How is glycogen typically stored in the body?
a. Half in the liver and half in the muscle cells
b. Three fourths in muscle tissue and one fourth in brain tissue
c. One fourth in the liver and three fourths in the muscle cells
d. Half in the muscle cells, one fourth in the peripheral tissues, and one fourth in the stomach
The correct answer and explanation is :
Correct Answer:
c. One fourth in the liver and three fourths in the muscle cells
Explanation:
Glycogen is a polysaccharide that serves as the primary storage form of glucose in the body. It is primarily stored in the liver and muscle cells, playing distinct physiological roles in each location.
1. Liver Glycogen (≈ 25%)
The liver acts as the central glycogen reservoir, holding about one-fourth of the body’s total glycogen. Liver glycogen is crucial for maintaining blood glucose homeostasis, especially during fasting or periods of low food intake. When blood glucose levels drop, the hormone glucagon signals the liver to break down glycogen into glucose and release it into the bloodstream, ensuring a steady supply of energy to the brain and other organs.
2. Muscle Glycogen (≈ 75%)
Skeletal muscle cells store about three-fourths of the body’s glycogen. Unlike liver glycogen, muscle glycogen is used exclusively for muscle activity and contraction. This stored glycogen provides rapid energy during physical activity, such as exercise or strenuous movements. However, muscle cells lack the enzyme glucose-6-phosphatase, which means they cannot release free glucose into the bloodstream like the liver can. Instead, muscle glycogen is broken down into glucose-6-phosphate and used directly for ATP production in the muscles.
3. Other Sites (Minimal Amounts)
Small amounts of glycogen are found in other tissues such as the brain, kidneys, and adipose tissue, but these stores are minor compared to liver and muscle glycogen.
Importance of Glycogen Storage
- Energy Homeostasis: Ensures a balance between glucose supply and demand.
- Exercise Performance: Provides a rapid source of fuel for muscles during activity.
- Blood Sugar Regulation: The liver helps maintain stable blood glucose levels between meals.
Image Representation of Glycogen Storage
Here is an educational illustration showing glycogen storage in the human body. It highlights the liver (storing 25% of glycogen) and muscle cells (storing 75%), along with arrows indicating glucose release from the liver into the bloodstream and glucose usage in muscles for energy.