By I. Umul. Norfolk State University.
Fructose is taken up by the liver and phosphorylated by fructokinase to form fructose 1-phosphate purchase lexapro 10 mg otc anxiety symptoms heart pain. This molecule is either isomerized to form glucose 6-phosphate or metabo- lized by the glycolytic pathway buy 5mg lexapro anxiety symptoms face numbness. Fructose 1-phosphate is used by the glycolytic pathway more efficiently than glu- cose 6-phosphate. Galactose is an important sugar used not only to provide energy but also in the biosynthesis of glycoproteins and glycolipids. When galactose is taken up by the liver, it is phosphorylated to form galactose 1-phosphate, which then reacts with uridine diphosphate-glucose, or UDP-glucose, to form UDP-galactose and glucose 1-phosphate. The UDP-galactose can be used for glycoprotein and glycolipid biosynthesis or converted to UDP-glucose, which can then be recycled. Gluconeogenesis is the production of very low density lipoprotein; TG, triglycerides; TCA, tricar- glucose from noncarbohydrate sources such as fat, amino boxylic acid. CHAPTER 28 The Physiology of the Liver 519 cible; the lipid droplets coalesce in an aqueous medium. The human liver normally has a consider- lipoprotein particles stabilize the hydrophobic triglyceride able capacity to produce VLDLs, but in acute or chronic center of the particle. During fasting, fatty acids are mobilized from adipose Liver VLDLs are associated with an important class of tissue and are taken up by the liver. The two forms of circulating hepatocytes to provide energy via -oxidation, for the gen- apo B are B48 and B100. The human liver makes only apo eration of ketone bodies, and to synthesize the triglyceride B100, which has a molecular weight of about 500,000. After feeding, chylomi- B100 is important for the hepatic secretion of VLDL. In crons from the small intestine are metabolized peripherally, abetalipoproteinemia, apo B synthesis and, therefore, the and the chylomicron remnants formed are rapidly taken up secretion of VLDLs is blocked. The fatty acids derived from the triglycerides seen in the cytoplasm of the hepatocytes of abetalipopro- of the chylomicron remnants are used for the formation teinemic patients. Although considerable amounts of circulating plasma LDLs and HDLs are produced in the plasma, the liver also Fatty Acid Oxidation and Synthesis. Fatty acids derived produces a small amount of these two cholesterol-rich from the plasma can be metabolized in the mitochondria of lipoproteins. LDLs are denser than VLDLs, and HDLs are hepatocytes by -oxidation to provide energy. The function of LDLs is to transport are broken down to form acetyl-CoA, which can be used in cholesterol ester from the liver to the other organs. HDLs the tricarboxylic acid cycle for ATP production, in the syn- are believed to remove cholesterol from the peripheral tis- thesis of fatty acids, and in the formation of ketone bodies. Because fatty acids are synthesized from acetyl-CoA, any The formation and secretion of lipoproteins by the liver substances that contribute to acetyl-CoA, such as carbohy- is regulated by precursors and hormones, such as estrogen drate and protein sources, enhance fatty acid synthesis. For instance, during fasting, the fatty The liver is one of the main organs involved in fatty acid acids in VLDLs are derived mainly from fatty acids mobi- synthesis. Palmitic acid is synthesized in the hepatocellular lized from adipose tissue. In contrast, during fat feeding, cytosol; the other fatty acids synthesized in the body are fatty acids in VLDLs produced by the liver are largely de- derived by shortening, elongating, or desaturating the rived from chylomicrons. As noted earlier, the fatty acids taken up by the liver can be used for -oxidation and ketone body formation. One of the major functions of the ative amounts of fatty acid channeled for these various pur- liver in lipid metabolism is lipoprotein synthesis. The four poses are largely dependent on the individual’s nutritional major classes of circulating plasma lipoproteins are chy- and hormonal status. More fatty acid is channeled to keto- lomicrons, very low density lipoproteins (VLDLs), low- genesis or -oxidation when the supply of carbohydrate is density lipoproteins (LDLs), and high-density lipoproteins short (during fasting) or under conditions of high circulating (HDLs) (Table 28. These lipoproteins, which differ in glucagon or low circulating insulin (diabetes mellitus).
The nucleus is thought to represent divided into a ventrocaudal parvocellular a relay station in the limbic system (p buy 20mg lexapro visa anxiety drugs. However lexapro 20mg cheap anxiety 30000, its functional significance is not The fibers of the superior cerebellar yet precisely known. Electrical stimulation peduncle, which terminate in this nucleus, leads to autonomic reactions (changes in originate from the emboliform nucleus of the blood pressure and respiration rate) due to cerebellum (C10). Medial Nuclear Group (B) Fibers from the internal segment of the globus pallidus (C12) branch off from the lenticular The medial nuclear group (medial complex) fasciculus (Forel’s field H2) and radiate into (B5) consists of a medial magnocellular nu- the nucleus. Fibers from the precentral cor- cleus, a lateral parvocellular nucleus, and a tex (area 4) are thought to terminate here as caudal nucleus. Efferent fiber bundles run from the frontal lobe, namely, to the premotor cortex, magnocellular region to the caudate nucleus the polar cortex, and the orbital cortex (B6). These tracts provide a thalamic radiation from the globus pallidus connection between cerebellum and stri- (B7) and from the basal nucleus of Meynert atum. The medial magno- cellular nucleus has fiber connections to the hypothalamus (B8) (preoptic area and tuber cinereum) and to the amygdaloid body (amygdala). The lateral parvocellular nu- cleus receives fibers from the adjacent ven- tral nuclei of the thalamus. The medial nuclear complex is thought to receive visceral and somatic impulses via pathways from the hypothalamus and ven- tral nuclei; the impulses are integrated here and then transmitted via the anterior thalamic radiation to the frontal cortex. The basic affective mood, which is essentially de- termined by unconscious stimuli from the visceral and somatic spheres, is thought to enter consciousness in this way. Anterior and Medial Nuclear Groups, Centromedian Nucleus 183 22 11 44 33 A Fiber connections of the anterior complex (anterior thalamic nuclei) 55 66 88 77 99 B Fiber connections of the medial complex (medial thalamic nuclei) 1313 1212 1414 1010 C Fiber connections of the centromedian nucleus 1111 Kahle, Color Atlas of Human Anatomy, Vol. A narrow caudal region of the nucleus is distinguished as ventral inter- The lateral nuclei form the dorsal tier of the mediate nucleus (B13). Neither of tegmental fasciculus from the ipsilateral the two lateral nuclei, the lateral dorsal nu- vestibular nuclei terminates here (head and cleus (A1) and the lateral posterior nu- gaze turn to the same side). The thalamic nuclei and are therefore viewed as nucleus is the terminus for the crossed, sec- integration nuclei. It re- fibers of the gracile nucleus lie laterally, ceives afferent fibers mainly from the inter- those of the cuneate nucleus medially. The nal segment of the globus pallidus (A5) resulting somatotopic organization of the (they probably originate in the caudate nu- nucleus can also be demonstrated electro- cleus [A6]) and from the nonspecific physiologically; the lower limb is repre- thalamic nuclei. Additional fibers are sented laterally, trunk and upper limb me- thought to stem from the substantia nigra, dially. The secondary trigeminal fibers the interstitial nucleus of Cajal, and the re- (lemniscus trigeminal) terminate in the me- ticular formation. The nucleus projects to dial segment of the nucleus, the ventralpost- the premotor cortex (A7) but depends only eromedial nucleus (VPM) (B17). They transmit partially on the cortex because only half of sensory information from the head and oral its neurons die after injury to the cortical re- cavity, thus completing the homunculus of gion. The ventral anterior nucleus is inte- the contralateral half of the body. The ter- grated into the ascending activation system; minus of the secondary gustatory pathway stimulation within the nuclear zone causes (p. The trigeminal pain fibers, are thought to termi- most important afferent system of the nu- nate bilaterally in the basal areas of the nu- cleus are the fibers of the crossed superior cleus. In the anterior (A18) extend to the sensory postcentral area segment of the ventral lateral nucleus there (p. The efferent of the ventral posterior nucleus and its pro- fibers (A11) extend to the cortex of the pre- jection to the cerebral cortex. The somatotopic or- ganization of the ventral lateral nucleus is obvious in this system (AB8); the lateral part of the nucleus is connected to the leg region of the precentral cortex, the adjacent parts to the trunk and arm regions, and the medial part to the head region. Thus, thalamic nucleus and cortical area show a corresponding topical subdivision. Informa- tion from the cerebellum (body posture, coordination, muscle tone) reaches the motor cortex via the ventral lateral nucleus; the cerebellum influences voluntary move- Kahle, Color Atlas of Human Anatomy, Vol.
Even though the drug is used for non-medical reasons 10 mg lexapro sale anxiety before period, there will still be sought-after and unwanted effects generic 10mg lexapro with amex anxiety symptoms duration. The desired effects may be pleasurable or the drug may simply be used to escape from the world Ð here the sought-after effect is oblivion. The continued use of a drug can lead to dependence on it so that the effects of abstinence or withdrawal from it will reinforce further use. Dependence can be compounded by tolerance, so that more of a drug is needed to produce the desired effect. The cost of the drug may well lead on to further problems with the law as commonly, burglary, prostitution and dealing in the drug become necessary to finance the habit. In fact, it has been estimated that a large part of crime results from the need for drugs. Although drugs associated with the dance culture are primarily the amphetamine type, including Ecstasy, it is now felt that heroin use has been spreading involving younger people from 14 years old onwards. Although heroin use remains a minority activity, there is probably more heroin available than ever before at low prices and in smaller, more affordable quantities. Webster &2001 John Wiley & Sons Ltd 500 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION The number of individuals having ever taken an illicit drug is estimated currently at around 28% of the UK adult population, with around a quarter of 16±29-year-olds having taken a drug within the last 12 months. Not only are young people coming into contact with drugs at a younger age than before but a wider range of drugs are available, including those currently not controlled under the Misuse of Drugs Act such as amyl nitrite and ketamine. Government-sponsored campaigns and media attention can have varying effects on drug consumption. There appears to have been a positive impact of campaigns on the misuse of solvents as the most recent figures show only a slight increase in the number of deaths which reached an all-time low in 1994. Overall, the rates of HIV among drug injectors are steadily declining and great credit must be paid to the damage-limitation strategies (needle exchanges, free condoms, etc. The most reliable numerical data available probably comes from the number of people registered seeking help for their drug habit. Here the number becoming addicted to the notifiable drugs (mainly opiates) continues to rise steadily and is now about 30 000. Research suggests that now perhaps one in three come forward, possibly as a result of more common prescribing of methadone as a replacement therapy and general concern about drugs and HIV/AIDS. Another guide to the extent of the problem is the number of drug seizures by the authorities. In 1998, this increased by 8% to 14 000 with the largest increases in heroin and cocaine (20±30%) although 76% of the total seizures are still cannabis. The number of drug-related prosecutions was just under 130 000 in that year of which 90% were for possession, and the majority of the cases dealt with were cannabis. This is despite many police forces giving warnings and cautions for low-level possession of cannabis rather than proceeding with prosecution. DEFINITIONS AND DRUG CLASSIFICATION Drug dependence has been defined as a state, psychological and/or physical, resulting from an interaction between a drug and an organism characterised by a compulsion to take the drug on a continuous or periodic basis to experience its psychic effects and/or avoid the discomfort of its absence. This definition of dependence (WHO) covers all forms of drug dependence which may be psychological or physical or combinations of both, accom- panied or not by tolerance to the drug. Because of these complexities drug dependence is classified somewhat on the basis of the effects produced or nature of the dependence- producing compound. The major groups to be considered are: DRUG DEPENDENCE AND ABUSE 501 Figure 23. The psychological effects must somehow reinforce the administration of the drug. On repeated use tolerance may develop leading to an increase in the dose of drug required to produce the required effect. Psychological dependence varies from mild to strong depending on the drug used. Physical dependence is not produced by all drugs of abuse and is most pronounced after use of depressant drugs such as alcohol or heroin. If a drug usage is halted withdrawal or abstinence occurs, the symptoms of which can be psychological (i. To avoid withdrawal symptoms drug administration is continued and a cycle is set up (see Table 23. It contains morphine and codeine, both effective and widely used analgesics, along with heroin which can be made from morphine and in its pure form is a white powder.
Carbohydrates are an ex- tremely important component of food intake order 20 mg lexapro free shipping anxiety 3 months postpartum, since they constitute about 45 to 50% of the typical Western diet and provide the greatest and least expensive source of en- ergy buy lexapro 5 mg low cost anxiety tattoos. The Diet Contains Both Digestible and Nondigestible Carbohydrates Humans can digest most carbohydrates; those we cannot di- gest constitute the dietary fiber that forms roughage. The monosaccharides are mainly hexoses (six-carbon sugars), and glucose is by far the most abundant of these. Glucose is obtained directly from the diet or from the digestion of dis- Carbohydrates Are Digested in Different Parts of accharides, oligosaccharides, or polysaccharides. The next the GI Tract most common monosaccharides are galactose, fructose, and The digestion of carbohydrates starts when food is mixed sorbitol. Galactose is present in the diet only as milk lactose, with saliva during chewing. The enzyme salivary amylase a disaccharide composed of galactose and glucose. Fructose acts on the -1,4-glycosidic linkage of amylose and amy- is present in abundance in fruit and honey and is usually lopectin of polysaccharides to release the disaccharide present as disaccharides or polysaccharides. Sorbitol is de- maltose and oligosaccharides maltotriose and -limit dex- rived from glucose and is almost as sweet as glucose, but sor- trins (Fig. Because salivary amylase works best at bitol is absorbed much more slowly and, thus, maintains a neutral pH, its digestive action terminates rapidly after the high blood sugar level for a longer period when similar amounts are ingested. It has been used as a weight-reduction bolus mixes with acid in the stomach. Sucrose, present in sugar cane and honey, is composed of glucose and fructose. Amylose The digestible polysaccharides are starch, dextrins, and glycogen. Starch, by far the most abundant carbohydrate in the human diet, is made of amylose and amylopectin. Amy- α-Amylase lose is composed of a straight chain of glucose units; amy- lopectin is composed of branched glucose units. Glycogen is a highly branched polysaccharide that stores carbohydrates in the body. Normally, about 300 to 1,6 Link 400 g of glycogen is stored in the liver and muscle, with more stored in muscle than in the liver. Muscle glycogen is 1,4 Link used exclusively by muscle, and liver glycogen is used to α-Amylase provide blood glucose during fasting. Dietary fiber is made of polysaccharides that are usually Maltotriose α-Limit dextrin Maltose poorly digested by the enzymes in the small intestine. They have an extremely important physiological function in that they provide the “bulk” that facilitates intestinal motility and function. Many vegetables and fruits are rich in fibers, The digestion products of starch after ex- FIGURE 27. CHAPTER 27 Gastrointestinal Secretion, Digestion, and Absorption 499 fore this point. Pancreatic amylase continues the digestion of the remaining carbohydrates. However, the chyme must first be neutralized by pancreatic secretions, since pancre- atic amylase works best at neutral pH. The products of pan- creatic amylase digestion of polysaccharides are also malt- ose, maltotriose, and -limit dextrins. The digestion products of starch and glycogen, to- gether with disaccharides (sucrose and lactose), are fur- ther digested by enzymes located at the brush border membrane. Enterocytes Play an Important Role in Carbohydrate Absorption and Metabolism Monosaccharides are absorbed by enterocytes either ac- tively or by facilitated transport. Glucose and galactose are absorbed via secondary active transport by a symporter (see FIGURE 27. The movement of Na into the cell, down concentration and electrical gradients, effects the uphill movement of glucose into the cell.
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