The Large Intestine Pages 470 472 and 484486

The Large Intestine Pages 470 -472 and 484486 …Of a senior

Large Intestine • Extends from the ileocecal valve to the anus • Subdivisions: § § § Cecum Appendix Colon (has it’s own subdivisions) Rectum Anal canal • Functions: § Dry out food residue (absorb any remaining water) § elimination © 2015 Pearson Education, Inc.

Figure 14. 8 The large intestine. Transverse mesocolon Transverse colon Haustrum Descending colon Ascending colon Ileum (cut) Ileocecal valve Teniae coli Sigmoid colon Cecum Appendix Rectum Anal canal External anal sphincter

Large Intestine Anatomy • Cecum—first part of the large intestine – Connects to the ileum via the ileocecal valve • Appendix – Cluter of lymphoid tissue • can become inflamed (appendicitis) – Its twisted arrangement allows bacteria to accumulate – Appendage of the cecum © 2015 Pearson Education, Inc.

Large Intestine Anatomy • Colon – – first 3 subdivisions create an upside down “U” • Ascending—travels up right side of abdomen • Transverse—travels across the abdominal cavity • Descending—travels down the left side – Sigmoid—S-shaped region; enters the pelvis • Rectum- connects sigmoid colon to anus – Walls stretch to initiate the defecation reflex © 2015 Pearson Education, Inc.

Anus—opening of the large intestine ◦ Internal anal sphincter—smooth muscle, involuntary control ◦ Remains closed to prevent feces from leaking between defecations ◦ External anal sphincter—skeletal muscle, voluntary control • Sphincters stay closed until neural signals tell them to open • Peristalsis initiates defecation • Waves of reflexive contractions continue until defecation takes place • Defecation can be helped by use of diaphragm and abdominal muscles

Figure 14. 8 The large intestine. Transverse mesocolon Transverse colon Haustrum Descending colon Ascending colon Ileum (cut) Ileocecal valve Teniae coli Sigmoid colon Cecum Appendix Rectum Anal canal External anal sphincter

Additional anatomical features • Goblet cells : line the interior surface – produce alkaline mucus – lubricates the passage of feces • Muscularis externa : (the muscular tunic) – three bands of muscle called teniae coli – cause the wall to pucker into haustra (pocketlike sacs) © 2015 Pearson Education, Inc.

Activities of the large intestine • Few nutrients remain in food • No digestive enzymes are produced • Bacterial flora within: – metabolize what’s left • This creates gas! Yum (methane and hydrogen sulfide) – Synthesize Vitamins K and some B vitamins • Absorption is limited to: – Vitamins produced – Remaining water and ions • Feces- includes undigested food, mucus, bacteria, and any remaining water