Digestive System

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  1. Function of the digestive system
    to break down the food to a form that can be absorbed by the blood and lymph, and utilized by the cells for nutrition
  2. Organization of the digestive system
    • organs form a continuous tube
    • mouth--> pharynx--> esophagus--> stomach--> small intestine--> large intestine
    • there are also accessory organs
  3. accessory organs (examples)
    • important but not in the main tube
    • either cause physical changes in the food or release secretions to the GI tract through a duct
    • ex: teeth tongue (oral cavity)
    • ex: salivary glands, liver, gall bladder, and pancreas all secrete into ducts
  4. Processes of digestion
    • all physical changes of food, moving of food, or enzymatic breakdown
    • 1.) Ingestion
    • 2.) Propulsion
    • 3.) Mechanical Digestion
    • 4.) Chemical Digestion
    • 5.) Absorption
    • 6.) Excretion of wastes (defecation)
  5. Ingestion
  6. Propulsion (2 examples)
    • moving of food through the GI tract- due to smooth muscle contraction
    • ex: deglutition- swallowing; food goes from the mouth to the stomach
    • ex: peristalsis- a wave like contraction to push the food along
  7. 2 phases of deglutition
    • 1.) mouth--> pharynx (voluntary)- bucal phase
    • 2.) pharangeal-esophageal phase- involuntary; pharynx--> esophagus--> stomach (regulated by a center in the lower part of the pons and part of the medulla)
  8. What is the form of the food that is swallowed called?
    a bolus
  9. Mechanical Digestion (examples)
    • physical changes in the food
    • allows enzymes to work bc food is in smaller pieces
    • ex: Mastication, Churning, and segmentation
  10. Mastication
    • chewing
    • most significant physical change in the food
    • also mixes food with saliva
  11. churning
    stomach contraction mixing the food with the gastric secretions
  12. segmentation
    • contraction back and forth in sections of the intestines and then moving the food along
    • this allows more efficient enzyme action and absorption
  13. Chemical Digestion (ex)
    • the action of enzymes to break down molecules to smaller subunits
    • ex: hydrolysis- breakdown in the presence of water
  14. Nutrients absorbed without enzymatic breakdown
    • water
    • minerals
    • vitamins
  15. Nutrients that must be broken down for absorption
    • carbohydrates
    • fats
    • protein
    • (also nucleic acids are broken down but these aren't nutrients)
  16. Absorption
    • passage of the end products of digestion and the vitamins, minerals, and water go into mucosa (cells lining the GI tract) from lumen (opening of the GI tract)
    • most absorption occurs in small intestine
  17. How are nutrients absorbed and where do they go from the small intestine?
    • nutrients are absorbed either by active transport or passive transport
    • nutrients go from small intestine either into the blood (water soluble nutrients + small fatty acids) or to the lymph (most fats)
  18. Excretion of wastes
    • defecation
    • elimination of the undigestable material in the feces
  19. 3 types of salivary glands
    • parotid
    • sublingual
    • submandibular
    • these all produce saliva which is secreted into ducts to mouth where the saliva acts
  20. Saliva
    • enzyme to digest starch (complex carbohydrates)
    • only substance that enzymatically digests in the mouth
    • made of amylase
  21. Stomach Function
    • gastric secretions important for protein digestion (only nutrient digested in the stomach)
    • contains HCl + enzyme, chime, mucosa
    • stomach has limited absorption of substances (some water, alcohol, and some drugs such as asprin)
  22. Chime
    form of food going from stomach to the small intestine
  23. mucosa
    produces mucous which protects the cells of the GI tract from damage from the HCl in the stomach
  24. Liver Function
    • makes bile (which contains bile salts made from cholesterol)
    • stores some nutrients, metabolizes nutrients, and tries to detoxify our food
  25. Bile
    • substance made by the liver and stored in the gall bladder
    • bile salts important for fat digestion + absorption
    • not an enzyme but breaks fat globules into smaller pieces to help enzymes act
    • bile goes by duct to duodenum and acts in small intestine
  26. duodenum
    first part of the small intestine
  27. Hepatic Portal System
    • hepatic portal vein goes directly from small intestine to the liver
    • all nutrients absorbed by the blood go this way
  28. Gall Bladder Function
    stores and concentrates the bile and releases it to the duodenum
  29. Pancreas Function
    • has an exocrine and endocrine portion
    • makes enzymes for digestion of all (carbs, fat, protein, nucleic acids)
    • pancreatic cells make bicarbonate (pH=8) which is critical bc it empties into duodenum with the enzymes and nutralizes acid coming from the stomach
  30. Exocrine portion of pancrease
    aciman cells
  31. endocrine portion of the pancreas
    makes hormones
  32. Small intestine Function
    • cells of the mucosa (lining) make enzymes for carbohydrate, protein, and nucleic acid digestion
    • --> these enzymes act last to complete digestion
    • the bile and pancreatic secretions act in the lumen (opening) of the small intestine before small intestine enzymes act
    • has most absorption
  33. Small intestine structure
    has villi (fingerlike projections) and cells with microvilli to increase surface area for maximum absorption
  34. lacteal
    lymphatic capillary and regular capillary
  35. Large Intestine function
    • has bacteria that can be helpful to body, but no enzymes
    • absorbes the rest of the water that needs to be absorbed and some vitamins/minerals
    • forms feces
  36. feces
    • water
    • salts
    • mucous
    • cell debri
    • bacteria (normal flora) + bacterial products
    • undigested material
    • bile pigments (from the breakdown of hemaglobin)
  37. Carbohydrates in our food
    • complex carbs such as starch
    • you must break them all down to the simple sugars for absorption
  38. starch
    • a polymer of glucose
    • polysaccharide (many sugars)
  39. Simple sugars that can be absorbed
    • monosaccharides: glucose and fructose
    • absorbed without breakdown
  40. cellulose
    • another polymer of glucose but it has different linkages and we dont have an enzyme to digest it
    • comes from the cell walls of plants
    • we cant digest it for energy but it helps stimulate motility of smooth muscle of GI tract preventing constipation
    • an insoluble fiber
  41. Disaccharides
    • sugar made of 2 monosaccharides
    • sucrose: table sugar, fruit, veg- glucose + fructose
    • lactose: milk sugar- made of glucose+ galactose
  42. Where all all the simple sugars absorbed
    into the blood of the hepatic portal system
  43. Starch breakdown
    • Mouth: salivary amylase that starts to break down starch
    • Stomach: nothing
    • Small Intestine: Pancreatic amylase (results in mixture of substances containing glucose- oligosaccharides [made of 3-8 glucoses linked] and some maltose [a disaccharide of 2 linked glucoses]); next intestinal dextrinase acts on olygosaccharides and maltase acts on maltose breaking it down into 2 separate glucoses
  44. results after digestion of carbohydrates
    glucoses in the simplest sugar form (from oligosaccarides) and 2 seperate glucoses from each maltose
  45. intestinal dextrinase
    acts in the small intestine on oligosaccharides
  46. maltase
    acts in the small intestine on maltose, breaking it down into 2 seperate glucoses
  47. Disaccharide breakdown
    • sucrose and lactase
    • sucrose: sucrase (intestinal) breaks it down into glucose and fructose

    lactose: lactase acts on it in the intestine to break it down into glucose and galactose
  48. Lactose intolerance
    • not a milk allergy
    • people (usually as adult) lose the ability to make the enzyme lactase, or they make less of it
  49. symptoms and treatments of lactose intolerance
    • gastrointestinal symptoms: gas, bloating, cramping
    • lactaid products that have been treated with lactase already have lactose broken down so these are OK; yogurt also has bacteria that help break lactose down
  50. Protein Digestion
    proteins broken down to free amino acids for absorption
  51. exceptions to proteins being broken down in digestion
    • 1. newborn babies can absorb some whole proteins and can absorb antibodies in mother's milk if they breastfeed (passive natural immunity- gives temp. protection against diseases)
    • 2. in food allergies you can absorb full proteins- more common when you are young (at birth digestive system is still somewhat immature)
  52. Enzymes for protein digestion
    • proteases
    • they are first made in an inactive form and are activated in the presence of substrate (this is good for energy conservation and prevents degradation of your own proteins)
  53. exopeptidase
    an enzyme that breaks the peptide bond between amino acids at either end of the peptide chain
  54. endopeptidase
    breaks bond at a specific amino acid within the peptide chain
  55. Where are the amino acids resulting from protein digestion absorbed?
    into the blood hepatic portal system (when they are in small intestine)
  56. Protein digestion: mouth
    no digestion
  57. Protein digestion: stomach
    • 1. gastric secretions followed by HCl (denatures the protein, made by parietal cells of the stomach)
    • result after these secretions: denatured protein- simple protein to break down
    • 2. Pepsin (previously pepsinogen, activated by HCl)- breaks down denatured protein into a mixture of large polypeptides to go to the small intestine
  58. Protein Digestion: small intestine
    • 3 pancreatic enzymes (trypsin, chimotrypsin, carboxypeptidase) act followed by bicarbonate
    • 3 Intestinal enzymes (aminopeptidase, carboxypeptidase, + dipeptidase) then act
  59. Order of pancreatic enzymes acting on proteins in the small intestine
    1. Trypsinogen (inactive)- activated by intestinal endopeptidase to trypsin2. Chymotrypsinogen (inactive) stimulated by trypsin to form chymotrypsin which acts next3. Procarboxypeptidase (inactive)- stimulated by trypsin to form carboxypeptidase which acts last
  60. Result of protein in small intestine after 3 pancreatic enzymes have acted
    mixture of small peptides and polypeptides
  61. Order of intestinal enzymes acting on mixture of small peptides and polypeptides in small intestine
    • 1. Aminopeptidase: lops off amino acid at amino end
    • 2. Carboxypeptidase: lops off amino acid at carboxyl end
    • 3. Dipeptidase: breaks down larger peptides
  62. Final result of proteins after small intestine digestion is complete
    • free amino acids (some possible dipeptides + tripeptides)
    • these are water soluble and ready to be absorbed into the hepatic portal system
  63. Fat Digestion
    • true fats (triglycerides- made of glycerol + 3 fatty acids attached)
    • only enzyme is pancreatic lipase which acts in the small intestine (takes triglycerides and breaks them down to glycerol + fatty acids +monoglycerides)
  64. Process of bile salts + enzymes acting in fat digestion (before absorption)
    • Bile salts act in the small intestine
    • 1. bile salts emulsify the fat (disperse it into smaller droplets- physical step)
    • 2. pancreatic lipase acts
    • end products: glycerol and small faty acids (water soluble- absorbed into HPS) other fatty acids and monoglycerides need to go into lymph first, but are not water soluble right now so can't be taken up by intestinal cells to go to lymph
  65. Continuation of digestion for larger fatty acids and monoglycerides
    • 3. bile salts form micelles making remaining fats soluble so intestinal cells can take them up
    • 4. intestinal cells absorb these but then in intestines, products go back together to form triglycerides and aren't water soluble anymore and they need to be to go to the lymph and blood
    • 5. Chylomicrons form in intestine to go to the lacteals of small intestine to lymphatics to the thoracic duct to the venous blood to the cells, but now they have to get into the tissues
    • 6. In the tissues, capillaries have lipase to breakdown triglycerides to fatty acid and glycerol which will go into the cells
  66. micells
    particles made of fat droplets coated with bile salts (also contain phospholipids [H2O soluble fats])
  67. chylomicrons
    • particles that form in the intestine
    • triglycerides + phosopholipds + cholesterol + protein= lipoprotein droplets
  68. Nucleic Acid digestion
    • not nutrients but we do digest them in the small intestine only
    • First: Pancreatic Enzymes
    • Then: intestinal enzymes
  69. Pancreatic Enzymes in nucleic acid digestion
    • Deoxyribonuclease: breaks down DNA
    • Ribonuclease: breaks down RNA
  70. Intestinal enzymes of nucleic acid digestion
    • nucleosidases + phophatases
    • Process start: Nucleic Acids ----->pentose sugars from NDA and RNA , Nitrogen Bases, phosphate (these are end products that are absorbed by hepatic portal system)
  71. Carbohydrate Absorption
    • glucose and galactose: absorbed by active transport
    • fructose: absorbed by facilitated diffusion
  72. Protein Absorption
    • free amino acids: absorbed by active transport with a carrier based on amino acid structure
    • in a newborn: whole protein (large) absorbed through endocytosis
  73. Fat Absorption
    • fatty acids and monoglycerides: absorbed in small intestine into lymph by diffusion
    • glycerol + small fatty acids: absorbed by diffusion into the blood
  74. Nucleic Acid absorption
    • products of digestion absorbed by active transport
    • water: absorbed by osmosis
    • vitamins: some dissolve in fats (A,E,D,K)- absorbed through diffusion and follow the other fats into the lymph; others are water soluble (all B + C vitamins)absorbed through diffusion or active trasport
    • Vitamin B12: absorption requires intrinsic factor (made in stomach) by endocytosis
  75. Mineral absorption
    • Absorbed by passive or active transport
    • calcium: absorption requires vitamin D
  76. Regulation of Digestion by the nervous and endocrine system
    • more control by nervous system at top of digestive system and more hormone control as you go down
    • stimulus: food in the body or specific nutrients int the food like protein or fat
  77. Regulation of digestion by Nervous and Endocrine systems: Saliva
    • production and release: salivation completely under nervous control
    • parasympathetic nerves: facial and glossopharangeal, brain nuclei in medulla and pons
    • stimulus: smell, taste, presence of food (chemical or mechanical)
  78. What is saliva made up of?
    • amylase
    • water
    • mucin (lubricant)
    • salts
    • and some nitrogen wastes
    • lysozymes- destroy bacteria; antibodies protect against infection
    • saliva is a passive barrier defense (mucin)
  79. Regulation of Digestion by the nervous and endocrine system: Stomach
    • important in protein digestion- HCl (parietal cells) and pepsinogen (chief cells)
    • there is a 3-phase regulation of the gastric secretions and the muscle contractions in the stomach
  80. 3-phase digestion regulation in stomach
    • 1. Cephalic Phase
    • 2. Gastric Phase
    • 3. Intestinal Phase
  81. Cephalic Phase
    • sight smell and taste of food stimulate a nervous reflex to stimulate increase of gastric secretions
    • vagus nerve regulates
  82. Gastric Phase
    • food in the stomach (not in the mouth like cephalic) is stimulus- increases gastric secretions
    • specific stimulus in the food: peptides- in the stomach stimulates gastrin (made in stomach) which increases gastric secretions, especially HCl + pepsinogen (this happens for protein digestion)
  83. Intestinal Phase
    stimulus: partially digested food but the food is now going into the duodenum of the small intestine- this triggers intestinal gastrin (hormon made by small intestine) which stimulates stomach to have increased secretions and increased contraction to churn the food.
  84. Inhibitory effects on the stomach (Nervous and Endocrine systems)
    • both nervous and hormonal: stimulus is chime in the duodenum, but esp if theres a large amount to cause physical distention of the duodenum, or especially if fat is in chime
    • vagus nerve is inhibited- slowing stomach digestion
    • fatty chime stimulates enterogastrons
  85. enterogastrons
    • hormones that have an inhibitory effect on the stomach
    • includes several hormones like choleycistokinin and seretin
    • these hormones decrease the force of contraction of the pylorus region (closest to small intestine) of the stomach and decreases gastric secretions emptying into small intestine. This allows time for digestion (esp of fat- bile and lipase) in the small intestine
  86. Why do fatty foods keep us fuller longer
    food with fat stays in the stomach longer than food without fat because it takes longer to digest
  87. Regulation of Digestion by Nervous and Endocrine Systems: Bile and Pancreatic Secretions
    • 2 hormones in the small intestine that affect both bile and pancreatic secretions
    • --> Choleycystikinin (CCK)
    • --> Secretin
    • both of these are stimulated by acidic fatty chime
    • they are both synergistic- they enhance each other
  88. Cholecystikinin
    • Effect on bile: stimulates gall bladder to contract and release the bile into the cystic duct which goes to the small intestine
    • Effect on pancreas: stimulates pancreas to increase secretions esp rich in enzymes including lipase to break down fat (the more food with fat the more bile you will need and the more lipase to digest it)
  89. Secretin
    • stimulates the liver to make the bile
    • stimulates pancrease to release a lot of bicarbonate to the small intestine to neutralize acids
  90. Vagas nerve relation to bile and pancreatic secretions
    • stimulates gall bladder contraction to secrete bile
    • stimulates release of pancreatic secretions
  91. Regulation of Digestion by Nervous and Endocrine systems: Small Intestine
    • control of smooth muscle contraction, motility of small intestine by the nervous system and hormones
    • stimulus: the distention of small intestine by partially digested food; there will be a nervous reflex (vagus nerve)
    • response to stimulus: increase force of sm. intestine contraction in segmentation (allowing more digestion)
    • if you haven't eaten: low intestinal volume stimulates motilin (hormone made in sm. intestine) which stimulates parastolsys (wave like gentler contraction) of small intestine which moves along bacteria sloughed off cells, etc, until next meal
  92. Defecation
    • the release of feces from the rectum (last part of the large intestine) out the anus (opening)
    • large intestine has normal flora bacteria that make some vitamins that we absorb (Vitamin K and some B vitamins)
  93. Regulation of Digestion by Nervous and Endocrine Systems: Defecation
    • 2 Anal Sphincters: Control release of feces
    • first one: smooth muscle (involuntary) regulated by parasympathetic spinal nerve
    • second sphincter muscle: skeletal (voluntary), you learn to control
    • stimulus: food waste- stimulates muscle contraction of large intestine (cellulose also stimulates smooth muscle preventing constipation)
  94. 2 types of contraction of the large intestine
    • Haustral Contraction
    • Mass Parastolsis
  95. Haustral Contraction
    in colon: causes slow segmentation movement
  96. mass parastolsis
    mass movement, strong movement after eating to move things towards the rectum
  97. Defecation Reflex
    • stimulus: stretch of the rectum by the feces, due to the mass movement of the material from the colon to the rectum- due to spinal parasympathetic nerve
    • you contract the sigmoid colon and the rectum, causing a relaxation and opening of the internal sphincter
    • you have voluntary control to open the external sphincter to release the feces out the anus
  98. what aids the defecation process?
    the contraction of the diaphragm and abdominal wall muscles which helps push the feces out
  99. Emesis
    • vomiting
    • stimulated by stretching or irritants such as bacteria
    • mediated by emetic center in medulla oblongata
    • contraction diaphragm, abdominal muscles, relax cardiac sphincter at top of stomach an emetic stimulus induces vomiting
  100. Heartburn
    • symptom of Gastroesophageal reflex disease
    • burning and pain when acidic gastric juice regurgitates through cardiac sphincter (gastroesophageal sphincter) into esophagus
    • stimulated by pressure from overeating, obesity, pregnancy, running, sphincter problem
  101. hiatal hernia
    structural abnormality, weaken sphincter, top of stomach protrudes above diaphragm
  102. Gastric (peptic) ulcers
    • Damage to stomach tissue
    • inflammation and pain, protective mucosa not intact mostly due to Helicobacter pylori
    • acid contributes but not main cause
    • treat with antibiotics and medication/antacids
    • there can also be duodenal ulcers, although less common
  103. Jaundice
    yellowish skin or whites of eyes due to build up of bile pigments from poor liver or gall bladder functioning
  104. cirrhosis
    • chronic inflammation of liver, primary from alcoholism
    • damaged liver cells infiltrated with fat and fibrous tissue, may need liver transplant
  105. Gallstones (biliary calculi)
    • cholesterol crystallization from high cholesterol or low bile salts
    • bile salts are made from cholesterol
    • treat by dissolving with drugs, ultrasound vibration or remove gallbladder surgically
  106. Diverticula
    • pouches of colon that form
    • may be worsened by low fiber diet
  107. Diverticulosis
    condition where diverticula are present
  108. Diverticulitis
    • diverticula are present and inflamed
    • if infected, treat with antibiotics
    • may either rupture or intestine may become possibly blocked
  109. Inflammatory bowel disease
    • includes crohn's diesease and ulcerative colitis
    • IBD- periodic inflammation of intestinal wall, abdominal immune and inflammatory response to bacteria normally present in the intestine
  110. IBD symptoms
    crams diarrhea, possible intestinal bleeding
  111. symptoms of crohn's
    more serious than IBD, may have ulcers/fissures, especially ileum
  112. Ulcerative colitis
    • shallow inflammation, especially rectum
    • Treat with antibiotics, anti inflammatory/immunosuppressnt medication, special diet, maybe surgery for crohns
Card Set:
Digestive System
2015-02-27 21:09:15
Anatomy Physiology

Test of 2/2/2015
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