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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

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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

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

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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

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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

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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 Its not actually all about gravity

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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

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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

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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.

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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

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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

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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

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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

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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.

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

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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

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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

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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

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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.