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    the sight of food can trigger a series of events that results in the release of gastric juice. all but one of the following is true in regards to the previous statement. select the one answer that is not true.

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    15.4 Digestive System Regulation – Concepts of Biology – 1st Canadian Edition

    15.4 DIGESTIVE SYSTEM REGULATION

    Learning Objectives

    By the end of this section, you will be able to:

    Discuss the role of neural regulation in digestive processes

    Explain how hormones regulate digestion

    The brain is the control center for the sensation of hunger and satiety. The functions of the digestive system are regulated through neural and hormonal responses.

    NEURAL RESPONSES TO FOOD

    In reaction to the smell, sight, or thought of food, like that shown in Figure 15.20, the first hormonal response is that of salivation. The salivary glands secrete more saliva in response to the stimulus presented by food in preparation for digestion. Simultaneously, the stomach begins to produce hydrochloric acid to digest the food. Recall that the peristaltic movements of the esophagus and other organs of the digestive tract are under the control of the brain. The brain prepares these muscles for movement as well. When the stomach is full, the part of the brain that detects satiety signals fullness. There are three overlapping phases of gastric control—the cephalic phase, the gastric phase, and the intestinal phase—each requires many enzymes and is under neural control as well.

    Figure 15.20.

    Seeing a plate of food triggers the secretion of saliva in the mouth and the production of HCL in the stomach. (credit: Kelly Bailey)

    DIGESTIVE PHASES

    The response to food begins even before food enters the mouth. The first phase of ingestion, called the cephalic phas, is controlled by the neural response to the stimulus provided by food. All aspects—such as sight, sense, and smell—trigger the neural responses resulting in salivation and secretion of gastric juices. The gastric and salivary secretion in the cephalic phase can also take place due to the thought of food. Right now, if you think about a piece of chocolate or a crispy potato chip, the increase in salivation is a cephalic phase response to the thought. The central nervous system prepares the stomach to receive food.

    The gastric phase begins once the food arrives in the stomach. It builds on the stimulation provided during the cephalic phase. Gastric acids and enzymes process the ingested materials. The gastric phase is stimulated by (1) distension of the stomach, (2) a decrease in the pH of the gastric contents, and (3) the presence of undigested material. This phase consists of local, hormonal, and neural responses. These responses stimulate secretions and powerful contractions.

    The intestinal phase begins when chyme enters the small intestine triggering digestive secretions. This phase controls the rate of gastric emptying. In addition to gastrin emptying, when chyme enters the small intestine, it triggers other hormonal and neural events that coordinate the activities of the intestinal tract, pancreas, liver, and gallbladder.

    HORMONAL RESPONSES TO FOOD

    The endocrine system controls the response of the various glands in the body and the release of hormones at the appropriate times.

    One of the important factors under hormonal control is the stomach acid environment. During the gastric phase, the hormone gastrin is secreted by G cells in the stomach in response to the presence of proteins. Gastrin stimulates the release of stomach acid, or hydrochloric acid (HCl) which aids in the digestion of the proteins. However, when the stomach is emptied, the acidic environment need not be maintained and a hormone called somatostatin stops the release of hydrochloric acid. This is controlled by a negative feedback mechanism.

    In the duodenum, digestive secretions from the liver, pancreas, and gallbladder play an important role in digesting chyme during the intestinal phase. In order to neutralize the acidic chyme, a hormone called secretin stimulates the pancreas to produce alkaline bicarbonate solution and deliver it to the duodenum. Secretin acts in tandem with another hormone called cholecystokinin (CCK). Not only does CCK stimulate the pancreas to produce the requisite pancreatic juices, it also stimulates the gallbladder to release bile into the duodenum.

    CONCEPT IN ACTION

    Visit

    this website to learn more about the endocrine system. Review the text and watch the animation of how control is implemented in the endocrine system.

    Another level of hormonal control occurs in response to the composition of food. Foods high in lipids take a long time to digest. A hormone called gastric inhibitory peptide is secreted by the small intestine to slow down the peristaltic movements of the intestine to allow fatty foods more time to be digested and absorbed.

    Understanding the hormonal control of the digestive system is an important area of ongoing research. Scientists are exploring the role of each hormone in the digestive process and developing ways to target these hormones. Advances could lead to knowledge that may help to battle the obesity epidemic.

    SUMMARY

    The brain and the endocrine system control digestive processes. The brain controls the responses of hunger and satiety. The endocrine system controls the release of hormones and enzymes required for digestion of food in the digestive tract.

    Source : opentextbc.ca

    A&P2 Exam 3 Flashcards

    Start studying A&P2 Exam 3. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

    A&P2 Exam 3

    Which of the following is not true of saliva?

    A. cleanses the mouth

    B. contains enzymes that begin the breakdown of carbohydrates

    C. moistens food and aids in compacting of the bolus

    D. contains acids which aid in chemical digestion

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    Contains acids which aid in chemical digestion

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    You have just eaten a meal high in complex carbohydrates (starches). Which of the following enzymes will help to digest the meal?

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    Amylase

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    1/47 Created by tsantosbabaran

    Terms in this set (47)

    Which of the following is not true of saliva?

    A. cleanses the mouth

    B. contains enzymes that begin the breakdown of carbohydrates

    C. moistens food and aids in compacting of the bolus

    D. contains acids which aid in chemical digestion

    Contains acids which aid in chemical digestion

    You have just eaten a meal high in complex carbohydrates (starches). Which of the following enzymes will help to digest the meal?

    Amylase

    From the esophagus to the anal canal, the walls of every organ of the alimentary canal are made up of the same four basic layers. Arrange them in order from the lumen.

    Mucosa, submucosa, muscularis externa, serosa

    All but one of the following is a function of the low pH found in the stomach. Select the description below that does not reflect a role of stomach acid.

    A. The stomach's acid catabolically breaks down food stuffs in preparation for absorption

    B. Stopach acid denatures proteins makin gthe polypeptide chain more accessible to pepsin digestive enzymes

    C. Many potentially harmful bacteria will be prevented entry to the small intestine by stomach acid

    D. Low pH converts pepsinogen to its active form of pepsin, preventing the protease enzyme from digesting the cells that produce it

    The stomach's acid catabolically breaks down food stuffs in preparation for absorption

    The sight of food can trigger a series of events that results in the release of gastric juice. All but one of the following is true in regards to the previous statement. Select one answer that is not true.

    A. This is an example of a long reflexive pathway

    B. This prepares the stomach for food before its arrival in the stomach

    C. The motor nerves of this pathway are part of the sympathetic division of the ANS

    D. The cerebral cortex, hypothalamus and medulla oblongata are all involved in processing the stimulatory information

    The motor nerves of this pathway are part of the sympathetic division of the autonomic nervous system.

    Bile salts bind at their hydrophobic regions to large fat globules within the chyme that enters the duodenum. Bile salts break up the fat globule into smaller fat droplets. This role of bile salts is best described as

    Lipid emulsification

    Generally the hormones secretin and cholecystokinin which are released by duodenal enteroendocrine cells will

    Increase the release of pancreatic digestive enzymes and bile

    Select the one response below that would not result from a drug that blocks histamine receptors in the cells lining the stomach

    A. It would lower the activity of parietal cells

    B. It would reduce the symptoms of heartburn

    C. It would cause the release of secretin and CCK

    D. It would raise the pH of the stomach

    It would cause the relase of secretin and cholecystokinin

    The function of the hepatic portal circulation is to

    Collect absorbed nutrients for metabolic processing in the liver

    The ducts that deliver bile and pancreatic juice from the liver and pancreas, respectively, unit to form the

    Hepatopancreatic ampulla

    Which vitamin requires intrinsic factor in order to be absorbed

    B12 Chief cells Produce pepsinogen

    Which of the following enzymes would be most active in the presents of a high concentrations of protein fragments?

    Trypsin

    As the body progresses from the absorptive to the postabsorptive state, the __________ continues to burn glucose while virtually every other organ in the body switches to fatty acids as its major energy source.

    Brain

    Which of the following nutrients yield the highest amount of energy per gram when metabolized?

    Fats

    Select the correct statement about the regulation of gastric secretion

    Gastric secretion can be stimulated before food has entered the mouth

    The activities of the digestive system are regulated by

    Hormones, parasympathetic and sympathetic neurons, the contents of the digestive tract, intrinsic nerve plexuses

    Which of these descriptions best matches the term myenteric plexus?

    Coordinates activity of musclaris externa

    The molecule that serves as the major source of readily available fuel for neurons and blood cells is ________

    Glucose

    Cholesterol, though it is NOT an energy molecule, has importance in the body because it

    Is a stabilizing component of the plasma membranes and is the parent molecule of steroid hormones

    Which of the choices below describes the pathway of cellular respiration (the complete oxidation of glucose)

    Glycolysis, citric acid (Krebs) cycle, electron transport chain, oxidative phosphorylation

    Anabolism includes reactions in which

    Source : quizlet.com

    human digestive system

    The gastric mucosa secretes 1.2 to 1.5 litres of gastric juice per day. Gastric juice renders food particles soluble, initiates digestion (particularly of proteins), and converts the gastric contents to a semiliquid mass called chyme, thus preparing it for further digestion in the small intestine. Gastric juice is a variable mixture of water, hydrochloric acid, electrolytes (sodium, potassium, calcium, phosphate, sulfate, and bicarbonate), and organic substances (mucus, pepsins, and protein). This juice is highly acidic because of its hydrochloric acid content, and it is rich in enzymes. As noted above, the stomach walls are protected from digestive juices by the

    Gastric secretion

    The gastric mucosa secretes 1.2 to 1.5 litres of gastric juice per day. Gastric juice renders food particles soluble, initiates digestion (particularly of proteins), and converts the gastric contents to a semiliquid mass called chyme, thus preparing it for further digestion in the small intestine. Gastric juice is a variable mixture of water, hydrochloric acid, electrolytes (sodium, potassium, calcium, phosphate, sulfate, and bicarbonate), and organic substances (mucus, pepsins, and protein). This juice is highly acidic because of its hydrochloric acid content, and it is rich in enzymes. As noted above, the stomach walls are protected from digestive juices by the membrane on the surface of the epithelial cells bordering the lumen of the stomach; this membrane is rich in lipoproteins, which are resistant to attack by acid. The gastric juice of some mammals (e.g., calves) contains the enzyme rennin, which clumps milk proteins and thus takes them out of solution and makes them more susceptible to the action of a proteolytic enzyme.

    The process of gastric secretion can be divided into three phases (cephalic, gastric, and intestinal) that depend upon the primary mechanisms that cause the gastric mucosa to secrete gastric juice. The phases of gastric secretion overlap, and there is an interrelation and some interdependence between the neural and humoral pathways.

    The cephalic phase of gastric secretion occurs in response to stimuli received by the senses—that is, taste, smell, sight, and sound. This phase of gastric secretion is entirely reflex in origin and is mediated by the vagus (10th cranial) nerve. Gastric juice is secreted in response to vagal stimulation, either directly by electrical impulses or indirectly by stimuli received through the senses. Ivan Petrovich Pavlov, the Russian physiologist, originally demonstrated this method of gastric secretion in a now-famous experiment with dogs.

    The gastric phase is mediated by the vagus nerve and by the release of gastrin. The acidity of the gastric contents after a meal is buffered by proteins so that overall it remains around pH3 (acidic) for approximately 90 minutes. Acid continues to be secreted during the gastric phase in response to distension and to the peptides and amino acids that are liberated from protein as digestion proceeds. The chemical action of free amino acids and peptides excites the liberation of gastrin from the antrum into the circulation. Thus, there are mechanical, chemical, and hormonal factors contributing to the gastric secretory response to eating. This phase continues until the food has left the stomach.

    The intestinal phase is not fully understood, because of a complex stimulatory and inhibitor process. Amino acids and small peptides that promote gastric acid secretion are infused into the circulation, however, at the same time chyme inhibits acid secretion. The secretion of gastric acid is an important inhibitor of gastrin release. If the pH of the antral contents falls below 2.5, gastrin is not released. Some of the hormones that are released from the small intestine by products of digestion (especially fat), in particular glucagon and secretin, also suppress acid secretion.

    Source : www.britannica.com

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