The Digestive System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Organs of the Digestive System Two main groups Alimentary canal or GI tract Accessory digestive organs Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Digestive Organs Salivary glands Teeth Pancreas Liver Gall bladder Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Mouth (Oral Cavity) Lips – sense temp. and texture; protect mouth Hard palate and Soft palate – form the roof Uvula – fleshy projection at the back of the soft palate Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Mouth (Oral Cavity) Tonsils palatine tonsils - on either side of the back of the mouth lingual tonsils– at the back of the tongue both play a role in the immune system Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Digestive Processes in the Mouth mastication (chewing) of food mixing of masticated food with saliva (secreted by salivary glands) saliva contains enzymes that begin the digestion of carbohydrates initiation of “deglutition” (swallowing) by the tongue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Pharynx (throat) food and air share this passageway muscular tube that moves food into the esophagus when we swallow food, a flap of tissue known as the “epiglottis” covers the trachea Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Esophagus muscular tube that runs from pharynx to stomach through the diaphragm moves food by peristalsis (slow rhythmic contractions) cardiac sphincter (lower esophageal sphincter) group of muscles, at the bottom of the esophagus, that contracts and closes the entrance to the stomach when food is present – this prevents backflow

The Stomach pouch-like organ in the left hypochondriac region of the abdominal cavity regions of the stomach: cardiac region – portion closest to the heart fundus – upper rounded portion body – middle portion pylorus – narrow bottom portion pyloric sphincter – circular muscle at the base of the stomach which controls the emptying of the stomach’s contents into the small intestine Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Stomach Anatomy the lining of the stomach is thick and has many folds called “rugae” as the stomach fills up, the wall distends and the folds disappear Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Digestive Processes in the Stomach food is mixed with gastric juice (contains hydrochloric acid and enzymes) pepsin begins to break down protein muscle movements of the stomach form a semifluid mass called “chyme” (processed food) muscles move chyme, in small batches, into the small intestine Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Small Intestine it is about 20 feet long from stomach to large intestine lined with villi (tiny, one-cell-thick fingerlike projections with capillaries) through which digested nutrients are absorbed into the bloodstream Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Subdivisions of the Small Intestine “Dogs Just Itch!” Duodenum 10 inches long chyme mixes with bile (digests fat), pancreatic juice (digests starch, proteins, and fat) and intestinal juice (digests sugars) Jejunum 8 feet long Ileum connects small intestine to large intestine Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Subdivisions of the Small Intestine “Dogs Just Itch!” Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Large Intestine about 5 feet long forms a rectangle around the tightly packed small intestine waste products usually remain in the large intestine from 12 – 24 hours Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Large Intestine Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Subdivisions of the Large Intestine Cecum saclike first part of the large intestine has 3 openings: one from the ileum into cecum, one from the cecum into the colon, and one from the cecum into the appendix Appendix is filled with lymphatic tissue and can become inflamed (appendicitis) Water and necessary substances are absorbed into the bloodstream and feces is formed Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Subdivisions of the Large Intestine Colon ascending colon: extends upward transverse colon: extends across descending colon: extends downward, where it connects to the sigmoid colon Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Subdivisions of the Large Intestine Sigmoid Colon S-shaped body that goes across the pelvis to the middle of the sacrum, where it connects to the rectum Rectum attaches to the anal canal sphincter muscles of the anus open during the release of feces from the body (defecation) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings