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***Don’t forget that we covered enzymes, so you will likely have to know more detail than is given in this chart.*** ***Study Tip: Draw a long tube on a piece of paper (the bigger, the better) and label the different parts of the digestive tract (mouth, esophagus, stomach, etc.). Then label all the secretions and changes to the food (bolus to chyme to feces/waste) and where digestion and absorption happens for carbohydrates, protein and fat.*** Organ/Body Part Structure Function Secretions MOUTH -contains teeth, tongue, -Mechanical Digestion occurs via the Teeth -Saliva (contains amylase to hard and soft palates and mechanically breaking food down. Incisors at break down starches and Eg. “Park gates” salivary glands the front of the mouth are specialized for provides lubrication for the –separate groups of people -the point of ingestion cutting; Canines are specialized for tearing; food). into individuals (break apart -beginning of physical (and molars specialized for grinding. food). some chemical) digestion -often send you straight to the -Tongue is 1) involved in tasting of food; it showers to rinse before contains taste buds and when food is in solution, getting in the water (saliva it is able to activate taste bud receptors and 2) moistens food). pushes food between the teeth while chewing and to the back of the mouth to initiate swallowing. -Hard Palate is involved in the crushing of food -Soft Palate (uvula) can cause regurgitation -Chemical Digestion begins in the mouth via saliva produced by the Salivary Glands. Saliva has multiple functions, which include 1) to moisten/lubricate food so its easier to swallow, 2) putting food into solution so that we can taste with our taste buds, and 3) contains amylase which breaks down starches into simpler carbohydrates. Overall Function: Mouth The mouth is primarily involved in breaking food into smaller pieces and lubricating it so it travels easily down the esophagus. Saliva secreted by the salivary glands into the mouth begins digestion of carbohydrates. No absorption occurs in the mouth. ESOPHAGUS -approximately 25 cm -smooth, circular, muscular tube -mucus membrane begins at the back of the mouth in an area called -mucus secreting cells line the the pharynx esophagus to moisten the food Eg. “The bullet” (water slide) -the pharynx also houses the opening to the bolus and prevent food from -a straight shoot down, very trachea (windpipe) getting caught. quick ride -once the food is mixed with saliva and starts -slide is kept wet so no one traveling down the esophagus, it is referred to gets stuck. as a bolus. -if you were to get stuck, -during swallowing, the esophagus undergoes someone would likely come peristalsis, which is a series of wave-like, save you, push you down rhythmic, involuntary contractions that pushes (muscles) the food bolus down to the stomach…like squeezing a tube of toothpaste from the bottom to the top to push the toothpaste out through the opening. -involuntary peristalsis means that food will always move down the esophagus towards the stomach, regardless of body position. -a flap called the epiglottis covers the opening to the trachea (windpipe) during swallowing to prevent food from going “down the wrong tube” and ending up in the lungs. Overall Function: Esophagus The only purpose of the esophagus is to transport food (a bolus) from the mouth to the stomach. This is accomplished via peristalsis (think: tube of toothpaste) and mucus lubrication. No digestion or absorption occurs here. STOMACH -J-shaped or saddle-bag shaped. -can store up to 1.5 litres of food. -VERY acidic – pH ranges from 2 – 3. -strong muscular layer surrounds mucosal epithelium (lining) Eg. “The Wave Pool” -this is where everyone floats around and gets mixed up by the huge waves (similar to the food bolus’ that are mixed with acid and pepsin by the waves/ churning of the stomach). -The cardiac sphincter allows for the passage of the food bolus into the stomach (you wouldn’t want food stuck in your esophagus), but prevents backflow of stomach juices (chyme) back into the esophagus. This can occur, however, and is known as acid reflux or heartburn. -Mechanical digestion occurs via the contraction of the muscular stomach walls, churning and mixing the stomach contents. -mucus (protects stomach lining from acid) -HCl (acid kills bacteria/viruses) -Pepsinogen (converted into its active form, pepsin, by HCl, which then breaks apart protein) -there are 2 sphincters (muscles) in the stomach; one at the opening from the esophagus (cardiac), and one where the stomach meets the small intestine (pyloric). -Chemical digestion occurs via the secretion of gastric juices by cells lining the stomach. -Gastric juices include mucus, HCl, and pepsinogen (as well as other substances). -Mucus is involved in the protection of the stomach lining (from HCl and pepsin). -HCl is a very strong acid that kills bacteria and viruses (pathogens) and also converts pepsinogen into pepsin. -Pepsinogen (inactive form) is secreted into the stomach, and in the presence of HCl, is converted to pepsin (active form of enzyme). -Pepsin is an enzyme that breaks peptides (proteins). -food stays in the stomach for quite a while (4 hours), which is the reason we feel full/satisfied for hours after we eat. -Once food is mixed with gastric juices (the food mixed with the juices is now called chyme), it leaves the stomach in small squirts into the small intestine. -The pyloric sphincter prevents too much chyme from entering the small intestine, instead allowing for small amounts of chyme to be squirted into the small intestine little by little. Associated Disorder/Disease: -Ulcers can happen when the stomach doesn’t properly produce mucus; stomach lining is exposed to acid, causing damage. -Ulcers can also occur due to bacterial infections Overall Function: Stomach The stomach is a very acidic environment due to HCl acid secretions. A mucus coating (secretions) protects the lining from the acid. The stomach secretes pepsinogen, which is converted to its active form, pepsin in order to break down proteins. The muscular wall of the stomach contracts to mix the contents. 2 sphincters control what enters and leaves the stomach. Digestion of protein begins here. No absorption occurs in the stomach. SMALL INTESTINE -long tube-like structure, -When chyme enters the small intestine, it is -mucus to protect the lining. approximately 7m in length, very acidic and contains protein-digesting pepsin -prosecretin (converted to Eg. “Lazy River” 2.5cm in diameter. -arrival of chyme in the S.I.(duodenum) triggers secretin in the presence of -People float slowly and gently -Inside, the small intestine the conversion of prosecretin (inactive) into chyme) through the park, perhaps has folds on top of folds to secretin (active). Secretin then signals the getting hit by rambunctious increase the surface area pancreas to secrete bicarbonate, which kids occasionally. This is and allow for maximal buffers/neutralizes the acid. similar to the chyme moving absorption (villi and slowly through the small microvilli). -Chemical Digestion occurs within the intestine, occasionally being -The length of the small duodenum via secretions from the pancreas joined by secretions from intestine is broken into 3 (digestive enzymes – discussed below) and liver ducts (pancreatic, bile). areas: 1)the duodenum, 2) (bile – discussed below). the jejunum and 3)the OR ileum. -Absorption occurs in the small intestine. “River full of fish” -The small intestine has Nutrients from the food/bolus/chyme that has -If a river full of fish is slowly both a muscular wall and been digested are absorbed through the rapidly past you, it is quite mucus secreting cells membrane lining the small intestine and are difficult to catch very many (especially at the passed along into the capillaries (circulatory fish. 1) Slower river increases duodenum). system – carbohydrates and amino number of fish you are able to acids/proteins) or the lacteal system (fats). catch (Small amounts of slowly moving chyme allow for more time for absorption). 2) The number of fish you can catch is limited by the number of people that can stand along the river bank to catch them. If the river bank curves in and out, more (surface) area allows for more people to catch the fish. (Villi increase surface area and therefore increase absorption). 3) There is some sort of mutation in your family that results in more than 2 hands for each person. More hands catch more fish. (Microvilli on top of the villi further increase surface area for maximal absorption). Overall Function: Small Intestine The small intestine is very long and therefore can be broken into areas based on function. The beginning of the small intestine (duodenum) is where more digestion occurs via secretions from the pancreas and liver (pancreatic and bile ducts, respectively). These secretions are also of particular importance in neutralizing/buffering the acidic chyme entering from the stomach. Digestion of proteins and fats occurs early in the small intestine/duodenum (thanks to secretions from accessory organs). Absorption of nutrients (completely digested food) occurs in the small intestine as well, but later on. PANCREAS -thin, “feathery”, looks like a - Exocrine compartment is involved in -trypsinogen (inactive) is tongue. production and secretion of digestive enzymes converted to trypsin (active – Unfortunately, there is no -very soft/squishy tissue required for digestion and bicarbonate required breaks large water –park reference for the that is lobuled (bumpy). for the neutralization/buffering of chyme. proteins/polypeptides into accessory organs. Feel free to -“2 for the price of 1”; the -Digestive enzymes include: smaller ones/peptides) in the make your own, or use other pancreas is comprised of 2 -Trypsinogen (inactive) is secreted by the small intestine by an enzyme analogies as a study tool. compartments – exocrine pancreas and is converted to trypsin (active) called enterokinase. and endocrine. The by enterokinase (another enzyme) once it -erepsins (break down small exocrine compartment is enters the small intestine. Trypsin breaks proteins/peptides into individual made up of cells that down large proteins into smaller ones. amino acids) are also released secrete digestive enzymes -Erepsin are also released by the pancreas to by the pancreas. into ducts (“tubes”) that further break down proteins -pancreatic amylase further merge into a common -Amylase continues to break down breaks down carbohydrates. pancreatic duct. This duct carbohydrates (digestion of which began in -Lipases break down lipids to empties into the small the mouth). continue fat digestion. intestine. -Lipases break down lipids. Overall Function: Pancreas The pancreas is dual-purpose organ. There is an endocrine and an exocrine compartment; it is the exocrine compartment that contains the digestive enzymes. The pancreas secretes many enzymes that continue digestion of protein, lipids and carbohydrates in the small intestine. These enzymes travel through the pancreatic duct to the small intestine. Although no digestion or absorption occurs in the pancreas, enzymes secreted from the pancreas are essential for digestion in the small intesitine. Liver and Gall Bladder Liver -Produces and secretes bile, which is comprised -Bile is produced by the liver -a very large and heavily of bile salts, which are important in the and stored in the gall bladder. vascularized (has a lot of digestion of fats -Bile emulsifies fat in the small blood vessels supporting it) -bile is secreted by the liver and stored in the intestine once released. organ. gall bladder. -sits above the stomach -when there is fat in the small intestine, the liver Gall Bladder secretes CCK (cholecystokinin) into the blood, -a round sac tucked which travels to the gall bladder, instructing it to underneath the liver. release bile salts. -Bile is released from the gall bladder into the bile duct, which carries it to the small intestine. -Once it reaches the small intestine, bile emulsifies fats (breaks them apart) -the liver is also important in detoxification, which is why liver damage is associated with alcoholics. Overall Function: Liver and Gall Bladder The liver’s primary function is to produce and secrete bile, which is stored in the gall bladder. When fat is present in the small intestine, a message is sent to the liver resulting in the release of CCK. CCK travels through the blood stream to signal the gall bladder to release bile into the bile duct, which leads to the small intestine. Bile then acts on the fat and emulsifies it. No digestion or absorption occurs in the liver or gall bladder, but the bile produced and secreted by these organs is important for fat digestion in the small intestine. Large Intestine -1.5m long, 7.6 cm diameter -Digestion is already complete as (waste) -Made up of the ascending material enters the large intestine. (going up), transverse -Material moves slowly through the large (across) and descending intestine, allowing for the absorption of water (going down) colon. before the waste is excreted. -The large intestine lines the -Components such as cellulose in the diet cannot perimeter of the small be digested and slow the material moving intestine. through the large intestine, allowing for increased water absorption and a thorough cleaning of the intestine. Rectum and Anus Eg. “The Log Ride” -6-8 inches long. - a muscular organ that contracts VOLUNTARILY. -When waste is present/building up in the large intestine, the nervous system signals a bowel movement. -waste is received from the large intestine and stored in the rectum until a voluntary muscle contraction expels the waste through the anus.