Hassall's corpuscles are a unique and characteristic feature of: (A) spleen. (B) thymus. (C) lymph nodes. (D) bone marrow. (E) tonsils.

Lymphatic nodules are found in: (A) cortex of lymph nodes (B) tonsils (C) spleen (D) respiratory and gastrointestinal mucosa. (E) all of the above

Which of the following statements concerning epithelial reticular cells of the thymus is FALSE ? (A) They are supporting cells. (B) They are not located in the thymic medulla. (C) They have long processes. (D) They assist in forming the blood-thymus barrier.

Department of Histology and Embryology Digestive System Department of Histology and Embryology Yu Hongwei

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 small intestine.

Digestive System oral cavity, esophagus, stomach, small and large intestines, rectum, and anus. Digestive tract: small gland: fundis gland, small intestinal gland large gland: salivary gland, pancreas, liver Digestive glands:

Digestive System Figure 14.1 Slide 14.1 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 connective tissue that is rich capillaries and lymphatic tissues. 2.Lamina propria: 3.Muscularis mucosae: is a thin layer smooth muscle fibers

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

Gastrointestinal (GI) Tract Wall Figure 14.2 Slide 14.2A Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestive System Function Mechanical processing and movement: chewing, mixing Secretion: fluid, digestive enzymes and hormones, bile, acid, alkali, mucus Digestion: breaking down food to smallest absorbable units Absorption: through mucosa, into blood or lymph vessels Elimination: undigested material eliminated Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc. Slide 14.3

 Tongue 1.Layers 2.Papillae 3.Taste bud Skeletal muscle fibers Stratified squamous epithelium Lamina propria, Connective tissue Circumvallate papillae Filiform papillae Fungiform papillae Foliate papillae 3.Taste bud

2.Papillae Circumvallate papillae Filiform papillae Fungiform papillae Foliate papillae

3.Taste bud Figure. showing the taste cells and the taste pore. The drawing also illustrates several cell types (basal, taste, and supporting) and afferent nerve fibers that, upon stimulation, will transmit the sensory information to the central gustatory neurons.

Taste bud These are clustered in taste buds. Each taste bud has a pore that opens out to the surface of the tongue enabling molecules and ions taken into the mouth.

There are five primary taste sensations: salty sour sweet bitter Taste bud There are five primary taste sensations: salty sour sweet bitter Umami is the response to salts of glutamic acid,a flavor enhancer used in many processed meats and cheeses.

Taste bud

Ⅰ.Salivary glands Minor salivary glands Major salivary glands Parotid, submandibular and sublingual glands

Source: parotid, submandibular, sublingual salivary glands Functions Produce saliva, to wet and lubricate the oral cavity and initiate the digestion of carbohydrates and lipids, and protective functions Saliva Source: parotid, submandibular, sublingual salivary glands Composition: mucin, salivary amylase, bicarbonate, lysozyme

1. General structure

myoepithelial cells they are contractile epithelial cells, they are located between the secretory cells and the basement membrane.   Each myoepithelial cell has long cytoplasmic processes which wrap around a secretory unit.  Hence, contraction of the myoepithelial processes can squeeze secretory product from the secretory unit into its duct.

Serous acini

Mucous acini

Mixed acini

2. Type-specific structure Parotid glands Contain only serous acini. Submandibular glands Serous demilunes are numerous. Have mucous acini associated with serous demilunes. Sublingual glands Are composed almost exclusively of mucous acini.

Parotid glands

Submandibular glands

Sublingual glands

Duct system Intercalated ducts Striated ducts Excretory ducts lined by a low cuboidal epithelium, many contain myoepithelial cells. Striated ducts lined by columnar cells. They have prominent basal surface invaginations associated with many mitochondria. Excretory ducts Lined simple cuboidal, Are the larger ducts that empty into the oral cavity.

A.Mucosa B.Submucosa C.Muscularis D.Adventitia ESOPHAGUS 1.Epithelium: 2.Lamina propria: 3.Muscularis mucosae: B.Submucosa dense CT (Esophageal submucosal glands, blood) The upper one third Skeletal muscle C.Muscularis The middle third Intermix The distal third Smooth muscle D.Adventitia

Esophageal mucosa Esophageal submucosal glands

Gastroesophageal Reflux Disease Reflux of gastric contents into esophagus Result of Transient LES relaxations

Mucosa Submucosa Muscularis Adventitia Ⅰ. Stomach 1.Epithelium: Mucosa 2.Lamina propria: Glands, lymphoid tissue 3.Muscularis mucosae: Smooth muscle Submucosa DCT Muscularis Three layers Adventitia

Regions of the stomach and their histological structure.

C. Glands 1.Surface mucous cells 2.Mucous neck cells 3. Chief cells Glands are present throughout the fundus and corpus. pit 1.Surface mucous cells 2.Mucous neck cells glands 3. Chief cells 4.Parietal cells 5. Stem cells 6.Endocrine cells

1. Surface mucous cells a. They form a simple columnar epithelium that covers the gastric mucosa. b. They secrete a continuous mucous layer that prevents the proteinase solutions in the stomach.

2.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.

3. 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

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

5.Stem cells Found in the isthmus and neck regions. 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.

6. Endocrine cells a. In the neck and base of gastric glands

Stomach Function Functions: food storage, digestion, regulation of delivery. Gastric juice: --Hydrochloric acid: breaks down large of food Intrinsic factor; made by cells making acid, Mucus: protects stomach lining from acid Pepsinogen: with acid, breakdown the protein Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc. Slide 14.9B

pernicious anaemia. Vitamin B12's primary functions are in the formation of RBC and the maintenence of a nervous system. Absorption of B12 requires the secretion of intrinsic factor. Certain people are unable to produce intrinsic factor.

What prevents the proteolytic enzymes and low pH from damaging the stomach? A thick coat of bicarbonate containing mucus coats the stomach wall. Mucosal epithelial cells are joined by tight junctions Damaged epithelial cells are shed & quickly replaced.

Ⅱ. 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.

B. Mucosa 1. The epithelium of intestine villi 2. Intestinal glands (intestinal crypts) 3. Five types of cells in intestinal mucosal epithelium Absorptive cells Goblet cells Paneth’s cells Endocrine cells Microfold cells

a. Absorptive cells (Enterocytes) Tall columnar an oval N in the basal of the cell striated border at the apex microvilli Increasing the area Absorption

absorptive cell The function of the columnar absorptive cell is the absorption of water, minerals, amino acids and simple sugars.    

Absorption of Proteins and Carbohydrates Figure 14.13 Slide 14.14A

Absorption of Fats Figure 14.14 Slide 14.14B

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

The Paneth cells occur in small groups at the base of the intestinal crypt. These have both phagocytic and secretory properties They secrete lysozyme (which dissolves the cell wall of bacteria) and secretory IgA.

Peyer‘s patches Peyer‘s patch Appears as a dome shape area lack of villi. the covering epithelium consist of M cells. villi Peyer‘s patch

M cells (microfold cells) are specialized epithelial cells overlying the lymphoid follicles of Peyer‘s patches. M cells can endocytose antigens and transport them to the underlying macrophages and lymphoid cells. Which then migrate to other compartments of lymphoid system (nodes).

1. intestinal villi Absorptive cells epithelium Goblet cells Blood capillary Smooth muscle Lamina propria Lymphatic capillary Lymphocytes Plasma cells macrophages

2. Intestine glands (intestine crypts) Absorptive cells Goblet cells Paneth’s cells epithelium Enteroendocrine cells Stem cells

Small Intestine Functions: Digestion: neutralize acid from stomach, add digestive enzymes and bile, break proteins, carbohydrates and lipids to absorbable materials Absorption: 95% of food absorbed here Slide 14.10B

Location: in submucosa of duodenum. BRUNNER GLANDS Location: in submucosa of duodenum. Function: protection the proximal small intestine by neutralizing the acid-containing chyme.

Ⅲ. Large intestine The mucous membrane does differ from that of the small intestine in several aspects:     1. There are no villi.     2. The intestinal crypts are larger, more numerous and more densely packed.     3. One-fourth of the epithelial cells are goblet cells. Thus the large intestine is well lubricated             4. There are no Paneth cells.

Large intestine

Appendix

Appendicitis It is thought that the opening from the appendix into the cecum becomes blocked. The lymphatic tissue in the Appendix may swell and block the Appendix. Bacteria which normally are found within the appendix then begin to invade the wall of the Appendix.

Homework Describe the structure of the stomach fundus gland. Describe the cell type of the small intestine.