Messenger substances are signaling substances that serve to transmit signals and information between organisms or between the cells of an organism. In this process, the signaling substances fulfill different functions. Disruptions in signaling within an organism can lead to significant health problems.
What are second messengers?
Messenger substances represent differently structured chemical substances that transmit signals between organisms or between the cells of an organism in different ways. They are chemically completely different substances or groups of substances. They are usually classified according to their function or effect. There are sliding transitions in the classification, which are often very arbitrary. Thus, compounds that perform similar functions can have completely different chemical structures. Every organism, whether plant, animal or human, sends out messengers and at the same time receives messengers. The same applies to every cell within an organism. With regard to their function, messenger substances are divided into hormones, kairomones, neurotransmitters, parahormones, pheromones or phytohormones. According to their mode of action, a distinction is also made between intraspecific and interspecific signal substances. Intraspecific messengers exchange information within the species, while interspecific signaling agents are responsible for interspecies communication. Thus, intraspecific agents are referred to as pheromones. The interspecific messengers are known as allochemicals. However, pheromones and allochemicals comprise only the part of the signaling substances that cause communication between organisms. Hormones and neurotransmitters, in turn, transmit signals between cells or even within cells of an organism.
Anatomy and structure
Among the most important messengers within the organism are hormones. They control metabolic processes in the body. In the process, they are either transferred from cell to cell or pass from a hormone-producing organ (endocrine gland) to a target organ via the blood or serum. There are also hormones that exert their effect within the cell where they are formed. The common feature of all hormones is that they perform control and regulatory functions within the organism. Chemically, they are completely heterogeneous. There are steroid hormones, steroid-like hormones, peptide hormones and hormones with a different chemical structure. Parahormones, on the other hand, control bodily functions but do not fulfill all the criteria of hormones. Parahormones include, for example, carbon dioxide, which is involved in the control of respiratory functions. Neurotransmitters are another group of important messenger substances. They are the signal substances of the nervous system and exert their effect by binding to so-called receptors. Their effect is limited to the nerve cells. Pheromones as another group of signal substances are emitted by an organism and received again by an organism of the same species. Allochemicals are messenger substances emitted by one organism and received by an organism of another species.
Functions and roles
The only common property of all second messengers is their function of transmitting information and thereby triggering reactions at the target site. However, the form of information transmission and the chemical structure of the signaling substances differ seriously. Hormones have the task of directing and controlling metabolic processes and regulatory mechanisms within the organism. In doing so, they are largely responsible for the function of the individual organs. Among other things, they regulate growth, mineral balance, blood sugar levels, sexual functions, energy metabolism and even the function of other hormones within the organism. Neurotransmitters have a localized effect on the nervous system. They excite and inhibit nerve cells and ensure the transmission of stimuli. They exert their effect by docking to special receptors. Among other things, they produce feelings of happiness, suppress pain or generate reactions to certain stimuli. Well-known neurotransmitters are the endorphins or the cytokines. Pheromones in turn control the behavior of the organisms of a species. Among other things, they also influence how people live together. Sympathy and antipathy also develop on the basis of pheromones.Allochemicals are messenger substances that influence the behavior of organisms of different species.
Diseases
Because of the diverse functions of messenger substances, disturbances in their interaction can cause serious health problems. In particular, dysregulation in the endocrine system leads to hormone-related diseases. Hyperfunctions or hypofunctions of individual endocrine organs develop typical symptoms. Insulin, for example, regulates the blood sugar level. Insulin deficiency leads to diabetes mellitus. The thyroid gland produces the thyroid hormones thyroxine and triiodothyronine. They regulate energy metabolism. In the case of hyperthyroidism, metabolism accelerates dramatically, while hypothyroidism leads to a slowing of metabolism with the formation of depression, fatigue and poor performance. If the adrenal cortex produces too much cortisol, the typical symptoms of Cushing’s syndrome appear with truncal obesity, full moon face, increased blood sugar level and weakening of the immune system. If even superordinate organs of the endocrine system become diseased, complex disease processes often occur due to the failure of several hormones at the same time. A typical example is panhypopituitarism. In this case, the anterior pituitary gland becomes diseased and all seven hormones produced there may fail. If the mother’s pituitary gland is destroyed during the birth of a child, the so-called Sheehan syndrome develops. It is not only a hormone deficiency or surplus that can lead to disease. Misregulations in the function of neurotransmitters are also often the cause of severe diseases. These are usually neurological or psychological disorders. Depression is often caused by a deficiency of dopamine. Its binding to receptors may also be disturbed. On the other hand, dysregulation of neurotransmitters can also cause such diseases as Parkinson’s disease or epilepsy.
