Digestive system 1

From the esophagus on… The rest of the digestive system from the esophagus onward is organized into four specific layers: Layer 1 – Mucosa A. Mucosal epithelium B. Lamina propria C. Muscularis mucosae Layer 2 – Submucosa Layer 3 – Muscularis externa Layer 4 – Adventitia or serosa 2

Esophagus Muscular tube (skeletal and smooth muscle) line with nonkeratinized stratified squamous epithelium 3

Digestive system 4

Stomach 1 - Villi 2 - submucosa 3 - muscularis propria 7 - gastric pits in the mucosa 5

Stomach Main portion of the stomach (fundus) have five epithelial cell types with distinct function Simple columnar epithelial cells (surface mucous cells) – secrete bicarbonate-rich mucus to protect the gastric tissue Mucous neck cells – secrete mucous and serve as stem cells Parietal cells – Functions to secrete a fluid rich in acid have a centrally located nucleus, brightly staining, eosinophilic cytoplasm and a distinctive round shape Have deep cytoplasmic invaginations called canaliculi that have long, flexible microvilli as well as abundance of mitochondria 6

Parietal Cells 7

Stomach (cont’d) Main portion of the stomach (fundus) have five epithelial cell types with distinct function Chief cell (at the bottom of gastric pit) Secrete enzymes such as pepsin and rennin to help digest food proteins basophilic Neuroendocrine cell Light- staining cytoplasm Produces peptide hormones including gastrin stimulate acid secretion by parietal cells 8

Stomach 9

Digestive system 10

Intestines Lined by a simple columnar epithelium, that similar to the stomach, is highly folded 11 jejunum

Small Intestines Mucosa of the small intestines posess finger-shaped epithelial projections called villi Villi serve as an expanded surface to absorb nutrients Small intestines divided into three regions: Duodenum Jejunum Ileum 12

Duodenum Short portion of small intestines Broad villi Submucosa contains mucous glands call Brunner’s gland Secrete alkaline mucus that neutralizes acid from the stomach 13

Jejunum 14 -narrow and taller villi-functions in absorption -no Brunner’s glands

Ileum Distinguishing feature of ileum is the presence of unusually prominent masses of lymphocytes, macrophages and dendritic cells in the submucosa called the Peyer’s patch Presence linked to increase in the mass of intraluminal microorganisms along the length of the gut Reflects hostile environment between the host epithelium and bacteria of the gut 15

Ileum 16

Digestive system 17

Large Intestine (Colon) Histologic feature of the large intestine are similar to small intestine except for: The mucosa of large intestine possess intestinal gland but lack villi Percentage of goblet cells within the lining of epithelium is much higher in the large intestine This is due to the absorptive ability of the intestine 9 Liters of fluid enters gut daily – only 100 ml (1%) leaves the body in stool – rest reabsorbed 18

Large Intestines 19

Hirschsprung’s disease Mature neurons are present in the gut These are derived during development from a stem cell population called neural crest cells Hirschsprung’s disease Affects 1 in 5000 newborns The neural network of the colon does not form Colonic ganglia or ganglion of the myenteric plexus do not form As a result, portions of the colon do not contract The colon becomes overfilled with material and is very painful and debilitating 20

Questions 21