Download Practical Histology Digestive system Components: Digestive Tract

Practical Histology
Digestive system
 Components:
1. Digestive Tract: Gastrointestinal (Gl) tract (Alimentary canal)
Mouth, pharynx, and esophagus, stomach, small intestine, and large
intestine (colon)
2. Accessory Organs:
Teeth, tongue, salivary glands, pancreas, liver, and gallbladder
 Functions of the Digestive System
1.
2.
3.
4.
5.
6.
Ingestion
Mechanical processing
Chemical digestion
Secretion
Absorption
Excretion
 Basic Histological Organization

Layers
1. Mucosa (mucous membrane). Innermost layer facing the lumen.
a) Epithelium. Either a stratified squamous moist or a simple columnar
epithelium.
b) Lamina propria. Loose connective tissue; usually possesses digestive
glands.
c) Muscularis mucosae of smooth muscle is usually present.
2. Submucosa. Denser connective tissue than the lamina propria. The submucosa
possesses glands in the esophagus and duodenum.
3. Muscularis externa of smooth muscle is usually arranged into inner circular
and outer longitudinal layers.
4. Serosa (serous membrane) is present if the organ protrudes into the peritoneal
cavity, or an adventitia (only the connective tissue portion of the serosa) is
present if the organ is retroperitoneal.
 The Esophagus
1. The esophagus is a hollow muscular tube begins posterior to the
cricoid cartilage
2. The primary function of the esophagus is to convey solid food and
liquids to the stomach.
3. The mucosa contains a nonkeratinized, stratified squamous epithelium.
4. The mucosa and submucosa are thrown into large folds that extend the
length of the esophagus.
5. The muscularis mucosae consists of an irregular layer of smooth
muscle.
6. The submucosa contains scattered esophageal glands, which produce a
mucous secretion that reduces friction between the bolus and the
esophageal lining.
7. The muscularis externa has the usual inner circular and outer
longitudinal layers.
8. Lacks serosa , anchored by an adventitia
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Practical Histology
Digestive system
 The stomach
1. The stomach is a holding tank in which food is saturated with gastric juices
and exposed to stomach acids and the digestive effects of pepsin.
2. Functions
a) Bulk storage of undigested food
b) Mechanical breakdown of food
c) Disruption of chemical bonds via acids and enzymes
d) Production of intrinsic factor, such as glycoprotein required for the
absorption of vitamin B12.
 Histology of the stomach
1. Simple columnar epithelium facing the lumen is modified so that all cells
secrete mucus, forming a sheet gland that protects the stomach from its acidic
environment.
2. Gastric pit. A channel formed by the invagination of the surface epithelium
into the underlying lamina propria.
3. The gastric glands simple, branched tubular glands begin at a gastric pit and
extend through the lamina propria to the muscularis mucosae.
4. Gastric glands are dominated by two types of secretory cells:
a) Parietal cells secrete hydrochloric acid .
b) Chief cells are most abundant near the base of a gastric gland. These cells
secrete pepsinogen
5. The muscularis mucosae and muscularis externa of the stomach contain extra
layers of smooth muscle cells in addition to the usual circular and longitudinal
layers.
6. Serosa: thin layer composed of blood vessels, adipose cells and nerves
 The Small Intestine
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
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Subdivided into duodenum, jejunum, and ileum.
Common features of the small intestine
1. Mucosal epithelium is composed of:
a) Absorptive cells, forming a simple columnar epithelium with microvilli,
absorb digested food.
b) Goblet cells (unicellular glands) are interspersed among absorptive cells
and secrete mucus.
2. Intestinal glands (crypts of Lieberkuhn) are simple tubular glands that begin at
the bases of the villi in the mucosa and extend through the lamina propria to
the muscularis mucosae.
3. Muscularis externa of inner circular and outer longitudinal layers
4. Serosa covers all of small intestine except for the beginning of the duodenum,
which is retroperitoneal and possesses an adventitia.
5. The intestinal lining bears a series of transverse folds called plicae, or plicae
circulares. Which are permanent features that do not disappear when the small
intestine fills.
Practical Histology
Digestive system
The duodenum
1. It the first segment of small intestine closest to the stomach
2. Function: receives chyme from the stomach and digestive secretions from the
pancreas and liver
3. has numerous mucous glands in submucosa layer called Brunner’s glands,
which produce copious quantities of mucus when chyme arrives from the
stomach.
4. The duodenum has few plicae, and their villi are small.
The jejunum
1. The second segment of small intestine
2. Composed of mucosae, submucosae (plicae circulares), villi (folds of lamina
propria), and serosa (visceral peritoneum)
3. Functions: The bulk of chemical digestion and nutrient absorption occurs in
the jejunum
The ileum
1. the final segment of the small intestine
2. oval or round lymphoid follicles (similar to lymph nodes) located in the
lamina propria and extending into the submucosa called Peyer's patches
3. Peyer's patches they differentiate the ileum from the duodenum and jejunum
4. function of these cells is to defend the body against inadequately digested food
particles crossing the gut wall and entering the blood.
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