Digestive System- Continued

Absorption in Small Intestine All food,80% electrolytes and most water absorbed in small intestine Absorption of glucose:Secondary active transport- absorbed into capillaries Absorption of Amino acids:Secondary active transport- absorbed into capillaries Absorption of fatty acids:Movement from lumen to intestinal wall by bile salts. Once they cross the intestinal wall they are absorbed into lymphatic ducts.

Large Intestine Regions: Caecum Appendix Ascending Colon Transverse Colon Descending Colon Rectum Anal Canal

© 2013 Pearson Education, Inc. Figure 23.29a Gross anatomy of the large intestine. Left colic (splenic) flexure Transverse mesocolon Right colic (hepatic) flexure Epiploic appendages Transverse colon Superior mesenteric artery Descending colon Haustrum Ascending colon IIeum Cut edge of mesentery IIeocecal valve Tenia coli Sigmoid colon Cecum Appendix Rectum Anal canal External anal sphincter © 2013 Pearson Education, Inc. 4

© 2013 Pearson Education, Inc. Colon Retroperitoneal except for transverse and sigmoid regions Ascending colon (right side – to level of right kidney)  right colic (hepatic) flexure  Transverse colon  left colic (splenic) flexure  Descending colon (left side)  Sigmoid colon in pelvis  rectum © 2013 Pearson Education, Inc. 5

© 2013 Pearson Education, Inc. Bacterial Flora Enter from small intestine or anus Colonize colon Synthesize B complex vitamins and vitamin K Ferment indigestible carbohydrates Release irritating acids and gases (~500 ml/day) Bacteria are prevented from breaching the mucosal barrier by antibodies present on the gut wall. © 2013 Pearson Education, Inc. 6

Digestive Processes in the Large Intestine Residue remains in large intestine 12–24 hours No food breakdown except by enteric bacteria Vitamins (made by bacterial flora), water, and electrolytes (especially Na+ and Cl–) reclaimed Major functions - propulsion of feces to anus; defecation Colon not essential for life © 2013 Pearson Education, Inc. 7

Motility of the Large Intestine Most contractions of colon Haustral contractions Slow segmenting movements Haustra sequentially contract in response to distension Gastrocolic reflex-Initiated by presence of food in stomach Irritable Bowel Disorder:Recurring abdominal pain, stool changes,flatulence,nausea, depression. Functional bowel disorder. © 2013 Pearson Education, Inc. 8

© 2013 Pearson Education, Inc. Rectum and Anus Rectum Three rectal valves stop feces from being passed with gas (flatus) Anal canal Last segment of large intestine Opens to body exterior at anus Sphincters Internal anal sphincter—smooth muscle External anal sphincter—skeletal muscle © 2013 Pearson Education, Inc. 9

© 2013 Pearson Education, Inc. Defecation Mass movements force feces toward rectum Distension initiates spinal defecation reflex Parasympathetic signals Stimulate contraction of sigmoid colon and rectum Relax internal anal sphincter Conscious control allows relaxation of external anal sphincter © 2013 Pearson Education, Inc. 10

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