Cui Dongmei. Atlas of Histology: with functional and clinical correlations. 1st ed

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285

Epithelium

Lamina propria

Muscularis mucosae

4. Serosa / adventitia

4. Serosa

1. Mucosa

Longitudinal

muscle

Circular

muscle

Oblique

muscle

1. Mucosa

2. Submucosa

3. Muscularis

externa

3. Muscularis

externa

Inner circular muscle

Outer longitudinal muscle

Epithelium

Lamina propria

Muscularis mucosae

2. Submucosa

1. Mucosa

3. Muscularis

externa

Circular muscle

Longitudinal muscle

band (teniae coli)

4. Serosa/adventitia

Small intestine

Stomach

Large intestine

Figure 15-3. General structure of the wall of the digestive tract.

The wall of the digestive tract can be divided into several basic tunics (layers) based on histologic organization. (1) Mucosa: epithelium,

lamina propria, and muscularis mucosae. The epithelium is composed of simple columnar cells in most of the digestive tract, except

for stratiﬁ ed squamous cells in the esophagus and anal canal. The lamina propria is a layer of loose connective tissue beneath the

epithelium. The muscularis mucosae is a thin layer of smooth muscle; it marks the boundary between the mucosa and the submucosa.

(2) Submucosa: dense irregular connective tissue with blood vessels, lymphatic vessels, and submucosal plexuses (Meissner plexuses).

Mucous glands may be present in this layer. (3) Muscularis externa: two or three layers of smooth muscle. It may also include skeletal

muscle as in the esophagus. There are blood vessels and myenteric (Auerbach) plexuses that lie between the muscle layers. (4) Serosa/

adventitia: The outermost layer is called serosa if it is composed of loose connective tissue with blood vessels and nerves passing

through and is covered by mesothelium. It is called adventitia if covered by a layer of connective tissue without mesothelium lining.

The serosa covers organs within the abdominal or pelvic cavities (intraperitoneal), whereas the adventitia covers organs and serves

as a capsule and attachment between the organs or between an organ and the body wall (retroperitoneal).

1. Mucosa

Epithelium

Lamina propria

Muscularis mucosae

2. Submucosa

Mucous glands and lymphatic nodules may be present

3. Muscularis Externa

Inner circular muscle layer

Outer longitudinal muscle layer

Oblique muscle layer (stomach)

4. Serosa/Adventitia

Serosa: outermost layer composed of connective tissue

covered by mesothelium

Adventitia: outermost layer composed of connective tissue

without mesothelium covering

Tunics (Layers) of the Digestive Tract

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Esophagus

Submucosa

Muscularis

externa

Mucosa

Lumen

Esophageal

glands

Muscularis

mucosae

Figure 15-4A. Overview of the esophagus. H&E, 11

The esophagus can be divided into three regions: the upper,

middle, and lower esophagus. The esophagus is a long tube

that connects the oropharynx to the stomach. Like other parts

of the digestive tract, the esophagus has mucosa, submucosa,

muscularis externa, and adventitia/serosa. (1) The mucosa is

composed of epithelium, lamina propria, and muscularis muco-

sae. The mucosa of the esophagus has folds extending into the

lumen. Stratiﬁ ed squamous epithelium covers the inner surface of

the esophagus. The muscularis mucosae is composed of a single

layer of longitudinal smooth muscle. (2) The submucosa contains

mucous glands called esophageal glands, which secrete mucus and

provide lubrication that aids in swallowing. (3) The muscularis

externa is composed of two layers of muscle organized into inner

circular and outer longitudinal layers. (4) The outermost wall of

the esophagus is commonly covered by adventitia (Fig. 15-4B),

but the lower esophagus is covered by serosa.

Inner circular

(skeletal) muscle

Inner circular

(skeletal) muscle

Outer longitudinal

(skeletal) muscle

Outer longitudinal

(skeletal) muscle

Esophageal

glands

Esophageal

glands

Esophageal

glands

Inner circular muscle

Outer longitudinal muscle

Adventitia

Mucosa

Submucosa

Duct of

glands

Duct of

glands

Esophageal

glands

Inner circular muscle

Outer longitudinal muscle

Adventitia

Mucosa

Submucosa

Figure 15-4B. Upper esophagus. H&E, 17; (upper inset)

40; (lower insets) 216

The upper esophagus, connecting to the oropharynx, is the ﬁ rst

segment of the esophagus. The muscularis externa of the upper

esophagus contains two layers of skeletal muscle. The skeletal

muscle is a voluntary muscle that helps to initiate swallowing.

This muscle is innervated by the glossopharyngeal nerve. The

muscularis externa of the esophagus has distinguishable muscle

components, which vary in different regions. The upper esopha-

gus has skeletal muscle, the middle esophagus has mixed skeletal

and smooth muscles, and the lower esophagus has only smooth

muscle in the muscularis externa. The muscularis externa plays

an important role in producing contractions of the esophagus

that transport food from the oral cavity to the stomach. The

major movement of the esophagus is peristalsis (waves of invol-

untary contraction), as in other parts of the digestive tract. The

initiation of swallowing is voluntary because the upper esophagus

contains only skeletal muscle ﬁ bers in the muscularis externa.

Epithelium

Muscularis

mucosae

Muscularis

mucosae

Epithelium

Lamina

propria

Lamina

propria

Mucosa

Inner circular muscle

Outer longitudinal muscle

Submucosa

Smooth muscle

Skeletal

muscle

Skeletal

muscle

Figure 15-4C. Middle esophagus. H&E, 34; insets (left)

208, (right) 116

The mucosa of the esophagus is covered by a thick layer of

nonkeratinized stratiﬁ ed squamous epithelium, which reﬂ ects

its function in resisting abrasion and friction. The epithe-

lium of the esophagus is continuously renewed by basal cells

that migrate and differentiate from the basal layer. Most of

the digestive tract is covered by simple columnar epithelium;

only the two ends (esophagus and anal canal) are covered by

stratiﬁ ed squamous epithelium. The muscularis externa of the

middle esophagus contains mixed skeletal and smooth muscle

ﬁ bers, which are organized in inner circular and outer longitu-

dinal muscle bundles. Each skeletal muscle ﬁ ber is larger, has

multiple nuclei positioned peripherally, and stains darker than

the smooth muscle ﬁ ber. Each smooth muscle ﬁ ber has a single

nucleus located in the center of the muscle ﬁ ber.

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287

Submucosa

Lamina

propria

Lamina

propria

Esophageal

cardiac glands

Esophageal

cardiac glands

epithelium

Mucosa

Simple

columnar epithelium

Simple

columnar epithelium

Stratified squamous

epithelium

Stratified squamous

epithelium

Muscularis

externa

Muscularis

externa

Mucosa

Figure 15-5A. Lower esophagus, esophagogastric junction

(esophagus on left; stomach on right of illustration). H&E, 11;

insets (upper) 57; (lower) 45

The lower esophagus meets the stomach at the esophagogastric junction.

The esophagus is lined by stratiﬁ ed squamous epithelium, and the car-

diac region of the stomach is lined by simple columnar epithelium. The

change in the lining epithelium reﬂ ects the change in function from a

conduit for food transport to an organ of digestion. The muscularis

externa of the lower esophagus is composed of two layers of smooth

muscle ﬁ bers, which are controlled by the vagus nerve. Mucous glands

are also found in the lamina propria of the lower esophagus (right

inset). These glands are called esophageal cardiac glands. They pro-

duce mucus to protect the epithelial wall of the esophagus from the

reﬂ ux of acidic gastric juices coming from the stomach.

In some patients, the epithelium of the lower esophagus (stratiﬁ ed

squamous epithelium) changes to stomachlike epithelium (simple

columnar epithelium). This pathologic change is called metaplasia.

It is due to the long-term chemical irritation caused by gastroesopha-

geal reﬂ ux.

CLINICAL CORRELATIONS

Figure 15-5B.

Barrett Esophagus. H&E, 48; inset 82

Barrett esophagus is a chronic complication of gastroesophageal

reﬂ

ux disease (GERD), characterized by metaplasia of the strati-

ﬁ ed squamous epithelium of the lower esophagus into a special-

ized glandular epithelium with goblet cells. Patients with Barrett

esophagus have an increased risk of developing adenocarcinoma

(cancer of the esophagus) of the distal esophagus. Common symp-

toms include heartburn, trouble swallowing, and weight loss.

Endoscopically, Barrett esophagus appears as salmon-colored

“tongues” of mucosa extending proximally from the gastroe-

sophageal junction. This photomicrograph shows the metaplastic

glandular epithelium with goblet cells that have replaced the

normal squamous epithelium and the inﬂ ammatory cells (mainly

lymphocytes and plasma cells) inﬁ ltrating the connective tissue.

Figure 15-5C.

Esophageal Carcinoma. H&E, 97

Esophageal carcinoma is a malignant neoplasm that stems

from the epithelial cells lining the inner surface of the esopha-

gus. W

orldwide, squamous cell carcinoma is the most common

type of esophageal cancer, and it is associated with alcohol and

tobacco use in the United States and Europe and with mutagenic

substances and nutritional deﬁ ciencies in less-well-developed

parts of the world. In the United States, adenocarcinoma of the

lower esophagus is becoming more frequent, representing about

50% of esophageal cancers. The major known risk factor for

the development of adenocarcinoma is chronic GERD causing

Barrett esophagus, a metaplastic change in the squamous mucosa

of the distal esophagus to a glandular type of epithelium with

goblet cells. Esophageal cancer is characterized by progressive

difﬁ culty in swallowing, loss of weight, fatigue, and chest pain.

Pathological changes include ulcerations, exophytic masses, and

thickening and narrowing of the lumen. Treatment includes sur-

gery (esophagectomy) and chemotherapy. This photomicrograph

shows a moderately differentiated squamous cell carcinoma with

focal keratin production in the center, called a keratin pearl.

Metaplastic

Barrett

epithelium with

goblet cells

Squamous

epithelium

Goblet cell

Keratin pearl

Squamous cell

carcinoma

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Organ Systems

Stomach

Figure 15-6. Overview of the stomach. H&E, insets (upper left) 5; (lower left) 9; (right) 7.

The stomach is a “J”-shaped hollow organ. It connects the esophagus and duodenum of the small intestine. The stomach initiates

digestion of food and temporarily stores food. It can be divided into four parts: the cardia, fundus, body, and pylorus. Histologically,

stomach tissue can be distinguished by its mucosal glands (glands in the mucosa). (1 and 2) The cardia connects to the esophagus,

and the pylorus connects to the duodenum. These two ends of the stomach have similar histological characteristics. The mucosal

glands of the cardia and pylorus are called cardiac glands and pyloric glands, respectively. Both contain many mucus-secreting

cells and produce mucus, which is a thick, gel-like material that coats the surface of the stomach and protects it from acidic gastric

ﬂ uid. Mucus-secreting cells contribute a small volume to the gastric juices. (3 and 4) The fundus and body of the stomach form the

largest part of the stomach (about two thirds). The mucosal glands in this region are called fundic (gastric) glands. These glands

are composed mainly of parietal and chief cells, which produce large volumes of gastric juices. A small number of various types of

enteroendocrine cells are found at the base of the gastric glands. The gastric juices contain primarily water, HCl, mucus, pepsin, IF,

rennin, and lipase. This is a highly acidic ﬂ uid and plays an important role in digesting food.

Fundus of stomach

Pylorus of stomach

Esophagus

Fundus

Body

Gastric

rugae

Serosa

Submucosa

Mucosa

Oblique

muscle

Circular

muscle

Cardia

Longitudinal

muscle

Pylorus

Duodenum

Esophagogastric

junction

Stomach

I. Cardia

A. Cardiac glands

B. Mucus-secreting cells (produce mucus and lysozyme)

II. Fundus and Body

A. Fundic (gastric) glands

B. Mucous neck cells (secrete mucus)

C. Parietal cells (secrete HCl and gastric IF)

D. Chief cells (secrete pepsinogen, rennin, and lipase)

E. Enteroendocrine (diffuse neuroendocrine) cells (release,

e.g., gastrin, histamine, and serotonin)

III. Pylorus

A. Pyloric glands

B. Mucus-secreting cells (produce mucus and lysozyme)

C. Enteroendocrine cells

D. G cells (secrete gastrin)

E. D cells (release somatostatin)

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Figure 15-7A. Cardiac region, esophagogastric junction. H&E,

34; insets (left) 192, (right) 331

The inner surface of the stomach is lined by columnar epithelium,

which forms a secretory sheath and is composed of mucus- secreting

cells called surface mucous cells. These cells cover the entire inner

surface of the stomach and also line the surface of the gastric pits.

The gastric pits are invaginations of the epithelium and are sur-

rounded by the lamina propria. This is an example of the cardiac

region of the stomach at the esophagogastric junction. The lamina

propria (loose connective tissue) contains cardiac glands. These

glands are branched tubular glands (see Fig. 3-22A,B) and are

composed of mucus-secreting cells. The secretions of the cardiac

glands empty directly into the gastric pits. The cardiac glands con-

sist of mucous cells, which are similar in appearance to the surface

mucous cells. They have basally positioned nuclei and lightly stain-

ing cytoplasm.

Mucus-secreting cells

of cardiac glands

Mucus-secreting cells

of cardiac glands

Esophagus

Gastric

pits

Gastric

pits

Cardiac

glands

Cardiac

glands

Surface

mucous cells

Surface

mucous cells

Stomach

Figure 15-7B. Fundic region of the stomach. H&E, 51;

insets 245

The surface of the fundus region of the stomach is covered by

surface mucous cells, which produce mucus to protect the epi-

thelium from the acidic gastric juice. The fundic glands in the

lamina propria are different from the cardiac glands but similar

to the glands in the body of the stomach. Fundic glands con-

tain stem cells, mucous neck cells (Fig. 15-7C), parietal cells, and

chief cells. The stem cells can differentiate into other types of

cells in the glands. The parietal cells are large, round cells with

centrally positioned nuclei (“fried-egg” appearance). Their cyto-

plasm stains paler than that of chief cells. The parietal cells are

more numerous in the superior half of the fundic glands (upper

inset). The chief cells are small, columnar cells and have darkly

stained cytoplasm. Their nuclei are commonly located at the base

of the cells. The chief cells are more numerous in the inferior half

of the fundic glands (lower inset).

Muscularis

mucosae

Muscularis

mucosae

Muscularis

mucosae

Muscularis

mucosae

Chief cells

Mucosa

Fundic

glands

Fundic

glands

Gastric

pits

Gastric

pits

Epithelium

(mucous

surface cells)

Epithelium

(mucous

surface cells)

Parietal

cells

Parietal

cells

Figure 15-7C. Body region of the stomach. H&E,

34; insets (left) 232; (right upper) 164; (right

lower) 394

Histologically, the body and fundus of the stomach are

similar to one another, and their glands are identical.

They are called fundic (gastric) glands. The mucous

neck cells are commonly found between the parietal

cells at the neck region of the gastric glands. They secrete

acidic mucus. The parietal cells secrete large quanti-

ties of HCl and gastric IF. The parietal cells are also

called oxyntic (acid-forming) cells. The chief cells are

often called zymogenic or peptic cells; their cytoplasm

contains zymogen granules. They secrete pepsinogen

and precursors of rennin and lipase. Enteroendocrine

cells may also be found at the neck and base of the

gastric glands. They release endocrine molecules (e.g.,

serotonin, gastrin, histamine). These cells are similar

in appearance to the enteroendocrine cells in the small

intestine (see Fig. 15-13B). Stem cells may also be

found at neck regions of the gastric glands.

Submucosa

Lamina

propria

Lamina

propria

Mucosa

Fundic

glands

Fundic

glands

Muscularis mucosae

Lumen

Gastric

pits

Gastric

pits

Surface

mucous cells

Surface

mucous cells

Mucous neck cell

Parietal cells

Chief cellChief cell

Chief cell

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CLINICAL CORRELATIONS

Figure 15-8B.

Gastric Ulcer (Peptic Ulcer). H&E, 19

Peptic ulcers are chronic mucosal lesions that occur in the gastro-

intestinal tract. The duodenum and stomach are the most common

sites for ulcers. Causes of these ulcers include Helicobacter pylori

infection, long-term use of nonsteroidal anti-inﬂ ammatory

drugs

and corticosteroids, and cigarette smoking. Epigastric burning or

pain, bleeding, and even perforation are the common signs and

symptoms of the peptic ulcers. Morphologically, peptic ulcers are

usually small, round to oval in shape, less than 4 cm in diameter with

well-deﬁ ned margins without elevation, and have a clean, smooth

base. Histologically, a thin layer of necrotic ﬁ brinoid debris with

neutrophil inﬁ ltration is seen, beneath which lies granulation tis-

sue. Treatments include using H

receptor antagonists; antibiotics;

proton pump inhibitors; and surgery for severe, refractory cases.

Care must be taken to differentiate benign ulcers from malignant

adenocarcinomas, which may appear ulcerated. This image shows

the transition from gastric mucosa to ulcer, showing a ﬁ brinopuru-

lent surface with underlying granulation tissue. The gastric mucosa

shows chronic gastritis with plasma cells within the lamina propria

and intestinal metaplasia (note the goblet cells).

Figure 15-8C.

Gastrinoma (Zollinger-Ellison Syndrome). H&E, 97

Gastrinomas, also called Zollinger

-Ellison syndrome, are neoplasms

producing the hormone gastrin, which commonly arise in the duo-

denum and pancreas. Hypersecretion of gastrin by the tumor leads

to hypergastrinemia, resulting in excess production of gastric acid.

Patients have symptoms of peptic ulcers, with clinical ﬁ ndings, such

as epigastric tenderness, bleeding, and perforation. Pathologic ﬁ nd-

ings include hyperplasia of the parietal cells that produce gastric

acid within the mucosa of the stomach. Tumor cells resemble pan-

creatic endocrine cells, are well differentiated, and contain gastrin

peptides within the secretory granules. Proton pump inhibitors and

surgical removal of the tumor are the ﬁ rst treatment choice for this

syndrome. This image shows normal pancreatic parenchyma (upper

portion) and a well-circumscribed gastrinoma (lower portion). Note

the relatively uniform neoplastic cells within the gastrinoma.

Gastric mucosa

(with intestinal

metaplasia)

Chronic gastritis

Granulation

tissue

Fibrinopurulent

exudate (ulcer)

Normal

pancreatic

parenchyma

Gastrinoma

Figure 15-8A. Pyloric region of the stomach. H&E, 68;

insets 283

The pylorus is the last region of the stomach and connects to the

duodenum. The mucosa of the pylorus has deep gastric pits. Pyloric

glands, composed primarily of mucus-secreting cells, empty their

secretory products into the base of the gastric pits. These mucus-

secreting cells are pale staining and have basally located nuclei, as

do the cells of the cardiac glands. They produce mucus to protect the

epithelium of the pylorus from acidic gastric secretions. Two types

of enteroendocrine cells are found at the base of the pyloric glands.

G cells release gastrin, which stimulates parietal cells to secrete HCl.

Another type of enteroendocrine cell, called the D cell, releases

somatostatin, which inhibits the release of gastrin by G cells. These

two types of enteroendocrine cells are also found in the mucosa of

the duodenum (see Fig. 15-13B). The upper inset shows a gastric

pit and surface mucous cells in the superior portion of the mucosa.

The lower inset shows pyloric glands and mucus-secreting cells in

an inferior portion of the mucosa. Both cell types have basally posi-

tioned nuclei and clear cytoplasm containing secretory granules.

Pyloric

glnads

Pyloric

glands

Muscularis

mucosae

Muscularis

mucosae

Submucosa

Pyloric

glnads

Pyloric

glands

Surface

mucous cells

Surface

mucous cells

Mucus-secreting

cells

Mucus-secreting

cells

Gastric pits

Mucosa

Gastric pits

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Small Intestine

Figure 15-9. Overview of the small intestine.

The small intestine is a very long, tubular organ, about 6 to 7 m long, with a relatively small diameter. It connects the stomach to the

large intestine and can be divided into three regions based on anatomy and function. (1) The duodenum, the most proximal region

of the small intestine, is a short, C-shaped segment about 20 to 25 cm long. Mucous glands called Brunner glands are present only

in the duodenum. Bile and pancreatic secretions enter the duodenum through their duct systems. (2) The jejunum makes up about

two ﬁ fths of the rest of the small intestine. It has a larger diameter and thicker wall than the ileum. The jejunum has long villi and

has neither Brunner glands nor Peyer patches. (3) The ileum is the most distal portion of the intestine, and it makes up about three

ﬁ fths of the small intestine. The ileum has a thinner wall and fewer villi than the jejunum, and it has clusters of lymphatic nodules,

called Peyer patches, in the lamina propria. This illustration shows the general tunics (layers) of the small intestine. Like the other

parts of the digestive tract, the small intestine consists of a mucosa (epithelium, lamina propria, and muscularis mucosae), submu-

cosa, muscularis externa, and serosa/adventitia. Several myenteric (Auerbach) plexuses are illustrated between the two layers of the

muscularis externa; submucosal (Meissner) plexuses are located in the submucosal layer.

Mucosa

Myenteric (Auerbach) plexus

Jejunum

Submucosa

Epithelium

Lamina

propria

Muscularis

mucosae

Vein

Submucosal

(Meissner) plexus

Artery

Nerve

Muscularis

externa

Serosa/adventitia

Esophagus

Stomach

Inner circular

muscle

Outer

longitudinal

muscle

Duodenum

Small Intestine

I. Duodenum

A. Mucosa

B. Submucosa (Brunner glands)

C. Muscularis externa

D. Serosa/adventitia

II. Jejunum

A. Mucosa

B. Submucosa

C. Muscularis externa

D. Serosa

III. Ileum

A. Mucosa (Peyer patches)

B. Submucosa (Peyer patches may extend into this layer)

C. Muscularis externa

D. Serosa

Cell Types in the Small Intestine

Villi: columnar absorptive cells and goblet cells

Glands (crypts) of Lieberkühn: absorptive cells, goblet cells,

Paneth cells, enteroendocrine cells, and stem cells

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CLINICAL CORRELATION

Figure 15-10C.

Peptic Duodenitis. H&E, 48

Peptic duodenitis is an inﬂ

ammatory process caused by chronic

exposure of the duodenal mucosa to increased levels of gastric

acid and is usually found in the ﬁ rst portion of the duodenum, the

duodenal bulb. Symptoms of peptic duodenitis include epigas-

tric pain and dyspepsia. Histologic features include ﬂ attening, or

blunting, of the normally ﬁ ngerlike villi, increased inﬂ ammatory

cells within the lamina propria, Brunner gland hyperplasia, crypt

hyperplasia, and gastric foveolar metaplasia of the epithelium.

Metaplasia to a gastric foveolar type of epithelium is an adaptive

protective response to the increased levels of acid. H. pylori may

be found in the metaplastic mucosa as seen in the stomach. In

time, a duodenal ulcer may result from peptic duodenitis. This

photomicrograph shows duodenal mucosa with complete replace-

ment of the normal epithelium with goblet cells by gastric foveo-

lar epithelium. Note the widened, distorted villi and increased

inﬂ ammatory cells within the lamina propria.

Metaplastic

gastric mucosa

with loss of

goblet cells

Blunt, widened

villous with

inflammation

Figure 15-10A. Duodenum, small intestine. H&E, 14

The duodenum connects to the stomach. The mucosa of the duode-

num is composed of simple columnar epithelium, lamina propria,

and muscularis mucosae. Epithelial cells lining the surface of the villi

and the glands of Lieberkühn include absorptive cells, goblet cells,

Paneth cells, enteroendocrine cells, and stem cells. The lamina pro-

pria is a layer of loose connective tissue, which forms the core of the

villus and contains various types of connective tissue cells includ-

ing ﬁ broblasts, plasma cells, macrophages, and some leukocytes

(see Fig. 4-3A). The muscularis mucosae is a thin layer of smooth

muscle (Fig. 15-10B). The submucosa is a layer of dense connec-

tive tissue containing mucous glands called Brunner glands, which

produce mucus to protect the duodenal wall from acidic gastric juice

from the stomach. The muscularis externa consists of two layers of

smooth muscle: an inner circular layer and an outer longitudinal

layer. The outer layer of the duodenum is mostly covered by serosa;

areas where it is attached to other organs are covered by adventitia.

Villi

Glands of

Lieberkühn

Glands of

Lieberkühn

Submucosa

Mucosa

Brunner

gland

Brunner

gland

Muscularis

externa

Muscularis

externa

Figure 15-10B. Duodenum, small intestine. H&E, 45; inset

112

An example of the mucosa and submucosa of the duodenum is

shown. A thin layer of muscularis mucosae lies between the lamina

propria and the submucosa. Fingerlike villi project into the lumen

(Fig. 15-11B). Brunner glands are distributed in the submucosa

and extend into the lamina propria of the mucosa. Brunner glands

produce mucus that protects the epithelium from HCl secreted in

the stomach. They also secrete large numbers of bicarbonate ions,

which neutralize acidic gastric juice from the stomach. Two types

of enteroendocrine cells associated with the regulation of gastric

secretion are also found in the glands of Lieberkühn of the duode-

num: (1) G cells that release gastrin, which stimulates parietal cell

secretion of HCl and (2) D cells that release somatostatin, which

inhibits gastrin release. G cells and D cells are predominantly found

in the pylorus of the stomach but are also found in the duodenum.

Lumen

Glands of

Lieberkühn

Villi

Glands of

Lieberkühn

Villi

Brunner

glands

Brunner

glands

Muscularis

mucosae

Muscularis

mucosae

Submucosa

Brunner

glands

Brunner

glands

Brunner

glands

Brunner

glands

If Brunner cells are not able to produce enough mucus and bicar-

bonate ions over the long term, a duodenal (Brunner) ulcer may

develop.

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Figure 15-11A.

Plicae circulares, villi, and microvilli. H&E, 124; inset (left) 15, (right) 882

The small intestine is a long tube with three levels of folds that increase the surface area for absorption. (1) Plicae circulares (valves

of Kerckring) are gross folds involving the mucosa and submucosa that project into the lumen (left inset). (2) Villi are smaller folds

than the plicae circulares and involve only mucosa. The central core of each villus is formed by the lamina propria; the nutrients

absorbed from the lumen by absorptive cells are transported into the lamina propria. The lamina propria contains a central lacteal (a

blind-ended lymphatic vessel) and many capillaries involved in the transport of absorbed nutrients. (3) Microvilli (see Fig. 15-12B)

are at the apical surfaces of columnar absorptive cells, increasing the surface area at the cellular level. They appear as a pink border

in light microscopy and form a brush border. The drawing on the right shows various types of cells arranged in the epithelium of

the mucosa. These cells include column-shaped absorptive cells (enterocytes), goblet cells, Paneth cells, and enteroendocrine cells.

The central lacteals are also illustrated.

T. Yang

Lacteal

Microvilli

(brush border)

Stem

cell

Goblet

cell

Capillary

Paneth

cells

Columnar

absorptive

cell

Entero-

endocrine

cell

Goblet

cell

Goblet

cell

Columnar

absorptive cells

Columnar

absorptive cells

Lamina propria

Microvilli

Villus

Plicae circulare

Villus

Submucosa

Gland (crypt)

of Lieberkühn

Gland (crypt)

of Lieberkühn

Lumen of the

gland (crypt)

of Lieberkühn

Lamina

propria

Lamina

propria

Villi

Lamina propria

Submucosa

Epithelium

Serosa

Muscularis

externa

Figure 15-11B. Villi of the

small intestine. SEM, 170

An example of a scanning electron

microscopy image showing ﬁ n-

gerlike villi extending from the

intestinal wall and projecting into

the lumen is shown. Each villus is

composed of mucosa (epithelium

and lamina propria). The lamina

propria (connective tissue) forms

the central core of the villus. Epi-

thelium with microvilli forms the

outer layer of the villus. The villi

are unique structures in the small

intestine; they are found neither

in the stomach nor in the large

intestine. The villi are tallest in

the duodenum and shortest in the

ileum. They gradually reduce in

height and size from the proximal

regions to the distal regions of the

small intestine. The submucosa

and muscularis externa are also

shown here. The outermost layer

of the intestinal wall is serosa.

CUI_Chap15.indd 293 6/2/2010 3:24:17 PM

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UNIT 3

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Organ Systems

Figure 15-12B. Goblet cells, columnar absorptive cells, and microvilli. EM, (left, large intestine) 4,831, (right, small intestine)

6,906

There are numerous mitochondria in the apical cytoplasm of the columnar absorptive cells. Junction complexes are located between

neighboring cells near the lumen, and microvilli are present on the apical surfaces of the absorptive cells. A goblet cell with many

mucus-secretory granules in the cytoplasm is also shown here. These granules contain mucinogen and are released onto the surface

of the epithelium by exocytosis. During exocytosis, mucinogen becomes hydrated and forms mucin, which expands greatly in

volume after it is released from the goblet cell.

Mucus (mucinogen) granules

Goblet cell

Microvilli

Tight junctions

Desmosome

Mitochondria

of absorptive cells

Mitochondria

of absorptive cells

Absorptive cells

Microvilli

Goblet

cells

Goblet

cells

Columnar

absorptive

cells

Columnar

absorptive

cells

Microvilli

Figure 15-12A. Columnar absorptive and goblet cells of

the small intestine. H&E, 1,422

The columnar absorptive cells of the small intestine are also

called enterocytes or intestinal absorptive cells. They are tall

and columnar in shape; oval-shaped nuclei lie in the basal

region of the cells. The columnar absorptive cells are the

predominant cells in the epithelium of the small intestine.

The apical surfaces of the cells are covered by microvilli,

which are coated with glycocalyx. The microvilli increase

the cellular surface area for absorption. Goblet cells are

interspersed among the absorptive cells. These are unicellu-

lar glands (see Fig. 3-20A,B) with a distinctive goblet shape.

The goblet cells are mucus-secreting cells, and their numbers

gradually increase from the proximal (duodenum) to the dis-

tal (ileum) portions of the small intestine.

CUI_Chap15.indd 294 6/2/2010 3:24:21 PM