In which organs does digestion primarily occur?

Digestion primarily takes place in the mouth, stomach, and small intestines because these organs are crucial for breaking down food into nutrients that the body can absorb.

In the mouth, mechanical digestion begins with chewing, and enzymatic digestion starts with saliva breaking down carbohydrates. As food moves into the stomach, it undergoes further mechanical mixing and is exposed to gastric juices that contain acids and enzymes, permitting the digestion of proteins. The small intestine is where the majority of nutrient absorption occurs, as it receives digestive enzymes from the pancreas alongside bile from the liver. These substances help break down carbohydrates, proteins, and fats into their respective absorbable units, allowing nutrients to enter the bloodstream.

Other options include organs that either play a minor role in digestion or are not involved in the digestive process. The lungs and heart are primarily involved in respiration and circulation, while the pancreas and liver, while important for producing digestive chemicals, are not places where digestion itself occurs. The large intestine is mainly involved in absorbing water and forming waste, but it does not play a primary role in the digestive breakdown of food. Thus, the correct choice emphasizes the key organs where digestion actively takes place.