Accessory Organs and Enzymes Unit D – Human Systems

Accessory Organ An organ that assists with the functioning of some other organ within a system. For example, the gallbladder, liver and pancreas are not part of the gastrointestinal tract, but they play key roles in aiding digestion. Digestion Review Video

The liver, pancreas and gallbladder all secrete (or release) fluids from their cells. These fluids contain enzymes that break down large organic molecules (carbs, proteins, lipids) into smaller molecules that can be absorbed into the bloodstream to be transported to cells of the body.

Salivary Glands Secrete amylase enzyme. Amylase breaks down starches or polysaccharides into shorter chains of sugars.

Stomach Secretes pepsinogen enzyme. Pepsinogen is the inactive form of the enzyme. It is “switched on” by the presence of hydrochloric acid and converted into pepsin. Pepsin takes proteins and breaks them into longer chains of amino acids called polypeptides.

Liver Continuously produces a fluid called bile, which is concentrated and stored in the gallbladder. When the presence of fats is detected in the small intestine, a hormone called is released and signals the gall bladder to release bile salts.

Bile salts travel to the small intestine where they emulsify or break down large fat globules. The fat globules can then be exposed to enzymes which can break the fats down.

Other Functions of Liver Storage of vitamins and of excess glucose in the form of glycogen. Detoxifies potentially harmful compounds like alcohol. Breaks down and removes nitrogen from amino acids, forming urea, the major component of urine.

Pancreas When acidic fluids from the stomach reach the small intestine, a hormone called secretin enters the bloodstream and signals the pancreas to release bicarbonate (HCO 3 - ) ions. Bicarbonate ions are basic or alkaline and neutralize the acidic stomach fluids.

The enzymes enterokinase, trypsinogen, erepsin, amylase, and lipase are also secreted from the pancreas when food from the stomach enters the small intestine. Enterokinase enzyme activates trypsinogen into its active form, trypsin.

Trypsin takes long chain polypeptides and breaks the chemical bonds between them, and converts them into shorter chain polypeptides. Erepsin enzymes take short chain polypeptides, dissolve the chemical bonds and release individual amino acids.

Starches that have not been broken down can be digested in the small intestine by pancreatic amylase into shorter chains of sugars called disaccharides. Fats are broken down by enzymes called lipases into glycerol and fatty acids.

Small Intestine As well as being the major site of chemical digestion, also releases enzymes. Disaccharidases break down disaccharides into monosaccharides. The three major disaccharidases are maltase, lactase and sucrase.

Once food has been broken down into individual monosaccharides, amino acids and fatty acids, these can be absorbed by villi into the bloodstream and lymphatic system. Undigested food carries on travelling to the large intestine.

Student Tasks for Lesson Complete “Enzymes of the Digestive System” Table. Complete pg. 263 #10, 12, pg. 266 #1-7 for your homework book. Major assignment to be handed in: Complete a flow chart involving all organs of digestion, major sites of chemical and physical digestion and all enzyme action.