Digestive Tract Anatomy and Functions
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Questions and Answers

Which of the following statements about the tunics of the digestive tract is NOT true?

  • Minor structural modifications to the tunics can occur depending on the local requirements of the digestive tract.
  • The tunics may be reduced or absent in certain regions of the digestive tract.
  • All four tunics are present in every part of the digestive tract. (correct)
  • The tunics are responsible for the overall structural plan of the digestive tract.

    • The muscularis mucosae layer in the esophagus is composed of:

  • Connective tissue
  • Elastic fibers
  • Smooth muscle (correct)
  • Skeletal muscle

    • What differentiates the upper portion of the esophagus from the lower portion?

  • The type of muscle in the tunica muscularis (correct)
  • The presence of muscularis mucosae
  • The presence of submucosal glands
  • The presence of stratified squamous epithelium

    • Which of the following is NOT found in the submucosa of the esophagus?

    <p>Stratified squamous epithelium (B)</p> Signup and view all the answers

    What is the primary function of the deep esophageal glands found in the submucosa?

    <p>Production of mucus for lubrication (B)</p> Signup and view all the answers

    What is the primary type of epithelial tissue found in the stomach?

    <p>Simple columnar epithelium (A)</p> Signup and view all the answers

    The tunica muscularis in the lower third of the esophagus is composed of:

    <p>Smooth muscle (B)</p> Signup and view all the answers

    Which of the following is NOT a descriptive division of the stomach?

    <p>Duodenum (A)</p> Signup and view all the answers

    Which of the following statements accurately describes the adventitia of the esophagus?

    <p>It is a layer of connective tissue that anchors the esophagus (A)</p> Signup and view all the answers

    What is the significance of the high number of cell layers in the stratified squamous epithelium of the esophagus?

    <p>To provide a barrier against abrasion (C)</p> Signup and view all the answers

    What is the function of the rugae in the stomach?

    <p>To increase the surface area for digestion (D)</p> Signup and view all the answers

    Where are the cardiac glands located in the stomach?

    <p>Cardio-esophageal junction (B)</p> Signup and view all the answers

    What is the primary function of the mucous neck cells in the fundic glands?

    <p>Secrete mucus (B)</p> Signup and view all the answers

    How do the gastric pits in the stomach vary by region?

    <p>They are more numerous in the pylorus than in the fundus (A)</p> Signup and view all the answers

    Which of the following accurately describes how rugae are affected by distention of the stomach?

    <p>The number and height of rugae increase (B)</p> Signup and view all the answers

    What is the approximate total secreting surface area of the stomach?

    <p>30 sq. feet (B)</p> Signup and view all the answers

    Which cell type is most commonly found in the gastric glands between mucous neck cells?

    <p>Parietal cells (B)</p> Signup and view all the answers

    What is the primary role of the muscularis mucosae in the stomach?

    <p>To help with the movement of food through the stomach (A)</p> Signup and view all the answers

    Which of the following statements is TRUE regarding the arrangement of the muscle layers in the muscularis of the stomach?

    <p>The inner layer is oblique, the middle layer is circular, and the outer layer is longitudinal. (C)</p> Signup and view all the answers

    What is the function of the argentaffin cells in the stomach?

    <p>To produce serotonin (A)</p> Signup and view all the answers

    What is the primary location of the chief cells in the stomach?

    <p>The fundus (D)</p> Signup and view all the answers

    Which of these cell types is responsible for secreting mucus?

    <p>Goblet Cells (C)</p> Signup and view all the answers

    What is the function of the striate border in simple columnar cells?

    <p>Absorption of nutrients (A)</p> Signup and view all the answers

    Where are Paneth cells most numerous?

    <p>Small intestine (A)</p> Signup and view all the answers

    What is the characteristic feature of Paneth cells that distinguishes them from other cell types?

    <p>Large, round, acidophilic granules above the nucleus (B)</p> Signup and view all the answers

    What is the term used to describe the felt-like ectoplasm near the surface of simple columnar cells?

    <p>Terminal web (D)</p> Signup and view all the answers

    What is the most prominent characteristic of the vermiform appendix?

    <p>Its mucosa is characterized by a large number of argentaffin cells compared to other parts of the gut. (C)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the colon?

    <p>The epithelial cell types are different from those in the small intestine. (B)</p> Signup and view all the answers

    Which of the following is NOT a component of the intestinal glands?

    <p>Chief cells (A)</p> Signup and view all the answers

    In which part of the small intestine are the aggregate nodules (Peyer’s Patches) most commonly found?

    <p>Ileum (C)</p> Signup and view all the answers

    Which cells are responsible for serotonin production?

    <p>Argentaffin cells (B)</p> Signup and view all the answers

    What is the primary function of Brunner's glands found in the duodenum?

    <p>Secretion of bicarbonate-rich fluid to neutralize stomach acid (A)</p> Signup and view all the answers

    Which of these structures can be found in the Lamina Propria?

    <p>Solitary lymph nodules (A)</p> Signup and view all the answers

    What is the difference in muscularis organization between the small and large intestine?

    <p>The small intestine has its longitudinal muscle arranged in three bands (Taenia coli). (B)</p> Signup and view all the answers

    Where are the Argentaffin cells most numerous?

    <p>Duodenum (D)</p> Signup and view all the answers

    What distinguishes the intestinal epithelium from the surface covering?

    <p>The surface covering of the intestines is primarily found in the intervals between glands. (C)</p> Signup and view all the answers

    Flashcards

    Chief Cells

    Cells in the stomach that secrete digestive enzymes like pepsin.

    Parietal Cells

    Cells in the gastric glands that secrete hydrochloric acid and intrinsic factor.

    Argentaffin Cells

    Cells that contain granules stained by chrome salts, involved in serotonin production.

    Pyloric Glands

    Glands in the stomach's pyloric region, simpler and branched compared to fundic glands.

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    Lamina Propria

    Connective tissue layer in the stomach mucosa with collagenous and reticular fibers.

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    Digestive Tube

    The digestive tube starts at the esophagus and ends at the anus, featuring a common structural plan of tubular and saccular organs.

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    Four Tunics of Digestive Tube

    The digestive tube is composed of four concentric tunics: Tunica Mucosa, Tunica Submucosa, Tunica Muscularis, and Tunica Adventitia (or Serosa).

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    Tunica Mucosa Components

    The Tunica Mucosa includes epithelium, lamina propria, and muscularis mucosae, adapting for local needs.

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    Tunica Muscularis

    The Tunica Muscularis contains inner circular and outer longitudinal muscle layers, aiding in peristalsis.

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    Esophagus Structure

    The esophagus consists of stratified squamous epithelium, with a lamina propria and muscularis mucosae composed of smooth muscle.

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    Epithelium Types in Esophagus

    The upper portion of the esophagus has stratified squamous epithelium to protect against abrasion from food.

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    Adventitia Composition

    The Adventitia is a loose fibrous tissue layer containing blood vessels and nerves associated with the esophagus.

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    Muscularis in Esophagus

    The Muscularis has three segments: upper (skeletal), middle (mix of skeletal/smooth), and lower (smooth) muscle layers.

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    Mucosa

    Innermost layer of the intestine featuring epithelial tissue.

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    Simple Columnar Cells

    Tall, absorptive cells with a striated border, primarily in the intestine.

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    Goblet Cells

    Unicellular mucous glands that increase in number from duodenum to rectum.

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    Paneth Cells

    Large, zymogenic cells in the small intestine, rich in secretory granules.

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    Cell Types in Intestine

    Four main cell types: Simple Columnar, Goblet, Paneth, and Argentaffin Cells.

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    Large Intestine Structure

    The large intestine is about 5 feet long and has a double width of the small intestine, consisting of the caecum, appendix, colon, and rectum.

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    Caecum

    The caecum is a blind sac at the beginning of the large intestine, marked by an abrupt transition from the ileum.

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    Ileo-cecal Valve

    A valve that regulates the flow between the ileum and caecum, with apposed folds of mucosa and a support structure of smooth muscle.

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    Vermiform Appendix

    A small blind-ended tube with a thick wall, filled with lymphoid tissue, situated at the caecum.

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    Colon Mucosa

    The colon's mucosa consists of simple columnar cells, with a thin striate border and scattered goblet cells, lacking folds.

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    Muscularis mucosae

    Layer of smooth muscle in the gastrointestinal tract.

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    Gastro-esophageal junction

    The area connecting the esophagus and stomach.

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    Stomach divisions

    The main parts of the stomach: Cardia, Fundus, Corpus, Pylorus.

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    Rugae

    Longitudinal folds in the stomach lining that allow expansion.

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    Foveolae

    Gastric pits that open on mounds in the stomach lining.

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    Gastric glands

    Branched tubular glands in the stomach that secrete mucus and enzymes.

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    Cardiac glands

    Glands located at the cardio-esophageal junction of the stomach.

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    Four cell types in gastric glands

    Different cells in fundic glands: Mucous Neck Cells, Parietal Cells, etc.

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    Intestinal Glands

    Pit-like structures in the intestine known as crypts of Lieberkuhn, composed of various cell types.

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    Plicae Circulares

    Ring-like folds in the small intestine that increase surface area for absorption.

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    Brunner's Glands

    Glands located in the duodenum that secrete alkaline fluid to neutralize stomach acid.

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    Mesenteries

    Double sheets of peritoneum that attach the intestines to the abdominal wall, providing support.

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    Study Notes

    Digestive System Histology

    • The digestive system's histology is studied to identify and differentiate histological structures in the digestive tube, parts of the small intestine, and small and large intestines.

    Digestive Tube

    • The digestive tube starts with the esophagus and ends with the anus.
    • It comprises tubular and saccular organs.
    • Its structure consists of four concentric tunics.
    • Sometimes tunics may be partially or completely missing.
    • Minor structural modifications can be present to meet specific local requirements.

    Structural Plan

    • The tunica mucosa is composed of epithelium, membrana propria, lamina propria mucosae, and lamina muscularis mucosae.
    • The tunica submucosa is present.
    • The tunica muscularis is present.
    • The tunica adventitia (serosa) is present.

    Esophagus

    • The esophagus connects the pharynx and the stomach.
    • It represents a transition.
    • The muscularis mucosae replaces the elastic layer of the pharynx.
    • The muscularis layer is more regular in the esophagus.

    Stomach

    • The stomach is a dilated, distorted, and capacious sac.
    • It is divided into cardia, fundus, corpus (body), and pylorus.
    • The mucosa lining is 0.3 mm thick at the cardia and 1.5 mm at the pylorus.
    • The mucosa and submucosa form longitudinal folds called rugae.
    • Distension changes the number and height of the rugae.
    • Finer furrows form mound-shaped areas (foveolae) across the gastric areas, ranging in size from 1-5 mm.
    • Foveolae vary in density by region (17/sq mm in fundus, 9/sq mm in pylorus).
    • The stomach contains 3,400,000 foveolae.
    • The surface epithelium is simple columnar and mucous-secreting.
    • The mucigen is unique to the epithelium type.
    • Gastric glands, of a branched tubular type, penetrate the full thickness of the mucosa.
    • Foveolae serve as ducts for the glands.
    • A human stomach has around 15,000,000 gastric glands.

    Cardiac Glands

    • Cardiac glands are a narrow band located at the cardio-esophageal junction.
    • They measure 5-40 mm in width.
    • These glands resemble superficial glands from the lower esophagus.
    • They are small and sometimes compound tubular glands, and foveolae are about ½ the length of the gland.
    • The secretory portion is tortuous, resembling the mucous cells.
    • The lumen is clear and obvious.

    Fundic Glands

    • These glands are straight and tubular with minor branching.
    • They are located in the fundus and corpus regions of the stomach.
    • The gland regions are foveola (short duct), neck (constricted duct), body (long duct), and fundus (minor dilation & bend).
    • The ducts and main gland have a 1:4 ratio.

    Four Cell Types

    • Mucous Neck Cells: Increase in number towards the pyloric end; nuclei are flattened and basal; mucus is watery.
    • Chief Cells: Increase in number towards the cardiac end; comprise the gland below the neck; spherical nucleus with granular elements; basally striated chromidial substance; presecretion granules during rest; activity is reduction in granules.
    • Parietal Cells: More abundant in the pyloric end; commonly wedged between mucous neck and chief cells, and position is peripheral; cell shape is wedge-like to conical; lack distinct secretory granules, but intercellular channels connect to the main lumen. Secrete hydrochloric acid.
    • Argentaffin Cells: Enterochromaffin elements; located between chief cells and basement membrane; slender extension may reach the lumen; granules stain with chrome salts (precursors of serotonin—vasoconstrictive hormone).

    Small Intestine

    • The small intestine is a long, slender tube, longer than the peritoneal cavity, and coils within the cavity.
    • The small intestine comprises the duodenum, jejunum, and ileum.
    • The mucosa is lined with simple columnar epithelium covering villi and dipping into glands.
    • Four cell types are present: simple columnar cells (absorptive), goblet cells, Paneth cells, and argentaffin cells. Cells are not evenly distributed.
    • The lamina propria contains a delicate network of collagenous and reticular fibers, lymphocytes, and solitary lymph nodules ( Peyer's patches); especially in the ileum.
    • The submucosa is loose areolar connective tissue with blood vessels and nerve plexuses. Ring-like folds (plicae circulares) are prominent. Brunner's glands are in the duodenum.
    • The muscularis has inner circular and outer longitudinal layers.
    • The small intestine serosa is continuous with mesenteries.

    Large Intestine

    • The large intestine is about 5 feet long and wider than the small intestine.
    • It comprises the cecum, appendix, colon, and rectum.
    • The lining lacks plicae circulares and villi.
    • Intestinal glands are longer than in the small intestine and are arranged closer together.
    • The epithelial cell types are identical to the small intestine.
    • The ileocecal valve is an abrupt change from the ileum to the cecum, with opposing folds of mucosa and submucosa supported by a central smooth muscle plate.
    • The cecum is a blind sac.
    • The appendix is a finger-like process attached to the cecum. The gland count decreases with age. The wall is thick, and the lumen is relatively small, often filled with debris. It has deep pockets between mucosal folds.
    • The colon forms haustra; taenia coli are longitudinal ribbons shorter than the colon's length. The serosa is incomplete. Appendices epiploicae are redundant serosa. The lamina propria is similar to that in the small intestine. Colon mucosa does not form folds but has regular rows of glands. Eosinophils are numerous in the lamina propria. Muscularis mucosae typically has two layers of smooth muscle.

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