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Gastrointestinal
Physiology Block D:Support Systems
| Question | Answer |
|---|---|
| what are the 4 support systems | gastrointestinal balance mechanisms reproduction defence mechanisms |
| what are the functions of the GI system (4) | ingest food transfer nutrients, water and minerals from food to internal organs excrete leftovers protection of internal environment |
| MSDA stands for.... | motility, secretion, digestion, absorption |
| What are the accessory organs for GI system | Gall bladder Liver Pancreas Salivary glands |
| what do the accessory organs do for the GI system | add water, bicarbonate and other ions, enzymes, bile salts to the GI tract contents |
| what are the processes of the GI system | Motility - move and mix Secretion - substance and release digestion : dissolve and break down Absorption: acquire nutrients |
| what is the GI tract wall made up of (6) | secreting epithelium transporting epithelium enteric nervous system muscle system endocrine system defence system |
| what is the enteric nervous system's function | autonomous functions: coordination of reflexes it can and does operate independently of the brain and the spinal cord |
| what are the 4 layers of the GI tract wall | mucosa submucosa muscularis externa serosa |
| what contains the lamina propria, epithelium and muscularis mucosa | mucosa |
| what contains the submucosal nerve plexus with major blood and lymphatic vessels | submucosa |
| what contains circular muscle, myenteric nerve plexus,and longitutinal muscle | muscularis externa |
| Chew | form food bolus |
| swallow | move food bolus through upper esophageal sphincter |
| what takes place in the oral cavity - mouth and pharynx | chew swallow |
| what takes place in the esophagus | swallow continued - transport food bolus to lower esophageal sphincter and into stomach |
| fundus | (Latin for "bottom") is an anatomical term referring to the portion of an organ opposite from its opening |
| What does the stomach do | storage mixing dissolve breakdown |
| what does the small intestine do | break down and move nutrients into internal environment propel remaining contents towards large intestine |
| What is the function of the villi found in the small intestine? | villi increases surface area for absorption as it contains lacteal which absorbs glycogen and fatty acids. blood capillaries in villi absorbs amino acids and glucose and then send them in the live |
| what is the function of the crypts of lieberkuhn in the small intestine | lined largely with younger epithelial cells which are involved primarily in secretion. At the base of the crypts are stem cells, which continually divide and provide the source of all the epithelial cells in the crypts and on the villi. |
| how does the small intestine increase surface area | villi, crypts and brush border microvilli |
| enterocytes | transporting epithelial cells |
| goblet cells | secrete mucus |
| endocrine cells | secrete hormones |
| what is the function of the large intestine in GI | storage for undigested fecal material moves to end of tract for excretion |
| what are the sphincters associated with the large intestine | ileocecal sphincter internal and external anal sphincters |
| what is the function of the Peyer's patch | Peyer's patches are importnat for the immune surveillance of the intestinal lumen and in facilitating the generation of the immune response within the mucosa. |
| explain the process of motility in GI fucntion | move luminal contents along the tract mix contents with secretions to aid digestion bring contents in contact with absorptive epithelia |
| what type of muscle is the GI tract made up of | smooth muscles |
| describe the action potential in the smooth muscle cells | upstroke - (depolarization of cell) entry of Ca ions through voltage-gated channels repolarization due to K voltage-gated channels |
| smooth muscles move as a _____________ | single unit |
| describe how the smooth muscle in the GI function | cell connected by gap junctions action potentials spread cells contract as one unit |
| what do the pacemaker cells in the GI do | interstitial cells of Cajal generate basic electrical rhythm (BER) set maximum frequency of contraction |
| describe the BER in the stomach and small intestine | 3/min stomach 12/min small intestine |
| what determines the strength of the contraction of smooth muscles | neural and hormonal input and organ contents |
| how is motility regulated to maximize digestion and absorption of nutrients | autonomic nervous system - long reflexes enteric nervous system - short reflexes Gi peptides - paracrines and hormones |
| what is the cephalic phase of gastric secretion | Thinking of food– Stimulates cerebral cortex – Sends messages to hypothalamus– medulla oblongata –parasympathetic nervous system–to stomach –secrete gastric juice. 20 percent of the gastric secretion associated with eating a meal. |
| what is the gastric phase of gastric secretion | Takes 3 to 4 hours. stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Food enters stomach – stomach stretches, activates stretch Receptors – medulla oblongata– to stomach —parietal cell secrete gastric juice. |
| what is the intestinal phase of gastric secretion | 2 parts - excitatory and inhibitory Chemical Stimuli (partially digested proteins, caffeine) – activates G cells -secrete gastrin – Gastrin stimulates – Gastric Glands to secrete gastric Juice. |
| what are the motility patterns | tonic contraction phasic contraction peristalsis segmentation |
| tonic contraction | contraction maintained for long time (sphincters and upper stomach) |
| phasic contraction | short contractions - relaxation cycles |
| peristalsis | propulsion circular muscles contract behind food bolus |
| segmentation | mixing chyme with intestinal juice, bring in contact with transporting epithelium circular muscles in short segments contract and relax rhythmically |
| What are the GI organs and accessory organs in the oral cavity | mouth, pharynx salivary glands |
| mastication | chewing begins mechanical digestion - voluntary control of jaw and mouth reflex - presene of food in mouth tongue forms bolus, pushed to back of mouth |
| deglutition | swallowing move food bolus out of oral cavity into esophagus and then the stomach |
| explain the swallowing reflex | food at the back of the mouth triggers reflex Upper esophageal sphicter relaxes, epiglottis closes bolus moves into esophagus (peristalsis and gravity) |
| describe motility in the esophagus | peristalsis (7-10 sec) from esophagus to stomach Lower esophageal sphincter opens for food bolus to pass through upper stomach relaxes to receive food |
| primary peristalsis | swallowing reflex |
| secondary peristalsis | local control distension of esophagus by leftover food bolus |
| describe gastric motility | ingested food is crushed, ground and mixed, liquefying it to form what is called chyme. chyme is forced through the pyloric canal into the small intestine, a process called gastric emptying. |
| receptive relaxation | stomach relaxes and expands to receive incoming food |
| describe food vs liquids in gastric motility | Liquids readily pass through the pylorus in spurts, but solids must be <1-2 mm before passing the pyloric gatekeeper. Larger solids are propelled by peristalsis toward the pylorus, but then refluxed backwards when they fail to pass through the pylorus |
| retropulsion results in .... | mixing and grinding |
| what are leading causes of heartburn and acid reflux | large meal pregnancy pressure in stomach is enough to force LES open |
| what is heartburn and acid reflux | acidic chyme forced up through LES, irritates mucosa of esophagus |
| What organ is the most important for motility during a meal | small intestine |
| what controls segmentation force in the small intestine | varies with distension of small intestine crontrolled by ENS, parasympathetic increases sympathetic decreases |
| what are the reflex controls of the small intestine? | gastrileal reflex intestino-intestinal reflex |
| gastrialeal reflex | gastric empything incrases force of contraction in ileum chyme moved into large intestine through relaxed ileocecal sphincter |
| intestino-intestinal reflex | cessation of motility due to large distension of small intestine, injury to intestinal wall, bacterial infection |
| how long does it take slow peristaltic waves that start in the stomach to arrive at the end of ileum | 2 hours |
| what does the MMC do? | housekeeping functions move undigested material to large intestine prevent excessive bacterial group |
| what initiates/ stops the MMC | migrating motor complex motilin initiates goof arriving in stomach stops MMC and starts segmentation contraction |
| Haustrations | mixing of feces to expose it to the surface of intestine to absorb water sac like structures foldings in large intestine every 30 mins |
| how often are the mass movement of the large intestine | 3-4 times a day peristaltic-like wave of intense contraction |
| gastrocolic reflex | gastric emptying initiates mass movements |
| defacation reflex | mass movements of propel the contents of the colon toward the rectum defactation stimulated by feces enter rectum rectum contracts internal anal sphincter relaxes external anal sphincter (voluntary control) |
| diarrhea | increased colon motility decreased concentration time increased fecal water output (dehydration, metabolic acidosis) |
| constipation | decreased colon motility increased concentration time decreased fecal water output - hard feces |
| vomiting | reverse peristalsis goes from stomach to oral cavity (dehydration, metabolic alkalosis) |
| describe secretion: ions water mucus digestive enzymes bile | ions - Na, K, Cl, HCO, H water - moves by osmosis (follow ions) digestive enzymes - released as inactive zymogens; activated in lumen of tract bile - secreted by liver, stored in gall bladder |
| what is secreted in the oral cavity | saliva salivary glands: parotid, submandibular, sublingual |
| what do the water, ions, and mucins do in digestion | soften and lubricate food dissolve substances (taste) wash food paritcles from teeth and tongue |
| salivary amylase | begins carbohydrate digestion |
| sysozyme and immunoglobulins | disable bacteria and viruses |
| what are the secretions in the oral cavity | salivary amylase lysozyme and immunoglobulins saliva |
| long neural reflexes in the cephalic phase | parasympathetic - main; high volume, watery sympathetic - low volume; mucus |
| what is the purpose of secretion in the esophagus | mucus: lubrication |
| what are the different secretions of the stomach | exocrine endocrine paracrine |
| what are the exocrine secretions of the stomach | parietal cells - HCl, intrinsic factor (B12 absorption) chief cells - pepsinogen (inactive pepsin) mucous cells - mucus, bicarbonate |
| what are the endocrine secretions of the stomach | G cell - gastric (hormone) |
| what are the paracrine secretions of the stomach | Enterochromaffin-like (ECL) cell - histamine D cell - somatostatin |
| what does the parietal cell secrete | HCl intrinsic factor |
| what is the purpose of HCl | gastric acid create acidic environment pH ~2 kill bacteria denatures proteins activates pepsin |
| what is the purpose of the intrinsic factor | acid secreting stomach cell needed for the absorption of Vit B12 lack of this causes - pernicious anemia |
| how does HCl denature proteins | denaturation of salt bridges double replacement reaction occurs where the positive and negative ions in the salt change partners with the positive and negative ions in the new acid or base added. AB + CD = AD + CB |
| What is gastric regulation what stimulates it and what inhibits it | cephalic reflexes or food initiate gastric secretion stimulate HCl: gastrin, histamine, ACh inhibit: Somatostatin acid stimulates short reflex secretion of pesinogen |
| what does the chief cell secrete | pepsinogen (zymogen) HCl converts it to pepsin (active form) which digests proteins in acid environment |
| what does the mucous cell secrete | mucus - physical barrier HCO3 - chemical barrier to protect epithelial cells of mucosa from acid in stomach lumen |
| which phase of gastric function always inhibits gastric function | intestinal phase |
| what is the intestinal phase of gastric function | presence of chyme in the small intestine inhibits gastric acid release and gastric motility (gastric empuything) |
| what is the greatest inhibitor in Gastric functioning | fat in the small intestine |
| in digestion, the pancreas is necessary for what type of secretion | exocrine |
| what regulates the secretion of enzymes | CCK |
| what enzymes are needed for carbohydrate digestion | pancreatic amylase |
| what enzymes are needed for lipid digestion | pancreatic lipase procolipase (colipase) Its function is to prevent the inhibitory effect of bile salts on the lipase-catalyzed intraduodenal hydrolysis of dietary long-chain triglycerides. |
| what enzymes are needed for protein digestion | trypsinogen (trypsin) chymotrypsinogen (chymotrypsin) procarboxypeptidase (carboxypeptidase) |
| enteropeptidase | a brush border enzyme that activates trypsin |
| trypsin | pancreatic enzyme that activates other symogens |
| list 4 zymogens inactive and and active form | chymotrypsinogen - chymotrypsin procarboxypeptidase - carboxypeptidase procolipase - colipase prophospholipase = phospholipase |
| what are the two main classes of exocrine pancreatic secretions | bicarbonate ions - from centroacinar cells - signaled by secretin digestive enzymes from basophilic cells, signaled by CCK |
| duct cell secretion in the pancreas | bicarbonate ions, water |
| what cells produce bicarbonate secretion | pancreatic duct cells and intestinal epithelial cells |
| what is the function of bicarbonate secretion | neutralizes acidic chyme from stomach |
| what is the chemical formula for bicarbonate | H2O + CO2 (carbonic anhydrase) = HCO3- |
| Cl- HCO3- antiport function | secretes bicarbonate into lumen |
| cell transport Cl- into lumen via.... | CFTR channels Cystic fibrosis transmembrane conductance regulator CFTR is an ABC transporter-class ion channel that transports chloride and thiocyanat ions across epithelial cell membranes. |
| after bicarbonate secretion where to water and sodium go | follow bicarbonate via paracellular pathway |
| what are the liver secretions | bicarbonate bile salts bile pigment cholesterol |
| what is the regulator of the gallbaldder and sphincter of oddi | cck |
| where is bile stored | in gallbladder if sphincter of oddi closed here it concentrates bile, when it contracts and sphincter of oddi relaxes, bile enters duodenum |
| what is the function of the large intestine | store, concentrate and eliminate |
| what are the secretions of the large intestine | mucus, fluid with bicarbonate and potassium |
| different types of carbohydrates are __________ | starch cellulose (no enzymes can break this down in humans) sucrose lactose |
| types of fats are ___________________ | triglycerides (tricylglycerol) cholestrol phopholipids |
| in order for absorption of carbohydrates they must be______ | monosaccharides |
| amylase | digests starch to maltose need neutral environment in salivary and pancreatic juices |
| diasccharidases | digest di to monosaccharides produced in brush border enzymes |
| maltose | 2 glucose |
| sucrose | glucose and fructose |
| lactose | glucose and galactose |
| carbohydrate absorption: glucose and galactose | luminal membrane - secondary active transport with sodium basolateral membrane - facilitated diffusion |
| carbohydrate absorption: fructose | facilitated diffusion through both membranes |
| what is the MSDA of the oral cavity and esophagus | M - swallowing, chewing S - saliva (salivary glands), lipase D - carbohydrates, fats (minimal) A - none |
| what is the MSDA of the stomach | M - peristaltic mixing and propulsion S - HCL; pepsinogen and gastric lipase; mucus and bicarbonate; gastrin ; histamine D - proteins, fats A - lipid-soluble substances (alcohol and aspirin) |
| what is the MSD of the small intestine | M - mixing and propulsion primarily by segmentation S - enzymes; bicarbonatre and enzymes (pancreas); bile; mucus; hormones; CCK, secretin, GIP D - carbohydrates, fats, polypeptide, nucleic acids |
| what is the absorption of of the small intestine | A - peptides by active transport; amino acids, glucose and fructose by secondary active transport; fats by simple diffusion; water by osmosis ions, minerals and vitamins by active transport |
| what is the MSDA of the large intestine | M - segmental mixing; mass movement for proopulsion S - mucus D - none (except by bacteria) A - ions, water , minerals, vitamins and small organic molecules produced by bacteria |
| describe the hepatic portal system | nutrients enter capillaries in GI tract hepatic portal vein takes them to the liver liver removes many nutrients for processing and storage blood leaves liver through hepatic vein |
| what is insulin and glucagon's role in maintaining homeostasis | low blood sugar - pancreas alpha cells release glucagon - signals liver to release glucose into the blood high blood glucose - pancreas secretes insulin from beta cells - fat cells take in glucose from blood |
| proteins are digested into_______ | amino acids and dipeptides and tripeptides |
| what enzymes are used to break down proteins | protesases, peptidases |
| what is the enzyme produced in the stomach to break down protein | pepsin (acidic environment) |
| what is the enzyme produced in the pancreas that breaks down proteins | trypsin chymotrypsin (neutral environment) |
| where are many endopeptidases located | luminal membrane of small intestine |
| what are two different types of exopeptidases | aminopeptidase - luminal membrane carboxypeptidase - pancreas |
| protein absorption: amino acids | secondary active transport sodium facilitated diffusion out |
| protein absorption: di and tripeptides | secondary active transport hydrogen ion digested into amino acids facilitated diffusion out |
| protein absorption: very small peptides | endocytosis exocytosis |
| fat and lipid digestion | breakdown of triglycerides to monoglycerides and free fatty acids |
| where is the most fat digestion | small intestine - pancreatic lipase |
| where is there very little fat digestion | mouth - lingual lipase stomach - gastric lipase |
| why does the lipase need help with fat digestion | ingested fasts are insoluble in water so they form large lipid droplets lipase is water solute and fat insoluble and function on droplet surface only must use emulsification to break up droplets |
| how is fat emulsified in the body | contractile activity and emulsifying agents bile |
| colipase's function in fat digestion | lets lipase through the bile salt coat on emulsified droplet |
| in fat absorption, digestive products and bile salts form_____________ | micelles - keeps them soluble |
| monoglycerides and free fatty acids are absorped by | simple diffusion |
| what is a micelle made up of | bile salts fatty acids monoglycerides phospholipids cholesterol fat-soluble vitamins (DAKE) |
| where do FFAs and monoglycerides go after the breakdown of the micelle | reform triglycerides packaged in chylomicrons and leave by exocytosis |
| chylomicrons are made up of | triglycerides vit DAKE cholestrol apoproteins too large to enter blood capillary and go into lacteal (lymph)to vena cava, bypassing the hepatic protal vein and therefore the liver |
| enterohepatic circulation | where bile salts are recycled most (>90%) are reabsorbed in the ileum returned ot liver, re-secreted |
| nucleic acid digestion | digested by pancreatic and intestinal enzymes into nucleotides and then bases and monosaccharides |
| how are fat soluble vitamins absorbed | fat pathways |
| how are water soluble vitamins absorbed | diffusion, mediated transport except for B12 |
| how is B12 absorped | binds to intrinsic factor, absored in ileum by endocytosis this is necessary for RBC production |
| water is most abundant in what substance in digestion | chyme |
| small intestine is very permeable/impermeable | permeable, water follows solutes |
| what is the input and output of the GI tract | input: ingestion 2L; secretion 7L output: absorption 8.9L; excretion 0.1L |
| what stimulates or inhibits motility | smooth muscle |
| what stimulates or inhibits secretion | secretory cells, accessory organs |
| long reflexes are integrated in the _____ _____ _______ | central nervous system |
| short reflexes originate in the ______ ______ _____ | enteric nervous system |
| how is each phase controlled? cephalic gastric intestinal | cephalic - head gastric - stomach intestinal - intestine |
| what is a stimuli for the cephalic phase | thought, sight, aroma, presence of food in oral cavity long neural reflexes: oral cavity, stomach, small intestine |
| how is the gastric activity regulated in the cephalic phase | increased activity stimuli - sight, smell, taste, etc. parasympathetic nerves to ENS |
| how is the gastric activity regulated in the gastric phase | increased activity stimuli - distension, peptide, acidity in stomach short neural reflexes, gastrin, histamine |
| how is the gastric activity regulated in the intestinal phase | decreased activity stimuli distension, acididty, osmolarity, nutrient concentration in small intestine secretin, CCK, GIP, GLP-1 |
| how is intestinal activity regulated - cephalic phase | taste parasympathetic signals to pancreas increased pancreatic secretion and intestinal motility |
| how is intestinal activity regulated - gastric phase | distension of stomach parasympathetic signals to pancreas increased pancreatic secretion and intestinal motility gastrin - increase intestinal motility |
| how is intestinal activity regulated - intestinal phase | increased acidity increased fatty acids and amino acids increased glucose and fat |
| what does increased acidity stimulate in the intestine | stimulates secretion of hormone secretin that stimulates secretion of pancreatic bicarbonate |
| what does increased fatty acids and amino acids stimulate in the intestinal phase | stimulates secretion of hormone CCK that stimulates secretion of pancreatic enzymes; contracts gallbladder and relaxes sphincter of Oddi and potentiates activity of secretin |
| what does increased glucose and fat stimulate in the intestinal phase | increase secretion of hormone GIP, GLP -1 that stimulate insulin secretion from endocrine pancreas |
| what are the immune functions of the oral cavity | salivary enzymes and immunoglobulins |
| what are the immune functions of the stomach | acidic environment |
| what are the immune functions of the small intestine | GALT - gut associated lymphoid tissue peyer's patches, M cells macrophages, lymphocytes |
| what does the mucous cell do? | protect epithelial cells of mucosa from acid in stomach lumen |
| ulcers | perforations of mucosa, helicobacter pylori |
| vomiting | protective reflex - remove contents from stomach lumen 'reverse peristalsis' |
| what are the problems is there is excessive vomiting | H ions are lost instead of absorbed metabolic alkalosis |
| diarrhea | increased fecal water output metabolic acidosis |
| what is the main cause of death or disability in the world today | diarrhea |
| diarrhea: what causes impaired absorption of NaCl | E coli |
| Diarrhea: what causes accumulation of solutes | lactose intolerance |
| Diarrhea: what causes excess secretion | Cholera (salt and glucose solution) |
| Diarrhea: what causes increased colon motility | decreases concentration time |
| Constipation | decreased colon motility, hard feces |
| lactose intolerance | lack of lactase, increased osmolarity |
| gallstones | crystallized cholesterol, block ducts |
| vomiting | dehydration, metabolic alkalosis |
| ulcers | perforations of mucosa, helicobacter pylori |
| inflammatory bowel diseas | Crohn's disease, immune response triggered by normal contents |
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