Homeostasis (from Greek - homois - meaning similar, stasis - duration or state) the unique ability of the system to maintain the stability of the internal environment regardless of the influence of external factors. What is homeostasis? What are the causes of homeostasis disorders?

Homeostasisis nothing but the body's ability to maintain a relative internal balance. Maintaining the internal stability of vital functions requires constant monitoring of the values ​​of the most important system parameters. The human body has about a thousand different control and regulation systems - and life and he alth often depend on their proper functioning.

The most important factors subject to change and precise control include:

  • concentration of chemicals in body fluids (blood or plasma)
  • osmotic pressure,
  • pH of body fluids,
  • blood pressure,
  • body fluid volume,
  • body temperature (in warm-blooded organisms).

Building a cell and maintaining homeostasis

All human systems take part in maintaining proper homeostasis. However, already at the basic level of cell structure, the essential features of maintaining homeostasis at the global level are perfectly visible.

One of the most important organelles necessary to maintain the proper parameters of fluids and pressure is the cell membrane that separates the cell from the external environment. It has the construction of the so-called "Liquid mosaic", where proteins float in a double layer of phospholipid molecules.

Thanks to the complex and polar structure, cell membranes enable the selective transport of various substances, which is carried out both by diffusion - that is, flowing in accordance with the concentration gradient of solutions, but also actively - through proteins.

In turn, thanks to special receptor proteins on the surface of membranes, it is possible to receive information from the outside. The reception of the signal triggers a series of short and long-term reactions, the purpose of which is:

  • activation or deactivation of enzymes,
  • stimulation or weakening of cellular metabolism,
  • expression of genes in the cell nucleus (containing the genetic information necessary for synthesisnew proteins modifying cell metabolism).

In order for cells and entire systems to remain energetically independent, the mitochondria must constantly work.

These tiny organelles act like little energy factories in the cell. Thanks to the special, comb-shaped internal structure of mitochondria, it is possible to carry out a number of processes that make up the so-called intracellular respiration.

In this process, it is possible to produce energy from nutrients (including glucose). It is stored in ATP, which is the universal energy carrier in the cell and is used in hundreds of other reactions. This process is subject to modifications depending on the presence of oxygen.

During intense exercise, our muscles begin to lack essential oxygen - that's why mitochondria "switch" to anaerobic respiration, where lactic acid is formed as a by-product.

It is this mechanism that is responsible for the formation of painful soreness. Despite temporarily unfavorable conditions, the body can still perform work and respond to stimuli.

Brain and homeostasis

The main center controlling all processes in the body is, of course, the brain - and more specifically the nerve centers of the central nervous system (CNS), which receive information from the receptors of the entire body.

The information received is processed mainly in the part of the brain called the hypothalamus. The response to a specific stimulus is passed on through the autonomic nervous system (i.e. the system that conducts nerve impulses to internal organs) and through the endocrine glands.

Chemical transmitters released from neuron endings (acting as transmitters) also play an important role in communication and regulation of internal balance.

One of the most important evolutionary achievements of warm-blooded organisms was independence from dangerous temperature changes in the inhabited environment. It became possible thanks to the development of the brain and the formation of a thermoregulation center located in the hypothalamus.

This medium acts as a sensitive thermostat that, when needed, decides either to increase heat generation or to limit heat loss. It is thanks to this mechanism that we experience chills (i.e. muscle cell contractions that stimulate heat production in skeletal muscles) or narrowing of the subcutaneous vessels.

Other, invisible to the eye changes regulating the body temperature, also controlled by the thermoregulation center are, for example :

  • stimulation of the sympathetic nervous system and secretion of norepinephrine(accelerating, among others, the metabolism of adipose tissue cells),
  • stimulation of the secretion of endocrine glands (e.g. the release of adrenaline which accelerates glucose metabolism),
  • stimulation of the secretion of thyroid hormones.

As can be seen from the example of the thermoregulation center, the control of just one changing parameter in our body (temperature) is a very complex network of interactions of both the nervous and endocrine systems.

Homeostasis as an effect of efficient communication

In the human system, the proper course of almost all functions depends on efficient communication between cells and systems - not only in the immediate vicinity, but also further away.

Such distant communication is possible, among others by secreting active chemicals into body fluids (e.g. blood or cerebrospinal fluid). This is called humoral regulation.

Chemical messengers include hormones that can be produced by the endocrine glands (such as the thyroid gland, pituitary gland or adrenal glands), but also act locally (such as histamine or prostaglandins, acting in allergic reactions) or within a given tissue ( e.g. secretin or gastrin).

The key role hormones play in maintaining homeostasis in the human body can be illustrated by the example of adrenaline - also known as the fear, fight or flight hormone.

Adrenaline is produced by the adrenal medulla in all vertebrates' instantaneous response to the threat. Its most important effects include:

  • faster heart rate,
  • increase in blood pressure,
  • bronchodilation,
  • pupil dilation,
  • stimulation of the central nervous system,
  • increase in blood glucose (by increasing the breakdown of glycogen in the liver).

All these reactions are aimed at putting the body in a state of "readiness", which in the course of evolution protected the individual from eating or motivated to escape efficiently.

Feedback in maintaining homeostasis

In higher organisms, the functioning of some systems is under constant control by others. Such a complex control system is the basis for maintaining homeostasis.

Most of the human physiological processes are regulated thanks to the so-called feedback. Unlike unidirectional control (both nervous and humoral) - where information is transmitted in only one direction between two organs, there is a two-way transmission of information in the feedback system.

In the feedback loopfeedback, the action of one organ affects the stimulation of another, and this in turn sends information that inhibits the activity of the first (negative feedback).

Negative feedbackis the most common type of parameter regulation in the human body. An example of such a loop can be, for example, the secretion of thyroid hormones.

Thyroid hormones (T3 and T4) - in general - increase metabolism and control the function of most tissues. Their operation is necessary for the proper functioning of many systems and functions of our body.

The work of the thyroid gland is in turn regulated by the pituitary gland and another hormone - thyrotropin (TSH), which stimulates the thyroid gland to produce hormones. With an increased concentration of T3 and T4, the concentration of TSH decreases, while with a deficiency of these two hormones - the concentration of TSH increases. This type of regulation protects the body against excessive production of substances, acting as a natural brake.

Positive feedbacksoccur much less frequently and involve speeding up the production of a specific product. A good example of such a mechanism in mammals is e.g. lactation.

Suckling the mother's breast by the baby stimulates the production of prolactin, which results in increased milk production.

The more milk there is, the more willing the baby is to eat, which increases the production of milk. When you stop breastfeeding, your prolactin levels will decrease and milk secretion will stop.

What are the effects of disturbed homeostasis?

The described examples of physiological regulations ensure not only the proper functioning of organs and internal systems. Maintaining homeostasis enables the body to adapt to changes in the conditions of the surrounding environment.

It was probably one of the key abilities of the human species that has provided it with unprecedented evolutionary success over the centuries. Wavering and damaging regulatory mechanisms is the most common cause of many human diseases.

Disturbances in parameters, the values ​​of which will exceed certain established critical thresholds, may lead to the death of the organism. Although each of us has an individual predisposition to tolerate certain factors (which results, among others, from genetic conditions), such inter-individual differences are small.

What can affect homeostasis disorders?

Examples of such factors include:

  • genetic defects,
  • congenital defects in the structure of organs,
  • environmental pollution,
  • no exercise,
  • inappropriate diet,
  • chronic stress.

Though onwe have no influence on genetic conditions or environmental factors, but it is worth taking care of the correct body weight, physical fitness and the right dose of relaxation.

Let's not forget that our body is a kind of "connected vessel system", where the balance of the whole consists of the proper functioning of all individual systems.

Category:

Genetic diseases