Chemical Digestion

Introduction Food cannot be broken down into small enough nutrients by physical digestion alone. Special enzymes in our body help chemically break down food into small nutrients.

Enzymes Enzymes are special proteins made at ribosomes. There are different classes of enzymes: 1. Carbohydrases break down carbs 2. Proteinases break down proteins 3. Lipases break down lipids.

Enzymes These enzymes are secreted into the digestive system by special groups of secretory cells called glands. Glands are usually connected to the digestive system through special tubes called ducts.

Enzymes The item that an enzyme breaks down is called a substrate. The enzyme is not changed at all during this process. Every enzyme performs best under its own optimal conditions. This depends on temperature, pH and the presence/absence of certain ions or vitamins and minerals.

The Mouth Three salivary glands produce saliva which contains: Water and mucous: lubricates the food Sodium bicarbonate: reduces the acidity of the bolus Salivary amylase: enzyme that begins to break down carbohydrates

The Stomach Hydrochloric acid (HCl) kills off any invading bacteria or viruses. The enzyme pepsin breaks down proteins. The enzyme lipase breaks down lipids. Mucus protects the lining of the stomach from being eaten away by the acid.

The Pancreas Produces and releases into the small intestine: Enzymes that act on proteins, carbohydrates, and fats. Bicarbonate solution to raise the pH of the chyme. Produces and releases into the blood stream: Insulin that converts glucose to glycogen, which gets stored in the body cells for later use.

The Liver Makes bile, which aids in fat digestion Most of the glycogen is stored here Vitamins A, D, E, K are stored here Detoxifies poisons that are ingested (including ethanol)‏ Cirrhosis: breakdown of liver cells due to high levels of poisons.

The Gall Bladder Stores the bile produced in the liver. Releases bile into the small intestine. Illnesses of the gall bladder include Gall stones: crystals of bile salts around cholesterol. Jaundice: collection of bile pigment in blood.

Digestion and Homeostasis A large meal activates receptors that churn the stomach and empty it faster. If the meal was high in fat, digestion is slowed, allowing time for the fat to be broken down. Hence why we feel fuller after eating a high fat meal.

Digestion and Homeostasis The endocrine, nervous, digestive and circulatory systems all work together to control digestion. Before we eat, smelling food releases saliva in our mouths and gastrin in our stomachs which prepares the body for a snack. The Hormone Gastrin

Hormones Hormones are chemical regulators, they also help control digestive enzymes. The hormone gastrin stimulates the digestive glands around the stomach. The hormone secretin stimulates the pancreas to release its enzymes which help neutralize the stomach contents as they enter the small intestine.

“For Lunch” video