The Digestive System and Body Metabolism

Stomach AnatomyLocated on the left side of the abdominal

cavityFood enters at the cardioesophageal

sphincterFood empties into the small intestine at the

pyloric sphincter (valve)

Stomach AnatomyRegions of the stomach

Cardiac region—near the heartFundus—expanded portion lateral to the

cardiac regionBody—midportionPylorus—funnel-shaped terminal end

Stomach AnatomyRugae—internal folds of the mucosaExternal regions

Lesser curvature—concave medial surfaceGreater curvature—convex lateral surface

Stomach Anatomy

Figure 14.4a

Stomach Anatomy

Figure 14.4b

Stomach AnatomyLayers of peritoneum attached to the

stomach Lesser omentum—attaches the liver to the

lesser curvatureGreater omentum—attaches the greater

curvature to the posterior body wallContains fat to insulate, cushion, and protect

abdominal organsHas lymph nodules containing macrophages

Stomach Anatomy

Figure 14.5a

Stomach Anatomy

Figure 14.5b

Stomach PhysiologyTemporary storage tank for foodSite of food breakdownChemical breakdown of protein beginsDelivers chyme (processed food) to the

small intestine

Structure of the Stomach MucosaMucosa is simple columnar epitheliumMucous neck cells—produce a sticky

alkaline mucusGastric glands—situated in gastric pits and

secrete gastric juiceChief cells—produce protein-digesting

enzymes (pepsinogens)Parietal cells—produce hydrochloric acidEnteroendocrine cells—produce gastrin

Structure of the Stomach Mucosa

Figure 14.4c

Structure of the Stomach Mucosa

Figure 14.4d

Small IntestineThe body’s major digestive organSite of nutrient absorption into the bloodMuscular tube extending from the pyloric

sphincter to the ileocecal valveSuspended from the posterior abdominal

wall by the mesentery

Subdivisions of the Small IntestineDuodenum

Attached to the stomachCurves around the head of the pancreas

JejunumAttaches anteriorly to the duodenum

IleumExtends from jejunum to large intestine

Chemical Digestion in the Small IntestineChemical digestion begins in the small

intestineEnzymes are produced by

Intestinal cellsPancreas

Pancreatic ducts carry enzymes to the small intestine

Bile, formed by the liver, enters via the bile duct

Chemical Digestion in the Small Intestine

Figure 14.6

Small Intestine AnatomyThree structural modifications that increase

surface areaMicrovilli—tiny projections of the plasma

membrane (create a brush border appearance)

Villi—fingerlike structures formed by the mucosa

Circular folds (plicae circulares)—deep folds of mucosa and submucosa

Small Intestine Anatomy

Figure 14.7a

Small Intestine Anatomy

Figure 14.7b

Figure 14.7c

Small Intestine Anatomy

Large IntestineLarger in diameter, but shorter in length,

than the small intestineFrames the internal abdomen

Large Intestine AnatomyCecum—saclike first part of the large

intestineAppendix

Accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)

Hangs from the cecum

Large Intestine

Large Intestine AnatomyColon

Ascending—travels up right side of abdomenTransverse—travels across the abdominal

cavityDescending—travels down the left sideSigmoid—enters the pelvis

Rectum and anal canal—also in pelvis

Large Intestine AnatomyAnus—opening of the large intestine

External anal sphincter—formed by skeletal muscle and under voluntary control

Internal involuntary sphincter—formed by smooth muscle

These sphincters are normally closed except during defecation

Large Intestine AnatomyNo villi presentGoblet cells produce alkaline mucus which

lubricates the passage of fecesMuscularis externa layer is reduced to

three bands of muscle called teniae coliThese bands cause the wall to pucker into

haustra (pocketlike sacs)