Overview
This lecture covers how the body processes food for energy, focusing on metabolism, nutrient storage, cellular respiration, and the roles of hormones like insulin and glucagon.
Metabolism and Energy Conversion
- Metabolism includes all chemical reactions that build or break down molecules to manage energy.
- The law of conservation of energy states energy cannot be created or destroyed, only changed in form.
- Catabolic reactions release energy from food, while anabolic reactions store it.
- Cellular respiration converts glucose into usable energy (ATP) using oxygen, yielding COâ‚‚ and water.
Nutritional States and Energy Storage
- The absorptive (fed) state occurs during and shortly after eating, when nutrients are abundant.
- Excess carbohydrates and fats are stored as glycogen and triglycerides, respectively.
- ATP is used immediately for energy; it is not stored.
- The basal metabolic rate is the number of calories needed for basic body functions and varies with age, sex, and body composition.
Blood Glucose Regulation
- The body maintains blood glucose between 70-100 mg/dL for optimal function.
- High blood glucose triggers the pancreas to release insulin, which lowers blood sugar by storing glucose as glycogen or fat.
- Insulin shifts the body from catabolic to anabolic processes, like glycogenesis (storing glucose as glycogen) and lipogenesis (storing glucose as fat).
Lipid Transport and Cholesterol
- Fats are transported in blood by lipoproteins, as they are hydrophobic.
- Low-density lipoprotein (LDL) delivers fats to tissues; high-density lipoprotein (HDL) collects cholesterol from the blood for disposal or hormone production.
Postabsorptive State and Glucagon Function
- Several hours after eating, blood glucose drops, triggering glucagon release from the pancreas.
- Glucagon stimulates the breakdown of stored glycogen and fat to raise blood glucose.
- In prolonged fasting, gluconeogenesis converts amino acids and fats into glucose for the brain.
Metabolic Disorders: Diabetes
- Diabetes results from inadequate insulin production or abnormal insulin receptors.
- Without insulin, blood glucose stays high after eating and is excreted in urine, leading to energy loss and potential weight loss.
Key Terms & Definitions
- Metabolism — all chemical reactions in the body for energy management.
- Cellular Respiration — process that converts glucose and oxygen into ATP, CO₂, and water.
- Insulin — hormone that lowers blood glucose by promoting storage.
- Glucagon — hormone that raises blood glucose by releasing stored energy.
- Glycogenesis — process of forming glycogen from glucose.
- Lipogenesis — process of converting glucose into fat.
- Gluconeogenesis — creation of glucose from non-carbohydrate sources.
- Lipoprotein — protein that transports fats in the blood.
- Basal Metabolic Rate (BMR) — minimum calorie requirement for basic bodily functions.
Action Items / Next Steps
- Review the process of cellular respiration and associated metabolic pathways.
- Watch the recommended Crash Course Biology video on cellular respiration for further detail.