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Digestion And Metabolism > Gastrointestinal Tract > Flashcards

Gastrointestinal Tract Flashcards

1
Q

Whhatt does the gastrointestinal tract consost of?

A 
Consists of:
1. Alimentary canal
2. Associated organs
• Tongue
• Teeth
• Salivary glands
 • Pancreas
• Liver
• Gallbladder
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2
Q

What does the dorsal surface of the tongue consist of?

A 
Lingual Muscles: Striated 
    • Extrinsic
• Attaches tongue to outside structures
• Moves entire tongue 
    • Intrinsic
• Originate and insert within the tongue
• Alters shape of tongue

Sulcus Terminalis
• V-shaped depression which divides tongue into anterior 2/3 and posterior 1/3. Foramen cecum at its apex.

Lingual papillae on the anterior 2/3
 • Filiform
• Fungiform
• Circumvallate
• Foliate

Taste buds associated with select papillae

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3
Q

Whaat are the types of the Iingual paapillae?

A

Filiform

Fungiform

Foliate

Circumvillate

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4
Q

Describe filiform linguaal papillaae

A

Filiform
• Small and conical

• Lined by highly keratinized stratified squamous
epithelium

• Distributed over the entire dorsal surface with tips facing backwards

  • mechanical function
  • no taste buds
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5
Q

Describe the fungiform paapillae of the lingual papillae

A

Fungiform
• Mushroom shaped

  • Lined by stratified squamous epithelium
  • Scattered among the filiform, but most prominent on tip of tongue
  • Taste buds in the epithelium on the dorsal surface of the papillae
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6
Q

Describe the foliate papillae of the lingual pappilae

A

Foliate
• Found on the lateral edges of tongue

  • Parallel rows separated by deep clefts
  • Taste buds
  • Rudimentary in adults
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7
Q

Describe the circumvillare papillae of the lingual papillae

A

Circumvallate
• 8 to 12 large and dome shaped found anterior to sulcus terminalis

  • Surrounded by a moat-like invagination which receives ducts of serous Von Ebner’s glands
  • Taste buds in epithelium of lateral surfac
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8
Q

Describe taste buds

A

Taste buds extend through the entire thickness of epithelium and detect taste stimulating particles (tastants) from food.

Composition:
• Taste pore
• Three types of cells:
• Sensory neuroepithelial cells
• Interact with taste receptors on the apical surface of the cells
• Microvilli on apical surface
• Synapse with afferent neurons: CN VII, IX, X
• Express 1 class of receptor protein
  • Turnover ~ 10 days
  • Supporting cells
  • Microvilli on apical surface
  • Turnover ~ 10 days
  • Basal cells
  • Stem cells• Five basic stimuli: sour, bitter, sweet, salty, umam
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9
Q

What is the alimentary canal?

A
  • Extends from proximal esophagus to anal canal
  • Same basic structure throughout
  • Organized in four distinct layers:
  • Mucosa
  • Submucosa
  • Muscularis Externa
  • Serosa/Adventitia

• Different parts of the alimentary canal contains specializations in the different layers that are characteristic of that region

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10
Q

Describe the gross structure of the esophagus

A
  • ~25cm long muscular tube
  • Connects pharynx to stomach
  • Functionasaconduitforthe bolus of food from the mouth
  • Lumen normally collapsed with longitudinal folds
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11
Q

Describe the mucisa of the esophagus

A

• Epithelium (E)
• Stratified squamous non keratinized
epithelium
• Protects from mechanical and chemical injury

  • Lamina Propria (LP)
  • Connective tissue containing diffuse lymphatic tissue and lymphatic nodules

Esophageal Cardiac Glands ( NOT shown)
• Present mainly in terminal part of
esophagus
• Produces neutral mucus which protects from regurgitated gastric contents

 Muscularis Mucosae (MM)
• Single layer of longitudinal muscle
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12
Q

Describe the submucosa of the esophagus

A
  • Dense irregular connective tissue
  • Large blood and lymphatic vessels
  • Submucosal Plexus (Meissner’s plexus)

• Esophageal Glands Proper:
• Scattered throughout the
length
• Producesslightlyacidic mucus

  • Lubricates the lumen
  • Excretory duct: (green arrow) lined by stratified squamous epithelium
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13
Q

Describe the muscularis externa of the esophagus

A

Typical two layers: inner circular and outer longitudinal
• Upper third: striated

  • Middle third: striated and smooth
  • Lower third: smooth
  • Myenteric plexus (Auerbach’s plexus) – innervates muscularis externa for peristals
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14
Q

Describe the serosa and adventitia of the esophagus

A
  • Above the diaphragm
  • Fixed to adjacent structures by adventitia

• Below the diaphragm
• Serosa continuous with that of the
stomac

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15
Q

Describe the esophagogastric (gastroesophageal) junction

A

Mucosa undergoes an abrupt transition

Epithelium→Stratified squamous to simple columnar epithelium

Lamina propria→Esophageal cardiac glands replaced by cardiac glands of stomach

Muscularis mucosa→One layer to two layers of smooth muscles arranged as inner circular and outer longitudinal

Submucosa→Esophageal proper glands to NO glands in the submucosa Muscularis externa→added innermost oblique layer

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16
Q

What is the barrets esophagus and gastro-esophageal reglux disease?

A

• Frequent cause of chest pain ( burning nature)

• Main cause is a weakened lower esophageal sphincter which causes reflux back
into the lower esophagus

  • Chronic acid reflux results in reversible substitution of the normal stratified squamous epithelium of the lower esophagus for simple columnar epithelium (metaplasia)
  • Untreated chronic metaplasia can become irreversible→Dysplasia→ adenocarcinoma
17
Q

Describe the structure of stomach

A

Histologically, the stomach is divided into 3 regions based on the types of the glands:

  1. Cardiac region (cardia) near the esophageal orifice
    • Contains cardiac glands
  2. Fundic region (fundus) situated between cardia
    and pylorus – largest part
    • Contains fundic (gastric) glands
  3. Pyloric region (pylorus) is the distal, funnel- shaped region proximal to pyloric sphincter
    • Contains pyloric glands
18
Q

What are the functions of the stomach?

A

Functions:
• Mixing

  • Partial enzymatic digestion - secretes digestive enzymes: pepsin, lipase. Partially digested food→ Chyme
    • Minimal absorption of some water and certain drugs (Alcohol, Aspirin, NSAIDS)

Rugae are characteristic temporary longitudinal folds of mucosa and submucosa to accommodate expansion and filling of stomach

19
Q

Contrast a mucosa and submucosa of the stomach

A 
Mucosa:
• Gastric pits or foveolae 
• Glands
• Extend from muscularis mucosae
• Empty into gastric pits
  • Epithelium
  • Lines the surface and gastric pits
  • Simple columnar epithelium
  • Surface mucous cells
  • Lamina Propria
  • Loose connective tissue
  • Surrounds gastric glands
  • Muscularis mucosae
  • Inner circular and outer longitudinal

Submucosa
• Dense connective tissue
• Lymphatics, blood vessels and submucosal plexu

20
Q

Describe the muscularis externa of the stomach

A 
Muscularis Externa
• Three layers of muscle
• Innermost oblique
• Middle circular: thickens to form the pyloric sphincter
• Outer longitudinal

• Functions to mix stomach contents (chyme) and force the partially digested food into the small intestines

21
Q

Contrast the histology of the cardiac and pyloric region of the stomach

A

Cardiac region
• Relatively short pits & short cardiac glands
• Tubular with occasional branching
• Cells
• Mucus-secreting cells • Enteroendocrine

Pyloric region

  • Relatively long pits and short pyloric glands
  • Branched, coiled, tubular with wide lumen
  • Cells
  • Secretory cells secrete a viscous mucus
  • Enteroendocrine
22
Q

Describe the fundic region of the stomach

A 
• Short pits
• Lined by surface mucous cells
• Long fundic (gastric) glands
• Simple branched tubular
glands
• 2-4 glands empty into one gastric pit
  • Three parts
  • Isthmus
  • Neck
  • Fundus (base)
23
Q

What are the cell types of the glands in the fundic region?

A
  • Cell types found in glands
  • Mucous neck cells
  • Parietal (oxyntic)cells
  • Chief cells
  • Enteroendocrine cells
  • Stem cells
    • Found in isthmus of gland
24
Q

How much juices are produced to fundic gland secretions?

A

2L/day

25
Q

What are the 4 major components of fundic gas secretions?

A 
1.Hydrochloric acid (HCl)
• Produced by parietal cells
• Gives gastric juice low pH
• < 1.0 to 2.0
• Converts inactive pepsinogen
into pepsin
• Kills most bacteria
2. Pepsin
• Produced by chief cells
• Potent proteolytic enzyme
• Hydrolyzes proteins into small peptides
• Converted from pepsinogen
3.   Mucus
• Protective coating for the stomach
• Physiological barrier
• Neutral to alkaline
pH: bicarbonate • Physical barrier
  1. Intrinsic factor
    • Glycoprotein secreted by parietal cells
    • Binds to vitamin B12
    • Essential for B12 absorption in
    the distal ileum
    • Lack of intrinsic factor results in pernicious anemia & vitamin B12 deficiency
26
Q

What are the functions of surface mucosal cells?

A

Surface mucous cells
• Secretes thick viscous mucus that adheres to epithelium protecting from rough chyme
• Lines gastric pits
• Elongated nucleus
• Large apical cup of mucinogen granules takes up most of cytoplasm
• High bicarbonate and potassium content→protects from acidity of gastric juice
• Prostaglandins secreted by the cells of the mucosa stimulate the secretion of bicarbonate and increases the thickness of the mucus

27
Q

What are the functions of the neck mucosal cells?

A

Mucous neck cells
• Located in neck of gland
• Secretes soluble mucus that helps transports gastric secretion to lumen

  • Smaller than surface mucous cells
  • Less mucinogen in apical cytoplasm
  • Spherical nucleus
  • Release of mucinogen granules is triggered by vagal stimulation – no release of mucus in the resting stomach
28
Q

What are the functions if the parietal (oxynitic cells)?

A

• Secrete H+, Cl - and Intrinsic factor

  • Found throughout gland but concentrated in neck
  • Large mono or binucleated cells
  • Eosinophilic due to +++ mitochondria - for active proton pumps
  • Extensive intracellular canalicular system that communicates with lumen of gland

• Tubulovesicular system containing excess plasma membrane with proton pumps is present in the cytoplasm adjacent to the canaliculi.

  • Stimulated by gastrin
  • Receptors for histamine (H2)
29
Q

What are the significance of chief cells?

A
  • Located at the base of gland
  • Typical protein-secreting cell
  • Abundant rER
  • Gives cells basophilic appearance • Apical zymogen granules

Secretions
1. Pepsinogen converted to pepsin by low pH
(proteolytic enzyme)
2. Secretes weak lipase

30
Q

What are the functions of the enteroendicrine celld?

A
  • Secretes hormones into the lamina propria
  • Found throughout the gland
  • More prevalent in the base
  • Typically appear clear with H & E stain
  • 2 general cell types • Closed
  • Do not reach the lumen • Open
  • Exposed to lumen
  • Serve as primary chemoreceptors
  • Gastrin secreting cells are concentrated in the pyloric antrum

Digestion And Metabolism (57 decks)

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