Gastrointestinal Pathology Flashcards
What is the Major Functions of the GI
- Ingest and prepare food for digestion
- Mechanical and chemical digestion
- Regulated absorption of nutrients
- Metabolism of endogenous and exogenous chemicals
- Immune surveillance
- Regulated secretion of hormones, enzymes, lubricants and water
- Microbiome functions
- Propulsion of waste
- Regulated defecation
Regions of the GI
- Upper GI tract: mouth, esophagus,
stomach - Middle GI tract: (small bowel) duodenum (9”), jejunum (2.5 m), ileum (3 m)
- Lower GI tract: (large bowel) cecum, colon (ascending, transverse, descending), rectum
- Accessory structures: salivary glands, liver, pancreas
Mesentery, Serosa, Muxosa, Muscularis
Mesentery: Connection of fats, vessels, and. verves that hold the bowel in place
Serosa: Areolar connective tissue; Epithelium
Mucosa: Epithelium; Lamina propria, Muscularis mucosae
Muscularis: Circular muscle, Longitudinal muscle
Mechanics of Digestion
Mouth
Mastication breaks food into smaller segments
- Food mixes with salive that is released from three pairs of salivary glands
– Sublingual (under tongue), Submandibular (corner fo jaw), Parotid (angle of jaw; largest)
What do Saliva contain and it’s pH?
Saliva Contain:
- Amylase (begin carbohydrates digestion)
- Lingual Lipase (triglycerides to partial glycerides and FFA)
Saliva has a pH of 7.4
- Inhibit bacterial growth in the oral cavity
- Neutralizes acid from the stomach (hence the need to rinse the mouth after vomiting to prevent erosion of the teeth)
Mechanics of Digestion
Esophagus
Esophagus is a muscular tube that is 20-30 cm long
- Swallowing begin by expansion of the upper esophageal sphincter and peristaltic movement mediated by smooth muscle
- Upper 1/3 of esophagus is skeletal muscle and is voluntary. The rest is smooth muscle and is autonomic control
- Food takes 5-7 seconds to traverse the esophagus; this is why it is important to take pills with water
- Relaxation of lower esophageal sphincter permits movement of food into stomach; Contraction prevents reflux of gastric content
Mechanics of Digestion
Stomach
Function of the stomach is to mix the food (chyme;1.2pH) with acid and digestive enzymes
- HCI is formed by parietal cells (kills unwanted bacteria) and aids in digestion
– Provides optimal pH for pepsin, and kills organisms consumed with food
- Parietal cells also produce intrinsic factors (essential for RBC formation) and is essential for absorption of vitamin B12
- Pepsin is produced by Chief Cells as pepsinogens; it require low pH (around 2) for optimal activity
- Gastrin produced in the stomach stimulates production of HCI and pepsinogen
- Gastric digestion is inhibited by sympatheitc innervation (in response to fear, pain, aggression, unpleasant taste or smell)
- Digestion is enhanced under vagal control (para)
- Mucosa of stomach protected by mucus, production of which is stimulated by prostaglandins.
- Prostaglandin Inhibitors (eg. NSAIDs) may induce gastic erosion
Mechanics of Digestion
Stomach II
Muscle of stomach provide thorough mixing with acid and enzymes, progessiviely liquefying the content
- Peristaltic contractions around 3/min, gain forces as they approach the pyloric sphincter
- Chyme enter the duodenum through the pyloric sphincter, relaxation of which is coordinated with the stomach peristaltic waves
Excessive loss of gastric fluids may increase loss of sodium and potassium ==> hyponatremia and hypokalemia
Mechanics of Digestion
Small Intestine
Chyme enter the duodenum, where it is neutralized by mixing with bile, pancreatic juice and intestinal enzymes (maltase, lactase, sucrase, trypsin, and chymotrypsin) and bicarbonate from Brunner’s glands
- Rate of digestion is regulated by secretin, cholecystokinin, motilin, and gastric inhibitory peptide
- Bile and pancreatic fluid enter the duodenum via common duct through the ampulla of Vater, which is regulated by the sphincter of Oddi (has to dilate)
- The mucosal surface of the small intestine is modified to enchance absorption of nutrients, mineral, vitamins, etc
- Movement of chyme is the result of coordinated HAUSTRAL SEGMENTALl contraction of inner smooth muscle and longitudinal peristaltic movements
- These movements are controlled by both the autonomic and regional NS, and peptide producing paraneurons
- Movement of intestine in place is facilitated by the serosal secretion; limited by omentum
- Majority of nutrient absorption occurs in small intestine
Content of small intestine pass through liver via the portal system before entering systemic circulation, hence 1st-pass metabolism of drugs taken by mouth
Where do the majority of nutrient absorption happen?
It occurs in small intestine
What is the first pass metabolism of drugs
Liver
What happens if the small intestine do not neutralize the acidic chyme?
Ulcers occurs
What is rate of digestion regulated by?
Secretin, Cholecystokinin, Motilin, and Gastric inhibitory peptide
Bile and pancreatic fluid enter the duodenum through?
Common duct, through the ampulla of Vater which is regulated by sphincter of Oddi
Movement of chyme is result of?
coordinated haustral segmental contraction of inner smooth muscle and longitudinal peristaltic movements.
- Controlled by both the autonomic and regional NS, and peptide-producing paraneurons
Movement of intestine in place is facilitated by
the serosal secretion;
limited by the omentum
Mechanics of Digestion
Large Intestine
Chyme enters the cecum via the ileocecal valve
- Some digestion happen in the proximal large intestine, but primary function is to recover water and control the fluidity of the feces
- Defecation is signaled by the distention of the distal sigmoid colon and rectum
- Defecation require the coordinated relaxation of two sphincters;
– The internal anal sphincter (autonomic control)
– External anal sphincter (more or less voluntary control)
- 30% of fecal mass is bacteria
- Internal ecology of GI bacteria (microbiome) is critical for health
- Rectal blood does not return via the liver
Chyme enter the cecum via?
The ileocecal Valve
What happens in the proximal large intestine
Some digestion happen but primary function is to recover water
and control the fluidity of the feces
Defecation is signaled by
distention of the distal sigmoid colon and rectum
Defection requires the…
coordinated relaxation of two sphincters: the internal anal sphincter (autonomic control) and external anal sphincter
(more or less voluntary control)
Rectal blood
does not return via the liver
Gastrointestinal Microbiome
Microbiome: aggregate of all microbiota residing on or within tissues
- May be bacteria, fungi or viruses (majority are bacteria)
- Organisms may be commensal, mutualist or pathogenic
- GI tract has the broadest diversity of organisms
- Composition of microbiome changes with age, diet, and health
- Reconstitution of ‘normal’ microbiome by fecal microbiome transplants has high efficacy in some diseases
Composition of microbiome established at?
Established at birth
- vaginal delivery results in largely non-pathogenic microbiota resembling mother’s.
- Caesarian delivery results in more pathogenic organisms and delays the establishment of a normal GI microbiome
Mutualistic organisms contribute to normal GI function through cooperative synthesis (eg. Vit K) and metabolism
Changes in microbiome cause?
It Implicated in diseases ranging from diabetes, obesity, IBD, neurological diseases (eg. Parkinson’s), antibiotic-mediated
colitis to colon cancer
Major Diseases of the GI Tract
- Dysregulation of movement and fluid balance
– obstruction, diarrhea, constipation - Inflammation
- Ulceration
- Infection
- Neoplasia
Oral Disease
Infections (bacterial, fungal, viral), frequent in immunosuppressed hosts
Cancers (95% squamous cell Ca)
- Oral squamous cancer has poor prognosis <50% 5-year survival
- Up to 70% of oral cancer are result of HPV infections, particularly HPV 16 & 18
– National Cancer institute recommends HPV vaccination of children as young as 9 years
- HPV- related cancer in tonsil or tongue
- Other risk factors (smoking, alcohol, poor oral care, excessive dryness)
