The Digestive SystemThe Digestive System

Digestive SystemDigestive System

Built around an alimentary canal Built around an alimentary canal (one-way tube)(one-way tube)

IncludesIncludesMount, pharynx, esophagusMount, pharynx, esophagusStomachStomachSmall intestineSmall intestineLarge intestineLarge intestineSalivary glands, pancreas, liverSalivary glands, pancreas, liver

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The Digestive System

Mouth Mouth

Begins mechanical digestion with Begins mechanical digestion with chewingchewingTeeth crush food to make a fine paste Teeth crush food to make a fine paste

for swallowingfor swallowingBegins chemical digestion with salivaBegins chemical digestion with saliva

Digestive enzymes begin breakdown of Digestive enzymes begin breakdown of carbohydrates into smaller moleculescarbohydrates into smaller molecules

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Your Mouth

Teeth Teeth

Anchored in jaw bonesAnchored in jaw bonesProtected by mineralized enamelProtected by mineralized enamelUsed to cut, tear, and crush food into Used to cut, tear, and crush food into

smaller fragmentssmaller fragments

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Tooth

Saliva Saliva

Secreted by salivary glands in mouth Secreted by salivary glands in mouth to moisten food and make it easier to to moisten food and make it easier to chewchew

Controlled by nervous systemControlled by nervous systemBegins chemical digestionBegins chemical digestion

Enzyme amylase breaks down starches Enzyme amylase breaks down starches and releases sugarsand releases sugars

Lysozyme fights infection by digesting Lysozyme fights infection by digesting bacteria that may enter mouth with foodbacteria that may enter mouth with food

Esophagus Esophagus

Food (called a bolus) from mouth is Food (called a bolus) from mouth is swallowed (forced from mouth into swallowed (forced from mouth into esophagus by combined action of tongue esophagus by combined action of tongue and throat muscles)and throat muscles)

Bolus moved through esophagus by Bolus moved through esophagus by contractions (peristalsis) of smooth contractions (peristalsis) of smooth muscles to the stomachmuscles to the stomach

Cardiac sphincter at the bottom of Cardiac sphincter at the bottom of esophagus prevents food in stomach from esophagus prevents food in stomach from moving back into esophagusmoving back into esophagus

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Peristalsis

StomachStomach

Muscular sac that continues Muscular sac that continues mechanical and chemical digestionmechanical and chemical digestion

Three layers of smooth muscle Three layers of smooth muscle thoroughly churn and mix food to thoroughly churn and mix food to help with digestionhelp with digestion

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Stomach

Chemical digestion in Chemical digestion in stomachstomach

Glands in the stomach lining release Glands in the stomach lining release lubricants (to protect the stomach lubricants (to protect the stomach wall), hydrochloric acid (HCl), and wall), hydrochloric acid (HCl), and pepsin (enzyme)pepsin (enzyme)

Pepsin is activated by HCl to begin Pepsin is activated by HCl to begin protein digestion to break protein protein digestion to break protein into smaller pieces or amino acidsinto smaller pieces or amino acids

Other enzymes are denatured by HCl Other enzymes are denatured by HCl and stop carbohydrate digestionand stop carbohydrate digestion

Mechanical digestion in the Mechanical digestion in the stomachstomach

Stomach muscles contract to churn Stomach muscles contract to churn and mix stomach contentsand mix stomach contents

This makes chymeThis makes chymeAfter 1-2 hours the pyloric sphincter After 1-2 hours the pyloric sphincter

opens so chyme can pass into the opens so chyme can pass into the small intestinesmall intestine

Small intestineSmall intestine

Chyme enters the first part of the Chyme enters the first part of the small intestine called the duodenum small intestine called the duodenum

Digestive enzymes and fluids from Digestive enzymes and fluids from the pancreas and liver also enter at the pancreas and liver also enter at the duodenumthe duodenum

Most chemical digestion and Most chemical digestion and absorption of nutrients occurs in the absorption of nutrients occurs in the small intestinesmall intestine

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Pancreas & Liver

Effects of digestive enzymesEffects of digestive enzymes

Salivary amylase Salivary amylase (mouth)(mouth)

Pepsin (stomach)Pepsin (stomach)

Amylase (sm. Int. Amylase (sm. Int. from pancreas)from pancreas)

Trypsin (sm. Int. Trypsin (sm. Int. from pancreas) from pancreas)

Lipase (sm. Int. Lipase (sm. Int. from pancreas)from pancreas)

Breaks down starch Breaks down starch and disaccharidesand disaccharides

Breaks down Breaks down proteins into large proteins into large peptidespeptides

Continues Continues breakdown of starchbreakdown of starch

Continues Continues breakdown of breakdown of proteinprotein

Breaks down fatBreaks down fat

Effects of digestive enzymesEffects of digestive enzymes

Maltase, sucrase, Maltase, sucrase, lactase (sm. Int.)lactase (sm. Int.)

Peptidase (sm. Int.)Peptidase (sm. Int.)

Breaks down Breaks down remaining remaining disaccharides into disaccharides into single sugarssingle sugars

Breaks down Breaks down dipeptides into dipeptides into amino acidsamino acids

Accessory structures of Accessory structures of digestiondigestion

Pancreas (behind the stomach) has 3 Pancreas (behind the stomach) has 3 rolesrolesReleases hormones to regulate blood sugar Releases hormones to regulate blood sugar

levelslevelsReleases enzymes that break down Releases enzymes that break down

carbohydrates, proteins, lipids, nucleic acidscarbohydrates, proteins, lipids, nucleic acidsProduces sodium bicarbonate that Produces sodium bicarbonate that

neutralizes stomach acids so the enzymes neutralizes stomach acids so the enzymes can function (without neutralization, can function (without neutralization, enzymes denature and don’t function enzymes denature and don’t function properly)properly)

Accessory structures cont.Accessory structures cont.

Liver-(above and to the left of the Liver-(above and to the left of the stomach) produces bile loaded with stomach) produces bile loaded with lipids and saltslipids and salts

Bile dissolves fats in fatty foodsBile dissolves fats in fatty foodsBile is stored in the gallbladderBile is stored in the gallbladder

Absorption in the small Absorption in the small intestineintestine

Last 2 parts of the small intestine are the Last 2 parts of the small intestine are the jejunum and ileum, together are 6 meters jejunum and ileum, together are 6 meters longlong

When chyme enters these it is a mixture of When chyme enters these it is a mixture of medium and small nutrient molecules medium and small nutrient molecules (most chemical digestion is competed in (most chemical digestion is competed in the duodenum)the duodenum)

Lining of the small intestine is covered with Lining of the small intestine is covered with villi (fingerlike projections) each of which is villi (fingerlike projections) each of which is covered with microvilli, both are needed to covered with microvilli, both are needed to increase the surface area for absorptionincrease the surface area for absorption

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Villi

Absorption in the small int. Absorption in the small int. cont.cont.

Cells of small intestine absorb nutrientsCells of small intestine absorb nutrients Products of carbohydrate and protein Products of carbohydrate and protein

digestion are absorbed into capillaries in digestion are absorbed into capillaries in villi villi

Undigested fat and fatty acids are Undigested fat and fatty acids are absorbed by lymph vesselsabsorbed by lymph vessels

When food leaves small intestine and When food leaves small intestine and enters the large intestine it is nutrient free enters the large intestine it is nutrient free and contains only water, cellulose, and and contains only water, cellulose, and undigestible substancesundigestible substances

The large intestineThe large intestine

Also called the colonAlso called the colonPrimary function is to remove water Primary function is to remove water

from undigestible materialfrom undigestible materialWater is absorbed quickly through the Water is absorbed quickly through the

wall of the colonwall of the colonColonies of bacteria produce useable Colonies of bacteria produce useable

compounds such as vitamin Kcompounds such as vitamin KConcentrated waste that remains Concentrated waste that remains

passes through the rectum to be passes through the rectum to be excretedexcreted