controlling factors of the first stage of N-linked glycoprotein biosynthesis (ie, oligosaccharide assembly and transfer) include (1) the presence of suitable acceptor sites in proteins, (2) the tissue level of Dol-P, and (3) the activity of the oligosaccharide:protein transferase. These cells have often been found to synthesize different oligosaccharide chains (eg, they often exhibit greater branching) from those made in control cells. The differences in oligosaccharide chains could affect adhesive interactions between cancer cells and their normal parent tissue cells, contributing to metastasis. If a correlation could be found between the activity of particular processing enzymes and the metastatic properties of cancer cells, this could be important as it might permit synthesis of drugs to inhibit these enzymes and, secondarily, metastasis. The genes encoding many glycosyltransferases have already been cloned, and others are under study. The latter should also cast light on Some Glycan Intermediates Formed During N-Glycosylation Have Specific Functions the following are a number of specific functions of Nglycan chains that have been established or are under investigation. Calnexin is a protein present in the endoplasmic reticulum membrane that acts as a "chaperone" (Chapter 46). Factor Cell type Comment Different cell types contain different profiles of processing enzymes. Three inhibitors of enzymes involved in the glycosylation of glycoproteins and their sites of action. Previous enzyme Certain glycosyltransferases will only act on an oligosaccharide chain if it has already been acted upon by another processing enzyme. Species Same cells (eg, fibroblasts) from different species may exhibit different patterns of processing enzymes. Inhibition of glycosylation does not appear to have a consistent effect upon the secretion of glycoproteins that are normally secreted.
These signals are then sent to a computer womens health network buy estrace 1mg low cost, which has been trained to decode the signal and feed it to a tool-such as a cursor on a computer screen menstrual blood buy discount estrace 2mg on-line. The technology can require many hours of training and long periods of intense concentration for the patient; it can also require brain surgery to implant the devices menstrual tent 2mg estrace with visa. Synaptic plasticity allows for these changes women's health clinic brampton purchase estrace with a visa, which are all needed for a functioning nervous system women's health clinic toronto abortion discount estrace 2mg mastercard. These receptors are normally blocked by magnesium ions; however women's health clinic perth discount 2mg estrace fast delivery, when the postsynaptic neuron is depolarized by multiple presynaptic inputs in quick succession (either from one neuron or multiple neurons), the magnesium ions are forced out allowing Ca ions to pass into the postsynaptic cell. This makes the postsynaptic neuron less responsive to glutamate released from the presynaptic neuron. As the Latin suggests, the primary function for this thick layer is to protect the brain and spinal cord. The dura mater also contains vein-like structures that carry blood from the brain back to the heart. The last layer is the pia mater (Latin for "soft mother"), which directly contacts and covers the brain and spinal cord like plastic wrap. This swelling condition is called hydrocephalus ("water head") and can cause seizures, cognitive problems, and even death if a shunt is not inserted to remove the fluid and pressure. It includes the cerebral cortex, limbic system, basal ganglia, thalamus, hypothalamus, and cerebellum. There are three different ways that a brain can be sectioned in order to view internal structures: a sagittal section cuts the brain left to right, as shown in Figure 35. Cerebral Cortex the outermost part of the brain is a thick piece of nervous system tissue called the cerebral cortex, which is folded into hills called gyri (singular: gyrus) and valleys called sulci (singular: sulcus). The cortex is made up of two hemispheres-right and left-which are separated by a large sulcus. A thick fiber bundle called the corpus callosum (Latin: "tough body") connects the two hemispheres and allows information to be passed from one side to the other. Although there are some brain functions that are localized more to one hemisphere than the other, the functions of the two hemispheres are largely redundant. In fact, sometimes (very rarely) an entire hemisphere is removed to treat severe epilepsy. While patients do suffer some deficits following the surgery, they can have surprisingly few problems, especially when the surgery is performed on children who have very immature nervous systems. This causes a condition called split-brain, which gives insights into unique functions of the two hemispheres. This is because the visual input from the left visual field crosses and enters the right hemisphere and cannot then signal to the speech center, which generally is found in the left side of the brain. Remarkably, if a split-brain patient is asked to pick up a specific object out of a group of objects with the left hand, the patient will be able to do so but will still be unable to vocally identify it. Each cortical hemisphere contains regions called lobes that are involved in different functions. Scientists use various techniques to determine what brain areas are involved in different functions: they examine patients who have had injuries or diseases that affect specific areas and see how those areas are related to functional deficits. They also conduct animal studies where they stimulate brain areas and see if there are any behavioral changes. These techniques, and others, have given great insight into the functions of different brain regions but have also showed that any given brain area can be involved in more than one behavior or process, and any given behavior or process generally involves neurons in multiple brain areas. That being said, each hemisphere of the mammalian cerebral cortex can be broken down into four functionally and spatially defined lobes: frontal, parietal, temporal, and occipital. The frontal lobe also contains the motor cortex, which is important for planning and implementing movement. Areas within the motor cortex map to different muscle groups, and there is some organization to this map, as shown in Figure 35. For example, the neurons that control movement of the fingers are next to the neurons that control movement of the hand. Neurons in the frontal lobe also control cognitive functions like maintaining attention, speech, and decisionmaking. Studies of humans who have damaged their frontal lobes show that parts of this area are involved in personality, socialization, and assessing risk. Muscle groups that are neighbors in the body are generally controlled by neighboring regions of the motor cortex as well. For example, the neurons that control finger movement are near the neurons that control hand movement. The parietal lobe contains a somatosensory map of the body similar to the motor cortex. It is primarily involved in vision-seeing, recognizing, and identifying the visual world. The temporal lobe is located at the base of the brain by your ears and is primarily involved in processing and interpreting sounds. It also contains the hippocampus (Greek for "seahorse")-a structure that processes memory formation. His seizures went away, but he could no longer form new memories (although he could remember some facts from before his surgery and could learn new motor tasks). This increase in brain to body size ratio is especially pronounced in apes, whales, and dolphins. While this increase in overall brain size doubtlessly played a role in the evolution of complex behaviors unique to mammals, it does not tell the whole story. Scientists have found a relationship between the relatively high surface area of the cortex and the intelligence and complex social behaviors exhibited by some mammals. This increased surface area is due, in part, to increased folding of the cortical sheet (more sulci and gyri). Within mammals, increased cortical folding and surface area is correlated with complex behavior. Basal Ganglia Interconnected brain areas called the basal ganglia (or basal nuclei), shown in Figure 35. For example, when a wasp sting led to bilateral basal ganglia damage in a 25-year-old businessman, he began to spend all his days in bed and showed no interest in anything or anybody. But when he was externally stimulated-as when someone asked to play a card game with him-he was able to function normally. Interestingly, he and other similar patients do not report feeling bored or frustrated by their state. It receives sensory and motor inputs from the body and also receives feedback from the cortex. This feedback mechanism can modulate conscious awareness of sensory and motor inputs depending on the attention and arousal state of the animal. A rare genetic disorder called fatal familial insomnia causes the degeneration of thalamic neurons and glia. This disorder prevents affected patients from being able to sleep, among other symptoms, and is eventually fatal. It includes parts of the cerebral cortex located near the center of the brain, including the cingulate gyrus and the hippocampus as well as the thalamus, hypothalamus and amygdala. The hypothalamus controls the endocrine system by sending signals to the pituitary gland, a pea-sized endocrine gland that releases several different hormones that affect other glands as well as other cells. This relationship means that the hypothalamus regulates important behaviors that are controlled by these hormones. Neurons within the hypothalamus also regulate circadian rhythms, sometimes called sleep cycles. Limbic System the limbic system is a connected set of structures that regulates emotion, as well as behaviors related to fear and motivation. It plays a role in memory formation and includes parts of the thalamus and hypothalamus as well as the hippocampus. One important structure within the limbic system is a temporal lobe structure called the amygdala (Greek for "almond"), illustrated in Figure 35. The two amygdala are important both for the sensation of fear and for recognizing fearful faces. The cerebellum controls balance and aids in coordinating movement and learning new motor tasks. Motor and sensory neurons extend through the brainstem allowing for the relay of signals between the brain and spinal cord. Ascending neural pathways cross in this section of the brain allowing the left hemisphere of the cerebrum to control the right side of the body and vice versa. The brainstem controls several important functions of the body including alertness, arousal, breathing, blood pressure, digestion, heart rate, swallowing, walking, and sensory and motor information integration. Spinal Cord Connecting to the brainstem and extending down the body through the spinal column is the spinal cord, shown in Figure 35. The spinal cord is a thick bundle of nerve tissue that carries information about the body to the brain and from the brain to the body. The spinal cord is contained within the bones of the vertebrate column but is able to communicate signals to and from the body through its connections with spinal nerves (part of the peripheral nervous system). A cross-section of 1010 Chapter 35 the Nervous System the spinal cord looks like a white oval containing a gray butterfly-shape, as illustrated in Figure 35. Myelinated axons make up the "white matter" and neuron and glial cell bodies make up the "gray matter. Axons and cell bodies in the dorsal (facing the back of the animal) spinal cord convey mostly sensory information from the body to the brain. Axons and cell bodies in the ventral (facing the front of the animal) spinal cord primarily transmit signals controlling movement from the brain to the body. These reflexes are quick, unconscious movements-like automatically removing a hand from a hot object. For example, the knee reflex that a doctor tests during a routine physical is controlled by a single synapse between a sensory neuron and a motor neuron. While a reflex may only require the involvement of one or two synapses, synapses with interneurons in the spinal column transmit information to the brain to convey what happened (the knee jerked, or the hand was hot). Because the spinal cord is the information superhighway connecting the brain with the body, damage to the spinal cord can lead to paralysis. The extent of the paralysis depends on the location of the injury along the spinal cord and whether the spinal cord was completely severed. For example, if the spinal cord is damaged at the level of the neck, it can cause paralysis from the neck down, whereas damage to the spinal column further down may limit paralysis to the legs. Spinal cord injuries are notoriously difficult to treat because spinal nerves do not regenerate, although ongoing research suggests that stem cell transplants may be able to act as a bridge to reconnect severed nerves. Researchers are also looking at ways to prevent the inflammation that worsens nerve damage after injury. This cooling can prevent swelling and other processes that are thought to worsen spinal cord injuries. Autonomic responses are mediated by the sympathetic and the parasympathetic systems, which are antagonistic to one another. The sympathetic system activates the "fight or flight" response, while the parasympathetic system activates the "rest and digest" response. The parasympathetic pathway is responsible for resting the body, while the sympathetic pathway is responsible for preparing for an emergency. It controls the lungs, the heart, smooth muscle, and exocrine and endocrine glands. The autonomic nervous system controls these organs largely without conscious control; it can continuously monitor the conditions of these different systems and implement changes as needed. There are two divisions of the autonomic nervous system that often have opposing effects: the sympathetic nervous system and the parasympathetic nervous system. Sympathetic Nervous System the sympathetic nervous system is responsible for the "fight or flight" response that occurs when an animal encounters a dangerous situation. One way to remember this is to think of the surprise a person feels when encountering a snake ("snake" and "sympathetic" both begin with "s"). Examples of functions controlled by the sympathetic nervous system include an accelerated heart rate and inhibited digestion. Most preganglionic neurons in the sympathetic nervous system originate in the spinal cord, as illustrated in Figure 35. The axons of these neurons release acetylcholine on postganglionic neurons within sympathetic ganglia (the sympathetic ganglia form a chain that extends alongside the spinal cord). As anyone who has ever felt a rush before a big test, speech, or athletic event can attest, the effects of the sympathetic nervous system are quite pervasive. This is both because one preganglionic neuron synapses on multiple postganglionic neurons, amplifying the effect of the original synapse, and because the adrenal gland also releases norepinephrine (and the closely related hormone epinephrine) into the blood stream. The physiological effects of this norepinephrine release include dilating the trachea and bronchi (making it easier for the animal to breathe), increasing heart rate, and moving blood from the skin to the heart, muscles, and brain (so this OpenStax book is available for free at cnx. Parasympathetic Nervous System While the sympathetic nervous system is activated in stressful situations, the parasympathetic nervous system allows an animal to "rest and digest. Parasympathetic preganglionic neurons have cell bodies located in the brainstem and in the sacral (toward the bottom) spinal cord, as shown in Figure 35. The axons of the preganglionic neurons release acetylcholine on the postganglionic neurons, which are generally located very near the target organs. Most postganglionic neurons release acetylcholine onto target organs, although some release nitric oxide. Effects of acetylcholine release on target organs include slowing of heart rate, lowered blood pressure, and stimulation of digestion. Sensory-Somatic Nervous System the sensory-somatic nervous system is made up of cranial and spinal nerves and contains both sensory and motor neurons. Without its sensorysomatic nervous system, an animal would be unable to process any information about its environment (what it sees, feels, hears, and so on) and could not control motor movements.
Sensory photoreceptors absorb light in these particular regions of the visible light spectrum because of the quality of light available in the daylight spectrum breast cancer 98 curable purchase 2 mg estrace overnight delivery. In terrestrial habitats women's health clinic kansas city mo cheap estrace, light absorption by chlorophylls peaks in the blue and red regions of the spectrum pregnancy updates buy 2 mg estrace. As light filters through the canopy and the blue and red wavelengths are absorbed breast cancer nail decals buy 1 mg estrace fast delivery, the spectrum shifts to the farred end women's health clinic queen elizabeth gateshead purchase estrace with mastercard, shifting the plant community to those plants better adapted to respond to far-red light women's health utmb generic estrace 1 mg visa. Water absorbs red light, which makes the detection of blue light essential for algae and aquatic plants. The Phytochrome System and the Red/Far-Red Response the phytochromes are a family of chromoproteins with a linear tetrapyrrole chromophore, similar to the ringed tetrapyrrole light-absorbing head group of chlorophyll. Absorption of red or far-red light causes a massive change to the shape of the chromophore, altering the conformation and activity of the phytochrome protein to which it is bound. Pfr is the physiologically active form of the protein; therefore, exposure to red light yields physiological activity. The effect of red light is reversible by immediately shining far-red light on the sample, which converts the chromoprotein to the inactive Pr form. The active form of phytochrome (Pfr) can directly activate other molecules in the cytoplasm, or it can be trafficked to the nucleus, where it directly activates or represses specific gene expression. Once the phytochrome system evolved, plants adapted it to serve a variety of needs. Because chlorophyll absorbs strongly in the red region of the visible spectrum, but not in the far-red region, any plant in the shade of another plant on the forest floor will be exposed to red-depleted, far-red-enriched light. The preponderance of far-red light converts phytochrome in the shaded leaves to the Pr (inactive) form, slowing growth. The nearest non-shaded (or even less-shaded) areas on the forest floor have more red light; leaves exposed to these areas sense the red light, which activates the Pfr form and induces growth. In short, plant shoots use the phytochrome system to grow away from shade and towards light. Because competition for light is so fierce in a dense plant community, the evolutionary advantages of the phytochrome system are obvious. In seeds, the phytochrome system is not used to determine direction and quality of light (shaded versus unshaded). If they germinated even a centimeter under the soil surface, the seedling would never make it into the sunlight and would die. In the dark, phytochrome is in the Pr (inactive form) and the seed will not germinate; it will only germinate if exposed to light at the surface of the soil. Photoperiodism is a biological response to the timing and duration of day and night. Detection of seasonal 866 Chapter 30 Plant Form and Physiology changes is crucial to plant survival. Although temperature and light intensity influence plant growth, they are not reliable indicators of season because they may vary from one year to the next. As stated above, unfiltered sunlight is rich in red light but deficient in far-red light. Therefore, at dawn, all the phytochrome molecules in a leaf quickly convert to the active Pfr form, and remain in that form until sunset. If the night is short (as in summer), a considerable amount of Pfr may remain at sunrise. By sensing the Pr/Pfr ratio at dawn, a plant can determine the length of the day/night cycle. In addition, leaves retain that information for several days, allowing a comparison between the length of the previous night and the preceding several nights. Shorter nights indicate springtime to the plant; when the nights become longer, autumn is approaching. This information, along with sensing temperature and water availability, allows plants to determine the time of the year and adjust their physiology accordingly. Short-day (longnight) plants use this information to flower in the late summer and early fall, when nights exceed a critical length (often eight or fewer hours). Long-day (short-night) plants flower during the spring, when darkness is less than a critical length (often eight to 15 hours). Horticulturalist the word "horticulturist" comes from the Latin words for garden (hortus) and culture (cultura). This career has been revolutionized by progress made in the understanding of plant responses to environmental stimuli. Growers of crops, fruit, vegetables, and flowers were previously constrained by having to time their sowing and harvesting according to the season. Now, horticulturists can manipulate plants to increase leaf, flower, or fruit production by understanding how environmental factors affect plant growth and development. Long-day plants are irradiated with red light in winter to promote early flowering. For example, fluorescent (cool white) light high in blue wavelengths encourages leafy growth and is excellent for starting seedlings. Incandescent lamps (standard light bulbs) are rich in red light, and promote flowering in some plants. The timing of fruit ripening can be increased or delayed by applying plant hormones. Recently, considerable progress has been made in the development of plant breeds that are suited to different climates and resistant to pests and transportation damage. Both crop yield and quality have increased as a result of practical applications of the knowledge of plant responses to external stimuli and hormones. Horticulturists find employment in private and governmental laboratories, greenhouses, botanical gardens, and in the production or research fields. To prepare for a horticulture career, students take classes in botany, plant physiology, plant pathology, landscape design, and plant breeding. To complement these traditional courses, horticulture majors add studies in economics, business, computer science, and communications. The Blue Light Responses Phototropism-the directional bending of a plant toward or away from a light source-is a response to blue wavelengths of light. The aptly-named phototropins are protein-based receptors responsible for mediating the phototropic response. Like all plant photoreceptors, phototropins consist of a protein portion and a light-absorbing portion, called the chromophore. In phototropins, the chromophore is a covalently-bound molecule of flavin; hence, phototropins belong to a class of proteins called flavoproteins. Other responses under the control of phototropins are leaf opening and closing, chloroplast movement, and the opening of stomata. However, of all responses controlled by phototropins, phototropism has been studied the longest and is the best understood. In their 1880 treatise the Power of Movements in Plants, Charles Darwin and his son Francis first described phototropism as the bending of seedlings toward light. Darwin observed that light was perceived by the tip of the plant (the apical meristem), but that the response (bending) took place in a different part of the plant. They concluded that the signal had to travel from the apical meristem to the base of the plant. He cut off the tip of a seedling, covered the cut section with a layer of gelatin, and then replaced the tip. However, when impermeable mica flakes were inserted between the tip and the cut base, the seedling did not bend. A refinement of the experiment showed that the signal traveled on the shaded side of the seedling. When the mica plate was inserted on the illuminated side, the plant did bend towards the light. Therefore, the chemical signal was a growth stimulant because the phototropic response involved faster cell elongation on the shaded side than on the illuminated side. We now know that as light passes through a plant stem, it is diffracted and generates phototropin activation across the stem. Cryptochromes are another class of blue-light absorbing photoreceptors that also contain a flavin-based chromophore. Cryptochromes set the plants 24-hour activity cycle, also know as its circadian rhythem, using blue light cues. There is some evidence that cryptochromes work together with phototropins to mediate the phototropic response. Use the navigation menu in the left panel of this website openstaxcollege. Plant Responses to Gravity Whether or not they germinate in the light or in total darkness, shoots usually sprout up from the ground, and roots grow downward into the ground. A plant laid on its side in the dark will send shoots upward when given enough time. Gravitropism ensures that roots grow into the soil and that shoots grow toward sunlight. Growth of the shoot apical tip upward is called negative gravitropism, whereas growth of the roots downward is called positive gravitropism. Amyloplasts (also known as statoliths) are specialized plastids that contain starch granules and settle downward in response to gravity. A few hours later, the shoot or root will show growth in the new vertical direction. The effect slows growth on the lower side of the root, while cells develop normally on the upper side. After the shoot or root begin to grow vertically, the amyloplasts return to their normal position. Other hypotheses-involving the entire cell in the gravitropism effect-have been proposed to explain why some mutants that lack amyloplasts may still exhibit a weak gravitropic response. Plant hormones affect all aspects of plant life, from flowering to fruit setting and maturation, and from phototropism to leaf fall. They can act in their cell of origin or be transported to other portions of the plant body, with many plant responses involving the synergistic or antagonistic interaction of two or more hormones. In contrast, animal hormones are produced in specific glands and transported to a distant site for action, and they act alone. Plant hormones are a group of unrelated chemical substances that affect plant morphogenesis. In addition, other nutrients and environmental conditions can be characterized as growth factors. Auxins the term auxin is derived from the Greek word auxein, which means "to grow. They also control the differentiation of meristem into vascular tissue, and promote leaf development and arrangement. Apical dominance-the inhibition of lateral bud formation-is triggered by auxins produced in the apical meristem. Flowering, fruit setting and ripening, and inhibition of abscission (leaf falling) are other plant responses under the direct or indirect control of auxins. Auxins also act as a relay for the effects of the blue light and red/far-red responses. Commercial use of auxins is widespread in plant nurseries and for crop production. Applying synthetic auxins to tomato plants in greenhouses promotes normal fruit development. Outdoor application of auxin promotes synchronization of fruit setting and dropping to coordinate the harvesting season. Fruits such as seedless cucumbers can be induced to set fruit by treating unfertilized plant flowers with auxins. Cytokinins the effect of cytokinins was first reported when it was found that adding the liquid endosperm of coconuts to developing plant embryos in culture stimulated their growth. The stimulating growth factor was found to be cytokinin, a hormone that promotes cytokinesis (cell division). Cytokinins are most abundant in growing tissues, such as roots, embryos, and fruits, where cell division is occurring. Cytokinins are known to delay senescence in leaf tissues, promote mitosis, and stimulate differentiation of the meristem in shoots and roots. Many effects on plant development are under the influence of cytokinins, either in conjunction with auxin or another hormone. For example, apical dominance seems to result from a balance between auxins that inhibit lateral buds, and cytokinins that promote bushier growth. Seedless grapes are obtained through standard breeding methods and contain inconspicuous seeds that fail to develop. Plants adapted to temperate climates require a long period of cold temperature before seeds germinate. This mechanism protects young plants from sprouting too early during unseasonably warm weather in winter. As the hormone gradually breaks down over winter, the seed is released from dormancy and germinates when conditions are favorable in spring. Ethylene Ethylene is associated with fruit ripening, flower wilting, and leaf fall. Hundreds of years ago, when gas street lamps were installed in city streets, trees that grew close to lamp posts developed twisted, thickened trunks and shed their leaves earlier than expected. The best-known effect of the hormone, however, is the promotion of fruit ripening.
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