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

4 Layers of Digestive SystemMucosa

- Epithelium

- Lamina Propria

- Muscularis Mucosae

Submucosa- Connective tissue, blood vessels,

submucosal plexus

Muscularis Externa- 2 muscle layers, myenteric plexus

Adventitia / Serosa- Loose connective tissue

Plicae Circularis vs VilliBoth 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

Layer 1: Mucosal LayerEpithelium- 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

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

• If stain with PAS, will see the – Glycocalyx– Macrophages– Mast cells

Mucosal Epithelium: Enterocytes

Terminal bar

Microvilli

Terminal web

Cells of Mucosal Epithelium: Enterocytes

Terminal Bar

• 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: Goblet Cells

Cells of Mucosal Epithelium in SI: Paneth Cells

• Located in Crypts of Lieberkuhn (bases of glands of SI b/t villi)

• Antibiotic: Secrete lysozymes

• 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 (cytoplasm), 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: endothelial-lined lymphatic channels w/in villi that uptake lipid droplets

3. M Cells: more squamous epithelial cell (overlies the Peyer’s Patch). No microvilli.

Features of Mucosal Muscularis Mucosae in SI

• Boundary b/t mucosa and submucosa• Composed of two thin layers of smooth muscle

4 Layers of Digestive SystemMucosa

- Epithelium

- Lamina Propria

- Muscularis Mucosae

Submucosa- Connective tissue, blood vessels,

submucosal plexus

Muscularis Externa- 2 muscle layers, myenteric plexus

Adventitia / Serosa- Loose connective tissue

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– Inner - segementation

– Outer - peristalsis

• Myenteric (Auerbach’s) Plexus b/t muscle layersMyenteric Plexus Submucosal Plexus

Layer 4: Adventitia/Serosa

Loose connective tissue