Where does nutrient absorption primarily take place?
A.
Mouth
B.
Small intestine
C.
Large intestine
D.
Stomach
The Correct Answer and Explanation is:
The correct answer is B. Small intestine.
Explanation:
Nutrient absorption primarily takes place in the small intestine, which is the most important part of the digestive system for this function. The small intestine is a long, coiled tube about 20 feet in length in adults, and it is divided into three sections: the duodenum, jejunum, and ileum.
- Duodenum: The first part of the small intestine, the duodenum, receives partially digested food (chyme) from the stomach. Here, the chyme mixes with bile from the liver and gallbladder and pancreatic juice from the pancreas. These secretions contain enzymes and other substances that further break down proteins, carbohydrates, and fats into smaller molecules.
- Jejunum: In the second section, the jejunum, the majority of nutrient absorption occurs. The walls of the jejunum are lined with villi, small finger-like projections that increase the surface area available for absorption. Each villus is covered with even smaller hair-like structures called microvilli, creating a brush border that allows for the efficient absorption of nutrients. The cells on the surface of the villi absorb digested nutrients like amino acids, simple sugars, and fatty acids into the bloodstream.
- Ileum: The final section of the small intestine, the ileum, continues the process of absorption, particularly of vitamin B12, bile salts, and any remaining nutrients. The ileum also contains lymphoid tissue called Peyer’s patches, which play a role in immune function.
In contrast, the other parts of the digestive system have different roles:
- Mouth: The mouth initiates digestion by mechanically breaking down food and mixing it with saliva, which contains enzymes like amylase that begin the digestion of carbohydrates.
- Stomach: The stomach primarily functions to break down proteins and churn food into a semi-liquid form called chyme, which is then passed to the small intestine.
- Large intestine: The large intestine primarily absorbs water and electrolytes, and compacts the remaining indigestible food into feces for elimination.
Therefore, the small intestine is where the majority of nutrient absorption occurs, making it essential for providing the body with the nutrients it needs to function.