Accessory Organs of the Gastrointestinal Tract PDF

Accessory organs of the Gastrointestinal Tract Joyce El-Haddad [email protected] @orientatewithjoyce Lecture Outline • Exocrine Glands • Saliva • Salivary glands gross anatomy • Salivary glands histology • Pancreas gross anatomy • Pancreas histology Textbook references used: Ovalle, W.K. a...

Accessory organs of the Gastrointestinal Tract Joyce El-Haddad [email protected] @orientatewithjoyce Lecture Outline • Exocrine Glands • Saliva • Salivary glands gross anatomy • Salivary glands histology • Pancreas gross anatomy • Pancreas histology Textbook references used: Ovalle, W.K. and Nahirney, P.C., 2020. Netter's Essential Histology E-Book: With Correlated Histopathology. Elsevier Health Sciences. Stevens, R., 2006. Gray’s Anatomy for Students Overview of exocrine glands • EXO = outside • Crine (krinein – Greek) = sift • A gland that makes substances such as sweat, tears, saliva, milk and digestive surfaces and releases them through a duct or opening to a body surface Intralobular ducts @orientatewithjoyce SALIVARY GLANDS What is Saliva? Why do we need it? • pH ~ 6.7-7.4 • Lubricates and protects oral tissues • Immune in function – aid in control of microbial flora in oral cavity • Starts digestion of complex carbohydrates by secreting α- amylase • Produced by salivary glands • Salivary glands = compound tubuloacinar glands Major salivary glands Major Salivary Glands • Parotid gland = serous. • Submandibular gland = mostly serous and partially mucous. • Sublingual gland = almost completely mucous. • Mucous has the same refractive index as cytoplasm. • At times, we can find myoepithelial cells on top of the acini which will help with expulsion of saliva along the course of the duct. Ductal system of Salivary Glands • Basal striations are folds within the basal surface to maximize SA for ion channels. • Intercalated ducts – close to acini (simple cuboidal lining). • Striated ducts - become more columnar. • Interlobular duct = from the intralobular duct as they enter the CT between lobules - septas join together until the main duct is formed. • All digestive organs including pancreas and liver develop from gut tube and maintain contact via their ducts. PAROTID GLAND Parotid Gland • • • • • • • • • • • • • Parenchyma enclosed by fibrous capsule. Septa divides it into lobes and lobules. Septa act like a conduit for blood vessels and autonomic nerves. Parotid – branched tubuloacinar glands and is composed of clusters of elongated, branched serous acini. Pyramidal serous cells that surround a central lumen form each acinus. Cells = round basal nuclei and granular cytoplasm that is basophilic at the base and more eosinophilic toward the apex. Nuclei are acidophilic and organelles are basophilic. Number of granules in the cytoplasm = dependent on the phase of secretion. A basement membrane surrounds each acinus and encloses a few flat myoepithelial cells. Duct – starts off as one layer of squamous or cuboidal = intercalated. Striated ducts are present but not common. Duct continues as striated duct aka columnar cells with basal striations. Intralobular connect to interlobular ducts (stratified cuboidal-columnar and then pseudo). SUBMANDIBULAR & SUBLINGUAL SALIVARY GLANDS Submandibular H&E Submandibular and sublingual salivary glands Submandibular: • Egg shaped • Floor of oral cavity • Its watery secretion accounts for 60% of the saliva it produces • Most of it is serous but also contains mucous acini • Has many striated ducts and fewer intralobular Sublingual: • Smallest • Minor salivary glands scattered in lips, tongue cheeks and are mixed • Produces mucin • Serousmucous acini mixed = mucous lighter straining towards central lumen • Flattened serous cells around the surface of the acini • striated ducts - short almost absent altogether PANCREAS PANCREAS Pancreatic Juice: • Amylase • Lipase • Trypsin • Carboxypeptidase • Bicarbonate Pancreas Endocrine function Exocrine function • Hormones produced in the pancreatic islets (islets of Langerhans) • Glucagon stimulates glucose production via gluconeogenesis & glycogen breakdown • Insulin promotes glucose uptake by cells and glycogen production & storage • Cells and what they produce: ü Alpha – glucagon ü Beta – insulin ü Delta – somatostatin ( inhibits the exocrine portion of the pancreas) ü Gamma – Pancreatic polypeptide (inhibits the endocrine portion of the pancreas and pancreatic secretion of fluid, bicarbonate, and enzymes) • Secretion of pancreatic juice into the duodenum • Pancreatic juice is released into duodenum via main and accessory pancreatic ducts • Pancreatic juice contains enzymes for the digestion of proteins and fats, alkaline fluid rich in bicarbonate ions for neutralising stomach acid • Trypsin > secreted by pancreas as trypsinogen (protein) • Amylase- digestion of complex carbohydrate like starch • Lipase – digestion of fats • Centroacinar cells secrete bicarbonate fluid • The digestive enzymes of the pancreas are released in a ‘gift pack’ form known as Zymogen Granules - the enzymes are active once they reach the duodenum – if not, pancreas will digest itself. Liver 312 Liver, Gallbladder, and Exocrine Pancreas Anterior aspect. Diaphragm (pulled up) Coronary ligament Falciform ligament Round ligament (ligamentum teres) of liver Gallbladder (fundus) Visceral surface. Gallbladder (fundus) Round ligament (ligamentum teres) of liver Quadrate lobe Porta hepatis Falciform ligament Fissure for ligamentum teres Hepatic portal vein Proper hepatic artery Caudate lobe Cystic duct Common hepatic duct (Common) bile duct Right triangular ligament Hepatorenal portion of coronary ligament Inferior vena cava Hepatic veins 14.1 OVERVIEW OF THE LIVER The wedge-shaped liver, the largest and heaviest internal organ (weighs about 1.5 kg in an adult), is essential to life and is the most ducts, portal vein, hepatic artery, lymphatics, and nerves. The liver arises in the embryo as a diverticulum of foregut endoderm. Parenchymal cells proliferating from this diverticulum pass into Artery Hepatic ATED) N E G Y (OX Spleen Celiac Trunk Stomach Proximal Duodenum Pancreas Inferior Vena Cava Portal Vein (NUTRIENT RICH) Abdominal aorta 25 Liver Liver Lobule Central Vein @orientatewithjoyce PV L BD Low-magnification LM of a hepatic lobule. 35×. H&E. L HA PV BD Hepatocytes L HA LM of a portal tract. A portal venule (PV), hepatic arteriole (HA), and bile ductule (BD) make up the portal triad. They are accompanied by small lymphatic vessels (L). Surrounding stroma is loose and highly cellular. 250×. H&E. Hepatocytes LM of a central vein (CV) in the center of a hepatic lobule. This thin-walled vein is surrounded by parenchyma LM of a portal tract. A portal venule (PV), hepatic arteriole (HA), and bile ductule (BD) Sinusoids and receives blood from several sinusoids. 315×. H&E make up the portal triad. They are accompanied by small lymphatic vessels (L). Surrounding stroma is loose and highly cellular. 250×. H&E. Hepatocytes CV Sinusoids LM of a central vein (CV) in the center of a hepatic lobule. This thin-walled vein is surrounded by parenchyma and receives blood from several sinusoids. 315×. H&E Hepatocytes CV 14.4 HISTOLOGY OF THE PORTAL TRACT AND CENTRAL VEIN At their smallest branches, the three components of the portal triad are accompanied by small lymphatic vessels. Connective tissue stroma known as the portal tract encloses them all. In transverse section, the hepatic arteriole consists of one to three between hepatocytes. Best seen by electron microscopy, they are small intercellular channels formed by groove-like invaginations of adjacent hepatocytes. As canaliculi approach the periphery of each lobule, they are drained by small ducts, known as canals of Hering, lined by a low simple cuboidal epithelium. These canals drain to larger bile ducts in portal tracts. As the ducts widen, their Liver histology • Hepatocytes: cuboidal shaped • Hepatic sinusoids: lined with a thin discontinuous epithelium (deliver blood to central vein); • Kupffer cells (stellate sinusoidal macrophage) - detect and engulf bacteria and breakdown aged erythrocytes. • Portal space contains portal triads: branch of hepatic artery, branch of portal vein and bile duct (also contains lymph vessels). • Blood flows from portal triad through sinusoidal channels into a central vein → inferior vena cava > right atrium of the heart Bile canaliculi • Bile canaliculus located between hepatocytes • Bile: made in hepatocytes, collects in bile canaliculi, used or stored in gall bladder. Exocrine product of the liver. • Flows in the opposite direction to blood. http://www.lab.anhb.uwa.edu.au/mb140 Gallbladder • Gallbladder stores and concentrates bile • Lining of the GB mucosa = simple columnar cells with short microvilli • Water from the lumen is absorbed by the GB cells ( ^ concentration of bile) Mucosal folds Lumen Lumen Mucosa Muscularis * Serosa Lamina propria Lumen Surface epithelium Lamina propria Muscularis Mucous gland Dense connective tissue LM of the entire thin wall of the gallbladder in transverse section (above). The wall has three layers. In an empty or contracted gallbladder, the mucosa shows many folds, which flatten out when the organ fills with bile. This slightly distended gallbladder has just a few small folds. Bundles of smooth muscle fibers form the middle muscularis. The serosa contains a rich network of lymphatic channels (*) and is covered externally by simple squamous mesothelium of the peritoneum. 57×. H&E. LM of part of a nondistended gallbladder. The mucosa shows many folds, which are lined by simple columnar epithelium. The epithelium rests on loose, richly vascularized connective tissue—the lamina propria. Mucosal folds extend to the upper part of the muscularis and bear a resemblance to villi, but unlike villi, they disappear in a distended organ. Smooth muscle cells in the muscularis are oriented in different directions: longitudinally, circularly, and obliquely. An outermost layer of dense irregular connective tissue constitutes the serosa (or adventitia). 85×. H&E.