GI System & Development - Histology
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What is the primary function of Auerbach's plexus in the gastrointestinal tract?

  • Regulating blood flow to the stomach
  • Creating peristaltic activity (correct)
  • Absorbing nutrients
  • Secreting digestive enzymes

    • What is the primary function of myoepithelial cells in the salivary glands?

  • To produce connective tissue in the gland
  • To contract and expel salivary fluid (correct)
  • To form connections between ducts
  • To secrete mucin into saliva

    • What is the primary function of the gastrointestinal system?

  • To regulate body temperature
  • To break down food for absorption into the body (correct)
  • To facilitate speech during eating
  • To produce hormones for digestion

    • Which region of the stomach contains primarily cardiac glands?

    <p>Cardiac region</p> Signup and view all the answers

    Which salivary gland is primarily located under the floor of the mouth?

    <p>Submandibular gland</p> Signup and view all the answers

    What is the main structural unit of the salivary gland?

    <p>Salivon</p> Signup and view all the answers

    Which of the following statements about Barrett's esophagus is true?

    <p>It is characterized by a thickened red lining of the esophagus.</p> Signup and view all the answers

    Which type of papillae on the tongue is solely responsible for the sensation of touch and does not contain taste buds?

    <p>Filiform</p> Signup and view all the answers

    Which accessory organ is NOT part of the digestive system?

    <p>Bladder</p> Signup and view all the answers

    What role does the adventitia play in the structure of the esophagus?

    <p>Connects the esophagus to surrounding tissues</p> Signup and view all the answers

    Which of the following glands is mostly mucous?

    <p>Sublingual gland</p> Signup and view all the answers

    What type of epithelium lines the mucosa of the esophagus?

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

    In which phase of digestion does the gastrointestinal system absorb nutrients into the body?

    <p>Absorption</p> Signup and view all the answers

    What is chyme?

    <p>Partially digested food mixed with gastric secretions</p> Signup and view all the answers

    Which of the following types of papillae contain taste buds?

    <p>Fungiform and foliate</p> Signup and view all the answers

    Which part of the esophagus consists of striated muscle?

    <p>Upper third</p> Signup and view all the answers

    How does the gastric mucosa contribute to the stomach's function?

    <p>It has longitudinal folds called rugae that allow for distension.</p> Signup and view all the answers

    Which function is NOT associated with saliva?

    <p>Digestion of proteins</p> Signup and view all the answers

    Which of the following best describes the gastroesophageal junction (GEJ)?

    <p>Where the distal esophagus meets the proximal stomach.</p> Signup and view all the answers

    What is the correct order of the five main phases of digestion?

    <p>Ingestion, Fragmentation, Digestion, Absorption, Elimination</p> Signup and view all the answers

    What role do accessory cells play in the gastrointestinal tract?

    <p>They produce digestive enzymes.</p> Signup and view all the answers

    What is the major nerve supply responsible for GI tract motility?

    <p>Auerbach’s plexus</p> Signup and view all the answers

    What major structure does the esophagus connect to at its lower end?

    <p>Stomach</p> Signup and view all the answers

    Which of the following components is part of the alimentary canal?

    <p>Esophagus</p> Signup and view all the answers

    What are gastric pits primarily responsible for in the stomach?

    <p>Serving as entrances to gastric glands</p> Signup and view all the answers

    Which type of cell in the gastric mucosa secretes hydrochloric acid?

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

    What is the primary role of the surface mucous foveolar cells?

    <p>To protect the gastric mucosa</p> Signup and view all the answers

    What component of the gastric mucosal barrier helps to repel harmful fluids?

    <p>Tight junctions between epithelial cells</p> Signup and view all the answers

    Which gland in the stomach is known to secrete gastrin?

    <p>Pyloric glands</p> Signup and view all the answers

    What is the primary secretory product of zymogenic (chief) cells?

    <p>Pepsinogen</p> Signup and view all the answers

    How do bicarbonate ions contribute to the gastric mucosal barrier?

    <p>By neutralizing gastric acid</p> Signup and view all the answers

    Why is the gastric mucosal barrier important for digestion?

    <p>It prevents autodigestion of the stomach lining</p> Signup and view all the answers

    What is the main type of epithelium lining the zona columnaris of the anal canal?

    <p>Simple columnar</p> Signup and view all the answers

    Which zone of the anal canal is characterized by stratified squamous keratinized epithelium?

    <p>Zona cutanea</p> Signup and view all the answers

    What separates the zona hemorrhagica from the zona cutanea in the anal canal?

    <p>Hilton's white line</p> Signup and view all the answers

    Which part of the anal canal transitions between simple columnar epithelium to stratified squamous epithelium?

    <p>Anal transitional zone</p> Signup and view all the answers

    What is a key function of keratinized cells in the anal canal?

    <p>Waterproofing and reducing evaporation</p> Signup and view all the answers

    What is the primary secretion of cardiac glands in the stomach?

    <p>Mucus</p> Signup and view all the answers

    Which type of gastric gland predominantly secretes hydrochloric acid?

    <p>Fundic (oxyntic) glands</p> Signup and view all the answers

    Which component of the small intestine is specifically designed for digestion and absorption of food?

    <p>Duodenum</p> Signup and view all the answers

    What are plicae circularis in the small intestine?

    <p>Permanent transverse folds of the intestinal surface</p> Signup and view all the answers

    How does the structure of the small intestine enhance its absorptive capacity?

    <p>Specialization of the submucosa and mucosa</p> Signup and view all the answers

    What is a primary consequence of insufficient rotation of the intestinal loop?

    <p>Total rotation of 90° only</p> Signup and view all the answers

    Which condition results from twisting of the intestine due to malrotation?

    <p>Volvulus</p> Signup and view all the answers

    What is associated with a higher risk of omphalocele?

    <p>Environmental factors such as tobacco use</p> Signup and view all the answers

    What condition involves herniation of abdominal viscera through the umbilical ring?

    <p>Omphalocele</p> Signup and view all the answers

    Which of the following is NOT a characteristic of volvulus?

    <p>Herniation of viscera through the abdominal wall</p> Signup and view all the answers

    What is the primary characteristic of gastroschisis?

    <p>Protrusion of the abdominal viscera through the body wall</p> Signup and view all the answers

    Which demographic is more likely to have children with gastroschisis?

    <p>Teenage mothers</p> Signup and view all the answers

    What causes the connection between the liver bud and the foregut to narrow?

    <p>The penetration of hepatic cells into the septum transversum</p> Signup and view all the answers

    What is a possible consequence of pancreatic divisum?

    <p>Asymptoms in most cases</p> Signup and view all the answers

    What function does the gallbladder primarily perform?

    <p>Concentration and storage of bile</p> Signup and view all the answers

    Which of the following defects is associated with bile accumulation inside the liver?

    <p>Biliary atresia</p> Signup and view all the answers

    At what week of development does the liver begin to produce bile?

    <p>Week 12</p> Signup and view all the answers

    What is the typical incidence of biliary atresia at birth?

    <p>1 in 15,000</p> Signup and view all the answers

    What stimulates the development of the liver bud from the endodermal epithelium?

    <p>FGF2 signaling</p> Signup and view all the answers

    What is the primary function of the liver during the fetal stage?

    <p>Hematopoiesis</p> Signup and view all the answers

    What anatomical structure is primarily associated with the axis of intestinal rotation during development?

    <p>Superior mesenteric artery</p> Signup and view all the answers

    At which week do the intestinal loops usually return into the abdominal cavity after rotation?

    <p>10 weeks</p> Signup and view all the answers

    What is the developmental consequence of the physiological umbilical herniation during bowel rotation?

    <p>Omphalocele</p> Signup and view all the answers

    What percentage of live births are affected by gut rotation defects (malrotations)?

    <p>1 in 500</p> Signup and view all the answers

    Which part of the colon becomes retroperitoneal during intestinal rotation?

    <p>Ascending colon</p> Signup and view all the answers

    What additional degree of rotation do the intestinal loops undergo after initially returning to the abdominal cavity?

    <p>180 degrees</p> Signup and view all the answers

    What condition may arise if there is an abnormal twist or turn in the gastrointestinal tract?

    <p>Volvulus</p> Signup and view all the answers

    Which of the following is characterized by a failure of the abdominal wall to close properly, often leading to the exposure of internal organs?

    <p>Omphalocele</p> Signup and view all the answers

    Study Notes

    Gastrointestinal (GI) System: Digestive System I and II

    • The GI system breaks down food for absorption into the body.
    • This process occurs in five main phases: ingestion, fragmentation, digestion, absorption, and elimination of waste products.
    • Reading material includes Wheater's Functional Histology: Chapter 14 and lecture material.
    • Learning objectives include describing general histologic features of the tongue and salivary glands, outlining the histological features of the upper GI tract (esophagus and stomach) and accessory cells' function and outlining histological features of the lower GI tract (small and large intestine, rectum) and accessory cells' function.

    Reading Material

    • Wheater's Functional Histology: Chapter 14
    • Lecture material

    Learning Objectives

    • Describe general histologic features of the tongue and salivary glands.
    • Outline histological features of the upper GI tract (esophagus and stomach) and describe the function of accessory cells.
    • Outline the histological features of the lower GI tract (small and large intestine, rectum) and describe the function of accessory cells.

    Gastrointestinal System

    • The GI system's function is to break down food for absorption into the body.
    • Food breakdown occurs in five phases: ingestion, fragmentation, digestion, absorption, and elimination of waste products.

    Digestive Organs and Their Function

    • Mouth: taste, reduce food to small pieces, liquefy, and swallow food.
    • Esophagus: transport food.
    • Stomach: mix food, reduce it into small pieces, protein digestion, acid protection against bacteria.
    • Liver: protection against bacteria, breakdown of carbohydrates, proteins, and fats, absorption of nutrients, vitamins, water and fibre, concentration process, removal of water, fibre fermentation, shaping, transport and storage, and excretion.
    • Gallbladder: part of the liver's functions.
    • Pancreas: part of the liver's functions.
    • Small intestine: breakdown of carbohydrates, proteins and fats, absorption of nutrients, vitamins, water and fibre, concentration process, removal of water, fibre fermentation, shaping, transport and storage and excretion.
    • Large intestine: concentration of water, fibre fermentation, shaping, transport, storage and excretion of waste products.
    • Rectum: storing and excretion.
    • Anus: excreting waste products.

    Overview of the Digestive System

    • The digestive system consists of the alimentary canal (GI tract) and associated organs.
    • Food is broken down physically and chemically as it passes through the alimentary canal, allowing the body to absorb the degraded products.
    • Parts of the alimentary canal are morphologically specialized for digestion and absorption.
    • Undigested food is excreted as feces.

    Histology of the Alimentary Canal

    • The alimentary canal wall has four layers (from lumen inside to out): mucosa, submucosa, muscularis externa, and serosa. (or adventitia).

    Oral Cavity: Tongue

    • The tongue is a muscular organ projecting into the oral cavity.
    • Lingual muscles (tongue muscles) are voluntary muscles that function in speech, digestion, and swallowing.
    • The dorsal surface is covered in numerous lingual papillae (mucosal elevations) responsible for the sensation of touch and texture.
    • Four types of papillae exist: filiform, fungiform, foliate, and circumvallate (vallate). Taste buds are associated with all, except filiform, papillae.

    Oral Cavity: Taste Buds

    • Taste buds are present in fungiform, foliate, and circumvallate papillae.
    • Taste buds contain three cell types: sensory cells (neuroepithelial), supporting cells, and basal cells.

    Oral Cavity: Salivary Glands

    • Major glands: parotid, submandibular, and sublingual
      • Parotid: located outside the oral cavity
      • Submandibular: located under the floor of the mouth, mixed glands (mostly serous)
      • Sublingual: located in the floor of the mouth, anterior to the submandibular, mixed glands (mostly mucus)
    • Minor glands: lingual, labial, buccal, molar, and palatine

    Oral Cavity: Salivary Glands (Structure)

    • The structural unit is the salivon consisting of:
      • Acinar cells: secrete initial fluid and mucin
      • Intercalated ducts: short connections to striated ducts
      • Striated ducts: composed of epithelial cells
      • Myoepithelial cells: contract to expel salivary fluid into the oropharynx.

    Saliva

    • Saliva is a combined secretion of major and minor salivary glands.
    • Saliva functions include moistening mucosa and food, dissolving food material, buffering oral cavity, digesting carbohydrates, and immunological control by regulating the bacterial flora of the oral cavity.

    Oesophagus

    • A fibromuscular tube, ~25 cm long in adults.
    • It starts in the pharynx, travels behind the trachea and heart, passes through the diaphragm, and empties into the upper region of the stomach.

    Oesophagus - Wall Structure

    • The esophagus wall consists of:
      • Mucosa: stratified squamous epithelium
      • Submucosa: connective tissue
      • Muscularis Externa: layers of muscle fibers (mostly smooth muscle); striated in the upper third, with two sphincters in the wall.
      • Subserosa/adventitia: outer connective tissue layer, with a serous membrane (mesothelium), containing thin connective tissue.

    Oesophagus - Auerbach's Plexus

    • Auerbach’s plexus (myenteric plexus) is located between the outer and inner muscle layers.
    • It creates peristaltic activity.
    • It's the major nerve supply to the gastrointestinal tract and controls GI tract motility.

    Gastroesophageal Junction (GEJ)

    • The GEJ is the point where the distal esophagus joins the proximal stomach.
    • It is commonly exposed to injurious effects of GERD (gastroesophageal reflux disease) and/or Helicobacter pylori infection.
    • Barrett's esophagus is a condition where the esophagus' epithelium at the GEJ becomes damaged by acid reflux.
    • Thickenings and redness of the lining increase esophageal cancer risk.

    Stomach

    • Lies beneath the diaphragm.
    • Receives food from the esophagus.
    • Partially digested food mixed with gastric secretions leaves the stomach as chyme..
    • Histologically divided into three regions: cardia, fundus, and pylorus, based on gland types.

    Gastric Mucosa

    • Gastric mucosa has folds called rugae.
    • Rugae are poorly developed in the upper portion of the stomach.
    • The rugae allow the organ to distend.

    Gastric Mucosa (Structure)

    • The stomach lining has the same basic structure as the esophagus.
    • Gastric pits are openings in the mucosal surface, deeper in the pylorus than other parts of the stomach.

    Gastric Mucosa (Cells)

    • Surface mucous foveolar (pit) cells - secrete mucus
    • Oxyntic (parietal) cells - secrete acid (HCl)
    • Zymogenic (chief) cells - secrete pepsinogen
    • Enteroendocrine cells - hormone-secreting cells
    • Surface mucous cells have granules on their apical surface and secrete bicarbonate which protects the stomach lining from acid.

    Gastric Mucosal Barrier

    • The barrier consists of three protective components.

      • Compact epithelial cells bound by tight junctions.
      • Surface mucous foveolar (pit) cells.
        • Insoluble mucus creates a protective gel-like coating over the entire surface of the gastric mucosa.
        • Mucus protects gastric mucosa from autodigestion.

    • Bicarbonate ions secreted by surface epithelial cells neutralize harsh acids.

    Gastric Glands

    • Located in different regions of the stomach (cardia, fundus, and pylorus).
    • Secrete mucus, pepsinogen, hydrochloric acid, intrinsic factor, gastrin, and bicarbonate.

    Small Intestine

    • The longest part of the digestive tract.
    • Principle site of digestion and absorption.
    • Enterocytes secrete digestive enzymes.
    • Anatomically divided into three segments: duodenum, jejunum, and ileum.

    Small Intestine - Histological Characteristics

    • Duodenum: Brunner's glands (produce alkaline secretion that neutralizes the acidic chyme from the stomach); villi are short and broad (leaflike).
    • Jejunum: long finger-like villi, well developed lacteal (lymphatic capillary) which absorbs dietary fats and triglycerides, no Brunner's glands in submucosa
    • Ileum: Peyer's patches (lymphoid follicles) in the mucosa (GALT), lack of Brunner's glands, shorter finger-like villi

    Small Intestine - Villi

    • Villi structure consists of a core of loose connective tissue covered by simple columnar epithelium.
    • Lamina propria (connective tissue under epithelium), central lymphatic capillary (lacteal).

    Small Intestine - Lieberkuhn's crypts (Structure)

    • Lieberkuhn's crypts are intestinal simple tubular glands originating from the muscularis mucosa.
    • These structures are covered with simple columnar epithelium, continuous with villi epithelium.

    Small Intestine - Cells

    • Enterocytes (absorb water and electrolytes), goblet cells (secrete mucus), enteroendocrine cells (secrete hormones), cup cells, tuft cells, and Paneth cells (secrete antimicrobial peptides).
    • Stem cells replenish cells lost due to abrasion.

    Large Intestine

    • The large intestine is composed of cecum (projection: appendix), colon, rectum, and anal canal.
    • It absorbs water and sodium from the luminal contents.
    • It secretes mucus and some hormones.

    Large Intestine - Mucosa

    • The large intestine has a thick mucosa.
    • It has deep crypts, but no villi.
    • Columnar absorptive epithelial cells (goblet cells, endocrine cells, basal stem cells).
    • Surface epithelial cells are shed into the lumen.
    • The lamina propria and submucosa are similar to the small intestine.
    • The muscularis externa is smooth muscle arranged in three longitudinal bands (taenia coli).

    Large Intestine - Mucosa (Structure)

    • Contains numerous straight tubular glands extending through the full thickness of the mucosa.
    • Simple columnar epithelium covers the mucosa.

    Rectum

    • The rectum is 7-10cm long.
    • It can be distinguished by the presence of transverse rectal folds (or Houston Valves).
    • The anal canal is divided into three parts: colorectal zone, anal transitional zone, and squamous zone.

    Anal Canal

    • The anal canal is 7-10cm long.
    • It is considered the terminal portion of the large intestine divided into three zones:
      • Colorectal zone: simple columnar epithelium
      • Anal transitional zone: transition between simple columnar and stratified squamous epithelium
      • Squamous zone: stratified squamous epithelium.

    Summary

    • The provided document outlines the components of the digestive system, the organization of the alimentary canal, and the histology of different parts of the gastrointestinal tract, including the tongue, salivary glands, esophagus, stomach, small intestine, large intestine, rectum, and anal canal.

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    Description

    Test your knowledge on the gastrointestinal system with a focus on the digestive process. This quiz covers histological features of the tongue, salivary glands, and the upper and lower GI tract, based on Wheater's Functional Histology. Assess your understanding of key concepts and functions essential for absorption and digestion.

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