Biology notes: 6.1 digestion

Why do we digest anything?Smaller molecules are easier to be absorbed by the villi and enter the bloodstreamDigest via hydrolysis of bonds, prepares molecules for digestion.Other reasons to digest:Normal rate of reaction at body temp is too slow, thus need enzymes.Lipase = breaks down lipidsNeed enzyme to lower activation energy. Enzymes catalyze chemical reactions by increasing efficiency.Enzymes require optimum PH, body temp, very specific with what they break down. Generally need water to do their job.Specific enzymes:Protease breaks down proteinTripsin example of proteasePepsin dittoChymotripsin dittoLipase digests lipids (to glycerol and fatty acids)Amylase breaks down starches into disaccharides or monosaccaridesAmalase is found in salivary gland and pancreas. It works in neutral (bit alkaline) pH. Substrate is starch. Products are simple sugars (maltose)As food is exiting stomach, part of digesting is done but a lot is more to come.Food exiting stomach = chyme Stomach secretes pepsinogen (zymogen or inactive enzyme) and HCl which make pepsin when together. Also secretes mucous to neutralize some of the acid and keep pepsin from eating stomach wall.H. Pilori with lack of mucous productions and inflammation from HCl and pepsin can form an ulcer in stomach.Rugae allows stomach to stretch.Gastric pits and gland cells: chief cell secretes pepsinogen, parietal cells secrete hydrochloric acid that activades pepsinogen and kills off bacteria and viruses. Goblet cells are higher up in gastric pits and secrete mucous so acid and enzymes cannot destroy the stomach.Pepsin could digest the cells that secrete it , but it is inactive while secreted, activated by HCl and HCl and pepsin secreted by different cells.Pancreatic lipase made in pancreas exocrine cells, breaks down lipids into fatty acids and glycerol. Works best in neutral pH. Small intestine comes after stomach and digests everything after stomach is done, also absorbs nutrients.Duodenum is forst ten in. of SI, most chemical digestion, walls make enzymeJejeunum- next 8 ft of SI still chemical digestion but also absorbtion of nutrientsIleum last 12 feet still absorbing nutrients and beginning to absorb waterVillus is for absorbtion of soluble food, increased area for mixing of secretions and food.Hepatic portal system takes all digestion blood back to liverBio notes 10-14Lacteal- absorbs fat and fatty acidsA small blood vessel is smaller than a named blood vessel/artery, capillaries are much smaller.Microvili are vili on vili!Lipids are absorbed my simple, diffusion por que are polar so pass through cell membranes easily.Hydrophilic food substances such as fructose are absorbed by villus via facilitated diffusion.Channel proteins help hydrophilic food stuffs to get through cell membranes porque the phospholipid heads are hydrophobic. A TON of mtiochondria in vili epithelial cells because some cells need ATP for active transport: those that need it are: Glucose, amino acids, minerals. Pathway through protein called sympatic pathway.The sympatic pathway pump protons into the cell membrane with ATP and when enough flow back through the channel is opened up enough for Glucose, amino acids, etc.Things that are absorbable by water may be in pinocytotic vesticles. Pino=drink. The large intestines main job is to re-absorb water from the waste generated by ileum. It moves the undigested (cellulose, bile pigments, bacteria [e. Coli], mucus, cell fragments from small intestines).Egested= excretedE. coli makes Vitamin K (essential component for blood clotting).If E. coli exits intestines and enters the rest of the body cavity, it will be a deadly infection.LIVERHas many jobs. Stores excess glucose as glycogen.Glycogen is one of the few carbs body makes. Long chain of glucose. Used in between meals to keep blood sugar up.Liver releases glucose in the form of carb called glycogen may be accessed and added to blood later as needed.Liver breaks down old red Blood Cells. Breaks down into hemoglobin and iron. Stores iron, tears apart hemoglobin. Uses parts to make bile, stores iron. Stores fat-soluble vitamins (A, D, E, K). A, D, E, K can become toxic if too much is ingested. Vitamin C and other water-soluble vitamins can never be toxic. Also stores B-12 and folic acid. Liver is about the size of a football.Liver helps us overcome problem of lipid digestion in small intestine. How? It makes bile which takes hydrophobic lipids and surrounds them (emulsifies them) and adds a charge to lipid molecule that repels other lipids. Increases surface area of lipids by making droplets really small and better allows lipase to break it down better. Liver breaks down old red blood (erythrocytes) cells. Red blood cells live about 120 days, send out signals they are old, and Kupffer cells eat them. It splits hemoglobin into heme (iron) and globin (protein). The bile pigment is taken from heme and is expressed as biliruben which is yellow: causes jaundice. Iron is take off and is used to build new red blood cells. Globin gets digested to make new proteins. Bilirubin becomes main component in bile.From breaking down red blood cells you get:Urea BilirubenGlobinIronHemeBile is produced in liver, made in response to hormone secretin. Released into ducts (canaliculi) in liver and goes to hepatic (bile) ducts), then it gets backed up and stored in gall bladder. Travels down common bile duct and enters the duodenum where it joins duct from pancreas. Bile is released because of cholecystokinin (ccK) triggered from hi-fat food. SLIVASalt,BicarbonatesCalcium saltsPhosphate saltsThiocyanideAmylaseMucousHCL inhibitorsGland can be exocrine/endocrine Exocrine secretes stuff and has ducts, endocrine secretes stuff into blood, only make hormones. Secretory cells are one cell thick, cells contain secretory vesicles, arranged in rings called acini. Surrounded by basement membrane.All guts blood that has processed food molecules converges into a series of veins called the hepatic portal system. It brings all blood from gut back to liver. Hepatic artery brings in oxygenated blood to system for system health. Blood in liver converges into sinusoids of liver. Hepatic vein out of liverHepatic portal vein = in liver, hepatic vein = out of liver.The flow of blood to, through, and from the liver: hepatic portal systemA combination of all the veins that drain from intestines and stomach: hepatic portal vein.Sinusoids are sponge-like passages in the liver. They are the capillaries of the liver. (dont have to draw)The sinusoids merge to form the hepatic vein (DIFFERENT FROM HEPATIC PORTAL VEIN!!!)Vena cava is what the hepatic vein merges into once it leaves the liver.Final note on protease digestive enzyme: 2 basic kinds. Two basic ways to approach: endopeptidase or exopeptidease, slightly different ways to approach the protein to break it down. Endopeptideases chop proteins into large pieces, the exopeptidases attack the protein one amino acid at a time.Some of the exopepsidases are anchored in the wall of the duodenum.There are some hormones involved in digestions.Steroid vs. peptide hormone structure: steroid: estradiol, estriol, estrone. Protein-based: ADH, TRH, TSH, insulin, GH, FSH, LH, prolactin, HCG. Peptides are proteins, steroids are like lipids.