Lecture 2 - Metabolism energy balance

What is metabolic adaptation?

Changes in metabolism depending on time since last meal

What are the two major metabolic states?

Absorptive (fed) and postabsorptive (fasted)

What defines the absorptive state?

Nutrients entering the blood from the GI tract

What defines the postabsorptive state?

Energy supplied from breakdown of body stores

How long does the absorptive state last after a meal?

Approximately 4 hours

Which hormone dominates the absorptive state?

Insulin

What is the primary goal of the absorptive state?

Use nutrients for energy and store excess

What happens to glucose in the absorptive state?

Used for ATP or stored as glycogen

What happens to amino acids in the absorptive state?

Used for protein synthesis

What happens to dietary lipids in the absorptive state?

Mostly stored as triglycerides

What carbohydrate process increases in the absorptive state?

Glycogenesis

What lipid process increases in the absorptive state?

Lipogenesis

What protein process increases in the absorptive state?

Protein synthesis

What happens to triglycerides made in the liver?

Transported to adipose tissue via VLDLs

What does the liver do in the absorptive state?

Glycogen synthesis and lipogenesis

What does skeletal muscle do in the absorptive state?

Glucose uptake and protein synthesis

What does adipose tissue do in the absorptive state?

Triglyceride storage

Which hormone stimulates glucose uptake into most cells?

Insulin

Which hormone stimulates glycogen synthesis?

Insulin

Which hormone stimulates fat synthesis?

Insulin

Which hormone stimulates protein synthesis?

Insulin

Which cells take up glucose without insulin?

Hepatocytes and neurons

Which hormone dominates the postabsorptive state?

Glucagon

What is the primary goal of the postabsorptive state?

Maintain blood glucose and supply energy

Why does the postabsorptive state occur?

GI tract lacks nutrients

What process releases glucose from liver glycogen?

Glycogenolysis

What process produces glucose from noncarbohydrate sources?

Gluconeogenesis

What process breaks down triglycerides?

Lipolysis

What process produces ketone bodies?

Ketogenesis

What process breaks down proteins?

Protein catabolism

What does the liver do in the postabsorptive state?

Releases glucose and produces ketone bodies

What does adipose tissue do in the postabsorptive state?

Releases fatty acids and glycerol

What does skeletal muscle do in the postabsorptive state?

Uses fatty acids and releases amino acids

What fuels can the brain use?

Glucose and ketone bodies only

What is fasting?

Going without food for hours to days

What is starvation?

Prolonged fasting for weeks or months

What happens to ketone body production during fasting?

It increases

Why are ketone bodies important during starvation?

They spare glucose and protein

Which organ controls metabolic homeostasis?

Endocrine pancreas

Which two hormones primarily regulate metabolism?

Insulin and glucagon

What determines metabolic control more than absolute hormone levels?

Insulin-to-glucagon ratio

What happens to insulin in the fed state?

Increases

What happens to glucagon in the fed state?

Decreases

What happens to insulin in the fasted state?

Decreases

What happens to glucagon in the fasted state?

Increases

What is energy balance?

Matching energy intake with energy expenditure

What happens when energy intake equals energy output?

Body weight remains constant

What happens when energy intake exceeds output?

Weight gain

What happens when energy output exceeds intake?

Weight loss

What is a calorie?

Energy required to raise 1 g of water by 1°C

How many calories are in a kilocalorie?

1000 calories

How many kcal per gram do carbohydrates provide?

4 kcal/g

How many kcal per gram do proteins provide?

4 kcal/g

How many kcal per gram do fats provide?

9 kcal/g

How many kcal per gram does alcohol provide?

7 kcal/g

What are the two major long-term energy storage molecules?

Glycogen and fat

Why is fat a better long-term energy store?

Higher energy density and less water required

What is ATP used for?

Short-term energy storage

What is metabolism?

All chemical reactions in the body

What are anabolic pathways?

Build large molecules

What are catabolic pathways?

Break down large molecules

Which metabolic state is anabolic?

Absorptive state

Which metabolic state is catabolic?

Postabsorptive state

What are nutrient pools?

Readily available energy sources

What are examples of nutrient pools?

Plasma glucose, free fatty acids, amino acids

What is direct calorimetry?

Measures heat produced by the body

What is indirect calorimetry?

Estimates energy use from gas exchange

What gases are measured in indirect calorimetry?

Oxygen and carbon dioxide

How many kcal are burned per liter of oxygen consumed?

Approximately 4.8 kcal

What is basal metabolic rate (BMR)?

Energy used at rest under standard conditions

Under what conditions is BMR measured?

Quiet, resting, fasting

What is total metabolic rate?

Total energy expenditure per unit time

What contributes to total metabolic rate?

BMR, physical activity, food-induced thermogenesis

What factors influence metabolic rate?

Age, sex, muscle mass, activity, diet, hormones, genetics

Which factors can be voluntarily changed?

Energy intake and physical activity

What is appetite?

Desire for food

What is satiety?

Sense of fullness

Where are appetite and satiety centers located?

Hypothalamus

What neural inputs influence feeding behavior?

Cortex and limbic system

What hormonal inputs influence feeding behavior?

GI peptides and adipose hormones

What is the glucostatic theory?

Blood glucose controls feeding

What is the lipostatic theory?

Body fat regulates feeding via hormones

Which hormone increases hunger and is released from the stomach?

Ghrelin

Which hormone increases appetite and is released from the hypothalamus?

Neuropeptide Y

Which hormone signals satiety and fat stores?

Leptin

Which hormone decreases food intake?

Melanocortins

What determines body temperature?

Balance between heat input, production, and loss

What are the four mechanisms of heat loss?

Radiation, conduction, convection, evaporation

Which heat loss mechanism is most effective?

Evaporation

What produces most internal body heat?

Metabolism

What type of heat production involves muscle contraction?

Shivering thermogenesis

What is nonshivering thermogenesis?

Heat production without muscle contraction

What organ acts as the body’s thermostat?

Hypothalamus

What do peripheral thermoreceptors detect?

Environmental temperature

What do central thermoreceptors detect?

Core body temperature

Which neurons stimulate sweating?

Sympathetic cholinergic neurons

Which neurons cause vasoconstriction?

Sympathetic adrenergic neurons

Which neurons cause shivering?

Somatic motor neurons

What is the goal during high environmental temperature?

Maximize heat loss

What happens to cutaneous blood vessels in heat?

Vasodilation