lecture 20: GIT and its Disorders

Gastrin

• Produced by G cells in the antrum of stomach

• Stimulates secretion of gastric acid and pepsinogen

Simple: Gastrin makes the stomach release acid and pepsinogen to help break down food.

Cholecystokinin — CCK

• Produced by I cells in the intestinal mucosa

• Stimulates contraction of gall bladder

• Stimulates secretion of pancreatic enzyme

Simple: CCK makes the gallbladder squeeze and makes the pancreas release enzymes for digestion.

Secretin

• Produced by S cells in mucosa of duodenum and jejunum

• Released in response to acidic chyme in duodenum

• Inhibits gastric acid secretion by inhibiting gastrin

Simple: Secretin is released when acidic chyme enters the duodenum, and it decreases stomach acid by stopping gastrin.

Major GI Hormones

gastrin, cholecystokinin, and secretin

Parietal cells secrete:

• HCl / gastric acid

  • Chemically breaks down food

  • Disinfects ingested food

• Intrinsic factor — IF

  • Necessary for absorption of vitamin B12

Simple: Parietal cells make stomach acid and intrinsic factor, which helps your body absorb vitamin B12.

Chief cells secrete:

• Pepsinogen

  • Converted to pepsin when exposed to low pH of gastric juices

  • Pepsin is an enzyme that starts proteolysis (protein breakdown)

Simple: Chief cells make pepsinogen, which turns into pepsin in the acidic stomach. Pepsin starts breaking down proteins.

What can damage the gastric mucosa and disrupt the gastric mucosal barrier?

Aspirin, NSAIDs, Helicobacter pylori, ethyl alcohol, or bile salts.

What happens when the gastric mucosal barrier is disrupted?

Local ischemia, vascular stasis, hypoxia, and tissue necrosis.

What happens during fat absorption?

• Begins in the duodenum under influence of bile from liver and pancreatic lipase

• Bile forms micelles (fat carriers) that transport monoglycerides to the surface of intestinal villi

• In the intestine, MGs are taken up by epithelial cells to form new TGs

Simple: Bile helps carry fat pieces to the intestinal villi, where epithelial cells absorb them and rebuild them into triglycerides.

What is steatorrhea?

Fatty stools; fat not absorbed is excreted in stool.

What is dysphagia?

Difficulty swallowing

What are the causes of dysphagia?

• Esophageal strictures

  • Narrowing of esophagus

• Scleroderma

  • Autoimmune disorder that causes fibrous replacement of tissues throughout body and GIT

• Stroke

  • Weakness of muscular structures that propel food bolus toward stomach

  • Disruption of neural networks coordinating swallowing mechanism

• Esophageal cancer

Gastroesophageal Reflux Disease — GERD

• Acid and pepsin reflux from stomach into esophagus

• Involves mucosal injury to esophagus

• Causes hyperemia (increases blood flow to an area) and inflammation

Simple: GERD is when stomach acid and pepsin move back up into the esophagus and irritate/injure the lining.

What are complications of GERD?

Strictures

• Narrowing of esophagus

• Cause dysphagia

Barrett esophagus

• Metaplasia in lower portion of esophagus

• Associated with increased risk for development of esophageal adenocarcinoma (cancer)

What is esophageal adenocarcinoma related to?

• Barrett esophagus

• GERD

What are clinical manifestations of esophageal cancer?

• Progressive dysphagia — most frequent complaint

  • First with ingestion of bulky food

  • Later with soft food

  • Finally with liquids

• Painful swallowing

Acute gastritis

• Transient acute inflammation of gastric mucosa

• Accompanied by:

  • Emesis (vomiting)

  • Pain

  • In severe cases: hemorrhage and ulceration

• Associated with:

  • Helicobacter pylori

  • NSAIDs

  • Aspirin

  • Drugs and alcohol

Chronic gastritis

Types:

• Autoimmune gastritis

• H. pylori gastritis

Helicobacter pylori

• Produces enzymes and toxins

• These interfere with local protection of gastric mucosa against acid

• Can lead to:

  • Gastric atrophy

  • Peptic ulcer

• Associated with increased risk of gastric adenocarcinoma

Peptic Ulcer Disease — PUD

Causes

• H. pylori

• Prolong use of NSAIDs and aspirin

• Excessive use of alcohol, smoking, obesity

• >65 years old

• Socioeconomic status

Duodenal ulcers

Sxs: chronic intermittent pain in epigastric area

• Pain begins 30 min–2 hrs after eating when stomach is empty

• Pain is relieved by food and antacids

Gastric ulcers

• In antrum of stomach due to H. pylori

Sxs: chronic pain occurring immediately after eating

complication of peptic ulcer

• hemorrhage= bleeding

• obstruction = blockage; can prevent food from moving through normally

• perforation= a hole/tear through the stomach or intestinal wall

What is the hallmark of IBS?

• Intermittent, cramping lower abdominal pain

• Relieved by defecation

• Associated with change in:

  • Consistency of stools — lumpy/hard or loose/watery

  • Frequency of stools — > 3 times per day or < 3 times per week

What is Crohn’s disease and what are its clinical manifestations/complications?

Crohn’s disease

• Recurrent, granulomatous type of inflammatory response

• Can affect any part of GIT, from mouth to anus

Clinical manifestations:

• Rectal bleeding and diarrhea

• Abdominal tenderness

• Anemia

Complication:

• Fistulas

  • Abnormal communication between rectum and bladder

  • Can cause urine to look and smell like feces.

What is ulcerative colitis and what are its clinical manifestations?

• Chronic inflammatory disease that causes ulceration of colonic mucosa

• Confined to sigmoid colon and rectum

Clinical manifestations:

• Large volumes of watery diarrhea

• Bloody stools

• Cramps

• Tenesmus — pain with defecation

• Urge to defecate

• Remissions and exacerbations of bloody diarrhea

Appendicitis

Related to intraluminal obstruction (blockage) with:

• Fecalith — hard piece of stool

• Gallstones

• Tumors

• Parasites

• Lymphatic tissue

What are types of intestinal obstruction?

A) Intussusception

• Invagination or shortening of bowel

• Caused by movement of one segment of bowel into another

B) Volvulus of sigmoid colon

• Twist is counterclockwise

• Can lead to strangulated obstruction

• Impaired blood flow and necrosis of bowel tissue

malabsorption syndrome

interfere with nutrient absorption+ failure of intestinal mucosa to absorb (transport)

malabsorption syndrome

• diarrhea

• steatorrhea (fatty stool)

• bulky, yellow-gray, malodorous stools

• flatulence( gas) and bloating

• abdominal distension - belly looks swollen

• abdominal pain and cramps

celiac disease

immune- mediated disorder (immune attacks) triggered by ingestion of gluten- containing grains (including wheat, barley, and rye)

celiac disease- clinical manifestations

• Presents in infancy

• Failure to thrive- not growing

• Diarrhea, abdominal distention (belly looks swollen)

In adults:

• Diarrhea, constipation

• Symptoms of malabsorption: bloating, flatus or belching (burbing)

CRC - colorectal cancer - early manifestations

• hematochezia (bright red blood in stool)

• symptoms of anemia

• change in bowel habits

• weight loss

• fatigue