Actions of the major digestive hormones secreted by enteroendocrine cells

Actions of the major digestive hormones secreted by enteroendocrine cells.

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.

WikiPremed Resources

The Digestive System and Nutrition Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for The Digestive System and Nutrition
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals

Proficiency 

Be prepared to describe the basic anatomy of the human digestive tract.

Be able to describe how the composition of saliva relates to its digestive and immunological functions.

Distinguish the different types of cells within gastric glands in the stomach and be able to identify their secretions.

Know the function of intrinsic factor secreted by parietal cells.

Understand how the secretion of pepsinogen by chief cells is regulated.

Be able to describe the composition of bile from the bile duct and pancreatic juice from the pancreatic duct as they are released into the duodenum.

Understand how the secretion of bile is regulated by release of CCK from the duodenum.

Be familiar with the structure of the epithelial tissue constituting the inner lining of the small intestine.

Have a comprehensive understanding of the numerous functions of the liver in human physiology including production of bile, regulation of glycogen storage, decomposition of red blood cells, protein synthesis, lipid synthesis, production of hormones, and detoxification.

Be familiar with the structure and mechanisms of the hepatic portal system.

Be able to describe the functions of the various hormones of the gastrointestinal system.

Have basic familiarity with the essential vitamins and minerals.

Know which digestive enzymes, or zymogens, are secreted at which points in the digestive tract and to what end.

Know which digestive enzymes, or zymogens, are secreted at which points in the digestive tract and to what end.

Understand the anatomy and functioning of the enteric nervous system and why it is often called 'the second brain'.

Suggested Assignments

Review the terminology for the digestive system and nutrition using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Complete the advanced crossword puzzle for the digestive system and nutrition. Here is the solution to the puzzle.

Read pp. 141-151 and pp. 153-160 in ExamKrackers Biology II. Perform practice items 97-104 on pg. 152 and practice items 105-112 on pg. 161.

Review the web resources for the digestive system and nutrition.

Conceptual Vocabulary for The Digestive System and Nutrition

Gastrointestinal tract
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
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
Nutrition is a science that examines the relationship between diet and health.
Nutrient
A nutrient is a substance used in an organism's metabolism or physiology which must be taken in from the environment.
Mouth
The mouth, also known as the buccal cavity or the oral cavity, is the orifice through which an organism takes in food and water.
Esophagus
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
Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract.
Saliva
Saliva is the watery and usually frothy substance produced in the mouths of humans and some animals.
Swallowing
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.
Small intestine
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.
Liver
In addition to being the largest gland in the human body, producing bile for example, the liver plays a major role in metabolism.
Vitamin
A vitamin is a nutrient that is an organic compound required in tiny amounts for essential metabolic reactions in a living organism.
Pharynx
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
Mastication or chewing is the process by which food is mashed and crushed by teeth.
Gastric acid
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 cell
Parietal cells are the stomach epithelium cells which secrete gastric acid and intrinsic factor.
Duodenum
The duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum.
Large intestine
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 gland
Exocrine glands are glands that secrete their products into ducts.
Bile
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
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.
Bolus
A bolus is a round mass of organic matter moving through the digestive tract.
Chyme
Chyme is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum.
Gastric juice
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.
Microvilli
The microvilli are structures that increase the surface area of cells by approximately 600 fold, thus facilitating absorption and secretion.
Jejunum
The jejunum is the central of the three divisions of the small intestine and lies between the duodenum and the ileum.
Ileum
The ileum is the final section of the small intestine.
Intestinal villi
Intestinal villi are tiny, finger-like structures that protrude from the wall of the intestine.
Colon
The colon is another name for the large intestine.
Pancreatic juice
Pancreatic juice is produced by the pancreas, containing a variety of enzymes including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, and amylase.
Pancreatic duct
The pancreatic duct is a duct joining the pancreas to the common bile duct.
Gallbladder
The gallbladder, or cholecyst, is a pear-shaped organ that stores about 50 ml of bile until the body needs it for digestion.
Dietary mineral
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.
Submucosa
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
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein.
Gastric chief cell
A gastric chief cell is a cell in the stomach that releases pepsinogen and rennin.
Bile acid
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
Amylase is the name given to glycoside hydrolase enzymes that break down starch into glucose molecules.
Pepsin
Pepsin is a digestive protease released by the chief cells in the stomach that functions to degrade food proteins into peptides.
Sucrase
Sucrase is the name given to a number of enzymes that catalyse the hydrolysis of sucrose to fructose and glucose.
Maltase
Maltase is an enzyme produced by the cells lining the small intestine which specifically breaks down the disaccharide maltose.
Lactase
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
B vitamins
The B vitamins are eight water-soluble vitamins that play important roles in cell metabolism.
Thiamine
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.
Riboflavin
Also known as vitamin B2, riboflavin is the central component of the cofactors FAD and FMN. It is therefore required by all flavoproteins.
Niacin
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.
Pantothenic acid
Also called vitamin B5, pantotheric acid is a water-soluble vitamin needed to form coenzyme-A.
Biotin
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.
Folic acid
The B complex vitamin, folic acid, is necessary for the production and maintenance of new cells.
Vitamin D
Vitamin D represents a group of fat-soluble prohormones, the two major forms of which are ergocalciferol and cholecalciferol.
Ascorbic acid
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.
G cell
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 cell
S cells are cells which release secretin, found in the jejunum and duodenum.
Lacteal
A lacteal is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine.
Trypsin
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 protease
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
Gastric pits are indentations in the stomach which denote entrances to the glands.
Vermiform appendix
The vermiform appendix is a blind ended tube connected to the cecum, from which it develops embryologically.
Secretin
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.
Lipase
A lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water-insoluble, lipid substrates.
Chymotrypsin
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.
Hepatic portal vein
The hepatic portal vein is a portal vein in the human body that drains blood from the digestive system and its associated glands.
Carboxypeptidase
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
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
Beriberi is a nervous system ailment caused by thiamine deficiency.
Vitamin B6
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
Scurvy is a deficiency disease that results from insufficient intake of vitamin C, which is required for correct collagen synthesis in humans.
Advanced terms that may appear in context in MCAT passages
Rickets
Rickets is a softening of the bones in children potentially leading to fractures and deformity. The predominant cause is a vitamin D deficiency.
Pellagra
Pellagra is a vitamin deficiency disease caused by dietary lack of niacin and protein.
Foregut
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
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.
Ileocecal valve
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.
Hepatocyte
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
Ghrelin is a hormone produced by cells lining the fundus of the human stomach that stimulate appetite.
Leptin
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.
Flavoprotein
Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin: the flavin adenine dinucleotide or flavin mononucleotide.
Cyanocobalamin
Cyanocobalamin is a compound that is metabolized to a vitamin in the B complex commonly known as vitamin B12.
Choline
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
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 cell
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.
Pylorus
The pylorus is the region of the stomach that connects to the duodenum.
Chyle
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.
Brush border
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
Brunner's glands, or duodenal glands, are compound tubular submucosal glands located throughout the duodenum which produce an alkaline secretion containing bicarbonate.
Trypsinogen
Trypsinogen is the precursor form of the pancreatic enzyme trypsin.
Chymotrypsinogen
Chymotrypsinogen is a precursor of the digestive enzyme chymotrypsin.
Enteropeptidase
Enteropeptidase or enterokinase is an enzyme which transforms trypsinogen into trypsin, indirectly activating a number of pancreatic digestive enzymes.
Cecum
The cecum is a pouch connected to the ascending colon of the large intestine and the ileum.
Ampulla of Vater
The ampulla of Vater is formed by the union of the pancreatic duct and the common bile duct.
Alpha-Amylase
Alpha-amylase is the major form of amylase found in humans and other mammals.
Erepsin
Erepsin is an enzyme that digests peptides which works only on the outside peptide bonds.
Tocopherol
Tocopherol, also known as vitamin E, actually describes a series of organic compounds consisting of a methylated phenols.
Esophageal glands
The esophageal glands are small compound racemose exocrine glands of the mucous type.
Canaliculus
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.
Fundus
The fundus is the rounded part of the upper stomach which allows for an accumulation of gases produced by chemical digestion.
Rugae
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.
Acinus
An acinus refers to the berry-shaped termination where the secretion of an exocrine gland is produced, such with the exocrine pancreas.
Bile canaliculi
Bili canaliculi are thin tubes that collect bile secreted by hepatocytes, which merge and form bile ductules, eventually becoming the common hepatic duct.
Ergocalciferol
Ergocalciferol is a form of Vitamin D. It is created from viosterol, which in turn is created when ultraviolet light activates ergosterol.
Cholecalciferol
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
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.