‘ •Digestion is the mechanical and chemical breakdown of food from mouthfuls to molecules small enough to: (1) Be transportable, and (2) Fit into cells. •Mechanical Digestion: breaks big chunks of food up into little chunks - mouth and stomach. •Chemical Digestion: breaks little chunks of food up into molecules - stomach and small intestine. •Alternaterms for the Digestive System; Alimentary Canal, GI (gastrointestinal) tract, Food Tube •The digestive system includes organs through which food passes (mouth, esophagus, stomach, small intestine, large intestine, anal canal) AND accessory organs – organs that food doesn’t pass through - (salivary glands, liver, gall bladder, and pancreas.) •From beginning to end, the digestive system is between 20 and 30 feet long. •The wall (lining) of the digestive system is continuous and unbroken from beginning to end and contains 4 layers: •These four layers are: (1) The mucosa (mucous membrane). Formed of surface epithelium, goblet cells, connective tissue (lamina propria), and a small amount of smooth muscle. Sometimes folded into villi and microvilli. Might also secrete digestive enzymes. Functions: Absorption, secretion. (2) The submucosa. Areolar (loose) connective tissue, blood vessels, glands lymphatic vessels, and nerves. It's principle role is the delivery of blood to carry away nutrients. (3) Muscularis. Responsible for the movement of food through the tube. Consists of (usually) two layers of smooth muscle. Two layers of muscle fibers through the length of the canal –circular fibers and longitudinal fibers. (4) Serosa. The "outermost" layer. Epithelial tissue on the outside, connective tissue underneath. Secretes serous fluid to reduce friction when the organs of the abdominal cavity "rub" against each other. 2 •These four layers are found along the entire length of the digestive system. •The cavity in the interior of these tissue layers is the lumen. •The alimentary canal wall contains two important intrinsic nerve plexuses – the submucosal nerve plexus and the mycentric nerve plexus. These networks of nerve fibers are part of the autonomic nervous system and help regulate digestive system activity (smooth muscle contraction and glandular secretion) subconsciously. •The micrograph to the left shows a cross section through the esophagus. L – lumen M – mucosa S – submucosa TM – (tunica) muscularis. The serosa isn’t labeled, but it is the thin layer surrounding the muscularis. •The two types of movements of the alimentary canal wall are: (1) mixing movements - mixes food with digestive fluid (ex. stomach) (2) propelling movements - peristalsis (wavelike contraction) to move food through the tube. •The mouth is the organ of mastication (chewing). •Food is mixed with saliva to form a bolus. •The interior of the mouth is called the oral cavity. •The space between the teeth and the cheeks is called the vestibule. •The lining of the mouth is stratified squamous epithelium. •Beneath the lining are muscles (for chewing and facial expression), fat, and the outer layers of skin. •The lingual frenulum secures the tongue to the floor of the mouth. 3 Lips •Thin stratified squamous epithelium, no fat, impressive muscularity, highly-concentrated neurons, highly vascular - blood vessels are very close to the skin's surface - this is why lips bleed so easily and frequently. The lip-skin border is where the mucous membranes of the alimentary canal start! •Lips are necessary to maintain an air-tight seal while suckling during babyhood. •Lips are necessary for making some of the "letter sounds" during speech. •Which letters of the alphabet are difficult for ventriloquists? Write them here: __ __ __ __ __ __ Tongue •Thick, mostly muscular. •The tongue has several bony attachments – two of these are to the hyoid bone and the styloid processes of the skull. •Muscle fibers in the tongue run in a number of directions, resulting in the tongue's flexibility. •The lingual tonsils lie atop the posterior portions of the tongue. •It is urban legend that the tongue is “the strongest muscle in the human body”. The Palate •The palate is the roof of the oral cavity. Hard anterior, soft posterior. Hard palate - palatine processes of the maxillary bone. Soft palate - a muscular arch that ends in the uvula. •In the back of the mouth, on either side of the soft palate are the palatine tonsils. Composed of lymphatic tissue. •A third pair of tonsils, the pharyngeal tonsils (AKA the "adenoids") lie above and beyond the border of the soft palate. The Teeth 4 •Teeth are harder than bone. Teeth are made of enamel, not bone. •Two sets are formed during development, the deciduous (primary) teeth and the permanent teeth. •Deciduous (baby, primary, milk) teeth number 20. •The deciduous teeth erupt through the gingiva (gums) beginning at about 6 months and continuing until 2-4 years old. •The permanent teeth number 32 and have deeper roots. All of the permanent teeth but the third molars (wisdom teeth) have erupted by the end of adolescence. The Deciduous Teeth •The first to erupt is usually a lower front incisor at 6 months. •Number 20 when all have erupted. •The deciduous teeth are shed in the same order that they appear. •The roots are dissolved by odontoblasts, and then the teeth are pushed out of their socket by pressure from the permanent teeth. The Permanent Teeth •Usually begin to appear at about 6 yrs. old. •Last molars (3rd molars, wisdom teeth) appear at 17-25 years old. •3rd molars that do not erupt are called impacted teeth. •Incisors - chisel-shaped, used to bite off pieces of food. •Canines - pointed ("fangs"), used for ripping and tearing. •Premolars - AKA bicuspids and Molars are used for grinding. 5 The Tooth •Each tooth has a crown (above the gum) and a root (below the gum). •The crown and the root meet at the neck (gumline). •The tooth is covered by white, shiny enamel. Enamel is principally calcium. •Unlike bone: enamel, once lost, is not replaced. •Beneath the enamel is the dentin. - Still harder than bone. •Dentin surrounds the pulp cavity which contains blood vessels, nerves, and softer connective tissues. The pulp cavity becomes the root canal in each of the roots. •The roots are anchored to the mandible and maxillary bones by cementum and a tough periodontal ligament. •The periodontal ligament contains bundles of thick collagenous fibers that pass between the cementum and the bone, firmly attaching tooth to jaw. •Producers of the fluid that goes by the name "saliva". •Functions of saliva: •Moistens food, making it easier to swallow. •"Dissolves" food and helps separate "tastants" from the food mass so that they may be detected by the taste buds. •Begins the chemical digestion of carbohydrates by utilizing the enzyme amylase. •Contains bicarbonate ions (HCO3-) that help neutralize bacterial acids (carbonic acid) that cause tooth decay. •Maintains mouth pH between 6.5 and 7.5 (optimum for salivary amylase) •Saliva is produced in the 3 main pairs of salivary glands and in the minute salivary glands that are scattered throughout the walls of the mouth and on the tongue. •Within each salivary glands are two types of fluid-producing cells: (1) Serous cells - produce a watery fluid that contains amylase - an enzyme that splits polysaccharides into disaccharides. (2) Mucous cells - secrete a thick fluid called mucus. •The salivary glands are innervated by nerves that are branches of both the sympathetic and parasympathetic divisions of the autonomic nervous system. (1) Sympathetic impulses stimulate the glands to release small amounts of a very viscous form of mucous. The mouth lining becomes drier and "gooier" or “phlegmier”. (2) Parasympathetic impulses promote the release of a large amount of very watery saliva. Parasympathetic impulses are activated reflexly when a person sees, smells, tastes, or even thinks about favorite foods. 6 Parotid Glands •Largest of the salivary glands. •Lie underneath the skin of the cheek and over the masseter. •Secretes a clear, watery form of saliva which is rich in amylase. •This gland is also lymphoid. If you are suffering an infection, they can swell and make you look like a "chipmunk". Submandibular Glands (AKA Submaxillary Glands) •Located on the floor of the mouth on the inside surface of the jaw. •Most of the cells are serous, few mucosal cells. •The saliva is more viscous than that of the parotid glands. •The ducts open under the tongue and are called Wharton's ducts. It is through these ducts that you are able to "gleek". Sublingual Glands •Smallest of the 3 pairs of salivary glands. •Located under the tongue. •Cells are principally mucosal. Secretions are thick and stringy. 7 •The pharynx (note spelling) connects the mouth to the esophagus. •It has a muscular wall that aids in swallowing. •No digestive action....food is not present long enough for action to occur. •The pharyngeal muscles are skeletal muscles, arranged in two layers: the inner circular muscles and the outer longitudinal muscles. •When swallowing occurs, breathing is interrupted. Swallowing raises the pharynx, pushing the epiglottis up against the ceiling of the trachea, sealing it and so preventing food from "going down the wrong tube". When it does, we cough and use the force of air to remove the food or drink from the trachea and return it to the pharynx for re-swallowing. •Students are taught that the pharynx is divided into three regions: 1. The Nasopharynx – located above the soft palate. It communicates with the nasal cavity and provides a passageway for nose breathing. The eustachian (auditory) tubes open into the nasopharynx. 2. The Oropharynx is behind the mouth. This is where “postnasal drip occurs”. 3. The Laryngopharynx is located below the oropharynx. This portion is for the passage of food only; it is not a respiratory pathway. It connects to the esophagus. •The esophagus is 9 to perhaps 14 inches long. •The walls of the esophagus can and do collapse. If they did not, we would constantly "detect" and "share" the contents of our stomachs with others. •The esophagus descends behind the trachea. •It passes through the mediastinum down to an opening in the diaphragm the esophageal hiatus, below which it joins the stomach. •Mucous glands are found in the mucosa and submucosa of the esophagus. •At the base of the esophagus is the lower esophageal sphincter. (AKA the "cardiac sphincter") This sphincter is usually closed, and only opens to allow food's entry. •The action of contractile smooth muscle waves that pass through the esophagus (and the rest of the alimentary canal) are given the verb "peristalsis”. 8 •The stomach is not shaped like a basketball. It is shaped like the letter "J". •It underhangs the diaphragm on the body's left side. •Capacity for the Average Joe - 1 liter. •Its inner surface is lined with rugae (roo'-jee) that disappear when the stomach holds 4 Whoppers, 2 Fries, and an XL Mountain Dew. •The stomach receives food through the gastroesophageal sphincter, mixes it with gastric juice, kills bacteria in food, achieves a small amount of absorption, mixes all of the components of your meal (making them into a pasty substance called chyme) and passes them on to the duodenum in the small intestine. •When viewed from the exterior, the stomach can be divided into four regions: 1. The cardiac (or cardia) region - at the top of the stomach just past the gastroesophageal sphincter. 2. The fundus - The balloon-like portion that overlies the cardiac region. This is usually filled with air. 3. The body region - The part of the stomach that holds chyme. 4. The pyloric region - tapers down to the pyloric sphincter. •At the end of the stomach, the pyloric sphincter prevents food that passes into the small intestine from backing up into the stomach. This is, truly, the “Point of No Return.” 9 •The stomach has a superthick mucosa. •The inner surface of the stomach is dotted with gastric pits that are openings to the deeper gastric glands. •Gastric glands contain 3 types of secretory cells: (1) Goblet cells - for mucus secretion (2) Chief cells - secrete the protein-digesting enzymes of the stomach. (3) Parietal cells - secrete hydrochloric acid. The Digestive Enzymes of the Stomach •Pepsin is the most important of the stomach's digestive enzymes. Begins protein digestion. Pepsin will not, however, digest mucin. •Pepsin is secreted as the inactive precursor enzyme pepsinogen. When pepsinogen contacts hydrochloric acid, it is denatured into pepsin. •Gastric lipase - found in minute quantities. Acts on fats like butterfat. •Intrinsic factor - not an enzyme, but it is a gastric juice component that enables vitamin B12 absorption by the small intestine. Control Of Gastric Juice Production and Release •The hormone gastrin stimulates the gastric glands to secrete gastric juice. •Gastrin is produced under parasympathetic control when food enters the stomach or when one's thoughts turn to food. •Parasympathetic impulses to the stomach are carried by the Vagus nerve. 10 Absorption By The Stomach •The stomach wall is poorly adapted for food absorption; it has too much mucus. •The materials that WILL pass through the stomach wall include water, glucose, certain salts, alcohol, and lipid-based drugs of several types. Contraction Of The Wall Of The Stomach •Because the stomach has 3 muscle layers, peristalsis is non-directional and results in the mixing of food rather than the forward movement of food. •Chyme (food mixed with gastric juice) enters the small intestine one little squirt at a time so that it may be neutralized by duodenal secretions of bicarbonate. •Solid fat stays in the stomach the longest (3-6 hours), followed by proteins, carbs, and liquids, which remain in the stomach for only a short period of time. Reverse Peristalsis •The stomach may empty a 2nd way - vomiting. •The vomiting center is located in the medulla oblongata. •Imminent vomiting is signaled by taking deep breaths and excessive salivation accompanied by pallor and feelings of nausea. •Both the diaphragm and abdominal muscles contract during the act to increase the force of repulsion. •The vomiting center is stimulated by overstretching of receptors in the stomach wall, drugs which elicit vomiting (emetics), bacterial toxins in contaminate food, and sometimes rapid changes in the change of the body's direction (commonly caused by TheScrambler). 11 •Food next enters: •Chyme is squirted in small quantities into the duodenum (1st foot or so) of the small intestine. Chyme must be liquefied to pass through the pyloric sphincter. •As food enters the duodenum, it is mixed with fluids from the pancreas, liver, and gall bladder. •The pancreatic duct connects with the duodenum at the same place where the common bile duct from the liver and gall bladder enters the duodenum. A ring of smooth muscle - the sphincter of Oddi - surrounds this opening. The Sphincter of Oddi is here! •The small intestine fills most of the abdominal cavity. It is 0-14 feet long in a living person. •It is in the small intestine that chemical digestion is completed, most food materials are absorbed, and indigestible residues are passed on to the large intestine. •The small intestine has three "regions": one you already know about - the duodenum. The other two are the jejunum (2nd part of the S.I.) and the ileum (3rd. part). •The ileum and jejunum are suspended by a double-layered but thin membrane called the mesentary. •The mesentary contains blood vessels, nerves, lymphatic vessels, and lymph nodes. •A membrane called the greater omentum covers the stomach and small intestine like an apron. It is here that fat is deposited and one develops a "pot belly". •The inner wall of the small intestine is covered with uncountable tiny projections called (intestinal) villi (vee'-lee). They project inward toward the intestinal lumen. 12 Simple •Each villus has a lining of simple columnar Columnar Epithelium epithelium interspersed with goblet cells (for mucus production). Within the center of Goblet each villus are blood capillaries, a single lymph Cell capillary (called a lacteal), and nerve fibers. •In addition to goblet cells, the small intestine contains mucus-secreting glands called Brunner's glands that are buried in the submucosa. •Intestinal glands at the base of each villus secrete large amounts of a watery fluid. This fluid has a neutral pH and lacks enzymes. •Intestinal enzyme secretion occurs from epithelial cells on the surfaces of the microvilli. These enzymes include: Peptidases - split polypeptides into the 20 different amino acids. Sucrase, maltase, and lactase - split disaccharides into monosaccharides. Intestinal lipase - splits fats into fatty acids and glycerol. Nuclease - splits DNA and RNA into nucleotides. •Many adults secrete insufficient lactase, which is necessary to digest milk sugar. •If lactose remains undigested, it creates a hypertonic internal environment and draws water into the small intestine lumen. Concurrently, intestinal bacteria break the lactose down and produce organic acids and gases. The result is bloating, intestinal cramps, and diarrhea. •To avoid the symptoms of lactose intolerance, the victim can avoid dairy products or take lactase in pill form before eating or drinking dairy. 13 •The end products of organic molecule digestion are small enough to fit through the mucosa of the small intestine and the walls of the blood capillaries and lacteals. These end-products include monosaccharides, amino acids, fatty acids, and nucleotides – all major monomers of complex life polymers. •The small intestine has an internal absorptive surface area the size of a tennis court. •Absorption occurs by either active or passive mechanisms. Absorption involves not only nutrient monomers (listed above), but also water and electrolytes. •Water is absorbed passively, by osmosis. More water is absorbed in the small intestine than in the large intestine (2 liters per day for the S.I., 1 liter per day for the L.I.) •Electrolyte absorption is active (ie. it utilizes ACTIVE TRANSPORT). •Monosaccharide transport occurs by either facilitated diffusion or active transport into the epithelial cells lining the intestine. From there, the monosaccharides move passively into the blood capillaries by simple diffusion. •Amino acids are absorbed by active transport through the intestinal lining. Once across the lining, the monomers move passively into the bloodstream. •The end products of fat digestion are typically fatty acids, glycerol, phospholipids, and cholesterol molecules. These molecules readily diffuse into the epithelial walls of the small intestine BECAUSE THEY ARE FAT SOLUBLE. Here, they are resynthesized into fat droplets (called chlyomicrons) that diffuse into the lacteals. Lymph in the lacteals carries these droplets to the bloodstream. •The major mixing movement in the small intestine is termed segmentation. The chyme is cut into segments by sphincter-like contractions in the walls, and the food in each segment is "swished" back and forth so that digestion and absorption may occur. •Peristalsis in the small intestine is weaker and slower Where the small intestine and than in the esophagus or stomach. large intestine •A sphincter muscle called the ileocecal valve separates unite. chyme in the small intestine from the large intestine. 14 The appearance of the large intestine to the colonoscopist. •The large intestine as a diameter (not a length) greater than the small intestine. And thus, its name. •Its length can reach 1 1/2 meters (5 feet). •It begins on the lower right side of the abdominal cavity - here, the ileum and the cecum unite. Then, the L.I. rises, transverses the abdominal cavity over the small intestine, and plunges rapidly on the Ileocecal body's left side. Junction Sigmoid Colon •The cecum is a dilated, pouch-like structure that Cecum hangs beneath the ileocecal junction. Hanging underneath it is the appendix. •The appendix contains lymphatic tissue. If it becomes inflamed or infected, it might require removal. If it enlarges and breaks open, the peritoneum becomes infected (peritonitis), a potentially fatal condition. •The four sections of the L.I. are the ascending colon, the transverse colon, the descending colon, and the S- shaped sigmoid colon. •At the end of the sigmoid colon is the rectum, which lies against the sacrum, to which it is attached. •The last 1 1/2-2 inches of the L.I. is the anal canal. Two sphincter muscles, the internal and external anal sphincters, regulate the canal. •The wall of the large intestine includes the 4 tissue layers that typify the GI tract. •There are no villi in the large intestine. •The wall is arranged in a series of pouches called haustra. Here, fat is deposited in the serosa of the wall (this fat is not present in the small intestine serosa). •Hemmorrhoids - enlarged branches of the rectal vein. 15 Functions of the Large Intestine •Very limited or no chemical digestive function. •There is an overabundance of mucous-producing goblet cells line the mucosa. Mucus helps hold the fecal mass together and helps maintain a neutral pH (to combat bacterial acids). •Water and electrolytes are reabsorbed in the first half of the L.I. 90% of the water that enters the L.I. is reabsorbed. Intestinal flora - the bacteria that occupy the L.I. - chiefly E. coli. •These bacteria synthesize vitamin K, B12, thiamine, and riboflavin. These vitamins are absorbed by the intestinal mucosa. Vitamin K – helps modify proteins after they are synthesized on ribosomes. Vitamin B12 – aids the nervous system and helps in blood formation. Thiamine – necessary for neural function and carbohydrate metabolism. Riboflavin – plays a key role in energy metabolism. •Bacterial actions in the large intestine may give rise to flammable (methane) and odious (phenol, hydrogen sulfide, indole, skatole, and ammonia) intestinal gases (flatus). •Food materials that humans are incapable of digesting end up in the fecal mass: •Cellulose - because we lack the enzyme necessary to digest it! •Seed coats and covers •Bone, cartilage, and tendon •Certain lipids •Mucin •Capsaisins •The color of the fecal mass relates to the bile pigments from dead red blood cells. The bile pigments (shades of red, brown, and green) enter the food tube in the duodenum and are altered by intestinal bacteria. The color of the fecal mass does NOT relate to the items upon the dinner plate. •The fecal mass is about 75% water. •The defecation reflex occurs when a person holds and deep breath and forcefully contracts the abdominal wall muscles. Intestinal contraction ensues, followed by the relaxation of the external anal sphincter. 16 •Synthesizing digestive enzymes is the digestive system function of the pancreas. •Enzyme synthesis is an exocrine function (to contrast it with the endocrine function of the pancreas). The Structure of the Pancreas •The "head" of the pancreas is tucked in the duodenal loop and the tail bumps up against the This is the spleen. Pancreas! •The cells that synthesize the digestive pancreatic fluids are called acinar cells. •Acinar cells secrete their enzymes into small tubes, which unite to form larger tubes and , ultimately, form the pancreatic duct. •The pancreatic duct unites with the common bile duct to form a short tube called the hepatopancreatic ampulla. •It is here that digestive enzymes from the pancreas, mixed with bile from the liver, enters the small intestine to aid in food digestion. Common Bile Duct Pancreatic duct Hepatopancreatic Ampulla 17 Pancreatic Juice •Pancreatic juice contains several digestive enzymes that digest all 4 organic molecule groups (carbohydrates, lipids, proteins, & nucleic acids.) •Here are the most important Pancreatic Enzymes: Pancreatic amylase Splits starch or glycogen into disaccharides. Pancreatic lipase Splits triglycerides into fatty acids and glycerol. Trypsin, Chymotrypsin, and Carboxypeptidase Reduce proteins to amino acids. Pancreatic nucleases Split nucleic acids (DNA, RNA, ATP) into nucleotides. •Pancreatic juice also contains bicarbonate to neutralize the harsh acids arriving in the duodenum from the stomach. •The hormone secretin is released into the bloodstream from the intestinal mucosa upon the arrival of chyme in the duodenum. Secretin stimulates the pancreas, which secretes pancreatic juice. •The liver is sometimes called "The Elvis of Organs" •The liver is on the body's right side, underneath the diaphragm, protected by the lower ribs. It is reddish brown in color, highly vascular. Liver Functions •The liver has more functions than any other organ in the human body! •The liver is the chief chemical converter in the human body. •It also serves as a site of destruction, a storage facility, and a protein metabolizer. •It is a good organ to eat because it is where iron is recycled. 18 Liver Menu Items Matching – Match With Arrows Liver 'n Onions Liver Loaf Liver Pate' Braunshweiger Raw Liver Functions of the Liver •It helps maintain levels of blood sugar by storing excess carbohydrates as glycogen. •Lipids are metabolized in the liver and lipids are converted to phospholipids, lipoproteins, and cholesterol. •Carbohydrates and proteins are converted to fat in the liver. •Amino acid deamination occurs in the liver. This means that amino acids are stripped of their NH3 group so that they are structurally similar to carbohydrates. In this form, they may be used for energy. The leftover NH3 molecule is converted to urea and becomes a component of urine. •Blood proteins (clotting factors) are produced in the liver •The liver stores glycogen, iron, vitamins A, D, and B12. •Liver cells help destroy damaged red blood cells. •Liver cells phagocytize foreign antigens. •The liver removes toxic substances (such as alcohol) from the blood. •The liver stores 200-400 mL of blood. •The liver secretes bile for fat emulsification during digestion. •The liver is surrounded by a fibrous capsule. •The human liver has 2 major lobes and two minor lobes (your cat will have 5!) •Major lobes: Left lobe and Right lobe •Minor lobes: Quadrate lobe (near the gall bladder) and Caudate lobe (near the vena cava) •The falciform ligament separates the two lobes. 19 •Each lobe is divided into many hepatic lobules. •Within the lobule there are many hepatic cells that radiate outward from a central hepatic vein. Cells are separated by hepatic sinuses. •Also within the lobules are bile canals, which receive secretions from the liver cells. The bile canals unite to form bile ducts. •Blood is carried to the liver through the hepatic portal vein (from the stomach and small intestine) and the hepatic artery (which carries oxygenated blood from the aorta). The Composition of Bile •Bile is the yellowish, green fluid produced by hepatic (liver) cells. •Bile is the only secretion of the liver. It is a greenish-yellow fluid that exits the liver through the hepatic duct and goes to either the small intestine (for use) or to the gall bladder (for storage). In either instance, its fate is to end up in the small intestine. •The Composition of Bile: water, bile salts (most common bile solid), bile pigments, cholesterol, electrolytes. •The bile salts perform the digestive function of emulsification - reducing larger droplets of fat into tiny droplets that digestive enzymes (lipases) can act upon. •The bile pigments (bilirubin and biliverdin) are the breakdown products of hemoglobin. Bilirubin is reddish, biliverdin is green. You see traces of these colors in a bruise, as RBCs are broken down by phagocytes in the same way as they are in the spleen and liver. •The yellowish skin of jaundice results from the deposition of bile pigments. I’m a baby with jaundice! I’m •The liver secretes NO DIGESTIVE ENZYMES. in an incubator under a UV light. 20 •The gall bladder is a pear-shaped sac located in a depression on the inferior surface of the liver. •The liver sends bile to the gall bladder through the cystic duct, which unites with the hepatic duct to send bile to the duodenum through the common bile duct. •It is lined with columnar epithelial cells. •Its wall is lined with smooth muscle. •The gall bladder stores and concentrates bile between meals. When a meal arrives at the small intestine from the stomach, the gall bladder is filled with bile! •The gall bladder releases bile when stimulated by cholecystokinin from the small intestine. •Gallstones may form in the duct system or within the gall bladder if bile is too concentrated! The gall bladder and liver of a cat.
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