Ch 16B bb - Gastrointestinal System: Function & Diseases/Disorder

overview of GI system

• a complex organ system for digestion, absorption, and waste elimination

• hosts a diverse microbiota

• plays a pivotal role in maintaining overall health

• organs:

  • salivary glands

  • esophagus

  • stomach

  • pancreas

  • liver

  • small intestine

  • large intestine

salivary glands

• provide moisture; enzymes in saliva start digestion of starch

esophagus

• transports (controls) food to stomach, sphincter muscle between esophagus and stomach prevents regurgitation

stomach

• moistens & mixes food

• secretes hydrochloric acid and enzymes to digest protein (stomach lining is protected by layer of mucus)

pancreas

• secretes insulin & glucagon to manage blood sugar levels

• secrets enzymes that digest protein s, lipids & carbohydrates

• secretes alkaline solution that neutralizes acid in contents from stomach, so pH increases in small intestine

liver

• secretes bile which reduces large droplets of fat into smaller droplets so enzymes can digest the fat 

• high level of metabolizing enzymes

• first-pass effect:

  • drugs (and other chemicals) ingested orally go to liver via the portal vein before reaching other tissues 

  • the small intestine and liver may metabolize a significant fraction of drugs or chemicals

  • extent of first-pass effect differs between chemicals and between individuals

small intestine

• receives mucus & digestive enzymes from pancreas

• most digestion occurs in the first part of the small intestine

• has villi which provide a very high surface area to facilitate absorption of nutrients after digestion

large intestine (includes colon)

• undigested material moves to colon; water and minerals are absorbed here and remainder is excreted 

• in GI tract, the colon has the highest concentrations of gut microbiota

• there are ~30 feet of continuous muscular tube between mouth and anus

esophageal cancer

• narrows the inner diameter of the esophagus

• symptom include difficulty swallowing, worsening heartburn, chest pain or pressure

• spreads into adjacent organs and to remote sites through the lymph vessels; frequently metastasizes before it is detected

esophagitis (heartburn)

• inflammation of the esophagus with burning chest pains

• happens when lower esophageal sphincter doesn’t close properly and stomach acid flows up into esophagus

• often occurs after eating, at night, or when lying down

• frequent heartburn can damage the esophagus and lead to precancerous changes

• risk factors include being pregnant or overweight

• triggers include consumption of large meals or certain foods, e.g., spicy foods, fatty or fried foods, tomato products, alcohol, caffeinated beverages

crohn’s disease

• inflammatory disease

• intestine walls become thick & rigid, lumen becomes narrower causing chronic obstruction

• symptoms include diarrhea & constipation, stomach pain, stools with dark, tarry blood from upper digestive tract, and vomiting & weight loss

• remission and relapse are common 

• no cure, but treatable

• risk factors include family history, more common to develop before age 30, more common in caucasians, esp. ashkenazi jewish heritage, cigarette smoking, use of non-steroidal anti-inflammatory medicines (NSAIDs): these don’t cause disease, but can cause inflammation of the bowel, making it worse

celiac disease

• autoimmune disorder

  • immune system reacts to gluten (a protein in wheat)

  • immune response affects small intestine’s lining

    • atrophy and flattening of intestinal villi

• result is poor nutrient absorption

• symptoms include recurrent diarrhea, abdominal cramps, gas, and malnutrition

• risk factors include genetics, being female, being white of european ancestry

irritable bowel syndrome

• functional disorder of movement of the colon

• symptoms include diarrhea, constipation, abdominal pain, gas

  • symptoms do NOT include lesions, tumors, ulceration

• affects approx 20% of american adults

• risk factors include being female and abuse of laxatives

• triggers include stress

colorectal cancer

• an important cause of cancer death in the US; increasing in young adults

• symptoms include change in bowel habits (diarrhea & constipation), blood often appears in stools, anemia due to blood loss, as tumor grows abdominal discomfort & pressure along with obstruction due to tumor

• all people with suspicious symptoms should talk with doctor

• risk factors include diet (diet in high processed meats, low-fiber & high-fat diet, diet in low fruits and vegetables, and alcohol consumption), overweight and obesity, type 2 diabetes, physical inactivity, tobacco use

liver injury

• symptoms include yellowing of skin and whites of eyes, belly pain & swelling, swelling gin legs& ankles, itchy skin, dark urine and/or pale stools, constant tiredness, and loss of appetite

• causes include infection (hepatitis A, B, or C), long-term alcohol use, certain medicines or supplements, and frequent contact with toxic chemicals

• risk factors include obesity and type 2 diabetes

metabolic dysfunction-associated steatotic liver disease (MASLD)

• previously called nonalcoholic fatty liver disease (NAFLD)

• too much fat accumulates in liver

• advanced MASLD is called Metabolic Dysfunction-Associated Steatohepatitis (MASH)

• symptoms include fatigue, abdominal discomfort, but often there are no symptoms

• can progress to cirrhosis and liver failure

• risk factors include obesity, type 2 diabetes, high blood pressure, and high cholesterol

• as many as 30% of american adults and half of obese children have the disease

alcohol-related liver disease

• excessive alcohol consumption can contribute to:

  • fatty liver

  • acute hepatitis

  • cirrhosis

• symptoms include yellowing of skin and eyes, feeling ill, and kidney failure

fatty liver

• leads to an enlarged liver

• often no symptoms

acute hepatitis

• acute inflammation of the liver

• destruction of liver cells

• often causes permanent scarring

cirrhosis

• scar tissue replaces liver cells

• permanent scarring of the liver from any cause

• affects structure and function

• manifestations include liver failure, severe fatigue, and swollen belly

• most common causes include alcohol liver disease and chronic hepatitis cause by hepatitis B or hepatitis C viral infections

• less common causes include severe liver necrosis, repeated liver injury (drugs and chemicals), various genetic diseases, and longstanding bile duct obstruction (called biliary cirrhosis)

staying healthy

• eat more fiber

  • soluble fiber slows digestion, can help lower cholesterol and blood sugar 

    • sources: oats, peas, beans, apples, bananas, avocados, carrots, psyllium

  • insoluble fiber helps move waste material out of intestine, helps with constipation

    • sources: whole-wheat flour, nuts, beans, vegetables including cauliflower

• stay hydrated

• reduce alcohol consumption

• be careful with medications, supplements, and chemicals exposures

• 21 grams of fiber a day for women >50

• 25 grams for women aged 50 or younger

• 30 grams for men >50 

• 38 grams for men aged 50 or younger