Histology of the Digestive System Same four layers

Histology of the Digestive System

Same four layers from esophagus to anal canal 1. 2. 3. 4. Mucosa Submucosa Muscularis externa Serosa from lumen (inside) out

The mucosa Three sub-layers 1. Lining epithelium absorbs nutrients, secretes mucus 2. Lamina propria Loose connective tissue with nourishing and absorbing capillaries , mucosaassociated lymphoid tissue 3. Muscularis mucosae local movements

The submucosa • Connective tissue containing major blood and lymphatic vessels and nerves • Many elastic fibers so gut can regain shape after food passes

The muscularis externa • Two layers of smooth muscle ? ? !!!!! Inner circular layer Outer longitudinal layer

The serosa ? ? ? adventitia ? ?

Esophagus • Epithelium: nonkeratinized stratified squamous epithelium • Muscle (muscularis externa) changes as it goes down – Superior 1/3 of esophagus: skeletal muscle (like pharynx) – Middle 1/3 mixture of skeletal and smooth muscle – Inferior 1/3 smooth muscle (as in stomach and intestines

Stomach Mucosa • Simple columnar epithelium: • Gastric pits opening into gastric glands – Mucus neck cells – Parietal cells • HCL • Intrinsic factor (for B 12 absorption) – Chief cells • Pepsinogen (activated to pepsin with HCL) • Stimulated by gastrin: a stomach hormone

• Submucosa Connective tissue. • Muscularis 3 layers: Outer > Longitudinal Middle > Circular Inner > Oblique

Mucosa ? ? ? Submucosa ? ? ? Muscularis ? ?

Small intestine designed for absorption -Structural modifications also increase absorptive area -Circular folds (plicae circulares) -Villi (fingerlike projections) 1 mm high – simple columnar epithelium: velvety -Microvilli

Large intestine • No villi – Fewer nutrients absorbed • “Columnar cells” • A lot of goblet cells for mucus • More lymphoid tissue – A lot of bacteria in stool

Liver histology • Liver lobules (about one million of them) – Hexagonal solid made of sheets of hepatocytes (liver cells) around a central vein – Corners of lobules have “portal triads”

• Portal triad – Portal arteriole – Portal venule • Branch of hepatic portal vein • Delivers substances from intestines for processing by hepatocytes – Bile duct • Carries bile away • Liver sinusoids – Large capillaries between plates of hepatocytes – Contribute to central vein and ultimately to hepatic veins and IVC • Kupffer cells – Liver macrophages – Old blood cells and microorganisms removed

Pancreas exocrine and endocrine