Secretions of Small IntestineBY SYEDA BATOOL ABBAS

RECAP Layers of Small intestine (4)

1)Mucosa ( Innermost )

Absorb nutrients from chyme

2)Submucosa

Provides blood vessels ,lymphatic vessels and nerves to support mucosa on the surface.

3)Muscularis layer

Contracts and moves the small intestine

4)Serosa (outermost )

Continuous throughout and surrounds the intestine.

RECAP 3 major regions of Small intestine:

1:Duodenum: ( 10 inches)

Shortest region of small intestine

Chyme and bile mix completing digestion

2:Jejunum: (3 feet)

Middle section

Serves as primary site of nutrient absorption

3:Ileum: (6 feet)

Final section of small intestine

Empties into large intestine

Completes nutrient absorption

The interior walls of the small intestine are tightly wrinkled into projections called circular folds that greatly increase their surface area. Microscopic examination of the mucosa reveals that the mucosal cells are organized into finger-like projections known as villi, which further increase the surface area. Many villi are present on the surface of intestine. The cells on the surface of the mucosa also contain finger-like projections of their cell membranes known as microvilli, which further increase the surface area of the small intestine. Epithelial cells have a ‘brush like’ border Purpose:

All of these wrinkles and projections help to greatly increase the amount of contact between the cells of the mucosa and chyme to maximize the absorption of vital nutrients.

Each square inch of mucosa contains around 20,000 villi.

It is estimated that there are around 130 billion microvilli per square inch in the mucosa of the small intestine.

Circular folds

Villi

Microvilli

Crypts / glands of Lieberkuhan between villi.

Secretions from the intestine – enzymes and hormones

Digestive enzymes: Small intestine does not secrete any digestive enzymes ( comes from pancreas or found on enterocytes )

Except Enterokinase secreted from Duodenal mucosa

Hormones: secreted from endocrine cells in mucosa

Stimulated by activation of chemoreceptors in response to constituents of food and act to stimulate production of digestive secretions from other organs

Gastrin stomach ,duodenum , pancreas (G cells)

Cholecystokinin pancreas

Secretin pancreas

SECRETIONS OF SMALL INTESTINE( focus: channels and cells ) Secretions are from cells within the crypts of Lieburkuhn and fall into two groups: Secretions into the lumen ( from enterocytes)Secretions into the blood ( from endocrine cells)

Secretion of Bicarbonate

Nature of Secretion: Mucus / alkali secretions : mucosal protection Aqueous secretions :

• Under local nervous control

• Some minor hormonal control

a) Secretin is a peptide hormone that regulates water homeostasis throughout the body, and influences the environment of the duodenum by regulating secretions in the stomach and pancreas. Secretin is produced in the S cells of the duodenum, which are located in the intestinal glands.

b) CCK: Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein.

Summary – Points to remember ! Mucus and fluid :Involved in protection and absorption. Hormones :Control of pancreatic and bile secretions.

HELPFUL REFERENCES !!! Video links:

1) Focuses on Villi and digestion of fats, proteins and carbs inside http://playit.pk/watch?v=P1sDOJM65Bc

2) Focuses on Layers , major parts and nature of secretion in the intestine http://playit.pk/watch?v=xu5jDCX2cHM

3) Intestinal crypt http://playit.pk/watch?v=qq5k1sWqLO0

Article links:

1) Article that has everything related to the small intestine http://www.innerbody.com/image_digeov/dige10-new3.html