What Is the Process of Forcing Food Back Up the Esophagus So It Can Be Chewed Again Called

Learning Objectives

By the end of this section, y'all volition be able to:

• Discuss six fundamental activities of the digestive system, giving an example of each
• Compare and dissimilarity 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 ane provides an overview of the bones functions of the digestive organs.

Table one. 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, assuasive y'all to gustatory modality it Cleans and lubricates the teeth and oral cavity Has some antimicrobial activity
Pharynx	Propels nutrient from the oral cavity to the esophagus	Lubricates food and passageways
Esophagus	Propels food to the stomach	Lubricates nutrient and passageways
Stomach	Mixes and churns food with gastric juices to form chyme Begins chemical breakdown of proteins Releases nutrient into the duodenum equally chyme Absorbs some fatty-soluble substances (for example, alcohol, aspirin) Possesses antimicrobial functions	Stimulates protein-digesting enzymes Secretes intrinsic factor required for vitamin B12 assimilation in modest intestine
Pocket-sized intestine	Mixes chyme with digestive juices Propels food at a rate slow plenty for digestion and absorption Absorbs breakdown products of carbohydrates, proteins, lipids, and nucleic acids, along with vitamins, minerals, and water Performs concrete digestion via segmentation	Provides optimal medium for enzymatic activity
Accompaniment 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	Nutrient residue is concentrated and temporarily stored prior to defecation Mucus eases passage of feces through colon

Digestive Processes

The processes of digestion include half dozen activities: ingestion, propulsion, mechanical or concrete digestion, chemical digestion, absorption, and defecation.

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

Figure ane. 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 information technology into the esophagus. This act of swallowing, the final voluntary act until defecation, is an example of propulsion, which refers to the motility of food through the digestive tract. It includes both the voluntary process of swallowing and the involuntary procedure of peristalsis. Peristalsis consists of sequential, alternate waves of wrinkle and relaxation of alimentary wall smooth muscles, which human action to propel food forth (Figure 1). These waves also play a office in mixing food with digestive juices. Peristalsis is and so powerful that foods and liquids you consume enter your stomach even if you lot are standing on your head.

Digestion includes both mechanical and chemic processes. Mechanical digestion is a purely physical process that does non modify the chemical nature of the food. Instead, it makes the nutrient smaller to increase both surface expanse and mobility. It includes mastication, or chewing, too equally tongue movements that help intermission food into smaller bits and mix food with saliva. Although there may be a tendency to think that mechanical digestion is limited to the start steps of the digestive process, it occurs later on the nutrient leaves the mouth, equally well. The mechanical churning of food in the stomach serves to further break information technology autonomously and expose more than of its surface area to digestive juices, creating an acidic "soup" called chyme. Segmentation, which occurs mainly in the minor intestine, consists of localized contractions of circular muscle of the muscularis layer of the gastrointestinal tract. These contractions isolate pocket-sized sections of the intestine, moving their contents back and along while continuously subdividing, breaking up, and mixing the contents. By moving nutrient back and along in the intestinal lumen, partition mixes food with digestive juices and facilitates absorption.

In chemical digestion, starting in the oral fissure, digestive secretions break down circuitous food molecules into their chemical building blocks (for case, proteins into separate amino acids). These secretions vary in composition, but typically incorporate water, diverse enzymes, acids, and salts. The procedure is completed in the small intestine.

Food that has been broken down is of no value to the body unless it enters the bloodstream and its nutrients are put to piece of work. This occurs through the process of absorption, which takes place primarily within the small intestine. At that place, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through the epithelial cells that make up the mucosa. Lipids are absorbed into lacteals and are transported via the lymphatic vessels to the bloodstream (the subclavian veins about the heart). The details of these processes volition be discussed later on.

In defecation, the final footstep in digestion, undigested materials are removed from the trunk as feces.

Crumbling and the Digestive System: From Appetite Suppression to Constipation

Historic period-related changes in the digestive system brainstorm in the mouth and can affect virtually every attribute of the digestive arrangement. Sense of taste buds go less sensitive, so nutrient isn't as appetizing as it once was. A slice of pizza is a challenge, not a care for, when you accept lost teeth, your gums are diseased, and your salivary glands aren't producing enough saliva. Swallowing can exist difficult, and ingested nutrient moves slowly through the alimentary canal because of reduced forcefulness and tone of muscular tissue. Neurosensory feedback is likewise dampened, slowing the transmission of messages that stimulate the release of enzymes and hormones.

Pathologies that affect the digestive organs—such every bit hiatal hernia, gastritis, and peptic ulcer illness—can occur at greater frequencies as y'all age. Problems in the small intestine may include duodenal ulcers, maldigestion, and malabsorption. Problems in the large intestine include hemorrhoids, diverticular disease, and constipation. Atmospheric condition that affect the office of accessory organs—and their abilities to deliver pancreatic enzymes and bile to the small intestine—include jaundice, astute pancreatitis, cirrhosis, and gallstones.

In some cases, a single organ is in charge of a digestive procedure. For example, ingestion occurs only in the oral cavity and defecation simply in the anus. However, most digestive processes involve the interaction of several organs and occur gradually as food moves through the gastrointestinal tract (Figure 2).

Figure two. The digestive processes are ingestion, propulsion, mechanical digestion, chemic digestion, absorption, and defecation.

Some chemical digestion occurs in the mouth. Some absorption can occur in the mouth and breadbasket, for example, alcohol and aspirin.

Regulatory Mechanisms

Neural and endocrine regulatory mechanisms work to maintain the optimal conditions in the lumen needed for digestion and assimilation. These regulatory mechanisms, which stimulate digestive activity through mechanical and chemic activity, are controlled both extrinsically and intrinsically.

Neural Controls

The walls of the alimentary canal contain a diversity of sensors that assistance regulate digestive functions. These include mechanoreceptors, chemoreceptors, and osmoreceptors, which are capable of detecting mechanical, chemical, and osmotic stimuli, respectively. For example, these receptors tin sense when the presence of food has caused the stomach to expand, whether nutrient particles have been sufficiently cleaved down, how much liquid is present, and the type of nutrients in the food (lipids, carbohydrates, and/or proteins). Stimulation of these receptors provokes an advisable reflex that furthers the process of digestion. This may entail sending a message that activates the glands that secrete digestive juices into the lumen, or it may mean the stimulation of muscles inside the alimentary canal, thereby activating peristalsis and segmentation that move nutrient along the intestinal tract.

The walls of the entire gastrointestinal tract are embedded with nervus plexuses that interact with the central nervous system and other nerve plexuses—either within the same digestive organ or in different ones. These interactions prompt several types of reflexes. Extrinsic nerve plexuses orchestrate long reflexes, which involve the central and autonomic nervous systems and work in response to stimuli from exterior the digestive system. Short reflexes, on the other hand, are orchestrated by intrinsic nervus plexuses within the alimentary canal wall. These two plexuses and their connections were introduced earlier every bit the enteric nervous system. Short reflexes regulate activities in ane surface area of the digestive tract and may coordinate local peristaltic movements and stimulate digestive secretions. For instance, the sight, smell, and gustatory modality of nutrient initiate long reflexes that begin with a sensory neuron delivering a indicate to the medulla oblongata. The response to the signal is to stimulate cells in the tum to begin secreting digestive juices in grooming for incoming food. In contrast, food that distends the stomach initiates short reflexes that crusade cells in the tummy wall to increase their secretion of digestive juices.

Hormonal Controls

A variety of hormones are involved in the digestive process. The main digestive hormone of the stomach is gastrin, which is secreted in response to the presence of food. Gastrin stimulates the secretion of gastric acid past the parietal cells of the stomach mucosa. Other GI hormones are produced and act upon the gut and its accessory organs. Hormones produced past the duodenum include secretin, which stimulates a watery secretion of bicarbonate by the pancreas; cholecystokinin (CCK), which stimulates the secretion of pancreatic enzymes and bile from the liver and release of bile from the gallbladder; and gastric inhibitory peptide, which inhibits gastric secretion and slows gastric elimination and movement. These GI hormones are secreted by specialized epithelial cells, called endocrinocytes, located in the mucosal epithelium of the breadbasket and small intestine. These hormones then enter the bloodstream, through which they tin attain their target organs.

Chapter Review

The digestive system ingests and digests food, absorbs released nutrients, and excretes food components that are boxy. The six activities involved in this process are ingestion, movement, mechanical digestion, chemical digestion, absorption, and defecation. These processes are regulated by neural and hormonal mechanisms.

Self Check

Respond the question(s) below to come across how well you lot empathize the topics covered in the previous department.

https://oea.herokuapp.com/assessments/271

Critical Thinking Questions

1. Offer a theory to explain why segmentation occurs and peristalsis slows in the small intestine.
2. It has been several hours since you last ate. Walking by a bakery, y'all catch a whiff of freshly baked bread. What blazon of reflex is triggered, and what is the outcome?

Show Answers

Glossary

absorption: passage of digested products from the intestinal lumen through mucosal cells and into the bloodstream or lacteals

chemical digestion: enzymatic breakup of nutrient

chyme: soupy liquid created when food is mixed with digestive juices

defecation: emptying of undigested substances from the body in the course of feces

ingestion: taking food into the GI tract through the mouth

mastication: chewing

mechanical digestion: chewing, mixing, and sectionalisation that prepares food for chemical digestion

peristalsis: muscular contractions and relaxations that propel nutrient through the GI tract

propulsion: voluntary process of swallowing and the involuntary procedure of peristalsis that moves food through the digestive tract

partition: alternate contractions and relaxations of not-next segments of the intestine that move nutrient forwards and backward, breaking it autonomously and mixing it with digestive juices

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