Digestive System, Part II, Lecture 1+2, Dr. Hana Abusaida, 2024 PDF

ORGANS ASSOCIATED WITH THE DIGESTIVE TRACT Lecture 1  Salivary Dr. Hana Abusaida glands Department of Histology Faculty of Medicine, Sabha University 2024 ...

ORGANS ASSOCIATED WITH THE DIGESTIVE TRACT Lecture 1  Salivary Dr. Hana Abusaida glands Department of Histology Faculty of Medicine, Sabha University 2024  Learning Objectives Study the histological structure of the three types of salivary glands. Comparing the secretory units of the salivary glands. Compare the histology and exocrine function of the pancreas with that of the parotid salivary gland. Understand the overall organization of liver structure and hepatocytes. Understand the origin of bile and the duct system. Understand the structure of the gall bladder wall. Dr.Hana Abusaida, Histology Department, Sabha University  Organs Associated With the Digestive Tract Include: salivary glands, the pancreas, the liver, and the gallbladder I- Salivary Glands Exocrine glands in the mouth. Salivary glands divided into two groups: 1. Major glands. Produce 90% of saliva. Large, capsulated Produce 0.75 to 1.50 L of saliva daily. Three pairs of large salivary glands: 1) Parotid 2) Submandibular gland. 3) Sublingual gland. * 3 types of secretions for salivary glands: Serous, seromucous, or mucous. Dr.Hana Abusaida, Histology Department, Sabha University  Salivary Glands 2- Minor glands Small, non capsulated. Secrete 10% of saliva. Secretions mainly mucous except for Von Ebner glands. Present in mucosa and submucosa of oral cavity: a) Von Ebner glands: circumvallate and folliate papillae of the tongue. b) Glands of Blandin-Nuhn: on ventral tongue c) Palatine glands: in the palates. d) Weber glands: on sides of tongue. Dr.Hana Abusaida, Histology Department, Sabha University  Functions of Salivary glands: Produce Saliva Saliva comprises: 98% water, plus electrolytes, mucus, glycoproteins, enzymes (such as amylase and lipase), antimicrobial agents such as IgA , peroxidase, lactoferrin and lysozyme. 1. Protection a) Lubricant, moisturizes the inside mouth to creates smoother speech. b) formation of salivary pellicle ( protein film for teeth protection). 2. Digestion a) Converts starch into maltose with salivary amylase. b) Helps chewing and swallowing. 3. Antimicrobial a) Lysozyme, peroxidase and lactoferrin fight against pathogenic microorganisms. 4. Tissue repair a) Saliva accelerates blood coagulation, so bleeding time of oral tissues shorter than other tissues. b) Clot less solid than normal. Dr.Hana Abusaida, Histology Department, Sabha University  MEDICAL APPLICATION Dry mouth or xerostomia Insufficient secretions of saliva, leading to dry mouth or xerostomia, Caused by various factors such as:  Side effect of certain diseases and infections.  Dehydration.  The normal side effect of drugs. Sialorrhea or excessive saliva production, Associated with:  Inflammation of oral cavity,  Viral infection. Dr.Hana Abusaida, Histology Department, Sabha University Structure of major Salivary glands: 1- A stroma (capsule of connective tissue). 2- A parenchyma consists of lobules, 3- Lobules separated by septa (C.T.). 4- Lobules composed of acini (secretory unit) + ducts (duct system). 5- Secretory unit composed of cells. 6- Ducts composed of cells connected to acini. Dr.Hana Abusaida, Histology Department, Sabha University  Structure of major Salivary glands: Two major kinds of secretory unit cells 1- Serous cells Watery secretions. pyramidal in shape, with broad base and a narrow apical surface. Round central nucleus. Well-stained RER. Basophilic cytoplasm. Junctional complexes. Cells forming an acinus (rounded secretory unit) with a very small lumen. Apical zymogen granules. produce digestive enzymes and other proteins. Ex, Parotid gland & Pancrease. Dr.Hana Abusaida, Histology Department, Sabha University  Two major kinds of secretory unit cells 2- Mucous cells Mucus-secreting cells. More columnar in shape. With flat, basal nuclei. Apical granules with hydrophilic mucins (cause poor cell staining). Wider lumen. Organized as acini or tubules. Dr.Hana Abusaida, Histology Department, Sabha University  Dr.Hana Abusaida, Histology Department, Sabha University  Submandibular gland ( Mixed gland ) Dr.Hana Abusaida, Histology Department, Sabha University  Myoepithelial cells Found inside the basal lamina of the secretory units. Well developed and branched Sometimes called basket cells). Spindle-shaped, lie parallel to the duct's length. Their contraction accelerates secretion of the product. Dr.Hana Abusaida, Histology Department, Sabha University  Intralobular duct system of salivary glands Secretory acini and tubules empty into: 1- Intercalated ducts The smallest branches with small diameter. Lined by small cuboidal epithlial cells. Nucleus in the center. Some times secretory granules, few microvilli Myoepithelial cells are present 2- Striated ducts lined by columnar cells. Are cells specialized for ion transport pink striations in the basal half of the columnar cells. The striations produced by mitochondria in the folds of the cell membrane. Dr.Hana Abusaida, Histology Department, Sabha University  Intralobular duct system 3- Excretory Duct Increasing size and thicker C.T. Unusual, combining various epithelial types: Initially lined with pseudostratified or stratified cuboidal epithelium. more distal parts lined with stratified columnar epithelium. Reflects many diverse functions: cells for ion reabsorption, cells for secretion of mucin and other proteins, enteroendocrine cells, and basal stem cells, few goblet cells. 4- The main Excretory duct lined with nonkeratinized-stratified squamous epithelium. Dr.Hana Abusaida, Histology Department, Sabha University  Intralobular duct system of salivary glands Dr.Hana Abusaida, Histology Department, Sabha University  Types of major salivary glands 1- Parotid gland located in each cheek near the ear. branched acinar gland. the cells are purly serous with very small lumens. Cells secerte amylase which responsible for the hydrolysis of ingested carbohydrates. and proline-rich proteins have antimicrobial properties. Dr.Hana Abusaida, Histology Department, Sabha University  2- Submandibular gland (mixed gland) Branched tubuloacinar gland. The largest salivary glands, produce two- thirds of all saliva. Secretory portions containing both mucous and mainly serous cells. About 10% of mucous cells capped with serous cells called serous demilunes. Infoldings of the serous cells membrane increase the ion-transporting surface area. Secrete amylase, proline-rich proteins and lysozyme (bacteria hydrolysis). Dr.Hana Abusaida, Histology Department, Sabha University 2- Submandibular gland (mixed gland) Dr.Hana Abusaida, Histology Department, Sabha University  3- Sublingual gland (mixed gland) The smallest major glands Branched tubuloacinar gland. Formed of serous and mainly mucous cells. Serous cells demilunes on mucous tubules. The major product is mucus. Cells of serous demilunes secrete amylase and lysozyme. Dr.Hana Abusaida, Histology Department, Sabha University  Thank you END OF LECTURE 1 ‫قف على ناصية الحلم وقاتل‬  ORGANS ASSOCIATED WITH THE DIGESTIVE TRACT Lecture 2  Pancreas Dr. Hana Abusaida Department of Histology Faculty of Medicine, Sabha University 2024  The Pancreas Characters The main parts of the pancreas Is behind the stomach in the upper 1. Head is C-shaped curve of left abdomen. duodenum. It is spongy, pear shape. 2. Tail extends left to touch spleen. 25 cm long, 5 cm wide, and 1 to 2 cm 3. Body is the middle part. thick, weighs approximately 150 g 4. Main pancreatic duct runs the length of the pancreas, joins bile duct. Dr.Hana Abusaida, Histology Department, Sabha University  The pancreas Is a mixed exocrine-endocrine gland that produces both digestive enzymes and hormones. (95%)of pancreas are exocrine tissue that produces pancreatic enzymes for digestion. The remaining tissue consists of endocrine cells called islets of Langerhans to produce hormones (insulin and glucagon) that regulate blood sugar, carbohydrate metabolism and regulate pancreatic secretions. Dr.Hana Abusaida, Histology Department, Sabha University The pancreas: digestive enzymes These enzymes include: Proteases ( Trypsin and chymotrypsin), break down proteins, and help keep the intestine free of parasites. Amylase breaks down carbohydrates (starch) into sugars which are more easily absorbed by the body, (is also found in saliva). Lipase break down fat molecules so they can be easily absorbed. Enzymes are produced as inactivate molecules , or zymogens , to prevent the risk of self digestion within the pancreas. Enzymes go to duodenum, where activated. Dr.Hana Abusaida, Histology Department, Sabha University Histological structure of pancreas Stroma Capsule of C.T. Septa separating pancreatic lobules. Parenchyma pancreatic lobules Pancreatic islets (I) Pancreatic acini (A) Pancreatic ducts (D) Capillary network (V). Dr.Hana Abusaida, Histology Department, Sabha University  Pancreatic exocrine part: Pancreatic acini Pancreatic acini characters  Consists of serous cells  With very small lumen,  Without myoepithelial cells The serous acinar cells:  Are typical protein-secreting cells  with round basal nucleus  well developed RER, Golgi  basophilic cytoplasm  presence of zymogen granule (contains proenzymes, inactive precursor of an enzyme). at apex of the cell whose number decrease after a meal. Dr.Hana Abusaida, Histology Department, Sabha University  Pancreas: Duct system 1) Intercalated ducts Connected with the acini Lined by simple squamous epithelium. penetrate the lumens of the acini forming larger Centroacinar cell of simple columnar epithelium, which are small pale-staining cells. Cells of the intercalated ducts secrete a large volume of fluid, rich in HCO3 (bicarbonate ions), which alkalinizes and transports enzymes produced in the acini. Dr.Hana Abusaida, Histology Department, Sabha University Pancreas: Duct system 2) Intralobular ducts, is similar to the intercalated duct of salivary glands, lined by simple cuboidal epithelium. 3) Interlobular ducts, lined by simple columnar epithelia 4) Main pancreatic duct (duct of Wirsung), branches to accessory pancreatic duct (duct of santorini), which joins the common bile duct before opening in the duodenum at the ampulla of Vater.  Secretions into the duodenum are controlled by a muscular valve (the sphincter of Oddi). It surrounds the ampulla of Vater. Dr.Hana Abusaida, Histology Department, Sabha University  Compare of the pancreas & parotid salivary gland. Pancreas Parotid salivary gland Capsule & Septa of Present Present C.T. Lobules Present Present Secretory portion Serous acini Serous acini Intercalated ducts Simple squamous Simple cuboidal epith. epith. Acini Present Present Islets Present Absent Myoepithelial cells Absent Present Striated duct Absent Present Centroacinar cells Present Absent Dr.Hana Abusaida, Histology Department, Sabha University  Pancreatic secretions control Pancreatic acini secretion is controlled by hormone cholecystokinin (CCK) produced by enteroendocrine cells of the intestinal mucosa when chyme enters the duodenum. CCK promotes the exocytosis of enzymes from the pancreatic acini. Intercalated duct secretion (Bi-carbonate secretion) is Stimulated by the hormone secretin produced by enteroendocrine cells of the intestinal mucosa. CCK is called pancreozymin. Innervation of Pancreas Parasympathetic (vagus) nerve stimulate both exocrine and endocrine secretions. Sympathetic nerve inhibit secretions. Dr.Hana Abusaida, Histology Department, Sabha University  Pancreatic endocrine function (Production of Pancreatic Hormones) * Islets of Langerhans “islet cells” are the hormone secreting cells. Hormones secreted by 3 types of cells: Dr.Hana Abusaida, Histology Department, Sabha University  Medical application Acute pancreatitis, a sudden inflammation of pancreas that lasts for a short time, happens when the digestive proenzymes are activated before they are released into the small intestine and begin digest pancreatic tissues, leading to very serious complications. Causes include: infection, gallstones, alcoholism, drugs, and trauma. Most people recover completely after getting the right treatment. Severe pancreatitis can harm other vital organs such as the heart, lungs, and kidneys. Symptoms: severe abdominal pain which radiate to the back and cause nausea, vomiting and diarrhea. Chronic pancreatitis, is long-lasting inflammation of the pancreas. can produce progressive Dr.Hana Abusaida, Histology Department, Sabha fibrosis and loss of pancreatic function. University  Thank you END OF LECTURE 2 ‫قف على ناصية الحلم وقاتل‬