What is glycogen in human body?

During and immediately after a meal, glucose is converted in the liver into the storage polysaccharide glycogen by a process known as glycogenesis.

Although the total quantity of glycogen in the human body is low, considerably less than one-tenth percent of the total body weight, its role is primarily that of a storage carbohydrate, similar to the role of starch in plants cells. It occurs predominantly in the liver where it is important in the homeostatic mechanism regulating glucose level of the blood.

Glycogen is a branched chain polymer of 6,000 to 30,000 glucose units, that contains two types of glycosidic linkages, extended chains of alpha1-- 4 linked glucose residues with alpha 1-- 6 branches spaced about every four to six residues along the alpha 1-- 4 chain. It is similar to amylopectin in structure but is more highly branched. The average chain length is only 10 to 24 glucose units with 3 to 4 glucose units between branching points.

The highly branched structure of glycogen makes it possible for several glucose residues to be released at once to meet energy needs. 

Glycogen is stored in two tissues. In the liver, glycogen is stored for the short-termed maintenance of blood glucose. In muscle, glycogen is stored as a source of energy. Muscle glycogen is estimated to have a molecular weight of about 1000000 where as the liver of glycogen molecule is much larger, approximately 5 X 1000000. Both molecules, however, constantly change in size as glucose molecules are added or removed.

Glycogen plays an important role in the glucose cycle. The release of glycogen stored in the liver is triggered by low levels of glucose in blood. Liver glycogen breaks down to glucose-6-phosphate, which is hydrolyzed to give glucose.

The release of glucose from the liver by these breakdowns of glycogen replenishes the supply of glucose in the blood.

The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted.

Several hereditary defects have been identified in the synthesis and catabolism of glycogen including: Gierke’s disease, Type II glycogen disease, Type III glycogen, Type IV disease, and McArdle’s disease.
What is glycogen in human body?

Iodine deficiency disorder

The importance of iodine as an essential element arises from the fact that it is a constituent of the thyroid hormones thyroxine and triiodothyronine.

These hormones are essential for normal growth and physical and mental development in animals and man.

Iodine deficiency occurs worldwide and is a public health problem in 130 countries.

Deficiency arise when dietary iodine intake does not meet requirements. The diet is likely to be deficient whenever the soil content of iodine is low, which is often the case in mountainous regions.

The most severe deficient soils are those of the European Alps, the Himalayas, the Andes and the vast mountains of China.

Iodine deficiency leads to inadequate production of thyroid hormone that indispensible for brain growth and development.

The iodine deficiency disorders consist of wide spectrum, including mental retardation, impaired physical development, increased prenatal and infant mortality, hypothyroidism, cretinism and goiter.

The most visible manifestation of iodine deficiency is goiter. Goiter is defined as an enlargement of the thyroid gland and cretinism is a term used for a severe form of iodine deficiency characterized by severe mental retardation.

The most severe damage due to iodine deficiency occurs from the fetal period to the third month after birth, during which iodine deficiency can produce cretinism, an irreversible form of mental retardation.
Iodine deficiency disorder