Gastrointestinal Pathophysiology I. Nancy Long Sieber, Ph.D. December 6, 2010. GI processes. Digestion – The physical and chemical breakdown of large particles of food into smaller molecules that can be transported across the intestinal wall .
Gastrointestinal Pathophysiology I Nancy Long Sieber, Ph.D. December 6, 2010
GI processes Digestion – The physical and chemical breakdown of large particles of food into smaller molecules that can be transported across the intestinal wall. Secretion – The exocrine release of fluid, hydrochloric acid, bile, and digestive enzymes into the digestive tract to digest and solubilize foods. Also includes mucus and bicarbonate, which are secreted to protect the walls of the GI tract from these digestive substances. Absorption – Transport across the intestinal wall. Includes transmembrane transport by diffusion, endocytosis, carrier mediated transport, and facilitated diffusion. Motility – The movement of ingested material down the GI tract. Muscle layers of the wall mix, grind, and propel food along the GI tract. They also control the rate at which GI contents pass through the system, and how long the contents remain in each region of the tract. Coordination – Refers to the regulatory mechanisms, both neural and endocrine, which link the above processes.
The major function of the GI system is absorption of nutrients.. The surface area of the intestine is 300 m3. Intestinal villi maximize surface area https://eapbiofield.wikispaces.com/Digestive+System+Wilson
The GI tract is not a major site of waste product excretion. • Fecal material is mostly bacteria that never actually enter the body. • Major waste products excreted throough the GI tract: • Bilirubin – a breakdown product of hemoglobin • Cholesterol
Regulation of GI Processes - Stimuli • Lumenal stimuli provide info about what’s happening in the GI tract. • Eg: distension of GI walls by contents of the GI tract • Osmolarity of chyme (the food mixed w/ secretions) • pH of chyme • Concentration of specific nutrients (eg: fat) • Emotional states, hunger and other external stimuli also affect GI processing.
Regulation of GI Processes - Responses • Neural Regulation • Short reflexes communicate within GI tract • Long reflexes communicate w/ autonomic NS • Hormonal Regulation – Endocrine cells have two faces: • one face in lumen to monitor contents • the other to secrete hormone into the blood.
Major GI Hormones • Gastrin – stimulates acid secretion and motility of stomach • Secretin – inhibits acid secretion and motility of stomach i.e. slows gastric emptying, in response to acid in small intestine • Cholecystokinin (CCK) also inhibits acid secretion and motility of stomach, but in response to amino acids and fatty acids in small intestine. • Glucose-dependent insulinotropic peptide (GIP) stimulates insulin release in response to glucose and fat in small intestine.
Swallowing Swallowing requires functional teeth to break down food, salivary glands to soften and lubricate it and neural coordination of both skeletal and smooth muscle. What can go wrong?
What can interfere with swallowing? • Dental illness can interfere with chewing • Certain illnesses and some medications interfere with salivary secretion. • Sjogren’ssyndrome (autoimmune attack on salivary glands) interferes with the production of saliva, making it more difficult to chew and swallow food. • Many medications have dry mouth as a side effect. Eg: parasympathetic antagonists such as atropine (in anti-diarrhea drugs), and sympathetic agonists (in decongestants) • Certain CNS diseases and conditions can interfere with swallowing, such as amyotrophic lateral sclerosis (ALS), spinal cord injury and stroke.
Factors that increase the likelihood of Gastroesophageal Reflux • Being an infant • Obesity • Pregnancy • Postural changes (bending over, lying down) • Smoking • Certain foods relax the LES – why are these popular to have after dinner? • Peppermint • Coffee • Alcohol • People with lupus have more problems with GERD due to connective tissue problems
Barrett’s Esophagus http://www.barrettsinfo.com/figures/fig3a_4.jpg
The stomach is protected from acid by a layer of mucus and bicarbonate http://en.wikibooks.org/wiki/Medical_Physiology/Gastrointestinal_Physiology/Secretions
Helobacter Pylori passes though mucus layer that protects the stomach. Contact with stomach acid keeps the mucin lining the epithelial cell layer in a spongy gel-like state. This consistency is impermeable to H pylori. However, the bacterium releases urease which neutralizes the stomach acid. This causes the mucin to liquefy, and the bacterium can swim right through it. http://www.nsf.gov/news/news_images.jsp?cntn_id=115409&org=NSF
NSAIDS interfere with prostaglandin synthesis, which blocks production of prostaglandin. This blocks production of mucus and bicarbonate, and increases acid production, making the stomach vulnerable to injury from acid and enzymes. http://www.gastrosource.com/11674565?itemId=11674565
GastroparesisAbnormally slow emptying of stomach • Can result from neural damage from diabetes or autoimmune neuropathy. • Patients with this condition feel full after eating little food, may vomit after meals. • Liquid diet helps, since liquid leaves the stomach more quickly by gravity.
Bariatric Surgery Currently used for severely obese people who have not been able to lose weight through diet and exercise. Gastric banding was recently approved for less seriously obese people (eg: a 5’5” person who weighs 180 lbs)
Carbohydrate Digestion http://media.tiscali.co.uk/images/feeds/hutchinson/ency/thumbs/0013n025.jpg
Protein Digestion http://media.tiscali.co.uk/images/feeds/hutchinson/ency/thumbs/0013n023.jpg
Fat Digestion http://media.tiscali.co.uk/images/feeds/hutchinson/ency/thumbs/0013n024.jpg
Iron absorption is altered in response to changes in iron homeostasis. Ferritin traps iron and holds it in cells. When iron levels are low, you produce less ferritin. When iron levels are high, you produce more ferritin. http://www.mfi.ku.dk/ppaulev/chapter22/images/22-16.jpg
GI fluid imbalance can be caused by: • Vomiting – forceful emptying of stomach and upper intestinal contents through the mouth • Diarrhea – increased frequency of defecation and volume of feces. Diarrhea is the leading cause of death among children in the developing world
Consequences of prolonged vomiting • Dehydration • Metabolic Alkalosis (due to loss of gastric acid) • Low serum K+ (due to action of aldosterone, which is released after prolonged dehydration). • Malnutrition
Diarrhea • Potential for massive fluid loss, leading to hypotension. • Can cause acidosis, since intestinal contents are alkaline. • Can cause hypokalemia (low K+) since intestinal contents are high in K+.
Osmotic Diarrhea:Lactose intolerance results from a lactase insufficiency. Undigested lactose remains in the intestine, and osmotically draws water into the intestine, causing diarrhea. http://www.food-info.net/images/lactase.jpg
Secretory Diarrhea: Cholera. Cholera toxin increases the intracellular levels of cAMP. This leads to an increase in chloride secretion into the small intestine. Water follows osmotically http://www.surrey.ac.uk/SBMS/ACADEMICS_homepage/mcfadden_johnjoe/img/Cholera%20toxin.jpg
Cystic fibrosis and defense against cholera The chloride channel is called “CFTR”, and is defective in people with Cystic fibrosis. One copy of the CF gene is thought to confer protection against cholera.
Celiac Disease • Results from intolerance to gluten, specifically the gluten breakdown product gliaden. • Considered to be an autoimmune disease – the person makes antibodies against gliadin, which cross react with proteins in the small intestine.
Consequences of celiac disease • Pain and diarrhea, inflammation of intestinal villi. • Malabsorption of nutrients leading to • Osteoporosis (from lack of calcium) • Anemia (from lack of iron) • Short stature (from general malnutrition • Miscarriage, neural tube defects (lack of folic acid, and other nutrients)
Hemorrhagic Diarrhea • Infectious diarrhea leading to blood in stools • Example: recent outbreaks of E. coli 0157:H7 • May be a consequence of factory farming practices • Grows well in corn-fed factory farmed beef • Runoff contaminates vegetable farms
Diarrhea due to altered motilityDumping Syndrome • Typically caused by gastric surgery for peptic ulcer disease, or by gastric by-pass surgery. Part of the stomach typically including the pyloric sphincter is removed , and the meal instead of very slowly entering the duodenum can enter very quickly. • The increased osmolarity of the contents results in very rapid movement of water into the intestines. • In addition, the very rapid presentation of carbohydrates to the intestinal mucosa and their absorption causes a big spike in blood sugar resulting in a large increase in insulin.