Digestive System 5/6/16

Digestive System Oral Cavity Ingestion Mechanical breakdown Chemical breakdown Propulsion (swallowing)

Digestive System Oral Cavity Salivary glands 1st Accessory Organ Parotid Sublingual Submandibular

Digestive System Oral cavity -> Pharynx -> Esophagus -> Stomach Stomach Mechanical breakdown Chemical breakdown Rugae: folds on the inside of the wall of the stomach Allows the stomach to stretch Empty stomach: approx 50ml Full stomach: approx 2 liters

Digestive System Stomach 3 layers pH of 1.5 – 2.5

Digestive System Small Intestine 3 segments Duodenum: first and shortest Jejunum Ileum

Digestive System Duodenum Where liver, gallbladder and pancreas secretions enter

Digestive System Jejunum: Follows duodenum, about 8 feet long

Digestive System Small intestine lining Villi Microvilli : “brush border”

Digestive System Ileum 3-5 feet long

Digestive System Small intestine: Major site for absorption for the end products of digestion

Digestive System A few more notes about enzymes and hormones. The gallbladder releases bile into the small intestine. The hormone that stimulates this release is called cholecystokinin-pancreozymin. The pancreas can release a bicarbonate into the small intestine, in addition to its digestive enzymes. The hormone that stimulates the release of bicarbonate is secretin.

Digestive System Proteins are broken down by enzymes in gastric and intestinal juices. Fats are broken down by lipase enzyme in the small intestine. Carbohydrates are broken down by enzymes in the mouth and small intestine. The major final product that results from the digestion of carbohydrates is glucose.

Digestive System A chemical digestion process called enzymatic hydrolysis can break the bonds holding the molecular ‘building blocks’ within the food together. Water splits larger compounds into smaller ones. Hydrochloric acid converts pepsinogen into pepsin.

Digestive System Enzymes are very specific, they fit their substrates like a “key-in-a-lock.” Enzymes are pH sensitive because changes in hydrogen ion concentrations can affect the shape of the protein molecule.

Digestive System A wavelike muscle contraction that moves food along the digestive system is called perstalsis