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Digestive Tract By: Yasmeen Cabrera

Digestive tract (Histology)

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Page 1: Digestive tract (Histology)

Digestive Tract By: Yasmeen Cabrera

Page 2: Digestive tract (Histology)

Digestive System• In the human digestive system, large organic

masses are broken down into smaller particles that the body can use as fuel.

• The breakdown of the nutrients requires the coordination of several enzymes secreted from specialized cells within the mouth, stomach, intestines, and liver.

• The major organs or structures that coordinate digestion within the human body include the mouth, esophagus, stomach, small and large intestines, and liver.

Page 3: Digestive tract (Histology)

Digestive System• Digestive Tract• Layer• Cells of the Stomach• Specializations of the Mucosal Surface of Small Intestine• Cells of the Small and Large Intestine

• Digestive Glands• Pancreas• Liver• Gall Bladder

Page 4: Digestive tract (Histology)

Digestive Tract• The digestive tract, from the esophagus to the

anus, is characterized by a wall with four layers, or tunics.

Page 5: Digestive tract (Histology)

A. Layers of the Digestive Tract

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Microscopic View of the GI Tract

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B. Cells of the Stomach

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C. Specialization of the Mucosal Surface of Small Intestine

• The mucosa of the small intestine is highly modified. • The luminal surface is completely covered by a number of

finger- or leaf-like projections called villi, 0.5-1.5 mm in length.

• The core of a villus is an extension of the lamina propria, and its surface is covered by a simple columnar epithelium.

• Opening onto the luminal surface at the bases of the villi are simple tubular structures called intestinal glands or crypts of Lieberkuhn.

• The crypts extend downward toward the muscularis mucosae.

• The simple columnar epithelium lining them is continuous with that covering the villi.

Page 9: Digestive tract (Histology)

• Mucosal folds: The inner surface of the small intestine is not flat, but thrown into circular folds. This not only increases the surface area, but helps regulate the flow of digested food through your intestine.

• Villi: The folds form numerous tiny projections which stick out into the open space inside your small intestine (or lumen), and are covered with cells that help absorb nutrients from the food that passes through.

• Microvilli: The cells on the villi are packed full of tiny hairlike structures called microvilli. This helps increase the surface of each individual cell, meaning that 5.

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Mucosal Folds Villi

Microvilli

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D. Cells of the Small and Large Intestine

• Small Intestine•The epithelium of the villi is made up of tall columnar absorptive cells called enterocytes, and goblet cells, which secrete mucin, for lubrication of the intestinal contents, and protection of the epithelium.• Enterocytes or absorptive cells - tall

columnar cells with microvilli and a basal nucleus, specialized for the transport of substances. • Goblet cells- These mucus-secreting

cells are the second most abundant epithelial cell.

Page 12: Digestive tract (Histology)

• Paneth cells (at the base of the crypts) - they have a defensive function, and stain intensely eosinophilic, due to secretory granules of antimicrobial peptides called defensins, as well as lysozyme and phospholipase A. These cells last for several weeks.• Endocrine cells, (also eosinophilic) which

produce secretin, somatostatin, enteroglucagon and serotonin. One type of endocrine cell for each type of hormone.• Stem cells, found at the base of the crypts,

which divide continuously to replace enterocytes (every 2-3 days), goblet cells, paneth cells and neuroendocrine cells. • Intraepithelial lymphocytes (mostly T-cells).

Page 13: Digestive tract (Histology)

Microscopic View of Small Intestinal Cells

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• Large Intestine•Goblet cells• are scattered among the absorptive cells

in the epithelium of the small intestine and colon. • These epithelial cells are specialized for

secretion of mucus, which facilitates passage of material through the bowel.

•Enterocytes• are the predominant epithelial cell type

lining the lumen of the small intestine and colon. • These cells are specialized for absorption

of nutrients across the apical plasma membrane and export of these same nutrients across the basal plasma membrane.

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• Chief Cells• secret pepsinogen

• Stem Cell•Stem cells of the intestinal mucosa line the walls of the crypts and continually replenish the intestinal epithelium • completely replacing all the absorptive cells and goblet cells approximate once every four days.•These cells are inconspicuous when resting, but mitotic figures (intensely basophilic condensed chromatin) are common and easily noticed in the crypts of the small intestine.

Page 16: Digestive tract (Histology)

Microscopic View of Large Intestinal Cells

Page 17: Digestive tract (Histology)

Digestive Glands• Pancreas• The pancreas is a long flattened

gland located deep in the belly (abdomen). • It is a vital part of the digestive

system and a critical controller of blood sugar levels. • The bulk of the pancreas is

composed of “exocrine” cells that produce enzymes to help with the digestion of food. These exocrine cells release their enzymes into a series of progressively larger tubes (called ducts) that eventually join together to form the main pancreatic duct. • The secretions of the acini empty into

ducts lined with a simple low cuboidal epithelium, which becomes stratified cuboidal in the larger ducts.

Page 18: Digestive tract (Histology)

• Liver• The liver has a thin capsule of dense

connective tissue, and a visceral (inferior) layer of peritoneal mesothelium, and is divided into left and right lobes.• It is a major metabolic organ, and is

important for degrading alcohol and drugs. • It stores glycogen, secretes glucose,

plasma proteins and lipoproteins into the blood, and secretes bilirubin (by-produce of haemoglobin), secretory IgA, and bile salts (which emulsify fats) as components of bile (endocrine secretion of the liver).

Page 19: Digestive tract (Histology)

• Gall Bladder• The gall bladder is a

simple muscular sac, lined by a simple columnar epithelium. • It receives and stores

bile from the liver via the hepatic and then cystic duct, and can store about 50 to 100ml in humans.

Page 20: Digestive tract (Histology)

Diseases of the Digestive Tract

• Celiac Disease• is an autoimmune disorder of the small intestine that occurs in genetically predisposed people of all ages from middle infancy onward. Symptoms include pain and discomfort in the digestive tract, chronic constipation and diarrhoea, failure to thrive (in children), anaemia and fatigue, but these may be absent, and symptoms in other organ systems have been described. Vitamin deficiencies are often noted in people with coeliac disease owing to the reduced ability of the small intestine to properly absorb nutrients from food.

Page 21: Digestive tract (Histology)

Biopsy of small bowel showing coeliac disease manifested by blunting of villi, crypt

hyperplasia, and lymphocyte infiltration of crypts

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• Inflammatory Bowel Disease• Inflammatory bowel disease (IBD) occurs when the small or large

intestine (bowel) becomes inflamed. When the intestine is inflamed, it becomes swollen and painful. This causes symptoms such as diarrhea, bloating, stomach cramps and, sometimes, weight loss.

• There are two main types of IBD: Crohn’s disease and ulcerative colitis.

• Crohn’s disease can affect any part of the GI tract . It causes the walls of the affected part to thicken and develop a cobblestone-like surface. Depending on where Crohn’s disease occurs, symptoms can include stomach pain, vomiting, loss of appetite, bloody diarrhea, poor growth and mouth ulcers.

• Ulcerative colitis is similar to Crohn’s disease, but it affects only the colon (large intestine). When a person has ulcerative colitis, the lining of their colon develops ulcers, or tears. This can lead to stomach pain, bloody diarrhea, bleeding from tears around the anus, weight loss and decreased appetite.

Page 23: Digestive tract (Histology)

Crohn’s Disease

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Normal Colon VS Ulcerative Colitis

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• Irritable Bowel Syndrome • is a chronic (long-term) condition that affects the large

and small intestine. In IBS, food moves through the colon too slowly, too quickly or unpredictably. As a result, the colon does not absorb the right amount of water from food. This can lead to diarrhea or constipation.