The body needs a continual supply of macronutrients and micronutrients to survive. Macronutrients are required in bulk quantity for energy, ie. carbohydrates, proteins, and lipids. Micronutrients are trace substances required for normal metabolism, ie. vitamins and minerals. Virtually all nutrients enter the body in the form of food that has been broken down and processed by the digestive system. The digestive system consists of the gastrointestinal (GI) tract and accessory organs. The GI tract consists of the oral cavity, pharynx, esophagus, stomach, small intestine and large intestine. Accessory organs include the pancreas, liver, and gallbladder.
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Conceptual Vocabulary for The Digestive System and Nutrition
The gastrointestinal tract is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste.
Digestion is the process of metabolism whereby a biological entity processes a substance in order to chemically and mechanically convert the substance for the body to use.
Nutrition is a science that examines the relationship between diet and health.
A nutrient is a substance used in an organism's metabolism or physiology which must be taken in from the environment.
The mouth, also known as the buccal cavity or the oral cavity, is the orifice through which an organism takes in food and water.
The esophagus or gullet is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach.
Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract.
Saliva is the watery and usually frothy substance produced in the mouths of humans and some animals.
Swallowing, known scientifically as deglutition, is the reflex in the human body that makes something pass from the mouth, to the pharynx, into the esophagus, with the shutting of the epiglottis.
The small intestine is where the majority of digestion takes place, the part of the gastrointestinal tract (gut) between the stomach and the large intestine which includes the duodenum, jejunum, and ileum.
In addition to being the largest gland in the human body, producing bile for example, the liver plays a major role in metabolism.
A vitamin is a nutrient that is an organic compound required in tiny amounts for essential metabolic reactions in a living organism.
The pharynx is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea.
Mastication or chewing is the process by which food is mashed and crushed by teeth.
Gastric acid is one of the main secretions of the stomach, an acid solution consisting mainly of hydrochloric acid, and small quantities of potassium chloride and sodium chloride.
Parietal cells are the stomach epithelium cells which secrete gastric acid and intrinsic factor.
The duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum.
The large intestine, 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.
Exocrine glands are glands that secrete their products into ducts.
Bile is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver with components including cholesterol, lecithin, bilirubin, biliverdin, sodium glycocholate and sodium taurocholate.
Vitamin A is an essential human nutrient. In foods of animal origin, the major form of this vitamin is retinol, but all forms have a beta-ionone ring to which an isoprenoid chain is attached.
A bolus is a round mass of organic matter moving through the digestive tract.
Chyme is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum.
Gastric juice is a strong acidic liquid, pH 1 to 3 in humans, released by gastric glands in the lining of the stomach. Its main components are digestive enzymes pepsin and rennin, hydrochloric acid, and mucus.
The microvilli are structures that increase the surface area of cells by approximately 600 fold, thus facilitating absorption and secretion.
The jejunum is the central of the three divisions of the small intestine and lies between the duodenum and the ileum.
The ileum is the final section of the small intestine.
Intestinal villi are tiny, finger-like structures that protrude from the wall of the intestine.
The colon is another name for the large intestine.
Pancreatic juice is produced by the pancreas, containing a variety of enzymes including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, and amylase.
The pancreatic duct is a duct joining the pancreas to the common bile duct.
The gallbladder, or cholecyst, is a pear-shaped organ that stores about 50 ml of bile until the body needs it for digestion.
Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen which are present in common organic molecules.
In the gastrointestinal tract, the submucosa is the layer of loose connective tissue that supports the mucosa, as well as joins the mucosa to the bulk of underlying smooth muscle.
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein.
A gastric chief cell is a cell in the stomach that releases pepsinogen and rennin.
Released from the gall bladder, bile acids serve multiple functions including elimination of cholesterol from the body, elimination of catabolites from the liver, and emulsifying lipids and fat soluble vitamins in the intestine.
Amylase is the name given to glycoside hydrolase enzymes that break down starch into glucose molecules.
Pepsin is a digestive protease released by the chief cells in the stomach that functions to degrade food proteins into peptides.
Sucrase is the name given to a number of enzymes that catalyse the hydrolysis of sucrose to fructose and glucose.
Maltase is an enzyme produced by the cells lining the small intestine which specifically breaks down the disaccharide maltose.
Lactase, a member of the beta-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers
The B vitamins are eight water-soluble vitamins that play important roles in cell metabolism.
One of the B vitamins, thiamine plays an important role in helping the body metabolize carbohydrates and fat to produce energy. It is essential for proper functioning of the heart, nervous and digestive systems.
Also known as vitamin B2, riboflavin is the central component of the cofactors FAD and FMN. It is therefore required by all flavoproteins.
Also known as nicotinic acid or vitamin B3, niacin is a water-soluble vitamin whose derivatives such as NADH, NAD, NADP play essential roles in energy metabolism and DNA repair.
Also called vitamin B5, pantotheric acid is a water-soluble vitamin needed to form coenzyme-A.
Biotin is a water-soluble B-complex vitamin which is composed of an ureido ring fused with a tetrahydrothiophene ring. It is important for fatty acid synthesis, in gluconeogenesis, and to metabolize leucine.
The B complex vitamin, folic acid, is necessary for the production and maintenance of new cells.
Vitamin D represents a group of fat-soluble prohormones, the two major forms of which are ergocalciferol and cholecalciferol.
Vitamin C or ascorbic acid is a highly effective antioxidant. It acts to lessen oxidative stress, as a substrate for ascorbate peroxidase, as well as an enzyme cofactor in biosynthesis.
The G cell is a type of cell in the stomach that secretes gastrin. It works in conjunction with gastric chief cells and parietal cells.
S cells are cells which release secretin, found in the jejunum and duodenum.
A lacteal is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine.
Trypsin is a serine protease found in the digestive system, where it breaks down proteins. It is also often used in the laboratory for numerous procedures.
Serine proteases or serine endopeptidases are a class of peptidases that are characterised by the presence of a serine residue in the active site of the enzyme.
Gastric pits are indentations in the stomach which denote entrances to the glands.
The vermiform appendix is a blind ended tube connected to the cecum, from which it develops embryologically.
Secretin is a peptide hormone produced in the S cells of the duodenum for regulation of the pH of the duodenal contents via the control of gastric acid secretion and buffering with bicarbonate.
A lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water-insoluble, lipid substrates.
Chymotrypsin is a digestive enzyme that can perform proteolysis which cleaves peptides favorably at the carboxyl side of tyrosine, tryptophan, and phenylalanine because those three amino acids contain phenyl rings.
The hepatic portal vein is a portal vein in the human body that drains blood from the digestive system and its associated glands.
Carboxypeptidase is an enzyme that hydrolyzes the carboxy-terminal (C-terminal) peptide bond of proteins and peptides thus releasing the last amino acid of the chain.
Vitamin K denotes a group of lipophilic, and hydrophobic, vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation.
Beriberi is a nervous system ailment caused by thiamine deficiency.
Also known as vitamin B6, pyridoxal phosphate is the active form and is a cofactor in many reactions of amino acid metabolism, including transamination, deamination, and decarboxylation.
Scurvy is a deficiency disease that results from insufficient intake of vitamin C, which is required for correct collagen synthesis in humans.
Rickets is a softening of the bones in children potentially leading to fractures and deformity. The predominant cause is a vitamin D deficiency.
Pellagra is a vitamin deficiency disease caused by dietary lack of niacin and protein.
The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct.
Alkaline tide refers to a condition, normally encountered after eating a meal, when stomach acid is released into the stomach that causes a temporary increase in pH of the blood.
The ileocecal valve is a sphincter muscle situated at the junction of the small intestine and the large intestine to regulate the flow of chyme into the bowels.
Making up 70-80% of the cytoplasmic mass of the liver, hepatocytes are involved in protein synthesis, protein storage and transformation of carbohydrates, synthesis of cholesterol, bile salts and phospholipids, and detoxification.
Ghrelin is a hormone produced by cells lining the fundus of the human stomach that stimulate appetite.
Leptin is a protein hormone produced by adipose tissue that plays a key role in regulating energy intake and energy expenditure, including the regulation of appetite and metabolism.
Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin: the flavin adenine dinucleotide or flavin mononucleotide.
Cyanocobalamin is a compound that is metabolized to a vitamin in the B complex commonly known as vitamin B12.
Classified as an essential nutrient, choline is usually grouped with the B vitamins. This natural amine is found in the lipids that make up cell membranes as well as within many other physiologically important substances.
Gastrin releasing peptide is released by the post-ganglionic fibres of the vagus nerve which innervate the G cells of the stomach and stimulate them to release gastrin.
Enterochromaffin-like cells are a type of neuroendocrine cells found in the gastric glands of the gastric mucosa, particularly in the vicinity of parietal cells. ECL cells synthesize and secrete histamine.
The pylorus is the region of the stomach that connects to the duodenum.
Chyle is a milky fluid consisting of lymph and emulsified fats, or free fatty acids. It is formed in the small intestine during digestion of ingested fatty foods and taken up by lymph vessels specifically known as lacteals.
A brush border is the name for the microvilli-covered surface of pseudostratified columnar epithelium and simple columnar epithelium found in small intestine and in the distal tubule of the kidney.
Brunner's glands, or duodenal glands, are compound tubular submucosal glands located throughout the duodenum which produce an alkaline secretion containing bicarbonate.
Trypsinogen is the precursor form of the pancreatic enzyme trypsin.
Chymotrypsinogen is a precursor of the digestive enzyme chymotrypsin.
Enteropeptidase or enterokinase is an enzyme which transforms trypsinogen into trypsin, indirectly activating a number of pancreatic digestive enzymes.
The cecum is a pouch connected to the ascending colon of the large intestine and the ileum.
The ampulla of Vater is formed by the union of the pancreatic duct and the common bile duct.
Alpha-amylase is the major form of amylase found in humans and other mammals.
Erepsin is an enzyme that digests peptides which works only on the outside peptide bonds.
Tocopherol, also known as vitamin E, actually describes a series of organic compounds consisting of a methylated phenols.
The esophageal glands are small compound racemose exocrine glands of the mucous type.
A canaliculus is an adaptation found on gastric parietal cells, which is a deep infolding, or little channel, serving to increase the surface area for secretion.
The fundus is the rounded part of the upper stomach which allows for an accumulation of gases produced by chemical digestion.
Rugae is a term used in anatomy that refers to a series of ridges produced by folding of the wall of an organ, most commonly applied to the internal surface of the stomach.
An acinus refers to the berry-shaped termination where the secretion of an exocrine gland is produced, such with the exocrine pancreas.
Bili canaliculi are thin tubes that collect bile secreted by hepatocytes, which merge and form bile ductules, eventually becoming the common hepatic duct.
Ergocalciferol is a form of Vitamin D. It is created from viosterol, which in turn is created when ultraviolet light activates ergosterol.
Cholecalciferol is a form of Vitamin D. Its precursor is 7-Dehydrocholesterol which only forms the vitamin after being exposed to UV radiation.
Dehydroascorbic acid is an oxidized form of ascorbic acid. It is actively imported into the endoplasmic reticulum of cells and generates the oxidative potential found there.
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