which of the following is the major process or function that occurs in the stomach?

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Digestive System Processes and Regulation

LEARNING OBJECTIVES

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

Discuss six fundamental activities of the digestive system, giving an example of each

Compare and contrast the neural and hormonal controls involved in digestion

The digestive system uses mechanical and chemical activities to break food down into absorbable substances during its journey through the digestive system. Table 1 provides an overview of the basic functions of the digestive organs.

Visit this site for an overview of digestion of food in different regions of the digestive tract. Note the route of non-fat nutrients from the small intestine to their release as nutrients to the body.

Table 1. Functions of the Digestive Organs

Organ Major functions Other functions

Mouth Ingests food

Chews and mixes food

Begins chemical breakdown of carbohydrates

Moves food into the pharynx

Begins breakdown of lipids via lingual lipase

Moistens and dissolves food, allowing you to taste it

Cleans and lubricates the teeth and oral cavity

Has some antimicrobial activity

Pharynx

Propels food from the oral cavity to the esophagus

Lubricates food and passageways

Esophagus

Propels food to the stomach

Lubricates food and passageways

Stomach

Mixes and churns food with gastric juices to form chyme

Begins chemical breakdown of proteins

Releases food into the duodenum as chyme

Absorbs some fat-soluble substances (for example, alcohol, aspirin)

Possesses antimicrobial functions

Stimulates protein-digesting enzymes

Secretes intrinsic factor required for vitamin B12 absorption in small intestine

Small intestine

Mixes chyme with digestive juices

Propels food at a rate slow enough for digestion and absorption

Absorbs breakdown products of carbohydrates, proteins, lipids, and nucleic acids, along with vitamins, minerals, and water

Performs physical digestion via segmentation

Provides optimal medium for enzymatic activity

Accessory organs

Liver: produces bile salts, which emulsify lipids, aiding their digestion and absorption

Gallbladder: stores, concentrates, and releases bile

Pancreas: produces digestive enzymes and bicarbonate

Bicarbonate-rich pancreatic juices help neutralize acidic chyme and provide optimal environment for enzymatic activity

Large intestine

Further breaks down food residues

Absorbs most residual water, electrolytes, and vitamins produced by enteric bacteria

Propels feces toward rectum

Eliminates feces

Food residue is concentrated and temporarily stored prior to defecation

Mucus eases passage of feces through colon

Digestive Processes

The processes of digestion include six activities: ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation.

The first of these processes, ingestion, refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that begin breaking down the carbohydrates in the food plus some lipid digestion via lingual lipase. Chewing increases the surface area of the food and allows an appropriately sized bolus to be produced.

Figure 1. Peristalsis moves food through the digestive tract with alternating waves of muscle contraction and relaxation.

Food leaves the mouth when the tongue and pharyngeal muscles propel it into the esophagus. This act of swallowing, the last voluntary act until defecation, is an example of propulsion, which refers to the movement of food through the digestive tract. It includes both the voluntary process of swallowing and the involuntary process of peristalsis. Peristalsis consists of sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along (Figure 1). These waves also play a role in mixing food with digestive juices. Peristalsis is so powerful that foods and liquids you swallow enter your stomach even if you are standing on your head.

Digestion includes both mechanical and chemical processes. Mechanical digestion is a purely physical process that does not change the chemical nature of the food. Instead, it makes the food smaller to increase both surface area and mobility. It includes mastication, or chewing, as well as tongue movements that help break food into smaller bits and mix food with saliva. Although there may be a tendency to think that mechanical digestion is limited to the first steps of the digestive process, it occurs after the food leaves the mouth, as well. The mechanical churning of food in the stomach serves to further break it apart and expose more of its surface area to digestive juices, creating an acidic “soup” called chyme. Segmentation, which occurs mainly in the small intestine, consists of localized contractions of circular muscle of the muscularis layer of the alimentary canal. These contractions isolate small sections of the intestine, moving their contents back and forth while continuously subdividing, breaking up, and mixing the contents. By moving food back and forth in the intestinal lumen, segmentation mixes food with digestive juices and facilitates absorption.

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Anatomy and physiology of the stomach

The stomach is a muscular, sac-like organ in the upper abdomen. It is part of the digestive system. Learn about the anatomy and physiology of the stomach.

What is stomach cancer

Anatomy and physiology of the stomach

The stomach is a muscular, J-shaped organ in the upper part of the abdomen. It is part of the digestive system, which extends from the mouth to the anus. The size of the stomach varies from person to person, and from meal to meal.

Structure

The stomach is part of the digestive system and is connected to the:

esophagus – a tube-like organ that connects the mouth and throat to the stomach. The area where the esophagus joins the stomach is called the gastroesophageal (GE) junction.

small intestine (small bowel) – a long tube-like organ that extends from the stomach to the colon (large intestine or large bowel). The first part of the small intestine is called the duodenum, and it is this part that is connected to the stomach.

The stomach is surrounded by a large number of

lymph nodes .

Regions of the stomach

The stomach is divided into 5 regions:

The cardia is the first part of the stomach below the esophagus. It contains the cardiac sphincter, which is a thin ring of muscle that helps to prevent stomach contents from going back up into the esophagus.

The fundus is the rounded area that lies to the left of the cardia and below the diaphragm .

The body is the largest and main part of the stomach. This is where food is mixed and starts to break down.

The antrum is the lower part of the stomach. The antrum holds the broken-down food until it is ready to be released into the small intestine. It is sometimes called the pyloric antrum.

The pylorus is the part of the stomach that connects to the small intestine. This region includes the pyloric sphincter, which is a thick ring of muscle that acts as a valve to control the emptying of stomach contents (chyme) into the duodenum (first part of the small intestine). The pyloric sphincter also prevents the contents of the duodenum from going back into the stomach.

Layers of the stomach wall

The stomach is made up of several layers of tissue:

The mucosa (mucous membrane) is the inner lining of the stomach. When the stomach is empty the mucosa has a ridged appearance. These ridges (rugae) flatten out as the stomach fills with food.

The next layer that covers the mucosa is the submucosa. It is made up of connective tissue that contains larger blood and lymph vessels, nerve cells and fibres.

The muscularis propria (or muscularis externa) is the next layer that covers the submucosa. It is the main muscle of the stomach and is made up of 3 layers of muscle.

The serosa is the fibrous membrane that covers the outside of the stomach. The serosa of the stomach is also called the visceral peritoneum .

Function

The stomach has 3 main functions:

temporary storage for food, which passes from the esophagus to the stomach where it is held for 2 hours or longer

mixing and breakdown of food by contraction and relaxation of the muscle layers in the stomach

digestion of food

The mucosa contains specialized cells and glands that produce hydrochloric acid and digestive enzymes to help digest food. The mucosa in the cardiac and pyloric regions of the stomach release mucus that helps protect the lining of the stomach from the acid produced for digestion. Other specialized cells in the mucosa of the pylorus release the

hormone gastrin into the blood. Gastrin helps to stimulate the release of acid and enzymes from the mucosa. Gastrin also helps the muscles of the stomach to start contracting.

Food is broken down into a thick, acidic, soupy mixture called chyme. The pyloric sphincter relaxes once chyme formation is complete. Chyme then passes into the duodenum. The duodenum plays a big role in absorption of the food we eat. The stomach does not play a big role in absorption of food. It only absorbs water, alcohol and some drugs.

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Mastering A&P Chapter 23 Flashcards & Practice Test

Start studying Mastering A&P Chapter 23. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

Mastering A&P Chapter 23

Absorption

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Which major process involves the removal of water from intestinal contents?

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Small intestine

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Which organ of the digestive tract is the body's major digestive organ?

small intestine large intestine stomach liver

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1/44 Created by kmccaffery1127

Terms in this set (44)

Absorption

Which major process involves the removal of water from intestinal contents?

Small intestine

Which organ of the digestive tract is the body's major digestive organ?

small intestine large intestine stomach liver Mucosa

Which layer of the alimentary canal is constructed from either stratified squamous or simple columnar epithelium?

serosa muscularis externa mucosa submucosa Muscularis externa

Which layer of the alimentary canal is responsible for segmentation and peristalsis?

muscularis externa serosa mucosa submucosa Orbicularis oris

What muscle forms the labia of the mouth and controls most lip movement, including puckering?

orbicularis oris

levator labii superioris

zygomaticus buccinator

Saliva contains enzymes that begin the chemical breakdown of proteins

Which of the following is NOT a function of saliva?

Saliva contains enzymes that begin the chemical breakdown of proteins.

Saliva cleanses the mouth.

Saliva moistens food and helps compact it into a bolus.

Saliva dissolves food chemicals so that they can be tasted.

Being stressed or frightened

Which of the following inhibits salivation?

being stressed or frightened

relaxing after a meal

the sight or smell of food

ingestion of spicy foods

Incisors

Which teeth are best suited for cutting or nipping off pieces of food in the permanent dentition?

premolars (bicuspids)

incisors canines molars Segmentation

Which digestive process does NOT occur in the mouth?

digestion ingestion

mechanical breakdown

segmentation

Sitting upright after a meal

Which of the following is not a common risk factor for acid reflux disease?

snacking near bedtime

eating fatty or spicy foods

being overweight or obese

sitting upright after a meal

Hiatal hernia

What is the condition called where a proximal portion of the stomach pushes through an opening in the diaphragm, allowing stomach acid to pass into the esophagus?

dysphagia dyspepsia esophageal varices hiatal hernia

The tooth lacks a nerve that would make the patient perceive pain

After root canal therapy, a tooth may become infected again due to poor dental hygiene. The patient might not seek treatment for this newly infected tooth because ______.

the tooth no longer has any pulp that could decay

the tooth no longer has any blood vessels that would allow the bacteria to spread to other regions within the tooth

the tooth lacks a nerve that would make the patient perceive pain

after root canal therapy, the tooth is dead and therefore there is no need to worry about losing it

Mucosa

Which layer of the stomach contains the gastric pits that secrete mucous, acid, and digestive enzymes?

serosa mucosa submucosa muscularis externa

Production of intrinsic factor

What role of the stomach is essential to life?