Overview of the Digestive System Digestive Tract: Mouth, pharynx, and esophagus, stomach, small intestine, and large intestine (colon) Accessory Organs: Teeth, tongue, salivary glands, pancreas, liver, and gallbladder
Functions of the Digestive System Ingestion Mechanical processing Chemical digestion Secretion Absorption Excretion
Histology of the Digestive Tract Mucosa Submucosa Muscularis Externa Serosa
Mucosa (Innermost Layer) Epithelium Connective Tissue (Blood vessels, lymphatic vessels, lymphatic nodules) Smooth Muscle
Submucosa Connective tissue Blood vessels Lymphatic vessels Nerve plexus May have glands and lymphatic tissue
Muscularis Externa Smooth or Skeletal Muscle If smooth muscle, usually 2 layers (circular and longitudinal)
Adventitia or Serosa Adventitia (organs superior to diaphragm) Serosa = visceral peritoneum
Small Intestine: Peyer’s Patches
Components of the Digestive System GI Tract: Oral Cavity Pharynx Esophagus Stomach Small Intestine Large Intestine
Oral Cavity
Oral Cavity
The Pharynx Nasopharynx Oropharynx Laryngopharynx
The Esophagus
The Esophagus Stratified squamous epithelium Mucous glands Muscularis externa – skeletal muscle first third of length
Peristalsis in Esophagus LE 21-8 Muscles contract Muscles contract, constricting passageway and pushing bolus down Muscles relax Bolus of food Muscles relax, allowing passageway to open Muscles contract Muscles relax Stomach
Stomach Site where food is churned into chyme Protein digestion begins
Stomach
Stomach
Stomach – Microscopic Anatomy
Stomach – Microscopic Anatomy
The Stomach – Microscopic Anatomy
Ulcers in stomach Helicobacter pylori
Small Intestine – Gross Anatomy Longest portion of the alimentary canal Site of most enzymatic digestion and absorption Three subdivisions Duodenum, jejunum, and ileum
Duodenum and Related Organs LE 21-11a Duodenum and Related Organs Liver Bile Gall- bladder Stomach Bile Pancreas Acid chyme Intestinal enzymes Pancreatic juice Duodenum of small intestine
Duodenum and Related Organs
Enzymes in Small Intestine
Small Intestine – Microscopic Anatomy
Amino acids and sugars Fatty acids and glycerol LE 21-11b Lumen of intestine Nutrient absorption Vein with blood en route to the liver Nutrient absorption into epithelial cells Microvilli Epithelial cells Amino acids and sugars Fatty acids and glycerol Muscle layers Lumen Fats Blood capillaries Large circular folds Villi Blood Lymph vessel Nutrient absorption Lymph Epithelial cells Villi Intestinal wall
Small Intestine: Duodenum Br = Brunner glands V = Villus G = Goblet cells Cr = Intestinal glands MM = Muscularis Mucosae LP = Lamina Propria
The Small Intestine – Structural Features
Gross Anatomy of Large Intestine Cecum Appendix Ascending Transverse Descending Sigmoid colon Rectum Anus
Large intestine (colon) Sphincter Small intestine End of small LE 21-12 Large intestine (colon) Sphincter Small intestine End of small intestine Rectum Anus Nutrient flow Appendix Cecum
Gross Anatomy of Large Intestine Rectum – descends along the inferior half of the sacrum Anal Canal – the last subdivision of the large intestine
Gross Anatomy of Large Intestine
Microscopic Anatomy of Large Intestine Villi are absent Contains numerous goblet cells Intestinal crypts – simple tubular glands Lined with simple columnar epithelial tissue Epithelium changes at anal canal Becomes stratified squamous epithelium
Microscopic Anatomy of Large Intestine
Teeth
Salivary Glands
Pancreas
Exocrine Pancreas: Histology
Liver Largest gland in the body Performs over 500 functions Digestive function – bile production Performs many metabolic functions
Visceral Surface of the Liver
Microscopic Anatomy of Liver
Microscopic Anatomy of Liver
Gallbladder Stores and concentrates bile Expels bile into duodenum Bile emulsifies fats
Gallbladder
Enzymes in Small Intestine
The Peritoneal Cavity and Peritoneum Mesentery – a double layer of peritoneum Holds organs in place Sites of fat storage Provides a route for circulatory vessels and nerves
Mesenteries Superficial view of the abdominal organs
Mesenteries Greater omentum and transverse colon reflected
Mesenteries Sagittal section through the abdominopelvic cavity
Segmentation Rhythmic local contractions of the intestine Mixes food with digestive juices
Disorders of the Digestive System Intestinal obstruction Mechanical obstructions Adhesions, tumors, or foreign objects Nonmechanical obstruction Halt in peristalsis Trauma Intestines touched during surgery
Disorders of the Digestive System Inflammatory bowel disease Inflammation of intestinal wall Crohn’s disease Ulcerative colitis Viral hepatitis – jaundice and flu-like symptoms Major types – A, B, C, and G Cystic Fibrosis and the Pancreas
The Digestive System in Later Life Middle age – gallstones and ulcers Old age – activity of digestive organs decline Fewer digestive juices and enzymes produced Absorption is less efficient Dehydration of fecal mass leads to constipation Diverticulosis and cancer of digestive organs