For the industrial process see anaerobic digestion Anaerobic digestion is the breakdown of organic matter by bacteria in the absence of oxygen. ...

Digestion is the process of metabolism whereby a biological entity processes a substance, in order to chemically and mechanically convert the substance into nutrients. Digestion occurs at the multicellular, cellular, and sub-cellular levels, usually in animals. This process takes place in the digestive system, gastrointestinal tract, or alimentary canal. Santorio Santorio (1561-1636) in his steelyard balance, from Ars de statica medecina, first published 1614 Metabolism (from μεταβολισμος (metabolismos)) is the biochemical modification of chemical compounds in living organisms anggjgjhnd cell (b). ... Chemistry (derived from alchemy) is the science of matter at or near the atomic scale. ... // Nutrients and the body A nutrient is any element or compound necessary for or contributing to an organisms metabolism, growth, or other functioning. ... Multicellular organisms are those organisms consisting of more than one cell, and having differentiated cells that perform specialized functions. ... Cells in culture, stained for keratin (red) and DNA (green). ... The word Animals when used alone has several possible meanings in the English language. ... The gastrointestinal tract or digestive tract, also referred to as the GI tract or the alimentary canal, (nourishment canal) or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and expels the remaining waste. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and...

Digestion is usually divided into mechanical manipulation and chemical action. In most vertebrates, digestion is a multi-stage process in the digestive system, following ingestion of the raw materials, most often other organisms. The process of ingestion usually involves some type of mechanical manipulation. Digestion is separated into five separate processes: 1) Injestion: Placing food into the mouth, 2) Mechanical digestion: Mastication, the use of teeth to tear and crush food, and churning of the stomach. 3) Chemical digestion: Addition of chemicals (acid, bile, enzymes, and water) to break down complex molecules into simple structures, 4) Absorption: Movement of nutrients from the digestive system to the circulatory and lymphatic capallaries through osmosis, active transport, and diffusion, 5) Elimination: Removel of undigested materials from the digestive tract through defecation. Underlying the process is muscle movement throughout the system, deglutition and peristalsis. Classes and Clades Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... In general terms, eating (formally, ingestion) is the process of consuming something edible, i. ... Osmosis is the diffusion of a liquid (most often assumed to be water, but it can be any liquid solvent) through a partially-permeable membrane from a region of low solvent potential to a region of high solvent potential. ... Active transport is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. ... This article or section does not cite its references or sources. ... Anatomy of the anus and rectum Defecation or feceation is the act or process by which organisms eliminate solid or semisolid waste material from the digestive tract. ... Swallowing, known scientifically as deglutition is the reflex in the human body that makes something pass from the mouth, through the esophagus. ... Peristalsis is the process of involuntary wave-like successive muscular contractions by which food is moved through the digestive tract. ...

Human digestion process

Human Gastrointestinal tract

In humans, digestion begins in the oral cavity where food is chewed (mastication) with the teeth. The process stimulates exocrine glands in the mouth to release digestive enzymes such as salivary amylase, which aid in the breakdown of carbohydrates, particularly carbohydrates. Chewing (mechanical catabolism) also causes the release of saliva, which helps condense food into a bolus that can be easily passed through the oesophagus. The oesophagus is about 20 centimeters long. Saliva also begins the process of chemical catabolism, hydrolysis. Once food is chewed properly, the food is swallowed. The bolus is pushed down by the movement called peristalsis, which is an involuntary wave-like contraction of smooth muscle tissue, characteristic of the digestive system. The mechanism for swallowing is co-ordinated by the swallowing centre in the medulla oblongata and pons. The reflex is initiated by touch receptors in the pharynx as a bolus of food is pushed to the back of the mouth by the tongue. The uvula is a small flap that hangs from the roof of the mouth. During swallowing it and the soft palate retract upward and to the rear to close the nasopharynx, which prevents the food from entering the nasal passages by triggering closure of the soft palate. When swallowed, the food enters the pharynx, which makes special adaptations to prevent choking or aspiration when food is swallowed. The epiglottis is a cartilage structure that closes temporarily during swallowing, preventing food and liquids from entering the trachea. Diagram of the stomach, colon and rectum from public domain source at http://www. ... Diagram of the stomach, colon and rectum from public domain source at http://www. ... Trinomial name Homo sapiens sapiens Linnaeus, 1758 Humans, or human beings, are bipedal primates belonging to the mammalian species Homo sapiens (Latin for wise man or knowing man) under the family Hominidae (the great apes). ... The gastrointestinal tract or digestive tract, also referred to as the GI tract or the alimentary canal, (nourishment canal) or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and expels the remaining waste. ... The mouth, also known as the buccal cavity or the oral cavity, is the opening through which an animal or human takes in food. ... Mastication or chewing is the process by which food is torn and/or crushed by teeth. ... Types of teeth Molars are used for grinding up foods Carnassials are used for slicing food. ... Exocrine gland refers to glands that secrete their products via a duct. ... Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... Salivary amylase is an enzyme produced by the salivary glands that begins carbohydrate digestion in the mouth and continues in the body of the stomach after the food and saliva have been swallowed. ... Carbohydrates are chemical compounds that contain oxygen, hydrogen, and carbon atoms, and no other elements. ... Anabolism is the aspect of metabolism that contributes to growth. ... Saliva, often informally known as spit, is the moist, clear, and usually somewhat frothy substance produced in the mouths of some animals, including humans. ... Look up bolus in Wiktionary, the free dictionary. ... The esophagus, oe/œsophagus*, or gullet is the muscular tube in vertebrates through which ingested food passes from the mouth area to the stomach. ... The esophagus, oe/œsophagus*, or gullet is the muscular tube in vertebrates through which ingested food passes from the mouth area to the stomach. ... Hydrolysis is a chemical process in which a molecule is split into two parts by the addition of a molecule of water. ... Peristalsis is the process of involuntary wave-like successive muscular contractions by which food is moved through the digestive tract. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... The medulla oblongata is the lower portion of the brainstem. ... Diagram showing the uvula, tonsils, soft palate, and tongue Uvula without tonsils (after tonsillectomy) The uvula is a small cone-shaped mass of tissue hanging down from the soft palate, near the back of the throat. ... Swallowing, known scientifically as deglutition, is the reflex in the human body that makes something pass from the mouth, through the esophagus. ... The soft palate, or velum, is the soft tissue comprising the back of the roof of the mouth. ... The pharynx is the part of the digestive system of many animals immediately behind the mouth and in front of the esophagus. ... The pharynx (plural: pharynges) is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial to the esophagus, larynx, and trachea. ... Choking is the obstruction of the flow of air into a persons lungs by a foreign object, commonly food. ... See: Aspiration (phonetics) Aspiration (medicine) Aspiration (long-term hope) - see for example, Robert Goddards response to the ridicule by the New York Times, 1920: Every vision is a joke until the first man accomplishes it; once realized, it becomes commonplace. ... Haha u cant see this b/c wiess The epiglottis is a thin, lid-like flap of cartilage tissue covered with a mucous membrane, attached to the root of the tongue, that guards the entrance of the glottis, the opening between the vocal cords. ... Trachea (IPA: ) is a common biological term for an airway through which respiratory gas transport takes place in organisms. ...

The food enters the stomach upon passage through the cardiac sphincter. In the stomach, food is further broken apart through a process of heuristic churning and is thoroughly mixed with a digestive fluid, composed chiefly of hydrochloric acid, and other digestive enzymes to further denature proteins. The parietal cells of the stomach also secrete a compound, intrinsic factor which is essential in the absorption of vitamin B-12. As the acidic level changes in the small intestines, more enzymes are activated to split apart the molecular structure of the various nutrients so they may be absorbed into the circulatory or lymphatic systems. In anatomy, the stomach (in ancient Greek στόμαχος) is an organ in the gastrointestinal tract used to digest food. ... The cardia is the anatomical term for the junction orifice of the stomach and the esophagus. ... Gastric acid is, together with several enzymes and the intrinsic factor, one of the main secretions of the stomach. ... The chemical compound hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride (HCl) gas. ... Denaturation is a structural change in biomolecules such as nucleic acids and proteins, usually caused by heat, acids, bases, detergents, or certain chemicals such as urea. ... Parietal cells (also called oxyntic cells) are cells located in the stomach epithelium. ... Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. ... Cobalamin or vitamin B12 is a chemical compound that is also known as cyanocobalamine. ... The title of this article should be pH. The initial letter is capitalized due to technical restrictions. ...

After being processed in the stomach, food is passed to the small intestine via the pyloric sphincter. This is where most of the digestive process occurs as chyme enters the first 10 inches of the small intestine, the duodenum. Here it is further mixed with 3 different liquids: (1)bile (which helps aid in fat digestion, otherwise known as emulsification), (2) pancreatic juice and enzymes, (made by the pancreas), and (3) intestinal enzymes of the alkaline mucosal membranes. The enzymes include: maltase, lactase and sucrase, to process sugars. Trypsin and chymotrypsin are other enzymes added in the small intestine. (Bile also contains pigments that are by-products of red blood cell destruction in the liver; these bile pigments are eliminated from the body with the feces.) Most nutrient absorption takes place in the small intestine. The nutrients pass through the small intestine's wall, which contains small, finger-like structures called villi. The blood, which has absorbed nutrients, is carried away from the small intestine via the hepatic portal vein and goes to the liver for filtering, removal of toxins, and nutrient processing. The primary activity here is regulation of blood glucose levels through a prosess of temporary storage of excess glucose that is converted in the liver to glycogen in direct response to the hormone insulin. Between meals, when blood glucose levels begin to drop, the glycogen is converted back to glucose in response to the hormone glucagon. Diagram showing the small intestine In biology the small intestine is the part of the gastrointestinal tract between the stomach and the large intestine (colon). ... From Greek pylorus; pyl- = gate, -orus = guard. ... Chyme is the liquid substance found in the stomach before passing the pyloric valve and entering the duodenum. ... In anatomy of the digestive system, the duodenum is a hollow jointed tube connecting the stomach to the jejunum. ... Bile (or gall) is a bitter, greenish-yellow alkaline fluid secreted by the liver of most vertebrates. ... Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. ... An emulsion is a mixture of two immiscible substances. ... Pancreatic juice is a juice produced by the pancreas. ... The pancreas is an organ in the digestive system that serves two major functions: exocrine - it produces pancreatic juice containing digestive enzymes. ... Maltase, drawn from PDB 1OBB. Maltase (EC 3. ... Lactase is a member of the β-galactosidase family of enzyme: enzymes that hydrolysis β 1,4 bonded attachments off of galactose. ... Headline text Sucrase (EC 3. ... Magnified crystals of refined sugar Magnification of typical sugar In general use, non-scientists take sugar to mean sucrose, also called table sugar or saccharose, a white crystalline solid disaccharide. ... Trypsin(EC 3. ... Chymotrypsin Chymotrypsin (bovine γ chymotrypsin: PDB 1AB9, EC 3. ... Human red blood cells Red blood cells are the most common type of blood cell and are the vertebrate bodys principal means of delivering oxygen from the lungs or gills to body tissues via the blood. ... The liver is the largest internal organ of the human body. ... Villi (singular: villus) are tiny, finger-like structures that protrude from the wall of the intestine to help absorb nutrients in the lumen. ... The portal vein is a major vein in the human body draining blood from the digestive system and its associated glands. ... Glucose (Glc), a monosaccharide (or simple sugar), is one of the most important carbohydrates. ... Electron micrograph of a section of a liver cell showing glycogen deposits as accumulations of electron dense particles (arrows). ... The structure of insulin. ... Glucagon ball and stick model Glucagon is a 29-amino acid polypeptide acting as an important hormone in carbohydrate metabolism. ...

After going through the small intestine, the food then goes to the large intestine. The large intestine has 3 parts: the cecum (or pouch that forms the T-junction with the small intestine), the colon, and the rectum. In the large intestine, water is reabsorbed, and the foods that cannot go through the villi, such as dietary fibre, can be stored in large intestine. Fibre helps to keep the food moving through the G.I. tract. The food that cannot be broken down is called faeces. Faeces are stored in the rectum until they are expelled through the anus. In anatomy of the digestive system, the colon is the part of the intestine from the cecum to the rectum. ... In anatomy of the digestive system, the cecum or caecum is a pouch connected to the large intestine between the ileum. ... Colon has several meanings: colon (anatomy) colon (punctuation) colon (rhetoric) See also Colón This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The posterior aspect of the rectum exposed by removing the lower part of the sacrum and the coccyx. ... Villi (singular: villus) are tiny, finger-like structures that protrude from the wall of the intestine to help absorb nutrients in the lumen. ... Dietary fibers are long-chain carbohydrates (polysaccharides) that are indigestible by the human digestive tract. ... Rabbit feces are usually 0. ... Male Human Anatomy Anal redirects here. ...

Significance of pH in Digestion

Digestion is a complex process which is controlled by several factors. pH plays a crucial role in a normally functioning digestive tract. In the mouth, pharynx, and esophagus, pH is typically about 6.8, a very weak acid. Saliva controls pH in this region of the digestive tract. Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides. Most digestive enzymes are sensitive to pH and will not function in a low-pH environment like the stomach. Low pH (below 5) indicates a strong acid, while a high pH (above 8) indicates a strong base. The title of this article should be pH. The initial letter is capitalized due to technical restrictions. ... Saliva, often informally known as spit, is the moist, clear, and usually somewhat frothy substance produced in the mouths of some animals, including humans. ... Salivary amylase is an enzyme produced by the salivary glands that begins carbohydrate digestion in the mouth and continues in the body of the stomach after the food and saliva have been swallowed. ... Monosaccharides are carbohydrates in the form of simple sugars. ... It has been suggested that strong base be merged into this article or section. ...

pH in the stomach is very low and inhibits the breakdown of carbohydrates while there. The strong acid content of the stomach provides two benefits, both serving to denature proteins for further digestion in the small intestines, as well as providing non-specific immunity, retarding or eliminating various pathogens. Carbohydrates (literally hydrates of carbon) are chemical compounds that act as the primary biological means of storing or consuming energy, other forms being fat and protein. ... Denaturation is a structural change in biomolecules such as nucleic acids and proteins, usually caused by heat, acids, bases, detergents, or certain chemicals such as urea. ... A pathogen (literally birth of pain from the Greek παθογένεια) is a biological agent that can cause disease to its host. ...

In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The pancreatic duct empties into the stomach, adding bicarbonate to neutralize the acidic chyme, thus creating a neutral environment. The mucosal tissue of the small intestines is alkaline, creating a pH of about 8.5, thus enabling absorption in a mild alkaline environment. A duct joining the pancreas to the bile duct to supply pancreatic juice which aid in digestion provided by the exocrine pancreas. ... In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Chyme is the liquid substance found in the stomach before passing the pyloric valve and entering the duodenum. ...

References:

• Kimball's Biology Pages, Digestion
• Chemistry lecture
• American Journal of Physiology, article
• Journal article on pH in digestion

Specialized organs

Organisms develop specialized organs to aid in the digestion of their food, for example different types of tongues or teeth. Insects may have a crop (or the enlargement of oesophagus) while birds and cockroaches may develop a gizzard (or a stomach that acts as teeth and mechanically digests food). An herbivore may have a cecum that breaks down the cellulose in plants. Ruminants, for example, cows and sheep, have a fourth and final stomach or abomasum. Tongue The tongue is the large bundle of muscles on the floor of the mouth that manipulates food for chewing and swallowing. ... The crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including earthworms, leeches, insects, and birds. ... The esophagus, oe/œsophagus*, or gullet is the muscular tube in vertebrates through which ingested food passes from the mouth area to the stomach. ... The gizzard is an adapted stomach that is found in birds, earthworms, and other animals. ... A deer and two fawns feeding on some foliage In zoology, an herbivore is an animal that is adapted to eat primarily plant matter (rather than meat). ... In anatomy of the digestive system, the cecum or caecum is a pouch connected to the large intestine between the ileum. ... Cellulose as polymer of β-D-glucose Cellulose in 3D Cellulose (C6H10O5)n is a long-chain polymeric polysaccharide carbohydrate, of beta-glucose. ... Families Antilocapridae Bovidae Cervidae Giraffidae Moschidae Tragulidae A ruminant is any hooved animal that digests its food in two steps, first by eating the raw material and regurgitating a semi-digested form known as cud, then eating the cud, a process called ruminating. ... COW is an acronym for a number of things: Can of worms The COW programming language, an esoteric programming language. ... Species See text. ... The abomasum is the fourth and final stomach compartment of the stomach in ruminants. ...

Digestive hormones

There are at least four hormones that aid and regulate the digestive system:

• Gastrin - is in the stomach and stimulates the gastric glands to secrete pepsinogen and hydrochloric acid. Secretion of gastrin is stimulated by food arriving in stomach. The secretion is inhibited by low pH .
• Secretin - is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver. This hormone responds to the acidity of the chyme.
• Cholecystokinin (CCK) - is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gall bladder. This hormone is secreted in response to fat in chyme.
• Gastric inhibitory peptide (GIP) - is in the duodenum and decreases the stomach churning in turn slowing the emptying in the stomach.

In humans, gastrin is a hormone that stimulates secretion of gastric acid by the stomach. ... In anatomy, the stomach (in ancient Greek στόμαχος) is an organ in the gastrointestinal tract used to digest food. ... Pepsin is a protease, a digestive enzyme that degrades food proteins in the stomach; the other important digestive enzymes are trypsin and chymotrypsin. ... The chemical compound hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride (HCl) gas. ... The title of this article should be pH. The initial letter is capitalized due to technical restrictions. ... Secretin is a peptide hormone produced in the S cells of the duodenum. ... In anatomy of the digestive system, the duodenum is a hollow jointed tube connecting the stomach to the jejunum. ... The pancreas is an organ in the digestive system that serves two major functions: exocrine - it produces pancreatic juice containing digestive enzymes. ... Bile (or gall) is a bitter, greenish-yellow alkaline fluid secreted by the liver of most vertebrates. ... The liver is the largest internal organ of the human body. ... Cholecystokinin (from Greek chole, bile; cysto, sac; kinin, move; hence, move the bile-sac (gall bladder)) is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. ... The gallbladder (or cholecyst) is a pear-shaped organ that stores bile (or gall) until the body needs it for digestion. ... Gastric inhibitory peptide (GIP) is a gastrointestinal hormone secreted by the duodenum. ...

Digestion Chemistry

Carbohydrate Digestion

Overview

Carbohydrates are formed in growing plants and are found in grains, leafy vegetables, and other edible plant foods. The molecular structure of these plants is complex, or a polysaccharide; poly is a prefix meaning many. Plants form carbohydrate chains during growth by trapping carbon from the atmosphere, initially carbon dioxide (CO₂). Carbohydrates (literally hydrates of carbon) are chemical compounds that act as the primary biological means of storing or consuming energy, other forms being fat and protein. ... Polysaccharides (sometimes called glycans) are relatively complex carbohydrates. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ...

Carbon is stored within the plant along with water (H₂O) to form a complex starch containing a combination of carbon-hydrogen-oxygen in a fixed ratio of 1:2:1 respectively.

Plants with a high sugar content and table sugar represent a less complex structure and are called disaccharides, or two sugar molecules bonded. Once digestion of either of these forms of carbohydrates are complete, the result is a single sugar structure, a monosaccharide. These monosaccharides can be absorbed into the blood and used by individual cells to produce the energy compound adenosine triphosphate(ATP). Sucrose, a common disaccharide A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides. ... Monosaccharides are the simplest form of carbohydrates. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide primarily known in biochemistry as the molecular currency of intracellular energy transfer. ...

The digestive system starts the process of breaking down polysaccharides in the mouth through the introduction of amylase, a digestive enzyme in saliva. The high acid content of the stomach inhibits the enzyme activity, so carbohydrate digestion is suspended in the stomach. Upon emptying into the small intestines, potential hydrogen (pH) changes dramatically from a strong acid to an alkaline content. The pancreas secretes bicarbonate to neutralize the acid from the stomach, and the mucus secreted in the tissue lining the intestines is alkaline which promotes digestive enzyme activity. Amalayse is present in the small intestines and works with other enzymes to complete the breakdown of carbohydrate into a monosaccharide which is absorbed into the surrounding capillaries of the villi. α-Amylase Amylase (EC 3. ... Saliva, often informally known as spit, is the moist, clear, and usually somewhat frothy substance produced in the mouths of some animals, including humans. ... The common (Arrhenius) definition of a base is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ... In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Villi (singular: villus) are tiny, finger-like structures that protrude from the wall of the intestine to help absorb nutrients in the lumen. ...

Nutrients in the blood are transported to the liver via the hepatic portal circuit, or loop, where final carbohydrate digestion is accomplished in the liver. The liver accomplishes carbohydrate digestion in response to the hormones insulin and glucagon. As blood glucose levels increase following digestion of a meal, the pancreas secretes insulin causing the liver to transform glusose to glycogen, which is stored in the liver, adipose tissue, and in muscle cells, preventing hyperglycemia. A few hours following a meal, blood glucose will drop due to muscle activity, and the pancreas will now secrete glycogon which causes glycogen to be converted into glucose to prevent hypoglycemia . The liver is the largest internal organ of the human body. ... The structure of insulin. ... Glucagon ball and stick model Glucagon is a 29-amino acid polypeptide acting as an important hormone in carbohydrate metabolism. ... Electron micrograph of a section of a liver cell showing glycogen deposits as accumulations of electron dense particles (arrows). ... Hyperglycemia or High Blood Sugar is a condition in which an excessive amount of glucose circulates in the blood plasma. ... Hypoglycemia is a medical term referring to a pathologic state produced by a lower than normal amount of sugar (glucose) in the blood. ...

Note: In the discussion of digestion of carbohydrates; nouns ending in the suffix -ose usually indicate a sugar, lactose. Nouns ending in the suffix -ase indicates the enzyme that will break down the sugar, lactase. For example: lactose, sugar found naturally in milk, is digested by lactase resulting on a less complex molecule, a monosaccharide. Lactose is a disaccharide that makes up around 2-8% of the solids in milk. ... Lactase is a member of the β-galactosidase family of enzyme: enzymes that hydrolysis β 1,4 bonded attachments off of galactose. ...

Discussion

The principal dietary carbohydrates are polysaccharides, disaccharides, and monosaccharides. Starches (glucose polymers) and their derivatives are the only polysaccharides that are digested to any degree in the human gastrointestinal tract. In glycogen, the glucose molecules are mostly in long chains (glucose molecules in 1:4a linkage), but there is some chain-branching (produced by 1:6a linkages. Amylopectin, which constitutes 80-90% of dietary starch, is similar but less branched, whereas amylose is a straight chain with only 1:4a linkages. Glycogen is found in animals, whereas amylose and amylopectin are of plant origin. The disaccharides lactose (milk sugar) and sucrose (table sugar) are also ingested, along with the monosaccharides fructose and glucose. Electron micrograph of a section of a liver cell showing glycogen deposits as accumulations of electron dense particles (arrows). ... Lactose is a disaccharide that makes up around 2-8% of the solids in milk. ... Sucrose (common name: table sugar, also called saccharose) is a disaccharide (glucose + fructose) with the molecular formula C12H22O11. ...

In the mouth, starch is attacked by salivary a-amylase. However, the optimal pH for this enzyme is 6.7, and its action is inhibited by the acidic gastric juice when food enters the stomach. In the small intestine, both the salivary and the pancreatic a-amylase also acts on the ingested polysaccharides. Both the salivary and the pancreatic a-amylases hydrolyze 1:4a linkages but spare 1:6a linkages, terminal 1:4a linkages, and the 1:4a linkages next to branching points. Consequently, the end products of a-amylase digestion are oligosaccharides: the disaccharide maltose; the trisaccharide maltotriose; some slightly larger polymers with glucose in 1:4a linkage; and a-dextrins, polymers of glucose containing an average of about eight glucose molecules with 1:6a linkages .

The oligosaccharidases responsible for the further digestion of the starch derivatives are located in the outer portion of the brush border, the membrane of the microvilli of the small intestine . Some of these enzymes have more than one substrate. a-Dextrinase, which is also known as isomaltase, is mainly responsible for hydrolysis of 1:6a linkages. Along with maltase and sucrase, it also breaks down maltotriose and maltose. Sucrase and a-dextrinase are initially synthesized as a single glycoprotein chain which is inserted into the brush border membrane. It is then hydrolyzed by pancreatic proteases into sucrase and isomaltase subunits, but the subunits reassociate noncovalently at the intestinal surface.

Sucrase hydrolyzes sucrose into a molecule of glucose and a molecule of fructose. In addition, there are two disaccharidases in the brush border of the vili: lactase, which hydrolyzes lactose to glucose and galactose, and trehalase, which hydrolyzes trehalose, a 1:1a-linked dimer of glucose, into two glucose molecules. Headline text Sucrase (EC 3. ... Glucose (Glc), a monosaccharide (or simple sugar), is one of the most important carbohydrates. ... Fructose (or levulose) is a simple sugar (monosaccharide) found in many foods and one of the three most important blood sugars along with glucose and galactose. ... Lactase is a member of the β-galactosidase family of enzyme: enzymes that hydrolysis β 1,4 bonded attachments off of galactose. ... Lactose is a disaccharide that makes up around 2-8% of the solids in milk. ... Glucose (Glc), a monosaccharide (or simple sugar), is one of the most important carbohydrates. ... Galactose (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages. ... Wikipedia does not have an article with this exact name. ...

Deficiency or absence of one or more of the brush border oligosaccharidases may cause diarrhea, bloating, and flatulence after ingestion of sugar. The diarrhea is due to the increased number of osmotically active oligosaccharide molecules that remain in the intestinal lumen, causing the volume of the intestinal contents to increase. In the colon, bacteria break down some of the oligosaccharides, further increasing the number of osmotically active particles. The bloating and flatulence are due to the production of gas (CO₂and H⁺) from disaccharide residues in the lower small intestine and colon. This condition causes lactose intolerance in some people.

Lactase is of interest because, in most mammals and in many human ethnicities, intestinal lactase activity is high at birth, then declines to low levels during childhood and adulthood. The low lactase levels are associated with intolerance to milk (lactose intolerance). Most Europeans and their American descendants retain their intestinal lactase activity in adulthood; the incidence of lactase deficiency in northern Europeans is only about 15%. It is highier still in western Europeans. However, the incidence in most Africans, American Indians, Asians, and Mediterranean populations is 70- 100%. Milk intolerance can be ameliorated by administration of commercial lactase preparations, but this is expensive. Yogurt is better tolerated than milk in intolerant individuals because it contains its own bacterial lactase. Lactase is a member of the β-galactosidase family of enzyme: enzymes that hydrolysis β 1,4 bonded attachments off of galactose. ...

Fat Digestion

A lingual lipase is secreted by Ebner's glands on the dorsal surface of the tongue, and the stomach also secretes a lipase . The gastric lipase is of little importance is active in the stomach and can Most fat digestion begins in the duodenum, pancreatic lipase being one of the most important enzymes involved. Us enzyme) with relative helix that covers the Ulipase, opening of the lid is facilitated. Colipase represents about 4% of the total cholesterol is in the form of free fatty (FF) acids. The breakdown of complex fat globules occurs in the duodenum as the contents of the pancreatic duct empty into the lumen. Bile acts as an emulsifier, eroding the edges of the larger globules into smaller globules for further digestion. The introduction of lipase, along with the concentration of bile salts, in contact with the brush border of the mucosal cells, creates the correct environment for final stage breakdown of fats. Final absorption of fat into the body occurs in the villi. Specialized lymphatic capillaries, lacteals, transport the FFs, chyle, to the lymph system for filtering and then are combined with the blood as lymph joins blood at the right and left subclavian veins. A duct joining the pancreas to the bile duct to supply pancreatic juice which aid in digestion provided by the exocrine pancreas. ... An emulsion is a mixture of two immiscible substances. ... A lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water–insoluble, lipid substrates. ... Bile is also another name for Belenus, a god in Brythonic mythology. ... Chyle is a milky fluid (bodily fluid) consisting of lymph and emulsified fats. ... The subclavian vein is a continuation of the axillary vein and runs from the outer border of the first rib to the medial border of anterior scalene muscle. ...

===in the intestine by the pancreatic nucleases, and the nucleotides are split into the nucleosides and phosphoric acid by enzymes that appear to be located on the luminal surfaces of the mucosal cells. The nucleosides are then split into their constituent sugars and purine and pyrimidine bases. The bases are absorbed by active transport..

References:

• Kimball Biology Pages
• The Digestive System
• Colorado State University, Intrinsic Factor

See also

• Anaerobic digestion
• Gastrointestinal tract
• Step-by-Step Digestion

Anaerobic digestion is the breakdown of organic matter by bacteria in the absence of oxygen. ... The gastrointestinal tract or digestive tract, also referred to as the GI tract or the alimentary canal, (nourishment canal) or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and expels the remaining waste. ...

External links

• Gastric Digestion (Animation)
• Human Physiology - Digestion
• NIH guide to digestive system