Digestion 2.txt

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Digestion 2.txt
2012-06-10 17:18:34

digestion 2
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  1. draw and label diagram showing transverse section ileum
    • absorption digested food occurs mainly in ileum latter part small intes
    • villi
    • epithelium
    • mucosa
    • submucosa
    • muscularis externa
    • inner circular layer
    • outer longitudinal layer
    • serosa
  2. Explain mechanisms used by ileum to absorb and transport food (3)
    simple diffusion, facilitated diffusion, active transport, endocytosis
  3. microvilli
    • protrusions o free surface plasma membrane o villus epithelial cells
    • greatly increase s,a, for absorption = rate o absorption
  4. simple diffusion
    accounts for absorption o lipids (glycerol & fatty acids) and other foods tt can pass through hydrophobic centra o plasma memb o villus epithelial cells
  5. facilitated diffusion
    channel proteins assist fructose & other hydrophilic food substances crossing hydrophobic centre o plasma membrane
  6. active transport
    • mitochondria produce atp needed for active transport
    • protein pumps in microvilli plasma memb move glucose, aa and mineral ions incl sodium, calcium, iron
  7. endocytosis
    • pinocytotic vesicles formed fr microvilli plasma memb
    • contains droplets fluid fr lumen o ileum
    • vesicle membranes move digested foods into cytoplasm (assimilation) via facilitated diffusion o active transport
  8. Explain how structure villus related to role in absorption and transport o products o digestion
    • great number increase sa for absorption in small intestine
    • also, own projections = microvilli
    • increase s.a. moremicrovill have protein channels and pumps in membr to allow rapid absorption food by facilitated diffusion and active transp
    • villi contains epithelial layer one cell thick = easy passage food absorbed quickly
    • blood capill in villus closely associated w. epithelium so distance for diffusion food molec small
    • thin layer cells contain mitochondria = atp needed for active transport certain food molec
    • lacteal branch centre villus carries fats away after absorption
    • goblet cells secrete mucus
  9. Explain why pepsin and trypsin initially synthesized as inactive precursors and how activated
    • pepsin and trypsin known as proteases
    • enzymes tt catalyze hydrolysis o peptide bonds in proteins
    • proteases can't distin b.twn protein ingested and structural protein o human body
    • to control hydrolysis essential proteins, proteases initially released in inactive molec form
    • pepsin = pepsinogen, trypsin = trypsinogen
    • inactive molec form o pepsin has 44 aa attached to prim structure o enzyme, when released and exposed to HCL and pH of stomach removes extra am ac -> pepsin
    • lining mucus protects stomach fr being digested
    • trypsinogen released fr pancreas v/ pancreatic duct, enters small intes at duodenum
    • partially digested food stimulates release o enzyme enterokinase converts trypsinogen into active form trypsin
  10. discuss role helicobacter pylori in developm stomach ulcers and stomach cancers
    • past thought stomach infections ulcers = excess secretion gastric juice w/ acid
    • now suggests presence acid tolerant bacterium important factor
    • Helicobactor pylori
  11. stomach ulcers
    • stomach ulcer area damage stomach wall
    • infection h. pylori strongly associ w/ presence stomach ulcers
    • trials shown cause gastritis leads stomach ulcers
    • half baterial strains isolated fr patients w/ stomach disease produce inflammation causing toxis; infected patients most severe ulceration
    • proteases other enzymes released by bacteria damage stomach lining = ulcers
    • antimicrobial treatments eliminate h. pylori cure stom ulcers long term
    • antacids only temp relief
  12. stomach cancers
    • stomach cancers cause tumour growth in stomach wall
    • far more patients who have stomach cancer also have h,pylori infections compared to general pop
    • bacterial infec associated reduction vit c concentration in gastric juice, = increase chance tumor formation
    • further research needed to est causal link b.twn h. pylori infection + stomach cancer incidence
  13. What are hepatocytes?
    liver cells
  14. What do hepatocytes do in liver?
    imp functions imp in maintaining homeostasis, steady state in body
  15. how many things liver responsible for?
    • 6
    • regulation nutrient lvls in blood
    • storage nutrients
    • bile secretion
    • breakdown erythrocytes
    • synthesis plasma proteins
    • synthesis cholesterol
  16. regulation nutrient lvls in blood
    • certain nurtrients = excess in blood after absorption
    • high lvls some nutrients would damage other organs o body esp brain if too high
    • liver helps control blood nutrient lvls, including glucose, maintaining homeostatis
    • liver hepatocytes can absorb + store nutrients
    • nutrients released when lvls low
  17. storage nutrients
    • when certain nutrients in excess stored in liver released as needed
    • when gluc lvls high, insulin stimulates hepatocytes absorb glucose fr blood + convert to glycogen for storage when gluc lvls low, hormone glucagon stimulates hepatocytes to break down stored glycogen + release glucose into blood
    • iron, copper, vitamin a (retinol) vitamin d (calciferol) stored in liver
  18. bile secretion
    • bile needed for emulsification o lipids in small intes
    • liver contains many small chnnls called analiculi which hepatocytes secrete bile
    • bile moves fr canoliculi into gall bladder for storage
    • bile contains
    • hydrogen carbonate ions to neutralize low pH fr stomach contents, protects small intestine
    • bile salts for lipid emulsification
    • bile pigments, waste fr hemoglobin breakdown
    • bilirubin (yellow ish color)
    • cholesterol made by hepatocytes to produce bile + used elsewhere in body
    • bile concntrated by water reabsorption fr gall bladder + even discharged into small intes through bile duct
  19. breakdown o erythrocytes
    • erythrocytes, red blood cells live abt 120 days
    • rbc plasma memb become fragile + rupture
    • hemoglobin released into blood plasma; absorbed by phagocytosis, mainly kupffer cells in sinusoids o liver
    • kupffer cells break hemoglobin into heme groups (containing ions) + globins (proteins)
    • iron released fr heme groups into blood, much goes to bone marrow produce new hemoglobin + rbc
    • remainder heme bile pigment (bilirubin) yellow coloured substance absorbed by hepatocytes form bile; eliminated in feces
    • globins hydrolyzed into amin acids for use elsewhere
  20. What does hemoglobin get broken into?
    • globins -> amino acids: reused hydrolyzed by kupffer cells
    • heme groups -> iron: reused, bile pigments: mod by hepatocyes secreted as part o bile
  21. What does the liver do? (3)
    • synthesizes plasma proteins
    • cholesterol
    • role in detoxification
  22. synthesis plasma proteins
    • rough er o hepatocytes produce 90% proteins in blood plasma
    • main plasma proteins albumin, globulin, fibrinogen
    • hepatocytes synthesize all albumin + fibrinogen + much o globulin (some made by lymphocytes)
  23. synthesis o cholesterol
    • some cholesterol obtained fr nutrient absorption but most made by hepatocytes
    • some used in bile production in liver; rest transported by blood for use elsewhere
    • stabilize bent phospholipid in plasma memb
  24. how does the liver help detoxify the body?
    • hepatocytes absorb toxins + produce enzymes tt convert toxins to less harmful or harmless substance
    • alcohol -> ethanol
  25. explain detoxification by liver w. alcohol and liver damage
    • alcohol converted to less harmful products (acetaldehydes) to acetic acid to acetyl-(oA) by hepatic enzymes
    • excessive alcohol consumption damages liver cells more than other parts o body
    • fatty deposits accumulate, cause hepatitis (inflammation o liver) associated w. nauseau + jaundice
    • chronic excessive drinking, more than 10 yrs can cause cirrhosis where normal tissue replaced w/ scar tissue
    • liver cells die = not replaced, liver functions deteriorates
    • liver failure = death
  26. outline protein digestion
    • large polypeptides must be hydrolyzed into single amino acids for absorption to occur in small intes
    • cewing assists physical breakdown food increase s.a. for chemical digestion
    • begins in stomach w/ pepsin, pepsinogen, secreted by glands in stomach wall; hydrochloric acid activates pepsinogen -> pepsin
    • continues in intes w. trypsin, trypsinogen secreted by pancreatic glands; enzyme enterokinase fr small intestine activates trypsinogen -> trypsin
    • both pepsin and trypsin = endopeptidases, enzymes that being protein digestion by hydrolyzing peptid linkages in polypeptide chains resulting in smaller chains
    • protein digestion completed by exopeptidases, which removes single amino acids fr two ends o smaller chain polypeptides
    • include carboxypeptidase (removes carboxyle end) and aminopeptidase (Removes fr amino end) use o two speed up process
  27. carbohydrate digestion
    • chewing w/ salivary glands produces salivary amylase breaks down polysaccharides (starch, glycogen) into smaller polysaccharides like maltose
    • chewing increases s.a. for chemical digestion
    • further chemical digestion occurs in small intes where pancreatic amylase secreted by pancrease hydrolyze starch, glycogen, smaller polysacc into disaccharides
    • continues in epithelium o small intes where enzyme disaccharidases breaks disaccharides into monosaccharides
    • enzyme maltose hydrolyzes maltose, sucrase for sucrose, lactase for lactose
    • monosaccharides can be absorbed by small int epithelium
  28. draw and roughly label liver
    • gallbladder
    • common bile duct to small intes
    • hepatic artery fr heart
    • portal vein
    • inferior vena cava to heart
  29. hepatic portal system
    refers to all blood flow fr digestive organs that passes through liver before returning to heart
  30. what does hepatic portal vein do? hepatic artery? hepatic vein?
    • hepatic portal vein and hepatic artery supply liver with blood
    • hepatic vein carries it away
  31. draw and kind of explain sinusoid w/ arteries and liver cells
  32. outline circulation blood through liver tisue, including hepatic artery, hepatic portal vein, sinusoids and hepatic vein
    • hpv: deoxygenated blood
    • carries blood and nutrients from capillaries and veins surrounding intestinal villi
    • low o2, high co2
    • hepatic artery: oxygenated blood, carries blood from heart via aorta
  33. in liver
    • hpv divides into vessels called sinusoids
    • hepatocytes regulated nutrient contenent o blood

    • branches HA join sinusoids
    • provide hepatocytes w/ oxygen
  34. after liver
    • sinusoids drain into branches hepatic vein
    • blood in hepatic vein carried to heart via inferiori vena cava
  35. What happens after blood has nutrients?
    • goes to heart and nutrients can be pumped to all parts o bodyt
    • more oxygen can be absorbed when blood pumped to lungs
  36. compare sinusoids and capillaries ***
    • sinusoids: vessels divided from hepatic portal vein
    • wider than normal capillaries
    • more porous
    • single layer very thin cells
    • no basement membrane
    • blood in close contact with hepatocytes
    • lumen is wider, greater exchange of materials
    • capillaries: single layer very thin cells
    • enormous area for the exchange of nutrients, gases, metabolites and water, between the blood and interstitial fluid.
    • exchange occurs for substances