Digestive System

Alimentary Canal

• Mouth• Pharynx• Esophagus• Stomach• Small Intestine• Large Intestine• Rectum• Anus

The Oral CavityThe Oral CavityAccessory organs

–Tongue

–Teeth

–Salivary glands

Salivary GlandsSalivary Glands1. Parotid2. Submandibular3. Sublingual

Saliva is comprised of water (99.4%) with an assortment of ions, buffer, metabolites, and enzymes.

Collectively, the

salivary glands produce 1-1.5L/day

2. Esophagus peristalsis pushes food to stomach.

• Peristalsis wavelike motion that propels food.

3. Stomach secretes acid and enzymes. Mixes food with secretions to begin enzymatic digestion of proteins.

Digestive System StructuresDigestive System Structures

Digestive tract Accessory organs

• Teeth • Tongue• Salivary glands• Liver• Gall bladder• pancreas

• Oral cavity • Pharynx• Esophagus• Stomach• Small intestine• Large intestine

4. Small Intestine mixes food with bile and pancreatic juice. Final enzymatic breakdown of food molecules: main site of nutrient absorption.

Liver produces bile, which emulsifies fat. Gallbladder stores bile and introduces it into

small intestine. Pancreas produces and secretes pancreatic

juice, containing digestive enzymes and bicarbonate ions, into sm. Intestine.

Accessory organs are organs that are not a direct route of the digestive system.

5. Large intestine absorbs water and electrolytes to form feces.

6. Rectum regulates elimination of feces.7. Anus eliminates feces. The digestive system is a tube, open at

both ends, that has a surface area of 186 square meters.

The main function is to supply body with nutrients.

Alimentary Canal1. Mucosa or mucous membrane the inner

most layer. Contains glands that secrete mucus and digestive enzymes. Carries on secretion and absorption. Also, has projections that increase the surface area. Lumen=passageway.

2. Submucosa contains loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves. Carry away absorbed materials.

3. Muscular layer produces the movements.4. Serosa or serous layer the outer

covering of the digestive tube. Secretes fluid that lubricates the tube’s outer surface so organs slide freely against one another.

The PharynxThe Pharynx• The pharynx is a

muscular structure with as epithelial lining that functions in both respiration and digestion.

• Pharyngeal muscles cooperate with the oral cavity and esophagus to initiate the swallowing process 3 Divisions:

NasopharynxOropharynxLaryngopharynx

Three Phases of SwallowingThree Phases of Swallowing1. Buccal

(Oral)Phase

2. Pharyngeal Phase

3. Esophageal phase

• During swallowing, muscles draw the soft palate and uvula upward to separate the oral and nasal cavities.

• Salvia cleanse the mouth and teeth, dissolve chemicals necessary to tasting food, and help in the formation of food bolus.

Tonsils

• Palatine are lymphatic tissue in the back of the mouth, on either side of the tongue and closely associated with the palate. Help to fight infection.

• Pharyngeal or adenoids are on the posterior wall of the pharynx. They can be removed.

• Tonsillectomy tonsil are surgically removed.

Teeth

• 4 types of teeth1. Incisors (Front 4 teeth) bite off pieces of

food.2. Cuspid grasp and tear food. 3. Bicuspids or premolars grind food.4. Molars grind food.

The StomachThe Stomach • Landmarks:– Lesser curvature– Greater curvature

• Functions:– Bulk storage of ingested

food– Mechanical breakdown of

ingested food– Chemical digestion of

ingested food via the disruption of chemical bonds by acids and enzymes

*The mixing of ingested substances with the gastric juices (secreted by gastric glands) produces chyme.

Stomach

• The stomach is divided into four regions.1. Cardiac2. Fundic is the area that acts as a

temporary storage area for ingested food.3. Body4. Pyloric Fatty food stay in the stomach the

longest.

Gastric Gland Gastric Gland SecretionsSecretions

–Mucous cells

–Parietal cells

–chief cells

–Enteroendocrine cells (G cells)

Gastric Secretions

• Gastric juice1. Hydrochloric acid2. Pepsin begins to digest protein Chyme is a semifluid paste of food

particles and gastric juice.

Time Spent in organs

• Mouth a few minutes• Esophagus a few minutes• Stomach 4 hours• Small Intestine 12 hours• Large Intestine 5 hours• Total time in digestive system 21 hours.

The Small IntestineThe Small Intestine• Duodenum – “mixing

bowl” receives chyme from stomach and digestive enzymes from pancreas and liver

• Jejunum – bulk of chemical and nutrient absorption

• Ileum– controls flow of material into the large intestine via Pyloric Sphincter

Absorptive structures Absorptive structures

• Villi–These structures function to increase the surface area of the inner

intestinal wall thereby facilitating absorption.

The Large IntestineThe Large Intestine• Divisions:

–Cecum–Colon–Rectum

• Functions:–Re-absorption of water

and electrolytes–Compaction of intestinal

contents into feces–The absorption of

vitamins

Rectum and AnusRectum and Anus• Internal anal

sphincter – involuntary smooth muscle.

• External anal sphincter – voluntary skeletal muscle whose relaxation allows for defecation

Gall BladderGall Bladder• The gallbladder is a sac located under the liver. It

stores and concentrates the bile produced in the liver.

• Bile is released from the gallbladder in response to food, especially fats, in the upper small intestine.

15.7 Pancreas

• The pancreas make three different enzymes. One enzyme break down fats (pancreatic lipase), one enzyme break down protein (proteolytic), and the third enzymes break down carbohydrates.

15.8 Liver

• The liver is the largest organ in the body it is the heaviest organ in the body at around 3 pounds.

• It makes the chemical bile.• Bile is a green liquid that breaks large fat

droplets into small fat droplets.• Gallbladder is a small, baglike part located

under the liver. It stores bile until it is needed by the small intestine.

Hepatitis

• Hepatitis is an inflammation of the liver.• Types of Hepatitis1. Hepatitis A spreads by contact with food

or objects contaminated with virus-containing feces.

2. Hepatitis B spreads by contact with virus-containing body fluids, such as blood, saliva, or semen.

Digestive enzymes• Salivary glands make chemicals that

digest only carbohydrates.• Pancreas makes chemicals that digest fat,

protein, and carbohydrates.• Liver makes chemicals that digest only fat.• Stomach makes chemicals that digest only

protein.• Small intestine makes chemicals that

digest protein and carbohydrates.• Large intestine makes no chemicals to

digest food.

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