ESSENTIALS

Unit

7Digestive System:Small and Large Intestine

ESSENTIALS

OF HUMAN

ANATOMY

& PHYSIOLOGY

Small Intestine

�Body’s major digestive organ

�Site of nutrient absorption into blood

�Muscular tube extends from pyloric

sphincter to the ileocecal valve

�Suspended from the posterior abdominal �Suspended from the posterior abdominal

wall by the mesentery

Subdivisions of the Small Intestine

�Duodenum�Attached to the stomach�Curves around the head of the pancreas

�Jejunum�Attaches anteriorly to the duodenum

�Ileum�Ileum�Extends from jejunum to large intestine

Chemical Digestion in Small Intestine

�Source of enzymes that mix with chyme� Intestinal cells�Pancreas

�Bile enters from the gall bladder

Folds of the Small Intestine

�Circular folds called plicae circulares

�Deep folds of mucosa and submucosa

�Do not disappear when filled with food

�Submucosa has Peyer’s patches

(lymphatic tissue)

Villi of the Small Intestine

�Fingerlike structures formed by mucosa

�Allow for more surface area

Microvilli of the Small Intestine

�Small projections of plasma membrane

�Found on absorptive cells

Nutrient Absorption Structures

�Absorptive cells

�Blood capillaries

�Lacteals� (lymphatic capillaries)

Large Intestine

�Larger in diameter, but shorter than the

small intestine

�Frames the internal abdomen

Functions of the Large Intestine

�Absorption of water

�Eliminates undigested food from body as

feces

�Does not participate in food digestion

�Goblet cells produce mucus (lubricant)

Structures of the Large Intestine

�Cecum- saclike first part

�Appendix�Accumulation of lymphatic tissue; can become

inflamed (appendicitis)�Hangs from the cecum

�Colon�Colon�Ascending�Transverse�Descending�S-shaped sigmoidal

�Rectum

�Anus- external body opening

Large Intestine Muscularis Externa

�Smooth muscle is reduced to three bands

(teniae coli)

�Muscle bands have some degree of tone

�Walls are formed into pocketlike sacs

called haustracalled haustra