Digestivw

Here are clear and concise notes based on the content from your “Lab Session 22: Digestive Organs” PDF. I’ve broken them into organized sections for easier review:

🌟 GENERAL PRINCIPLES

• Digestive System: Anatomy is specialized for:
  

  • Mechanical digestion (teeth, tongue, smooth muscle).

  • Chemical digestion (enzymes, glands).

  • Absorption (maximized by large surface area).

🧬 STRUCTURAL OVERVIEW OF GI TRACT

All organs from esophagus to anal canal share a 4-layered structure:

1. Mucosa
   

   • Secretion (enzymes, mucus, hormones)

   • Absorption (nutrients → blood)

   • Protection (from pathogens)

   • Contains: Lamina propria & Muscularis mucosae

3. Submucosa
   

   • Connective tissue for elasticity

   • Contains blood vessels, lymphatics, and nerves

5. Muscularis Externa
   

   • Smooth muscle: circular (inner) & longitudinal (outer) layers

   • Responsible for peristalsis (propulsion) and segmentation (mixing)

7. Serosa
   

   • Outer visceral peritoneum

   • CT + squamous epithelium

🧠 CEPHALIC PHASE (Oral Cavity)

• Ingestion, mechanical digestion (teeth, tongue), chemical digestion (salivary amylase).

• Oral cavity lined with stratified squamous epithelium (resists friction/chemicals).

• Tongue
  

  • Intrinsic muscles: change shape

  • Extrinsic muscles: change position

  • Functions: mechanical digestion, swallowing, speech

🧠 PROPULSION & SWALLOWING

• Voluntary (tongue/mouth): skeletal muscle

• Involuntary (pharynx/esophagus): smooth muscle

• Peristalsis: wave-like contraction to move bolus

• Segmentation: mixes bolus, no forward motion

🧪 GASTRIC PHASE (Stomach)

• Functions: storage, mechanical digestion (churning), chemical digestion (proteins, fats)

• Muscularis has 3 layers: circular, longitudinal, and inner oblique for strong churning

• Mucosa contains Gastric Pits → Gastric Glands
  

  • Parietal cells: secrete HCl & intrinsic factor

  • Chief cells: secrete pepsinogen + lipases

  • Mucous cells: protect lining

  • Enteroendocrine cells: secrete gastrin

Myenteric Plexus (between muscle layers): regulates motility via enteric nervous system

🌿 INTESTINAL PHASE (Small Intestine)

• Main site of digestion & absorption

• 3 Regions:
  

  1. Duodenum: receives bile (liver/gallbladder), enzymes (pancreas), and secretes its own enzymes

  2. Jejunum: most nutrient absorption

  3. Ileum: absorbs vitamins, bile salts

Structural adaptations for absorption:

• Plicae circulares (folds), villi, and microvilli

• Enterocytes: absorb nutrients

• Goblet cells: secrete mucus

• Crypts of Lieberkühn: glands between villi

• Brunner’s glands (duodenum): secrete alkaline mucus from submucosa

• Peyer’s patches (ileum): immune function (MALT)

Nutrient Transport:

• Blood vessels: amino acids, sugars

• Lacteals (lymph): fats

🍃 LARGE INTESTINE

• Regions: cecum → ascending → transverse → descending → sigmoid → rectum → anus

• Functions: absorb water & vitamins, compact feces

• Ileocecal Valve: regulated by gastroileal reflex and gastrin

• Appendix: immune role (MALT), bacterial storage

• No villi, but deep crypts and thin submucosa

• Teniae coli: longitudinal muscle strips

• Haustra: segmented pouches

🚽 DEFECATION

• Rectum/anal canal

• Two sphincters:
  

  • Internal (involuntary)

  • External (voluntary)

• Triggered by stretch receptors → parasympathetic reflex

Let me know if you want this as printable flashcards or a Quizlet-style review!