What Two Substances Change Food Into Chyme

Chapter 16

Digestive System Processes and Regulation

OpenStax, Digestive Organization Processes and Regulation. OpenStax CNX. Jun 28, 2013 http://cnx.org/contents/afe83b13-0c1c-4d09-aa0b-4a0590580358@four. © Jun 28, 2013 OpenStax. Textbook content produced by OpenStax is licensed under a Artistic Commons Attribution License iii.0 license.

Past the cease of this section, y'all volition be able to:

Hash out half-dozen key activities of the digestive arrangement, 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 i provides an overview of the basic functions of the digestive organs.

Tabular array 1: Functions of the Digestive Organs

Organ	Major functions	Other functions
Mouth	Ingests food Chews and mixes food Begins chemical breakup of carbohydrates Moves food into the pharynx Begins breakdown of lipids via lingual lipase	Moistens and dissolves nutrient, assuasive you to sense of taste it Cleans and lubricates the teeth and mouth Has some antimicrobial activity
Pharynx	Propels food from the rima oris to the esophagus	Lubricates food and passageways
Esophagus	Propels nutrient 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 poly peptide-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 plenty for digestion and absorption Absorbs breakdown products of carbohydrates, proteins, lipids, and nucleic acids, forth with vitamins, minerals, and water Performs concrete digestion via segmentation	Provides optimal medium for enzymatic action
Accessory organs	Liver: produces bile salts, which emulsify lipids, aiding their digestion and assimilation Gallbladder: stores, concentrates, and releases bile Pancreas: produces digestive enzymes and bicarbonate	Bicarbonate-rich pancreatic juices help neutralize acidic chyme and provide optimal surroundings for enzymatic activity
Large intestine	Farther breaks downward food residues Absorbs most residual water, electrolytes, and vitamins produced by enteric leaner Propels feces toward rectum Eliminates feces	Food residue is full-bodied and temporarily stored prior to defecation Mucus eases passage of carrion through colon

Sentinel the video linked to below for an overview of digestion of food in unlike regions of the digestive tract. Note the route of non-fat nutrients from the small-scale intestine to their release every bit nutrients to the body.

Digestive Processes

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

The beginning of these processes, ingestion, refers to the entry of food into the gastrointestinal tract through the mouth. At that place, 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 nutrient and allows an accordingly sized bolus to be produced.

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 comestible wall smooth muscles, which act to propel food along (Figure 1). These waves also play a part in mixing food with digestive juices. Peristalsis is then powerful that foods and liquids you swallow enter your tummy even if you are continuing on your caput.

This image shows the peristaltic movement of food. In the left image, the food bolus is towards the top of the esophagus and arrows pointing downward show the direction of movement of the peristaltic wave. In the center image, the food bolus and the wave movement are closer to the center of the esophagus and in the right image, the bolus and the wave are close to the bottom end of the esophagus. — Figure one: Peristalsis moves food through the digestive tract with alternating waves of muscle contraction and relaxation.

Digestion includes both mechanical and chemical processes. Mechanical digestion is a purely concrete procedure that does not change the chemical nature of the food. Instead, it makes the food smaller to increase both surface surface area and mobility. It includes mastication, or chewing, as well as tongue movements that assist break nutrient into smaller bits and mix food with saliva. Although in that location may be a trend to think that mechanical digestion is express to the offset steps of the digestive process, it occurs subsequently the nutrient leaves the mouth, as well. The mechanical churning of food in the tummy serves to further break it apart and betrayal more of its surface area to digestive juices, creating an acidic "soup" called chyme. Segmentation, which occurs mainly in the small-scale 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 along while continuously subdividing, breaking up, and mixing the contents. By moving food back and along in the intestinal lumen, sectionalisation mixes food with digestive juices and facilitates absorption.

In chemical digestion, starting in the oral cavity, digestive secretions suspension down complex nutrient molecules into their chemical building blocks (for instance, proteins into split amino acids). These secretions vary in limerick, but typically incorporate water, diverse enzymes, acids, and salts. The process is completed in the pocket-size intestine.

Food that has been broken down is of no value to the body unless information technology enters the bloodstream and its nutrients are put to work. This occurs through the process of absorption, which takes place primarily within the small intestine. In that location, virtually nutrients are absorbed from the lumen of the gastrointestinal tract into the bloodstream through the epithelial cells that make upwards the mucosa. Lipids are absorbed into lacteals and are transported via the lymphatic vessels to the bloodstream (the subclavian veins most the heart). The details of these processes will be discussed later.

In defecation, the concluding stride in digestion, undigested materials are removed from the body as feces.

Aging and the…

Digestive System : From Appetite Suppression to Constipation

Age-related changes in the digestive system brainstorm in the mouth and tin affect most every aspect of the digestive organisation. Taste buds become less sensitive, and so food isn't as appetizing as it once was. A slice of pizza is a challenge, not a care for, when you have lost teeth, your gums are diseased, and your salivary glands aren't producing plenty saliva. Swallowing can be difficult, and ingested nutrient moves slowly through the gastrointestinal tract because of reduced force and tone of muscular tissue. Neurosensory feedback is too dampened, slowing the transmission of messages that stimulate the release of enzymes and hormones.

Pathologies that bear upon the digestive organs—such as hiatal hernia, gastritis, and peptic ulcer disease—can occur at greater frequencies equally you lot age. Problems in the modest intestine may include duodenal ulcers, maldigestion, and malabsorption. Issues in the large intestine include hemorrhoids, diverticular disease, and constipation. Conditions that affect the function 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 unmarried organ is in charge of a digestive process. For case, ingestion occurs only in the mouth and defecation only in the anus. Withal, most digestive processes involve the interaction of several organs and occur gradually as food moves through the alimentary canal (Figure 2).

This image shows the different processes involved in digestion. The image shows how food travels from the mouth through the major organs. Associated textboxes list the different processes such as propulsion, chemical and mechanical digestion and absorption near the organs where they take place. — Effigy two: The digestive processes are ingestion, propulsion, mechanical digestion, chemical digestion, assimilation, and defecation.

Some chemical digestion occurs in the mouth. Some assimilation can occur in the mouth and stomach, 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 absorption. These regulatory mechanisms, which stimulate digestive activity through mechanical and chemical activity, are controlled both extrinsically and intrinsically.

Neural Controls

The walls of the alimentary canal contain a multifariousness of sensors that help 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 tum to expand, whether food particles have been sufficiently broken downwardly, how much liquid is present, and the type of nutrients in the food (lipids, carbohydrates, and/or proteins). Stimulation of these receptors provokes an appropriate reflex that furthers the process of digestion. This may entail sending a bulletin that activates the glands that secrete digestive juices into the lumen, or information technology may mean the stimulation of muscles within the comestible culvert, thereby activating peristalsis and sectionalization that motion food along the intestinal tract.

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

Hormonal Controls

A multifariousness of hormones are involved in the digestive procedure. The main digestive hormone of the tum is gastrin, which is secreted in response to the presence of nutrient. Gastrin stimulates the secretion of gastric acid past the parietal cells of the stomach mucosa. Other GI hormones are produced and human activity upon the gut and its accompaniment 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 emptying and motility. These GI hormones are secreted past specialized epithelial cells, called endocrinocytes, located in the mucosal epithelium of the stomach and small intestine. These hormones so enter the bloodstream, through which they can reach their target organs.

Chapter Review

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