Gastrointestinal Tract Flashcards
(30 cards)
Whhatt does the gastrointestinal tract consost of?
Consists of: 1. Alimentary canal 2. Associated organs • Tongue • Teeth • Salivary glands • Pancreas • Liver • Gallbladder
What does the dorsal surface of the tongue consist of?
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
Whaat are the types of the Iingual paapillae?
Filiform
Fungiform
Foliate
Circumvillate
Describe filiform linguaal papillaae
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
Describe the fungiform paapillae of the lingual papillae
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
Describe the foliate papillae of the lingual pappilae
Foliate
• Found on the lateral edges of tongue
- Parallel rows separated by deep clefts
- Taste buds
- Rudimentary in adults
Describe the circumvillare papillae of the lingual papillae
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
Describe taste buds
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
What is the alimentary canal?
- 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
Describe the gross structure of the esophagus
- ~25cm long muscular tube
- Connects pharynx to stomach
- Functionasaconduitforthe bolus of food from the mouth
- Lumen normally collapsed with longitudinal folds
Describe the mucisa of the esophagus
• 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
Describe the submucosa of the esophagus
- 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
Describe the muscularis externa of the esophagus
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
Describe the serosa and adventitia of the esophagus
- Above the diaphragm
- Fixed to adjacent structures by adventitia
• Below the diaphragm
• Serosa continuous with that of the
stomac
Describe the esophagogastric (gastroesophageal) junction
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
What is the barrets esophagus and gastro-esophageal reglux disease?
• 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
Describe the structure of stomach
Histologically, the stomach is divided into 3 regions based on the types of the glands:
- Cardiac region (cardia) near the esophageal orifice
• Contains cardiac glands - Fundic region (fundus) situated between cardia
and pylorus – largest part
• Contains fundic (gastric) glands - Pyloric region (pylorus) is the distal, funnel- shaped region proximal to pyloric sphincter
• Contains pyloric glands
What are the functions of the stomach?
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
Contrast a mucosa and submucosa of the stomach
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
Describe the muscularis externa of the stomach
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
Contrast the histology of the cardiac and pyloric region of the stomach
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
Describe the fundic region of the stomach
• 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)
What are the cell types of the glands in the fundic region?
- Cell types found in glands
- Mucous neck cells
- Parietal (oxyntic)cells
- Chief cells
- Enteroendocrine cells
- Stem cells
- Found in isthmus of gland
How much juices are produced to fundic gland secretions?
2L/day
