SBI3U1

The Digestive System is made up of 1)The Digestive Tract 2)Accessory Organs

Mouth Esophagus Liver Stomach Gallbladder Pancreas Small Intestine Large Intestine Appendix Rectum Anus

Mechanical digestion: -Teeth break down the food into small pieces ( mouth) -Stomach muscles further break down pieces ( stomach) Chemical digestion: -Saliva which contains amylase (enzyme) breaks down the bonds in carbohydrates (mouth) -Digestive enzymes & stomach acid break down food ( stomach)

 Salivary glands in the mouth secrete saliva, which begins chemical digestion.  Amylase is released to break down starch into simple sugars.  Teeth begin the process of mechanical digestion, and the tongue helps turn the food into a soft bolus.

 Saliva is secreted from 3 salivary glands: sublingual, parotid, submandibular  The secretion of saliva is triggered before you have food in your mouth.

 The bolus is swallowed, entering the esophagus.  The epiglottis at the top of the trachea (next to the esophagus) closes to ensure the bolus does not enter the trachea.  Lined with epithelial tissue  Glands in the lining produce mucus  keeps the tube moist  facilitates movement of food

The esophagus transports the bolus to the stomach by wave-like muscular contractions called peristalsis (shown above).

The bolus enters the stomach through the esophageal sphincter. The food triggers the secretion of gastric juice–a mixture of salts, enzymes, hydrochloric acid, water, and mucus. Mucus protects the stomach from the acid The protein enzyme pepsin is secreted in a form that remains inactive until the acid is present, also protecting the stomach.

 Stomach walls are folded and can expand after a meal  Three layers of muscle fibres contract and relax to physically break food particles down.  The food is reduced to chyme (a thick liquid) before it leaves the stomach via the pyloric sphincter into small intestine.

 Most absorption of nutrients occurs here  Made up of 3 parts: Duodenum, Jejunum, Ileum  Intestinal glands secrete trypsin and chymotrypsin (further breaks down proteins and carbohydrates)

As food passes through the duodenum, the many microvilli absorb nutrients that have been broken down further by enzymes from the pancreas and the gall bladder. UNIT 4 Chapter 10: The Digestive System

 U shaped, first region after the stomach  Further breaks down proteins, fats and carbohydrates  Folds are covered in finger-like projetions called villi. Each villi is covered with microvilli.  The folds increase the surface area which increases absorption of nutrients. Note* Nutrients diffuse from small intestine into villi, then diffuses into capillary network

 Approximately 2.5 m long  Contains more folds than the duodenum  Breaks down remaining proteins and carbohydrates to be absorbed

 Approx. 3 m long  Has fewer villi than the dueodenum and jejunum  Absorbs nutrients and pushes undigested material into the large intestine

 The large intestine (a.k.a colon) reabsorbs fluids and electrolytes  Absorbs 90% of water back into the blood  food is pushed through by muscle contractions to the rectum where feces are produced

 Main component of feces: Cellulose: makes up plant cell walls, cannot be digested by humans Living and dead bacteria Water Toxic wastes are removed  Feces is eliminated from your body via the anus

 Secretes about 1 L of pancreatic fluid into the duodenum each day  Pancreatic Fluid contains: Pancreatic Enzymes - chemically digest nutrients Bicarbonates – alters pH of chyme so that enzymes can be activated. (pH 1 to pH 8)  Secretes the enyzme insulin which is used to regulate blood/glucose levels

 Largest internal organ in the human body  Releases bile (greenish-yellow fluid made up of bile pigments and salts)  Bile is used to breakdown of fats

Bile is sent to the gallbladder where it is temporarily stored

Enzymes: proteins that help speed up chemical reactions. (ex. hydrolysis)

A.k.a. lock & key model The substrate and enzyme have complementary shapes. They must fit perfectly into one another. Therefore, the enzyme is highly specific to its substrate.

1) Temperature: optimal temperature for enzyme function Most human enzymes have an optimal activity at 37˚ If temperature is too high the chemical bond in the enzyme breaks thus denaturing the enzyme 2) pH: Optimal pH at which enzymes work best Pepsin, is only active when it is immersed in a low pH Trypsin works best at a pH of 6 to 8.

Read & make notes 10.2 Pg. 419 #1, 3, 4, 6, 7, 13, 15