There are no exact reasons of the obesity in general, and especially in childgood obesity. This is a multi-trigger pathology. The essence of the disease is an excessive deposition of adipose tissue in reserve, which is accompanied by numerous metabolic, neurohumoral disorders, and changes in the functioning of internal organs and systems. From the article you will learn what is the role of leptin in the development of childhood obesity.
- How does adipose tissue exist in the body.
- The structure of adipose tissue.
- Control mechanisms of energy balance.
- Obesity problem.
How does adipose tissue exist in the body
Normally, a balance of energy constantly maintains in a body. Its violation leads to obesity. Scientists’ researches have proven that the imbalance of different tissues in the human body due to malnutrition or overeating leads to completely various consequences. Fo example, the skeleton and muscles during starvation or overeating practically do not change their functions, but lipids react very sharply to any changes in the diet. Even +10% increase mortality by more than 20% due to disruption of the heart and blood vessels, the development of diabetes, and the pathology of the digestive system.
Adipose tissue is formed in the fourth month of fetal development. Its basis is adipocytes (lipocytes or fat cells). Their mass is concentrated in the subcutaneous tissue and around the internal organs. The condition of the fat layers is correlated with the number of fat cells and their size. During the first years of life, lipocytes actively grow in number and increase in size: their hyperplasia and hypertrophy occur. By the time of puberty, their number becomes a constant, which is different for each child. Normally, this trend persists throughout life.
Fat cells are more than 80% triglycerides, which are synthesized from dietary fat and stored in the body in this form. Triglycerides are a source of energy; when broken down, they provide more than 90% of all energy reserves in the body. Reproduction and other vital physiological processes are impossible without these cells. Energy stores of liver glycogen and protein are only a small part of the energy reserves that take part in the body’s rapid energy demand during stress or physical exertion.
Adipose tissue performs a number of functions in a human body:
- energy reserve: one kilogram of fat contains almost 9000 kcal;
- protection of internal organs and the digestive tube from injury;
- thermal protection;
- cumulation of fat-soluble vitamins: A, D, E, K;
- function of the endocrine glands.
There are three layers of adipose tissue that have different localization. They are under the muscles (a strategic reserve), around the internal organs and under the skin. In men, the lipid layer is evenly distributed, fairly dense and accounts for up to 20% of body weight. In women, adipose tissue is thicker, the favorite place of localization is the mammary glands, the pelvic region and the thigh.
The structure of adipose tissue
Adipose tissue consists of white and brown adipocytes. Brown cells predominate in children; the body needs them to control heat transfer. In brown fat layers, there are many capillaries and intracellular mitochondria which are known as the powerhouses of cells. They allow the production of a large amount of heat, which, starting from birth, allows babies to adapt to the external environment. White fat is the prerogative of an adult. It controls the balance of energy production and energy consumption. It looks like one big drop of fat in the cell. Brown fat is located intracellularly in the form of many small droplets.
Lipid layers are active metabolites, they are constantly undergoing metabolic processes: the synthesis and hydrolysis of fats, the synthesis of fatty acids, their esterification into triglycerides or neutral fat, accumulation and breakdown to fatty acids, which are used for energy purposes.
The process of fat deposition in cells can be in two ways:
- capture of triglycerides from plasma;
lipogenesis from glucose.
Triglycerides in the bloodstream circulate as part of lipoprotein complexes. In order for fat to get into lipocytes, the latter produce the enzyme lipoprotein lipase. It breaks down triglycerides into free fatty acids. The capture of free fatty acids by the adipose cell occurs with the help of an active specific carrier. Enzyme activity is correlated with insulin, which initiates both the uptake and accumulation of circulating fats in adipose tissue.
Insulin also plays an important role ss for the transformation of fats from glucose and other carbohydrates. Normally, a third of food glucose goes to the synthesis of endogenous fat; in obese children, the amount of glucose for these purposes doubles. In this case, insulin, through enzymes, on the one hand, promotes the deposition of fat in adipose tissue, but at the same time blocks its mobilization.
Abdominal fat is considered as an active hormone-producing organ unlike subcutaneous fat, which accounts for up to 75% of all adipose tissue. Its hormones are involved in the regulation of energy balance, the cardiovascular system, and the endocrine system. Leptin is one of them.
Control mechanisms of energy balance
A person enjoys food. This is provided by several body systems at once: opioid, dopaminergic, and serotonergic. Dopamine levels rise, and dopamine antagonists reduce appetite after eating delicious food. Hypothalamus is the center of energy balance regulation. It contains peptides that control body weight. These are neuropeptide Y (NPU) and agouti-like protein (APP), which stimulate appetite. On the other hand, it is proopiomelanocortin (POMC), which suppresses the food stimulus. Alpha-melanocyte-stimulating hormone (α-MSH), ACTH is involved in the pigmentation of the dermis are formed in the latter. But it also reduces feelings of hunger through melanocortin receptors, makes it actively consume fats and inhibits the accumulation of fat.
These groups of neurons draw information about the energy potential of the body through orexins. One of them is leptin, a hormone produced by subcutaneous fat. It affects the centers of satiety and hunger in the hypothalamus, correlating body weight through a decrease in synthesis and release of NPU. This neuropeptide causes a feeling of hunger. Leptin contacts its receptor (LEPR) in the cells of the hypothalamus and stimulates the expression of various genes, including the POMK gene. The peak of leptin secretion is at noon, the minimum is at night. Leptin is important as a signaling factor in the reproductive system.
Leptin levels rise in parallel with weight gain, reaching a maximum at puberty. Leptin is a trigger that initiates timely puberty. For example, the first menstruation is delayed with its deficiency. Another hormone that controls weight is adiponectin, which increases the sensitivity of tissues to insulin, reduces the concentration of free fatty acids in the liver, and activates their oxidation. The secretion of this hormone in obesity is minimal, but even against this background, adiponectin resistance develops.
It is impossible to forget about resistin, the hormone of insulin resistance. It is an insulin antagonist, but there is no relationship between hormone levels and insulin resistance. This hormone is called ghrelin. This is an orexigen synthesized in the stomach and regulates hunger by stimulating food intake through the hypothalamus.
The problem of extra pounds is becoming an epidemic. About a billion people has met with obesity. More than two billion people will be overweight, and +700 million will be obese in the current decade according to the WHO forecast.
Ten years ago, there were about 30 million overweight children and adolescents in the world, half of them were obese. In Russia, according to statistics, the number of children with overweight was about 10%, and children with obesity were more than 5%. Today, the number of small patients with obesity has increased by 10-15% and has become a socially significant pathology. In most cases, uncontrolled childhood and adolescent obesity progresses in adults.
This is due to a change in lifestyle and stands on the «three pillars»:
- Inactivity: computer, car, urbanization.
- Overeating with unbalanced and irrational nutrition.
- Heredity: today more than 430 genes have been discovered that are markers of obesity.
Thus, taking control of the hypthalamus hormones, which are responsible for the child’s eating behavior, is a paramount task. The main role is given to diet and physical activity. And this is good if the process is physiological and not associated with serious concomitant pathologies. Otherwise, patients need drugs that correct the synthesis and consumption of food hormones.