Exercise 41 Digestive System

Digestion and absorption It is the physical and chemical break down of food Absorption It is the passing of the digested food through the epithelial cells into the blood stream

Digestive system

Gastrointestinal tract It is the alimentary canal Mouth Pharynx Esophagus Stomach Small intestine Large instestine

Accessory digestive organs Salivary glands Gallbladder Liver Pancreas Teeth

General histology of the gastrointestinal tract It has 4 tunics Mucosa Epithelium – simple columnar Lamina propria – areolar tissue Muscularis mucosa Smooth muscle that enables movement of the mucosa

General histology of the gastrointestinal tract Functions of the mucosa are secretion, absorption, protection Submucosa Dense connective tissue Blood vessels Lymph nodes and vessels Submucosal plexus Functions are nutrition and protection of the mucosa

General histology of the gastrointestinal tract Muscularis externa Inner circular layer of smooth muscle Outer longitudinal layer of smooth muscle Myenteric plexus Allows GI movements

General histology of the gastrointestinal tract Serosa (abdominal organs) Most outer layer Mesothelium – areolar tissue Functions is to reduce friction between GI organs Adventitia Coarse fibrous tissue that binds the GI organs to the surrounding tissues. Anchors and protects them

Oral cavity

Macroscopy of the digestive tract Oral cavity or mouth Oral cavity Lips or labia Superior and inferior labial frenulum Cheeks Palate Soft with uvula Hard Palatine raphe

Macroscopy of the digestive tract Tongue Lingual frenulum Vestibule Palatine tonsil Palatoglossal arch Palatopharyngeal arch

Macroscopy of the digestive tract Lingual tonsil Salivary glands Saliva Salivary amylase Pharynx Nasopharynx Oropharynx Laryngopharynx

Macroscopy of the digestive tract Esophagus Peristalsis Gastroesophageal sphincter Adventitia and not serosa Stomach Cardiac region Fundus Body

Macroscopy of the digestive tract Pyloric region Pyloric sphincter Greater curvature Greater omentum From the greater curvature down to the abdominal organs Lesser curvature

Macroscopy of the digestive tract Lesser omentum From the lesser curvature to the liver Gastric pit Gastric rugae Function of the stomach is to process the food forming the chyme

Histology of the stomach

Histology of the stomach Mucosa Gastric glands Chief or zymogenic cells: Located on the fundus Produce pepsinogen

Histology of the stomach Parietal cells: Located on the fundus Produce HCL Produce intrinsic factor Enteroendocrine cells: Located on the pyloric region Release hormones Submucosa

Histology of the stomach Muscularis externa Oblique layer Circular layer Longitudinal layer Gastroesphageal junction (Cardioesophageal) Stratified squamous epithelium on the esophagus Simple columnar on the stomach

Small intestine From the pyloric sphincter to the ileocecal valve Mesentery Proper Double layer of peritoneum that attaches the small intestine to the posterior body wall

Small intestine Plicae Deep folds of the mucosa and submucosa They cause the chyme to spiral through the intestine slowing and mixing it Intestinal crypts of crypts of Lieberkuhn It is the invaginated area of the mucosa between the villi

Small intestine Lacteal It is the lymphatic capillary present in each villus Function of the small intestine Nutrients absorption

PART B

Subdivisions of the small intestine

Small intestine Duodenum Pancreatic duct Bile duct Hepatopancreatic ampulla Major duodenal papilla Hepatopancreatic sphincter or sphincter of Oddi Duodenal glands or Brunner’s glands – located in the submucosal layer

Small intestine Jejunum Where the food is most absorbed Ileum Ileocecal valve Peyer’s patches Aggregation of lymphoid tissue more prominent in the ileum

Small intestine Superficial structures of the small intestine that increases the absorptive area of the mucosa Villi Fingerlike projections of the mucosa

Small intestine Microvilli or brush border Projections of the cell membrane of the columnar epithelium Brush border enzymes Plicae

Histology of the small intestine Identify these structures on the slide: Plica Cripts Villi Brush border Layers of the intestine

Histology of the small intestine Duodenum Submucosa with Brunner’s glands Jejunum Longest, leafy villi Ileum Submucosa with Peyer’s patches

The large intestine

Large intestine From the ileocecal valve to the anus Mesocolon Attaches the large intestine to the body wall Cecum It is the first part Appendix A blind tube like structure connected to the cecum

Large intestine Colon: Ascending Right side of the abdominal cavity Right colic (hepatic) flexure It is retroperitoneal Transverse Cross the abdominal cavity Left colic (splenic) flexure

Large intestine Descending It is retroperitoneal Sigmoid S-shaped Located in the pelvis Rectum

Large intestine Anus External sphincter - skeletal muscle Voluntary Internal sphincter – smooth muscle involuntary

Large intestine - structures Tenia coli It is the longitudinal muscle layer of muscularis externa It is in the shape of a muscle band Haustra Pocket like sacs of the large intestine It is caused by the tenia coli

Large intestine - structures Epiploic appendages Fat-filled pouches of visceral peritoneum hanging for the colon’s surface

Large intestine Functions of the large intestine Consolidate and propel the fecal matter to the anus Site for intestinal bacteria to synthesize vitamins B and K Site for water absorption

Histology of the large intestine Lumen Crypts Layers of the digestive tract Mucosa with the maximum amount of goblet cells No villi

Accessory digestive organs Teeth: Deciduous (milk teeth) They appear between 6 month and 2 ½ years of age They begin to shed at 6 years of age They are completely shed by the age of 12

Accessory digestive organs Permanent They begin to appear at 6 years of age They last for a lifetime

Types of teeth

Accessory digestive organs Classification of the teeth Incisors Chisel shaped Shearing action when biting 4 superiors and 4 inferiors (2 centrals and 2 laterals) Single-rooted

Accessory digestive organs Canines Cone-shaped It tears the food 2 superiors and 2 inferiors Single-rooted

Accessory digestive organs Premolars Two cusps It grinds the food 4 superiors and 4 inferiors 2 first premolars 2 second premolars Generally single-rooted 1st premolar may have 2 roots

Accessory digestive organs Molars They have broad crowns Rounded cusps 6 superiors and 6 inferiors 2 first molars 2 second molars 2 third molars or wisdom teeth They have 2 roots They grind food into fine pieces

Accessory digestive organs Dental formula: Deciduous 2,1,0,2 Permanent 2,1,2,3

Accessory digestive organs Anatomy of the teeth Crown Clinical Anatomical Enamel It consists mainly of calcium salts Gum or gingival Gingival sulcus and margin

Accessory digestive organs Neck Root Cementum Periodontal ligament Dentin Pulp Contain blood vessels and nerves Pulp cavity

Accessory digestive organs Odontoblasts Root canal Apical foramen

PART C

Accessory digestive organs Salivary glands Parotid glands Anterior to the ear He parotid duct open at the level of the second superior molar Mainly a serous gland

Accessory digestive organs Submandibular gland Located on the floor of the mouth He submandibular duct opens at the base of the lingual frenulum Serous and mucous gland

Accessory digestive organs Sublingual gland Located on the floor of the mouth There are many sublingual ducts that open under the tongue Serous and mucous gland Saliva composition Mucin - Forms the bolus Serous fluid – contain amylase

Accessory digestive organs Histology of the salivary glands Mucous cells forming the acini Serous cells forming demilunes around the mucous cells Ducts with cuboidal epithelium

Salivary glands

Accessory digestive organs Liver Located mainly in the right hypochondriac region 4 lobes Right, left, caudate, quadrate Falciform ligament Suspend the liver from the diaphragm and anterior abdominal wall

Bile duct system

Accessory digestive organs Bile Produced by the liver Responsible for emulsification of the lipid from the diet Bile duct system Bile canaliculus Carries the bile to the duct of the nearest portal area

Accessory digestive organs Bile ducts carry bile to the: Right and left hepatic ducts Common hepatic duct

Accessory digestive organs Histology Lobules Structural and functional units of the liver They have cords of hepatocytes running away from the central vein Hexagonal shape Central vein

Histology of the liver

Accessory digestive organs Portal triad or portal tract Located at each of the six corners of the lobule Hepatic artery Hepatic portal vein Bile duct Sinusoids Blood-filled Kupffer cells Macrophage lining the sinusoids

Accessory digestive organs Gallbladder Stores the bile not being used Concentrates the stored bile Cystic duct

Accessory digestive organs Pancreas It is a retroperitoneal organ Endocrine and exocrine organ Secretes the pancreatic juice into the duodenum It alkalinizes the chyme coming from the stomach Pancreatic duct or duct of Wirsung Accessory pancreatic duct or duct of Santorini

Accessory digestive organs Histology of the pancreas Acinar or exocrine pancreas Islets or endocrine pancreas Septa Connective tissue

Microscopic structures to be identified Identify the organ and its layers: Mucosa, submucosa, muscularis externa, adventitia or serosa Esophagus Stratified squamous epithelium Gastroesophageal junction

Microscopic structures to be identified Stomach Simple columnar epithelium Gastric pit Duodenum Villi Brush border Goblet cells Intestinal cripts Brunner’s glands

Microscopic structures to be identified Jejunum Leafy villi, crypts Brush border Goblet cells Ileum Villi with goblet cells and brush border, crypts Peyer’s Patch

Microscopic structures to be identified Large intestine Cripts, abundant goblet cells Salivary glands Serous acini (demilunes) Mucous acini Ducts Pancreas Acinar exocrine vs. endocrine pancreatic islets

Microscopic structures to be identified Liver Hexagonal lobules Triad Hepatic portal vein Hepatic artery Bile duct Central vein Sinusoids vs. plates of hepatocytes

Cat structures to be identified Esophagus Stomach Lesser and greater curvatures Lesser and greater omentum Small intestine Mesentery proper Ileocecal valve

Cat structures to be identified Large intestine Mesocolon Rectum Anus Liver Gall bladder Pancreas