The Digestive System (also known as the Gastrointestinal System)• A collection of organs whose purpose is to break down foods into
compounds that are small enough to be taken up into the body
Gastrointestinal (GI) Tract Organs• Food and nutrients pass through these organs
Accessory Organs that AID in Digestion• Chemicals necessary for digestion are supplied by these
organsMouth Salivary glands
Esophagus LiverStomach Gallbladder
Small Intestine Pancreas
Large Intestine
Sphincters!
• Sphincter – a ring-like muscle that relaxes or contracts to open or close bodily passageways• Regulate the rate at which food and nutrients pass from one organ to the next
• Four important sphincters in the digestive process• Upperesophageal sphincter
• Loweresophageal sphincter
• Pyloric sphincter
• Ileocecal valve
The Digestive Process
The Digestive Process has 4 basic steps:
1. Food is ingested – taken into the gastrointestinal (GI) tract via the mouth
2. Food is digested – broken down into smaller units
3. Small units of nutrients are absorbed – they pass from the GI tract into the blood stream
4. Anything leftover is excreted – eliminated through the anus
The Gastrointestinal Tract• A tubular channel extending from the mouth
to the anus; digestion and absorption occur here.• Includes what 5 organs?• Intestinal Lumen - the inner space of the GI
tract. This space is lined with mucosal cells, which produce mucus, a viscous solution that lubricates and protects the GI tract
Digestion
• Mechanical Digestion – Physical breakdown of food into small particles• Mastication and mixing
• Chemical Digestion – breaks chemical bonds to turn large molecules into smaller ones• Involves chemicals from the salivary glands, stomach, pancreas, liver, and
gallbladder
Mechanical Digestion• Peristalsis – rhythmic,
wavelike contractions of smooth muscle to propel food through the GI tract• Gastric Peristalsis
Mechanical Digestion
• Segmentation – Circular muscles in the small & large intestine contract so that fluid contents slosh back and forth between the segments. • Helps mix intestinal
contents
Chemical Digestion• Enzymes – Protein molecules that
catalyze (speed up) chemical reactions.• Without enzymes, digestion could not
occur• Produced by the salivary glands, stomach,
pancreas, and small intestine. • Only work for specific molecules
• Hormones – Chemicals that serve as messengers and help to control and regulate body processes• Regulate appetite, secretions, and physical
digestion
The Path of Digestion: The MouthThe mouth is the beginning of both physical and chemical digestion• Saliva – fluid secreted from the
salivary glands to moisten the food and provide lubrication• Salivary Amylase – Enzyme that
starts the digestion of carbohydrates• Lingual Lipase – Enzyme that starts
the digestion of lipids• The tongue helps mix the saliva with
food
The Path of Digestion: The Esophagus• After being swallowed, food is pushed through
(1)_______________________ into the esophagus and then through the (2)________________________ into the stomach.
A. Loweresophageal sphincterB. Ileocecal valveC. Upperesophageal sphincterD. Pyloric sphincterE. None of the above
The Path of Digestion: The Stomach• The stomach churns food to help break it
down. • The stomach cells release chemicals to break
bonds between nutrients• GASTRIC JUICE
• Hydrochloric acid (HCl) – dentatures (unravels) protein
• Protease – enzyme that helps digest protein• Gastric Lipase – enzyme that helps digest lipids• Mucus – protects lining of the stomach from HCl
• Chyme – partially digested, liquefied food that leaves the stomach through the ___________?
The Path of Digestion: The Small Intestine
• Main site of digestion & absorption of nutrients• Specialized structures to increase
surface area and increase absorption• Carbohydrates, protein, fats, and
other nutrients (like what??) are digested & absorbed in the small intestine
Digestion in the Small Intestine
• Mechanical Digestion – does it happen here?
• Chemical Digestion• Three organs provide enzymes needed (Hint: these are the accessory
organs that aid in digestion)
Pancreas
• Pancreas releases a liquid solution called Pancreatic Juice• Pancreatic Juice moves from the pancreas into the small intestine
where it digests nutrients by breaking down chemical bonds• Amylase – digests carbohydrates • Protease – digests proteins • Pancreatic Lipase – digests lipids • Bicarbonate – neutralizes HCl
Liver and Gallbladder
• Liver produces Bile• Bile – a substance necessary for digestion of lipids. It works with the
enzyme ____________ to maximize lipid digestion.• Gallbladder – storage facility for bile
In what organ along the gastrointestinal tract does bile interact with lipids to assist in digestion?
Absorption
• After food and nutrients are small enough, nutrients move out of the lumen of the small intestine into either the blood vessels OR the lymph vessels• Blood vessels: proteins (amino acids), carbohydrates, minerals, water-soluble
vitamins• Lymph vessels: lipids, fat-soluble vitamins
• The blood and lymph vessels are like highways that transport nutrients to the organs and tissues in the body
• Simple Diffusion – movement of a substance down a concentration gradient• Facilitated Diffusion –
movement of a substance down a concentration gradient with the help of a transport protein
Diffusion in the Small Intestine
• Active Transport – movement of a substance against a concentration gradient; requires both a transport protein and energy
Diffusion in the Small Intestine
The Path of Digestion: The Large Intestine• Waste products move from the small intestine through the
__________________ into the large intestine• Remaining nutrients are absorbed• Water is absorbed into the body• Over 1000 different species of bacteria feed on undigested fiber
• Produces gas!• Produces short chain fatty acids, which either feed the bacteria or are absorbed into the
body