Gastrointestinal Flashcards
4 layers of the GI tract
Mucosa: epithelium, lamina propria, muscularis mucosae
Submucosa: glands, blood vessels, nerves
Muscularis propria/externa: inner circular and outer longitudinal muscle layer
Adventitia/Serosa
Circumvallate papillae
Dome-shaped
Sunken structures
8-12 of them
Taste buds
Filiform papillae
Small conical prominences on lingual surface
No taste buds
Fungiform papillae
Mushroom shaped projections on the surface among the filiform but mainly at the tip and lateral margins
Have taste buds on the upper surface
Foliate papillae
Short vertical folds on the lateral margins
Taste buds scattered over the surface
Serous glands drain into the fold and clean the taste buds
How many teeth do children vs adults have?
Children: 20
Adults: 32
3 major salivary glands
Parotid
Sublingual
Submandibular
Function in the salivary glands
- Serous cells
- Intercalated duct cell
- Striated duct cell
- Secrete amylase - digests starch into maltose
- Secretes bicarbonate, absorbs Cl-
- Modifies saliva to be hypotonic with plasma
Upper 1/3 of esophagus is…
Striated muscle! Voluntary
GERD
Gastrointestinal reflux disease
Lower esophageal sphincter fails to close properly
Stomach contents leak back, reflux
Can taste stomach fluid in the back of the mouth
Frequent heartburn
Eosinophilic Esophagitis
Inflammation or swelling of the esophagus
Diagnose with endoscopy and biopsy
Large number of eosinophils cause inflammation
Stiffening or narrowing of the esophagus
Can lead to difficulty swallowing (dysphagia)
3 types of stomach glands
Cardiac glands
Pyloric glands
Gastric/fundic glands
4 types of cells in the stomach glands
Mucous cells
Parietal cells or oxyntic cells
Chief cells
Enteroendocrine cells
What do 1. Mucous cells 2. Parietal cells or oxyntic cells 3. Chief cells 4. Enteroendocrine cells secrete?
- Secretes mucus into the lumen
- Secretes HCl, intrinsic factor into lumen and bicarbonate into blood
- Pepsinogen (zymogen, gets converted to pepsin) into lumen
- hormones - G cells secrete gastrin into blood
How is the stomach unique?
Has 3 layers of muscle (oblique muscle is extra)
Barrett’s esophagus
Stratified squamous epithelium of the esophagus is replaced by simple columnar epithelium with goblet cells
Strong association with esophageal adenocarcinoma
Brunner’s glands
Only in the small intestine (submucosa)
Secrete alkaline fluid containing neutral and alkaline glycoproteins and bicarbonate ions
Crypts of Liberkuhn
Secrete carbohydrases, proteases, and lipases
In the mucosa
4 principle cell types in the small intestine
Enterocytes
Paneth cells
Goblet cells
Enteroendocrine cells
What do 1. Enterocytes 2. Paneth cells 3. Goblet cells 4. Enteroendocrine cells secrete?
- Digest and absorb things
- Secrete lysozyme and defensins into lumen
- Mucus into lumen
- Secretin, CCK, GIP, others into blood
Period acid-Schiff stain
Used to detect polysaccharides such as glycogen, and glycoproteins, glycolipids, and mucins
Endopeptidases
Cleave the polypeptide at interior bonds
Exopeptidases
Cleave the terminal amino acid
2 subclasses of exopeptidases and where they cut
Aminopeptidases: cleave off the terminal amino acid at the amine end of the chain
Carboxypeptidases: cleave off the terminal amino acid at the carboxyl end of the chain
Colipase
Binds to the lipidase and enhances its activity by anchoring to the lipid-water interface
Free fatty acids and monglyceride are generated, which combine with other lipids and bile salts to form water-soluble micelles
Zonula occludens
Tight junctions
Proteins are occludins and claudins
Most important barrier in making it tight
Most apical
Zonula adherens
Adherens/intermediate junctions, belle desmosome
Cadherins (homophilic) - bind to each other
Catenins are linked to cellular actin
Desmosomes
Macula adherens
Cadherins and desmoplakin linked to intermediate filaments
Junction communicates with the skeleton of the cell
Plicae circulares
In the small intestine
Folds of the mucosa into the lumen (has crypts and villi)
Even more surface area
Glycocalyx
Acidic mucopolysaccharides and glycoprotein matrix on the apical surface, on the microvilli
Gastrin
secreted by, source and stimulus, target organ, response
S: stomach mucosa
SS: stomach in response to food
TO: stomach, small intestine
R: release of HCl, increase of intestine movement, release of pepsinogen
Secretin
secreted by, source and stimulus, target organ, response
S: Small intestine
SS: duodenum in response to acidic chyme
TO: pancreas
R: secretion of alkaline digestive proenzyme, inhibits intestine motility
Cholecystokinin
(secreted by, source and stimulus, target organ, response)
More details
S: Small intestine SS: intestinal cells in response to food TO: pancreas, gallbladder R: secretion of proenzymes and bile Secreted by I cells in the epithelium Inhibits gastric emptying and gastric acid secretion, stimulates acinar cells of the pancreas to release digestive enzymes, increased production of bile, contraction of the gall bladder, relaxation of the sphincter so bile can enter duodenum
Gastric Inhibitory Peptide
secreted by, source and stimulus, target organ, response
S: Small intestine (K cells)
SS: Intestinal cells in response to fat
TO: stomach, pancreas
R: insulin secretion, inhibits gastric secretion and motility
Actions on fat cells and bone remodelling
Haustr
Pouches formed by the taenia coli
Taenia coli
3 independent long ribbons of smooth muscle just below the serosa, along the colon length
Condensations of the longitudinal muscle layer
Cecum functions
Salt recovery (uptake)
Lubricates sold waste
Bacterial digestion of cellulose
Appendix
Same histology as the rest of the intestine Small blind ending pouch from the cecum Thickened walls (due to lymphoid tissue) Longitudinal smooth muscle layer does not aggregate into taenia coli
4 different kinds of epithelium and their location in the large intestin
Simple columnar epithelium in the upper zone
Stratified squamous epithelium in the middle and lower zones
Simple columnar epithelium of the anal glands
Stratified columnar epithelium of the anal sinuses, crypts, and ducts of the anal glands
Myenteric Plexus
Aka Auerbach’s plexus
Major role in motility and passing food through the digestive tract
Submucosal Plexus
Aka Meissner’s plexus
A secondary plexus
Derived and formed by branches that have perforated the circular muscle
Innervates the epithelial layer and muscularis mucosae
Celiac disease
Genetic predisposition to an autoimmune, crossreactive reaction to gluten (modified by transglutaminase)
Pale, loose and greasy stool affecting absorption
Range from almost asymptomatic to very bad malnutrition
Lactose intolerance
Lack of lactase (cleaves lactose into glucose and galactose)
Results in high concentrations of lactose reaching the colon and affecting the osmotic state, passively drawing water into the lumen
Normally the amount of lactase declines with age
Colitis
Inflammation of the colon
Multiple causes
Abdominal pain and diarrhea
Chron’s vs ulcerative colitis
C: inflammation affects the alimentary tract
UC: inflammation affects colon and rectum
Irritable bowel syndrome
Non-inflammatory symptom based diagnosis
Chronic abdominal pain, discomfort, bloating, and diarrhea/consitpation
Diverticulosis
Small weak areas in the colon wall allowing the mucosa to protrude through, forming tiny pouches called diverticuli
Usually no problem but can bleed, become inflamed or infected to become diverticulitis
Colon polyps
Familial adenomatous polyposis
Small growths
Some develop into cancer over a long time
Occult vs frank blood
O: high GI bleed
F: low GI bleed
Triad in portal area
Hepatic artery
Bile duct
Portal vein
Sinusoids
Low pressure channels that receive blood from terminal branches of hepatic artery and portal vein and deliver it to central canal
Lined with fenestrated endothelial cells and flanked by hepatocytes
Space of Disse
Between endothelium and hepatocytes
Plasma accumulates and retrogradely flows back into the lymphatics
Kupffer cells
Type of macrophage that engages bacteria coming from the intestine
In the sinusoids
Deal with foreign particles (gut endotoxins)
Stellate cell
Between sinusoid and hepatocytes (in space of Disse)
Make collagen fibrils and ECM materials
Hepatocyte function
Bile production, uptake and transport Lipid uptake and metabolism Glycogen synthesis Detoxification by p450 enzymes Protein synthesis (ex: albumin, complement, fibrinogen, lipoproteins)
2 functions of bile
Emulsification of lipid aggregates
Solubilization and transport of lipids
Hering’s canal
Vessels collecting bile from the canaliculli
Bile ducts
Collect bile from Hering’s canals
Parallel to hepatic arteries and portal veins
Common hepatic duct
Collects bile from hepatic ducts and branches into the cystic duct and then the common bile duct which then empties into the duodenum
Jaundice
Increased bilirubin in the blood
Cirrhosis
Normal liver cells are replaced by scar tissue due to chronic liver disease
Alcohol abuse most common
Steatosis
Fatty liver disease
Cholesterol or TAGs accumulate
Types of exocrine cells in pancreas
Acinar: secretes digestive enzymes
Ductal: secrete bicarb
Types of endocrine cells in pancreas
Alpha cells: glucagon
Beta: insulin
Delta: somatostatin
Action, precursor and activator for:
- Trypsin
- Chymotrypsin
- Elastase
- Carboxy’dase A/B
- Endopeptidase, trypsinogen, enteropeptidase/enterokinase and trypsin
- Endopeptidase, chymotrypsinogen, trypsin
- Endopeptidase, proelastase, trypsin
- Exopeptidase, procarboxy’dase A/B, trypsin
What activates enteropeptidase?
Duodenase
Somatostatin
Produced by delta cells in the pancreas
Reduces smooth muscle contractions in tract and gall bladder
Pancreatic insufficiency
Lose about 90% ability to secrete digestive enzymes
Patients unable to digest food, resulting in malabsorption of nutrients (including vitamins)
Impaired absorption of fats causes diarrhea, weight loss, malnutrition
Cystic fibrosis
Loss of the CFTR
Decreased production of sodium bicarbonate makes secretions dehydrated, thickened, blocking ducts
Pancreas continues to make enzymes that damage it, leading to fibrosis
Peyer’s patches
Mucosal inductive site
Where the cells become stimulated
Have M cells
Intraepithelial lymphocyte
Function is not entirely clear
Likely play a role in detecting pathogens or react to infected or damaged (and cancerous) epithelial cells
Have cytotoxic properties so are able to kill abnormal cells
Histatins
Antifungal properties
Made in salivary glands
