Digestive System- Large Intestine

Question 1

The Large Intestine

Answer 1

• Part of the digestive tube between the terminal ileum and anus
• Ingesta from the small intestine enters the large intestine through the ileocaecal valve
• Length 1.5m, width 7.5cm
• SI → LI via ileocecal valve

Question 2

Functions of the large intestine

Answer 2

• Reabsorb water and compact material into faeces
• Absorb vitamins: K, biotin, and B5
• Store faecal matter prior to defaecation

Question 3

3 major segments

Answer 3

1. Cecum + appendix (first portion of large intestine)
2. Colon (main, largest portion)
3. Rectum (short, terminal segment)

Question 4

Cecum

Answer 4

• Material enters the cecum via the
  ileocecal valve on the medial aspect of the cecum
• Its function is collection and storage
• Compaction of fecal matter

Question 5

The appendix

Answer 5

an organ of the lymphoid system

Question 6

Colon

Answer 6

• Teniea coli (longitudinal muscle)
• Haustra (muscular “puckering”)
• Serosa contains teardrop-shaped sacs of fat (omental appendices or fatty appendices of colon

Question 7

Subdivided Segments of the Colon

Answer 7

1. Ascending (retroperitonal)
2. Transverse (peritonal)
3. Descending (retroperitonal)
4. Sigmoid (peritonal)

Question 8

Rectum

Answer 8

• Distension of rectum triggers the urge to defecate
• Terminates at the anal canal
• Internal (smooth muscle) and external (skeletal muscle) anal sphincters
• Forms bands that prevent the faecal mass being passed with gas

Question 9

Histology of Large intestine

Answer 9

• Absence of villi
• Presence of goblet cells
• Deep intestinal glands

Question 10

Absorption

Answer 10

• < 10% of total absorption (mostly water)
• Goblet cells (alkaline mucus); lubrication & pH neutralization
• Water absorption increased by the action of the hormone aldosterone (adrenal cortex)
• Colonic bacteria generate; Vit K (clotting), & Vit B 5 (hormones/ neurotransmitters/blood/ metabolism)

Question 11

Elimination

Answer 11

Faeces; mostly water, some bacteria, bilirubin, epithelial cells & inorganic materials

Question 12

Motility

Answer 12

• Haustral contractions
  -slow segmental movements occurring every 30 min
• Mass movements
  
  • long slow movements, 3-4 times a day, move contents into the rectum - defecation reflex

Question 13

Defecation

Answer 13

• Distension of rectum triggers the urge to defecate
• Defecation Reflex
• Internal (smooth muscle) and external (skeletal muscle) anal sphincters
• Forms bands that prevent the fecal mass being passed with gas

Question 14

Defecation reflex

Answer 14

• initiated by stretching of the rectal wall following mass movements from sigmoid colon
• Long & Short reflexes
• Initial involuntary contraction of external anal sphincter followed by voluntary relaxing of the sphincter if appropriate
• Movement aided by increasing abdominal pressure (Valsalva manoeuvre) and raising the anal canal

Question 15

Digestive secretion and water
reabsorption

Answer 15

• Approximately 2200ml of water enters the digestive tract each day in the form of food and drink
• Saliva, gastric secretions, bile, intestinal secretions, and mucus provide an additional 7200ml
• Only about 150ml is lost in faeces

Question 16

Absorption of nutrients

Answer 16

• Large organic molecules must be chemically broken down before they can be absorbed
• Water, minerals, and vitamins
  can be absorbed without processing–> but may require special transport mechanisms