Chapter 23 - The Digestive System

Amylase E

breaks down starchy food into simple sugars.

Ribonucleaes E

From pancreas and processes nucleic acids

Deoxyribonuclease E

From pancreas and processes nucleic acids.

Motilin H

by duodenal mucosa, in b/w meals (during fasting) stimulate migrating motor complex (peristalsis)

Lipid absorption

*Know this process! 1. Emulsification: Bile salts in the duodenum break large fat globules into smaller fat droplets, increasing the surface area available to lipase enzymes 2. Digestion: pancreatic lipases hydrolyze triglycierides, yielding monoglycerides and fatty acids. 3. Micelle formation: Micelles (fatty acids, monoglycerides, and bile salts) ferry their contents to epithelial cells. 4. Diffusion: Fatty acids and monoglycerides diffuse from micelles into epithelial cells. 5. Chylomicron formation: Fatty acids and monoglycerides are recombined and packaged w other fatty substances and proteins form chylomicros. 6. Chylomicron transport: Chylomicrons are extruded from the epithelial cells by exocytosis, enter lacteals, and are carried away from the intestine in lymph.

Teeth

-2 incisors -1 cuspid/canine -2 premolars -3 molars

Salivary glands

-Cleanse the mouth and dissolves food -moistens food and helps form a bolus -Contains amylase (helps break down starchy food to simple sugars. 1. Major/extrinsic: secrete contents via ducts. They include: parotid (surgery can result in facial paralysis), submandibular, and sublingual. 2. Minor/Intrinsic: secrete directly into the mouth and are scattered throughout the oral cavity (buccal glands). Types of secretory cells: 1. Serous: produce watery secretion that contain enzymes, ions, and mucin. 2. Mucous cells: produce mucus. * Salivation is controlled primarily by the parasympathetic division of the atonomic NS by motor neurons of the facial (VII) and glossopharyngeal (IX) nerves in response to mechanoreceptors and chemoreceptors in the mouth and/or higher brain centers. Sympathetic innervation causes dry mouth, inhibits saliva release.

GI tract layers

-Peritoneum 1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa -Splanchnic circulation (blood supply)

Intraperitoneal (peritoneal) organs

Digestive organs that keep their mesentery and remain in the peritoneal cavity. (stomach)

Small intestine histology

1. Absorptive cells: contain microvilli called brush border for increased surface of absorption. Secrete brushborder enzymes (dextrinase, glucoamylase, lactase, maltase, sucrase for carb digestion), amino peptidase and dipeptidase (protein digestion), nucleosidases and phophatases (for nucleic acid digestion). 2. Globet cells: produce mucus, it is alkaline (contains HCO3-, bicarbonate) 3. Paneth cells: secrete lysozymes that lyse bacteria 4. Enteroendocrine cells: in intestinal crypts or crypts of lieberkuhn. Secrete: - secretin: slows gastric motility, stimulates bile production and pacreatic juice release. Decreases gastric secretions. -cholecystokinin (CCK): slows gastric motility, stimullates gallbladder to release bile, pancreatic juice release. - GIP: inhibits HCl production in stomach, stimulates insulin release in pancreas.

Liver microscopic anatomy

1. Liver lobules: hexagonal shape, consists of hepatocytes. Each corner contains a ... 2. portal triad consists of: -Portal vein that brings venous blood to the lobules from the hepatic portal circulation -Hepatic artery proper branches into portal arteriole which brings oxygenated blood to the lobules. -a bile duct, exports bile and waste products ultimately to the GI tract. *stellate macrophages and hepatic macrophages remove debris (ex. bac and worn-out blood) from the blood as it flows past. produced by kupffer cells.

Motility of the sm intestine

1. After a meal: segmentation, a motor pattern, ensures that chyme is thoroughly mixed w bile and pancreatic and intestinal juices. It also ensures that the absorbable products of digestion come in contact w the mucosa for absorption. It moves intestinal contents slowly and steadily toward the iliocecal valve, this allows enough time for absorption. 2. Between meals: migrating motor complex, peristalisis, is largely a housekeeping function that sweeps debris and bateria toward the large intestine. It happens after most nutrients have been absobed. Motilin is released to stimulate migrating motor complex (MMC). Transit from duodenum to ileum takes about 2 hrs. The process stops as food enters again and segmentation begins again. 3. Ileocecal vlave control: It is closed most of the time except when: -Gastroileal reflex, relaxes the ileocecal valve. -Gastrin increases motility of the ileum and relaxes the ileoccecal valve Closes when chyme has passed through and it is completely cleared as the next meal is eaten. *Enterogastric reflex: responds to chyme in sm intestine as well as on the intestinal wall and results in less vagal innervation (and less motility)of the stomach and more innervation of the small intestine (more motility).

Bile and pancreatic juice secretion mechanism

1. CCK and secretin are secreted by duodenal enteroendocrine cells. -CCK realease is stimulated by proteins and fats in chyme. -Secretin release is stimulated by acidic chyme -both enter the circulation and cause... 2. Pancreatic secretion -CCK induces secretion by acinar cells of enzyme rich pancreatic juice -Secretin causes secretion by duct cells of HCO3- rich pancreatic juice -Vagus nerve weakly stimulates during cephalic and gastric phases. 3. Bile secretion by liver: -bile salts returning from enterohepatic circulation are the most powerful stimulus for bile secretion -secretin is a minor stimulus 4. Gallbladder contraction: -CCK causes it -Vagus nerve stimulates weak gallbladder contraction during cephalic and gastric phases. 5. Hepatopancreatic sphincter relaxation: -CCk causes hepatopancreatic sphincter to relax. Bile and pancreatic juice enter duodenum.

Tooth and gum disease

1. Cavities: destruction of enamel and dentin by bacteria. Form when plaque (sugar, bacteria, debris) adheres to the teeth. The bac produce acids and enzymes, which dissolve calcium salts, enamel and dentin in the teeth. 2. Calculus = tartar: Calcified plaque that causes the gingiva to separate from the tooth setting the stage for infection. 3. Gingivitis: less severe than caculus 4. Periodontal disease: more severe than calculus. It can involve the dissolving of bone. It is a natural process of aging.

Large intestine anatomy

1. Cecum 2. appendix: contains masses of lymphoid tissue, and as part of MALT, it plays an important role in body immunity. It also stores bacteria and recolonizes the gut when needed. Susceptible to blockage. 3. Colon: ascending, right colic (hepatic flexure), transverse colon, left colic (splenic) flexure, descending colon, Sigmoid colon. 4. Rectum 5. Anal canal: anal columns w anal sinuses secrete mucus when compressed by feces. 6. Anus: internal, external (voluntary) sphincters. 7. Teniae coli: muscularis layer reduced to 3 bands that run down the middle and how the intestins together and hold the haustra shape. 8. Haustra: pocket like sacs throughout the colon.

Stomach regulations

1. Cephalic (reflex) phase 2. Gastric phase 3. Intesinal phase

Disorders of the liver

1. Cirrhosis: chronic inflammation causes gradual scaring of liver lobules. Common in alcoholics. 2. Hepatitis viruses: -A and E are transmitted by fecal oral route. Food preparers, contaminated sewage and raw food are vectors. Self limiting, flu-like symptoms, and other symptoms (diarrhea, abdominal craps, some jaundice) -B and C are typ. transmitted by blood-blood (shared needles, piercings, tattoos) or sexual exposure, some are unknown. Hep B has an increased risk of liver cancer and CA. Hep C has an increase risk of liver failure.

Teeth structure

1. Crown: exposed part 2. Neck: Gum line 3. Root: Part imbedded in the jaw * Pulp cavity: soft dissue structures (blood vessels, nerve fibers, connective tissue) it extends to the root via the root canal. 4. Gingiva: The gum 5. Enamel: very hard substance composed of Ca and other minerals. Does not replenish or replace itself after tooth eruption 6. Cemetum: calcified connective tusse, covers the root and attaches to the... 7. Periodontal ligament: anchors the tooth into the jaw 8. Dentin: bone-like material lying deep to the enamel. It replaces itself throughout life.

Large intestine disorders

1. Diarrhea: when food moves through intestines too quickly and/or is not properly digested. Not enough water is absorbed. Electrolyte imbalances may result (dehydration) 2. Constipation: when food remains in intestine too long w too much water absorption smooth muscle does not contract well. Causes include lack of fiber, emotional upset (sympathetic innervation and no much action from parasympathetic), and lack of exercise. 3. Hemorrhoids: varicosities of the hemorrhoidal veins 4. Malabsorption syndrome: decrease absorption of nutrients and/or water in the GI tract. Ex. food allergies, intestinal pathogen, liver disease (ex. decreased bile), cystic fibrosis (over production of mucus, ti blocks the pancreatic duct), intestinal surgery (spc. removal of a portion of intestine), any inflammation of the intestines. Typ. accompanied by severe diarrhea.

Disorder of sm intestine

1. Diveriticulitis: lack of fiber results in "pits" that can catch foods and become infected. Can occur in sm intestine but mostly in the lg intestine 2. Duodenal ulcers: due to leakage of stomach acids through the pyloric sphincter of lack of ability of sm intestine to buffer chyme. They can be treated w H2 or pumping protons blockers. *Chyme is hypertonic, too much entering the sm intestine too rapidly would cause water to diffuse out of the interstitial space and cause dehydration.It is also very acidic and it is buffered by pancreatic juices but takes time to adjust pH upwards. Therefore, it must enter slowly, 1-3 ml at a time.

Exocrine/endocrine part of the pancreas

1. Exocrine: part of the pancreas that produces pancreatic juice, consists of: -ACINI: cluster of secretory cells that produce enzyme-rich component of pancreatic juice. Contain zymogen granules which contain inactive digestive enzymes (proenzymes), they activate until enzymes in the brush border of sm intestine. They also secrete active enzymes that require ions or bile in intestine for optimal activity. They are amylase, lipase, and nuclease. -Ducts: transport the secretions of the acinar cells. 2. Endocrine: scattering of miniendocrine glands, pancreatic islets. They release insulin and glucagon.

Defecation process

1. Feces move into and distend the rectum, stimulating stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons. 2. A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectum and sigmoid colon, and relaxation of the internal anal sphincter. 3. If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so feces may pass. * we have some voluntary control over defecation via cortical efferent motor neurons to external anal sphincter.

Tongue Papillae

1. Filiform papillae: roughen the tongue surface to help lick and provide friction to manipulate food. 2. FUngiform papillae: Scattered over the surface, give the red color. 3. Vallate papillae: V-shape in the back of the tongue 4. Foliate papillae: lateral aspects of the posterior tongue.

Disorders of the gallbladder

1. Gallstones: too much cholesterol or too few bile salts cause crystalization of cholesterol = gallstones. Treated w lithotrypsy (soundwaves) drugs, laprospcopic removal. 2. Jaundice: Blocked bile duct causes bilirubin to be absorbed from the hepatic circulation into the blood. Liver failure can also cause it.

Stomach disorders

1. Gastritis: inflammation of the stomach wall 2. Ulcers: Due to hypersecretion of HCl, hyposecretion of mucous or Helicobacter pylori infection. It is treated by cauterizing the area, H2 blockers, antibiotics if it is an H. pylori infection.

Esophagus disorders

1. Heart burn: Stomach acids splash into the esophagus, causing pain or burning. More severe is Gastroesophageal Reflux Disease (GERD) 2. Hiatal hernia: superior part of the stomach protrudes above the diaphragm, causing reflux of stomach acids and possible esophagitis or esophageal ulcers. -proton pump inhibitors (nexium, prevacid, prilosec) and histamine receptors (H2) blockers (tagament, pepsid, Zantac) to reduce HCl production. used in the treatment of GERD and heartburn.

Cells of the liver

1. Hepatocytes: they produce bile. 2. Kupffer cells: macrophages (special kind) in case we eat bacteria.

Digestive processes

1. Ingestion: intake food (eating) 2. Propulsion: moving food through the alimentary canal. -Deglutition: voluntary swalloing -Peristalsis: contraction and relaxation of smooth muscle of GI organs involuntarily. Some mixing occurs too. 3. Mechanical digestion: increase surface area of ingested food, prepares it for digestion. -Mastication, mixing food w saliva by tongue, churning food in the stomach -Segmentation: mixes food w digestive juices and makes absorption more efficient by moving diff. parts of the food mass over the intestinal wall. 4.Chemical digestion: Breaking down nutrients into monomers w the help of enzymes or secreted into the alimentary canal. 5. Absorption: Digested food, vitamins, minerals and water are absorbed from the G.I. tract into the blood or lymph. 6. Defecation: elimination of indigestible substances (feces) via the anus.

Liver anatomy

1. It has 2 main lobes (L/R), and 2 lesser lobes (Caudate and quadrate) 2. falciform ligament: separates L/R lobes and suspends it from diaphragm and anterior abdominal wall 3. hepatic ducts: bile exit from lobes 4. Common hepatic duct: union of L/R hepatic ducts and travels downward toward the duodenum. It then fuses w... 4. Cystic duct: drains the gallbladder to form the... 5. Common bile duct

Control of digestion

1. Mechanoreceptors: stretch receptors in the GI organs. 2. Chemoreceptors: sense pH in the gut 3. Osmoreceptors: sense osmolarity (solute concentration) in the gut.

Digestive process of lg intestine

1. Motility: -Haustral contraction: slow segmenting movements that last about one minute and occur every 30 min. -Mass movements: long, slow moving but powerful contractile waves that move over large areas of the colon 3-4 times daily and force contents outwards, typ. after eating. -Gastrocolic reflex: it is initiated by food in the stomach (gastroileal reflex in the sm intestine) 2. Defecation: stretching of the rectal wall initiates this process. It is a parasympathetic spinal reflex and causes the sigmoid color and rectum to contract and the internal anal sphincter to contract. If it is delayed, the reflex contractions end w/in a few seconds and the rectal walls relax.

Carbohydrates absorption

1. Pancreatic amylase breaks down starch and glycogen into oligosaccharides and disaccharides. 2. Brush border enzymes break oligosaccharides and disaccharides into monosaccharides. 3. Monosaccharides (glucose and galactose) are cotransported across the apical membrane of the absorptive epithelial cell. This active transport uses the Na concentration grradient stablished by the NaK ATPase pump in the basolateral membrane. 4. Monosaccharides exit across the basolateral membrane by facilitated diffusion and enter the capillary via intercellular clefts.

Disorder of the pancreas

1. Pancreatistis: inflammation of the pancreas due to rare activation of pancreatic enzymes in the pancreatic duct (before they enter then sm intestine) 2. Type I diabetes Mellitus: autoimmune disease that destroys beta cells resulting in zero production of insulin.

Protein absorption

1. pancreatic proteases break down proteins and protein fragments into smaller pieces and some individual amino acids. 2. Brush border enzymes break protein fragments into amino acids. 3. Amino acids are cotransported across the apical membrane of the absorptive epithelial cell. This active transport uses the Na concentration gradient stablished by the NaK ATPase pump in the basolateral membrane. 4. Amino acids exit across the basolateral membrane via facilitated diffusion and enter the capillary via intercellular clefts.

Pancreatic juice

1200-1500 ml produced daily. It is mainly water, and contains enzymes and electrolytes (mainly HCO3-). It neutralizes acidic chyme entering the duodenum, provides optimal environment for intestinal and pacreatic enzymes. Enzymes include:protease, amylase, lipase, and nucleases from Acinar cells.

Saliva composition

97-99.5% water (hyposmotic), pH 6.75-7.00, slightly acidic but it might vary. -Fights tooth decay via lysozymes, defensins, Nitric Oxide. (vasodilates) -Electrolytes -Digestive enzymes: amylase and lingual lipase -Contains IgA antibodies -Metabolic wastes (urea and uric acid)

Large intestine

Absorbs water, some vitamins, some electrolytes, and some short chain fatty acids. bacteria metabolize some molecules and ferment indigestible cellulose, etc. It synthesises vit. B and K by bacteria. It begins at the ileocecal valve and ends at the anus. No digestion and absorbs water, Na and K, and vit B and K.

Alimentary canal

Aka gastrointestinal (GI) tract (mouth to anus). Purpose is propulsion, digestion (break down), and absorption food. Organs include (8): oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anal canal.

The mouth

Aka, oral cavity it is lined w stratified squamous epithelium to withstand considerable friction. THe epithelium in gums, hard palate, and dorsum of the tongue is slightly keratinized for extra protection during eating. -Mucosa produces defensins: peptides that destroy bac and promote migration of lymphocytes and neutrophils. -Hard and soft palate make up the roof of the mouth -Uvula closes off the nasopharynx when we swallow. -The tongue aids in speech and mechanical digestion. Secured to the flood by the frenulum. The papillae house the taste buds and roughen the surface of the tongue. *Digestive processes: (1) ingest, (2) mechanical breakdown by chewing, (3) initiates propulsion by swallowing, (4)Starts polysaccharides digestion (amylase)

Sources of enzymes (sm intestine)

Bile, digestive enzymes (except for brush border enzymes), and bicarbonate ions are imported from the liver and pancreas.

Small intestine

Body's major digestive organ. Performs intestinal phase of digestion (bile + pancreatic enzymes) and virtually all absorption occurs via villi + microvilli (huge absorptive surface). Relies on accessory organs (liver, gallbladder, and pancreas) to complete its role in digestion. -Digestion: carbs via brush border enzymes and pancreatic enzymes. Proteins via brush border and pancreatic enzymes. Lipids via pancreatic lipase and bile (dont come from sm intestine) -Absorption: 90% of all vitamins, minerals, ions, electrolytes, water, etc.

Secretin H

By duodenum inhibits gastric gland secretion and gastric motility. Stimulates liver to produce bile and pancreas to produce pancreatic juice. Decreases gastric secretions (sm intestine)

Bile salts

Cholesterol derivatives that emulsify fats. They are ultimately recycled back into the liver after they are used for digestion.

Intestinal phase

Chyme in small intestine inhibits vagus innervation of the stomach (enterogastric reflex). Intestinal hormones are secreted. -Secretin by duodenum inhibits gastric gland secretion and gastric motility. -GIP (Gastric inhibitory peptide) secreted by duodenum inhibits HCl production -VIP (Vasoactive intestinal peptide) Secreted by enteric neurons also inhibits HCl secretion

Chymotrypsin E

Chymotrypsinogen = inactive, From pancreas and digest proteins

Electrolyte/Minerals absorption

Come from both ingested foods and gastrointestinal secretions. Most are actively absorbed along the entire length of sm intestinel Except Fe and Ca -Iron is actively transported into the epithelial cells of the intestinal wall and binds to ferritin (storeouses for iron). If not needed, it will be lost as the epithelial cells slough off. When needed, iron binds to transferrin and is transported to the liver or bone marrow. -Cacium requires vit. D in order to be absorbed in the sm intestine. Active vit. D is made by the kidneys (w help of keratinocytes and hepatocytes) and the process is facilitated by parathyroid hormone (PTH)

Submucosa

Connective tissue containing blood and lymphatic vessels, lymphoid follicles and vessels and nerve fibers.

zymogen

Contain innactive digestive enzymes (proenzymes) and activate until in touch w brush border of sm intestine. This is so they don't digest the pancreas, they all promote breakdown of protein. They are: -Trypsinogen --> Trypsin, activated by enterokinase/enteropeptidase -Procarboxypeptidase --> carboxypepetidase, activated by trypsin -Chymotrypsinogen --> chymotrypsin, activated by trypsin

Rennin E

Digest milk proteins in babies

Mesentery

Double layer of peritoneum (sheet of 2 serous membranes fused back to back) that extends to the digestive organs from the body wall. Provide routes for blood vessels, lymphatics, and nerves to reach the digestive viscera, hold organs in place, store fat. All alimentary canal organs are suspended by a mesentery.

Bacterial flora

Ferments cellulose and other fibers releasing dimethyl sulfide gas in the process (flatulence). They also synthesize some B complex and K vitamins. They outnumber body cells 10 to 1 and account for a couple of lbs.

Gastric Phase

Food in stomach promotes gastrin release and HCl production and digestion of food. Also promotes vagal stimulation of stomach as well as local enteric reflexes. It lasts about 3-4 hours and provides about 2/3 of the gastric juice released.

Esophagus

Food is route here when epiglottis closes of the larynx after food has passed down the pharynx. Descends through the thorax, pierces the diaphragm at the esophageal hiatus, it enters the abdomen, joins the stomach at the cardiac/gastroesophageal sphincter. Layers: mucosa, submucosa, muscularis, and adventitia instead of serosa.

Gastrin H

From G cells. stimulates HCl production and gastric emptying. Increases motility of the ilieum and relaxes the ileocelcal valve (sm. intest.)

Serotonin H

From endoendocrine cells, causes smooth muscle contraction of the stomach

Somatostatin H

From enteroendocrine cells, Inhibits stomach secretions and gastric motility. Inhibits activity of all other GI organs.

Bile E

From liver, digests lipids.

Small intestine anatomy

From teh pyloric sphincter to the ileocecal valve (sphincter). 1. Duodenum: 1st 10" 2. Jejunum: next 8' 3. Ileum: next 12' 4. ileocecal valve Microscopic: 1. Circular folds: (1 cmm high) force chyme to spiral through the lumen slowing it down to allow time for absorption. 2. Villi: fingerlike projections of the mucosa (1mm high in the duodenum, they narrow and shorten along the lenght). 3. Lacteal: at the core of every villus, processes lipids. 4. Microvilli: extensions of the absorptive cells of the mucosal surface (brush border). THey have brush border enzymes, complete carb and protein digestion in sm intestine.

Pharynx

From the mouth food passes through the oropharynx and then onto the laryngopharynx. The mucsosa contains friction-resistant stratified squamous epithelium well supplied w mucus-producing glands.

Mucosal barrier

Gastric juice is corrosively acidic (pH 1.5). It protects itself by lots of mucous; tight junctions; rapid replication of gastric epithelial cells.

Splanchnic circulation

Includes arteries that branch off the abdominal aorta to serve the digestive organs and the hepatic portal circulation.

Peritonitits

Inflammation of the peritoneum

The pancreas

It has a digestive and metabolic role. Produces metabolic hormones insulin and glucagon that aid in CHO metabolism. It produces pancreatic juice that contains bicarbonate ion produced by epithelial cells of the pancreatic duct. it helps buffer acidic chyme. Produces enzymes that digest CHOs and fats. It releases it via the pancreatic duct which empties its digestive enzymes into the sm intestine via the hepatopancreatic ampulla and papilla of vater. Digestion does not occur in the pancreas, it just helps digest CHOs, lipids, and proteins w the help of pancreatic digestive enzymes. No absorption either.

Hepatic Portal System

It receives venous blood from all the GI organs so potentially toxic substances absorbed into the blood stream can be filtered through the liver before it enters general circulation. 1. Hepatic portal vein: venous blood entrance and it branches into smaller veins. After it has been filtered it enters the inferior vena cava for general circulation. - It also helps put all the things the liver makes into general circulation when needed (ferritin, lipoproteins, albumin, cholesterol, glucose, hormones, etc).

Liver

Its digestive role is to produce and export bile, which emulsifies (breaks up) fat sot that it is more accessible to digestive enzymes. Stores and metabolizes glucose, produces and exports cholesterol (on lipoprotein transporters), deaminaties amino acids, makes coagulation factors, make regulatory proteins (albumin, transferin), stores iron, makes TPO and EPO, conjugates biliruben, neutralizes toxins (alcohol), excretes drugs (antibiotics), stores vit A, B12, D, E, K, and phagocytize ingested pathogens. An accessory organ, no absorption is done here. Bile is necessary for the absorption of lipids in the sm intestine.

Retroperitoneal

Lie posterior to the peritoneal cavity (most of the pancreas and duodenum)

Stomach cell types

Lining epithelium of stomach mucosa is simple columar epithelium composed entirely of mucous cells. -Gastric pits: on smooth lining that lead to... -gastric glands: produce gastric juice. 1. Mucous neck cells: in epithelial lining of stomach and produce mucous 2. Parietal cells:in gastric glands secrete HCl and intrinsic factors. -Use proton pumps to pump H+ into the stomach lumen. -They are targeted by histamine to produce HCl -proton pump inhibitors (nexium, prevacid, prilosec) and histamine receptors (H2) blockers (tagament, pepsid, Zantac) to reduce HCl production. used in the treatment of GERD and heartburn. 3. Chief/zymogenic cells: in gastric glands secrete pepsinogen, which is converted to pepsin in the presence of HCL. 4. Enteroendocrine cells: secrete hormones and are located in gastric glands. -Secrete gastrin (from G cells) a hormone like substance that stimulates parietal cells to produce HCl and stimulates gastric emptying. -Secrete histamine: stimulates parietal cells to produce HCl -Secrete serotonin: Causes smooth muscle contraction of the stomach. Acts locally (paracrine) -Secrete Somatostatin: Inhibits stomach secretions in gastric motility. Also inhibits activity of all other GI organs.

Stomach

Located in the upper left quadrant of peritoneal cavity. Temporary "store tank" where chemical breakdown of proteins begin and food is converted into chyme (paste). -Digestion of: protein via pepsin, milk via rennin in babies, lipids via lingual lipase. -Absorption: alcohol, some drugs, aspirin, some water.

Mucosa

Moist epithelial membrane that lines the alimentary canal from mouth to anus. -Secretes mucus, digestive enzymes, and hormones -Absorbs nutrients into blood -Protects against infection. Macrophages live here (contains MALT). -Epithelium is simple columnar epithelium rich in mucus-secreting cells. +Lamina propia, underliner, nourish and absorbs. It has lymphoid follcles. * Muscularis mucosae

Pancreas cells

Part of the pancreatic islets. 1. Beta cells: located in the pancreatic islets (islets of langerhans) produce the hormone insulin, which lowers blood glucose levels. 2. Alpha cells: located in the pancreatic islets (isles of langerhans) produce the hormone glucagon, it raises blood glucose levels.

Brush border enzymes

Perform the final digestion of food into simple components that can be absorbed by intestinal cells. They are not secreted, they remain bound to brush border plasma membranes. 1. Dextrinase (CHO) 2. Glucoamylase (CHO) 3. lactase (CHO) 4. maltase (CHO) 5. sucarse (CHO) 6. amino peptidase (prot) 7. Dipeptidase (prot) 8. Nucleosidases (nucleic acid) 9. Phosphatases (nucleic acid)

Regulation of Chyme (sm intestine)

Presence of hypertonic, fatty, acidic chyme stimulates the release of secretin and CCK. Both stimulate release of bile from gallbladder and pancreatic enzymes that aid in intestinal digestion and they help it to continue. Secretin inhibits gastric secretion and motility, it begins the intestinal phase of digestion.

Carboxypeptidase E

Procarboxypeptidase = inactive, From pancreas and digest proteins

Insulin E

Produced by beta cells of the pancreatic islets (islets of langerhans)

Accessory digestive organs

Purpose: produce saliva, bile and digestive enzymes, help mechanically digest food. Organs/structure (7): teeth, tongue, gallbladder, salivary glands, liver, and pancreas.

Enterogastric reflex

Put brakes on gastric secretion and gastric emptying to protect the sm intestine from excessive acidity and massive influx of chyme. The duodenum inhibits acid secretion in the stomach by short reflexes through the enteric nervous system and by long reflexes involving sympathetic and vagus nerves.

Muscularis

Responsible for peristalsis and forms sphincters that prevent backflow in GI tract (pyloric valve bw stomach and duodenum)

Gallbladder

Sac-like structure inferior to the liver that stores bile, which drains into the common bile duct. CCK causes contraction and releases bile into the cystic duct into the common bile duct. Relaxes the sphincter of Oddi. Vagal stimulation also causes contraction and release bile.

Control of digestion - Nerves

Stimulation of various receptors results in stimulation of certain nerve plexuses or reflex arcs or hormone producing cells, which can alter digestion in various ways. 1. Vagus nerve: promotes gastric and intestinal motility, bile production by the liver and contraction of the gallbladder. 2. Cranial nerves VII and IX: promote salivation.

Serosa

Same as visceral peritoneum and it is made of areolar connective tissue covered in mesothelium. *Adventitia is found in the esophagus (outside the peritoneal cavity) instead of serosa. It is made of fibrous connective tissue .

Regulation of the liver

Secretin from the sm intestine promotes bile production as well as vagal stimulation (when it innactivates the stimulation of the stomach). CCK potentiates actions of secretin, stimulates gallbladder to release bile, relaxes the hepatopancreater sphincter (of oddi) which then releases bile into the sm intestine.

Vitamins absorption

Sm intestine absorbs dietary vitamins and the lg intestine absorbs some of the K and B vitamins made by its enteric bacterial "guests". -A D E K, fat soluble, couple w food containing natural fats -B and C are water soluble, absorbed via specific active or passive diffusion -B12 requires intrinsic factor which bind to specific mucosal receptor sites in the terminal ileum.

Nucleic acid absorption

The nuclei of ingested foods contain DNA and RNA. Pancreatic nucleases in pancreatic juice hydrolyze the nucleic acids to their nucleotide monomers. Brush border enzymes break the nucletides apart to release their nitrogenous bases, pentose sugars, and phosphate ions. Special carriers actively transport the products across the epithelium. Then enter the blood.

Stomach anatomy

Triderectional muscle layers allow for major mechanical churning. 1. Rugae: longitudinal folds allow for maximal expansion, up to 1 gallon. 2. Cardiac region: where food enters 3. Fundus: dome-shaped part 4. Body: mid portion -Lesser curvature -Greater curvature 5. Pyloric region: pyloric antrum, pyloric canal, terminates at the pylorus 6. pyloric sphincter/valve: controls stomach emptying. -Lesser omentum: from liver to lesser curvature. -Greater omentum: from greater curvature to coils of sm intestine.

Trypsin E

Trypsinogen = inactive form, From pancreas and digest proteins

Digestive system

Two main groups: 1. Alimentary canal (nourish) 2. Accessory digestive organs

Swallowing

aka deglution. Phases: 1. Buccal: in the mouth and it is voluntary. Bolus leaves the mouth and stimulates tactile receptors in the posterior pharynx 2. Pharyngela-esophageal phase: involuntary, controlled by the swallowing center in the brain stem (medulla and lower ponds). Vagus nerve transmit impulses to pharynx and esophagus. Once food enters, respiration is inhibited momentarily. from oropharynx to stomach in about 8 sec. fluids 1-2 seconds.

Water absorption

approx 9 L, mostly derived from GI tract secretions, enter the sm intestine daily. Most abundant in chyme and 95% of it is absorbed by the sm intestine by osmosis. Most is absorbed by the lg intestine, leaving only about 0.1 l to soften feces.

Bile

excreted from liver via L/R hepatic ducts, join to form the common bile duct which ulitmately dumps into the small intestine via hepatopancreatic amupulla and major duodenal papilla. Yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids, and electrolytes. Bilirubin is the bile pigment (yellow).

HIstamine H

from enteroendocrine cells, stimulates HCl production

Lipase E

from pancreas, digests lipids

Bicarbonate Ions

from pancreas, provide proper pH for enzymatic catalysis

GIP H

gastric inhibitory peptide, by duodenum inhibits HCl production. glucose dependent insulinotropic peptide, an incretin. Inhibis HCl stimulates insulin release (pancreas) (sm intestine)

Intrinsic factor

glycoprotein required for vit B12 (needed to produce mature erythrocytes) absorption in the small intestine. Takes the vit. to the ileum. If not present it can result in pernicious anemia.

Gastroileal reflex

long neutral reflex triggered by stomach cavity, increases force of sementation in the ileum and relaxes the ileocecal valve.

VIP H

vasoactive intestinal peptide, by enteric neurons inhibits HCl secretion. Increases blood flow to the intestines and relaxes intestinal sm muscle, part. in the stomach. (sm intest.)

HCl

makes stomach contents extremely acidic, necessary for activation and optimal activity of the protein digesting enzyme Pepsin. It also helps denature proteins and breaking cell walls of plant foods.

Lingual lipase E

minor importance, from mouth and digests lipids

Gastric lipase E

minor importance, produced in the mouth and slightly processes lipids.

Migrating motor complex (MMC)

pattern of peristaltic activity that is stimulated by motilin

Pepsin E

pepsinogen predecessor, converted into pepsin in the presence of HCl

Goblet cells

secrete mucus and contain many of these to protect colon from acids produced by bacteria.

Peritoneum

serous membrane of the abdominopelvic cavity, most extensive of those membranes. 1. Parietal peritoneum: lines the body wall 2. Visceral peritoneum: covers external surfaces of most digestive organs (continuous w parietal peritoneum). 3. Peritoneal cavity: space containing a slippery fluid secreted by the serous membranes. -Serous fluid allows the mobile digestive organs to glide easily across one another and along the body wall as they are active.

Cephalic (reflex) Phase

sight, smell and taste of food stimuli received in the cerebral cortex/hypothalamus/medulla. Ultimately results in stimulation of the Vagus nerve and increased gastric motility.

CCK H

slows gastric motility, stimulates gallbladder to release bile and pancreas to release pancreatic juice. (sm intestine)

Bilirubin

yellow waste prodcut fo the heme of hemoglobin formed during the breakdown of worn-out erythrocytes. It is absorbed from the blood, conjugated and excreted via bile. It breaks into urobilinogen and Stercobilin after it passes to the sma intestine, it gives feces a brown color. No fats are digested or absorbed w/o it and feces are gray-white. * premies don't have well-functioning livers yet, they might become jaundiced due to lack of excretion of bilirubin