Digestion 2.txt

• absorption digested food occurs mainly in ileum latter part small intes
• villi
• epithelium
• mucosa
• submucosa
• muscularis externa
• inner circular layer
• outer longitudinal layer
• serosa

simple diffusion, facilitated diffusion, active transport, endocytosis

• protrusions o free surface plasma membrane o villus epithelial cells
• greatly increase s,a, for absorption = rate o absorption

accounts for absorption o lipids (glycerol & fatty acids) and other foods tt can pass through hydrophobic centra o plasma memb o villus epithelial cells

channel proteins assist fructose & other hydrophilic food substances crossing hydrophobic centre o plasma membrane

• mitochondria produce atp needed for active transport
• protein pumps in microvilli plasma memb move glucose, aa and mineral ions incl sodium, calcium, iron

• 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

• 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

• 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

• past thought stomach infections ulcers = excess secretion gastric juice w/ acid
• now suggests presence acid tolerant bacterium important factor
• Helicobactor pylori

• 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

• 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

liver cells

imp functions imp in maintaining homeostasis, steady state in body

• 6
• regulation nutrient lvls in blood
• storage nutrients
• bile secretion
• breakdown erythrocytes
• synthesis plasma proteins
• synthesis cholesterol

• 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

• 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

• 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

• 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

• globins -> amino acids: reused hydrolyzed by kupffer cells
• heme groups -> iron: reused, bile pigments: mod by hepatocyes secreted as part o bile

• synthesizes plasma proteins
• cholesterol
• role in detoxification

• 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)

• 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

• hepatocytes absorb toxins + produce enzymes tt convert toxins to less harmful or harmless substance
• alcohol -> ethanol

• 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

• 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

• 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

• gallbladder
• common bile duct to small intes
• hepatic artery fr heart
• portal vein
• inferior vena cava to heart

refers to all blood flow fr digestive organs that passes through liver before returning to heart

• hepatic portal vein and hepatic artery supply liver with blood
• hepatic vein carries it away

• 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

• hpv divides into vessels called sinusoids
• hepatocytes regulated nutrient contenent o blood

• branches HA join sinusoids
• provide hepatocytes w/ oxygen

• sinusoids drain into branches hepatic vein
• blood in hepatic vein carried to heart via inferiori vena cava

• goes to heart and nutrients can be pumped to all parts o bodyt
• more oxygen can be absorbed when blood pumped to lungs

• 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