Gastrointestinal Tract 7 - Large Intestine

Question 1

Ileocecal valve

Answer 1

• Sphincter between the cecum and ileum
• Open when ileum contracts (post-meal)
• Closed when large intestine distended
• Retains large intestine contents including bacteria

Question 2

The large Insteon functional domains:

Answer 2

• Cecum/appendix
• Ascending/transverse/descending/sigmoidal colon
• rectum : stores feces
• Anus: 2 sphincters, internal (smooth muscle) and external (skeletal muscle)

Question 3

Cecum/appendix

Answer 3

• No apparent function in humans
• In some other species well developed and contains commensal bacteria important for complex carbohydrate digestion (cellulose)

Question 4

Ascending/transverse/descending/sigmoidal colon

Major functions are:

Answer 4

• Reabsorption of water
• Reservoir for the storage of wastes and indigestible materials prior to elimination by defecation
• Absorption of products of bacterial metabolism

Question 5

Does the ;large intestine contain both crypts and villi?

Answer 5

No just crypts = lower SA then SI

Question 6

The stem cells differentiate into four different types of cells :

Answer 6

1) Absorptive cells/enterocytes
- Similar to small intestine but no brush border enzymes

2) Goblet cells (Abundant)
3) paneth (few)
4) endocrine cells

Question 7

Ecosystem of Bacteria

Answer 7

• “Gut Microbiome”
• Can liberate short chain fatty acids from dietary fibre [e.g., butyrate (C4), proprionate (C3)] that are then absorbed
• {roduce vitamins (e.g., vitamin K) that are absorbed
• Microbiome population influenced by diet, medications, and bowel function.

Question 8

Absorption of water in the large intestine Predominantly depends on

Answer 8

Na+ gradients generated by the Na+/K+ ATPase

Question 9

Secretion of water in the large intestine

Predominantly depends on

Answer 9

Cl- gradients generated by secondary active Na+/K+/2Cl- transporter (NKCC1)

(Identical to small intestine)

Question 10

Purpose of the motility

Answer 10

Mixing the contents and retaining them for optimal salvage of
fluid and bacterial products

Question 11

Mixing

Answer 11

Segmentation

• Much slower basic electrical rhythm (one every 30 min)
• Allows retention in the colon for 18-24 hr

Question 12

Propulsion

Answer 12

• Three to four times/day a wave of intense contraction known as a “mass movement” spreads rapidly over the large intestine, pushing contents towards the anus
• Occurs after eating and prior to defecation

Question 13

Feces made up of water, undigested food, bacteria, and

Answer 13

sloughed epithelial cells.

Question 14

Dedication is initiated by

Answer 14

the mass movement of large intestine contents into rectum (rectum distends and mechanoreceptors activated).

Question 15

Defecation REFLEX:

Answer 15

Rectum contracts, internal anal sphincter relaxes and outer anal sphincter contracts (initially). Increased peristaltic activity in the sigmoid colon, increasing pressure results in reflex relaxation of the external anal sphincter. Feces voided.

Question 16

After toilet training, brain can over ride the

Answer 16

reflex relaxation of the outer sphincter-defecation delayed

• Reverse peristalsis then occurs and rectal contents move back into the sigmoidal colon.