What are the three folds of the small intestine called? What is their purpose?

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The small intestine has three main folds that increase its surface area for absorption: plicae circulares, villi, and microvilli.

Step 1: Plicae circulares are large, circular folds of the mucosa and submucosa. These folds slow down the movement of chyme, allowing more time for nutrient absorption.

Step 2: Villi are small, finger-like projections on the surface of the plicae circulares. Each villus contains blood vessels and a lymphatic vessel (lacteal) to absorb nutrients like amino acids, sugars, and lipids.

Step 3: Microvilli are tiny, hair-like structures on the surface of the epithelial cells of the villi. They form the brush border, which contains enzymes that aid in the final stages of digestion and further increase the surface area for absorption.

Step 4: Together, these folds maximize the efficiency of nutrient absorption by significantly increasing the surface area of the small intestine.

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Duodenum

The duodenum is the first section of the small intestine, measuring about 25-30 centimeters long. It plays a crucial role in digestion by receiving chyme from the stomach and mixing it with bile from the liver and pancreatic juices. This combination helps to neutralize stomach acid and further break down food, allowing for nutrient absorption.

Jejunum

The jejunum is the middle section of the small intestine, approximately 2.5 meters long. Its primary function is the absorption of nutrients, including carbohydrates, proteins, and fats. The jejunum has a highly folded inner surface, which increases the surface area for absorption, making it highly efficient in nutrient uptake.

Ileum

The ileum is the final section of the small intestine, about 3-4 meters long. It is primarily responsible for the absorption of vitamin B12 and bile salts, as well as any remaining nutrients not absorbed by the jejunum. The ileum connects to the large intestine at the ileocecal valve, regulating the flow of material into the colon.