Department of Histology and Embryology Digestive System Department of Histology and Embryology Zhang Xi-Mei

What is the Digestion? Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy. Digestion begins in the mouth when we chew and swallow, and is completed in the large intestine.

Digestive System Digestive tract: Digestive glands: Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestive Tract Ⅰ.GENERAL STRUCTURE OF THE DIGESTIVE TRACT Epithelium Mucosa Lamina propria Muscularis mucosae Submucosa Muscularis Adventitia

A.Mucosa 1.Epithelium: is highly variable. contains loose connective tissue that is rich capillaries, lymphatic tissues, and glands. 2.Lamina propria: 3.Muscularis mucosae: smooth muscle fibers.

B.Submucosa C.Muscularis D.Adventitia dense connective tissue, many blood , lymph vessels. C.Muscularis smooth muscle fibers D.Adventitia Serosa or fibrosa.

ESOPHAGUS A.Mucosa B.Submucosa C.Muscularis D.Adventitia 1.Epithelium:nonkeratinized stratified squamous epithelium. A.Mucosa 2.Lamina propria: esophageal cardiac glands. 3.Muscularis mucosae: longitudinal smooth muscles. dense CT Esophageal glands, mucus-secreting. B.Submucosa The upper one third Skeletal muscle C.Muscularis The middle one third Intermix The distal one third Smooth muscle D.Adventitia Fibrosa.

Esophageal mucosa Esophageal glands

STOMACH Mucosa Submucosa Muscularis Adventitia 1.Epithelium: simple columnar epihelium surface mucous cells, form gastric pits. 1.Epithelium: Mucosa 2.Lamina propria: Glands, lymphoid tissue. 3.Muscularis mucosae: Smooth muscle. Submucosa Dense connective tissue. Oblique Circular longitudinal Muscularis Three layers smooth muscles: Adventitia Serosa.

Surface mucous cells a. They form a simple columnar epithelium that covers the gastric mucosa. b. They secrete a continuous mucous layer that protects stomach lining from acid.

Regions of the stomach and their histological structure

Glands 1.Mucous neck cells 2.Chief cells 3.Parietal cells 4.Stem cells Glands are present throughout the fundus and body, branched, tubular gastric glands. pit 1.Mucous neck cells glands 2.Chief cells 3.Parietal cells 4.Stem cells 5.Enteroendocrine cells

Parietal cells Chief cells Enteroendocrine cells

Mucous neck cells a. They are present between parietal cells in the necks of gastric glands. b. They can secrete mucous. They are difficult to distinguish from chief cells in plain H&E stained section.

Chief cells a. In the lower region of tubular glands, and have the characteristics of protein-synthesizing cells. b. The granules in their cytoplasm contain the inactive enzyme pepsinogen. pepsinogen pepsin H+ Chief cell Parietal cell Diagram of a chief cell

Parietal cells a. Rounded or pyramidal cells, intensely eosinophilic cytoplasm. Resting---tubulovesicles---few microvilli. Activity---canaliculus---more microvilli. b. Parietal cells secrete HCl and Intrinsic factor. Diagram of a parietal cell

Enteroendocrine cells Stem cells a. Found in neck regions. b.These cells have a high rate of mitosis: some of them move upward to replace the pit and surface mucous cells, other cells migrate more deeply into the glands and differentiate into parietal, chief cells and etc. Enteroendocrine cells In base of gastric glands.

Small intestine A. Basic anatomy duodenum, jejunum, ileum Structure of small intestine Plicae circulares, villi, and microvilli increase the absorptive surface area of small intestine.

The Wall of the Small Intestine Figure 14.9 Slide 14.10A Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Intestinal villi Absorptive cells Epithelium Goblet cells Blood capillary Smooth muscle Lamina propria Lymphatic vessel Lymphatic tissue

Mucosa 1. The epithelium of intestine villi 2. Intestinal glands 3. Five types of cells in intestinal glands Absorptive cells Goblet cells Paneth’s cells Endocrine cells Stem cells

1. Absorptive cells Tall columnar, an oval nucleus in the basal half of the cell, striated border at the apex. Microvilli Increasing the area Absorption The function of the columnar absorptive cell is the absorption of water, minerals, amino acids, simple sugars, and lipid.    

2. Goblet cells Interspersed between the absorptive cells. duodenum increasing jejunum ileum Goblet cell secretion of mucin . The mucus lubricates and forms a barrier which protects the mucosal epithelium from potentially noxious intraluminal substances.

3. Paneth’s cells Occur in small groups at the base of the intestinal glands. They have both large eosinophilic secretory granules. They secrete lysozyme.

Large intestine The mucosa does differ from that of the small intestine in several aspects:     1. There are no villi.     2. The intestinal glands are larger, more numerous and more densely packed.     3. Numerous goblet cells.     4. There are no Paneth’s cells.

Appendix Small, narrow, and irregular lumen. Abundant lymphoid nodules. Fewer and shorter intestinal glands.

Homework Describe the structure of the stomach fundus gland. Describe the cell type of the small intestine gland. Describe the structure of intestinal villi. What prevents the proteolytic enzymes and low pH from damaging the stomach?