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Digestive System

Xiao Yuan Inglés 61 fichas

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  1. 1intracelluar digestionpart of metabolism, involves the oxidation of glucose and fatty acids for energy, however our diets do not consist of pure glucose and fatty acids , rather these substances have to be extracted from food
  2. 2extracellular digestionprocess by which nuetrients are obtained from food (fatty acids and glucose needed for intracellular digestion), process occurs within the lumen of the alimentary canal
  3. 3alimentary canalruns from the mouth to the anus and is sectioned off by spincters (circular smooth muscles around the canal that can contract to allow compartmentalization of function)
  4. 4digestionthe breakdown of food into its constituent organic molecules
    starches / other carbs -> monosaccharides
    lipids -> free fatty acids and glycerol
    proteins -> amino acids
    can be divided into mechanical and chemical processes
  5. 5mechanical digestionthe physical breakdown of large food particles into smaller food particles, but does not involve breaking down chemical bonds
  6. 6chemical digestionis the enzymatic cleavage of chemical bonds sucha s the peptide bonds of proteins or the glycosidic bonds of starches
  7. 7absorptioninvolves the transport of products of digestion from the digestive tract into the circulatory system for distribution to the body's tissues and cells
  8. 8pathway of the digestive tractbeings with oral cavity (mouth) -> pharynx (shared pathway for both food and air) -> esophagus -> stomach -> small intestine -> large intestine -> rectum (where feces are stored until the appropriate time of release
    organs of the digestive tract
    salivary glands, pancreas, liver and gall bladder help to provide the enzymes and lubrication necessary to aid the digestion of food
  9. 9enteric nervous systemcollection of one hundred million neurons that govern the function of the gastrointestinal system, these neurons are present in the walls of the digestive tract and trigger peristalsis (rhythmic contractions of the gut tube, in order to move materials through the system) the system can function independently of hte brain and spianl chord, although it is heavily regulated by the autonomic nervous system
  10. 10autonomic nervous system and digestionparasympathetic division is involved in stimulation of digestive, activities, increasing secretions from exocrine glands and promoting peristalsis
    sympathetic division is involved in inhibition of these activities,
    the fact that we feel so sleepy and lethargic after eating a big meal is due to the parasympathetic nervous system
  11. 11which glands are innervated by the parasympathetic nervous system?all glands except the sweat glands
  12. 12ingesteat
  13. 13what triggers the sensation of thirst?vasopressin (ADH) and aldosterone
  14. 14what stimulates feelings of hunger?glucagon secreted by the pancreas, ghrelin secreted by the stomach and pancreas
  15. 15what gets rid of the feeling of hunger?cholecystokinin and leptin, stimulating feelings of satiety
  16. 16where does digestion start and end?digestion begins in the oral cavity and continues in the stomach and hte first part of the small intestine known as the duodenum
  17. 17oral cavity mechanicalmechanical digestion in the mouth involves the breaking up of large food particles into smaller particules by using the teeth, tongue and lip, this process is called mastication, this helps increase surface area and prevents large food particles from blocking up the alimentary canal, our tongue forms the food into a bolus which is forced back to the pharanx and swallowed
  18. 18oral cavity (chemical digestion)relies on enzyme from saliva produced by the three pairs of salivary glands, saliva also aids mechanical digestion by moistening and lubricating food, salivary glands are innervated by parasympatheitc nervous system, saliva can be triggerd by signals that food is near such as smell or sight, chemical digestion is limited in the oral cavity,
  19. 19enzymes in salivalipase - catalyzes the hydrolysis of lipids
    salivary amylase (hydrolyzes starch into smaller sugars)
    has the same function of pancreatic amylase which is active in the small intestines, (small is intestines is where chemical digestion is completed)
  20. 20pharanxis the cavity that leads from the mouth and the posterior nasal cavity to the esophagus/larnx
    can be divided into three parts
    nasopharynx (behind the nasal cavity)
    oropharynx (at the back of the mouth)
    laryngopharynx (above vocal chord)
  21. 21esophagusis a muscular tube that connects the pharnx to the stomach, the top third of the esophagus is composed of skeletal muscle, the bottom third is composed of smooth muscle, and the middle is a mixture of both, the top esophagus is under somatic (voluntary) motor control, the bottom is under autonomic nervous control
  22. 22reversal of peristalsisreverse of peristalsis is emesis (vomitting)
  23. 23process of swallowinginitiated in the muscles of hte oropharnx, which constitute the upper esophageal sphincter , as the bolus approaches the stomach a muscular ring known as the LOWER ESOPHAGEAL SPHINCTER (CARDIAC SPHINCTER) relaxes and opens to allow the passage of food
  24. 24stomachhighly muscular organ with a capacity of approximtely two liters, uses hydrochloric acid and enzymes to digest food
    its mucosa is quite thick to prevent autodigestion, stomach can be divided into four divisions
  25. 25what are the four main divisions of the stomach? (page 312 for picture reference)fundus and body : contain mostly gastric glands
    antrum and pylorus: contain mostly pyloric glands
    the internal curvature of the stomach is known as the lesser curvature and the external curvature is called the greater curvature, the lining of the stomach is thrown into folds called rugae
  26. 26gastric glands (one of the two glands of the stomach mucosa)gastric glands: responds to signals from the vagus nerve (parasympathetic, acivated by the brain in response to the sight, taste and smell of food)
    composed of three different cell types, mucous cells, chief cells, and parietal cells
  27. 27mucous cellspart of the gastric gland, produce bicarbonate rich mucus that protects the musculature wall from the harshly acidic (pH=2) and proteolytic environment of the stomach
  28. 28gastric juicecombination of secretions from the other two cell types in the gastric glands,
    chief cells secrete pepsinogen which is inactive (zymogen form of pepsin, a proteolytic enzyme)
    hydrogen ions are secreted by partietal cells as hydrochloric acid cleave pepsinogen to pepsin
    the parietal cell also secretes intrinsic factor (a glycoprotein involved in proper vitamin B 12 absorption)
    gastric juice kills most harmful bacteria
  29. 29what does pepsin do?pepsin (after cleavage and activation by HCl) digests proteins by cleaving peptide bonds near aromatic amino acids, resulting in short peptide fragments, pepsin is most activated by an acidic environment
  30. 30where are G cells produced and what do they do?G cells are produced in the pyloric glands, they secrete gastrin, a peptide hormone
  31. 31where is gastrin produced and what does it do?gastrin is produced by the G cells, it induces the parietal cells in the stomach to secrete more HCl and signals the stomach to contract which mixes its contents
  32. 32chymethe result of the digestion of solid foods in the stomach, is acidic and semifluid mixture, resulting chyme has significant increased surface area and absorption of nutrients can be maximized
  33. 33what are the three segements of the small intestine?the small intestine consists of three segments, the duodenum, the jejunum and the ileum, small intestine is quite large can be up to 7 meters, duodenum is responsible for the majority of chemical digestion, and has minor involvement in absorption, most absorption takes place in the jejunum and the ileum
  34. 34functions of the duodenum /brushborder enzymes? what triggers their release and what do they do?food leaves through the pyloric sphincter, and enters the duodenum, presence of chyme in the dd causes it to release brush border enzymes which are present in the luminal surface of cells lining the dd, these enzymes causes the breakdown of dimers and trimers into absorbable monomers (lactase)
  35. 35enteropeptidase?released by the duodenum and is invovledi nt he actavtion of other digestive enzymes from the accessory organs of digestion, one of which is a pancreatic enzyme trypsinogen, trypsin initiates can activation cascade, enteropeptidase can also activate procarboxypeptidases A and B to their active form
  36. 36what are the 6 products that the stomach secretes?pepsinogen, water(dissolves and dilutes ingested material), mucus, HCl, gastrin, bicarbonate
  37. 37why do lactose intolerant people have their symptoms?bacteria have to digest the dissachride because the duodenum does not have the brush border enzyme lactase, this causes a production of methane gas, also dissacharides can pull water into the stool causing diarrhea
  38. 38peptidases, aminopeptidase, dipeptidase (how are dimers and trimers peptides different from carbs)?break down proteins or peptides, aminopeptidase is a peptidase secreted by glands in the duodenum that removes N terminal amino acid from a peptide, dipeptidases breaks dipeptides to free amino acids, di/tripeptides can be directly absorbed across the small intestine wall whereas sugars have to be broken down into monosaccharides
  39. 39secretin / enterogastroneis a peptide hormone that causes pancreatic enzymes to be released into the duodenum, it also causes decreased HCl production and increased bicarbonate production, is an enterogastrone which means a hormone that slows motility through the digestive tract, this allows for increased time for digestive enzymes to act on chyme, most importantly fats
  40. 40cholecystokinin (CKK), how does it affect hunger?secreted in response to entry of chyme, specifically (amino acids and fats) into the duodenum, this peptide hormone stimulates the release of both bile and pancreatic juices and also acts in the brain where it promotes satiety, also promotes the secretion of pancreatic juices into the duodenum
  41. 41bileis a complex fluid composed of bile salts, pigments and cholesterol ,
    bile salts are derived from cholesterol, they are not enzymes and do not perform chemical digestion, they serve an important role in the mechanical digestion of fats and ultimately facilitate the chemical digestion of lipids, bile salts have hydrophobic and hydrophillic regions allowing them to serve as a bridge between aqueous and lipid environments, bile salts are like common soaps, in the small intestine bile salts EMULSIFY fats and cholesterol into micelles
  42. 42what does lipase do and what is required to make it function?lipase is water soluble that hydrolyze the ester bonds holding the lipids together (chemical digestion)
    and requires bile to get fats into micelles otherwise the fats would spontaneously seperate out of the aqueous mixure in the duodenum and not be accessible to lipase, micelles also increase the surface area of fats increasing the rate at which lipase can act
  43. 43pancreatic juicesare a complex mixture of several enzymes in a bicarbonate rich alkaline solution, this bicarbonate helps neutralize acidic chyme as well as provide an ideal working environment for each of the digestive enzymes which are most active around ph 8.5, pancreatic juices contain enzymes that digest all three types of nutrients
  44. 44accessory organs of digestionorgans that are required for digestion that are not part of the alimentary canal, are derived from the endoderm during development, pancreas, liver and gallbladder
  45. 45acinar cellsbulk of pancreas are exocrine cells called acinar cells that produce pancreatic juices, these juices include the enzymes
    pancreatic amylase - breaks down large polysaccharides into small disaccharides
    pancreatic peptidases (trypsinogen, chymotrypsinogen and carboxypeptidases A & B) are released in their zymogen form
    enteropeptidase is the master switch, it activates trypsinogen to trypsin which can activate other zymogens and activate procaroxypeptidases A and B to their active form
    pancreatic lipase - capable of breaking down fats into free fatty acids and glycerol
  46. 46how does the pancreas get its juices into the small intestine?like all exocrine cells acinar cells secrete their products into ducts, these ducts then empty into the duodenum through the MAJOR and MINOR DUODENAL PAPILLAE
  47. 47where is the liver located? what does it do in relationship to digestion? hepatic portal veinthe liver is located in the upper right quadrant of the abdomen and contains two unique structures for comminicating with the digestive system, bile ducts connect the liver with both the gallbladder and small intestines, bile can either be stored in the gallbladder or secreted into the duodenum, liver also recieves all blood draining from the abdominal portion of the digestive tract through the hepatic portal vein, this nutrient rich blood can be processed by the liver before emptying into the inferior vena cave -> right heart , the liver takes up this excess sugar to create glycogen, and stores fats as triacyglycerols, liver can also reverse the process through glycogenolysis and gluconeogensis and mobilizing fats in lipoproteins
  48. 48functions of the liver simplifiedhepatic portal vein blood (nutrient rich) -> liver stores as glycogen and fats as triglycerides, can also reverse IE gluconeogeneis / mobilizing fats in lipoproteins
    liver detoxifies both endo and exo waste products
    produces bile which emulsifies fats
    synthesis of albumin and clotting factors
  49. 49detoxification functions of the liverthe liver detoxifies endogenous and exogenous wastes, e.g ammonia -> urea which can then be excreted by the kidneys
    liver also detoxifies and metabolizes alcohol and medications
    some drugs require activation by enzymes of the liver, in addition some drugs cannot be taken orally because modification of these drugs by the liver renders the drugs inactive
  50. 50bilirubinbyproduct of the breakdown of hemoglobin, bilirubin travels to the liver where it is conjugated (attached to a protein) and secreted into the bile for excretion
    if the liver is unable to excrete or process bilirubin, jaundice or yellowing of the skin may occur
  51. 51proteins that the liver synthesizes and their functions?liver synthesizes albumin which is important in plasma oncotic pressure and serves as a carrier for many drugs and hormones
    liver also synthesizes clotting factors used during blood coagulation
  52. 52where is the gall bladder located and what does it do?gall bladder is located beneath the liver and stores and concentrates bile
    upon release of CKK, the gall bladder contracts and pushes bile out into the biliary tree, the bile duct merges with the pancreatic duct before emptying into the duodenum
    cholesterol and bilirubin stones are often formed in the gall bladder, and may travel and get stuck in the biliary tree, sometimes they get stuck right before entering the duodenum resulting in blockage of not only the biliary tree but the pancreatic ducts as well, causing pancreatitis
  53. 53villismall intestine is lined with villi, which are small finger like projections from the epithelial lining, each villus has many microvilli, at the middle of each villus is a capillary bed for the absorption of water soluble nutrients and a lacteal, a lymphatic channel that takes up fats for transport into the lymphatic system
  54. 54how do simple sugars such as glucose etc and amino acids get taken to the liver?simple sugars and amino acids can enter the cell via secondary active transport (ATP is used to create a gradient, Na + for example, then the nutrients can enter along with a Na + into the epithelial cells of the small intestine [symport cotransporter] )
    because the blood is constantly passing and carrying away molecules of carbs / amino acids away from the epithelial cells they have a low concentration of them, therefore carbs/ amino acids can simply diffuse into the capillary beds
    the absorbed molecules then go to the liver via the hepatic portal circulation
  55. 55how are fats transported?simple small fats can diffuse through the epithelial cell and into the capillaries since the they are non polar and easily transverse the cellular membrane, larger fats, glycerol, cholesterol move separately into the intestinal cells but then reform into triglycerides, the triglycerides and esterified cholesterol molecules are packaged into chylomicrons, instead of entering the bloodstream the chylomicrons enters the lymphatic circulation through lacteals (small vessels that form the beginning of the lymphatic system), these lacteals converge and enter the venous circulation through the thoracic duct in the base of the neck, which empties into the left subclavian
  56. 56where are vitamins absorbed? and which vitamins are fat soluble? how are fat soluble vitamins transported?vitamins are absorbed in the small intestine
    the water soluble vitamins are ADEK
    fat soluble vitamins are directly dissolved into the chylomicrons to enter the body, failure to digest and absorb fat properly may lead to a deficiencies of fat soluble vitamins
    water soluble vitamins are absorbed along with water, amino acids and carbohydrates across the endothelial cells of the small intestine passing directly into the plasma
  57. 57how is water absorbed? how much water do we consume average daily? how much from secretions?small intestines absorb most of all the water in the system, we consume on average 2 liters, we secrete about 7 liters daily, water is reabsorbed by osmosis as it is pulled in with solutes when absorbed,
    water passes through not only transcellularly but also paracelluarly (squeezing between cells)
  58. 58large intestine, what are the different sections?divided into three major sections, the cecum, the colon and the rectum
  59. 59cecumthe cecum is simply an outpocketing that accepts fluid from the small intestines via the ileoccal vavlve, the cecum is also attached to the appendix
  60. 60what is the function of the colon?the main function of the colon is to absorb water and salts (such as sodium chloride) from the undigested material left over from the small intestines, the colon primarily concentrates the remaining material to form feces
  61. 61rectumserves as the storage site for feces, which consists of indigestible material, water, bactiera, and certain digestive secretions that are not reabsorbed (enzymes and some bile)
    the anus is the opening to which wastes are eliminated and consists of two sphincters (internal and external anal sphincters), the external sphincter is under voluntary control (somatic) but the internal sphincter is under involuntary control (autonomatic)

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Fichas sobre Digestive System, creado por Xiao Yuan el 09/01/2018.
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