Chapter 6: Digestion, Absorption, Metabolism The Organs and Functions of Digestion-Digestion occurs in the digestive or gastrointestinal (GI) tract-Consists of:oSeries of organsoComplex outer layers of musclesoInner mucosal layer of glands and absorptive cells-Starts with mouth and ends with anus Components of GI TractIdentify the components of the gastrointestinal tract-The digestive tractoMouthoEsophagusoStomachoSmall intestineoLarge intestineoRectum-Other organs assistoSalivary glandsoLiveroPancreasoGallbladder The Organs and Functions of DigestionDefine digestion and absorption-Main functions of GI tract:oDigestion-Move food through GI-Before getting it into the body, breakdown of food to smaller compounds/units-Primary (MAIN not first) site for digestion is the small intestineoAbsorption-Cross lining of the intestine to enter the body-(Crosses the intestinal wall and gets into the body)-The period of time it takes food to travel the length of the digestive tract is called transit time (when we digest food, we move it through the GI tract, progressively moves from the mouth all the way down, move appropriately = appropriatedigestion and absorption)oToo slow, result in constipationoToo fast, diarrhea The Organs and Functions of Digestion-Food moved through GI tract via muscular constrictive movementoKnown as peristalsis (constriction, relaxation, constriction, relaxation = relaxations that moves the food through, starts from first part of GI called esophagus)-Digestion is a combination of mechanical and chemical processes (breaking down products into smaller units to be absorbed)Discuss the differences between mechanical and chemical digestion and list an example of each in the mouth, stomach and small intestine-Two forms of digestion:-MechanicaloChewing, mixing and peristalsis-ChemicaloMixing the food with various gestational (GASTROINTESTINAL?) secretions and enzymes (help reactions occur quicker) of the GI tractoDigestive enzymes are meant to breakdown… Helps break the larger (macronutrients) compounds into smaller forms that can be absorbed-Undigested or unabsorbed substances moved through GI tract and, ultimately, to elimination by defecation The Organs and Functions of Digestion***learning objective KNOW STRUCTURE OF GI TRACT, INCLUDES the sphinctersName the location of the 3 sphincters discussed in this lecture and the purpose of each-Components of GI tract separated by circular muscles called:oSphincters***** (help compartmentalize portions of the GI tract, these muscles will constrict/relax/constrict/relax)o3 in particular-Lower esophageal sphincter****-Pyloric sphincter-Ileocecal valveoPurpose of sphincters-"one-way doors"-Prevents food from flowing backwardoExamples of when sphincter does not work properly-Heartburn (burning sensation in chest - when lower esophageal sphincter doesn't close completely)-Vomiting Digestion Must Occur Before AbsorptionoOnce food is broken into its smallest units, it is ready to be absorbed into the body, into the blood, and finally into the cells, where it can be used for energy or storedoOnce it's absorbed, used for energy = Macronutrients (energy yielding):oCarbohydratesoProteinoFatoSome food components do not need to be digested to be absorbed:oWater (macronutrient but not energy-yielding)oVitaminsoMineralsoSmall molecules such as glucose Sum of the Parts: The Process of DigestionThe Sum of the Parts: The NoseoTaste is 80% smell (the nose ties into taste)List the 5 taste sensationsoFive primary tastesoSaltyoSweetoSouroBitteroUmami - savoryoThere is a strong connection between our brain, digestive system, and sense of smelloThe sight, smell, and thought of food can trigger the release of digestive secretions and enzymes The Sum of the Parts: Mouth and EsophagusDescribe the process of digestion starting in the mouth and ending at the large intestineoDigestive process begins in the mouthoMechanical digestion-ChewingIdentify the digestive enzymes discussed in this lecture with the location it is secreted in the GI tract and the macronutrient it is responsible for digestingoChemical digestionoSaliva is added to help lubricate food (hard to swallow if not moistened appropriately)o(In saliva are digestive enzymes) Enzymes are released-Salivary amylase (starts the digestion of the macronutrient carbohydrates)oDevelop nice, moist Bolus formed (the tongue help move food around and initiate swallowing)-The tongue helps with the mixing of foodoHelps initiate swallowing*****LEARNING OBJECTIVE - identify various digestive enzymes that is discussed in class and to know what they're responsible of digesting (breaking apart) The Sum of the Parts: Stomach-We swallow and the food starts traveling down the esophagus-What moves the food down to the esophagus is peristalsis-Peristalsis moves food down to the esophagus-Esophagus is connected to the stomach-The stomach is a J-shaped sac that mixes food with gastric secretions and assists with digestion-The esophagus is separated from the stomach by theoLower esophageal sphincter (opens up and closes again)oOnce food enters the stomach, the cells of the stomach start producing gastric juicesoHydrochloric acid (HCL)oMucusoPepsinogenoThe hormone, gastrin oLower esophageal sphincter (at the lower portion esophagus opening to stomach)oBottom portion of stomach (first part of the small intestine called the duodenum, that is known as pyloric sphincter) - shuts to trap food in stomachoLower esophageal sphincter shutsoPyloric sphincter shuts to trap food in the stomach-The stomach can act as a reservoir-Keeps food in long enough to get a mix with gastric juices-Three layers of muscle that face different directions, all this churny motion that occurs in the stomach that is part of mechanical digestion The Sum of the Parts: Stomach (REVIEW)List the functions of gastric secretions in the stomach for digestion oFIND TABLE IN TEXTBOOK o***LEARNING OBJECTIVES*** Go back to know the functions of the gastric juicesoMUCUSoPurpose: it protects the lining of the stomach from the HCloSo once we start eating, we start secreting more HCloTo keep the lining from being irritated by HCl we secrete mucus-Do not have that ability in the esophagus-Reaches esophagus = causes heartburnoHCloFunctions: denatures proteins (denaturing changes shape and can unfold a protein), also activates the enzymes, PEPSIN and lingual lipaseoAlso assists with neutralizing bacteria - part of immune responseoINTRINSIC FACTORoCorrelate to vitamin