Seminar 2

Question 1

Can you name the three major endogenous energy stores?

Answer 1

Three Major Endogenous Energy Stores
1. Glycogen
2. Triglycerides (fat)
3. Muscle protein (used in energy emergencies)

Question 2

Can you name the organ and specific cells where two important hormones for regulation are secreted?

Answer 2

Insulin
• Secreted by: Beta cells in the pancreas (Islets of Langerhans)
• Glucagon
• Secreted by: Alpha cells in the pancreas (Islets of Langerhans)

Question 3

Can you explain the main action of these two hormones in controlling whether the three endogenous energy stores store or release substrates?

Answer 3

Insulin
Promotes storage of energy after a meal
Increases glycogen synthesis, lipogenesis, protein synthesis
Anabolic

Glucagon
Promotes release of energy during fasting
Stimulates glycogenolysis, lipolysis,
Catabolic

Question 4

Can you describe which specific enzymes the two hormones regulate to direct storage or release - particularly following the consumption of a mixed meal?

Answer 4

Insulin activates and glucagon inhibits:
Glycogen synthase (glycogen synthesis )
Phsophofructokinase-1.(Glycolysis)
Acetyl CoA carboxylase (lipogenesis)

Glucagon activates and Insulin inhibits:

Glycogen phosphorylase (glycogen breakdown)
PEP carboxykinase (gluconeogenesis)
Hormone sensitive lipase (lipolysis)

Question 5

Can you explain the protocol of an oral glucose tolerance test (OGTT)?

Answer 5

Used to assess insulin response and glucose handling

1.	Overnight fast (8–12 hours)
2.	Baseline blood glucose measured
3.	Drink 75g glucose solution (adults)
4.	Blood samples taken at 0, 30, 60, 90, and 120 minutes
5.	Measure plasma glucose at each time point

Question 6

Can you define healthy and unhealthy outcomes of the OGTT?

Answer 6

Healthy Glucose Level
<100 mg/dL (<5.6 mmol/L) when fasted
<140 mg/dL (<7.8 mmol/L) after 2 hours
Unhealthy
≥200 mg/dL (≥11.1 mmol/L) after 2 hours = Diabetes
140–199 mg/dL (7.8–11.0 mmol/L) after 2 hours = Prediabetes
≥126 mg/dL (≥7.0 mmol/L) fasted = Diabetes

Question 7

Can you plot blood concentration of glucose after a mixed meal

Answer 7

Glucose: Sharp rise (30–60 min), then falls as insulin clears it

Question 8

Can you plot blood concentration of chylomicrons after a mixed meal

Answer 8

Chylomicrons: Rise more slowly (~2–3 hours), then decrease as they are cleared

Question 9

Can you plot blood concentration of VLDL after a mixed meal

Answer 9

VLDL: Increases later (3–6 hours), as liver packages leftover carbs into fat

Question 10

Can you plot blood concentration of free fatty acids/NEFA after a mixed meal

Answer 10

NEFA (Free fatty acids): Decrease after the meal due to insulin inhibiting lipolysis

Question 11

Can you explain how the three major endogenous energy stores differ in size (e.g. weight in (kilo)grams of the substrate stored within (not the organs themselves!)) and stored energy (kcal)?

Answer 11

Fat (Adipose Tissue)
• Largest store: ~15 kg in a typical adult.
• Contains about 140,000 kcal, making it the main long-term energy reserve.
• Energy density is about 9 kcal/g of pure fat, but adipose tissue is ~80% fat, so stored energy is about 7.2 kcal/g.
Glycogen (Carbohydrate)
• Much smaller store: ~100 g in liver and ~350–400 g in muscle; total ~500 g.
• Provides about 2,000 kcal.
• Energy density is about 4 kcal/g, but each gram of glycogen is stored with at least 3 g of water, so actual stored substrate is much less than the total wet weight.
Protein (Muscle)
• Usable protein store is about 6 kg (from muscle mass, not total body protein).
• Stores about 24,000 kcal.
• Energy density is roughly 4 kcal/g.
Summary
• Fat: by far the largest and most energy-rich store.
• Protein: substantial but not primarily for energy; used mainly when other stores are depleted.
• Glycogen: smallest, rapidly available, but quickly depleted