Chapter 3 Notes on Digestion and Absorption

Chapter 3 Notes: Digestion & Absorption Review: Ribosomes- site of protein translation Mitochondria- "powerhouse" of the cell, site of the citric acid cycle & the electron transport chain Lysosome- degradation of cellular components Peroxisomes- contain enzymes for the breakdown of peroxide and...

Chapter 3 Notes: Digestion & Absorption Review: Ribosomes- site of protein translation Mitochondria- "powerhouse" of the cell, site of the citric acid cycle & the electron transport chain Lysosome- degradation of cellular components Peroxisomes- contain enzymes for the breakdown of peroxide and/or alcohol Nucleus- storage of DNA, site of RNA synthesis - Digestion: the breaking apart of foods into smaller & smaller units - Absorption: the movement of those small units from the gut into the bloodstream or lymphatic system for circulation - Digestive system is designed to digest carbs, proteins, & fats, while preparing other substances- minerals, vitamins, & cholesterol - Cephalic phase responses: a sight, smell, thought, taste, & some cases, event the sound of food can trigger a set of physiological responses - Cephalic phase responses are innate & learned physiological responses to sensory signal that prepare the GI tract for processing food - Stimuli that trigger cephalic phase responses: cognition (thinking about food), sound (hearing description of food), appearance (seeing food), odor (smelling food), taste/tactile (tasting food, mouth feel) - Cephalic food responses: - Heat production system = increased heat production - Salivary glands = increased flow of saliva, changes in saliva composition - Cardiovascular system = increased heart rate & blood flow, decreased cardiac output & stroke volume - GI tract = increased acid & digestive enzyme secretion, motility, gut hormone released - Pancreas = increased digestive enzyme secretions & hormone release - Renal system = alterations in urine volume & osmolarity - Flavor of food is in combination of olfactory, gustatory, & other stimuli The Gastrointestinal Tract: - Gastrointestinal tract (GI): alimentary canal, it's a long, hollow tube that begins in the mouth & ends at the anus- mouth, esophagus, stomach, small intestine, large intestine & rectum - Accessory organs: salivary glands, liver, gallbladder & pancreas - GI functions: - Ingestion- the receipt & softening of food - Transport of ingest food - Secretion of digestive enzymes, acid, mucus, & bile - Absorption of end products of digestion - Movement of undigested material - Elimination- the excretion of waste products - Ingestion occurs in the mouth- breaking down food & enzyme amylase, starch digestion starts here - The esophagus moves food form the mouth to stomach - Digestion & absorption occurs in the stomach- secreting gastric juices & acid, which aid in digestion, mixes food & converts it into liquid chyme, kills pathogenic bacteria, starts digestion of protein, fat & secretes intrinsic factor which is needed for B12 absorption, slowly releases chyme into the small intestine - Small intestine- where the digestion of protein, fat, & carbs is completed, where a majority of nutrients are absorbed - Large intestine- absorbs water & electrolytes, forms & stores feces where most gut microbiota exist - The accessory organ the salivary gland- secrete saliva which moistens food, allowing for more easy swallowing - The liver produces bile, which aids in the digestion & absorption of fat - The gallbladder stores & concentrates bile from the liver - The pancreas secretes enzymes that affect digestion & absorption, it releases hormones which help regulate metabolism & how nutrients are used in the body - Elimination is done by the rectum which holds and releases feces via the anus Gastrointestinal Structure: - Innermost layer, the **mucosa**, is a layer of epithelial cells & glands - The **submucosa** is made of loose, fibrous connective tissue, glands, blood vessels, & nerves- substances are carried both to & from the GI tract - There are 2 layers of muscle fibers in the GI tract, **circular** muscle & **longitudinal** muscle - Circular muscle: where muscle fibers go around the tub - Longitudinal muscle: where fibers lie lengthwise along the tube - Serosa: provides a covering & protection for the entire GI tract- secretes fluid to help protect the GI tract & reduce friction as it & other organs move - Lumen: the interior of the gut through which food travels - Sphincters: circular bands of muscle fibers that surround the entrance or exit of a hollow body structure & act as valves to control the flow of material - At points along the tract, where one organ connects with another, the muscle are thicker & form **sphincters** - **Sphincters** contract & relax, & make these muscular rings act like one-way doors, allowing the mixture of food & digestive juices to flow progressively along the GI tract into an organ but not back out Overview of Digestion: Physical & Chemical Processes - Breaking down food into smaller & absorbable units involves chemical & physical processes - Chewing is the first physical process that starts to breakup food & muscular contractions of the GI tract continue it - GI tract breaks up food, mixes it with various secretions and moves **chyme** - Chyme: a mass of partially digested food & digestive juices moving from the stomach into the duodenum - Enzymes & other chemicals help complete the breakdown process & absorb nutrients The Physical Movement & Breakdown of Food: - Peristalsis: is the involuntary constriction & relaxation of the muscles of the intestine that cause wave like motions that propel food stuff forward - Peristalsis transports food & nutrients along the GI tract - Waves in from stomach muscles occur 3x per minute - Waves in the small intestine & circular & longitudinal bands of muscle contract ever 4-5 seconds - Large intestine uses slow peristalsis to move feces - Segmentation: a series of muscular contractions that occurs in the small intestine, divides & mixes chyme- breaks a part food - Alternating constrictions every few centimeters on the gut wall "chop" chyme into smaller portions - Segmentation increases absorption by bringing chyme to interact w/ intestinal wall The Chemical Breakdown of Food: - Enzymes divide nutrients into compounds small enough for absorption - Enzymes: proteins that catalyze/speed up, chemical reactions but aren't altered in the process - Catalyze: to speed up a chemical reaction - Chemical reactions divide substances into small compounds through **hydrolysis** (breaking apart by water) Overview of Absorption: - Water, minerals & vitamins don't need to be digest before they are absorbed but energy-yielding nutrients, carbs, fat, & protein are too large & must be digested first - Lumen: cavity of hollow channel in any organ or structure of the body - Passive diffusion, facilitated diffusion, active transport, & endocytosis allow nutrients to be absorbed from the GI tract - **Passive diffusion**- movement by diffusion from high concentration to low - **Facilitated diffusion**- require a pore or channel - **Active transport**- requires a protein pump & energy in form of ATP - **Endocytosis:** material is absorbed by the cell membrane of the absorbing cell wrapping around it - **Concentration gradients** drive passive diffusion - Concentration gradients: a driver of passive diffusion in which one side of the cell has a higher concentration of molecules than the other side of the cell wall - The larger the concentration of molecules on one side of the cell membrane, the fast those molecule move across the membrane to the area of lower concentration - The cell membrane mainly consists of fat-soluble substances so it welcomes fats & other fat-soluble substances (oxygen, nitrogen carbon dioxide & alcohol easily diffuse across the membrane) - Most water-soluble nutrients (carbs, amino acids, vitamins & minerals) can't be absorbed by passive diffusion, they need help to cross into intestinal cells - In facilitated diffusion, special carriers help transport a substance across the cell membrane - Diffusing molecule become lightly bound to the carrier protein, which changes its shape to open a pathway for the diffusing molecules to move into or out of the cell - Concentrate gradients also help drive facilitated diffusion - Active transport is usually for substances that require transport across some cell membranes including minerals (sodium, potassium, calcium, iron, chloride & iodine), several sugar (glucose & galactose) & amino acids - Most substances are either diffused or actively transported across membranes but some are engulfed & ingested (endocytosis) - During endocytosis a portion of the cell membrane forms a sac around the substance to be absorbed, pulling it into the interior of the cell - Pinocytosis: when cells ingest small molecules & fluids - Phagocytosis: the process which cells engulf large particles & small microorganisms, receptors on the surface of cells bind these particles & organisms to bring them into large vesicles in the cytoplasm Accessory Organs: - The GI tract works together with these organs, which assist in digestion by providing fluid, acid neutralizers, enzymes & emulsifiers Salivary Glands: - 3 pairs- parotid, sublingual, submandibular located in the mouth which secrete saliva into the oral cavity - Saliva moistens food to lubricate it for swallowing - Sight, smell, or thought of food can start the flow of saliva Liver: - Bile s yellow-green, pasty material that helps digest fat - Contains water, bile, salts, & acids, pigments, cholesterol, phospholipids, & electrolytes - Produces 600-1,000 milliliters of bile each day - Bile acts as an emulsifier by reducing large globs of fat to smaller globs - Emulsification doesn't break bonds in fat molecules but increases the surface area of fat, allowing more contact between fat molecules & enzymes in the small intestine - Bile is stored & concentrated in the gallbladder & released in the small intestine - Enterohepatic circulation: after emulsification when bile salts are reabsorbed & returned to the liver for recycling - Liver = cholesterol used to generate bile - Gallbladder = stores bile - Small intestine = bile emulsifies fats - Colon = bile trapped by fiber & lost in feces - Also detoxification center that filters out toxic substances from the blood & alters their chemical forms - Toxic substances filtered out from the liver may be sent to the kidney for excretion or carried by bile to the small intestine & removed from the body feces - Produces more than 500 chemical functions including the production of blood, proteins, cholesterol, & sugars - "active warehouse"- it stores vitamins, hormones, minerals, & sugars & releases them to the bloodstream as needed Gallbladder: - Primary function is to store & concentrate bile from the liver - Small, muscular, pear-shaped sac in the right underside of the liver - Fills with bile & thickens it until a hormone released after eating signals the gallbladder to squirt out its colorful contents - Gallbladder is normally relaxed in between meals - When dietary fat enters the small intestine it stimulates the production of **cholecystokinin (CCK)** - Cholecystokinin (CCK): a hormone in the intestinal wall that stimulates the release of digestive enzymes from the pancreas & bile from the gallbladder - Squirts bile into the duodenum (upper part of the small intestine) Pancreas: - Secretes enzymes that affect the digestion & absorption of nutrients in the small intestine - Releases hormones that are involved in other aspects of nutrient use by the body - The pancreatic hormones insulin & glucagon regulate blood glucose levels Putting It All Together: Digestion & Absorption Mouth- - When you chew you break down food into smaller pieces, increasing the surface area available to enzymes - Saliva contains salivary **amylase**, which breaks down starch into small sugar molecules - Amylase: salivary enzyme that catalyzes the hydrolysis of amylose, a starch - Salivary amylase works until strong acid content in the stomach deactivates in & starts the process of fat digestion - Cells on the tongue also secrete **lingual lipase** - Lingual lipase: a fat-splitting enzyme secreted by cells at the base of the tongue - Saliva & other fluids blend with food to form a **bolus** - Bolus: chewed, moistened lump of food that is soft & easy to swallow - The **bolus** will slide past the epiglottis when swallowed & a valve-like flap of tissue closes off your air passage so that you don't choke & then goes through the esophagus to the stomach Stomach: - The **bolus** the stomach through the **esophageal sphincter** which closes to keep the **bolus** from sliding back into the esophagus - The esophageal sphincter must close quickly so that acidic stomach contents don't back into the esophagus- causing pain/tissue damage heartburn - Esophageal sphincter: the opening between he esophagus & the stomach that relaxes & opens to allow the bolus to travel into the stomach & then closes behind it- also acts a barrier to reflux of gastric acid - Gastric juice; water, hydrochloric acid, mucus, pepsinogen (inactive pepsin), gastric lipase, gastrin & intrinsic factor - Hydrochloric acid: makes stomach contents extremely acidic, killing many pathogenic bacteria & mucus secreted by stomach cells coats the stomach lining, protecting it from strong gastric juices - Pepsin: begins breaking links in protein chains, cutting dietary proteins smaller - Gastric lipase: minor role in digestion of lipids, specifically triglycerides with a lot of short-chain fatty acids - Gastrin: hormone that stimulates gastric secretion & mobility - Intrinsic factor: necessary for vitamin B12 absorption - Gastric content has a pH of 1.0-3.0 - The stomach releases chyme through the **pyloric sphincter** into the small intestine & the **pyloric sphincter** closes to prevent chyme from returning into the stomach - Pyloric sphincter: circular muscle that forms the opening between the stomach & the duodenum, regulating the passage of food into the small intestine - Stomach normally empties in 1-4 hours, depending on amount of food eaten & higher fat content meal will take longer to leave the stomach - Weak acids; alcohol aspirin & a few fat-soluble compounds Small intestine: - Completes the digestion of protein, fat & nearly all carbs - Absorbs most nutrients - 10 feet long - 3 parts: duodenum (10-12 inches), jejunum (4 feet), ileum (5 feet) - Most digestion happens in the duodenum & the remainder of the small intestine primarily absorbs previously digested nutrients - The jejunum & ileum absorb digested nutrients - In the duodenum, bicarbonate from the pancreas neutralizes acidic chyme to be delivered through the pyloric sphincter, neutralizing the chyme - **Secretin** is the stimulus for the release of bicarbonate - Fat presence in the duodenum stimulates the release of stored bile by the gallbladder - Bile acts as an emulsifier as lipids don't usually mix with water & without it lipids wouldn't come into contact with pancreatic lipase & digestion would be incomplete - Vitamins, minerals & cholesterol aren't digest & are usually absorbed unchanged - Most dietary fats, carbs, & proteins are completely digest & absorbed in the small intestine - 90% of carbs, fat & protein are absorbed - Surface of the small intestine is wrinkled into folds, tripling the absorption surface area - Folds are carpeted with fingerlike projections call **villi** - Microvilli: minute, hairlike projections that extend from the surface of absorptive cells facing intestinal lumen - 85% of water absorption by the gut occurs in the jejunum & ileum - Nutrients absorbed through the intestinal lining pass into the interior of the villi - Each villus contains blood vessels & lymph vessel that transports nutrients to other parts of the body - Fat-soluble lipids are absorbed into the lymph rather than into the blood - Minerals compete for absorption & the absorption of one mineral that can decrease the absorption of another - Small intestine goes through constant wear & tear & the intestinal lining is renewed continually as mucosal cell are replaced every 2-5 days - When chyme has completed it 3-10 hour & passes through the ileocecal valve, the connection to the large intestine Large Intestine: - About 5 ft long & includes the cecum, colon, rectum & anal canal - Chyme fills the cecum, a local reflex signals that ileocecal valve to close, preventing material from reentering the ileum of the small intestine - The colon absorbs water, sodium, chloride, potassium, & vitamin k - The peristaltic movements are sluggish in the large intestine compared to the small intestine- 18 to 24 hours - Minimal nutrient absorption takes place in the large intestine, limited to water, sodium, chloride, potassium & some vitamin K by bacteria - The colon dehydrates the watery chyme, removing the remaining fluid - The semisolid feces consist roughly of about 60% solid matter & 40% water, then going through the rectum - Strong muscles in the rectum hold back the waste until it is excreted - GI tract contains microorganisms called **gut microbiota** (bacteria, fungi, & viruses) - Majority of microorganisms live in the colon where the ileocecal valve prevents the movement of microbes into the small intestine - Gut microbiota extract energy from dietary compounds that are not digestible by the human gut, synthesize essential vitamins, & provide immune benefits - Acids produced by bacteria change the pH of the colon, which may interfere with cancer development - Types of microbiota in the gut are influenced by age, what we eat, & medicine we take - Probiotics & prebiotics affect the microbiota of the gut in specific wats to provide health benefits - Probiotics are living microbes in the diet, while prebiotics can be thought as "food" for the probiotics - Prebiotics are nondigestible substances in food Circulation of Nutrients: - After food is digested & nutrients are absorbed nutrients are transported by the vascular & lymphatic systems to specific destinations throughout the body - Vascular system: network of veins & arteries through which the blood carries nutrients - From intestinal cells, water-soluble nutrients are absorbed directly into tiny capillary tributaries of the bloodstream before being dispersed - Once cells have used the oxygen & nutrients, carbon dioxide, & waste products are picked up by the blood & transported for excretion - Lymphatic system: network of vessels that drain lymph, the clear fluid formed in spaces between cells - Lymph eventually empties into the bloodstream near the neck - Nutrients absorbed into the vascular system, bypass the liver before entering the bloodstream - Major lymph vessels contain one-way valves when the vessel fills with lymph, smooth muscles contract & pump the lymph forward - Lymphatic system performs cleanup of the blood Excretion & Elimination: - Excretion regulates contraction of minerals & other substances the body removes - Metabolic waste arises from all the chemical reactions that take place in cells throughout the body - Digestive waste is the unabsorbed "leftovers" passing out the GI tract - Lungs excrete water & carbon dioxide - Kidney filters blood & excretes substances to remove waste & maintain the body's water balance - Kidney's excrete salts; nitrogen-containing wastes (urea) - Kidneys vary the amount/concentration of urine to help maintain physiological conditions Signaling Systems: command, control, defense - GI tract plays major role in the immune system, a coordinated system of cells & tissues that defend against invading microorganisms - The central nervous system regulates the GI tract in 2 ways, enteric nervous system, autonomic nervous system - Enteric nervous system: local system of nerves in the gut wall that is stimulated both by the chemical composition of chyme & by the stretching of the BI lumen that results in the GI tract - Plays essential role in the mobility, blood flow, water & electrolyte transport & acid secretion of the GI tract - Autonomic nervous system (portion of CNS that controls organ function): responds to the sight, smell, & thought of food - Carries signals to & from the GI tract through vagus nerve & enhances GI motility & secretion Hormonal System: - Hormones: chemical messengers that are produced at one location & travel into the bloodstream to affect another location in the body - GI hormonal signals increase or decrease GI motility & secretions & influence your appetite by sending signals to your CNS - 4 major hormones that regulate GI function: gastrin, secretin, cholecystokinin, & gastric inhibitory peptide - Nerve cells & hormones coordinate the movement & secretion of the GI tract so that enzymes are released when & where they are needed & chyme moves at a rate that optimizes digestion & absorption Immune System: - First line of defense is preventing infectious agents from entering the body- the skin & the GI system - Tight junction between cells that line the intestine, normal peristalsis, & intestinal secretions all work to keep foreign bodies out - Natural killer cells: cells that attack virus-infected cells & cells that have turned cancerous - Macrophages: large immune system cells that function as patrol cells & engulf & kill foreign invaders - Lymphocytes: white blood cells of the immune system - Some lymphocytes produce antibodies, other remember a prior invader, enabling the body to respond should the same invader appear again - When an invader is recognized, helper cells trigger the mass production of killer cells - Absorbed nutrients are carried by either the vascular or lymphatic system - Water-soluble nutrients are absorbed directly into the bloodstream, carried to the liver, & then distributed around the body - Fat-soluble vitamins & large lipid molecules are absorbed into the lymphatic vessels & are carried by the system before entering the vascular Influences of Digestion & Absorption: - Taste, small, & presentation of food can have positive effects on digestion - Stressful emotions have the opposite effect & can activate the autonomic nervous system - Plant proteins are usually less digestible than animal proteins - Cooking food increases digestibility & cooking meat softens its connective tissue, making it easier to chew & increasing digestive secretions - Frying foods in high temperatures produces small amounts of **acrolein** which decreases the flow of digestive secretions - Acrolein: pungent decomposition product of fats, generated from dehydrating the glycerol components of fats - Cold food can cause intestinal spasms in people who suffer from IBS or Crohn's disease Bacterial Influences: - When there is a lower concentration of hydrochloric acid, more bacteria can survive & multiply - Harmful bacteria can cause gastritis & peptic ulcers - Large intestine has lots of bacteria that are apart of a microbiome & ingest small amounts of fiber to produce small energy amounts - Bacteria in the large intestine also synthesize hydrogen, ammonia, methane, & other acids & various substances that contribute to the odor of feces - Incomplete digestion/absorption in the small intestine can lead to excessive gas, bloating & pain Nutrition & GI Disorders: - Almost all GI disorders are influenced to some degree by your emotional state - Heartburn: occurs when the lower esophageal sphincter relaxes to allow stomach acid to flow into the unprotected esophagus - Ulcers: sores on the wall of the stomach of duodenum primarily due to N. pylori infection or NSAID use - Lactase deficiency: lactose isn't digested, leading to gas, discomfort, & diarrhea - Functional dyspepsia: no obvious physical cause - Gas: results from bacterial breakdown of undigested carbs - Diverticulosis: common where people eat low-fiber diets - Constipation: high-fat, low-fiber diet is the most common cause - Irritable bowel syndrome: unknown cause - Diarrhea: results from any disorder that increases peristalsis - Colon cancer: the fourth leading cause of cancer-related deaths - **Constipation** is defined as having bowel movement fewer than 3x a week - Stress, inactivity, cessation of smoking, illnesses, a diet that is low in fiber & water & high in fats can cause constipation - The bulk & soft texture of fiber help prevent hard, dry stills that are difficult to pass - Diarrhea is loose, watery stool that occurs more than 3x in one day & is caused by products moving through the large intestine too quickly for sufficient water to be reabsorbed - Eating food contaminated with bacteria/viruses often causes diarrhea when the digestive tract speeds the offending food along the alimentary canal & out of the body - Diarrhea can cause dehydration which means a lack of fluids to function properly - A diet of broth, team & toast & avoidance of lactose, caffeine & sorbitol can reduce diarrhea until it goes away - As people age, the colon develops small pouches that bulge outward through weak spots on the digestive tract that's known as diverticulosis - One risk factor for diverticulosis is a low-fiber diet, making stool too hard to pass & if still is too hard muscles strain to move it - When the colon struggles to move stool, it causes weak spots to bulge outward, & 10-35% of peoples pouches become infected, inflamed, or cause diverticulitis - Treatment to diverticulitis includes usually managing the diet but in serious cases it may require removal of the affected part of the colon - Diverticulosis & diverticulitis are common in developed countries like the U.S, England, Australia, where low-fiber diets are common - Higher intakes of dietary fiber reduce the risk of several chronic diseases - Fiber keeps stool soft, & lowers pressure inside the colon so that bowel contents can move through easier Heartburn & Gastroesophageal Reflux: - Heartburn occurs when the sphincter between the esophagus & stomach relaxes inappropriately, allowing the stomach's contents to flow back into the esophagus - The esophagus has no protective mucous lining, so acid can damage it quickly, causing pain - Gastroesophageal reflux is something that is experienced occasionally but heartburn can be chronic & a daily occurrence for some - Gastroesophageal reflux disease (GERD): condition which gastric contents move backward (reflux) into the esophagus, causing pain, & tissue damage - GERD along with obesity are both risk factors in esophageal cancer - In order help with GERD portion size & fat content of helps should be decreased - The cause of IBS is unknown but emotional stress & specific foods can aggravate the symptoms in most who have it - IBS can be controlled with diet & lifestyle modifications & use of medication too - The diet strategy FODMAP (low fermentable, oligosaccharides, disaccharides, monosaccharides & polyol diet) have also shown to decrease symptoms of IBS - Short chain carbs (oligo-, di-, & monosaccharides) are incompletely absorbed in the GI tract & can be easily fermented by our bacteria & fermentation & osmosis cause gas, pain & diarrhea - Stress management is important for IBS Colorectal Cancer: - Cancer of the cancer or colon or rectum, 4^th^ leading cause of cancer-related deaths in the US - Consumption of large amounts of red & processed meats increase the risk of colorectal cancer - Important to recognize dietary factors & behavioral factors related to cancer risk - Fiber-rich diets have been known to lower the risk of colorectal cancer - Vegan plant based-diets & pesco-vegetarian diet & the mediterranean-style diet have offered protection against colorectal cancer Gas: - Gas is made primarily of odorless vapors & the unpleasant odor of flatulence comes from bacteria in the large intestine that releases small amounts containing sulfur - Gas in the stomach is caused by swallowing air- everyone swallows small amount of air when they eat or drink - Drinking rapidly, chewing gum, smoking, or wearing loose dentures can cause more air to be taken in - Burping is the way most swallowed air leaves the stomach; the remaining gas goes to the small intestines where it is partially absorbed - Frequent passing of rectal gas can be annoying but is needed to not develop serious disease - Flatus: composition depends largely on dietary carb intake & the activity of the colon's bacterial population - Most foods that contain carbs cause gas, however most foods containing fats don't - Starches including potatoes, corn, noodles, & wheat produce gas as they break down in the large intestine - Rice is the only starch that doesn't cause gas - Fiber in oat bran, beans, peas & most fruits isn't broken down until it reaches the large intestine, where digestion causes gas - Fiber in wheat bran, some veggies: green beans, cauliflower, zucchini, & celery, passes through the intestine, producing little gas Ulcers: - Gnawing, burning pain in the upper abdomen is a sign of a peptic **ulcer** - Peptic ulcer- sore that forms in the duodenum or lining of the stomach - Helicobacter pylori cause most ulcers - H. pylori are spiral-shaped bacteria found in the stomach that can cause ulcers damaging mucous coating that protect lining of the stomach & duodenum - An ulcer is caused when H. pylori damage the mucous coating, stomach acid can penetrate into the stomach & duodenum, allowing acids to irritate the lining of the stomach/duodenum - NSAIDS (aspirin, ibuprofen, & naproxen sodium) can cause ulcers by interfering with the GI tracts ability to protect itself from acidic stomach juices - The stomach & duodenum have 3 defenses against digestive juices: mucus that coats the lining & shields, the chemical bicarbonate, neutralizing acid & blood circulation, aids in cell renewal & repair - NSAID ulcers heal usually once the person stops taking medication - Patient ulcers today are treated with proton pump inhibitors, or histamine blockers & possibly protectant like sucralfate