Lecture 31: Upper GI Histology II

Question 1

Functions of the esophagus

Answer 1

• Digestion (initiated in the mouth)

* Addition of mucous to food bolus

Question 2

Structural Specializations of the esophagus

Answer 2

• Mucosa:
• Stratified squamous nonkeratinized epithelium
• Mucous glands are found in the lamina propria and submucosa.
• Muscularis externa:
• Undergoes transition from skeletal muscle in the upper third to a mixture of skeletal and smooth in the middle third to smooth muscle only in the lower third
• See slide 6

Question 3

Components of the stomach:

Answer 3

• Epithelial lining:
• Gastric mucosa consists of a simple columnar epithelium with mucous columnar cells.
• Surface mucous cells secrete a protective insoluble mucous.
• Rugae(Refer to Figure 15-11) are longitudinal mucosal folds that are most prominent in an empty stomach.
• Gastric glands:
• Gastric glands open into gastric pits.
• Muscularis externa:
• Has three layers of smooth muscles
• Third layer is an inner oblique layer
• See Slide 9

Question 4

Regions of the Stomach

Answer 4

• Cardia(Refer to Figure 15-12):
• Contains mostly mucous glands
• Fundus:
• Contains gastric glands (Refer to Figures 15-13 and 15-14):
• Long tubular glands extending down to the muscularis mucosae
• Composed of mucous neck cells, parietal cells, chief cells, stem cells, and enteroendocrine cells.
• Body:
• Contains gastric glands (See above under “Fundus”)
• Pylorus (Refer to Figure 15-20):
• Contains mucous glands and hormone-secreting enteroendocrine cells
• See Slides 11-12

Question 5

Describe Gastric Glands

Answer 5

• Simple branched tubular glands
• Narrow isthmus opens into bottom of a gastric pit.
• Fundus (base) of the gland extends into the lamina propria.
• Cells of the gastric glands:
• Mucous neck cells secrete soluble mucous
• Stem cells in neck replace other cells of the gastric pit.
• Chief cells (zymogenic cells): Secrete pepsinogen
• Parietal cells (oxyntic cells): Manufacture HCl and Secrete intrinsic factor
• Enteroendocrine cells (APUD cells): Diffuse neuroendocrine cells that secrete hormones.
• APUD = Amine Precursor Uptake and Decarboxylation
• See Slides 15-18

Question 6

Describe the cells of gastric glands

Answer 6

• Parietal Cells:
• Unique cell of the gastric gland
• Large pyramidal shaped, eosinophilic cell
• Produces HCl and gastric intrinsic factor:
• • Gastric intrinsic factor is necessary for absorption of vitamin B12 by the terminal ileum.
• Generates hydrogen ion from carbonic acid similar to osteoclast
• Prominent intracellular canaliculi lined by microvilli
• Tubulovesicle pools are part of exocytosis-endocytosis function.
• Chief cell
• Secretes pepsinogen
• Enteroendocrine cell:
• Small cells with secretory vesicles polarized toward basal surface in proximity to blood vessels.
• Produce peptide hormones and serotonin
• See Slide 20

Question 7

List the major structural features that increase surface area for absorption in the G.I. tract.

Answer 7

• Length of small and large intestine.
• Plicae circulares (valves of Kerckring)
• Villi
• Microvilli

Question 8

Describe the Three Orders of Folding

Answer 8

Three levels of folding increase surface area in the small intestine:

• Plicae: Refer to Figures 16-1, 16-2, and 16-6.
• These are folds of the mucosa, each with a submucosal core.
• Crypt-villus system:
• Each villus contains a core of lamina propria.
• The crypts extend down between the villi below the bases of the villi.
• Crypts and villi constitute glands of the small intestine.
• Wall of villus is composed of a simple columnar epithelium with goblet cells.
• Each villus contains a capillary plexus.
• Each villus contains a blind-ending lymphatic referred to as a lacteal.
• Microvilli
• Covered with glycoprotein and glycocalyx (glycolipid coat):
• • Glycocalyxcontains an array of brush-border enzymes:
• – Maltase, sucrase, isomaltase, lactase, lipase, peptidases
• – Produced by small intestinal epithelial cells
• Bundles of actin filaments within microvillus is covered by a formin cap.
• Supported by core of actin microfilaments:
• • Actin filaments are tied to terminal web intermediate filaments (cytokeratins) via spectrin fibrils.
• • Actin filaments are bound to plasma membrane covering villus via membrane-linking proteins:
• – Myosin I and calmodulin
• • Actin filaments are bound to each other via actin cross-linking proteins:
• – Villin and fimbrin
• See Slide 28-29