Small Intestine and Its Histology MCQ - Practice Questions with Answers

• The stomach opens into the small intestine through the pyloric orifice.
• The small intestine is the longest and thinnest part of the alimentary canal.
• The average length of the small intestine in an adult human male is 6.9 m and in the adult female 7.1 m.
• Hence, it is highly coiled and occupies the lower part of the abdominal cavity.
• The small intestine is approximately 2.5–3 cm in diameter, and is divided into three sections:
  • Duodenum
  • Jejunum 
  • Ileum 

Layers of Small Intestine:

• The mucosa is made up of simple columnar epithelium. It secretes digestive enzymes and hormones.
• The submucosa is the layer of dense, irregular connective tissue or loose connective tissue that supports the mucosa.
• The muscularis is a region of muscle adjacent to the submucosa membrane. It is responsible for gut movement, or peristalsis. It usually has two distinct layers of smooth muscle: circular and longitudinal.
• The serosa is a smooth membrane consisting of a thin layer of cells that secrete serous fluid and a thin layer of connective tissue. Serous fluid is a lubricating fluid that reduces friction from the movement of the muscularis.
   

Duodenum:

• It follows the stomach and its somewhat C-shaped in structure.
• It curves towards the left. The head of the pancreas fit into the concavity.
• Duodenum is U-shaped in rabbits.
• It receives the hepatopancreatic ampulla (called the ampulla of Vater) of the hepatopancreatic duct. 
• The opening of the ampulla is guarded by the sphincter of Oddi.

Jejunum:

• It is the middle part of the small intestine.
• It follows the duodenum and is about 2.4 m long.
• Its wall is thicker and muscular than ileum.

Ileum:

• It is the lower part of the small intestine.
• It is about 3.5 m long.
• It opens into the large intestine.
   

Circular Folds:

• These are also called folds of Kerckring or plica circulare. 
• These are deep ridges in the mucosa and submucosa.
• They begin near the proximal part of the duodenum and end near the middle of the ileum. 
• These folds facilitate absorption.
• Their shape causes the chyme to spiral, rather than move in a straight line, through the small intestine. 
• Spiraling slows the movement of chyme and provides the time needed for nutrients to be fully absorbed.

Villi:

• These are present within the circular folds.
• These are hairlike vascularized projections that give the mucosa a furry texture.
• There are about 20 to 40 villi per square millimetre, increasing the surface area of the epithelium tremendously.
• In addition to muscle and connective tissue to support its structure, each villus contains a capillary bed composed of one arteriole and one venule, as well as a lymphatic capillary called a lacteal.

Microvilli:

• Microvilli (singular = microvillus) are much smaller (1 μm) than villi.
• They are cylindrical apical surface extensions of the plasma membrane of the mucosa’s epithelial cells and are supported by microfilaments within those cells.
• Due to their presence, the epithelium of intestinal mucosa is called brush-border epithelium.