Includes a brief overview of the digestive system and its functions, and in-depth descriptions of the layers of the digestive tract (and their innervations and functions), the oral cavity (tongue, palate, teeth, salivary glands), the pharynx and esophagus, the stomach (regions, curvatures, omentum,...
Abdomen and Digestive
system
Thursday, 21 October 2021 10:31 AM
Overview of our digestive system
- Digestive tract (Alimentary tract / canal)
- Gi tract
○ Stomach and intestines
- Accessory organs
○ Not part of canal but they provide enzymes / fluids etc to
supplement digestion
○ Primarily glands
○ Secrete fluids into the tract
- Regions
○ Oral cavity
○ Pharynx
○ Esophagus
○ Stomach
○ Small intestines
§ Duodenum / ileum / jejunum
§ liver, gallbladder and pancreas as major accessory organs
○ Large intestines
§ Cecum, colon, rectum and anal canal with mucous glands
○ Anus
Major functions
- Ingestion
- Mastication
- Propulsion
○ Deglutition
§ Swallowing
○ Peristalsis
§ Moves material through digestive tract
§ Unidirectional movement of food
○ Mass movement
§ In large intestines
- Secretion
○ Lubricate, liquefy, digest
○ Mucus, water, bile, enzymes
- Digestion
, ○ Mass movement
§ In large intestines
- Secretion
○ Lubricate, liquefy, digest
○ Mucus, water, bile, enzymes
- Digestion
○ Mechanical and chemical
- Absorption
○ Movement from tract into circulation or lymph
○ Most in small intestines
- Elimination
○ Waste products removed from body
○ Feces - defecation
Digestive tract histology
- Layers
○ Mucosa
§ In contact with food
§ Mucous membrane
§ Epithelium
§ Lamina propria
□ Loose connective tissue
□ Provides vascular support for the epithelium
□ Often contains mucosal glands
§ Muscularis mucosae
□ Thin double layer of smooth muscle
□ For local movement of the mucosa
§ Lymphatic nodule intestinal gland
○ Submucosa
§ Loose connective tissue layer
§ Mucous secreting glands
□ And their Ducts
§ Plexus to control the secretion from glands
□ Submucosal plexus
□ The nerves are derived from the myenteric nerve plexus
® Nerves from myenteric perforate the muscle fibres
to reach the submucosa
□ Innervates cells in the epithelial layer and the smooth
muscle of the muscularis mucosae
□ Involuntarily induce secretion of enzymes from mucous
○ Muscularis
§ 2 layers
□ Circular inner muscle layer
□ Longitudinal outer muscle layer
§ Segmentation / peristalsis
§ Myenteric plexus
□ Bundle of nerves between the 2 layers of muscle
, § 2 layers
□ Circular inner muscle layer
□ Longitudinal outer muscle layer
§ Segmentation / peristalsis
§ Myenteric plexus
□ Bundle of nerves between the 2 layers of muscle
□ Regulates peristalsis in the GI tract
○ Serosa
§ Provides protection layer to reduce friction when visceral
moves around in abdomen
□ Surrounded by visceral peritoneum
§ Serous membrane
§ Connective tissue
- Structure of the wall
○ Distinct epithelium in different parts of GI tract
○ Small intestines
§ Microvilli
§ Simple epithelium that allows efficient diffusion of nutrients
General characteristics of alimentary canal
- Muscular tube about 8 meters long
- Innervation of tube
○ Branches of sympathetic and parasympathetic divisions of
autonomic nervous system innervate alimentary canal
§ Submucosal plexus
□ Controls secretion
□ In submucosa
§ Myenteric plexus
□ Controls gastrointestinal mobility
○ Parasympathetic increases the activity of the digestive system
○ Sympathetic inhibits certain digestive actions
Oral cavity
- Bound by lips anteriorly and fauces (opening into pharynx) posteriorly
○ Vestibule
§ Space between lips / cheeks and alveolar processes with teeth
§ Kept moist by secretions from parotid gland
§ Alveolar processes
□ Thick ridge of bone which contains the tooth sockets
□ Holds the teeth
○ Oral cavity proper
§ Medial to alveolar processes
- Many layers of epithelium
○ Lined with moist stratified squamous epithelium
○ Moist
§ To protect
- Tongue
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