By I. Mason. North Georgia College and State University, the Military College of Georgia.
If amino acids exist in excess discount 120mg silvitra with mastercard, the body has no capacity or 1176 Chapter 24 | Metabolism and Nutrition mechanism for their storage purchase 120 mg silvitra; thus order 120 mg silvitra with amex, they are converted into glucose or ketones silvitra 120mg without a prescription, or they are decomposed quality silvitra 120mg. Urea Cycle The urea cycle is a set of biochemical reactions that produces urea from ammonium ions in order to prevent a toxic level of ammonium in the body. In these reactions, an amine group, or ammonium ion, from the amino acid is exchanged with a keto group on another molecule. This transamination event creates a molecule that is necessary for the Krebs cycle and an ammonium ion that enters into the urea cycle to be eliminated. Because the processing of amino acids results in the creation of metabolic intermediates, including pyruvate, acetyl CoA, acetoacyl CoA, oxaloacetate, and α-ketoglutarate, amino acids can serve as a source of energy production through the Krebs cycle (Figure 24. Treatments can include diet modification, vitamin supplementation, and gene therapy; however, damage to the central nervous system usually cannot be reversed. Because of this, levels of phenylalanine rise to toxic levels in the body, which results in damage to the central nervous system and brain. Symptoms include delayed neurological development, hyperactivity, mental retardation, seizures, skin rash, tremors, and uncontrolled movements of the arms and legs. Babies exposed to excess phenylalanine in utero may present with heart defects, physical and/or mental retardation, and microcephaly. The person must closely follow a strict diet that is low in phenylalanine to avoid symptoms and damage. Some animal products and certain starches are also high in phenylalanine, and intake of these foods should be carefully monitored. Your body processes the food you eat both to use immediately and, importantly, to store as energy for later demands. If there were no method in place to store excess energy, you would need to eat constantly in order to meet energy demands. Distinct mechanisms are in place to facilitate energy storage, and to make stored energy available during times of fasting and starvation. The Absorptive State The absorptive state, or the fed state, occurs after a meal when your body is digesting the food and absorbing the nutrients (anabolism exceeds catabolism). Digestion begins the moment you put food into your mouth, as the food is broken down into its constituent parts to be absorbed through the intestine. The digestion of carbohydrates begins in the mouth, whereas the digestion of proteins and fats begins in the stomach and small intestine. The constituent parts of these carbohydrates, fats, and proteins are transported across the intestinal wall and enter the bloodstream (sugars and amino acids) or the lymphatic system (fats). From the intestines, these systems transport them to the liver, adipose tissue, or muscle cells that will process and use, or store, the energy. Depending on the amounts and types of nutrients ingested, the absorptive state can linger for up to 4 hours. The ingestion of food and the rise of glucose concentrations in the bloodstream stimulate pancreatic beta cells to release insulin into the bloodstream, where it initiates the absorption of blood glucose by liver hepatocytes, and by adipose and muscle cells. By doing this, a concentration gradient is established where glucose levels are higher in the blood than in the cells. Insulin also stimulates the storage of glucose as glycogen in the liver and muscle cells where it can be used for later energy needs of the body. If energy is exerted shortly after eating, the dietary fats and sugars that were just ingested will be processed and used immediately for energy. If not, the excess glucose is stored as glycogen in the liver and muscle cells, or as fat in adipose tissue; excess dietary fat is also stored as triglycerides in adipose tissues. The Postabsorptive State The postabsorptive state, or the fasting state, occurs when the food has been digested, absorbed, and stored. You commonly fast overnight, but skipping meals during the day puts your body in the postabsorptive state as well. However, due to the demands of the tissues and organs, blood glucose levels must be maintained in the normal range of 80–120 mg/ dL. In response to a drop in blood glucose concentration, the hormone glucagon is released from the alpha cells of the pancreas. Glucagon acts upon the liver cells, where it inhibits the synthesis of glycogen and stimulates the breakdown of This OpenStax book is available for free at http://cnx. Gluconeogenesis will also begin in the liver to replace the glucose that has been used by the peripheral tissues.
Hair also has a sensory function due to sensory innervation by a hair root plexus surrounding the base of each hair follicle 120 mg silvitra overnight delivery. Hair is extremely sensitive to air movement or other disturbances in the environment buy generic silvitra 120 mg line, much more so than the skin surface order silvitra 120mg amex. This feature is also useful for the detection of the presence of insects or other potentially damaging substances on the skin surface generic silvitra 120mg line. Each hair root is connected to a smooth muscle called the arrector pili that contracts in response to nerve signals from the sympathetic nervous system generic silvitra 120mg with amex, making the external hair shaft “stand up. This is visible in humans as goose bumps and even more obvious in animals, such as when a frightened cat raises its fur. Of course, this is much more obvious in organisms with a heavier coat than most humans, such as dogs and cats. The first is the anagen phase, during which cells divide rapidly at the root of the hair, pushing the hair shaft up and out. The catagen phase lasts only 2 to 3 weeks, and marks a transition from the hair follicle’s active growth. The basal cells in the hair matrix then produce a new hair follicle, which pushes the old hair out as the growth cycle repeats itself. Hair loss occurs if there is more hair shed than what is replaced and can happen due to hormonal or dietary changes. Hair Color Similar to the skin, hair gets its color from the pigment melanin, produced by melanocytes in the hair papilla. Different hair color results from differences in the type of melanin, which is genetically determined. As a person ages, the melanin production decreases, and hair tends to lose its color and becomes gray and/or white. Nails The nail bed is a specialized structure of the epidermis that is found at the tips of our fingers and toes. The nail body is formed on the nail bed, and protects the tips of our fingers and toes as they are the farthest extremities and the parts of the body that experience the maximum mechanical stress (Figure 5. The nail body forms at the nail root, which has a matrix of proliferating cells from the stratum basale that enables the nail to grow continuously. The nail fold that meets the proximal end of the nail body forms the nail cuticle, also called the eponychium. The nail bed is rich in blood vessels, making it appear pink, except at the base, where a thick layer of epithelium over the nail matrix forms a crescent-shaped region called the lunula (the “little moon”). Sweat glands develop from epidermal projections into the dermis and are classified as merocrine glands; that is, the secretions are excreted by exocytosis through a duct without affecting the cells of the gland. These glands are found all over the skin’s surface, but are especially abundant on the palms of the hand, the soles of the feet, and the forehead (Figure 5. They are coiled glands lying deep in the dermis, with the duct rising up to a pore on the skin surface, where the sweat is released. This type of sweat, released by exocytosis, is hypotonic and composed mostly of water, with some salt, antibodies, traces of metabolic waste, and dermicidin, an antimicrobial peptide. Eccrine glands are a primary component of thermoregulation in humans and thus help to maintain homeostasis. An apocrine sweat gland is usually associated with hair follicles in densely hairy areas, such as armpits and genital regions. Apocrine sweat glands are larger than eccrine sweat glands and lie deeper in the dermis, sometimes even reaching the hypodermis, with the duct normally emptying into the hair follicle. In addition to water and salts, apocrine sweat includes organic compounds that make the sweat thicker and subject to bacterial decomposition and subsequent smell. The release of this sweat is under both nervous and hormonal control, and plays a role in the poorly understood human pheromone response. Most commercial antiperspirants use an aluminum-based compound as their primary active ingredient to stop sweat. When the antiperspirant enters the sweat gland duct, the aluminum-based compounds precipitate due to a change in pH and form a physical block in the duct, which prevents sweat from coming out of the pore. Sebaceous Glands A sebaceous gland is a type of oil gland that is found all over the body and helps to lubricate and waterproof the skin and hair. They generate and excrete sebum, a mixture of lipids, onto the skin surface, thereby naturally lubricating the dry and dead layer of keratinized cells of the stratum corneum, keeping it pliable. The fatty acids of sebum also have antibacterial properties, and prevent water loss from the skin in low-humidity environments. The underlying hypodermis has important roles in storing fats, forming a “cushion” over underlying structures, and providing insulation from cold temperatures.
The distinction between phase 3 120mg silvitra fast delivery, phase 4 and phase 5 is based on an assessment of the risk of a pandemic purchase silvitra 120 mg mastercard. Various factors and their relative importance according to current scientific knowledge may be considered generic silvitra 120 mg line. Factors may include: rate of transmission buy generic silvitra 120 mg online; geographical loca- tion and spread generic 120mg silvitra with visa; severity of illness; presence of genes from human strains (if derived from an animal strain); other information from the viral genome; and/or other scientific information. Inter-Pandemic Period and Pandemic Alert Period Surveillance Surveillance has been defined as “an ongoing systematic collection, analysis, and interpretation of outcome-specific data for use in the planning, implementation, and evaluation of public health practices”, and not merely collection of data (Flahault Inter-Pandemic Period and Pandemic Alert Period 113 1998). In order to be able to detect an unusual cluster or number of cases of illness that may be due to a new influenza virus, it is essential for every country to have an early warning system for human disease. By participating in the Global Influenza Surveillance Network, a country contributes to the detection of influenza viruses with pandemic potential. During the interpandemic period and the pandemic alert period (phase 1–5), sur- veillance in all countries should target the rapid identification of the circulating strain and the early detection and reporting of the potential pandemic strain in ani- mals and humans. Countries affected by a pandemic threat should also determine how widespread the outbreak is, as well as whether or how efficiently human-to- human transmission is occurring. Activities during these periods should include: laboratory surveillance; a clinical case reporting system including reporting from hospitals; an early warning system for investigating clusters of acute respiratory disease; a basic system for animal surveillance; and collaboration with a reference laboratory to identify non-typable influenza. Activities in countries affected by animal outbreaks should also include case investigation and contact tracing, cluster investigation and health monitoring of high-risk groups. Sentinel hospital-based surveillance is crucial for the timely triggering of public health measures and laboratory investigations. A national network of hospital senti- nel surveillance should detect individuals with acute respiratory illness among hos- pitalised patients, unexplained deaths caused by acute respiratory illness, or clusters of severe acute respiratory illness in the community. Healthcare staff from sentinel hospitals should receive specific training for responding during influenza pandem- ics. Education and training needs for healthcare workers, laboratory personnel, vol- unteers, and others who may be working outside their area of competence and training, must be considered. In the interpandemic phase, all countries should have access to at least one laboratory able to offer routine influenza diagnosis, typing and subtyping, but not necessarily strain 114 Pandemic Preparedness identification. In the absence of labo- ratories able to offer routine influenza diagnosis, typing and subtyping, countries may use commercial rapid antigen detection kits. However, governments should designate resources or seek them in other countries in order to build the necessary laboratories for epidemiological surveillance. In the early stages of a pandemic, in- creased testing will be required when the diagnosis of pandemic strain influenza in patients with influenza-like illness cannot be assumed. For countries whose pandemic prepar- edness plan includes the use of antiviral drugs, laboratory facilities will need to be in place for monitoring antiviral drug resistance. Vaccines Antiviral therapy and vaccination are the only options for controlling an influenza virus infection (Yen 2005, Korsman 2006). Vaccination represents the best protec- tion against influenza (van Dalen 2005), but an appropriate vaccine cannot be de- veloped before a new virus strain emerges. Normally, it takes at least six months to develop a vaccine and manufacture it on a large scale (Flemming 2005). But even then, most countries without production facilities will have no access to vaccines during the first pandemic wave, as a result of limited global production capacity and concentration of these facilities in developed countries. Countries with production facilities should support and ensure by all means that rapid and large-scale production can take place during a pandemic. In some devel- oped nations, the government considers it to be its responsibility to provide the highest possible protection at the onset of a pandemic. For example, the Dutch gov- ernment is currently negotiating with a manufacturer to ensure that a vaccine against any future pandemic influenza strain is available in the Netherlands as soon as possible following its development (van Dalen 2005). Plans for pandemic vaccine use should include: designation of mass immunisation clinics, strategies for staffing and staff training, strategies to limit distribution to persons in the priority groups, vaccine storage capacity of the cold chain, identifi- cation of current and potential contingency depots, vaccine security (theft preven- tion) during its transport, storage and use in clinics. Antiviral Drugs Antiviral drugs include M2 inhibitors, which are ion channel blockers (amantadine and rimantadine), and the neuraminidase inhibitors (oseltamivir and zanamivir) (Hoffmann 2006b). Treatment with M2 inhibitors can cause emergence of fully pathogenic and transmissible resistant variants in at least 30 % of individuals (Hay- den 1997). After treatment with neuraminidase inhibitors, resistant variants were initially found in approximately 4 % to 8 % of children and < 1 % of adults (McKimm-Breschkin 2003, Stilianakis 2002), and were identified later in 18 % of Japanese children dur- ing treatment with oseltamivir (Kiso 2004).
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