Digestive System

Food Processing Food is processed in 4 stages: Ingestion Digestion Absorption Elimination

Digestion Digestion: the process that breaks down food into small molecules so they can be absorbed and move into the blood 2 types: Mechanical: when food is chewed, mixed, and churned Chemical: chemical reactions break down large molecules into smaller ones

Chemical Digestion Made possible through enzymes Enzyme: protein that speeds up the rate of a chemical reaction in the body Reduce the amount of energy needed for chemical reactions to begin Aid with chemical digestion without being used up

Enzyme Examples Amylase (produced by glands near mouth) speeds up breaking down complex carbs into simple carbs Pepsin in stomach aids with chemical reactions that break down proteins Enzymes in small intestine aid in breaking down proteins into amino acids Pancreas releases enzymes into small intestine to help break down sugars and fats

Digestive System 2 types of organs: digestive tract and accessory organs Digestive tract: organs that food passes through Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus Accessory organs: food doesn’t pass through them but they are essential for digestion Tongue, teeth, salivary glands, liver, gallbladder, pancreas

The Mouth Mechanical digestion: Chemical digestion: Chew food with your teeth Mix food with your tongue Chemical digestion: Salivary glands release saliva, which mixes with food Enzyme in saliva begins to break down starch into sugar Food is swallowed and ingestion is complete

The Esophagus Epiglottis covers windpipe to ensure food enters esophagus and prevent choking Esophagus: muscular tube about 25 cm long Peristalsis moves food down esophagus Peristalsis: waves of muscular contractions that move food through the digestive system No digestion (mechanical or chemical) takes place

The Stomach Mechanical digestion: Chemical digestion: Peristalsis causes food to mix Chemical digestion: Strong digestive solutions such as hydrochloric acid mix with food to break it down Pepsin works with hydrochloric acid to digest protein

The Stomach Mucus makes food slippery and protects stomach from acid Takes 2-4 hours for food to move through stomach and change into thin, watery liquid called chyme Chyme then enters small intestine

The Small Intestine Most digestion takes place in the first part of the small intestine, called the duodenum Mechanical digestion: Peristalsis continues to mix chyme Chemical digestion: Bile from liver breaks up large fat particles Digestive solution from pancreas containing enzymes and bicarbonate ions aids digestion of carbohydrates, proteins, and fats Bicarbonate ions neutralize stomach acid that is mixed with chyme

The Small Intestine Entire small intestine is 4-7m long Villi increase surface area and allow absorption of nutrients to take place Villi: fingerlike projections covering walls of the small intestine Gives nutrients more places to be absorbed Peristalsis moves undigested and unabsorbed materials into large intestine

The Large Intestine Main job: absorb water from remaining chyme Helps maintain homeostasis in body Homeostasis: regulation of an organism’s internal, life-maintaining conditions Peristalsis slows down here – chyme may stay for as long as 3 days Remaining undigested materials become solid Rectum (last section of large intestine) and anus control release of solid waste as feces

Accessory Organs Tongue Teeth Salivary glands Liver Gallbladder Pancreas

Accessory Organs in the Mouth Tongue: moves food around (mechanical digestion) Teeth: chew food into smaller parts that can be swallowed (mechanical digestion) Salivary glands: produce saliva containing enzymes that help with the beginning of chemical digestion Ex: saliva contains amylase, which breaks down starch into simpler carbohydrates

The Liver Largest solid organ in the body and largest gland in the body Gland: part of the body that makes and secretes (releases) a substance Liver is a gland because it makes and secretes bile, a fluid that aids digestion and transports fats and waste Liver releases bile into small intestine, and bile helps with digestion of fat and fat-soluble vitamins (A, D, E, K)

The Liver Also helps store some fats and carbohydrates Eliminates harmful chemicals produced by the body, such as bilirubin Bilirubin: harmful substance produced by the breakdown of red blood cells Handles detox and removal of alcohol, drugs, and other toxins

The Gallbladder Gallbladder: small organ located just below liver that stores bile secreted by the liver Transports bile from liver to small intestine You can live without a gallbladder Surgery can connect liver directly to small intestine, and a steady stream of less-concentrated bile will flow directly from liver to duodenum Less efficient but will still work

The Pancreas Pancreas: produces hormones that aid in digestion, such as insulin Insulin: hormone that regulates the amount of glucose (sugar) in the bloodstream and helps break down glucose into usable energy Diabetes: pancreas no longer produces insulin

The Appendix Contains large numbers of B-cells and T-cells “Reboots” the digestive system by ensuring it has the bacteria needed to protect the body from harmful food Aids the immune system You can survive without it