Digestion

• Digestion


  Breakdown/simplification of food into smaller or usable form
• Digestion


  1. Ingestion

  2. Peristalsis

  3. Digestion

  4. Absorption

  5. Defecation
• Types of digestion


  • Mechanical
  • Chemical
• Mechanical digestion


  • Food is broken down into smaller pieces by mastication and peristalsis
• Chemical digestion


  • Food is acted upon by catalytic enzymes to be broken down into their smaller molecular and absorbable forms
• Main organs of the digestive system

  • Mouth/Oral cavity/Buccal Cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
  • Rectum
  • Anus
• Accessory organs of the digestive system

  • Teeth
  • Tongue
  • Salivary Glands
  • Liver
  • Gall Bladder
  • Pancreas
• Oral/Buccal Cavity or Mouth


  • Where taste (tongue) occurs
  • Contains 3 pairs of salivary glands (parotid, sublingual, submandibular)
  • Saliva is 99.5% H2O, lubricates food and begins digestion by breaking down carbohydrates using the protein ptyalin or salivary amylase
• Teeth


  • Mechanical digestion
  • 32 teeth with varied shapes for different functions (incisors, canines, premolars, molars)
  • Lips prevent and seal off food in the mouth while masticating
• Pharynx/Throat


  • Common passageway for food and air
  • Where swallowing begins
• Esophagus


  • 25 cm or 10 inches long
  • Secretes mucus
  • Transport food through peristalsis (muscle contractions that propel food thru sphincters)
• Esophagus


  1. Upper esophageal sphincter

  2. Lower esophageal sphincter

  3. Sphincters involve a pair of muscles; one works to close, the other dilates or open
• Stomach


  • Rugae – folds; these expand to increase stomach's capacity
  • Storage
  • Mixes and stores ingested food with HCL into chime
  • Chemical and mechanical breakdown of food
• Stomach


  1. Peristalsis

  2. HCL and digestive juices
• Small Intestine


  • Final breakdown of food
  • Most enzymes are present here
  • Turns macromolecules into their simple forms then absorbs it
  • Villi – aids with absorption finger-like projection
  • Has capillaries which transports nutrients into the blood stream
  • 6 meters long
  • Duodenum – 25 cm/10 inches
  • Jejunum – 8 ft.
  • Ileum – 12 ft. (longest)
• Small Intestine


  1. Digestion (mechanical and chemical)

  2. Absorption
• Large Intestine


  • Concentrates and stores undigested matter by absorbing Na, Vit. k and H20
  • No villi nor coils
  • Abundance of bacteria which process undigested material into feces (E.coli, normal micro flaura)
  • Feces is dark bc of the presence of bile
  • 1 m long
• Cecum


  • Pouch-like area
• Colon


  • Ascending, transverse, descending, sigmoid
  • With haustrae – pouches
• Rectum


  • Short extension of the large intestine
  • Final segment of DT
  • Peristalsis of compacted undigested food
  • Distention triggers impulsive expulsion of feces
• Anus


  • Terminal opening of the digestive system
  • Where feces are expelled
  • Controlled by internal and external sphincters
• Passageway of Food (Specific)

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Duodenum
  • Jejunum
  • Ileum
  • Cecum
  • Ascending Colon
  • Transverse Colon
  • Descending Colon
  • Sigmoid Colon
  • Rectum
  • Anal Canal
  • Anus
• Accessory Organs


  • Pancreas
  • Liver and Gall bladder
• Pancreas


  • Acini - secrete digestive enzymes that break down all major food molecules
  • Islets Of Langerhans Or Pancreatic Islets - secrete insulin or glucagon that control glucose and metabolism
• Liver


  • Largest gland of the body
  • Produces bile salts that emulsify fats
• Gall bladder


  • Stores bile produced by the liver
• Lobes of the Liver


  • Left
  • Right
  • Quadrate
  • Caudate
• Hepatocyte


  Basic structural component of the liver
• Hepatic Vein


  For blood circulation in the liver
• Portal Vein


  Carries nutrients, chemicals, drugs, etc. in the blood absorbed by the intestines into the liver
• Functions of the Liver


  • Neutralizes & eliminates toxins in the blood thru portal vein
  • Stores vitamins, iron and glucose
  • Synthesizes proteins like albumin & fibrinogen
  • Converts highly toxic ammonia (accumulates from breakdown of proteins) into urea
  • Produces bile that contains cholesterol, bile acids, bilirubin which aids in lipid digestion which is stored in the gallbladder
• Hepatobiliary Tree


  • Canaliculi from Liver form bile ducts or intrahepatic ducts drain to R & L hepatic ducts merge to form common hepatic duct
  • Gallbladder's cystic duct & CHD form common bile duct
  • CBD & pancreatic duct/duct of wirsung form ampulla of vater that drains into duodenum
• Pancreas


  • Endocrine - Islets of Langerhans secrete insulin and glucagon
  • Exocrine - Acinar Glands secrete digestive enzymes like trypsinogen, chymotrypsinogen, carboxypeptidase