Where are most macro-nutrients broken down?
A stomach.
B large intestine.
C cecum.
D small intestine.
The correct answer and explanation is:
The correct answer is D) small intestine.
The small intestine is the primary site where most macronutrients are broken down and absorbed. It plays a central role in digestion, specifically in the digestion of proteins, carbohydrates, and fats. Here’s how each macronutrient is processed:
- Proteins: Once proteins enter the stomach, they are partially digested by stomach acids and enzymes, like pepsin. However, most protein digestion happens in the small intestine. Pancreatic enzymes such as trypsin and chymotrypsin break proteins down into smaller peptides and amino acids, which can then be absorbed by the intestinal cells.
- Carbohydrates: In the small intestine, carbohydrate digestion continues with the help of pancreatic amylase. This enzyme breaks down starches into simpler sugars like maltose and dextrins. Further digestion occurs through enzymes located on the surface of the small intestine’s villi, such as sucrase, lactase, and maltase, which break disaccharides into monosaccharides (like glucose). These monosaccharides are then absorbed into the bloodstream.
- Fats: The digestion of fats begins in the stomach with the help of gastric lipase, but most fat breakdown occurs in the small intestine. The liver secretes bile, which emulsifies fats, breaking them down into smaller droplets. Pancreatic lipase then further digests these fats into fatty acids and glycerol, which can be absorbed by the intestinal cells.
The walls of the small intestine are lined with villi and microvilli, which increase surface area and help maximize nutrient absorption. After digestion, the broken-down nutrients enter the bloodstream through capillaries in the villi and are transported to various parts of the body for energy, growth, and repair.
In contrast, the large intestine, cecum, and stomach play more minor roles in digestion compared to the small intestine. The large intestine primarily absorbs water and electrolytes, while the cecum is involved in some fermentation of undigested material. The stomach’s role is mainly to initiate protein digestion and churn food into chyme.