27. Small intestine. Embryonic development. Parts. Duodenum. Macroscopic, microscopic, ultramicro-scopic and functional characteristics. Blood and nerve supply.

SMALL INTESTINE

• The small intestine is the longest part of the digestive system.
• Approximately 3-5 m long and its width is 2-4 cm

* Is the primary site for absorbtion of nutrients from ingested material.

• Extends from the pylorus of the stomach to the ileocaecal junction

Parts:

1. (1) Duodenum
2. (2) Jejunum
3. (3) Ileum

Fixation:

The small intestine is fixed and supported within the abdominal cavity by several structures, preventing excessive movement and ensuring proper function.

1. Mesentry: double layer fold of the peritoneum

The small intestine is connected to the posterior abdominal wall by it.

2. Root of menestry:

• the attachmant of the menestery to the posterir abdominal wall
• extends from the duodenojejunal flexure to the right iliac fossa.

Histology:

4 layers:

1. Mucosa: lined by Simple columnar epithelium. with vilve
2. Submucosa: Connective tissue layer
3. Muscular Externa: smooth muscle layer

• inner (circular)
• outer (longitudinal)

4. Serosa.

DUODENUM

• Originates at the pyloric orifice continues into the jejunum at the duodenojejunal flexure.
• Located at the level of L1-L3
• It length abouth 25-30 cm
• Fixed (retroperitoneal)
• C-shaped.