The Digestive System

The carbohydrates, proteins, and lipids that you eat are not in a usable form for your cells. The digestive system must break down these biomolecules into their simplest form in order to be used by your cells. Digestion is both a chemical and a physical process. Mechanical digestion is a physical change. Mechanical digestion breaks down food into smaller pieces through processes, such as chewing and swallowing. Chemical digestion involves chemical changes. During chemical digestion, chemicals, such as saliva and acid in the stomach, are used to break down food into nutrients the body can utilize. Some organs, such as the liver and pancreas, aid in the digestive process by producing special chemicals called enzymes that are needed to break down the food. The food does not pass through these organs.

Interactive exercise. Assistance may be required. Scroll over each part of the digestive system below to learn more.

The Excretory System

The excretory system or urinary system removes and excretes waste. The excretory system consists of the kidneys, ureter, urinary bladder, and urethra.

Interactive exercise. Assistance may be required. Click on each part of the excretory systems below to learn more.