Fate and Utilisation of Glucose in Human Body (With Diagram) | Biology

In this article we will discuss about the fate and utilisation of glucose in human body with the help of suitable diagram.

Although glucose is used up by all tissues, yet the different tissues do not use the carbohydrate in the same manner.

The peculiarities of carbohydrate metabolism of some of the important tissues are given below:

i. In the Skeletal Muscles:

Recent evidence suggests that pyruvic acid and not lactic acid is the end product of the glucose oxidation. It is converted into lactic acid due to certain conditions (anaerobic). Pyruvic acid is finally oxidised into CO₂ and H₂O through an elaborate cycle of chemical reactions known as citric acid cycle or Krebs cycle (Fig. 10.10).

ii. In the Cardiac Muscle:

Although in broad principles, it is similar to that in voluntary muscles yet it varies in certain details. In starvation and in depancreatised animals glycogen in heart increases in amount, whereas, that in the liver and muscles falls. Cardiac muscle utilises lactic acid directly and completely in preference to glucose. Experimentally, it is seen that the dog’s heart can take up about three more lactic acid than glucose from blood.

Adrenaline (epinephrine) has got no effect on cardiac glycogen. Glucose utilisation by the heart of a diabetic animal is less than normal, but as regards lactate, the diabetic heart uses it almost as readily as the normal heart. The rate of usage of glucose by the diabetic heart is increased by insulin whereas it is not in case of lactate.

iii. In the Brain:

The R.Q. value of brain indicates that carbohydrates are utilised by the brain exclusively. The brain forms lactic acid from sugar and oxidises further into lactic acid. Since there is very little glycogen in brain, it was formerly believed that lactic acid was formed directly from blood sugar.

But recent findings indicate that brain uses sugar in the form of galactose only which is locally synthesised from blood glucose and it is from the breakdown of galactose that lactic acid is derived. It is interesting to note that brain tissue is very rich in fat, but it derives its energy from sugar. Brain can synthesise galactose from blood glucose and convert it into cerebroside.

iv. In the Blood:

The red blood corpuscles readily form lactic acid from sugar. The blood lactic acid in resting subjects is supposed to be formed in this way. Lactic acid from muscles enters the blood stream only in heavy muscular exercise. If a sample of blood is kept standing, its glucose content rapidly falls due to the conversion of glucose into lactic acid along with the rise of concentration of lactic acid in blood (glycolysis).

From this fact it is obvious that the blood sample, whose glucose content to be estimated, should be (preferably) freshly collected or otherwise anti-glycolytic preservative treated (in case of old sampe).

v. In other Tissue.