How is energy absorbed from nutrients in the digestive system?

Energy is absorbed from nutrients in the digestive system through the process of digestion and absorption.

The process of digestion involves the breakdown of food into smaller molecules that can be absorbed into the bloodstream. This process begins in the mouth, where mechanical digestion (chewing) and chemical digestion (enzymes in saliva) start to break down the food. The food then travels down the oesophagus and into the stomach, where it is further broken down by stomach acid and enzymes.

The partially digested food, now a thick liquid called chyme, moves into the small intestine. Here, it is broken down further by enzymes produced by the pancreas and the walls of the small intestine. These enzymes break down proteins into amino acids, fats into fatty acids and glycerol, and carbohydrates into simple sugars. These smaller molecules can then be absorbed through the walls of the small intestine and into the bloodstream.

The absorption of these nutrients is facilitated by the villi and microvilli, small finger-like projections that line the walls of the small intestine. These structures increase the surface area of the intestine, allowing for more efficient absorption of nutrients. The nutrients are then transported to the liver via the hepatic portal vein, where they are processed and distributed to the rest of the body.

The energy from these nutrients is then used by the body's cells in a process called cellular respiration. During this process, glucose (a simple sugar) is broken down to produce ATP (adenosine triphosphate), the body's main energy currency. This process occurs in the mitochondria of cells and involves three stages: glycolysis, the Krebs cycle, and the electron transport chain.

In summary, the energy from nutrients is absorbed in the digestive system through the processes of digestion and absorption. The nutrients are broken down into smaller molecules that can be absorbed into the bloodstream, transported to the liver, and then distributed to the rest of the body. The energy from these nutrients is then used by the body's cells in the process of cellular respiration to produce ATP.