 Food must be broken down into nutrients that can be absorbed into the blood and carried to our body  The collection of organs that carry out digestion is the digestive system

 1. Ingestion – the taking in of nutrients  2. Digestion – the physical and chemical breakdown of complex food molecules into smaller molecules  3. Absorption – the transfer of digested nutrients from the digestive system to the bloodstream  4. Egestion – the removal of waste food materials from the body

 Human digestive system is complete  Two openings  Specialized regions  GI tract is approximately 9 meters long.

 Digestion begins!  Physical digestion by teeth  Teeth related to diet! Ex. Carnivores, need canine teeth to grab and kill prey  Presence, sight, smell of food triggers salivary glands to secrete saliva

 Contains enzymes  Dissolves food particles, letting you taste your food  Contains mucus Lubricant and aids in swallowing  Contains water Which moistens the food into a ball, or bolus

 Long, muscular tube that undergoes rhythmic, wavelike contractions of smooth muscles  Peristalsis Ensures the movement of food down the esophagus into the stomach in approximately 8 seconds It’s not actually all about gravity

 J-shaped, muscular organ  Can store up to 2L of food  Proteins are partly digested  Lipids and carbohydrates are NOT digested at all  Movement into and out of stomach is controlled by circular muscles called sphincters Gastroesophageal Pyloric

 Gastroesophageal sphincter does not close completely  Acid from stomach can enter the esophagus causing a burning sensation in the lower throat  Common causes:  Overfilled stomach  Smoking

 Stomach acid is usually strong enough to kill most bacteria  Helicobacter pylori is able to survive Prevent mucus producing cells from producing enough mucus to protect the stomach lining  Lining becomes exposed to acid, causes an open sore, called an ulcer.

 Long tube that is only about 2.5cm in diameter and can be up to 7 meters long  Most digestion and absorption of nutrients takes place in the small intestine  Lipids and carbohydrates, as well as any remaining proteins are digested in the small intestine

 Duodenum: first 25 cm, where most enzymes are added and digestion begins  Jejunum: digestion continues and some nutrients are absorbed  Ileum: Majority of nutrients are absorbed

 Inner surface of the small intestines is adapted to provide the maximum surface area for efficient nutrient absorption  Villi: the ridges and small finger-like projections that increase the surface area tenfold  Microvilli: Even smaller microscopic projections from the cell membrane of villi epithelial cells

 Long flat nestled between the stomach and the duodenum.  Dual role Secretes enzymes for digestion and secretes hormones that regulate the absorption and storage of glucose

 Liver is the largest internal organ  In terms of digestion it is considered a gland because it produces and secretes bile  Bile: a substance that helps break down fats This increases the surface area for the lipases to act on.

 Liver is also involved with the removal and breakdown of toxins, such as alcohol.

 Once proteins, carbohydrates, and lipids are digested they can be absorbed in the jejunum and ileum; along with vitamins, minerals and water  Structure of the small intestine is very important for absorption of nutrients

 Most absorption has been completed before the large intestine  Cellulose, which cannot be broken down by humans  Approximately 20L of fluids pass through the large intestine Most of this is absorbed back into the body  Vitamins B and K, sodium and chloride are also absorbed

 More than 500 species of bacteria normally inhabit the large intestine  Most common is E Coli. Mutually beneficial relationship They get food, we get essential substances such as Vitamin K and some B vitamins

 Removal of waste food materials  Absorption of water in the large intestine Changes liquid material to soft solid called feces  Defecation reflex caused by the nerves in the wall of the intestines  The anus is surrounded by two sphincter muscles: the internal smooth and external skeletal sphincter.