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StatPearls . Treasure Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

Food digestion is the breakdown of huge food particles into smaller absorbable nutrients needed for energy production, growth, and also cellular repair. It begins with ingestion and also ends v defecation. Cradle takes ar in the cradle tract in two major forms: mechanical and also chemical. Mechanically digestion is the physical destruction of big food particles into smaller pieces that digestive enzyme can accessibility through chemical digestion. Chemical digestion is the enzymatic cleavage the proteins, carbohydrates, and also fats into tiny amino acids, sugars, and also fatty acids. When food start the mouth, that mixes with saliva and gets chewed with the process of mastication. Saliva is well-off in mucus and salivary enzymes, and together, with the results of mastication, it create a mass dubbed a food bolus. The food bolus then travels under the esophagus via wave-like muscular contractions, dubbed peristalsis, before it reaches the stomach.

The stomach theatre a an important role in the beforehand stages the food digestion. Asides from squeezing and churning the food bolus, it also secretes a mixture the compounds, collectively known as "gastric juice." Gastric juice comprises water, mucus, hydrochloric acid, pepsin, and intrinsic factor. The these 5 components, pepsin is the principal enzyme affiliated in protein digestion. That breaks down proteins right into smaller peptides and also amino mountain that can be quickly absorbed in the little intestine. Particular cells within the gastric lining, known as chief cells, release pepsin in an inactive form, or zymogen form, called pepsinogen. By act so, the stomach avoids the auto-digestion the protective proteins in the lining that the cradle tract. Because chief cells release pepsin together a zymogen, activation by an acidic atmosphere is necessary. Hydrochloric acid (HCl), another component the the gastric juice, theatre a crucial role in developing the pH compelled for pepsin activity. Parietal cells create HCl by secreting hydrogen and also chloride ions. Once pepsinogen and hydrochloric acid exist with each other in the gastric juice, pepsin bring away its active form. Through the actions of pepsin and also the squeezing nature of the stomach, the food bolus enters the intestines as a liquidy mixture of partly digested food particles, called chyme.


Issues of Concern

Pepsin depends on one acidic atmosphere for protein digestion. Therefore, it is most effective at a pH of around 1.5 to 2. Low pH permits pepsinogen to cleave chin and type active pepsin. When it get the duodenum, though, the assumes one inactive kind as the pH rises over 6. Nonetheless, protein digestion proceeds to take place throughout the tiny intestines via the effects of pancreatic enzymes: trypsin, chymotrypsin, elastase, and carboxypeptidase. Together such, pepsin is not vital for life, and also protein digestion have the right to still take place in the lack of pepsin. That is worth stating that pepsin stays structurally steady until at least a pH the 8. Therefore, it can constantly be reactivated as lengthy as pH remains below 8. This characteristics proves appropriate in the pathophysiology of laryngopharyngeal reflux, as debated later in the article.<1>

As discussed earlier, the stomach provides pepsin with an ideal environment for protein digestion. Doing so helps v breaking under proteins right into smaller nutrients, but at the very same time, puts the stomach at hazard of autodigestion. Therefore, a protective system should exist to help maintain mucosal integrity. Fortunately, a mucus lining loaded through bicarbonate molecules helps protect against hydrochloric acid and also creates a near-neutral pH environment that deactivates pepsin.<2>


Function

Pepsin is an endopeptidase that breaks down dietary proteins getting to the stomach right into amino acids. It features by digesting peptide bonds, the primary chemical bonds discovered in proteins. In an answer to assorted stimuli, small basophilic cell in the deeper layers of gastric glands, well-known as chef cells, develop pepsinogen. Notably, acetylcholine, gastrin, and low pH straight stimulate chief cells to secrete pepsinogen. Acetylcholine is a neurotransmitter exit from vagal parasympathetic nerve terminals in the "cephalic phase" that food digestion. Besides improving chief cell activity, it likewise stimulates parietal cell to create hydrochloric acid (HCl) via their proton pumps. The short pH applied by HCl breaks under pepsinogen right into its active form, pepsin. Gastrin is an additional gastrointestinal hormone exit by G cell in the stomach antrum and the duodenum. G cell secrete gastrin in solution to countless stimuli, consisting of stomach distension, amino acids and peptides, high pH, and vagal stimulation. Comparable to acetylcholine, gastrin additionally activates parietal cell to secrete hydrochloric mountain (HCL) on peak of the chief cabinet stimulatory effects. It does so both directly, and also indirectly, with the activity of histamine released by enterochromaffin-like (ECL) cells. Histamine is, in fact, the most potent activator of parietal cells. Somatostatin, ~ above the other hand, is an inhibitory gastrointestinal hormone exit by D cell in the duodenum and also stomach antrum. That inhibits pepsinogen relax from cook cells, thereby opposing the results of gastrin, HCl, and also acetylcholine.<3>


Related Testing

As mentioned earlier, the stomach protects itself from the digestive properties that pepsin by developing an adherent layer of bicarbonate-rich mucus lining. As such, pepsin should always remain in the stomach and also should never ever regurgitate ago to the top tracts. As lengthy as the lower esophageal sphincter attributes accurately, pepsin resides withing the stomach and the duodenum, and the esophagus lining continues to be intact. However, a weak esophageal sphincter permits pepsin to with not only the esophagus but likewise the upper airways. Gastroesophageal reflux condition (GERD) and laryngopharyngeal reflux (LPR) are two an illness processes identified by weak esophageal sphincters.<2>

The outstanding pepsin test is a non-invasive, low-cost check that have the right to detect the existence of pepsin in saliva, as the surname implies. The has presented some promise as a useful diagnostic device for LPR. However, more research need to assess the sensitivity, specificity, and also clinical utility of the test. Top top the contrary, the outcomes are no that encouraging with GERD, and also the check is no longer as useful as previously thought.<4><5>


Pathophysiology

Pepsin dram a role in the pathophysiology that laryngopharyngeal reflux (LPR), a condition that originates native the digestive tract and significantly results the top airway structures. Take into consideration LPR in the differential diagnosis the a patient presenting v hoarseness, soft dysphagia, chronic cough, and also non-productive neck clearing.

In suitable digestive tract, pepsin is energetic only in the stomach, especially when the pH is between 1.5 and also 2. This low pH occurs as soon as the cradle (GI) street senses a food bolus, effectively releasing the three principal stimulants the proton pumps in parietal cells: gastrin, histamine, and also acetylcholine.<6>

A weak reduced esophageal sphincter (LES) allows gastric juice to take trip retrogradely from the stomach approximately the esophagus. If the top esophageal sphincter (UES) stops working as well, gastric juice can reach the larynx. In the larynx, hydrochloric acid and pepsin can damage an essential structures, such as the vocal cords. It might even relocate past the larynx to influence the lung themselves. In healthy people, the larynx has dense neural tissue that prevents an important damage to structures in the larynx by inducing the sneeze reflex ~ above exposure to caustic stimuli. Unfortunately, patients through laryngopharyngeal reflux have altered neural sensitivity and cannot accordingly cough in response to acidic injury. Without an undamaged defense mechanism, acid and pepsin deserve to readily enter the reduced airways and also damage the larynx. These structures room susceptible to gastric juice, and also epithelial damage rapidly ensures, causing hoarseness, dysphagia, and also chronic cough.<7><8>

In a patient with a weak UES, rise in intraabdominal press further reduces the sphincter"s function and predisposes come LPR symptoms. Thus, symptom are an ext likely to occur in the upright position upon exertion, such as during exercise or once doing the Valsalva maneuver.<9>

Gastroesophageal reflux an illness (GERD) is similar to LPR in that both obstacle occur due to the reflux of the acidic materials from the stomach. However, two crucial differences exist between GERD and LPR. The very first is one anatomical distinction as patients with GERD have weak LES while patients with LPR have weak LES and also UES. The 2nd is the pepsin plays a critical role in the pathophysiology of LPR while playing a minimal or unknown duty in GERD.<10>

It might be beneficial to think that GERD and also LPR as 2 separate illness on the exact same spectrum. A selection of food, consisting of chocolate, peppermint, alcohol, fat foods, and coffee, have the right to impair the function of the upper and lower esophageal sphincters secondary to delay gastric emptying. Avoidance of these foodstuffs plays a crucial role in to decrease the incidence that GERD and LPR.


Clinical Significance

Evaluating a patient through LPR should always begin v a thorough history to identify the presence of arguing symptoms such together chronic cough, hoarseness, dysphagia, or throat clearing. Because gastroesophageal reflux condition shares plenty of similarities through LPR, the next step is to dominion out GERD. Symptoms the worsen while upright and also during periods of physical exertion are an ext suggestive the LPR. On the other hand, symptom that obtain worse if lying under are an ext indicative that GERD. An example would be nocturnal asthma-like symptom in GERD. One more symptom that says GERD rather than LPR is retrosternal burning chest pains (heartburn). A laryngoscope aids in the diagnosis of LPR by mirroring posterior laryngeal edema or vocal cord edema.<7><9>

Treatment of LPR relies on a mix of dietary change and pharmacological interventions. Dietary changes include avoidance of acidic food such together citrus fruits, tomatoes, and salad dressings. Other dietary changes involve staying clear of foods that can weaken the esophageal sphincters, including caffeine, peppermint, alcohol, chocolate, and also fatty foods. As soon as these interventions prove ineffective, including a pharmacological treatment can help. The score of treatment is to inhibit acid release native parietal cells. Recall that histamine is the major stimulant of proton pumps in parietal cells. Therefore, histamine-blockers such as ranitidine and also cimetidine can efficiently suppress acid release, thereby decreasing pepsin activity.<11> Proton pump inhibitors are another class of acid-suppressing agents that work-related by straight inhibiting mountain release. Instances of PPIs room omeprazole and also esomeprazole.

Pepsin Pearls


Parietal cells within the stomach lining secrete hydrochloric acid that lowers the pH of the stomach.
Acetylcholine, gastrin, and also histamine stimulate the proton pump in parietal cell to relax hydrogen ions and decrease pH.
A patient v weak upper and lower esophageal sphincters (UES and also LES) deserve to experience a retrograde circulation of gastric juice, enabling pepsin come damage critical structures in ~ the larynx.

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A weak UES and also LES rise the threat of laryngopharyngeal reflux (LPR), a condition identified by pepsin-mediated damages of structures within the larynx.