THE SMALL INTESTINE
NOTE: The Central Hub of Digestion and Absorption.
The small intestine is the longest part of the gastrointestinal (GI) tract, typically measuring 6-7 meters
(20 feet) in an adult. Despite its name "small," it refers to its diameter (approximately 2.5-3 cm)
compared to the large intestine.
It is the primary site for digestion of food and absorption of nutrients, water, and electrolytes.
Virtually all nutritional absorption occurs here, making it indispensable for life.
1. Anatomy:
wSegmentation and Structure
The small intestine is a convoluted tube extending from the pyloric sphincter of the stomach to the
ileocecal valve, where it joins the large intestine.
It is divided into three sequential regions:
A. Duodenum (∼25 cm, "12 fingers" length):
· Location:
, Retroperitoneal (fixed to the posterior abdominal wall).
· Features:
Receives chyme (partially digested food) from the stomach.
· Critical Inputs:
The hepatopancreatic ampulla (of Vater) delivers bile (from liver/gallbladder) and pancreatic juice
(containing digestive enzymes and bicarbonate) via the major duodenal papilla.
Bicarbonate neutralizes the acidic chyme.
· Function:
Chemical digestion hub. The bulk of enzymatic breakdown occurs here.
· B. Jejunum (∼2.5 meters):
· Location: Intraperitoneal, in the upper left abdomen.
· Features:
Characterized by a rich blood supply, large circular folds, and thick walls.
· Function:
Primary site of nutrient absorption (especially carbohydrates and proteins).
· C. Ileum (∼3.5 meters):
· Location:
Intraperitoneal, in the lower right abdomen.
NOTE: The Central Hub of Digestion and Absorption.
The small intestine is the longest part of the gastrointestinal (GI) tract, typically measuring 6-7 meters
(20 feet) in an adult. Despite its name "small," it refers to its diameter (approximately 2.5-3 cm)
compared to the large intestine.
It is the primary site for digestion of food and absorption of nutrients, water, and electrolytes.
Virtually all nutritional absorption occurs here, making it indispensable for life.
1. Anatomy:
wSegmentation and Structure
The small intestine is a convoluted tube extending from the pyloric sphincter of the stomach to the
ileocecal valve, where it joins the large intestine.
It is divided into three sequential regions:
A. Duodenum (∼25 cm, "12 fingers" length):
· Location:
, Retroperitoneal (fixed to the posterior abdominal wall).
· Features:
Receives chyme (partially digested food) from the stomach.
· Critical Inputs:
The hepatopancreatic ampulla (of Vater) delivers bile (from liver/gallbladder) and pancreatic juice
(containing digestive enzymes and bicarbonate) via the major duodenal papilla.
Bicarbonate neutralizes the acidic chyme.
· Function:
Chemical digestion hub. The bulk of enzymatic breakdown occurs here.
· B. Jejunum (∼2.5 meters):
· Location: Intraperitoneal, in the upper left abdomen.
· Features:
Characterized by a rich blood supply, large circular folds, and thick walls.
· Function:
Primary site of nutrient absorption (especially carbohydrates and proteins).
· C. Ileum (∼3.5 meters):
· Location:
Intraperitoneal, in the lower right abdomen.
