Large Intestine

Question 1

Describe the large intestine.

Answer 1

• extends from the ileocecal junction to the anus

- about 1.5 m in length

Question 2

What is the function of the large intestine?

Answer 2

• to convert the liquid contents of the ileum into semisolid feces by absorbing water
• also involved in synthesis and absorption of some vitamins, which require bacterial activity (vitamin K - involved in blood clotting)

Question 3

What are the parts of the large intestine?

Answer 3

• cecum
• appendix
• colon
• rectum and anal canal

Question 4

What is the cecum?

Answer 4

• a blind pouch found below the ileocecal junction

- lies within the right iliac fossa

Question 5

What is the ileal fold?

Answer 5

• consists of two flaps which surround the ileal orifice (opening of the terminal ileum into the cecum)
• the flaps fuse laterally to form the frenula
• function: prevents backflow of feces into the small intestine

Question 6

What is the appendix?

Answer 6

• a narrow muscular tube which contains lymphoid tissue in its walls
• it arises from the posteromedial aspect of the cecum, and is attached to the mesentery of the ileum by the mesoappendix
• functions in immune defense of the alimentary canal
• its lumen opens into the cecum via an orifice located below the ileal orifice
• the position of the appendix is variable; it’s most common position is retrocecal; second most common is pelvic

Question 7

What is appendicitis?

Answer 7

• inflammation of the appendix
• most common intra-abdominal inflammatory condition
• symptoms usually begin as umbilical pain, which then localizes to the right lower quadrant
• position of the appendix is variable and can affect where pain is felt
• if untreated, the appendix may rupture, leading to peritonitis
• cause by obstruction of the lumen due to:
  1. lymphoid hyperplasia - in kids and teenagers, also in lymphoma cases
  2. fecal impaction - affects people who have a lot of issues with constipation

Question 8

What are the parts of the colon?

Answer 8

1. Ascending colon: from the ileocecal junction to the right colic (hepatic) flexure; retroperitoneal
2. Transverse colon: from the right colic flexure to the left colic (splenic) flexure; lies within the peritoneal cavity and is attached to the posterior body wall by the transverse mesocolon
3. Descending colon: from the left colic flexure to the pelvic brim; retroperitoneal
4. Sigmoid colon: from the pelvic brim to the front of hte sacrum, where it becomes the rectum; some people have a long sigmoid colon, and are more prone to developing bowel obstruction; lies within the peritoneal cavity and is attached to the posterior body wall by the sigmoid mesocolon

Question 9

What are the taeniae coli?

Answer 9

three narrow longitudinal bands of muscle seen most prominently in the cecum and ascending colon

Question 10

What are the haustra of colon?

Answer 10

sacculations or outpouchings of the colon

Question 11

What are omental appendices?

Answer 11

small masses of fat which are covered with visceral peritoneum, and which extend from the colon

Question 12

What are the rectum and anal canal?

Answer 12

the terminal portions of the large intestine

Question 13

What is diverticulosis?

Answer 13

• herniations of the mucosa of the colon through the muscular layer, without inflammation
• most common in individuals over 40 years of age
• if the diverticuli become inflamed, the condition is called diverticulosis
• if results in abdominal pain, diarrhea, and in some cases, abscess
• related to a low fiber diet
• may be treated with laser endoscopy
• radiographically, it is characterized by numerous outpouchings along the colon

Question 14

What is ulcerative colitis?

Answer 14

• severe inflammation and ulceration of the rectum and lower colon
• usually restricted to the mucosa
• abdominal pain and diarrhea are symptoms
• bowel perforation may occur
• radiographically, the bowel appears restricted (tear-drop deformity)

Question 15

What is irritable bowel syndrome?

Answer 15

• a common condition involving recurrent abdominal pain and diarrhea with no inflammation or deterioration in health
• symptoms are caused by abnormal muscular contractions of the colon
• the cause is unknown, but symptoms are often brought on by stress and anxiety

Question 16

What does the superior mesenteric artery supply?

Answer 16

• midgut
• arises from the abdominal aorta below the celiac trunk
• its branches supply the intestine from the second part of the duodenum through the right 2/3 of the transverse colon

Question 17

What are the branches of the superior mesenteric artery and what do they supply?

Answer 17

• inferior pancreaticoduodenal artery: supplies the pancreas and distal part of the duodenum
• jejunal and ileal arteries: 12-15 arteries which branch and anastomose within the mesentery to form a series of arcades; supply the jejunum and ileum
• ileocolic artery: descends to the ileocecal junction; supplies the ascending colon, cecum, and appendix
• right colic artery: supplies the ascending colon
• middle colic artery: supplies the transverse colon

Question 18

What does the inferior mesenteric artery supply?

Answer 18

• hindgut
• arises from the lower part of the abdominal aorta
• its branches supply the large intestine from the left 1/3 of the transverse colon to the upper part of the anal canal

Question 19

What are the branches of the inferior mesenteric artery and what do they supply?

Answer 19

• left colic artery: supplies the descending colon
• sigmoid arteries: supply the sigmoid colon
• superior rectal artery: supplies the rectum and upper part of the anal canal; this is the terminal branch of the inferior mesenteric artery

Question 20

What is the marginal artery?

Answer 20

• an anastomotic channel which runs from the cecum to the sigmoid colon
• all of the branches of the superior and inferior mesenteric arteries empty into it

Question 21

What is bowel infarction?

Answer 21

• complete occlusion of intestinal vessels by lipid plaques
• endpoint of ischemic bowel disease
• if transmural, fatality rate is 95%

Question 22

What are the vasa recta?

Answer 22

• straight terminal branches from the marginal artery to the large intestine

Question 23

What is the innervation of the large intestine?

Answer 23

• cecum through right 2/3 of transverse colon: autonomic fibers from the superior mesenteric plexus
• left 1/3 of transverse colon to upper part of anal canal: autonomic fibers from inferior mesenteric plexus and hypogastric plexus (lowest part)

Question 24

What is the chiropractic note regarding the large intestine?

Answer 24

• diarrhea, constipation, and other colon problems may be related to lower thoracic, upper lumbar, or sacral subluxations
• chronic constipation is associated with increased risk of hiatal hernia, inguinal hernia, diverticulosis, and colon cancer