Functions of the Digestive System Activities of Each Digestive Organ

Mouth Ingestion Mechanical digestion – chewing Chemical digestion – salivary amylase begins breaking down starches to maltose

Pharynx & Esophagus Propulsion Deglutition (swallowing) –Buccal phase – voluntary; mouth to pharynx –Pharyngeal-esophageal phase – involuntary; pharynx to esophagus; peristalsis

Stomach – chemical digestion Gastric juices are secreted by the stomach Acidic environment caused by hydrochloric acid. Acidic environment activates pepsinogen to pepsin which breaks down protein No absorption occurs except for alcohol and aspirin

Stomach - propulsion As food is well mixed, peristalsis occurs in the lower half of the stomach As the pylorus of the stomach if filled with “chyme” (partially digested food), the stomach contracts and “spits” out small amounts of chyme through the pyloric sphincter into the duodenum.

Small Intestine - Chemical Digestion Chemical digestion is accelerated Brush border enzymes are found in the microvilli. It breaks down double sugars to simple sugars. Pancreatic juices enters the small intestine via pancreatic duct Bile mixes with pancreatic juices to mechanically break down large fat globules.

Function of Pancreatic Juices Digests starches completely Carry out half of protein digestion Responsible of fat digestion Digest nucleic acids Neutralizes acidic chyme by supplying bicarbonate

Small Intestine - Absorption Absorption of water and end products occurs through the intestinal cell plasma membranes by “active transport”. Lipids are absorbed through the cell via “diffusion”

Small Intestine - Propulsion Peristalsis and segmentation occurs through the entire small intestine Some water and indigestible food materials that remain in the ileum enters the large intestine

Large Intestine – Chemical Digestion No digestive enzymes Bacteria metabolizes some remaining nutrients, releasing gases (methane & hydrogen sulfide)

Large Intestine - Absorption Vitamin K and some B that are made by bacteria are absorbed. More water is also absorbed

Large Intestine - Propulsion Peristalsis and mass movements occurs Mass movements are long, slow-moving but powerful contractile waves that move large areas of the colon and force contents toward the rectum