Medical Education Semester 3: Digestive Structures

Study Notes

Comprises the digestive tract: oral cavity, esophagus, stomach, small and large intestines, anus, and associated glands including salivary glands, liver, and pancreas.

Formed of four layers: outer surface, inner surface, middle layer, and red margin.
Outer surface consists of thin skin with no hair or sebaceous glands.
Inner surface covered with oral mucosa; stratified squamous non-keratinized epithelium.
Middle layer contains striated muscle fibers (orbicularis oris) and connective tissue.
Red margin or vermilion border has modified thin skin with transparency from blood vessels.

Composed of skeletal muscle covered by mucosa; involved in mastication and swallowing.
Muscle fibers arranged in longitudinal, transverse, and oblique orientations.
Ventral surface has smooth, loosely attached mucous membrane; dorsal surface features lingual papillae.
Dorsal surface divided by V-shaped sulcus terminalis; anterior two-thirds with papillae, posterior one-third contains lingual tonsils.
Types of lingual papillae include filiform, fungiform, circumvallate, and foliate papillae.

Comprised of sustentacular and neuroepithelial (gustatory) cells with microvilli.
Stem cells regenerate gustatory cells every 7-10 days.

Four main layers: mucosa, submucosa, musculosa, adventitia/serosa.
Mucosa consists of epithelial lining, lamina propria (loose connective tissue), and muscularis mucosa (smooth muscle fibers).
Submucosa contains loose connective tissue and Meissner's Plexus.
Musculosa has inner circular and outer longitudinal smooth muscle; includes Auerbach's Plexus.
Adventitia or serosa is a protective outer layer.

Mucosa lined with non-keratinized stratified squamous epithelium and cardiac glands.
Submucosa includes loose connective tissue and esophageal glands.
Musculosa varies: striated muscle in upper third, smooth muscle in lower third, and both in the middle third.
Thin adventitia encases the esophagus.

Comprised of three regions: cardiac, fundic (body), and pyloric.
Mucosa features simple columnar epithelial lining with various cell types including surface mucous cells and parietal cells.
Fundic region contains gastric glands; pyloric region contains pyloric glands.

Surface mucous and mucous neck cells secrete mucus for neutralization.
Parietal (oxyntic) cells produce hydrochloric acid (HCl) and intrinsic factor for vitamin B12 absorption.
Chief cells release pepsinogen, enteroendocrine cells secrete hormones like gastrin and serotonin.
Stem cells located among other cell types regenerate the epithelial lining.

Fundic glands are long, branched, and crowded with six cell types; pyloric glands are short and less crowded.
Fundic mucosa is thick and highly folded, while pyloric mucosa is thinner and less folded.

Discusses a 65-year-old female with osteoarthritis and NSAID use, leading to epigastric pain, heartburn, weight loss, and potential gastric ulcer diagnosis.
NSAIDs may cause stomach mucosa erosions, possibly resulting in ulcers or bleeding.
The stomach's acidity is counteracted by mucus from surface mucous cells and mucous neck cells.
Enteroendocrine cells play a role in gastric functions, monitoring contents and secreting relevant hormones.

Enteroendocrine cells belong to the diffuse neuroendocrine system (DNES); they possess apical microvilli for monitoring.
Argentaffin cells stain with silver and represent neuroendocrine cell types.