Digestive System- Small Intestine

Question 1

Regions of small intestine

Answer 1

*Duodenum
*Jejunum
*Ileum

Question 2

Layers of the Small intestine

Answer 2

1. Mucosa – Simple columnar epithelia + microvilli (Brush- border)
2. Submucosa - Intestinal glands
3. Muscularis externa
4. Serosa

Question 3

Histology of the small intestine

Answer 3

• Plicae- transverse folds of the intestinal lining
• Villi- fingerlike projections of the mucosa
• Lymphatic vessels
• Intestinal glands- lined by enteroendocrine, goblet, and stem cells.
• Muscularis externa
• Serosa

Question 4

Mucosal folds

Answer 4

the inner surface of the small intestine is not flat, but thrown into circular folds, which not only increase surface area, but aid in mixing the ingesta.

Question 5

Villi

Answer 5

• A series of fingerlike projections which protrude into the lumen:
• in mucosa of small intestine
• Covered by simple columnar
  epithelium:
• covered with microvilli

Question 6

Microvilli

Answer 6

the lumenal plasma membrane of absorptive epithelial cells is studded with densely-packed microvilli.

Question 7

The Duodenum

Answer 7

• The segment of small intestine closest to stomach
• 25 cm (10 in.) long
• Submucosal glands secreting enterogasterones
• Brunner’s glands; alkaline mucus secretions for protection

Question 8

Functions of the duodenum

Answer 8

• To receive chyme from stomach and digestive secretions from pancreas and liver.
• To neutralize acids before they can damage the absorptive surfaces of the small intestine

Question 9

The Jejunum

Answer 9

• the middle segment of small intestine
• 2.5 meters (8.2 ft) long
• Is the location of most
  
  • Chemical digestion
  • Nutrient absorption
• Has few plicae
• Small villi

Question 10

The Ileum

Answer 10

• The final segment of small intestine
• 3.5 meters (11.48 ft) long
• Absorbs Vit B 12 & bile salts
• Ends at the ileocaecal valve

Question 11

Ileocaecal valve

Answer 11

a sphincter that controls flow of material from the ileum into the large intestine.

Question 12

Plicae circulares

Answer 12

• Transverse folds in intestinal lining
• Are permanent features- do not disappear when small intestine fills

Question 13

The Villus

Answer 13

• Epithelium
• Mucous cells (goblet cells)
• Capillaries
• Nerve
• Lymphatics

Question 14

Intestinal glands

Answer 14

• Mucous cells between columnar epithelial cells.
• Eject mucins onto intestinal surfaces.
• Mucin + water = mucous

Question 15

Crypts of Lieberkühn

Answer 15

• Openings from intestinal glands:
  
  • to intestinal lumen
  • at bases of villi
• Entrances for brush border (microvilli) enzymes.

Question 16

Brush Border Enzymes

Answer 16

• Integral membrane proteins
• On surfaces of intestinal microvilli
• Break down materials in contact with brush border

Question 17

Duodenal Glands

Answer 17

• Also called submucosal glands or Brunner glands.
• Produce copious quantities of mucous when chyme arrives from stomach

Question 18

Small Intestinal Secretions

Answer 18

• Watery intestinal juice
• 1.8 liters per day enter intestinal lumen
• Moisten chyme
• Assist in buffering acids
• Keep digestive enzymes and products of digestion in solution

Question 19

Small Intestinal Movements

Answer 19

• Chyme arrives in duodenum
• Weak peristaltic contractions move it slowly toward jejunum

Question 20

Reflexes

Answer 20

• The Gastro-enteric Reflex
• The Gastro-ileal Reflex

Question 21

The Gastro-enteric Reflex

Answer 21

• Stimulates motility and secretion along entire small intestine

Question 22

The Gastro-ileal Reflex

Answer 22

• Triggers relaxation of ileocecal
  valve
• Allows materials to pass from
  small intestine into large intestine

Question 23

Introduction to The Small Intestine

Answer 23

• Important digestive and absorptive functions
• Secretions and buffers are provided by pancreas, liver, gall bladder
• 90% of nutrient absorption occurs in the small intestine

Question 24

Ileocaecal sphincter

Answer 24

Transition between small and large intestine