Metabolism & Nutrition, Part 1: Crash Course Anatomy & Physiology #36

Summary

The episode explains metabolism as the ongoing set of biochemical reactions that lets the body break down food, obtain energy, and build or repair its tissues. Because the body continually replaces worn-out molecules, nutrients from food serve both as raw materials and as fuel.

Metabolism: Building and Breaking Down

Metabolism includes two complementary processes that happen simultaneously:

• Anabolism builds larger, more complex molecules from smaller building blocks. These reactions require energy.
• Catabolism breaks larger molecules down into smaller ones. Breaking chemical bonds can release energy for cellular work, movement, and heat.

The body cycles nutrients through both processes, continually breaking molecules down and rebuilding them.

Six Major Nutrient Groups

• Water makes up the largest share of the body and is vital to its functioning.
• Vitamins do not provide energy or serve as structural building blocks, but they help the body use nutrients and carry out essential processes. Examples include vitamins C and K, as well as some B vitamins.
• Minerals do not provide fuel, but support functions such as bone and tooth structure, hemoglobin, pH balance, and electrical signaling.
• Carbohydrates are a major source of glucose, which cells use to make ATP—the molecule that powers cellular work. Glucose can be stored as glycogen in the liver and muscles or converted into fat. Some cells, including neurons and red blood cells, rely exclusively on glucose for energy.
• Lipids (fats) store energy, cushion organs, carry fat-soluble vitamins, insulate neurons, and help form cell membranes. The body breaks down triglycerides into glycerol and fatty acids, which can be used for energy or rebuilt into other lipids. Omega-3 and omega-6 fatty acids are essential because the body cannot make them.
• Proteins form muscles, connective tissue, channels, pumps, enzymes, and other structures. Digested proteins are broken into amino acids, which cells reassemble into the proteins specified by DNA. The body can make some amino acids, but nine are essential and must come from food. Combining foods such as beans and rice can provide all essential amino acids.

The episode closes by emphasizing that the body depends on all these nutrients, and that metabolism is the continual balance between breaking molecules down and building them back up. The role of carbohydrates in producing energy is introduced as a topic for the next episode.

Speakers and Sources Featured

• Narrator/host: The episode’s presenter, who is not named in the subtitles.
• Dr. Brandon Jackson: Listed as the episode’s consultant, but not identified as a speaking source in the subtitles.
• Episode credits: Written by Kathleen Yale; edited by Blake de Pastino and Nicole Sweeney; directed by Nicholas Jenkins; sound design by Michael Aranda; graphics by Thought Cafe.