ANA 221: Histology of Alimentary Canal II

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Questions and Answers

What is the main function of the mucous secreted by the lining epithelium in the stomach?

To aid in the digestion of food

To protect the gastric mucosa against acid and enzymes (correct)

To produce blood group factors

To stimulate the contraction of smooth muscles

What is the type of epithelium found in the lining epithelium of the stomach?

Cuboidal

Columnar (correct)

Squamous

Transitional

What is the name of the depressions formed by the lining epithelium dipping into the lamina propria?

Gastric pits (correct)

Gastric glands

Mucous membrane folds

Lamina propria pits

What is the outermost layer of the stomach wall?

Serosa Signup and view all the answers

What is the layer of smooth muscle found in the mucous membrane of the stomach?

Muscularis mucosae Signup and view all the answers

What happens to the mucous membrane folds in the stomach when it is distended?

They disappear Signup and view all the answers

What is the function of the blood group factors produced by the mucous cells?

To determine an individual's blood type Signup and view all the answers

What is the layer of connective tissue that supports the epithelium in the mucous membrane of the stomach?

Lamina propria Signup and view all the answers

What is the primary function of the cells with a striated border in the colon?

To absorb excess water and electrolytes from intestinal contents Signup and view all the answers

What type of cells are present in the epithelium overlying solitary lymphatic follicles?

M-cells Signup and view all the answers

What is the function of mucous secreted by goblet cells?

To facilitate the passage of semisolid contents through the colon Signup and view all the answers

What is characteristic of the vermiform appendix?

It has a poorly formed crypts Signup and view all the answers

What type of cells are not present in the mucosa of the colon?

Paneth cells Signup and view all the answers

What is the function of antibodies secreted by columnar cells?

To provide protection against pathogenic organisms Signup and view all the answers

What is characteristic of the serous layer in the posterior aspect of the ascending and descending colon?

It is absent Signup and view all the answers

What are the yellow masses filled with fat that are present in the peritoneum?

Appendices epiploicae Signup and view all the answers

What is the characteristic of the mucosa in the stomach?

Thick and packed with numerous gastric glands Signup and view all the answers

What is the purpose of the circular folds in the small intestine?

To slow down the passage of contents through the small intestine Signup and view all the answers

What type of glands are present in the pyloric region of the stomach?

None of the above Signup and view all the answers

What is the shape of the main gastric glands?

Simple or branched tubular glands Signup and view all the answers

What is the name of the projections that increase the surface area of the mucous membrane?

Villi Signup and view all the answers

What is the orientation of the main gastric glands to the mucosal surface?

At right angles to the mucosal surface Signup and view all the answers

What is the function of the pyloric sphincter?

To regulate the passage of food from the stomach to the small intestine Signup and view all the answers

What is the most numerous type of cell in the epithelium lining the glands?

Chief cells, peptic cells, or zymogen cells Signup and view all the answers

What is the length of the small intestine?

Five meters Signup and view all the answers

What is the characteristic of the cytoplasm of chief cells?

Basophilic Signup and view all the answers

What is the name of the valves that are also known as circular folds?

Valves of Kerkring Signup and view all the answers

What is the function of the microvilli?

To increase the surface area of the mucous membrane Signup and view all the answers

What is the location of oxyntic or parietal cells?

Singly, amongst the peptic cells Signup and view all the answers

What is the characteristic of oxyntic or parietal cells?

Large and ovoid or polyhedral Signup and view all the answers

In which part of the small intestine are the circular folds most prominent?

Jejunum Signup and view all the answers

What is the number of layers that make up the wall of the small intestine?

Four Signup and view all the answers

What is a characteristic of the lymphoid tissue in the submucosa?

It gradually increases and is best seen in children around 10 years old. Signup and view all the answers

What is unique about the longitudinal muscle in the rectum compared to the colon?

It forms a continuous coat. Signup and view all the answers

Which part of the rectum is devoid of a serous covering?

The lower two-thirds. Signup and view all the answers

What is the length of the anal canal?

4 cm. Signup and view all the answers

What type of epithelium lines the upper part of the anal canal?

Columnar epithelium. Signup and view all the answers

What is the purpose of the anal valves?

To unite the lower ends of the anal columns. Signup and view all the answers

What is the characteristic of the mucosa in the pecten or transitional zone?

It has a bluish appearance due to a dense venous plexus. Signup and view all the answers

What is the name of the transverse line formed by the anal valves?

Pectinate line. Signup and view all the answers

Study Notes

Stomach

The wall of the stomach has four basic layers: mucous membrane, submucosa, muscularis externa, and serous layer.
The mucous membrane shows numerous folds (rugae) that disappear when the stomach is distended.
The mucous membrane is composed of:
- A lining epithelium that is columnar and mucous-secreting.
- A layer of connective tissue, the lamina propria, that supports the epithelium.
- A thin layer of smooth muscle called the muscularis mucosae.
The lining epithelium cells have apical parts filled with mucin that is usually removed during processing, making them appear empty or vacuolated.
Mucous secreted by the lining epithelium cells protects the gastric mucosa against acid and enzymes produced by the mucosa itself.
The lining epithelium dips into the lamina propria to form the walls of depressions called gastric pits, which extend for a variable distance into the thickness of the mucosa.
Deep to the gastric pits, the mucous membrane is packed with numerous gastric glands of three types: main gastric, cardiac, and pyloric.

Main Gastric Glands

The main gastric glands are present over most of the stomach, but not in the pyloric region and in a small area near the cardiac end.
The main gastric glands are simple or branched tubular glands that lie at right angles to the mucosal surface.
The glands open into gastric pits, each pit receiving the openings of several glands.
The epithelium lining the glands is composed of:
- Chief cells (peptic cells or zymogen cells) that are cuboidal or low columnar and contain prominent secretory granules in the apical parts of their cytoplasm.
- Oxyntic or parietal cells that are large, ovoid or polyhedral, and contain a large central nucleus.

Small Intestine

The small intestine is a tube about five meters long, divided into three parts.
The wall of the small intestine is made up of the four basic layers: mucous membrane, submucosa, muscularis externa, and serous layer.
The mucous membrane of the small intestine has a large surface area due to:
- Its considerable length.
- The presence of numerous circular folds (valves of Kerkring) in the mucosa.
- The presence of numerous finger-like processes (villi) that project from the surface of the mucosa into the lumen.
- The presence of numerous depressions (crypts) that invade the lamina propria.
- The presence of microvilli on the luminal surfaces of the cells lining the mucosa.

Large Intestine

The large intestine is composed of the colon, vermiform appendix, and rectum.
The colon has a mucous membrane with a large surface area due to:
- The presence of numerous circular folds (valves of Kerkring) in the mucosa.
- The presence of numerous finger-like processes (villi) that project from the surface of the mucosa into the lumen.
- The presence of numerous depressions (crypts) that invade the lamina propria.
- The presence of microvilli on the luminal surfaces of the cells lining the mucosa.
The mucous membrane of the colon is lined by an epithelium made up predominantly of columnar cells with a striated border.
The main function of the columnar cells is to absorb excess water and electrolytes from intestinal contents.
Many columnar cells secrete mucous and antibodies (IgA), providing protection against pathogenic organisms.

Vermiform Appendix

The structure of the vermiform appendix resembles that of the colon with the following differences:
- The appendix is the narrowest part of the gut.
- The crypts are poorly formed.
- The longitudinal muscle coat is complete and equally thick all around.
- Taenia coli are not present.
- The submucosa contains abundant lymphoid tissue that may completely fill the submucosa.

Rectum

The structure of the rectum is similar to that of the colon except for the following:
- A continuous coat of longitudinal muscle is present.
- There are no taenia.
- Peritoneum covers the front and sides of the upper one-third of the rectum, and only the front of the middle third.
- There are no appendices epiploicae.

Anal Canal

The anal canal is about 4 cm long, with the upper 3 cm lined by mucous membrane and the lower 1 cm lined by skin.
The area lined by mucous membrane can be further divided into an upper part (15 mm) and a lower part (15 mm).
The mucous membrane of the upper 15 mm of the canal is lined by columnar epithelium and shows six to twelve longitudinal folds (anal columns).
The lower ends of the anal columns are united to each other by short transverse folds (anal valves) that form a transverse line (pectinate line).
The mucous membrane of the next 15 mm of the rectum is lined by non-keratinized stratified squamous epithelium and does not have anal columns.

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Description

Lecture notes on the histology of the stomach, small intestine, and large intestine, covering the mucous membrane, epithelia, and muscles. Part of the ANA 221 course.