• 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.

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 glands:

Digestive SystemDigestive System

oral cavity, esophagus, stomach, small and large intestines, rectum, and anus.

small gland: fundis gland, small intestinal gland

large gland: salivary gland, pancreas, liver

Digestive tract:

Figure 14.1Slide 14.1Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestive System

Digestive TractDigestive TractⅠⅠ.GENERAL STRUCTURE OF THE DIGESTIVE TRACT.GENERAL STRUCTURE OF THE DIGESTIVE TRACT

Lamina propria

Submucosa

Muscularis

Adventitia

Mucosa

Epithelium

Muscularis mucosae

A.MucosA.Mucosaa

2.Lamina propria:

is highly variable.

3.Muscularis mucosae:

1.Epithelium:

contains connective tissue that is rich capillaries and lymphatic

tissues.

is a thin layer smooth muscle fibers

B.SubmucoB.Submucosasadense connective tissue, many blood , lymph vessels , glands

C.MuscularC.Muscularisissmooth muscle fibers

D.AdventitD.Adventitiaia

Figure 14.2Slide 14.2ACopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Gastrointestinal (GI) Tract Wall

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

Slide 14.3Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestive System Function

TongueTongue

2.Papillae

1.Layers

Skeletal muscle fibers

Stratified squamous epithelium

Lamina propria, Connective tissue

Circumvallate papillae

Filiform papillae

Fungiform papillae

Foliate papillae

3.Taste bud

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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.

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

ⅠⅠ.Salivary glands

Minor salivary glands

Major salivary glands

Parotid, submandibular and sublingual 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

Sublingual glands

Parotid glands

Submandibular glands

Contain only serous acini.

Serous demilunes are numerous.

Have mucous acini associated with serous demilunes.

Are composed almost exclusively of mucous acini.

Parotid glands

Submandibular glands

Sublingual glands

Duct Duct systemsystem

Intercalated ducts

Striated ducts

Excretory ducts

lined by a low cuboidal epithelium, many contain myoepithelial cells.

lined by columnar cells. They have prominent basal surface invaginations associated with many mitochondria.

Lined simple cuboidal, Are the larger ducts that empty into the oral cavity.

ESOPHAGUSESOPHAGUS

A.MucosA.Mucosaa

2.Lamina propria:

B.SubmucB.Submucosaosa

C.MuscularC.Muscularisis

D.AdventitD.Adventitiaia

1.Epithelium:

Skeletal muscle

dense CT (Esophageal submucosal glands, blood)

3.Muscularis mucosae:

The middle third

The distal third

The upper one third

Intermix

Smooth muscle

Esophageal mucosa Esophageal submucosal gland

s

Gastroesophageal Reflux Disease

– Reflux of gastric contents into esophagus– Result of Transient LES relaxations

ⅠⅠ. Stomach. Stomach

MucoMucosasa

2.Lamina propria:

SubmucoSubmucosasa

MuscularMuscularisis

AdventitiAdventitiaa

1.Epithelium:

Glands, lymphoid tissue

DCT

3.Muscularis mucosae: Smooth muscle

Three layers

Regions of the stomach and their histological structure.

C. C. GlandsGlandsGlands are present throughout the fundus and corpus.

5. Stem cells5. Stem cells

1.Surface mucous cells1.Surface mucous cells

2.Mucous neck cells2.Mucous neck cells

4.Parietal cells4.Parietal cells

6.Endocrine cells6.Endocrine cells

3. Chief cells3. Chief cells

pit

glands

1. Surface mucous cells1. 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 cells2.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.

Diagram of a chief cell

3. Chief cells3. 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 parietal cell

4. Parietal cells4. Parietal cells

a. Rounded or pyramidal cells, intensely eosinophilic cytoplasm.

Resting---tubulovesicular---few microvilliActivity---canaliculus---more microvilli

b. Parietal cells secrete HCl and Intrinsic factor

5.Stem cells5.Stem cells

a. Found in the isthmus and 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.

6. Endocrine cells6. Endocrine cells

a. In the neck and base of gastric glands

• 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

Slide 14.9BCopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Stomach Function

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.

– 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.

What prevents the proteolytic enzymes andlow pH from damaging the stomach?

Ⅱ. Small intestine

A. Basic A. Basic anatomyanatomy

duodenum, jejunum, duodenum, jejunum, ileumileum

Plicae circulares, villi, aPlicae circulares, villi, and microvilli increase tnd microvilli increase the absorptive surface ahe absorptive surface area of small intestine.rea of small intestine.

Structure of small intestine

Figure 14.9Slide 14.10ACopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

The Wall of the Small Intestine

B. B. MucosaMucosa

1. The epithelium of intestine villi2. 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)

microvilli

Absorption

Tall columnar

an oval N in the basal of the cell

striated border at the apex

Increasing the area

absorptive cell

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

Figure 14.13Slide 14.14A

Absorption of Proteins and Carbohydrates

Figure 14.14Slide 14.14B

Absorption of Fats

increasing

b. Goblet cells

Interspersed between the absorptive cells

duodenum

Goblet cell secretion of mucin .The mucous lubricates and forms a barrier which protects the mucosal epithelium from potentially noxious intraluminal substances.

jejunum

ileum

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

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

Lamina propria

Absorptive cells

Goblet cellsepithelium

Blood capillarySmooth muscleLymphatic capillary

LymphocytesPlasma cellsmacrophages

2. Intestine glands (intestine crypts)

Absorptive cells

Goblet cells

epithelium Enteroendocrine cells

Paneth’s cells

Stem cells

Slide 14.10B

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

BRUNNER GLANDS

Location: in submucosa of duodenum.

Function: protection the proximal small intestine by neutralizing the acid-c

ontaining 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.