Digestive System- Small Intestine Flashcards
Regions of small intestine
*Duodenum
*Jejunum
*Ileum
Layers of the Small intestine
- Mucosa – Simple columnar epithelia + microvilli (Brush- border)
- Submucosa - Intestinal glands
- Muscularis externa
- Serosa
Histology of the small intestine
- 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
Mucosal folds
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.
Villi
- A series of fingerlike projections which protrude into the lumen:
- in mucosa of small intestine
- Covered by simple columnar
epithelium: - covered with microvilli
Microvilli
the lumenal plasma membrane of absorptive epithelial cells is studded with densely-packed microvilli.
The Duodenum
- 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
Functions of the duodenum
- 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
The Jejunum
- 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
The Ileum
- The final segment of small intestine
- 3.5 meters (11.48 ft) long
- Absorbs Vit B 12 & bile salts
- Ends at the ileocaecal valve
Ileocaecal valve
a sphincter that controls flow of material from the ileum into the large intestine.
Plicae circulares
- Transverse folds in intestinal lining
- Are permanent features- do not disappear when small intestine fills
The Villus
- Epithelium
- Mucous cells (goblet cells)
- Capillaries
- Nerve
- Lymphatics
Intestinal glands
- Mucous cells between columnar epithelial cells.
- Eject mucins onto intestinal surfaces.
- Mucin + water = mucous
Crypts of Lieberkühn
- Openings from intestinal glands:
- to intestinal lumen
- at bases of villi
- Entrances for brush border (microvilli) enzymes.
Brush Border Enzymes
- Integral membrane proteins
- On surfaces of intestinal microvilli
- Break down materials in contact with brush border
Duodenal Glands
- Also called submucosal glands or Brunner glands.
- Produce copious quantities of mucous when chyme arrives from stomach
Small Intestinal Secretions
- 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
Small Intestinal Movements
- Chyme arrives in duodenum
- Weak peristaltic contractions move it slowly toward jejunum
Reflexes
- The Gastro-enteric Reflex
- The Gastro-ileal Reflex
The Gastro-enteric Reflex
- Stimulates motility and secretion along entire small intestine
The Gastro-ileal Reflex
- Triggers relaxation of ileocecal
valve - Allows materials to pass from
small intestine into large intestine
Introduction to The Small Intestine
- Important digestive and absorptive functions
- Secretions and buffers are provided by pancreas, liver, gall bladder
- 90% of nutrient absorption occurs in the small intestine
Ileocaecal sphincter
Transition between small and large intestine
