• Mouth
• Pharynx
• Esophagus
• Stomach
• Small Intestine
• Large Intestine

• Salivary glands
• liver
• gallbladdr
• pancrease

• breakdown of large food particles into smaller ones
  • teeth and stomach

breakdown of large molecules into small molecules

most occurs in the small intestine

The transport of molecules or atoms into the internal environment of the body from the lumen of the GI tract.

Most important process of the digestive system

• composed of thousands of small folds, called villi
• absorptive cells line the villi
  • inside each villi is a capillary bed
  • a lacteal (a blind-ended vessel of the lymhatic system)

• polysaccharides
  • starch
  • cellulose

are enzymes found in the saliva and in pancratic juice, which perform much carb digestion.

polysaccharides are digested by amylases located in saliva and pancreateic juice

proteins move glucose across the apical membrane of absorpitve cells (by active transport) and then across the basal membrane (by facilitated diffusion)

Once in the interstitial fluid, they can diffuse into the blood

• 90 % are triglycerides
• water-insoluble

• one component of bile, a fluid made by the liver, and stored and concentrated in the gallbladder
• emulsify fats

• an enzymes that digest lipids
• lipases are made and secreted by the pancreas
• the digestion products are monoglycerides and fatty acids

• fatty acids and monoglycerides diffuse into the absorptive cells
• inside they are re-assembled into triglycerides in the smooth ER
• the golgi apparatus packages the triglycerides into chylomicrons
• chylomicrons are secreted by exocytosis across the basal membrane of teh absorptive cell
• enter the lacteal and eventually reach the blood when the lymh duct drains into a vein

in the golgi apparatus

chylomicrons (a kind of lipoprotein)

• Hydrophobic vitamins - A,D,E,K - are absorbed along with lipids
• Hydrophillic vitamins - B and C - are absorbed by either active transport or facilitated diffusion

Water

Fluid flow in the GI tract

• Ingested = 2000 mL/day
• Secreted = 7000 mL/day
• Absorbed = 8900 mL/day
• Excreted = 100 mL/day

• secrete saliva
  • moistens food, begins chemical digestion
• contains
  • water
  • bicarbonate
  • mucus, to protect the mouth and lubricate food
  • salivary amylase, which begins carbohydrate digestion
  • lysozyme, that destroys some bacteria, to prevent tooth decay

• mechanical digestion of food
• makes chyme - the mixture of food and gastric juices that enters the small intestine
  • glands in the stomach lining secrete gasdtric juices
  • these juices are very acidic, and the low pH denatures proteins and kills bacterial

• contain
  • water
  • mucus
  • pepsinogen, which becomes pepsin, an important peptidase
  • HCI
  • other factors

• secretion of bile, which contains
  • bile salts that emulsify fats
  • bicarbonate
• metabolic activities
• removal of aged red blood cells from blood
• elimination of wastes from the body, including bilirubin and othe breakdown products of hemoglobin
• synthesis of plasma proteins like albumins
• secretes some hormones

• stores and concentrates bile, until after a meal
• a hormone (cholecystokinin) stimulates release of bile into the small intestine after a meal

• secretes pancreatic juice into the duodenum ( beginning of teh small intestine)

• water
• many enzymes, including pancreatic amylase, pancratic lipases, and peptidases
• bicarbonate

• waves of contractin of smoothe muscle in the GI tract propel food or chyme through the tract
• occurs during swallowing as well ad within the small and large intestine