Digestive System

• Nutrition - Process by which organisms obtain andutilize their food.
• There are two parts of Nutrition:

  • Ingestion
  • Digestion
• Ingestion- process of taking food intothe digestive system so that it may behydrolyzed or digested.
• Digestion- the breakdown of food(either chemically or mechanically) inorder to utilize nutrients.
• Mechanical digestion involves the physical breakdown of food. Mechanical digestion occurs in the following locations:

  • Mouth
  • Esophagus
  • Stomach
  • SI
• Chemical Digestion breaks down large molecules in food into their component subunits. This process is called hydrolysis.
• Amylase - enzyme digests starch
• Mucin

  • slippery protein (mucus)
  • protects soft lining of digestive system
  • lubricates food for easier swallowing
• Teeth

  • breaking up food
• buffers

  • neutralizes acid to prevent tooth decay
• anti-bacterial chemicals

  • kill bacteria that enter mouth with food
• A bolus (lump) is formed with saliva and the tongue
• Pharynx - it acts as apassage way from theoral cavity to theesophagus to make itsway down to thestomach.
• The pharynx is a cone-shapedpassageway that leads fromthe oral and nasal cavity to theesophagus and larynx. Thethree parts of the pharynx arethe nasopharynx,oropharynx, andthe laryngopharynx.
• Epiglottis• flap of cartilage• closes trachea (windpipe) when swallowing• food travels down esophagus
• Peristalsis involuntary muscle contractions to move food along
• Stomach - stores food and release it to the intestines at a rate whereby the intestines can process it. The stomach mixes the food and grinds it into a finely divided chyme that increases the surface area of the food in preparation for digestion.
• Chyme, a thick semifluid mass of partially digested food and digestive secretions that is formed in the stomach and intestine during digestion.
• Stomach

  • Food storage
  • Where gastric juices are secreted
  • Disinfects food - presence of HCl with the ph of 2.2 cankill bacteria - HCl converts pepsinogen to pepsin
  • Mechanical digestion takes place hereknown as churning
  • Chemical digestion takes place herewhen pepsin breaks down proteins intoamino acids
  • Food is further broken down into a thinliquid called chyme.
• Small Intestine

  • Complete digestion and mostchemical digestion takesplace here.
  • Simple sugars and aminoacids are absorbed into theinner lining.
  • Fatty acids and glycerol go tolymphatic system.
  • Lined with villi, whichincrease surface area forabsorption
• Complete Digestion – polymers ( also known as organic compunds,macromolecules & biomolecules) are broken down to monomers or its simplest form
• Small Intestine

  3 sections:duodenum = mostdigestion takesplacejejunum = absorptionof nutrients & waterileum = absorptionof nutrients & water
• Small Intestine

  • Absorptionthrough villi &microvillifinger-likeprojectionsincreasesurface areafor absorption
• Large Intestine -colon

  Re-absorb water(includingvitamins K and B) fromundigested materialsuse ~9 liters of water everyday in digestive juices> 90% of water reabsorbednot enough waterabsorbed diarrheatoo much waterabsorbed constipation
• Large Intestine -colon

  Living in the large intestine isa community of helpfulbacteria called scherichia coli (E. coli)which produce vitaminsvitamin K; B vitamins and generate gasesby-product ofbacterial metabolismmethane, hydrogensulfide
• Rectum

  • Last section of colon (largeintestines)eliminate fecesKnown as bowel movementor defecationundigested materialsextracellular wastemainly cellulose fromplantsroughage or fibermasses of bacteria
• Anus

  • last part of the digestivetract.
  • the lining of the upper anusis specialized to detectrectal contents. It lets youknow whether the contentsare liquid, gas, or solid.
  • the anus is surrounded bysphincter muscles that areimportant in allowingcontrol of stool.