By K. Hjalte. Andrews University. 2017.

Adaptive relaxation is triggered by distension of crease in intragastric pressure and distension of the gastric the gastric reservoir order bentyl 10 mg on line. Failure of this mechanism can lead to the uncomfort- stretch receptors in the gastric wall buy discount bentyl 10 mg on line, transmission over vagal able sensations of bloating, epigastric pain, and nausea. The afferents to the dorsal vagal complex, and efferent vagal second function is to maintain a constant compressive force on the contents of the reservoir. This pushes the contents into motor activity of 3 cycles/min for the antral pump. Brain Drugs that relax the musculature of the gastric reservoir (medulla) neutralize this function and suppress gastric emptying. The musculature of the gastric reservoir is innervated by Vagal efferents both excitatory and inhibitory motor neurons of the ENS. Vagal afferents The motor neurons are controlled by the efferent vagus Enteric nervous system nerves and intramural microcircuits of the ENS. They func- tion to adjust the volume and pressure of the reservoir to Interneuronal circuits Gastric stretch the amount of solid and/or liquid present while maintaining receptors constant compressive forces on the contents. Continuous Inhibitory adjustments in the volume and pressure within the reservoir motor neurons are required during both the ingestion and the emptying of a meal. Increased activity of excitatory motor neurons, in coor- Muscle dination with decreased activity of inhibitory motor neu- relaxation rons, results in increased contractile tone in the reservoir, a decrease in its volume, and an increase in intraluminal pres- FIGURE 26. Increased activity of inhibitory motor which information from gastric stretch receptors is the afferent neurons in coordination with decreased activity of excita- component and outflow from the medullary region of the brain is tory motor neurons results in decreased contractile tone in the efferent component. Vagal efferents transmit to the ENS, the reservoir, expansion of its volume, and a decrease in in- which controls the activity of inhibitory motor neurons that re- traluminal pressure. CHAPTER 26 Neurogastroenterology and Gastrointestinal Motility 471 25 tying of isotonic noncaloric liquids (e. If an experimental meal consisting of solid par- 15 ticles of various sizes suspended in water is instilled in the Discomfort stomach, emptying of the particles lags behind emptying of 10 X X the liquid (Fig. If the particles are plastic 0 spheres of various sizes, the smallest spheres are emptied 0 100 200 300 400 500 600 first; however, spheres up to 7 mm in diameter empty at a slow but steady rate when digestible food is in the stomach. Gastric volume (mL) The selective emptying of smaller particles first is referred Loss of adaptive relaxation following a to as the sieving action of the distal stomach.

Blood pressure and body temperature also have a profound Creek effect on the heart rate trusted 10 mg bentyl. Electrocardiogram The electrical impulses that pass through the conduction system of the heart during the cardiac cycle can be recorded as an elec- trocardiogram (ECG or EKG) purchase bentyl 10mg on line. The electrical changes result from depolarization and repolarization of cardiac muscle fibers and can fraction of a second. The ventricles of the heart are in diastole be detected on the surface of the skin using an instrument called during the expression of the P wave. The wave deflections, designated P, QRS, and T, are P-R Interval produced as specific events of the cardiac cycle occur. Any heart disease that disturbs the electrical activity will produce charac- On the ECG recording, the P-R interval is the period of time teristic changes in one or more of these waves, so understanding from the start of the P wave to the beginning of the QRS com- the normal wave-deflection patterns is clinically important. This interval indicates the amount of time required for the SA depolarization to reach the ventricles. A prolonged P-R in- terval suggests a conduction problem at or below the AV node. P Wave Depolarization of the atrial fibers of the SA node produces the P QRS Complex wave. The actual contraction of the atria follows the P wave by a The QRS complex begins as a short downward deflection (Q), continues as a sharp upward spike (R), and ends as a downward diastole: Gk. The QRS complex indicates the depolarization of Van De Graaff: Human VI. Circulatory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 554 Unit 6 Maintenance of the Body FIGURE 16. During this interval, the ventricles are in systole when the ventricles contract at systole, and the second sound is and blood is being ejected from the heart. It is also during this heard when the ventricles relax at the beginning of diastole. An abnor- information about the condition of the heart valves and may in- mal QRS complex generally indicates cardiac problems of the dicate heart problems. An enlarged R spike, for example, generally indicates murmurs and are caused by valvular leakage or restriction and the enlarged ventricles.

The structure and the function of the muscarinic acetyl- is regulated by short-term activation and long-term induc- choline receptor are different generic bentyl 10mg fast delivery. Short-term excitation of dopaminergic neurons results receptors have been identified cheap bentyl 10mg visa. The M1 and M2 receptors in an increase in the conversion of tyrosine to DA. This are composed of seven membrane-spanning domains, with phenomenon is mediated by the phosphorylation of TH each exerting action through a G protein. The activation of via a cAMP-dependent protein kinase, which results in an M1 receptors results in a decrease in K conductance via increase in functional TH activity. Long-term induction is phospholipase C, and activation of M2 receptors causes an mediated by the synthesis of new TH. A nonspecific cytoplasmic enzyme, aromatic L-amino As a consequence, when ACh binds to an M1 receptor, it acid decarboxylase, catalyzes the formation of dopamine results in membrane depolarization; when ACh binds to an from L-DOPA. Dopamine is then taken up in storage vesi- M2 receptor, it causes hyperpolarization. In NE- and EPI- synthesizing neurons, DBH, which converts DA to NE, is Catecholamines. The catecholamines are so named be- found within vesicles, unlike the other synthetic enzymes, cause they consist of a catechol moiety (a phenyl ring with which are in the cytoplasm. In EPI-secreting cells, PNMT two attached hydroxyl groups) and an ethylamine side chain. The PNMT adds a methyl The catecholamines dopamine (DA), norepinephrine (NE), group to the amine in NE to form EPI. Monoamine oxi- volved—tyrosine hydroxylase (TH), dopamine -hydroxy- dase (MAO) removes the amine group, and catechol-O- lase (DBH), and phenylethanolamine N-methyl transferase methyltransferase (COMT) methylates the 3-OH group (PNMT)—are unique to catecholamine-secreting cells and on the catechol ring. Dopaminer- calized in mitochondria, present in both presynaptic and gic neurons express only TH, noradrenergic neurons ex- postsynaptic cells, whereas COMT is localized in the cyto- press both TH and DBH, and epinephrine-secreting cells ex- plasm and only postsynaptically. Epinephrine-secreting cells include a small ergic neurons in the PNS (i. In the CNS, on the other hand, is tyrosine hydroxylase, which converts L-tyrosine to L-3,4- most of the COMT is localized in glial cells (especially as- dihydroxyphenylalanine (L-DOPA).