Digestion

9.3, 9.4

Digestion

4 steps

• ingestion

• digestion

• absorption

• egestion

Simple Organisms

• single-celled organisms

• jellyfish, flatworms have gastrovascular cavity

Complex Animals

• digestive tract with two openings

• why is two openings better than one?

Human Digestive System

Digestion in the Mouth

• physical digestion with teeth

• saliva contains enzyme amylase which digests starch

• mucus helps with swallowing

The Esophagus

• epiglottis closes over the trachea during swallowing

• bolus of food moves to stomach due to peristalsis

• see animation: http://animations.3d4medical.com/Peristalsis-animation_AN2441.html

The Stomach

• sphincters control movement of food in & out of stomach

• gastric juice contains enzymes, acid, and mucus

• hormone gastrin causes release of pepsinogen

• activated by acid to pepsin which digests proteins

• bolus becomes chyme

Acid Reflux

Stomach Ulcers