The Small Intestine and Pancreas: Anatomy, Histology, Motility, and Secretion, Lecture notes of Physiology

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Small intestine

Small Intestine

• Connects the stomach with the large intestine
• It is the major site of digestion
• It is also the major site of absorption
• Specialized structures (villi, microvilli) increase the surface area of the small intestine, aiding absorption.
• The small intestine has three parts (duodenum, jejunum, and ileum)
• The bile duct (from liver) and pancreatic duct (digestive juices) empty into the duodenum.

4. Motility of Small intestine

Types:

• Two basic motility patterns exist segmentation and peristalsis. Significance:
• Motility of the small intestine serves 3 functions:

1. Mixing contents with enzymes and other secretions → help digestion
2. Maximizing exposure of the contents to membranes of intestinal cells → help absorption and digestion.
3. Propulsion of contents into the large intestine. Motility of GIT

• C. Microvilli- microscopic folds on the apical side of the simple columnar epithelial cell in the mucosa.
• The folds increase the surface area of the cell's membrane allowing for greater interaction.
• This is also the area where chemical digestion is completed.
• Intestinal crypts contain cells that produce digestive juice in the small intestine and stem cell replace the epithelium every 3-6 days.
• Duodenal glands also secrete a solution that neutralizes stomach acid.

Villi & Crypts

Ganong, Fig. 26- 27

Vander, Fig. 15- 7

Motility of GIT

1 ~ 5 cm and cutting Segmentation movements

Orad caudad

Peristalsis

Motility of GIT

• The pancreas lies parallel to and beneath the stomach.
• It’s a large compound gland with most of it’s internal structure similar to that of the salivary gland.
• The pancreatic digestive enzymes are secreted by Pancreatic acini and a large volume of sodium bicarbonate solution are secreted by small ductless and larger ducts leading from the acini.

• The combined products of enzymes and sodium bicarbonate flow through a long pancreatic duct that normally joins the hepatic duct immediately before it empts into the duodenum through the papilla vater, surrounded by sphincter of Oddi.

• Blood supply
• Arterial
• Pancreatic branches of splenic artery
• Superior pancreaticoduodenal artery
• Inferior pancreaticoduodenal artery
• Venous
• Drain into splenic, superior mesenteric and portal veins

July 19, 2023 Pancreatic Secretions 20

Pancreatic Cell Types

• Contains endocrine, exocrine and ductal cells
• Endocrine cells
  • Arranged in small islets
    • Secrete insulin, Glucagon, Somatostatin and pancreatic polypeptides