Digestive System Review from Last Class

Digestive System Review From Last Class

Mechanical and Chemical Digestion Step 1: Mouth • Mechanical digestion occurs by chewing (teeth). • Chemical digestion occurs when salivary glands produce saliva which contains AMYLASE. • Amylase is an enzyme that chemically breaks down starch (AMYLOSE) . • The food is now a BOLUS (partially digested). Step 2: The Stomach • The bolus is stored here. • In the stomach ONLY protein digestion occurs. • Nerves in the stomach detect food, will release Gastrin • Gastrin is a hormone that stimulates the release of Gastric juices • Gastric juices are made up of enzymes, acids and mucus 1. HCl (hydrochloric acid) « kill any bacteria or virus that are contained in the undigested food « HCl stops the action of amylase « converts pepsinogen (inactive) to pepsin (active) by cleaving it. 2. Pepsin « is a protein digesting enzyme. It breaks proteins into shorter polypeptides. 3. Mucus « protects the stomach lining from the HCl and the digestive enzymes. Inactive (will not break down proteins)

Active (will break down proteins) Step 3 Small Intestine (SI)

Most of the digestion occurs in the SI. a)The partially digested food is bathed in acid and pepsin enzymes. Because the food is acidic when it enters the small intestine this causes the conversion of a chemical called prosecretin into another chemical called SECRETIN. Secretin is absorbed into the bloodstream to the pancreas. The secretin signals the release of BICARBONATE ions. These ions are carried to the SI where they neutralize the acid and inactivates pepsin.

The pH of 9. (The bicarbonate ions change the pH of the small intestine from acidic (the HCL) to a little bit basic, pH of 9) How is Secretin Activated

Recall from previous slide. Because the food is acidic when it enters the small intestine this causes the conversion of a chemical called prosecretin into another chemical called SECRETIN. Secretin is absorbed into the bloodstream to the pancreas. The secretin signals the release of BICARBONATE ions. These ions are carried to the SI where they neutralize the acid and inactivates pepsin.

HCl from Stomach

Prosecretin (inactive) Secretin (active)

Goes to the pancreas through the bloodstream

Neutralized the acid Bicarbonate ions and blocks pepsin Released from pancreas Back to SI Digestion in the Small Intestine

Pancreas secretes a pancreatic juice into the SI that breaks down proteins, fats and carbs

Protein digestion 1) An enzyme called TRYPSINOGEN is released from the pancreas 2) TRYPSINOGEN gets converted into TRYPSIN by ENTEROKINASE. Trypsin breaks down polypeptides into smaller polypeptides. 3) a group of enzymes call EREPSINS is released from the SI and the pancreas once short polypeptides are made. -Erepsins break the bonds of the short polypeptides and complete digestion to release amino acids. Flow chart of the digestion of proteins in the SI

*Recall Protein digestion 1) An enzyme called TRYPSINOGEN is released from the pancreas 2) TRYPSINOGEN gets converted into TRYPSIN by ENTEROKINASE. 3)Trypsin breaks down polypeptides into smaller polypeptides. 4) a group of enzymes call EREPSINS is released from the SI and the pancreas once short polypeptides are made. -Erepsins break the bonds of the short polypeptides and complete digestion to release amino acids.

Enterokinase

Trypsin & Shorter Trypsinogen Polypeptides Polypeptides

Erepsin Released from the pancreas & Si

Amino Acids Digestion in the Small Intestine

Starch Digestion - amylase are released from the pancreas to continue the digestion that started in the mouth. Converts starch into disaccharides.

Disaccharide Digestion - once amylase is finished its process, disaccharides are formed (2 chain sugar) The SI releases disaccharidases. These enzymes break down the disaccharides into glucose.

Digestion in the Small Intestine

Starch Digestion - amylase are released from the pancreas to continue the digestion that started in the mouth.

OH OH

Disaccharide Digestion - once amylase is finished its process, disaccharides are formed (2 chain sugar) The SI releases disaccharidases. These enzymes break down the disaccharides into glucose.

OH OH

Lipid Digestion - Pancreatic lipase enzymes are released from the pancreas and work to break down fats into fatty acids and glycerol. - Phospholipase enzyme released from the pancreas breaks down phospholipids. Lipid Digestion - Pancreatic lipase enzymes are released from the pancreas and work to break down fats into fatty acids and glycerol. - Phospholipase enzyme released from the pancreas breaks down phospholipids.

Phospholipase

+ +

Pancreatic Lipase

+ The Large Intestine! • No mechanical or chemical digestion. • Stores waste long enough for water, inorganic salts, minerals and vitamins to be absorbed into the body. • E.Coli bacteria is present here and uses the waste to produce vitamin K. • Cellulose is an undigestible carbohydrate that is a source of fibre. Initiates bowel movements. Accessory Organs of Digestion The Liver:

-Produces a fluid called bile, which is stored and concentrated in the gallbladder. -Bile contains bile salts, which speed up fat digestion.

Fats enter the small intestine and causes a hormone called CHOLECYSTOKININ (CCK) to enters the blood stream and travels to the the gallbladder.

CCK causes the gall bladder to contract and all the bile salts move into the small intestine

Bile salts work to emulsify the fats (physically break down fat) ** Emulsification prepares fat for chemical digestion by increasing its surface area Liver making Bile Gall Bladder stores the Bile

CCK enters by the bloodstream when fat enters S.I.

Bile is release into Fat is the small intestine emulsified

Example: The Liver, Gall Bladder Role in Fat Emulsification

Exit Card! Name something you learned Did you enjoy todays lesson, why or why not?