Protein hormones: description, properties, functions and structure

Hormones are the smallest elements produced by our body. However, without them, neither human existence nor other living systems are possible. In the article we invite you to get acquainted with one of their varieties - protein hormones. Here are the features, functions and description of these elements.

What are hormones?

Let's start with a key concept. The word comes from Greek. ὁρμάω - "exciting." These are organic biologically active substances that are produced by the body's own glands of internal secretion. Entering the blood, binding to the receptors of certain cells, they regulate physiological processes, metabolism.

Protein hormones (like all others) are humoral (blood-borne) regulators of specific processes that occur in organs and their systems.

The broadest definition: chemical signaling substances produced by one body cell to affect other parts of the body. Hormones are synthesized by vertebrates, which we relate to (special endocrine glands), and animals that are devoid of the traditional circulatory system, and even plants.

The main functions of hormones

These regulators, which include protein hormones, are designed to carry out a number of functions in the body:

• Stimulation or suppression of growth.
• Change of mood.
• Stimulation or suppression of apoptosis - the death of old cells in the body.
• Stimulation and suppression of the functions of the body's defense system - immunity.
• Regulation of metabolism - metabolism.
• Preparing the body for action, physical activity - from running to wrestling and mating.
• Preparing a living system for an important period of development or functioning - puberty, pregnancy, childbirth, fading.
• Reproductive cycle monitoring.
• Regulation of feelings of fullness and feelings of hunger.
• The challenge of sex drive.
• Stimulating the production of other hormones.
• The most important task is to maintain the body's homeostasis. That is, the constancy of its internal environment.

Types of hormones

Since we secrete protein hormones, it means that there is a certain gradation of these biologically active substances. By classification, they are divided into the following groups, distinguished by their special structure:

• Steroids. These are chemical polycyclic elements having a lipid (fat) nature. The structure is based on the steranium core. It is she who is responsible for the unity of their polymorphic class. Even the slightest differences in the steran base will cause differences in the properties of hormones in this group.
• Derivatives of fatty acids. These compounds are distinguished by high instability. They have a local effect on neighboring cells. The second name is eicosanoids. They are divided into thromboxanes, prostaglandins and leukotrienes.
• Derivatives of amino acids. In particular, these are still derivatives of the tyrosine element - adrenaline, thyroxine, norepinephrine. They are synthesized (formed, produced) by the thyroid gland, adrenal glands.
• Hormones of protein nature. This includes both protein and peptide, so the second name is protein-peptide. These are the hormones that the pancreas produces, as well as the pituitary and hypothalamus. Among them, it is important to isolate insulin, growth hormone, corticotropin, glucagon. We will get acquainted with some of the hormones of protein-peptide nature in more detail throughout the article.
  

Protein group

It differs among all of its variety. Here are the main hormones that "inhabit" it:

• Hypothalamic releasing factors.
• Tropic hormones produced by the adenohypophysis.
• The regulatory substances secreted by the endocrine tissue of the pancreas are glucagon and insulin. The latter is responsible for the proper level of glucose (sugar) in the blood, regulates its entry into the muscles and liver cells, where the substance turns into glycogen. If insulin is not produced or insufficiently excreted by the body, a person develops diabetes. Glucagon and adrenaline are similar in effect. On the contrary, they increase the sugar content in the blood mass, contributing to the breakdown of glycogen in the liver - during this process glucose is formed.
• A growth hormone. Growth hormone is responsible for the growth of the skeleton, and for the increase in body weight of a living creature. Its deficiency leads to anomaly - dwarfism, an excess - to gigantism, acromegaly (disproportionately large hands, feet, head).

Synthesis in the pituitary gland

This body produces most of the protein-peptide hormones:

• Gonadotropin hormone. Stimulates the processes in the body associated with reproduction. Responsible for the formation of sex hormones in the gonads.
• Somatomedin. A growth hormone.
• Prolactin. The hormone of protein metabolism is responsible for the functionality of the mammary glands, as well as for their production of casein (milk protein).
• Polypeptide low molecular weight hormones. These compounds no longer affect cell differentiation, but certain physiological processes of the body. For example, vasopressin and oxytocin regulate blood pressure, "monitor" the work of the heart.

Synthesis in the pancreas

In this body, the synthesis of protein hormones that control carbohydrate metabolism in the body occurs. These are insulin and glucagon already mentioned by us. In itself, this gland is exocrine. It also produces a number of digestive enzymes, which then enter the duodenum.

Only 1% of its cells will be part of the so-called islets of Langerhans. These include two distinct species of particles that function as endocrine glands. It is they who produce alpha cells (glucagon) and beta cells (insulin).

By the way, modern scientists already note that the action of insulin is not limited to stimulating the conversion of glucose to glycogen in liver cells. The same hormone is responsible for some processes of proliferation and differentiation in all cells.

Kidney synthesis

In this body, only one species is produced - erythropoietin. The functions of the protein hormones of this group are the regulation of the differentiation of red blood cells in the spleen and bone marrow.

As for the synthesis of the protein group itself, this is a rather complicated process. The central nervous system is involved in it - it acts through releasing factors.

Back in the thirties of the last century, the Soviet researcher M. M. Zavadovsky discovered a system, which he called "plus-minus-interaction." A good example of this law of regulation is based on the synthesis of thyroxine in the thyroid gland and the synthesis in the pituitary of thyroid-stimulating hormone. What do we see here? The plus effect is that thyroid-stimulating hormone will stimulate thyroid production of thyroxine. But what is the negative effect? Thyroxine, in turn, inhibits the production of the thyroid-stimulating hormone by the pituitary gland.

As a result of the regulation of plus-minus interaction, we note the maintenance of a constant thyroxine metabolism in the blood. With its deficiency, the activity of the thyroid gland will be stimulated, and with an excess, it will be suppressed.

The action of the protein group

Let's now follow the action of protein hormones:

1. By themselves, they do not penetrate the target cell. Elements find special protein receptors on its surface.
2. The latter "recognize" the hormone and in a certain way bind to it.
3. The ligament will, in turn, activate the enzyme located on the inside of the cell membrane. Its name is adenylate cyclase.
4. This enzyme begins to convert ATP into cyclic AMP (cAMP). In other cases, similarly, cGMP is obtained from GTF.
5. cGMP or cAMP will then proceed to the cell nucleus. There she will activate special nuclear enzymes, phosphorylating proteins - non-histone and histone.
6. The result is the activation of a specific set of genes. For example, those responsible for the production of steroids begin to work in the germ cells.
7. The last stage of the described algorithm is the corresponding differentiation.

Insulin

Insulin is a protein hormone known to almost every person. And not by chance - he is the most studied for today.

Responsible for the multifaceted effect on metabolism in almost all body tissues. However, its main purpose is to regulate the concentration of glucose in the blood:

• Increases the permeability of the plasma cell mass for glucose.
• It activates key phases, glycolysis enzymes - the process of glucose oxidation.
• Stimulates the formation of glycogen from glucose in special muscle and liver cells.
• Enhances the synthesis of proteins and fats.
• Suppresses the activity of enzymes that break down fats and proteins. In other words, it has both anabolic and anti-catabolic effects.

Absolute insulin deficiency leads to the development of type 1 diabetes mellitus, relative insufficiency leads to the development of type 2 diabetes.

The insulin molecule is formed by two polypeptide chains having 51 amino acid residues: A - 21, B - 30. They are connected by two disulfide bridges through cysteine ​​residues. The third disulfide bond is located in the A chain.

Human insulin differs from pig insulin in just one amino acid residue, from bovine in three.

A growth hormone

Somatotropin, STH, growth hormone are all its names. Growth hormone is produced by the anterior pituitary gland. It belongs to polypeptide hormones - also in this group prolactin and placental lactogen.

The main action is as follows:

• In children, adolescents, young people - acceleration of linear growth due to lengthening of the tubular long bones of the limbs.
• Powerful anti-catabolic and anabolic effects.
• Strengthening protein synthesis and inhibiting its breakdown.
• Contribute to the reduction of subcutaneous fat deposits.
• Enhances fat burning, seeks to even out the ratio of muscle to fat mass.
• Increases blood glucose by acting as an insulin antagonist.
• Participates in carbohydrate metabolism.
• Impact on islet sites of the pancreas.
• Stimulation of bone absorption of calcium.
• Immunostimulation

Corticogormone

Other names - adrenocorticotropic hormone, corticotropin, corticotropic hormone, etc. Consists of 39 amino acid residues. It is produced by basophilic cells of the anterior pituitary gland.

Main functions:

• Control over the synthesis and secretion of hormones of the adrenal cortex, the fascicular region. Its targets are cortisone, cortisol, corticosterone.
• Along the way, it stimulates the formation of estrogens, androgens, and progesterone.

The protein group is one of the important hormones in the family. It is the most diverse in functions, areas of synthesis.