Small & Large Intestines Small Intestine: principal site for digestion of food and absorption of the products of digestion Large Intestine: reabsorption of water and elimination of undigested food and waste
Mucosa - Epithelium 4 Layers of Digestive System - Lamina Propria - Muscularis Mucosae Submucosa - Connective tissue, blood vessels, submucosal plexus Muscularis Externa - 2 muscle layers, myenteric plexus Adventitia / Serosa - Loose connective tissue
Layer 1: Mucosal Layer Epithelium - enterocytes (with microvilli), - goblet cells, - paneth cells (SI only), - entero-endocrine cells, - M cells Lamina Propria - loose connective tissue - Peyer s Patches - lacteals Muscularis Mucosae - Boundary b/t mucosa and submucosa - 2 layers of smooth muscle
Layer 2: Submucosa & Layer 3: Muscularis Externae Submucosa: Connective Tissue Blood vessels Submucosal (Meissner s) Plexus (Brunner s glands in duodenum) Muscularis Externae: 2 smooth muscle layers Myenteric (Auerbach s) Plexus b/t muscle layers Myenteric Plexus Submucosal Plexus
Layer 4: Adventitia/Serosa Loose connective tissue
Plicae Circularis vs Villi Both are present in the small intestine as specializations to maximize absorptive surface area Plicae Circularis: circular folds w/in a core of submucosa. Contains many villi. Villus: finger-like mucosal projections w/in a core of lamina propria
Cells of Mucosal Epithelium: Enterocytes Absorptive Cells Columnar cells with basal nuclei Microvilli on apical surface Digestive enzymes in microvilli glycocalyx (breakdown sugars & proteins) Junctional complexes and terminal web
Cells of Mucosal Epithelium: Enterocytes Terminal bar Microvilli
Cells of Mucosal Epithelium: Enterocytes Junctional complexes and terminal web Terminal Bar
Cells of Mucosal Epithelium: Goblet Cells Produce mucus Interspersed among enterocytes Appear empty because mucus is washed out in slide preparation (more goblet cells in colon than SI)
Cells of Mucosal Epithelium in SI: Paneth Cells Located in Crypts of Lieberkuhn (bases of glands of SI b/t villi) Secrete lysozymes Basophilic base, eosinophilic granules at apex Regulate bacterial flora of gut
Cells of Mucosal Epithelium in SI: Paneth Cells Located in Crypts of Lieberkuhn (base of glands of SI b/t villi) Basophilic base, eosinophilic granules at apex
Cells of Mucosal Epithelium: Enteroendocrine Cells Secrete Hormones GIP, CCK, Secretin Seen with silver stain (Also in stomach)
Features of Mucosal Lamina Propria in SI Lamina Propria: loose cellular connective tissue Contains: 1. Peyer s Patches: lymph nodules and immune cells 2. Lacteals: endotheliallined lymphatic channels w/in villi that uptake lipid droplets
Features of Mucosal Muscularis Mucosae in SI Boundary b/t mucosa and submucosa Composed of two thin layers of smooth muscle
Duodenum Characterized by submucosal Brunner s Glands (protect duodenum by neutralizing stomach acid)
Duodenum vs Jejunum and Ileum Submucosal Brunner s Glands No Brunner s Glands
Large Intestine Function: Reabsorbs water and electrolytes and eliminates undigested food and waste
Large vs Small Intestine Similarities Same Layers Mucosa Submucosa Muscularis Externa Adventitia/Serosa Same Epithelial Cells -Enterocytes -Goblet cells -Enteroendocrine cells -M cells BUT Differences Large Intestine has NO plicae circularis and NO villi Large Intestine has MORE GOBLET cells NO PANETH cells in LI
Large vs Small Intestine
Junction: Rectum and Anal Canal Rectum -simple columnar epithelium with goblet cells -glands Recto-Anal Junction -stratified columnar/ cuboidal epithelium -No glands
Recto-Anal Junction -stratified columnar/cuboidal epithelium - as move toward anus, more stratified squamous - at perineum, stratified squamous epithelia is keratinized
Anal Transition Zone Stratified Columnar/Cuboidal Anal Stratified Squamous Epithelium
Hemorrhagic Vessels These vessels are in the submucosa of the anal canal. When dilated, they are internal hemorrhoids. Hemorrhagic vessel
Question 1 The organ shown : a. Digests carbohydrates and proteins b. Contains paneth cells c. Reabsorbs water d. Conjugates bile
Question 2 Villi are present in both images: True or False
Question 3 Which sequence is in the correct oral to rectum/anal order? B A D C