Lesson 1: System Integration

Key Idea

The digestive, respiratory, and circulatory systems act as subsystems within the larger machine of the human body. Each has a distinct role: digestion processes food, respiration captures air, and circulation moves materials.

These systems cooperate to solve the problem of distance. Since most cells are far from the stomach or lungs, they rely on this integrated network to transport nutrient and oxygen molecules to them.

Key Idea

The food we eat consists of large molecules like starch and protein. These are too big to enter cells. The digestive system is responsible for solving this problem by breaking these large molecules down.

Through chemical and physical processes, digestion turns food into smaller molecules, such as glucose and amino acids. These smaller units are the perfect size to be absorbed by cells and used for energy and repair.

Key Idea

The respiratory system handles the intake of gases. When we breathe, this system brings air into the lungs and captures oxygen molecules.

Unlike food molecules, oxygen molecules in the air are already small enough to fit into cells. Therefore, the respiratory system does not need to break them down; it simply captures them and prepares them for transport.