The main products deriving from the digestion and intestinal absorption of carbohydrates are glucose , galactose and fructose . Through the mesenteric vein and the portal vein, these sugars reach the hepatic capillaries , where they are retained in large quantities.
It is precisely in the liver that galactose and fructose are converted into glucose, which is, in practice, the only sugar present in the bloodstream. The term glycemia is used to indicate its concentration in the blood . In a healthy person this parameter fluctuates, fasting, between 80 and 100 mg/dl . For the individual to be healthy it is essential that blood sugar remains relatively constant throughout the 24 hours.
At the end of a meal, glycemic values of around 130-150 mg/100 ml are considered physiological. On the other hand, it is normal that during prolonged fasting , or in response to intense physical effort, blood sugar drops to 60-70 mg/dl. When the glucose concentration drops further it is called hypoglycemia , a condition that is accompanied by symptoms such as tremors , palpitations , intense hunger , paleness , drooling and seizures . When blood sugar levels fall below 20 mg/dl, there is even a risk of coma and death.
The importance of circulating glucose in the blood is related to the inability of neurons to draw energy from other energy substrates , such as fats and amino acids . Signs of cerebral suffering are already manifested by glycemic values lower than 60 mg/dl and are responsible for the typical symptomatology previously illustrated.
When blood sugar increases excessively, once the threshold value of 180 mg/dl is reached, the body begins to lose glucose in the urine ( glycosuria ). This, which at first glance might seem like an effective defense mechanism , is actually a dangerous phenomenon, since urine containing glucose attracts a lot of water due to osmotic issues , resulting in body dehydration .
In physiological conditions, glycosuria is equal to 0.
When sugars absorbed from the intestine enter the liver through the portal vein, they can undergo different fates.
First of all, they can be degraded by liver cells to obtain the energy necessary to satisfy the metabolic demands of the hepatocytes.
Glucose can also be converted into glycogen , which is our body’s sugar reserve. A certain amount can also be transformed into triglycerides .
The fate of sugars is heavily conditioned by the nutritional status of the subject.
In response to a particularly carbohydrate -rich meal , the liver attempts to bring blood sugar back to normal:
- converting its metabolism , normally based on the oxidation of fats , with the aim of consuming mainly sugars
- increasing glycogen stores in hepatocytes
- promoting the conversion of glucose into fatty acids
Note: Glycogen, which is reduced to single glucose monomers during fasting, can be stored at most in amounts equal to 5-6% of the liver mass (about 100 grams). Once these stocks are saturated, the liver is forced to convert the excess sugar into reserve adipose tissue . For this reason, a diet low in fat and rich in carbohydrates ( pasta , bread , cereals and derivatives, sweets, etc.) is not effective in promoting the reduction of body weight.
The liver also regulates blood sugar through the intervention of various hormones ; the best known and most influential are called, respectively, insulin and glucagon .
The regulatory action on glycemic values is not entrusted only to the liver; in the same way insulin does not act only on hepatocytes but influences the metabolism of various tissues. In muscle , for example, this hormone favors the entry of glucose which, in addition to being degraded with glycolysis , is transformed into stored glycogen.
Insulin also acts at the level of adipose tissue, increasing glucose uptake and stimulating its deposit in the form of triglycerides.
