Gastrointestinal Tract Flashcards
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
What are the 4 major components of fundic gas secretions?
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
- 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
What are the functions of surface mucosal cells?
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
What are the functions of the neck mucosal cells?
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
What are the functions if the parietal (oxynitic cells)?
• 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)
What are the significance of chief cells?
- 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
What are the functions of the enteroendicrine celld?
- 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
