Questions and Answers
What are the four main parts of the gastrointestinal (GI) tract?
The mouth, esophagus, stomach, and small and large intestines
What is the primary function of the digestive system?
To convert large food molecules into smaller substances that can be absorbed
What is bioavailability, and why is it important?
Bioavailability refers to the extent to which the digestive tract absorbs a nutrient and how well the body uses it
What are the accessory organs of the digestive system, and what role do they play?
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What happens to nutrients that are already in their simplest form, such as water, cholesterol, minerals, and most vitamins?
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Why is cooking food important for digestion?
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What is the length of the GI tract in a living person, and how does it compare to the length in a cadaver?
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What is the purpose of removing inedible parts or cooking raw foods before eating?
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What is the primary function of teeth in the digestive process?
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What is the purpose of saliva in the digestive process?
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What role do taste buds play in the digestive process?
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Why is the sense of taste important for overall health?
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What is the significance of the bitter taste in relation to food?
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What is the term for the complete loss of the sense of smell?
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What is the term for a distorted sense of taste?
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What is the function of the tongue in the digestive process?
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What is the significance of the umami taste in relation to nutrition?
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What is the purpose of salivary amylase in the digestive process?
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Why do people with COVID-19 often experience a loss of smell and taste?
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What is the primary function of the esophagus?
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What prevents food from entering the larynx and trachea during swallowing?
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What helps propel material through the digestive tract during swallowing?
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What is dysphagia, and what are its effects on the body?
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Who is most commonly affected by dysphagia?
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Why do children often reject strong-flavored foods?
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What happens to the sense of smell and taste in most people who have COVID-19?
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What is the relationship between the sense of smell and the ability to sense the taste of food?
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What is the significance of peristalsis in the digestive process?
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What is the primary function of the watery fluids secreted by the small intestine into the lumen?
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What is the purpose of segmentation in the small intestine?
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What is the function of microvilli on absorptive cells in the small intestine?
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What is the role of the pancreas in the small intestine?
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How do some nutrients enter absorptive cells in the small intestine?
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Where do water-soluble nutrients, such as sugars and minerals, enter after being absorbed in the small intestine?
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What is the term for the breakdown of nutrients requiring water, such as during digestion?
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What is the purpose of the mucus layer produced by cells lining the small intestine?
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What is the structure that increases the surface area of the lumen in the small intestine?
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What is the last portion of the small intestine?
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What is the function of the lower esophageal sphincter in the stomach?
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What is the composition of gastric juice, and what is its function?
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What is chyme, and how is it formed?
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Why does the stomach not digest itself, despite having digestive enzymes?
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What is the function of the pyloric sphincter, and how does it relate to gastric emptying?
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What is the significance of the small intestine's three sections?
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How does the presence of food in the stomach trigger gastric secretion?
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What is the difference between the small intestine and the large intestine in terms of diameter?
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What is the role of the duodenum in the small intestine?
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Why do fatty and protein-rich meals delay gastric emptying?
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What is the structure formed when cholesterol and other lipids are coated with a layer of protein?
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What is the approximate time it takes for chyme to move from the beginning of the duodenum to the end of the ileum?
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What is the purpose of Peyer's patches in the ileum?
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What is the function of bicarbonate ions secreted by the pancreas?
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What triggers the release of cholecystokinin from small intestinal cells?
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What is the result of a lack of nutrients for cell division in absorptive cells?
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What is the function of mucus in the intestinal tract?
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What are the signs of the immune system's response to an agent of infection or disease process?
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What is the primary role of the pancreas in digestion?
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What is the approximate amount of water that enters the GI tract daily from ingested foods and beverages and intestinal cell secretions?
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What is the function of cholecystokinin in the digestive system?
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What is the composition of gallstones, and what are the possible sizes?
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How do people with cystic fibrosis overcome the malabsorption problem?
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What is a bezoar, and where is it most likely to develop?
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What happens when a gallbladder that contains stones contracts or a gallstone lodges in the common bile duct?
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What is the result of having excess body fat in relation to gallstones?
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What is the function of bile in the digestive system?
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What happens to bile after surgery to remove the diseased gallbladder?
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What is the relationship between cystic fibrosis and the pancreatic ducts?
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What is trichobezoar, and how is it related to pica or trichotillomania?
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What is a bezoar, and how is it formed in the digestive tract?
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What is the role of gut microbiota in maintaining good health?
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How is a gastric bezoar typically removed from the stomach?
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What is the benefit of eating a high-fiber diet in relation to gut microbiota?
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What is the function of the appendix in relation to the immune system?
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What is the main function of the mucus produced by cells in the large intestine?
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What is the composition of feces, and how long does it take for undigested material to move through the large intestine?
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What is the result of intestinal dysbiosis?
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What is the condition characterized by the imbalance of the normal diversity of microbial populations in the GI tract?
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How do gut microbiota benefit their human host, and what do they produce?
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What is the role of the external anal sphincter in the elimination process?
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What is the purpose of gut microbiota transplantation (GMT)?
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Where are the majority of microorganisms found in a healthy person's digestive tract?
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What is the effect of antibiotic use on the population of C-diff bacteria?
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What is the result of C-diff infection?
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What is the significance of the timing of the development of voluntary control of the external anal sphincter in children?
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What is the significance of the appendix in relation to maintaining good health?
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What happens to the balance of gut microbiota in certain diseases, and what are scientists studying?
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How long is the large intestine, and what are its major sections?
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What is the link between intestinal bacteria and certain diseases?
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What occurs when the balance of the gut microbiota is disrupted, such as when antibiotics are used to treat bacterial infections?
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What is the primary purpose of probiotics?
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What is the role of prebiotics in the gut microbiota?
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What is the potential benefit of using fecal transplants in people with ulcerative colitis or Crohn's disease?
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Why is it important to wash your hands after having a bowel movement?
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What is the significance of the gut microbiota in a healthy person?
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What is the potential benefit of taking antifungal medications in people with gut fermentation syndrome?
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Why is the use of probiotics and prebiotics important for overall health?
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What is the primary role of Lactobacillus and Bifidobacterium in probiotics?
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Why is more research needed on the use of probiotics and prebiotics?
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What is the estimated number of adult Americans who have either ulcerative colitis (UC) or Crohn’s disease (CD)?
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What is the typical Western diet thought to do to the gut’s microbiota?
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What is characterized by the formation of ulcers (sores) in the inner lining of the large intestine?
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What is advised for people with ulcerative colitis when they experience flares of the illness?
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What is the part of the gastrointestinal tract that can be affected by Crohn's disease?
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What is the increased risk for patients with ulcerative colitis, especially when their entire colon is affected and they have had the disease for 8 or more years?
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What is similar in the treatment of ulcerative colitis and Crohn’s disease?
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What is thought to play a role in the development of IBD?
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What is the name for the general group of chronic diseases that cause inflammation and swelling of the intestines?
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What is the term used to describe the change in the kinds of bacteria that make up the gut’s microbiota?
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What was Alicia's initial symptom that led her to visit the emergency room?
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What is Alicia's occupation?
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What is the name of the disease Alicia was diagnosed with?
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What medication was Alicia initially prescribed to treat her Crohn's disease?
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Why is it not recommended to use 'high colonics' or enemas to cleanse the colon?
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What does Alicia have to constantly assess to manage her Crohn's disease?
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What treatment does Alicia currently take for her Crohn's disease?
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What is the term for the bouts of painful intestinal cramps followed by diarrhea that Alicia experiences?
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Study Notes
Digestive System Overview
- The digestive system, also known as the gastrointestinal (GI) tract, is a hollow, muscular tube that extends approximately 16 feet from the mouth to the anus.
- The process of digestion converts large food molecules into smaller substances that can be absorbed.
- Nutrients that are already in their simplest form, such as water, cholesterol, minerals, and most vitamins, are not digested but are absorbed intact.
Mouth
- Digestion starts in the mouth, where teeth begin the mechanical digestion of food by biting, tearing, and grinding it into smaller chunks.
- Saliva from salivary glands mixes with food and lubricates it, containing mucus and enzymes salivary amylase and lingual lipase.
- Salivary amylase enables a minor amount of starch digestion to occur in the mouth, while lingual lipase does not begin to digest fat until the food reaches the stomach.
- The sense of taste is important for stimulating appetite and detecting nutrients or toxic substances in substances that enter the mouth.
Esophagus
- The esophagus is a muscular tube that extends from the back of the mouth to the top of the stomach.
- Its primary function is to transfer a bolus of swallowed food into the stomach.
- The epiglottis, a flap of tough tissue, prevents food from entering the larynx and trachea when swallowing.
- Peristalsis, waves of muscular activity, help propel material through the digestive tract.
Stomach
- The stomach is a muscular sac that can expand and hold about 4 to 6 cups of food after a typical meal.
- The lower esophageal sphincter constricts, closing the opening between the esophagus and the stomach, after food enters the stomach.
- Gastric juice, a watery solution that contains hydrochloric acid (HCl) and enzymes, is secreted by the stomach to break down proteins and fats.
- HCl helps convert a chemically inactive digestive enzyme (pepsinogen) to its active form (pepsin) and makes proteins easier to digest.
Small Intestine
- The small intestine is a tightly-coiled hollow tube that extends from the stomach to the large intestine, measuring about 11 feet long.
- It has three sections: the duodenum, jejunum, and ileum, with most digestion and nutrient absorption occurring in the duodenum and jejunum.
- The small intestine secretes approximately 1½ quarts of watery fluids daily to lubricate the intestinal walls and facilitate the passage of chyme.
- Villi, tiny finger-like projections, and microvilli, tiny hair-like structures, increase the surface area of the lumen to aid in nutrient absorption.
Absorption and Transport of Nutrients
- The process of absorption occurs through various ways, including diffusion and the help of transport proteins or pumping mechanisms within the absorptive cell's membrane.
- Water-soluble nutrients, such as sugars and minerals, enter the villus's capillary and eventually the hepatic portal vein, which delivers them to the liver for processing.
- Lipids are coated with a layer containing protein, forming a chylomicron, which moves into a lacteal, a lymphatic system structure, and eventually enters the bloodstream.
Malabsorption
- Malabsorption can occur if the nutrients needed for cell division are lacking, leading to fewer dead absorptive cells being replaced, and resulting in weight loss and diarrhea.### Intestinal Tract: Immune Function
- The intestinal tract has special cells that produce mucus, which forms a barrier to reduce the absorption of harmful agents like microbes and viruses.
- Peyer's patches in the ileum contain immune system cells that can produce antibodies to fight against infection.
- Antibodies are proteins that recognize and bind to harmful agents, helping destroy them before they enter the bloodstream.
- Inflammation is a sign of the immune system's response to infection or disease, characterized by pain, tissue redness and swelling, loss of function, and fever.
Pancreas, Liver, and Gallbladder
- These organs play major roles in digestion, although chyme does not move through them.
- The pancreas produces digestive enzymes that break down carbohydrates, protein, and fat, as well as bicarbonate ions to neutralize HCl in the duodenum.
- The liver processes and stores nutrients, makes cholesterol, and produces bile to prepare fat and fat-soluble vitamins for digestion and absorption.
- Bile is stored in the gallbladder and released into the duodenum when acidic chyme and fat are present.
Gallstones
- Gallstones usually consist of cholesterol and can be small or large, causing considerable pain in the right upper part of the abdomen if they block the ducts.
- Risk factors for gallstones include having excess body fat, so maintaining a healthy weight can reduce the risk.
- Surgery may be necessary to remove the diseased gallbladder to prevent damage to the liver or pancreas.
Cystic Fibrosis
- This inherited disease causes thick, sticky mucus that blocks passageways, particularly in the respiratory and digestive systems.
- In the digestive system, pancreatic ducts become blocked, interfering with the delivery of digestive enzymes to the small intestine.
- Patients with cystic fibrosis can take capsules containing pancreatic enzymes to overcome malabsorption problems.
Bezoars
- Bezoars are dense masses of undigested material that can form in the digestive tract, particularly in the stomach.
- They can be composed of hair, plant material, or other substances, and can cause abdominal pain, vomiting, and intestinal blockages.
- Treatment options include endoscopy to remove the bezoar, or ingestion of enzymes and carbonated beverages to soften or dissolve it.
Large Intestine
- The large intestine is shorter than the small intestine but has a wider diameter.
- Cells in the large intestine produce mucus to protect and lubricate the walls of the colon and rectum.
- The large intestine has no villi, so little additional absorption occurs here, and its main function is to store and eliminate waste.
Elimination
- Feces remain in the rectum until muscular contractions move them into the anal canal and out of the body through the anus.
- The external anal sphincter is under voluntary control, allowing individuals to determine when to have a bowel movement.
Microbes in the Digestive Tract
- The gut microbiota consists of viruses, fungi, and vast numbers of bacteria, which benefit human health by maintaining a balance and limiting the growth of harmful species.
- Intestinal bacteria can break down undigested food, produce vitamins, and maintain good health by limiting harmful species.
- Dysbiosis, or imbalance of gut microbiota, can result in intestinal inflammation and diseases.
Gut Microbiota Transplantation (GMT)
- GMT involves transferring gut microbiota from a healthy person to an individual with a certain intestinal disorder, such as C-diff infection.
- GMT has been shown to be highly effective in treating cases of C-diff infection that are not cured by conventional medical therapies.
Probiotics and Prebiotics
- Probiotics are live, beneficial intestinal microbes, often bacteria or yeast, that can be found in fermented foods or dietary supplements.
- Prebiotics are forms of dietary fiber that support and promote the growth of probiotics in the colon.
- Probiotics may help prevent diarrhea associated with antibiotic use and may be useful in treating IBS, while prebiotics are found in fruits, vegetables, and whole grains.
Inflammatory Bowel Disease (IBD)
- IBD is a chronic disease that causes inflammation and swelling of the intestines, disrupting digestion and nutrient absorption.
- The two most common forms of IBD are ulcerative colitis (UC) and Crohn's disease (CD).
- Risk factors for IBD include genetic factors, cigarette smoking, and poor diet, particularly a Western diet high in animal protein and low in fiber.### Ulcerative Colitis (UC)
- Patients with UC have an increased risk of colon cancer, especially when their entire colon is affected and they have had the disease for 8 or more years.
- Managing inflammation with medication and having regular screening can reduce the risk of colon cancer.
Crohn's Disease (CD)
- More than 500,000 Americans have Crohn's disease, which can affect the entire gastrointestinal tract, including the mouth.
- The disease typically affects the last section of the small intestine (the ileum) and the beginning of the colon.
- Crohn's disease damages deeper layers of the intestines than does UC.
- Typical signs and symptoms of CD include diarrhea, painful abdominal cramps, loss of appetite, and weight loss.
- Treatment for Crohn's disease involves taking medications to reduce inflammation and promote healing, as well as avoiding foods and beverages that cause "flares".
- There is no cure for the disease, and in severe cases, surgery may be necessary to remove badly damaged portions of the intestinal tract.
- People with Crohn's disease have an increased risk of colon cancer.
Enemas and Colon Cleansing
- Using "high colonics" and other types of enemas to "cleanse" the colon is not necessary, as the large intestine does not need to be cleansed.
- Frequent enemas may deplete the body of vital minerals, including sodium and potassium.
Real People, Real Stories: Alicia Anne
- Alicia Anne was diagnosed with Crohn's disease at the age of 25.
- She experienced symptoms such as rapid weight loss, diarrhea, and abdominal pain.
- She was initially treated with prednisone, a powerful anti-inflammatory medication.
- Today, Alicia takes multiple medications to treat CD and monitors her food choices to identify foods that cause "flares".
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Description
Learn about the human digestive system, its function, and the process of digestion from mouth to anus. Understand how nutrients are absorbed and utilized by the body.