DIGESTIVE SYSTEM DIGESTIVE SYSTEM COMPONENTS OF THE GI TRACT The digestive tract consist of: •Oral cavity •Esophagus •Stomach •Small and large intestines • Organs associated with the digestive tract: •Salivary glands •Pancreas •Liver •Gallbladder • •FUNCTION of the GI tract: •To obtain from ingested food nutrients and energy •Ingestion, fragmentation, digestion, absorption, elimination fo waste products •Protective barrier DIGESTIVE SYSTEM BASIC HISTOLOGICAL ORGANIZATION Glands •Exocrine glands, aiding in digestion and/or lubrication, are located in: •Epithelium (e.g., goblet cells throughout the intestines) •Lamina propria (e.g., gastric glands) •Submucosa (e.g., Brunner's glands in the duodenum) •Glands located external to the digestive tract that open into the system (e.g., liver and pancreas) • •Endocrine and paracrine cells, belonging to the diffuse neuroendocrine system (DNES), are located throughout the mucosa of the gastrointestinal tract, influencing the secretion of glands and the motility of the gut DIGESTIVE SYSTEM ORAL CAVITY •In the oral cavity starts the digestive process with ingestion, fragmentation and moistening of food. •Oral cavity is involved in speech, facial expression, sensory reception and breathing. • •Major structures: •lips •teeth •tongue •oral mucosa •hard and soft palate •associated salivary glands Oral mucosa •Oral mucosa, the protective mucous membrane (mucosa) lining the oral cavity, is continuous with external skin and with the mucous membrane of the pharynx. • •Composition: •Epithelium. Stratified squamous keratinized or nonkeratinized depending on location •Lamina propria. Collagenous tissue •Muscularis mucosae is not present. •Although not part of the oral mucosa, a submucosa of dense connective tissue, containing the minor salivary glands, underlies much of the oral mucosa. 5 DIGESTIVE SYSTEM LIPS •Forms the anterior boundary of the oral cavity, the space between the inner surfaces of the lips and cheeks and the outer surface of the teeth and gingiva •Regions: •Exterior surface •Covered by thin skin •Hair follicles and sebaceous glands are present • •Vermilion zone •Forms the red-colored portion of the lip •Covered by a thin, stratified squamous keratinized epithelium •Mucosa contains numerous, densely packed dermal papillae •Papillae allow blood vessels close access to the surface •Lacks hair follicles • •Inner surface •Lined by oral mucosa, stratified squamous moist epithelium •Minor salivary glands (labial glands) in the submucosa secrete both mucous and serous products. 7 F015_003.jpg OM – oral mucosa S – skin F – hair follicles a přídatné žlázy V – vermilion zone – rumělka M – žíhaná svalovina G- malé slinné žlázy DIGESTIVE SYSTEM TONGUE Composition: •Mucosa: •Dorsum of the tongue is covered by a specialized oral mucosa, modified to form papillae. •The ventral surface of the tongue is covered by a lining mucosa. • •The submucosa possesses minor salivary glands that are mucus-secreting except for those associated with the circumvallate papillae, which are serous-secreting. • •Intrinsic tongue muscles. Skeletal muscle bundles are arranged in three separate planes, with connective tissue bands from the lamina propria separating the bundles and firmly anchoring the muscle to the mucous membrane. DIGESTIVE SYSTEM TONGUE •Papillae Each consists of a connective tissue core covered by a stratified squamous epithelium. •Filiform •Most numerous; cover body of tongue •Cone-shaped protrusions angled so that they aid in movement of food toward the pharynx •Fungiform •Less numerous than filiform but also located on anterior two-thirds of tongue •Mushroom shaped, possess taste buds on superior surface •Circumvallate •Eight to twelve papillae located just anterior to the sulcus terminalis •Mushroom shaped and surrounded by a narrow moat; lateral wall of each papilla possesses taste buds •Serous glands of von Ebner open into the base of the moat and flush the moat for reception of new tastes. •Foliate •Parallel folds on the posterolateral surface of the tongue; not well developed in humans 11 F015_004.jpg DIGESTIVE SYSTEM TONGUE •Taste buds are onion-shaped structures embedded in the surface of the fungiform and circumvallate papillae. Taste buds contain taste-receptor cells (gustatory) that communicate with the surface of the papilla through a taste pore. Other cells are supportive cells and basal stem cells. Depolarization of the taste cells leads to the stimulation of gustatory nerve fibers and the discrimination of sweet, salty, bitter, and sour sensations. DIGESTIVE SYSTEM BASIC HISTOLOGICAL ORGANIZATION Muscular tube with a lumen of variable diameter and wall made up of four main layers: •Mucosa (mucous membrane). Innermost layer facing the lumen •Epithelium. Either a stratified squamous moist or a simple columnar epithelium •Lamina propria. Loose connective tissue; usually possesses digestive glands •Muscularis mucosae of smooth muscle is usually present. •Submucosa. Denser connective tissue than the lamina propria. The submucosa possesses Meissner's nerve plexus that supplies innervation to the muscularis mucosae and to digestive glands in the mucosa and submucosa. The submucosa possesses glands in the esophagus and duodenum. •Muscularis externa of smooth muscle is usually arranged into inner circular and outer longitudinal layers. Auerbach's nerve plexus is located between the two muscle layers and provides innervation to this smooth muscle. •Serosa (serous membrane) is present if the organ protrudes into the peritoneal cavity, or an adventitia (only the connective tissue portion of the serosa) is present if the organ is retroperitoneal. DIGESTIVE SYSTEM ESOPHAGUS •Mucosa: •Epithelium. Stratified squamous nonkeratinized epithelium •Lamina propria possesses esophageal cardiac glands that resemble the mucus-secreting glands of the cardiac portion of the stomach. These glands are particularly prominent near the junction of the esophagus with the stomach and are sometimes located in the beginning of the esophagus. •Lamina muscularis mucosae. •Submucosa has mucus-secreting, esophageal glands proper. •Muscularis externa is composed of striated muscle in the upper portion of the esophagus, skeletal, and smooth muscle in the middle portion, and smooth muscle in the lower portion. •Adventitia. Composed of loose connective tissue. DIGESTIVE SYSTEM STOMACH •Function of the stomach •Mixed exocrine (digestion) and endocrine organ (hormones secretion) •To continue the digestion of carbohydrates initiated in the mouth, add an acidic fluid to the ingested food, mixes food to produce chyme •Initial digestion of proteins with enzyme pepsin •Gastric lipase – digestion of triglycerides •Produces intrinsic factor for absorption of vitamin B12 •Absorbs a few nutrients •Four regions: •Cardia •Fundus •Body •Pylorus •Wall of the stomach: •Tunica mucosa (epithelium, lamina propria, lamina muscularis mucosae) •Tunica submucosa •Tunica muscularis •Tunica serosa •Rugae. Longitudinal folds of the mucosa and submucosa in the undistended stomach allow for expansion. body fundus DIGESTIVE SYSTEM STOMACH •Structures present throughout the stomach •Surface epithelium •Simple columnar epithelium facing the lumen is modified so that all cells secrete mucus, forming a sheet gland that protects the stomach from its acidic environment. •Gastric pit. A channel formed by the invagination of the surface epithelium into the underlying lamina propria; connects the sheet gland with the gastric glands. The length of the gastric pit varies with each stomach region. •Gastric glands •Simple, branched tubular glands begin at a gastric pit and extend through the lamina propria to the muscularis mucosae. •The region of the gland that attaches to the gastric pit is called the neck region; the base region of the gland is located adjacent to the muscularis mucosae. •Secretory cells in these glands vary in each region of the stomach. •Muscularis externa. Subdivisions of this smooth muscle layer frequently interdigitate, making it difficult to distinguish one layer from another. •Internal oblique layer •Middle circular layer that is modified in the pyloric region to form the pyloric sphincter •Outer longitudinal layer is separated from the inner circular layer by Auerbach's plexus, nerve fibers from the autonomic nervous system that supply •Serosa F015_018.jpg F015_015.jpg DIGESTIVE SYSTEM STOMACH •Variations specific to the cardiac region (narrow region adjacent to the esophagus) •Abrupt transition of epithelium from stratified squamous moist of the esophagus to a sheet gland lining the cardiac stomach •Length of gastric pits is about equal to the length of cardiac glands •Cardiac glands primarily secrete mucus, although other products are also produced. Glands are frequently coiled. •Cardiac glands of the stomach extend into the lower esophagus, forming the esophageal cardiac glands. Esophagogastric junction DIGESTIVE SYSTEM STOMACH •Variations specific to the pyloric region • •Pits are longer in pylorus than in the cardiac region. •Pyloric glands, not as coiled as in the cardiac region; primarily secrete mucus. •Enteroendocrine cells are also present here. •Circular layer of muscularis externa is greatly thickened to form the pyloric sphincter. DIGESTIVE SYSTEM STOMACH •Variations specific to the fundic and body regions (Glands in both regions are called fundic glands.) •Fundic glands are about twice as long as their gastric pits. •Cell types present in fundic glands: •Stem cells replenish both the surface epithelial cells and cells of the glands. Stem cells are located in the neck region. •Mucous neck cells are irregular in shape and stain basophilically. They secrete protective mucus and are located in the neck region. •Parietal cells are large, spherical, eosinophilic cells that secrete hydrogen and chloride ions and gastric intrinsic factor. They possess numerous mitochondria. An umbrella-shaped canaliculus indents the luminal surface, increasing surface area. Although present throughout the gland, parietal cells are more numerous in the upper regions. •Chief or zymogen cells, typical protein-producing cells, predominate in the bases; stain blue with hematoxylin(due to rough ER) and secrete pepsinogen (which is converted into pepsin by HCl). •Enteroendocrine cells (part of the diffuse neuroendocrine system, DNES) are located on the basement membrane and do not usually reach the lumen of the gland. This population of cells secretes a variety of hormones (e.g., gastrin) with endocrine and paracrine influences on digestive activity. Secretory granules cluster toward the basement membrane for their subsequent release into the lamina propria. Most common at the bases of the glands. F015_020.jpg Gastric glands Neck Basal part of glands Popis!!!!! DIGESTIVE SYSTEM SMALL INTESTINE •Complete digestion of food •Absorb final products of digestion (amino acids, monosaccharides, fatty acids, etc.) •Secrete protective mucus •Secrete hormones • •Subdivided into duodenum (immediately distal to pylorus of stomach), jejunum (distal to duodenum), and ileum (most distal region) • •Common features of the small intestine Structures that increase the surface area of the small intestine: •Plicae circulares. Permanent circular folds formed by an up-welling of the submucosa and its overlying mucosa into the lumen. Villi protrude from the plicae. •Villi. Finger-like protrusions of the lamina propria and overlying epithelium into the lumen •Villi assume different shapes in each of the three intestinal subdivisions. •A lacteal (blind-ending lymphatic capillary) is located in the center of each villus to absorb digested fat. •Individual smooth muscle cells lie parallel to the long axis of each villus, "milking" the lacteal contents to the periphery. •Microvilli. Increase surface area of absorptive cells and, collectively, form a brush or striated border • DIGESTIVE SYSTEM SMALL INTESTINE •Common features of the small intestine • •Intestinal glands (Crypts of Lieberkühn) are invaginations of epithelium into the lamina propria •Epithelium covering the villi and lining the crypts is continuous (with different cell types in different part) • •Small intestine: layers • •Mucosa •Epithelium •Lamina propria •Lamina muscularis mucosae •Submucosa •Muscularis externa •Inner circular layer •Outer longitudinal layer •Serosa • DIGESTIVE SYSTEM SMALL INTESTINE •Mucosal epithelium is composed of: •Absorptive cells (enterocytes), forming a simple columnar epithelium with microvilli – „brush border“, absorb digested food •Goblet cells (unicellular glands) are interspersed among absorptive cells and secrete mucus for protection. These cells increase in number from duodenum to rectum. • •Intestinal glands (crypts of Lieberkühn) are simple tubular glands that begin at the bases of the villi in the mucosa and extend through the lamina propria to the muscularis mucosae. Possess: •Absorptive cells •Goblet cells •Paneth cells possess large, eosinophilic granules whose contents, e.g, lysozyme, digest bacterial cell walls. Deep in crypts. •Enteroendocrine cells – secrete hormones (e.g., cholecystokinin) related to digestion • •Muscularis externa of inner circular and outer longitudinal layers with an intervening Auerbach's nerve plexus. • •Serosa covers small intestine. F015_025.jpg DIGESTIVE SYSTEM SMALL INTESTINE •Variations specific to the intestinal subdivisions • •Brunner's glands in the submucosa are present only in the duodenum. These compound tubular glands open into the bases of the intestinal glands and secrete an alkaline mucus to neutralize the acidity of the stomach contents. • •Peyer's patches are clusters of 10-200 lymphoid nodules located primarily in the lamina propria of the ileum. Each cluster is positioned on the side of the intestine away from the mesentery and forms a bulge that may protrude into the lumen as well as into the submucosa. Absorpční buňka v různých stádiích, absorpce tuků Lymfatická céva - chylová Duodenum Jejunum Ileum Villi yes yes yes Microvilli on absorptive cells yes yes yes Goblet cells some more most Paneth cells yes yes yes Brunner’s glands yes no no Peyer’s patches no no yes DIGESTIVE SYSTEM LARGE INTESTINE (COLON) IV. •Function: •Absorption of water •Secretion of mucus to lubricate dehydrated feces • •Regions: •Ascending colon. Rises on the right side of the abdominal cavity. •Transverse colon. Horizontal region that passes across the abdomen from right to left below the stomach. •Descending colon. Descends on the left side of the abdominal cavity. •Sigmoid colon. “S”-shaped •Rectum is a 12-cm-long tube continuing from the sigmoid colon. The mucosa of the rectum is similar to that of the majority of the large intestine. The rectum narrows abruptly to become the anal canal. • DIGESTIVE SYSTEM LARGE INTESTINE (COLON) IV. •Layers and structures forming the wall of the large intestine: •Mucosal epithelium: •Absorptive cells form a simple columnar epithelium with microvilli. •Goblet cells increase in number toward the rectum and provide lubrication. •A reduced number of enteroendocrine cells is present. •Intestinal glands (crypts of Lieberkühn) are very straight in the large intestine. •No villi or plicae circulares are present in the large intestine. •Muscularis externa •Inner circular layer is complete around the circumference of the tube •Outer longitudinal layer is segregated into three longitudinal bands, the taeniae coli, that are placed equidistantly around the tube. The contraction of the taenia produces permanent sacculations in the large intestine, termed haustrae. •Either an adventitia or a serosa is present, depending on the particular portion of the large intestine. DIGESTIVE SYSTEM LARGE INTESTINE (COLON) • •Anal canal. The terminal portion of the intestinal tract is about 4 cm long. •The intestinal glands disappear and the epithelium undergoes an abrupt transition from simple columnar to stratified squamous with sebaceous and apocrine sweat glands. •The inner circular portion of the muscularis externa expands to form the internal anal sphincter. The external anal sphincter is composed of skeletal muscle. • •The anus is located at the level of the external anal sphincter and is covered by stratified squamous keratinized epithelium (skin). • • DIGESTIVE SYSTEM • APPENDIX • •Attached to cecum •No taenia coli •Lots of lymphatic tissue (diffuse and in nodules) present in lamina propria and submucosa • DIGESTIVE SYSTEM MAJOR SALIVARY GLANDS •All major salivary glands are compound, exocrine glands, and all open into the oral cavity. •Glandula parotis, glandula submandibularis, glandula sublingualis •Functions: •Produce saliva to wet, lubricate, and buffer the oral cavity and its contents •Produce amylase for the initial digestion of carbohydrates •Produce lysozyme to control bacteria in the oral cavity DIGESTIVE SYSTEM MAJOR SALIVARY GLANDS Major cell types •Serous cells •Synthesize, store, and release a thin, protein-rich secretion containing digestive enzymes, primarily amylase •Are pyramidal in shape and possess all organelles necessary for protein production and secretion (e.g., basal rough endoplasmic reticulum, Golgi, and apical secretory granules) •Are arranged into either: •Acini (singular, acinus) or alveoli (singular, alveolus). Flask-shaped sacs with tiny lumens •Serous demilunes. Half moon–shaped caps positioned over the ends of mucous tubules b. •Mucous cells •Synthesize, store, and release mucus, a viscous, thick, glycoprotein secretion that protects and lubricates epithelia •Have flattened nuclei that are located at the bases of the cells along with the rough endoplasmic reticulum. Abundant mucigen droplets are located in the apex of each cell, giving it a frothy, vacuolated appearance. •Are organized in test tube–shaped tubules with relatively wide lumens 3. •Myoepithelial cells are stellate-shaped epithelial cells with contractile functions that lie between the secretory or duct cells and the basement membrane. These cells contract to aid in movement of the secretory product. DIGESTIVE SYSTEM MAJOR SALIVARY GLANDS Duct system conducts secretions to oral cavity. Ducts are more numerous with serous acini than with mucous tubules because the tubules can act as their own ducts. •Intralobular ducts •Intercalated ducts exit from secretory acini and are smaller in diameter than the acini they drain. These ducts are lined by simple cuboidal epithelia. •Striated ducts continue from intercalated ducts and are larger in diameter than the secretory units they drain. They are lined by simple columnar epithelia. Numerous mitochondria and infoldings of the plasma membrane in the basal region of the cells give the duct a striated periphery. Striated ducts alter the content and concentration of the saliva. •Interlobular ducts form by the anastomosis of striated ducts and are located in the connective septa between lobules. Interlobular ducts are lined with simple columnar to stratified columnar epithelia. •The main excretory duct(s) is formed by the union of interlobular ducts. An excretory duct (s) is lined by a stratified epithelium that becomes stratified squamous moist just prior to its junction with the epithelium of the oral cavity. DIGESTIVE SYSTEM MAJOR SALIVARY GLANDS Major salivary glands Parotid glands •Compound acinar glands producing only serous products; their secretions account for 25% of the saliva •Possess the most highly developed duct system of the major salivary glands Submandibular glands •Compound tubulo-acinar glands producing both serous and mucous products, although serous acini predominate. Their secretions account for 70% of the saliva. •Serous cells are present as both acini and serous demilunes. • Sublingual glands •Secrete approximately 5% of the saliva. •These are compound tubulo-acinar glands, producing both mucous and serous products, although mucous tubules predominate. F16_04 F016_006.jpg Glandula submandibularis F16_05 Glandula sublingualis F016_006.jpg DIGESTIVE SYSTEM PANCREAS •Located in the abdomen in the curve of the duodenum and divided into a head, body, and tail • •Is both an exocrine and an endocrine gland •The exocrine portion produces an alkaline secretion containing digestive enzymes that empties into the duodenum. • •The endocrine portion secretes insulin, glucagon, and somatostatin that regulate blood glucose levels. DIGESTIVE SYSTEM PANCREAS Exocrine pancreas •Compound acinar gland; the acinar cells secrete numerous digestive enzymes that break down proteins (trypsin), carbohydrates (carbohydrates), lipids (lipase), and nucleoproteins (nucleases). •Cells show polarity with basal rough endoplasmic reticulum and apical secretory granules. •Duct system •Ducts begin as centroacinar cells located within the acini. •Intercalated ducts are lined with simple cuboidal epithelium. Centroacinar cells and cells of the intercalated ducts secrete bicarbonates to neutralize the acidity of the stomach contents (chyme) entering the duodenum. •Striated ducts are not present. •Interlobular ducts lead into one or more excretory ducts that empty into the duodenum. •Resembles the parotid gland except the pancreas has centroacinar cells and fewer ducts. •Secretion is regulated by cholecystokinin and secretin from enteroendocrine cells in the small intestine DIGESTIVE SYSTEM PANCREAS Endocrine pancreas (islets of Langerhans) •Small clusters of cells, richly supplied by fenestrated capillaries, are scattered throughout the exocrine pancreas; these clusters show no orderly arrangement of secretory cells within the cluster. •Predominate cell types and secretions •A cell (alpha cell). Secretes glucagon, which elevates glucose levels in the blood •B cell (beta cell). Secretes insulin, which lowers blood glucose levels; predominant cell type •D cell (delta cell). Secretes somatostatin, which modulates release of the other two major hormones •Individual cell types cannot be distinguished with routine hematoxylin and eosin staining. DIGESTIVE SYSTEM LIVER •Located in right, upper quadrant of abdominal cavity under the diaphragm; the biggest organ, weight about 1,5 kg; large right (lobus dexter) and smaller left (lobus sinister) lobe, lobus quadratus, lobus caudatus • •Both an exocrine and an endocrine gland •Exocrine secretion (bile) is stored in the gall bladder and released into the duodenum. This secretory product contains bile acids that aid in the emulsification of lipids, bilirubin (the breakdown product of hemoglobin), phospholipids, and cholesterol. • •Endocrine function is the synthesis of plasma proteins, including albumin, clotting factors, and lipoproteins that are released into the liver sinusoids. • •Additional functions include the metabolization of digested food, storage of glucose as glycogen, and detoxification of hormones and drugs. • DIGESTIVE SYSTEM LIVER ARCHITECTURE OF THE CLASSIC LIVER LOBULE •The classic liver lobule resembles a column of wheels. Polyhedral shape. Structural and functional unit of the liver. •Spokes of the wheels are cords or plates of hepatocytes radiating out from a central axis. •Spaces between the spokes are occupied by liver sinusoids (discontinuous sinusoidal capillaries). •Central axis of the lobule is a central vein into which sinusoids drain (i.e., blood is flowing from the periphery of the lobule to the center). The central vein runs parallel to the long axis of the lobule. •The perimeter of the lobule is denoted by the position of three to six hepatic portal triads situated at intervals around the lobule. •Portal triad run parallel to the long axis of the lobule. •Portal triad contain branches of the •Hepatic portal vein. Lined with simple squamous epithelium; has the largest diameter of the three structures •Hepatic artery. Lined with simple squamous epithelium and two-three layers of smooth muscle •Bile duct. Lined with simple cuboidal epithelium; multiple branches may be present F16_10 F16_11 F16_12 DIGESTIVE SYSTEM LIVER FUNCTIONAL MICROANATOMY •Hepatocytes (liver cells) •Arranged as walls one to two cells thick that radiate out from the central vein like the spokes of a wheel •Histology •Cells are polyhedral in shape. •Cells possess one or two nuclei. •Cells contain abundant smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes. They also contain large accumulations of electron-dense glycogen granules that stain strongly with PAS. Numerous peroxisomes, along with smooth endoplasmic reticulum, carry out detoxification. •At intervals between adjacent cells, the plasma membranes bulge inward to form a bile canaliculus, the beginning of the bile transport system. •Microvilli project into the space of Disse, increasing surface area of the cells. DIGESTIVE SYSTEM LIVER FUNCTIONAL MICROANATOMY •Sinusoids •A variation of discontinuous capillaries, in that gaps exist between endothelial cells and the fenestrations lack diaphragms •The basal lamina is lacking beneath the fenestrations. •Fenestrations open into a subsinusoidal space, the space of Disse, separating the sinusoids from the hepatocytes beneath the space. •Kupffer cells, liver macrophages, span the sinusoids, filtering debris from the blood. D. DIGESTIVE SYSTEM LIVER BLOOD SUPPLY AND DRAINAGE OF THE LIVER •Blood supply is from two sources: •Hepatic portal vein •Supplies about 75 % of the blood •Carries blood drained directly from the gastrointestinal tract, which, therefore, is deoxygenated and high in absorbed nutrients. •Hepatic artery. 35 % of the blood. Supplies oxygenated blood • •Branches from both vascular sources continue into smaller branches located in the portal triad. Portal triad branches supply the hepatic sinusoids that drain into a central vein. Multiple central veins anastomose to eventually form the three hepatic veins that empty into the inferior vena cava. IN hepatic artery, portal vein OUT hepatic vein, bile ducts DIGESTIVE SYSTEM LIVER FLOW OF BILE FROM LIVER •Bile is produced by hepatocytes in the liver and released into bile canaliculi located between two adjacent hepatocytes. • •Bile canaliculi form a meshwork configuration that continues into bile ducts lying in portal canals. These bile ducts anastomose to form the left and right hepatic duct. • •The hepatic ducts exit from the liver and fuse to form the common bile duct. • The bile it contains can either: •Travel directly to the duodenum •Be transported via the cystic duct to the gall bladder where it is stored until needed DIGESTIVE SYSTEM GALL BLADDER •Stores and concentrates bile produced in the liver by reabsorbing water •Connects, via the cystic duct, with the hepatic duct from the liver to form the common bile duct that empties into the duodenum •Mucosa Composed of: •Simple columnar epithelium with short microvilli. Accumulations of mitochondria and glycoprotein-filled secretory vesicles, particularly in the apices of the cells, are prominent. •Lamina propria •Muscularis mucosae is not present. Is thrown into complex, irregular folds that are particularly evident when the gall bladder is empty. •Submucosa •Smooth muscle is arranged in an irregular network surrounding the gall bladder. •A serosa covers most of the gall bladder; an adventitia surrounds the portion that is attached to the liver.