FR2- GUT 2

Question 1

What prevents reflux of gastric contents?

Answer 1

The gastroesophageal sphincter

Question 2

When does the gastroesophageal sphincter increase contractility?

Answer 2

During inspiration, reducing the chance of reflux of acidic gastric contents into the esophagus during the time when the subatmosphteric intrapleural pressure would favor backward movement of gastric contents

Question 3

What is heartburn?

Answer 3

If gastric contents do flow backward despite the sphincter, the acidity of these contents irritates the esophagus, causing the esophageal discomfort known as heartburn

Question 4

What is the function of esophageal secretion?

Answer 4

If gastric contents do flow backward despite the sphincter, the acidity of these contents irritates the esophagus, causing the esophageal discomfort known as heartburn

Question 5

Which part of the stomach lies above the esophageal opening?

Answer 5

The fundus is the part of the stomach that lies above the esophageal opening

Question 6

What is the middle or main part of the stomach called?

Answer 6

the body

Question 7

Describe the difference in musculature between the different parts of the stomach

Answer 7

• The smooth muscle layers in the fundus and body are relatively thin, but the lower part of the stomach, the antrum, has heavier musculature.
• This difference in muscle thickness plays an important role in gastric motility in these two regions, as you will see shortly.
• There are also glandular differences in the mucosa of these regions.

Question 8

What is the terminal part of the stomach and its function?

Answer 8

The terminal portion of the stomach is the pyloric sphincter, which acts as a barrier between the stomach and the upper part of the small intestine, the duodenum.

Question 9

The stomach performs three main functions:

Answer 9

1. The stomach’s most important function is to store ingested food until it can be emptied into the small intestine at a rate appropriate for optimal digestion and absorption. It takes hours to digest and absorb a meal that was consumed in only a matter of minutes. Because the small intestine is the primary site for this digestion and absorption, it is important that the stomach store the food and meter it into the duodenum at a rate that does not exceed the small intestine’s capacities.
2. The stomach secretes hydrochloric acid (HCl) and enzymes that begin protein digestion.
3. Through the stomach’s mixing movements, the ingested food is pulverized and mixed with gastric secretions to produce a thick liquid mixture known as chyme. The stomach contents must be converted to chyme before they can be emptied into the duodenum

Question 10

What are the four aspects of gastric motility?

Answer 10

(1) filling
(2) storage
(3) mixing
(4) emptying

Question 11

Describe Gastric filling

Answer 11

• When empty, the stomach has a volume of about 50 mL, but it can expand up to 20-fold to a capacity of about 1 liter (1000 mL) during a meal.
• Here’s how: the interior of the stomach is thrown into deep folds. During a meal, the folds get smaller and nearly flatten out as the stomach relaxes slightly with each mouthful, much like the gradual expansion of a collapsed ice bag as it is being filled.
• This vagally mediated response, called receptive relaxation, allows the stomach to accommodate the meal with little change in intragastric pressure. If more than a liter of food is consumed, however, the stomach becomes overdistended, intragastric pressure rises, and the person experiences discomfort

Question 12

Describe gastric storage

Answer 12

• A group of pacemaker cells (interstitial cells of Cajal) located in the upper fundus region of the stomach generate slow-wave potentials that sweep down the length of the stomach toward the pyloric sphincter at a rate of three per minute.
• This rhythmic pattern of spontaneous depolarizations—the basic electrical rhythm, or BER, of the stomach—occurs continuously and may or may not be accompanied by contraction of the stomach’s circular smooth muscle layer.
• Depending on the level of excitability in the smooth muscle, it may be brought to threshold by this flow of current and undergo action potentials, which in turn initiate peristaltic waves that sweep over the stomach in pace with the BER at a rate of three per minute

Question 13

What happens once the peristaltic wave is initiated?

Answer 13

• Once initiated, a peristaltic wave spreads over the fundus and body to the antrum and pyloric sphincter. Because the muscle layers are thin in the fundus and body, the peristaltic contractions in this region are weak.
• When the waves reach the antrum, they become stronger and more vigorous because the muscle there is thicker.

Question 14

Because only feeble mixing movements occur in the body and fundus, what happens to food delivered to the stomach from the esophagus?

Answer 14

It is stored in the relatively quiet body without being mixed. The fundus usually does not store food but contains only a pocket of gas. Food is gradually fed from the body into the antrum, where mixing does take place

Question 15

Gastric mixing takes place in the antrum of the stomach

What is retropulsion?

Answer 15

• The strong antral peristaltic contractions mix the food with gastric secretions to produce chyme. Each antral peristaltic wave propels chyme distally toward the pyloric sphincter.
• Tonic contraction of the pyloric sphincter normally keeps it almost, but not completely, closed.
• The opening is large enough for water and other fluids to pass through with ease, although particles larger than 2 mm in diameter typically do not leave. As the peristaltic wave reaches the pyloric sphincter and closes it.
• Tightly, the large particles are forced backward toward the body of the stomach. The bulk of the antral chyme that is forced backward is again propelled forward and then tumbled back as the next peristaltic wave advances.
• This churning action is called retropulsion, which thoroughly shears and grinds the chyme until the particles are small enough for emptying, mixing the contents in the proces.

Question 16

Gastric emptying is largely controlled by factors in the duodenum

Answer 16

• In addition to mixing gastric contents, the antral peristaltic contractions are the driving force for gastric emptying.
• The amount of chyme that escapes into the duodenum with each peristaltic wave before the pyloric sphincter tightly closes depends largely on the strength of antral peristalsis.
• The intensity of antral peristalsis and thus the rate of gastric emptying can vary markedly under the influence of various signals from both the stomach and duodenum.
• These factors influence the stomach’s excitability by slightly depolarizing or hyperpolarizing the gastric smooth muscle.
• The greater the excitability is, the more frequently the BER generates action potentials, the greater the strength of antral peristalsis, and the faster the rate of gastric emptying.

Question 17

Factors in the Stomach that Influence the Rate of Gastric Emptying:

The main gastric factor that influences the strength of contraction is the amount of chyme in the stomach.

Answer 17

• Other things being equal, the stomach empties at a rate proportional to the volume of chyme in it at any given time.
• Stomach distension triggers increased gastric motility through a direct effect of stretch on the smooth muscle and through involvement of the intrinsic plexuses, the vagus nerve, and the stomach hormone gastrin. (The source, control, and other functions of this hormone will be described later.) Furthermore, the degree of fluidity of the chyme influences gastric emptying.
• The stomach contents must be converted into a finely divided, thick liquid form before emptying.
• The sooner the appropriate degree of fluidity can be achieved, the more rapidly the contents are ready to be evacuated

Question 18

Factors in the Duodenum that Influence the Rate of Gastric Emptying:

Factors in the duodenum are of primary importance in controlling the rate of gastric emptying

Answer 18

The duodenum must be ready to receive the chyme and can delay gastric emptying by reducing the strength of antral peristalsis until the duodenum is ready to accommodate more chyme.

The presence of one or more of these stimuli in the duodenum activates appropriate duodenal receptors, triggering neural and hormonal responses that put brakes on antral peristaltic activity, thereby slowing the rate of gastric emptying

Question 19

What are the four most important duodenal factors that influence gastric emptying?

Answer 19

• fat, acid, hypertonicity, and distension.
• The presence of one or more of these stimuli in the duodenum activates appropriate duodenal receptors, triggering neural and hormonal responses that put brakes on antral peristaltic activity, thereby slowing the rate of gastric emptying

Question 20

Factors affecting gastric emptying:

Neutral response

Hormonal response

Answer 20

■ The neural response is mediated through both the intrinsic plexuses (short reflex) and the autonomic nerves (long reflex). Together these constitute the enterogastric reflex

■ The hormonal response involves the release from the smallintestine mucosa into the blood of several hormones collectively known as enterogastrones. The blood carries these hormones to the stomach, where they inhibit antral contractions to reduce gastric emptying. The two most important enterogastrones are secretin and cholecystokinin (CCK). Secretin was the first hormone discovered (in 1902). Because it was a secretory product that entered the blood, it was termed secretin. The name cholecystokinin derives from this same hormone also causing contraction of the bile-containing gallbladder (chole means “bile” cysto means “bladder”; and kinin means “contraction”). Secretin and CCK are major GI hormones that perform other important functions in addition to serving as enterogastrones.

Question 21

Examine why it is important that each of these stimuli in the duodenum delays gastic emptying: Fat

Answer 21

• Among the different nutrients that we consume, fat is most effective in delaying gastric emptying.
• This effect is important because fat digestion and absorption take more time than for the other nutrients and take place only in the smallintestine lumen.
• Triglycerides strongly stimulate duodenal release of CCK.
• This hormone inhibits antral contractions and also induces contraction of the pyloric sphincter, which both slow gastric emptying.
• This delay in emptying ensures that the small intestine has enough time to digest and absorb the fat already there before more fat enters from the stomach.

Question 22

Examine why it is important that each of these stimuli in the duodenum delays gastic emptying: Acid

Answer 22

• Because the stomach secretes HCl, highly acidic chyme empties into the duodenum, where it is neutralized by sodium bicarbonate (NaHCO₃) secreted into the duodenum primarily from the pancreas.
• Unneutralized acid may damage the duodenal mucosa and inactivate the pancreatic digestive enzymes secreted into the duodenum.
• Appropriately, unneutralized acid in the duodenum induces the release of secretin, a hormone that slows emptying of acidic gastric contents until complete neutralization can be accomplished

Question 23

Examine why it is important that each of these stimuli in the duodenum delays gastic emptying: Hypertonicity

Answer 23

• As molecules of protein and starch are digested in the duodenum, large numbers of amino acid and glucose molecules are released.
• If absorption of these amino acid and glucose molecules does not keep pace with the rate at which protein and carbohydrate digestion proceeds, these large numbers of molecules remain in the chyme and increase the osmolarity of the duodenal contents. Osmolarity depends on the number of molecules present, not on their size, and one protein molecule may be split into several hundred amino acid molecules, each of which has the same osmotic activity as the original protein molecule.
• The same holds true for one large starch molecule, which yields many smaller but equally osmotically active glucose molecules.
• Because water is freely diffusible across the duodenal wall, it enters the duodenal lumen from the plasma as the duodenal osmolarity rises.
• Large volumes of water entering the intestine from the plasma lead to intestinal distension, and, more important, circulatory disturbances result because of the reduction in plasma volume.
• To prevent these effects, gastric emptying is reflexly inhibited when the osmolarity of the duodenal contents starts to rise.
• Thus, the amount of food entering the duodenum for further digestion into a multitude of additional osmotically active particles is reduced until absorption processes have had an opportunity to catch up.

Question 24

Examine why it is important that each of these stimuli in the duodenum delays gastic emptying: Distension

Answer 24

• Too much chyme in the duodenum inhibits the emptying of even more gastric contents, giving the distended duodenum time to cope with the excess volume of chyme it already contains before it gets any more.
• the intra-abdominal pressure and forcing the abdominal viscera upward. As the flaccid stomach is squeezed between the diaphragm from above and the compressed abdominal cavity from below, the gastric contents are forced upward through the relaxed sphincters and esophagus and out through the mouth. The glottis is closed, so vomited material does not enter the trachea.
• Also, the uvula is raised to close off the nasal cavity.
• The vomiting cycle may be repeated several times until the stomach is emptied.

Question 25

TRUE or FALSO:

Emotions can influence gastric motility

Answer 25

Yes

Question 26

How do emotions influence gastric motility?

Can pain affect it?

Answer 26

Other factors unrelated to digestion, such as emotions, can alter gastric motility by acting through the autonomic nerves to influence the degree of gastric smooth muscle excitability. Even though the effect of emotions on gastric motility varies among people and is not always predictable, sadness and fear generally tend to decrease motility, whereas anger and aggression tend to increase it. In addition to emotional influences, intense pain from any part of the body tends to inhibit motility throughout the digestive tract. This response is brought about by increased sympathetic activity

Question 27

What is the medical term for vomiting?

Answer 27

Emesis

Question 28

Define emesis

Answer 28

Vomiting, or emesis, the forceful expulsion of gastric contents out through the mouth, is not accomplished by reverse peristalsis in the stomach, as might be predicted

Question 29

Is the stomach actively involved in vomiting?

Answer 29

• Actually, the stomach itself does not actively participate in vomiting.
• The stomach, the esophagus, and associated sphincters are all relaxed during vomiting.
• The major force for expulsion comes, surprisingly, from contraction of the respiratory muscles—namely, the diaphragm (the major inspiratory muscle) and the abdominal muscles (the muscles of active expiration)

Question 30

Where is the complex act of vomiting coordinated?

Answer 30

by a vomiting center in the medulla of the brain stem

Question 31

What are the warning signs that someone is about to vomit?

What processed occur as someone is about to vomit?

Answer 31

• Vomiting is usually preceded by profuse salivation, sweating, rapid heart rate, and sensation of nausea.
• Vomiting begins with a deep inspiration and closure of the glottis. The contracting diaphragm descends downward on the stomach while simultaneous contraction of the abdominal muscles compresses the abdominal cavity, increasing the intra-abdominal pressure and forcing the abdominal viscera upward
• As the flaccid stomach is squeezed between the diaphragm from above and the compressed abdominal cavity from below, the gastric contents are forced upward through the relaxed sphincters and esophagus and out through the mouth. The glottis is closed, so vomited material does not enter the trachea. Also, the uvula is raised to close off the nasal cavity. The vomiting cycle may be repeated several times until the stomach is emptied

Question 32

Vomiting can be initiated by afferent input to the vomiting center from various receptors throughout the body, including the following:

Answer 32

■ Tactile (touch) stimulation of the back of the throat, which is one of the most potent stimuli. For example, sticking a finger in the back of the throat or even the presence of a tongue depressor or dental instrument in the back of the mouth can trigger gagging and even vomiting in some people.

■ Irritation or distension of the stomach and duodenum.

■ Elevated intracranial pressure, such as that caused by cerebral hemorrhage. Thus, vomiting after a head injury is considered a bad sign; it suggests swelling or bleeding within the cranial cavity.

■ Rotation or acceleration of the head producing dizziness, such as in motion sickness.

■ Chemical agents, including drugs or noxious substances that initiate vomiting (that is, emetics) either by acting in the upper parts of the GI tract or by stimulating chemoreceptors in a specialized chemoreceptor trigger zone next to the vomiting center in the brain. For example, chemotherapeutic agents used in treating cancer often cause vomiting by acting on the chemoreceptor trigger zone.

■ Psychogenic vomiting induced by emotional factors, including those accompanying nauseating sights and odors and anxiety, as before taking an examination

Question 33

What are the effects of vomiting?

Answer 33

With excessive vomiting, the body experiences large losses of secreted fluids and acids that normally would be reabsorbed. The resulting reduction in plasma volume can lead to dehydration and circulatory problems, and the loss of acid from the stomach can lead to metabolic alkalosis.

We have completed our discussion of gastric motility and now shift to gastric secretion.

Question 34

Gastric digestive juice is secreted by glands located where?

Answer 34

At the base of gastric pits.

Question 35

Each day, the stomach secretes how many litres of gastric juice?

Where are the cells that secrete gastric juice located?

What are gastric pits?

What are gastric glands?

Answer 35

Each day, the stomach secretes about 2 liters of gastric juice. The cells that secrete gastric juice are located in the gastric mucosa, which is divided into two distinct areas:

(1) the oxyntic mucosa, which lines the body and fundus, and (2) the pyloric gland area (PGA), which lines the antrum.

The luminal surface of the stomach is pitted with deep pockets formed by infoldings of the gastric mucosa. The first parts of these invaginations are called gastric pits, at the base of which lie the gastric glands. A variety of secretory cells line these invaginations, some exocrine and some endocrine or paracrine

Question 36

Three types of gastric exocrine secretory cells are found in the walls of the pits and glands in the oxyntic mucosa:

Answer 36

■ Mucous cells line the gastric pits and the entrance of the glands. They secrete a thin, watery mucus. (Mucous is the adjective; mucus is the noun.)

■ The deeper parts of the gastric glands are lined by chief and parietal cells. The more numerous chief cells secrete the enzyme precursor pepsinogen.

■ The parietal (or oxyntic) cells secrete HCl and intrinsic factor (oxyntic means “sharp,” a reference to these cells’ potent HCl secretory product).

Question 37

Mucus, pepsinogen and HCL are exocrine secretions all released where?

Answer 37

• These exocrine secretions are all released into the gastric lumen. Collectively, they make up the gastric digestive juice

Question 38

Between the gastric pits, the gastric mucosa is covered by surface epithelial cells, which secrete what?

Answer 38

A sticky, alkaline mucus that forms a visible layer several millimeters thick over the surface of the mucosa

Question 39

TRUE OR FALSE:

Stem cells are found in gastric pits

Explain what happens to the cells in gastric pits that result from cell division

How many days does it take for the cells of the stomach mucosa to be replaced?

Why is it important for them to be replaced?

Answer 39

True

• These cells rapidly divide and are the parent cells of all new cells of the gastric mucosa.
• The daughter cells that result from cell division either migrate out of the pit to become surface epithelial cells or migrate deeper to the gastric glands where they differentiate into chief or parietal cells.
• Through this activity, the entire stomach mucosa is replaced about every 3 days.
• This frequent turnover is important because the harsh acidic stomach contents expose the mucosal cells to lots of wear and tear

Question 40

Explain the secretion of HCL by parietal cells and how it activates pepsinogen

Answer 40

• When stimulated, parietal cells form deep invaginations called canaliculi (singular canaliculus) along the luminal (or apical) membrane, which increase the membrane surface area bearing transport proteins that actively secrete HCl into the lumen of the gastric pits. Each pit drains acid into the lumen of the stomach, which can cause the luminal pH to fall as low as 2.
• Hydrogen ion (H1) and chloride ion (Cl₂) are actively secreted by separate pumps. H1 is actively transported against a tremendous concentration gradient, with the H1 concentration being as much as 3 million times greater in the lumen than in the blood.
• Cl₂ is secreted by a secondary active-transport mechanism against a much smaller concentration gradient of only 1.5 times.

Question 41

Describe the mechanism of H⁺ and Cl₂ Secretion

Answer 41

• The secreted H+ is not transported from the plasma but is derived from the breakdown of H2O molecules into H1 and OH2 (hydroxyl ions) within the parietal cell
• The stomach’s parietal cells actively secrete H+ and Cl₂ by the actions of two separate pumps.
• H+ is secreted into the lumen by a primary H+–K+ ATPase active-transport pump at the parietal cell’s luminal border.
• The H+ that is secreted, as well as HCO₃- 2, is formed within the parietal cell from H₂O and CO2 in a reaction catalyzed by carbonic anhydrase. Cl2 is secreted by secondary active transport. Driven by the HCO₃- 2 concentration gradient, a Cl₂–HCO₃- antiporter in the basolateral membrane transports HCO₃- down its concentration gradient into the plasma and simultaneously transports Cl₂ into the parietal cell against its concentration gradient.
• Cl₂ secretion is completed as the Cl₂ that entered from the plasma diffuses out of the cell down its electrochemical gradient through a luminal Cl₂ channel into the lumen

Question 42

What is the major digestive constituent of gastric secretion?

Where is it stored?

How is it released?

Answer 42

Pepsinogen, an inactive enzymatic molecule produced by the chief cells. Pepsinogen, once activated to the enzyme pepsin, begins protein digestion. Pepsinogen is stored in the chief cells’ cytoplasm within secretory vesicles known as zymogen granules, from which it is released by exocytosis on appropriate stimulation

Question 43

What happens when pepsinogen is secreted into the gastric lumen?

Why is it secreted in an inactive form?

Answer 43

• HCl cleaves off a small fragment of the molecule, converting it to the active form of pepsin. Once formed, pepsin acts on other pepsinogen molecules to produce more pepsin, a mechanism called an autocatalytic process
• Pepsin initiates protein digestion by splitting certain amino acid linkages in proteins to yield peptide fragments (small amino acid chains); it works most effectively in the acid environment provided by HCl.
• Because pepsin can digest protein, it must be stored and secreted in an inactive form so that it does not digest the proteins of the cells in which it is formed.
• Therefore, pepsin is maintained in the inactive form of pepsinogen until it reaches the gastric lumen, where it is activated by HCl secreted into the lumen by a different cell type

Question 44

Explain the protective properties of mucus

Answer 44

■ Through its lubricating properties, mucus protects the gastric mucosa against mechanical injury.

■ It helps protect the stomach wall from self-digestion because pepsin is inhibited when it comes in contact with the layer of mucus coating the stomach lining. (However, mucus does not affect pepsin activity in the lumen, where digestion of dietary protein proceeds without interference.)

■ Being alkaline, mucus helps protect against acid injury by neutralizing HCl in the vicinity of the gastric lining, but it does not interfere with the function of HCl in the lumen. Whereas the pH in the lumen may be as low as 2, the pH in the layer of mucus adjacent to the mucosal cell surface is about 7

Question 45

What is vitamin B₁₂ essential for?

What is the consequence of intrinsic factor absence?

Answer 45

• Vitamin B₁₂ is essential for normal formation of red blood cells.
• In the absence of intrinsic factor, vitamin B12 is not absorbed, so erythrocyte production is defective and pernicious anemia resuls. Pernicious anemia is typically caused by an autoimmune attack against the parietal cells

Question 46

In addition to the gastric exocrine secretory cells, other secretory cells in the gastric glands release endocrine and paracrine regulatory factors instead of products involved in the digestion of nutrients in the gastric lumen

Give some examples of these factors

Answer 46

■ Endocrine cells known as G cells, found in the gastric pits only in the PGA, secrete the hormone gastrin into the blood.

■ Enterochromaffin-like (ECL) cells, dispersed among the parietal and chief cells in the gastric glands of the oxyntic mucosa, secrete the paracrine histamine.

■ D cells, which are scattered in gastric glands near the pylorus but are more numerous in the duodenum, secrete the paracrine somatostatin.

These three regulatory factors from the gastric pits, along with the neurotransmitter ACh, primarily control secretion of gastric digestive juices

Question 47

G cells secrete the hormone gastrin into the blood in response to what?

How does gastrin indirectly promote HCL secretion?

Answer 47

• Protein products in the stomach lumen and in response to ACh. Like secretin and CCK, gastrin is a major GI hormone.
• After being carried by the blood back to the stomach mucosa, gastrin stimulates the parietal and chief cells, promoting secretion of a highly acidic gastric juice directly stimulating the parietal cells, gastrin indirectly promotes HCl secretion by stimulating the ECL cells to release histamine, which also stimulates the parietal cells.
• Gastrin is the main factor that brings about increased HCl secretion during meal digestion.
• Gastrin is also trophic (growth promoting) to the mucosa of the stomach and small intestine, thereby maintaining their secretory capabilities

Question 48

Somatostatin is released from the D cells in response to what?

Answer 48

• In response to acid.
• It acts locally as a paracrine in negative-feedback fashion to inhibit secretion by the parietal cells, G cells, and ECL cells, thus turning off the HCl-secreting cells and their most potent stimulatory pathway.

Question 49

The rate of gastric secretion can be influenced by which 3 factors?

Answer 49

(1) factors arising before food reaches the stomach
(2) factors resulting from food in the stomach
(3) factors in the duodenum after food has left the stomach. Accordingly, gastric secretion is divided into three phases: cephalic, gastric, and intestinal.

Question 50

Control of gastric secretion involves three phases: Explain the Cephalic Phase

Answer 50

• The cephalic phase of gastric secretion refers to increased secretion of HCl and pepsinogen that occurs in feedforward fashion in response to stimuli acting in the head even before food reaches the stomach (cephalic means “head”).
• Thinking about, seeing, smelling, tasting, chewing, and swallowing food increases gastric secretion via vagal stimulation in two ways.
• First, vagal stimulation of the intrinsic plexuses promotes increased secretion of ACh, which leads to increased secretion of HCl and pepsinogen by the secretory cells. Second, direct vagal stimulation of the G cells induces gastrin release, which in turn further enhances secretion of HCl and pepsinogen, with the effect on HCl being potentiated by gastrin promoting the release of histamine

Question 51

Control of gastric secretion involves three phases: Explain the Gastric phase

Answer 51

• The gastric phase of gastric secretion begins when food reaches the stomach. Stimuli acting on the stomach— namely protein, distension, caffeine, and alcohol—increase gastric secretion by overlapping efferent pathways.
• For example, the most potent stimulus, protein (especially short peptide fragments) in the stomach lumen, stimulates chemoreceptors that activate intrinsic-plexus pathways that induce gastric secretion.
• Furthermore, protein brings about activation of the extrinsic vagal fibers to the stomach.
• Vagal activity further enhances intrinsic nerve stimulation of the secretory cells and triggers the release of gastrin. Last, protein also directly stimulates the release of gastrin. Gastrin, in turn, is a powerful stimulus for further HCl and pepsinogen secretion. Through these synergistic and overlapping pathways, protein induces secretion of a highly acidic, pepsin-rich gastric juice, which continues digestion of the protein that first initiated the process

Question 52

Why should people with ulcers or gastric hyperacidity should avoid caffeinated and alcoholic beverages?

Answer 52

in that first initiated the process (❙Table 16-4). When the stomach is distended with protein-rich food that needs to be digested, these secretory responses are appropriate. Caffeine and, to a lesser extent, alcohol also stimulate secretion of a highly acidic gastric juice, even when no food is present. This unnecessary acid can irritate the linings of the stomach and duodenum

Question 53

Control of gastric secretion involves three phases: Explain the intestial phase

Answer 53

• The intestinal phase of gastric secretion encompasses the factors originating in the small intestine that influence gastric secretion. Whereas the other phases are excitatory, this phase is inhibitory.
• The intestinal phase is important in helping shut off the flow of gastric juices as chyme begins to be emptied into the small intestine

Question 54

TRUE or FALSE:

Gastric secretion gradually increases as food empties from the stomach into the intestine

Answer 54

False

Gastric secretion gradually increases as food empties from the stomach into the intestine

Question 55

Despite the protection provided by mucus, by the gastric mucosal barrier, and by frequent turnover of cells, the barrier occasionally is broken and the gastric wall is injured by its acidic and enzymatic contents, producing an erosion, or

Answer 55

peptic ulcer

Excessive gastric reflux into the esophagus and dumping of excessive acidic gastric contents into the duodenum can lead to peptic ulcers in these locations also

Question 56

The components of the gastric mucosal barrier enable the stomach to contain acid without injuring itself:

Answer 56

1. The luminal membranes of the gastric mucosal cells are impermeable to H+ so that HCI cannot penetrate into the cells.
2. The cells are joined by tight junctions that prevent HCI from penetrating between them.
3. A mucus coating over the gastric mucosa serves as a physical barrier to acid penetration.
4. The HCO₃ –-rich mucus also serves as a chemical barrier that neutralizes acid in the vicinity of the mucosa. Even when luminal pH is 2, the mucus pH is 7.