Download Functions of the Digestive System

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