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A simplistic view of the digestive system portrays a long tube (~ 9 m ~ 30 ft) within a (body) cavity (Figure 18). There are two outgrowths (the liver and pancreas) to aid the food processing. Normal daily intake is about 600 gm solid food plus a few cups of fluid. About 90% of the solid food is broken down into basic components (see Figure 19 for what, where, and how the processing is taken place) and absorbed as nutrient; the waste (the feces) exits through the anus consisting 75% water, 8% bacteria, 8% undigested fiber, 4% inorganic matter, the rest is fat and protein.
Digestive System Digestive Functions Digestive Diseases The system is controlled by the Central Nervous System globally and the Enteric Nervous System locally. In addition, there are symbiotic bacteria taking up residence inside. They can be friends or enemies depending on circumstance. The worse can cause illness, normally one of their end products (in the form of gas) is just a minor inconvenience upsetting only social etiquette. Table 05 lists some of the digestive system diseases as shown in Figure 20.

Figure 18 Digestive System

Figure 19 Digestive Functions
[view large image]

Figure 20 Digestive Diseases

BTW, the end product of nucleic acid, i.e., the nitrogenous bases looks innocent, but it can induce gout causing lot of pain in the joints.

Disease Symptom(s) Cause(s) Treatment(s)
Achalasia Difficulty in swallowing, regurgitation, chest pain Failure of smooth muscle fibers to relax Lifestyle change, medication, pneumatic dilatation, surgery
( see link)
Appendicitis Pain near the navel, loss of appetite, nausea and/or vomiting, abdominal swelling, fever of 99-102oF, inability to pass gas, ... Inflammation of blocked appendix often by stool, a foreign body, or cancer Surgery ( see link)
Barrett's Esophagus Chronic heartburn, trouble swallowing (dysphagia), vomiting blood (hematemesis)
(GERD progression to premalignant condition)
Normal tissue replaced by intestinal tissue Medications, diet, surgery
( see link)
Carcinoma in Epithelial Tissues Bleeding into the gastrointestinal (GI) tract, severe abdominal pain and vomiting Abnormal DNA, mostly genetic Surgery, chemotherapy, drug
( see link)
Cirrhosis Fatigue, loss of appetite, yellowing/itchy skin, swelling in ankles/legs/abdomen, blood in the stool, fever, brownish urine, light colored stools Scar tissue blocks blood flow in liver induced by virus, fat, alcohol abuse Lifestyle changes, medications, liver transplant ( see link)
Colon Polyps 95% no symptom, small amount of blood in stool DNA mutation, old age, obesity, smoker Mostly benignant but can become cancerous, removal by endoscope ( see link)
Diabetes Frequent urination, increased thirst, and increased hunger Insulin disorder causing high blood sugar levels - results of obesity and lack of exercise or genetic Lifestyle change, medications, pancreatic transplantation
( see link)
Diverticulosis of Colon No symptom, sometimes leading to infection in the pouches (diverticulitis) Pouches form in the wall of the colon by high pressure due to low fiber diet High fiber diet, plenty of fluid, exercise, regular bowel movement ( see link)
Gallstones Intense pain in the upper-right side of the abdomen, often accompanied by nausea and vomiting Stone formation in gallbladder/bile duct caused by inherited disposition or low calorie diet Medication, laparoscopy, lithotripsy (breaking up the stone by ultrasonic shock wave), surgery ( see link)
Gastritis (Greek : Gastro=Stomach, itis=inflammation) Nausea, abdominal bloating/pain, vomiting, indigestion, hiccups, loss of appetite, vomiting blood, black/tarry stools Damage to stomach lining via alcohol abuse, chronic vomiting, stress, anemia, medications, H. pylori Drug (such as antacids), antibiotics, avoiding spicy foods
( see link)
Heartburn / GERD (Gastroesophageal Reflux Disease) Burning sensation in the back of the throat, chronic cough, laryngitis (hoarse voice), nausea. Stomach acid back up into the esophagus via open sphincter Lifestyle changes, medicine, surgery for the more serious case of GERD ( see link)
Hemorrhoids Bleeding during bowel movements, itching, and rectal pain Pressure on the veins in the pelvic and rectal area (may be caused by persistent diarrhea or constipation) Changes to diet and bowel habits, fixative procedures, surgery ( see link)
Hernia Protrusion of intestines through the abdominal wall in the form of a bulge, may have pain, nausea, vomiting Old age, heavy lifting, hard coughing, sharp blows, incorrect posture Sewing the hole, using surgical mesh (preferably with Laparoscope) ( see link)
Hepatitis(Greek : Hepat=Liver, itis=inflammation) Loss of appetite, fatigue, mild fever, muscle/joint aches, nausea/vomiting, abdominal pain Alcoholism, medications, infection of the liver by the virus Hepatitis A, B, or C Antiviral agent ( see link)
Inflammatory Bowel Disease (IBD) : Crohn's Disease and Ulcerative Colitis Abdominal pain, diarrhea (may be bloody), fever and weight loss Genetic (immune system attacks the gastrointestinal tract); CD can occur in all gastrointestinal tract, UC only affects the colon Medically incurable, use immunosuppression to control the symptom ( see link)
Peptic Ulcers in esophagus, stomach, and duodenum Abdominal pain, bloating, nausea, vomiting, weight loss, hematemesis, melena (foul-smelling feces) Chronic inflammation (by H. pylori bacteria) Antibiotics, misoprostol, surgery
( see link)

Table 05 Gastroenterological Diseases

Digestive System of Boas Digestive System of Cow Some creatures have different digestive system from that in human. For example, the boa constrictor eats its prey in whole. It takes weeks to absorb the food following by weeks of fasting. The state and physical size of the digestive system actually change according to the requirement. Figure 21a shows the anatomy of a snake, every organ becomes elongated to suit the physical shape. Another example is the ruminants such as the cow, which relies on the bacteria in its many stomachs to digest the fibre that has no nutritional value to humans (Figure 21b). Surprisingly, they suffer similar kind of gastroenterological diseases inflicted on human.

Figure 21a Digestive System of Boa

Figure 21b Digestive System of Cow [view large image]

See Veterinary Care for snakes and cows

The Nature magazine has kindly provided "free full access" to a collection of Insight articles about "Intestinal Microbiota in Health and Disease" published on July 7, 2016.

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