The first half of this chapter explains how breathing is powered, controlled, and affected by disease.
Videos 51–55 explore the mechanics of respiration, beginning with the diaphragm and intercostal muscles that physically drive inhalation and exhalation. You then examine how the brainstem automatically regulates breathing through neural control and chemical feedback. Common respiratory diseases are introduced to show how airflow and gas exchange can be disrupted. The chapter then transitions into digestion, explaining the overall function of the digestive system and how food intake begins in the mouth through chewing, saliva, and swallowing. Together, these lessons connect respiration, oxygen supply, and the first stages of nutrient processing.
The second half of the chapter follows digestion from the stomach to nutrient absorption and metabolic control.
Videos 56–60 explain how the stomach chemically and mechanically processes food before passing it to the intestines. You then explore the small and large intestines, where nutrients are absorbed and waste is prepared for elimination. The liver and gallbladder are introduced for their roles in fat digestion, detoxification, and nutrient storage. The pancreas shows how digestive enzymes and hormones regulate digestion and blood sugar. Finally, digestion and absorption are brought together to demonstrate how carbohydrates, proteins, and fats are converted into cellular fuel that powers every body system.
This chapter has linked breathing, digestion, and metabolism into a continuous life-support process.
You now understand how respiration supplies oxygen, how digestion breaks down food, and how nutrients are absorbed and distributed as energy for cells. In the next chapter, this knowledge can be extended to metabolism, waste removal, and how the body maintains chemical balance through the urinary and endocrine systems.