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Encyclopedia > Digestion

Digestion is the process by which the body breaks down food into smaller components that can be absorbed by the blood stream. In mammals, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to break down starches. The stomach continues to break food down mechanically and chemically through the churning of the stomach and mixing with enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with excretion.[1] Anaerobic digestion component of Lübeck mechanical biological treatment plant in Germany, 2007 Anaerobic digestion is a process in which microorganisms break down biodegradable material in the absence of oxygen. ... Precipitation is the formation of a solid in a solution during a chemical reaction. ... In computer science, components are basic functional units of a program which allow for rapid development. ... Red blood cells (erythrocytes) are present in the blood and help carry oxygen to the rest of the cells in the body Blood is a circulating tissue composed of fluid plasma and cells (red blood cells, white blood cells, platelets). ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria For the folk-rock band see The Mammals. ... The cephalic phase of gastric secretion occurs even before food enters the stomach, especially while it is being eaten. ... For the band, see Saliva (band). ... For other uses, see Mouth (disambiguation). ... Digestive enzymes are enzymes in the alimentary tract that break down food so that the organism can absorb it. ... In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... Mastication or chewing is the process by which food is mashed and crushed by teeth. ... For the band, see Saliva (band). ... Starch (CAS# 9005-25-8, chemical formula (C6H10O5)n,[1]) is a mixture of amylose and amylopectin (usually in 20:80 or 30:70 ratios). ... Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. ... Gut redirects here. ... Anatomy of the anus and rectum For the death metal band Defecation, see Defecation (band). ...

Contents

Overview

Digestion is usually divided into mechanical processing to reduce the size of food particles and chemical action to further reduce the size of particles and prepare them for absorption. 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 and chemical processing. Digestion is separated into four separate processes: This article does not cite any references or sources. ... In general terms, eating (formally, ingestion) is the process of consuming something edible, i. ...

  1. Ingestion: placing food into the mouth
  2. Mechanical digestion & chemical digestion: mastication to tear and crush food, and churning of the stomach. Addition of chemicals (acid, bile, enzymes, and water) to break down complex molecules into simple structures
  3. Absorption: movement of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion
  4. Egestion: Removal of undigested materials from the digestive tract through defecation

Underlying the process is muscle movement throughout the system, swallowing and peristalsis. Mastication or chewing is the process by which food is mashed and crushed by teeth. ... For other uses, see acid (disambiguation). ... Bile (or gall) is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver of most vertebrates. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a solution with a high solute concentration, down a solute concentration gradient. ... Sodium-Potassium pump, an example of Primary active transport Active transport (sometimes called active uptake) is an energy-requiring process that moves material across a cell membrane and up the concentration gradient. ... diffusion (disambiguation). ... Anatomy of the anus and rectum For the death metal band Defecation, see Defecation (band). ... For the Bush song, see Swallowed (song). ... Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. ...


Human digestion process

Phases of human digestion

  • Cephalic phase - This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve.
  • Gastric phase - This phase takes 3 to 4 hours. It is stimulated by distention of the stomach and alkaline pH. Distention activates long and myentric reflexes. This activates the release of acetylcholine which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach to an alkaline[citation needed] level. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete HCl. HCl release is also triggered by acetylcholine and histamine.
  • Intestinal phase - This phase has 2 parts, the excitatory and the inhibitory. Partially-digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.

The cephalic phase of gastric secretion occurs even before food enters the stomach, especially while it is being eaten. ... For other uses, see Cortex. ... The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). ... The medulla oblongata is the lower portion of the brainstem. ... The vagus nerve (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (within the medulla oblongata) and extends, through the jugular foramen, down below the head, to the abdomen. ... For other uses, see PH (disambiguation). ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... Gastric juice is a strong acidic liquid, pH 1 to 3, which is close to being colourless. ... This article is about the chemistry of hydrogen. ... For other uses, see PH (disambiguation). ... In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... Sea surface alkalinity (from the GLODAP climatology) Alkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. ... In medicine, the G cell is a type of cell in the stomach that secrets gastrin. ... In humans, gastrin is a hormone that stimulates secretion of gastric acid by the stomach. ... Human parietal cells - stomach Parietal cells (also called oxyntic cells) are the stomach epithelium cells which secrete gastric acid and intrinsic factor. ... Hydrochloric acid is the aqueous solution of hydrogen chloride gas (HCl). ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... This article or section does not cite any references or sources. ... In anatomy of the digestive system, the duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum. ... The Sympathetic Nervous System (SNS) is a branch of the autonomic nervous system. ... From Greek pylorus; pyl- = gate, -orus = guard. ...

Oral cavity

Main article: Mouth (human)

In humans, digestion begins in the oral cavity where food is chewed. Saliva is secreted in large amounts (1-1.5 litre/day) by three pairs of exocrine salivary glands (parotid, submandibular, and sublingual) in the oral cavity, and is mixed with the chewed food by the tongue. There are two types of saliva. One is a thin, watery secretion, and its purpose is to wet the food. The other is a thick, mucous secretion, and it acts as a lubricant and causes food particles to stick together and form a bolus. The saliva serves to clean the oral cavity and moisten the food, and contains digestive enzymes such as salivary amylase, which aids in the chemical breakdown of polysaccharides such as starch into disaccharides such as maltose. It also contains mucin, a glycoprotein which helps soften the food into a bolus. Sagittal section of nose mouth, pharynx, and larynx. ... Image File history File links Stomach_colon_rectum_diagram. ... Image File history File links Stomach_colon_rectum_diagram. ... This article is about modern humans. ... Gut redirects here. ... Sagittal section of nose mouth, pharynx, and larynx. ... Mastication or chewing is the process by which food is mashed and crushed by teeth. ... For the band, see Saliva (band). ... Look up bolus in Wiktionary, the free dictionary. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Amylase is the name given to glycoside hydrolase enzymes that break down starch into glucose molecules. ... Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ... Polysaccharides (sometimes called glycans) are relatively complex carbohydrates. ... Starch (CAS# 9005-25-8, chemical formula (C6H10O5)n,[1]) is a mixture of amylose and amylopectin (usually in 20:80 or 30:70 ratios). ... Sucrose, a common disaccharide A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides. ... Maltose, or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) linkage. ... N-linked protein glycosylation (N-glycosylation of N-glycans) at Asn residues (Asn-x-Ser/Thr motifs) in glycoproteins[1]. Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide backbones. ... Look up bolus in Wiktionary, the free dictionary. ...


Swallowing transports the chewed food into the esophagus, passing through the oropharynx and hypopharynx. The mechanism for swallowing is coordinated by the swallowing center in the medulla oblongata and pons. The reflex is initiated by touch receptors in the pharynx as the bolus of food is pushed to the back of the mouth. For the Bush song, see Swallowed (song). ... The esophagus or oesophagus (see American and British English spelling differences), sometimes known as the gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. ... The pharynx is the part of the digestive system of many animals immediately behind the mouth and in front of the esophagus. ... In human anatomy, the hypopharynx is the bottom part of the pharynx, and is the part of the throat that connects to the esophagus. ... The medulla oblongata is the lower portion of the brainstem. ... For other uses, see Pons (disambiguation). ...


Esophagus

Main article: Esophagus

The esophagus, a narrow, muscular tube about 30 centimeters (12 inches) long, starts at the pharynx, passes through the larynx and diaphragm, and ends at the cardiac orifice of the stomach. The wall of the esophagus is made up of two layers of smooth muscles, which form a continuous layer from the esophagus to the rectum and contract slowly, over long periods of time. The inner layer of muscles is arranged circularly in a series of descending rings, while the outer layer is arranged longitudinally. At the top of the esophagus, is a flap of tissue called the epiglottis that closes during swallowing to prevent food from entering the trachea (windpipe). The chewed food is pushed down the esophagus to the stomach through peristaltic contraction of these muscles. It takes only seconds for food to pass through the esophagus, and little digestion actually takes place. The esophagus or oesophagus (see American and British English spelling differences), sometimes known as the gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. ... The esophagus or oesophagus (see American and British English spelling differences), sometimes known as the gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. ... The larynx (plural larynges), colloquially known as the voicebox, is an organ in the neck of mammals involved in protection of the trachea and sound production. ... For other types of diaphragm, see Diaphragm. ... This article is about the cardia in the human body. ... In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... Smooth muscle Layers of Esophageal Wall: 1. ... The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. ... The epiglottis is a lid-like flap of fibrocartilage tissue covered with a mucus membrane, attached to the root of the tongue. ... Windpipe redirects here. ... Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. ...


Stomach

Main article: Stomach

The food enters the stomach after passing through the cardiac orifice. In the stomach, food is further broken apart, and thoroughly mixed with a gastric acid and digestive enzymes that break down proteins. The acid itself does not break down food molecules, rather, the acid provides an optimum pH for the reaction of the enzyme pepsin. The parietal cells of the stomach also secrete a glycoprotein called intrinsic factor which enables the absorption of vitamin B-12. Other small molecules such as alcohol are absorbed in the stomach as well by passing through the membrane of the stomach and entering the circulatory system directly. In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... This article is about the cardia in the human body. ... Gastric acid is, together with several enzymes and the intrinsic factor, one of the main secretions of the stomach. ... Pepsin is a digestive protease (EC 3. ... Human parietal cells - stomach Parietal cells (also called oxyntic cells) are the stomach epithelium cells which secrete gastric acid and intrinsic factor. ... N-linked protein glycosylation (N-glycosylation of N-glycans) at Asn residues (Asn-x-Ser/Thr motifs) in glycoproteins[1]. Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide backbones. ... Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. ... Cyanocobalamin is a compound that is metabolized to a vitamin in the B complex commonly known as vitamin B12 (or B12 for short). ... This article does not cite any references or sources. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... For transport in plants, see Vascular tissue. ...

Main article: Histology of stomach

The transverse section of the alimentary canal reveals four distinct and well developed layers called serosa, muscular coat, submucosa and mucosa. Serosa: It is the outermost thin layer of single cells called mesothelial cells. Muscular coat: It is very well developed for churning of food. It has outer longitudinal, middle smooth and inner oblique muscles. Submucosa: It has connective tissue containing lymph vessels, blood vessels and nerves. Mucosa: It contains large folds filled with connective tissue. The gastric glands have a packing of lamina propria. Gastric glands may be simple or branched tubular secreting mucus, hydrochloric acid, pepsinogen and renin. A serosa is a serous membrane, Serous membranes line the pericardial, pleural, and peritoneal cavities, enclosing their contents. ... The muscular coat (or muscular layer, or muscular fibers, or muscularis externa) is a region of muscle in many organs in the vertebrate body, adjacent to the mucous membrane. ... In the gastrointestinal tract. ... The mucous membranes (or mucosa) are linings of ectodermic origin, covered in epithelium, that line various body cavities and internal organs. ... The fundus glands (or fundic glands, or gastric glands) are found in the body and fundus of the stomach. ...


Small intestine

Main article: Small intestine

After being processed in the stomach, food is passed to the small intestine via the Pyloric sphincter. The majority of digestion and absorption occur here as chyme enters the duodenum. Here it is further mixed with three different liquids: In biology the small intestine is the part of the gastrointestinal tract (gut) between the stomach and the large intestine and includes the duodenum, jejunum, and ileum. ... In biology the small intestine is the part of the gastrointestinal tract (gut) between the stomach and the large intestine and includes the duodenum, jejunum, and ileum. ... From Greek pylorus; pyl- = gate, -orus = guard. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Chyme, also known as Chymus is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum. ... In anatomy of the digestive system, the duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum. ...

  1. bile, which emulsifies fats to allow absorption, neutralizes the chyme, and is used to excrete waste products such as bilin and bile acids (which has other uses as well). It is not an enzyme, however.The bile juice is stored in a small organ called the gall bladder.
  2. pancreatic juice made by the pancreas.
  3. intestinal enzymes of the alkaline mucosal membranes. The enzymes include: maltase, lactase and sucrase, to process sugars; trypsin and chymotrypsin are also added in the small intestine

Most nutrient absorption takes place in the small intestine. As the acid 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. Nutrients pass through the small intestine's wall, which contains small, finger-like structures called villi, each of which is covered with even smaller hair-like structures called microvilli. 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. Bile (or gall) is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver of most vertebrates. ... A. Two immiscible liquids, not emulsified; B. An emulsion of Phase II dispersed in Phase I; C. The unstable emulsion progressively separates; D. The surfactant (purple outline) positions itself on the interfaces between Phase A and Phase B, stabilizing the emulsion An emulsion is a mixture of two immiscible (unblendable... For other uses, see FAT. Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. ... Neutralization is a chemical reaction, also called a water forming reaction, in which an acid and a base or alkali (soluble base) react and produce a salt and water. ... Bilins are blue or green pigments that consist of a linear arrangement of pyrroles. ... Bile acids (also known as bile salts) are steroid acids found predominantly in the bile of mammals. ... The gallbladder (or cholecyst) is a pear-shaped organ that stores bile (or gall) until the body needs it for digestion. ... Pancreatic juice is a juice produced by the pancreas. ... The pancreas is a gland organ in the digestive and endocrine systems of vertebrates. ... 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. ... This article is about sugar as food and as an important and widely-traded commodity. ... Trypsin (EC 3. ... Chymotrypsin (bovine γ chymotrypsin: PDB 1AB9, EC 3. ... For other uses, see PH (disambiguation). ... Villus (Latin: shaggy hair[1], plural villi) can refer to: Intestinal villus. ... The microvilli (singular: microvillus) are structures that increase the surface area of cells by approximately 600 fold (human), thus facilitating absorption and secretion. ... For other uses, see Blood (disambiguation). ... The portal vein is a major vein in the human body draining blood from the digestive system and its associated glands. ... The liver is the largest internal organ in the human body, and is an organ present in vertebrates and some other animals. ...


The small intestine and remainder of the digestive tract undergoes peristalsis to transport food from the stomach to the rectum and allow food to be mixed with the digestive juices and absorbed. The circular muscles and longitudinal muscles are antagonistic muscles, with one contracting as the other relaxes. When the circular muscles contract, the lumen becomes narrower and longer and the food is squeezed and pushed forward. When the longitudinal muscles contract, the circular muscles relax and the gut dilates to become wider and shorter to allow food to enter. In the stomach there is another phase that is called Mucus which promotes easy movement of food by wetting the food. It also nullifies the effect of HCL on the stomach by wetting the walls of the stomach as HCL has the capacity to digest the stomach. Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. ... artery anatomy, showing lumen The lumen (pl. ...


Large intestine

Main article: Large intestine

After the food has been passed through the small intestine, the food enters the large intestine. The large intestine is roughly 1.5 meters long, with three parts: the cecum at the junction with the small intestine, the colon, and the rectum. The colon itself has four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The large intestine absorbs water from the bolus and stores feces until it can be egested. Food products that cannot go through the villi, such as cellulose (dietary fiber), are mixed with other waste products from the body and become hard and concentrated feces.The feces is stored in the rectum for a certain period and then the stored feces is egested due to the contraction and relaxation through the anus. The exit of this waste material is regulated by the anal sphincter. The large intestine, an organ which is now more commonly referred to by its Greek name, the colon, is the last part of the digestive system: the final stage of the alimentary canal in vertebrate animals. ... The large intestine, an organ which is now more commonly referred to by its Greek name, the colon, is the last part of the digestive system: the final stage of the alimentary canal in vertebrate animals. ... The metre, or meter (symbol: m) is the SI base unit of length. ... The cecum or caecum (from the Latin caecus meaning blind) is a pouch connected to the ascending colon of the large intestine and the ileum. ... In biology the small intestine is the part of the gastrointestinal tract (gut) between the stomach and the large intestine and includes the duodenum, jejunum, and ileum. ... It has been suggested that this article or section be merged with Large intestine. ... The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. ... In anatomy of the digestive system, the colon or large intestine or large bowel is the part of the intestine from the cecum to the rectum. ... In anatomy of the digestive system, the colon is the part of the intestine from the cecum to the rectum. ... The Descending Colon passes downward through the left hypochondriac and lumbar regions along the lateral border of the left kidney. ... The sigmoid colon is the part of the large intestine after the descending colon and before the rectum. ... Look up bolus in Wiktionary, the free dictionary. ... Horse feces Feces, faeces, or fæces (see spelling differences) is a waste product from an animals digestive tract expelled through the anus (or cloaca) during defecation. ... Anatomy of the anus and rectum For the death metal band Defecation, see Defecation (band). ... Villi (singular: villus) are tiny, finger-like structures that protrude from the wall of the intestine to help absorb nutrients in the lumen. ... Cellulose as polymer of β-D-glucose Cellulose in 3D Cellulose (C6H10O5)n is a polysaccharide of beta-glucose. ... Dietary fibers are the indigestible portion of plant foods that move food through the digestive system, absorbing water and making defecation easier. ... Horse feces Feces, faeces, or fæces (see spelling differences) is a waste product from an animals digestive tract expelled through the anus (or cloaca) during defecation. ... This article is about the bodily orifice. ... Male Anatomy The anus, in anatomy, is the external opening of the rectum. ...


Carbohydrate digestion

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). 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. 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 (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...


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 that is most important as a 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. Amylase 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. Amylase is the name given to glycoside hydrolase enzymes that break down starch into glucose molecules. ... For the band, see Saliva (band). ... The common (Arrhenius) definition of a base is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ... For baking soda, see Sodium bicarbonate 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 glucose 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 glucagon which causes glycogen to be converted into glucose to prevent hypoglycemia. The liver is the largest internal organ in the human body, and is an organ present in vertebrates and some other animals. ... Not to be confused with inulin. ... Glucagon ball and stick model A microscopic image stained for glucagon. ... Glycogen Structure Segment Glycogen is a polysaccharide of glucose (Glc) which functions as the primary short term energy storage in animal cells. ... Adipose tissue is one of the main types of connective tissue. ... Hyperglycemia, hyperglycaemia, or high blood sugar is a condition in which an excessive amount of glucose circulates in the blood plasma. ... Hypoglycemia (hypoglycaemia in British English) is a medical term referring to a pathologic state produced by a lower than normal level of glucose (sugar) in the blood. ...


Note: In the discussion of digestion of carbohydrates; nouns ending in the suffix -ose usually indicate a sugar, such as lactose. Nouns ending in the suffix -ase indicates the enzyme that will break down the sugar, such as lactase. Enzymes usually begin with the substrate (substance) they are breaking down. For example: maltose, a disaccharide, is broken down by the enzyme maltase (by the process of hydrolysis), resulting in a two glucose molecules, a monosaccharide. Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose molecules bonded through a β1-4 glycosidic linkage. ... Lactase is a member of the β-galactosidase family of enzyme: enzymes that hydrolysis β 1,4 bonded attachments off of galactose. ... Look up substrate in Wiktionary, the free dictionary. ... Sucrose, a common disaccharide A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides. ... Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... Monosaccharides are the simplest form of carbohydrates. ...


Fat digestion

The presence of fat in the small intestine produces hormones which stimulate the release of lipase from the pancreas and bile from the gallbladder. The lipase (activated by acid) breaks down the fat into monoglycerides and fatty acids. The bile emulsifies the fatty acids so they may be easily absorbed. A computer-generated image of a type of pancreatic lipase (PLRP2) from the guinea pig. ... The gallbladder (or cholecyst, sometimes gall bladder) is a pear-shaped organ that can accomodate up to 60 ml of bile (or gall) until the body needs it for digestion. ... General chemical structure of a monoglyceride. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid (or organic acid), often with a long aliphatic tail (long chains), either saturated or unsaturated. ... A. Two immisicible liquids, not emulsified; B. An emulsion of Phase B dispersed in Phase A; C. The unstable emulsion progressively separates; D. The surfactant (purple outline) positions itself on the interfaces between Phase A and Phase B, stabilizing the emulsion An emulsion is a mixture of two immiscible (unblendable...


Short- and medium chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein just as other absorbed nutrients do. However, long chain fatty acids are too large to be directly released into the tiny intestinal capillaries. Instead they are absorbed into the fatty walls of the intestine villi and reassembled again into triglycerides. The triglycerides are coated with cholesterol and protein (protein coat) into a compound called a chylomicron. Short chain fatty acids are a sub-group of fatty acids with aliphatic tails of less than six carbons. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... The portal vein is a major vein in the human body draining blood from the digestive system and its associated glands. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... Triglyceride (blue: fatty acid; red: glycerol backbone) Triglycerides are glycerides in which the glycerol is esterified with three fatty acids. ... Cholesterol is a sterol (a combination steroid and alcohol). ... Chylomicrons are large lipoprotein particles (having a diameter of 75 to 1,200nm) that are created by the absorptive cells of the small intestine. ...


Within the villi, the chylomicron enters a lymphatic capillary called a lacteal, which merges into larger lymphatic vessels. It is transported via the lymphatic system and the thoracic duct up to a location near the heart (where the arteries and veins are larger). The thoracic duct empties the chylomicrons into the bloodstream via the left subclavian vein. At this point the chylomicrons can transport the triglycerides to where they are needed. In mammals including humans, the lymphatic vessels (or lymphatics) are a network of thin tubes that branch, like blood vessels, into tissues throughout the body. ... A lacteal is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine. ... In human anatomy, the thoracic duct is an important part of the lymphatic system — it is the largest lymphatic vessel in the body. ... 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. ...


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(an inactive form of the enzyme pepsin) 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. Another function is to induce insulin secretion.

In humans, gastrin is a hormone that stimulates secretion of gastric acid by the stomach. ... In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... The fundus glands (or fundic glands, or gastric glands) are found in the body and fundus of the stomach. ... Pepsin is a protease, a digestive enzyme that degrades food proteins in the stomach; the other important digestive enzymes are trypsin and chymotrypsin. ... Pepsin is a digestive protease (EC 3. ... Hydrochloric acid is the aqueous solution of hydrogen chloride gas (HCl). ... For other uses, see PH (disambiguation). ... 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 about 25-30 cm long connecting the stomach to the jejunum. ... The pancreas is a gland organ in the digestive and endocrine systems of vertebrates. ... Bile (or gall) is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver of most vertebrates. ... The liver is the largest internal organ in the human body, and is an organ present in vertebrates and some other animals. ... 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. ...

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, very weakly acidic. 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 concentration of the acid or base, however, does also play a role. For other uses, see PH (disambiguation). ... For the band, see Saliva (band). ... 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. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In...


pH in the stomach is very acidic 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. ... Irreversible egg protein denaturation and loss of solubility, caused by the high temperature (while cooking it) Denaturation is the alteration of a protein or nucleic acids shape through some form of external stress (for example, by applying heat, acid or alkali), in such a way that it will no... The innate immune system comprises the cells and mechanisms that defend the host from infection by other organisms, in a non-specific manner. ... 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 liver secretes bile into the duodenum to neutralise the acidic conditions from the stomach. Also the pancreatic duct empties into the duodenum, 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 in the environment. A duct joining the pancreas to the bile duct to supply pancreatic juice which aid in digestion provided by the exocrine pancreas. ... For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Chyme, also known as Chymus is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum. ...


Specialized organs in non-human animals

Organisms have evolved specialized organs to aid in the digestion of their food, modifying tongues, teeth, and other organs to assist in digestion. Certain insects may have a crop or enlarged esophagus, while birds and cockroaches have developed gizzards to assist in the digestion of tough materials. Herbivores have evolved cecums (or an abomasum in the case of ruminants) to break down cellulose in plants. This article is about evolution in biology. ... For other uses, see Tongue (disambiguation). ... A 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 gastropods, earthworms[1], leeches[2], insects, birds and clowns. ... The esophagus or oesophagus (see American and British English spelling differences), sometimes known as the gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. ... Duck gizzards The gizzard , also referred to as the ventriculus, gastric mill, and gigerium, is an organ in the digestive tract found in birds, reptiles, earthworms, some fish, and other creatures. ... A deer and two fawns feeding on some foliage A herbivore is often defined as any organism that eats only plants[1]. By that definition, many fungi, some bacteria, many animals, about 1% of flowering plants and some protists can be considered herbivores. ... The cecum or caecum (from the Latin caecus meaning blind) is a pouch connected to the ascending colon of the large intestine and the ileum. ... The abomasum is the fourth and final stomach compartment of the stomach in ruminants. ... It has been suggested that this article or section be merged with Ruminantia. ... Cellulose as polymer of β-D-glucose Cellulose in 3D Cellulose (C6H10O5)n is a polysaccharide of beta-glucose. ...


See also

The Nutrition Facts table indicates the amounts of nutrients which experts recommend you limit or consume in adequate amounts. ...

References

  • Kimball's Biology Pages, Digestion
  • Chemistry lecture
  • American Journal of Physiology, article

Other references

  1. ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. 

External links

  • Human Physiology - Digestion
  • NIH guide to digestive system
This article does not cite any references or sources. ... Pharmacology (in Greek: pharmakon (φάρμακον) meaning drug, and lego (λέγω) to tell (about)) is the study of how drugs interact with living organisms to produce a change in function. ... Pharmacokinetics (in Greek: pharmacon meaning drug, and kinetikos meaning putting in motion) is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Distribution in pharmacology is a branch of pharmacokinetics describing reversible transfer of drug from one location to another within the body. ... Drug metabolism is the metabolism of drugs, their biochemical modification or degradation, usually through specialized enzymatic systems. ... The kidneys are important excretory organs in vertebrates. ... In medicine, the clearance, also renal clearance or renal plasma clearance (when referring to the function of the kidney), of a substance is the inverse of the time constant that describes its removal rate from the body divided by its volume of distribution (or total body water). ... Pharmacodynamics is the study of the biochemical and physiological effects of drugs and the mechanisms of drug action and the relationship between drug concentration and effect. ... // Toxic and Intoxicated redirect here – toxic has other uses, which can be found at Toxicity (disambiguation); for the state of being intoxicated by alcohol see Drunkenness. ... It has been suggested that Neurotoxicity be merged into this article or section. ... The terms pharmacogenomics and pharmacogenetics tend to be used interchangeably, and a precise, consensus definition of either remains elusive. ... Pharmacogenomics is the branch of pharmacology which deals with the influence of genetic variation on drug response in patients by correlating gene expression or single-nucleotide polymorphisms with a drugs efficacy or toxicity. ... Technical advancements in recent years have allowed progress toward the understanding of the brain and how drugs can be made to affect it. ... Neuropharmacology is the branch of health science concerned with the study of drugs on the nervous system. ... Psychopharmacology is the study of the effects of any psychoactive drug that acts upon the mind by affecting brain chemistry. ...

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