The Digestive Process

Oct 07, 2019  Digestion is the process by which your body breaks down food and pulls out the nutrients your body needs to operate. Anything left is a waste product, which your body removes.

Mastication: The first step in obtaining nutrition is ingestion. Ingested food must be broken down into small pieces by mastication, or chewing.Besides nutritional items, other substances may be ingested, including medications (where ingestion is termed oral administration) and substances considered inedible, such as insect shells. Ingestion is also a common route taken by pathogenic organisms and poisons entering the body.Some pathogens transmitted via ingestion include viruses, bacteria, and parasites. Most commonly, this takes place via the fecal-oral route.

An intermediate step is often involved, such as drinking water contaminated by feces or food prepared by workers who fail to practice adequate hand-washing. This is more common in regions where untreated sewage is prevalent. Diseases transmitted via the fecal-oral route include hepatitis A, polio, and cholera. Mechanical and chemical digestion: Mechanical and chemical digestion of food takes place in many steps, beginning in the mouth and ending in the rectum. CarbohydratesThe digestion of carbohydrates begins in the mouth. The salivary enzyme amylase begins the breakdown of food starches into maltose, a disaccharide. As the food travels through the esophagus to the stomach, no significant digestion of carbohydrates takes place.

The acidic environment in the stomach stops amylase from continuing to break down the molecules.The next step of carbohydrate digestion takes place in the duodenum. The chyme from the stomach enters the duodenum and mixes with the digestive secretions from the pancreas, liver, and gallbladder.

Pancreatic juices also contain amylase, which continues the breakdown of starch and glycogen into maltose and other disaccharides. These disaccharides are then broken down into monosaccharides by enzymes called maltases, sucrases, and lactases. The monosaccharides produced are absorbed so that they can be used in metabolic pathways to harness energy. They are absorbed across the intestinal epithelium into the bloodstream to be transported to the different cells in the body. Digestion of carbohydrates: Digestion of carbohydrates is performed by several enzymes. Starch and glycogen are broken down into glucose by amylase and maltase.

Sucrose (table sugar) and lactose (milk sugar) are broken down by sucrase and lactase, respectively. ProteinA large part of protein digestion takes place in the stomach.

The enzyme pepsin plays an important role in the digestion of proteins by breaking them down into peptides, short chains of four to nine amino acids. In the duodenum, other enzymes – trypsin, elastase, and chymotrypsin – act on the peptides, reducing them to smaller peptides.

These enzymes are produced by the pancreas and released into the duodenum where they also act on the chyme. Further breakdown of peptides to single amino acids is aided by enzymes called peptidases (those that break down peptides). The amino acids are absorbed into the bloodstream through the small intestine. Protein digestion and absorption: Protein digestion is a multistep process that begins in the stomach and continues through the intestines. Proteins are absorbed into the blood stream by the small intestine. LipidsLipid (fat) digestion begins in the stomach with the aid of lingual lipase and gastric lipase.

However, the bulk of lipid digestion occurs in the small intestine due to pancreatic lipase. When chyme enters the duodenum, the hormonal responses trigger the release of bile, which is produced in the liver and stored in the gallbladder. Bile aids in the digestion of lipids, primarily triglycerides, through emulsification. Emulsification is a process in which large lipid globules are broken down into several small lipid globules. These small globules are widely distributed in the chyme rather than forming large aggregates.

Lipids are hydrophobic substances. Bile contains bile salts, which have hydrophobic and hydrophilic sides. The bile salts’ hydrophilic side can interface with water, while the hydrophobic side interfaces with lipids, thereby emulsifying large lipid globules into small lipid globules.Emulsification is important for the digestion of lipids because lipases can only efficiently act on the lipids when they are broken into small aggregates. Lipases break down the lipids into fatty acids and glycerides. These molecules can pass through the plasma membrane of the cell, entering the epithelial cells of the intestinal lining. The bile salts surround long-chain fatty acids and monoglycerides, forming tiny spheres called micelles.

The micelles move into the brush border of the small intestine absorptive cells where the long-chain fatty acids and monoglycerides diffuse out of the micelles into the absorptive cells, leaving the micelles behind in the chyme. The long-chain fatty acids and monoglycerides recombine in the absorptive cells to form triglycerides, which aggregate into globules, and are then coated with proteins. These large spheres are called chylomicrons. Chylomicrons contain triglycerides, cholesterol, and other lipids; they have proteins on their surface.

The surface is also composed of the hydrophilic phosphate “heads” of phospholipids. Together, they enable the chylomicron to move in an aqueous environment without exposing the lipids to water. Chylomicrons leave the absorptive cells via exocytosis, entering the lymphatic vessels. From there, they enter the blood in the subclavian vein. Intestinal flora: Escherichia coli is one of the many species of bacteria present in the human gut.

Common Problems with EliminationDiarrhea and constipation are some of the most common health concerns that affect digestion. Constipation is a condition where the feces are hardened because of excess water removal in the colon.

In contrast, if not enough water is removed from the feces, it results in diarrhea. Many bacteria, including the ones that cause cholera, affect the proteins involved in water reabsorption in the colon and result in excessive diarrhea. EmesisEmesis, or vomiting, is elimination of food by forceful expulsion through the mouth. It is often in response to an irritant that affects the digestive tract, including, but not limited to, viruses, bacteria, emotions, trauma, and food poisoning. This forceful expulsion of the food is due to the strong contractions produced by the stomach muscles. The process of emesis is regulated by the medulla. CC licensed content, Specific attribution.

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Digestion is the breakdown of large insoluble molecules into small water-soluble food molecules so that they can be absorbed into the watery. In certain organisms, these smaller substances are absorbed through the into the. Digestion is a form of that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed.

In chemical digestion, break down food into the small molecules the body can use.In the, food enters the mouth and mechanical digestion of the food starts by the action of (chewing), a form of mechanical digestion, and the wetting contact of. Saliva, a liquid secreted by the, contains, an enzyme which starts the digestion of in the food; the saliva also contains, which lubricates the food, and, which provides the ideal conditions of pH for amylase to work. After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a. It will then travel down the and into the by the action of. In the stomach starts. Gastric juice mainly contains.

In and gastric juice also contains. As the first two chemicals may damage the stomach wall, is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by, which is waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes.After some time (typically 1–2 hours in humans, 4–6 hours in dogs, 3–4 hours in house cats)the resulting thick liquid is called. When the opens, chyme enters the where it mixes with digestive enzymes from the and bile juice from the and then passes through the, in which digestion continues.

When the chyme is fully digested, it is absorbed into the blood. 95% of nutrient absorption occurs in the small intestine.

Water and minerals are reabsorbed back into the blood in the (large intestine) where the pH is slightly acidic about 5.6 6.9. Some vitamins, such as and (K 2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon. Waste material is eliminated from the during. Contents.Digestive systemDigestive systems take many forms. There is a fundamental distinction between internal and external digestion. External digestion developed earlier in evolutionary history, and most still rely on it.

In this process, are into the environment surrounding the organism, where they break down an organic material, and some of the products back to the organism. Have a tube in which internal digestion occurs, which is more efficient because more of the broken down products can be captured, and the internal chemical environment can be more efficiently controlled.Some organisms, including nearly all, simply secrete biotoxins and digestive chemicals (e.g., ) into the extracellular environment prior to ingestion of the consequent 'soup'. In others, once potential nutrients or food is inside the, digestion can be conducted to a or a sac-like structure, through a tube, or through several specialized organs aimed at making the absorption of nutrients more efficient. Main article:use several systems to obtain nutrients from other organisms in the environments.Channel transport systemIn a channel transupport system, several proteins form a contiguous channel traversing the inner and outer membranes of the bacteria. It is a simple system, which consists of only three protein subunits: the, (MFP), and (OMP). This secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20–900 kDa).

The molecules secreted vary in size from the small Escherichia coli peptide colicin V, (10 kDa) to the Pseudomonas fluorescens cell adhesion protein LapA of 900 kDa. Molecular syringeA means that a molecular syringe is used through which a bacterium (e.g. Certain types of Salmonella, Shigella, Yersinia) can inject nutrients into protist cells.

One such mechanism was first discovered in Y. Pestis and showed that toxins could be injected directly from the bacterial cytoplasm into the cytoplasm of its host's cells rather than simply be secreted into the extracellular medium. Conjugation machineryThe machinery of some bacteria (and archaeal flagella) is capable of transporting both DNA and proteins. It was discovered in Agrobacterium tumefaciens, which uses this system to introduce the Ti plasmid and proteins into the host, which develops the crown gall (tumor). The VirB complex of Agrobacterium tumefaciens is the prototypic system.The are an interesting case, wherein conjugative elements naturally engage in inter- conjugation. Such elements as the Ti or Ri plasmids contain elements that can transfer to plant cells.

Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of, which the bacteria use as carbon and energy sources. Infected plant cells form. The Ti and Ri plasmids are thus of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system (the tra, or transfer, operon) from that for inter-kingdom transfer (the vir, or, operon). Such transfer creates virulent strains from previously avirulent Agrobacteria.Release of outer membrane vesiclesIn addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: the formation of outer membrane vesicles. Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells.

While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective. Venus Flytrap ( Dionaea muscipula) leaf Gastrovascular cavityThe functions as a stomach in both digestion and the distribution of nutrients to all parts of the body. Extracellular digestion takes place within this central cavity, which is lined with the gastrodermis, the internal layer of. This cavity has only one opening to the outside that functions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus, which can be described as an incomplete.In a plant such as the that can make its own food through photosynthesis, it does not eat and digest its prey for the traditional objectives of harvesting energy and carbon, but mines prey primarily for essential nutrients (nitrogen and phosphorus in particular) that are in short supply in its boggy, acidic habitat.

Squid beak with ruler for size comparison Beakshave bony that are specialised according to the bird's. For example, primarily eat seeds, nuts, and fruit, using their impressive beaks to open even the toughest seed. First they scratch a thin line with the sharp point of the beak, then they shear the seed open with the sides of the beak.The mouth of the is equipped with a sharp horny beak mainly made of cross-linked. It is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species. The beak is the only indigestible part of the squid.Tongue. Main article:The tongue is skeletal muscle on the floor of the of most vertebrates, that manipulates for chewing and (deglutition).

It is sensitive and kept moist. The underside of the tongue is covered with a smooth. The tongue also has a touch sense for locating and positioning food particles that require further chewing.

The tongue is utilized to roll food particles into a before being transported down the through.The region underneath the front of the tongue is a location where the is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract.Teeth.

Main article:Teeth (singular tooth) are small whitish structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, milk and chew food. Teeth are not made of bone, but rather of tissues of varying density and hardness, such as enamel, dentine and cementum. Human teeth have a blood and nerve supply which enables proprioception. This is the ability of sensation when chewing, for example if we were to bite into something too hard for our teeth, such as a chipped plate mixed in food, our teeth send a message to our brain and we realise that it cannot be chewed, so we stop trying.The shapes, sizes and numbers of types of animals' teeth are related to their diets. For example, herbivores have a number of molars which are used to grind plant matter, which is difficult to digest.

Have which are used to kill and tear meat.CropA, or croup, is a thin-walled expanded portion of the used for the storage of food prior to digestion. In some birds it is an expanded, muscular pouch near the or throat. In adult doves and pigeons, the crop can produce to feed newly hatched birds.Certain insects may have a or enlarged.

Main article:have evolved (or an in the case of ). Ruminants have a fore-stomach with four chambers.

These are the,. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material.

Solids clump together to form the cud (or ). The cud is then regurgitated, chewed slowly to completely mix it with saliva and to break down the particle size.Fibre, especially and, is primarily broken down into the, and in these chambers (the reticulo-rumen) by microbes: (, and ). In the omasum, water and many of the inorganic mineral elements are absorbed into the blood stream.The abomasum is the fourth and final stomach compartment in ruminants.

It is a close equivalent of a monogastric stomach (e.g., those in humans or pigs), and digesta is processed here in much the same way. It serves primarily as a site for acid hydrolysis of microbial and dietary protein, preparing these protein sources for further digestion and absorption in the small intestine. Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. Microbes produced in the reticulo-rumen are also digested in the small intestine. Upper and lower human gastrointestinal tractThe is around 9 meters long. Digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal, and the process of digestion normally takes between 24 and 72 hours.Digestion begins in the with the secretion of saliva and its digestive enzymes. Food is formed into a by the mechanical and into the from where it enters the through the action of.

Contains and which would damage the walls of the stomach and is secreted for protection. In the stomach further release of enzymes break down the food further and this is combined with the churning action of the stomach. The partially digested food enters the as a thick semi-liquid. In the small intestine, the larger part of digestion takes place and this is helped by the secretions of,. The intestinal walls are lined with, and their is covered with numerous to improve the absorption of nutrients by increasing the of the intestine.In the large intestine the passage of food is slower to enable fermentation by the to take place.

Here water is absorbed and waste material stored as to be removed by defecation via the and.Neural and biochemical control mechanismsDifferent take place including: the, and.The cephalic phase occurs at the sight, thought and smell of food, which stimulate the. Taste and smell stimuli are sent to the. After this it is routed through the and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and (secretes gastrin) activity via secretion of.The gastric phase takes 3 to 4 hours. It is stimulated by of the stomach, presence of food in stomach and decrease in.

Distention activates long and myenteric reflexes. This activates the release of, which stimulates the release of more.

As protein enters the stomach, it binds to ions, which raises the of the. Inhibition of gastrin and secretion is lifted. This triggers to release, which in turn stimulates to secrete gastric acid. Gastric acid is about 0.5% (HCl), which lowers the pH to the desired pH of 1–3. Acid release is also triggered by and.The intestinal phase has two parts, the excitatory and the inhibitory.

Partially digested food fills the. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating causing the to tighten to prevent more food from entering, and inhibits local reflexes.Breakdown into nutrients.

This section needs expansion with: digestion of other substances. You can help.

( August 2011)Protein digestionProtein digestion occurs in the stomach and in which 3 main enzymes, secreted by the stomach and and secreted by the pancreas, break down food proteins into that are then broken down by various and into. The digestive enzymes however are mostly secreted as their inactive precursors, the.

For example, trypsin is secreted by pancreas in the form of, which is activated in the duodenum by to form trypsin. Trypsin then cleaves to smaller.Fat digestion. Main article:Digestion of some fats can begin in the mouth where breaks down some short chain lipids into. However fats are mainly digested in the small intestine. The presence of fat in the small intestine produces hormones that stimulate the release of from the pancreas and from the liver which helps in the emulsification of fats for absorption of.

Complete digestion of one molecule of fat (a ) results a mixture of fatty acids, mono- and di-glycerides, as well as some undigested triglycerides, but no free molecules. Carbohydrate digestion. Further information: andIn humans, dietary starches are composed of units arranged in long chains called amylose, a.

During digestion, bonds between glucose molecules are broken by salivary and pancreatic, resulting in progressively smaller chains of glucose. This results in simple sugars glucose and (2 glucose molecules) that can be absorbed by the small intestine.is an enzyme that breaks down the to its component parts, glucose. Glucose and galactose can be absorbed by the small intestine. Approximately 65 percent of the adult population produce only small amounts of lactase and are unable to eat milk-based foods.

This is commonly known as lactose intolerance. Lactose intolerance varies widely by genetic heritage; more than 90 percent of peoples of east Asian descent are lactose intolerant, in contrast to about 5 percent of people of northern European descent.is an enzyme that breaks down the disaccharide, commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars and glucose which are readily absorbed by the small intestine.DNA and RNA digestion. Main article:DNA and RNA are broken down into by the and (DNase and RNase) from the pancreas.Non-destructive digestionSome nutrients are complex molecules (for example ) which would be destroyed if they were broken down into their.

To digest vitamin B 12 non-destructively, in strongly binds and protects the B 12 molecules from stomach acid as they enter the stomach and are cleaved from their protein complexes.After the B 12-haptocorrin complexes pass from the stomach via the pylorus to the duodenum, pancreatic proteases cleave haptocorrin from the B 12 molecules which rebind to (IF). These B 12-IF complexes travel to the ileum portion of the small intestine where receptors enable and circulation of B 12-IF complexes in the blood. Digestive hormones.

Action of the major digestive hormonesThere are at least five hormones that aid and regulate the digestive system in mammals. There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control (largely the glucose-insulin system) have been uncovered in recent years. – is in the and stimulates the to secrete (an inactive form of the enzyme ). Secretion of gastrin is stimulated by food arriving in stomach.

The secretion is inhibited by low. – is in the and signals the secretion of sodium bicarbonate in the and it stimulates the secretion in the. This hormone responds to the acidity of the chyme.

(CCK) – is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the. This hormone is secreted in response to fat in chyme. (GIP) – is in the duodenum and decreases the stomach churning in turn slowing the emptying in the stomach. Another function is to induce.

– is in the duodenum and increases the component of gastrointestinal motility and stimulates the production of.Significance of pHDigestion is a complex process controlled by several factors. Plays a crucial role in a normally functioning digestive tract. In the mouth, pharynx and esophagus, pH is typically about 6.8, very weakly acidic. Controls pH in this region of the digestive tract.

Is contained in saliva and starts the breakdown of carbohydrates into. Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment.The stomach's high acidity inhibits the breakdown of within it. This acidity confers two benefits: it proteins for further digestion in the small intestines, and provides, damaging or eliminating various. In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the empties into the duodenum, adding to neutralize the acidic, thus creating a neutral environment. The mucosal tissue of the small intestines is alkaline with a pH of about 8.5. See also.