Overview
This lecture provides a comprehensive overview of the digestive system, covering the structure and function of the alimentary canal, major digestive organs, blood supply, and peritoneal relationships.
Digestive System Functions & Oral Cavity
- The digestive system's main role is to acquire and process nutrients from food.
- Digestion begins in the mouth, which houses the oral vestibule (between lips and teeth) and oral cavity proper (teeth inward).
- The hard palate transitions to the soft palate and uvula at the roof of the mouth.
- Palatine tonsils, located near the back of the mouth, are part of the immune system.
- The lingual frenulum anchors the tongue; labial frenula connect lips to gums.
- Mechanical digestion (chewing) and some chemical digestion (salivary amylase, lingual lipase) occur in the mouth.
- Food is formed into a bolus before being swallowed.
Alimentary Canal & Digestive Tract Regions
- The bolus moves from the oropharynx to the esophagus, then to the stomach.
- The alimentary canal is divided into foregut, midgut, and hindgut regions, each with distinct organs and blood supplies.
- The foregut includes the mouth, pharynx, esophagus, and stomach.
Stomach Anatomy & Function
- The stomach sections include cardia (entry), fundus (top), body (main), and pyloric part (exit through pyloric sphincter).
- The stomach primarily stores and churns food, forming acidic chyme.
- Rugae are folds inside the stomach allowing expansion.
Small Intestine & Blood Supply
- The duodenum (first part of the small intestine) is responsible for most chemical digestion.
- After the duodenum, food passes to the jejunum (absorption) and ileum (bile acid absorption).
- The ileocecal valve controls passage into the cecum of the large intestine.
- The celiac trunk supplies the foregut, superior mesenteric artery supplies the midgut, and inferior mesenteric artery supplies the hindgut.
Large Intestine & Peritoneal Relationships
- The cecum leads to the ascending, transverse, descending, and sigmoid colon, ending in the rectum and anus.
- Hepatic (right colic) and splenic (left colic) flexures mark colon bends near the liver and spleen.
- The colon features taenia coli (longitudinal muscle bands) and epiploic appendages (fat pouches).
- Intraperitoneal organs (e.g., transverse colon) are suspended within the abdominal cavity; retroperitoneal organs (e.g., kidneys, portions of the colon) lie behind it.
- The greater omentum is a fatty peritoneal fold covering abdominal organs.
Accessory Organs & Ducts
- Liver, gallbladder, and pancreas secrete digestive juices into the duodenum via major and minor duodenal papillae.
- The spleen and kidneys are not digestive organs, but are anatomically related.
Key Terms & Definitions
- Alimentary Canal — continuous muscular tube from mouth to anus for food passage.
- Bolus — chewed, moistened mass of food ready for swallowing.
- Rugae — folds inside the stomach.
- Ileocecal Valve — sphincter between ileum and cecum.
- Celiac Trunk — main artery supplying the foregut.
- Greater Omentum — fatty fold of peritoneum hanging over abdominal organs.
- Retroperitoneal — located behind the peritoneal cavity.
- Taenia Coli — longitudinal bands of muscle on the colon.
- Epiploic Appendages — fat-filled pouches attached to the colon.
Action Items / Next Steps
- Review the anatomical regions of the digestive tract and their blood supplies.
- Study the peritoneal relationships (intraperitoneal vs. retroperitoneal organs).
- Prepare for detailed study of accessory digestive organs in future lectures.