Hormones are the smallest elements produced by our body. However, without them, neither the existence of man nor other living systems is 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 the Greek. ὁρΜάω - "excite". These are organic biologically active substances that are produced by the body's own endocrine glands. Entering the bloodstream, binding to the receptors of certain cells, they regulate physiological processes, metabolism.
Protein hormones (like all others) are humoral (carried in the blood) regulators of specific processes occurring in organs and their systems.
Broadest definition: Chemical signaling substances produced by some body cells to affect other parts of the body. Hormones are synthesized by vertebrates, to which we belong (special endocrine glands), and animals that are deprived 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:
- Promotion or inhibition 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, extinction.
- Reproductive cycle control.
- Regulation of satiety and hunger.
- Sex drive call.
- Stimulation of other hormones.
- The most important task is to maintain the body's homeostasis. That is, the constancy of his internal environment.
Varieties of hormones
Since we secrete protein hormones, it means that there is a certain gradation of these biologically active substances. According to the classification, they are divided into the following groups, which differ in their special structure:
- Steroids. These are chemical polycyclic elements having a lipid (fatty) nature. At the heart of the structure is the sterane core. It is it that is responsible for the unity of their polymorphic class. Even the slightest differences in the sterane base will cause differences in the properties of the hormones of this group.
- Derivatives of fattyacids. These compounds are highly unstable. They have a local effect on neighboring cells. The second name is eicosanoids. Divided into thromboxanes, prostaglandins and leukotrienes.
- Derivatives of amino acids. In particular, these are still derivatives of the element tyrosine - adrenaline, thyroxine, norepinephrine. Synthesized (formed, produced) by the thyroid gland, adrenal glands.
- Hormones of protein nature. This includes both protein and peptide, which is why the second name is protein-peptide. These are hormones produced by the pancreas, as well as the pituitary and hypothalamus. Among them, it is important to highlight insulin, growth hormone, corticotropin, glucagon. We will get to know some of the hormones of a protein-peptide nature in more detail throughout the article.
Protein group
Different among all listed in its diversity. Here are the main hormones that "inhabit" it:
- Hypothalamic releasing factors.
- Tropic hormones produced by the adenohypophysis.
- Regulatory substances secreted by the endocrine tissue of the pancreas - glucagon and insulin. The latter is responsible for the proper level of glucose (sugar) in the blood, regulates its entry into muscle and liver cells, where the substance is converted into glycogen. If insulin is not produced or secreted by the body insufficiently, a person develops diabetes mellitus. Glucagon and adrenaline are similar in their action. On the contrary, they increase the amount of sugar in the blood mass,contributing to the breakdown of glycogen in the liver - in this process, glucose is formed.
- Growth hormone. Somatotropin is responsible for both the growth of the skeleton and the increase in the body weight of a living being. Its deficiency leads to an anomaly - dwarfism, excess - to gigantism, acromegaly (disproportionately large hands, feet, head).
Synthesis in the pituitary gland
This organ produces most of the protein-peptide hormones:
- Gonadotropic hormone. Stimulates the processes in the body associated with reproduction. Responsible for the formation of sex hormones in the gonads.
- Somatomedin. Growth hormone.
- Prolactin. Protein metabolism hormone 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
This organ is the synthesis of protein hormones that control carbohydrate metabolism in the body. These are insulin and glucagon already mentioned by us. By itself, this gland is exocrine. It also produces a number of digestive enzymes, which are then passed to the duodenum.
Only 1% of its cells will be in the so-called islets of Langerhans. These include two special types of particles,which function like endocrine glands. They 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 into glycogen in the liver cells. The same hormone is responsible for some processes of proliferation and differentiation in all cells.
Synthesis in the kidneys
This organ produces only one type - erythropoietin. The functions of protein hormones of this group are the regulation of erythrocyte differentiation in the spleen and bone marrow.
As for the synthesis of the protein group itself, this is a rather complicated process. It involves the nervous central system - it works through releasing factors.
Back in the thirties of the last century, the Soviet researcher Zavadovsky M. M. discovered a system that 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 of thyroid-stimulating hormone in the pituitary gland. What do we see here? Plus-action is that thyroid-stimulating hormone will stimulate the production of thyroxine by the thyroid gland. What is the negative action? Thyroxine, in turn, suppresses the production of thyroid-stimulating hormone by the pituitary gland.
As a result of the "plus-minus-interaction" regulation, we note the maintenance of a constant exchange of thyroxine in the blood. With a lack of it, the activity of the thyroid gland will be stimulated, and with an excess, it will be suppressed.
Action of the protein group
Let's now follow the action of protein hormones:
- On their own, they do not penetrate the target cell. Elements find special protein receptors on its surface.
- The latter "recognize" the hormone and bind to it in a certain way.
- The bundle will, in turn, activate an enzyme located on the inside of the cell membrane. Its name is adenylate cyclase.
- This enzyme starts converting ATP into cyclic AMP (cAMP). In other cases, cGMP is obtained in a similar way from GTP.
- cGMP or cAMP will then proceed to the cell nucleus. There it will activate special nuclear enzymes that phosphorylate proteins - non-histone and histone.
- The result is the activation of a certain set of genes. For example, those that are responsible for the production of steroids begin to work in the germ cells.
- The last step of the entire described algorithm is the appropriate differentiation.
Insulin
Insulin is a protein hormone known to almost everyone. And it is no coincidence - it is the most studied today.
Responsible for a multifaceted effect on metabolism in almost all tissues of the body. However, its main purpose is the regulation of blood glucose concentration:
- Increases the permeability of the plasma cell mass to glucose.
- Activates key phases, enzymes of glycolysis - 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 deficiency of insulin leads to the development of type 1 diabetes, relative deficiency leads to the development of type 2 diabetes.
The insulin molecule is formed by two polypeptide chains with 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 by only one amino acid residue, from bovine insulin by three.
Growth Hormone
Somatotropin, growth hormone, growth hormone - these are all its names. Growth hormone is produced by the anterior pituitary gland. It belongs to the polypeptide hormones - also in this group are 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 action.
- Increased protein synthesis and inhibition of its breakdown.
- Helps reduce subcutaneous fat deposits.
- Increases fat burning, aims to equalize the ratio of muscle and fat mass.
- Increases blood glucose levels by acting as an insulin antagonist.
- Participates in carbohydrate metabolism.
- Impact on isletssections of the pancreas.
- Stimulation of calcium absorption by bone tissue.
- Immunostimulation.
Corticohormone
Other names - adrenocorticotropic hormone, corticotropin, corticotropic hormone and so on. Consists of 39 amino acid residues. Produced by basophilic cells of the anterior pituitary gland.
Main functions:
- Control over the synthesis and secretion of hormones of the adrenal cortex, fascicular region. Its targets are cortisone, cortisol, corticosterone.
- Simulates the formation of estrogens, androgens, progesterone.
The protein group is one of the important hormones in the family. It is the most diverse in terms of functions, areas of synthesis.
