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By Z. Dimitar. Cleveland State University. 2017.

The importance of histamine as an effector of gastric acid The gastric phase is mainly a result of gastric distension secretion has been indirectly demonstrated by the effec- and chemical agents such as digested proteins purchase zyprexa 7.5 mg otc. Distension tiveness of cimetidine, an H2 blocker, in reducing acid se- of the stomach stimulates mechanoreceptors, which stimu- cretion. H2 blockers are commonly used for the treatment late the parietal cells directly through short local (enteric) of peptic ulcer disease or gastroesophageal reflux disease. Vago-vagal re- The effects of each of these three stimulants (ACh, gas- flexes are mediated by afferent and efferent impulses trav- trin, and histamine) augment those of the others, a phe- eling in the vagus nerves. Potentiation is said to are also potent stimulators of gastric acid secretion, an ef- 488 PART VII GASTROINTESTINAL PHYSIOLOGY TABLE 27. Second, excess acid icals, such as alcohol and caffeine, stimulate gastric acid se- can damage the gastric and the duodenal mucosal surfaces, cretion through mechanisms that are not well understood. The gastric phase accounts for about 50% of total gastric The body has an elaborate system for regulating the amount acid secretion. Gastric luminal pH is a sen- During the intestinal phase, protein digestion products sitive regulator of acid secretion. Proteins in food provide in the duodenum stimulate gastric acid secretion through buffering in the lumen; consequently, the gastric luminal pH the action of the circulating amino acids on the parietal is usually above 3 after a meal. Distension of the small intestine, probably via the re- pacity of protein is exceeded or if the stomach is empty, the lease of the hormone enterooxyntin from intestinal en- pH of the gastric lumen will fall below 3. The intestinal phase the endocrine cells (D cells) in the antrum secrete somato- accounts for only about 10% of total gastric acid secretion. Gastric Acid Secretion Is Inhibited by Another mechanism for inhibiting gastric acid secretion is acidification of the duodenal lumen. Acidification stimu- Several Mechanisms lates the release of secretin, which inhibits the release of The inhibition of gastric acid secretion is physiologically im- gastrin, and several peptides, collectively known as entero- portant for two reasons.

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Fortunately this is not the case as many people can reach 90 or 100 years without developing PD order 20mg zyprexa. In fact, PM studies show that in normal subjects nigra DA cell loss proceeds at 4±5% per 10 years but in PD sufferers it occurs at almost ten times this level (Fearnley and Lees 1991). Thus either the gradual loss of nigral cells and striatal DA is accelerated for some reason in certain people, so that these markers fall to below 50% of normal around 55± 60 years, or some people experience a specific event (or events) during life which acutely reduces DA concentration. This could be to a level which is not enough to produce PD at the time but ensures that when a natural ageing loss of DA is superimposed on it the critical low level will be reached and PD emerge before natural death. The first possibility is likely to have a genetic basis but although examples of familial PD are rare there is typically an increased incidence (2±14) of the disease in the family of a PD patient and initial PET studies show a much higher (53%) loss of DA neuron labelling in the monozygotic than the dizygotic twin of a PD sufferer even if the disorder is not clinically apparent. While a number of gene markers have been identified in different families there is no consistent mutation although parkin on chromosome 6 and a synuclein on 4 have aroused most interest. Mutations of the gene encoding the latter, such as threonine replacing alanine on amino acid 53 (A53T) or phenylalanine for alanine on 30 (A30P) have certainly been established in particular families with inherited PD. In fact ablation of the gene encoding a synuclein has been shown to produce locomotor defects in mice 320 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION and surprisingly in the fruitfly Drosophila melanogaster. By expressing normal human a synuclein in all the nerve cells of Drosophila, Feany and Bender (2000) found no neuronal abnormalities but with wild-type a synuclein or the mutants A53T and A30P they observed premature and specific death of dopaminergic neurons. Additionally some neurons showed intracellular aggregates that resembled Lewy bodies and were composed of the a synuclein filaments seen in the human counterpart. Of course, flies cannot be said to develop PD but unlike normal ones, the transengic fly found it more difficult to climb the sides of a vertical vial. The fact that some schizophrenics show PD symptoms when given DA antagonists has been considered to indicate that they already have a reduced DA function and are asymptomatic potential PD patients but the high incidence of PD side-effects after neuroleptics and its occurrence in young people (20±30 years) argues against this. A viral infection can lead to PD as evidenced by its high incidence (50%) in survivors of an outbreak of encephalitic lethargica in Europe around 1920.

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The ven- tral anterior nucleus does not receive significant cerebellar input generic zyprexa 20 mg without a prescription. Answer D: Glutamate is found in many efferent fibers of the While the ventral posterolateral nucleus receives a limited amount cerebral cortex including those of the corticospinal tract. Conse- of cerebellar input, its major role is the relay of somatosensory in- quently, there are many glutaminergic terminals in the spinal formation to the primary somatosensory cortex (postcentral cord. Answer B: The jerking movements of the upper extremity (as- their nigrostriatal terminals. Gamma aminobutyric acid (GAMA) terixis) are also called a flapping tremor and are seen in patients is an inhibitory neurotransmitter and is found in many interneu- with hepatolenticular degeneration (Wilson disease). Resting tremor is seen in patients with disease pothalamus, basal nuclei, and the raphe nuclei. Answer A: The loss of sensation on one side of the face and the tonia is the result of sustained muscle contractions that twist the opposite side of the body is an alternating hemianesthesia (also extremities, trunk, and neck into distorted and abnormal pos- called an alternate hemianesthesia or a crossed hemianesthesia). Answer A: This man is unable to recognize or comprehend the motor abnormalities. Answer D: Lesions in the lateral portions of the brainstem dam- ditory agnosia. Agraphia is the inability to write in a person with age descending projections from the hypothalamus to the ipsilat- no paralysis, and alexia is the inability to comprehend the mean- eral intermediolateral cell column at spinal levels T1-T4, these be- 288 Q & A’s: A Sampling of Study and Review Questions with Explained Answers ing the hypothalamospinal fibers. Weakness of the extremities may be seen, but on the side ipsilateral to the lesion. Horner syndrome may also be this almost always follows ocular movement disorders. A contralateral hemi- is most commonly seen in cerebellar disease and may be present plegia is not seen in lesions in lateral areas of the brainstem. Tremor is other choices are syndromes or deficits specific to medial brain- commonly seen in diseases or lesions of the basal nuclei and the stem areas or to only a particular level.

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