Homeostasis, balance of the body’s internal environment
Homeostasis is the equilibrium condition of the body’s internal environment. This balance can suffer a break due to alterations from the external environment. It is said that an organism is in homeostasis when it contains optimal concentrations of gases, nutrients, ions and water;And also when it presents an optimal temperature and pressure. In other words, the conditions regulated by homeostasis are temperature, pressure and chemical composition. The homeostatic interval is the range of values within which the body is in balance. Homeostatic limits, on the other hand, are the highest and lowest value within the homeostatic range or interval.
Fortunately, the body has certain regulation systems that allow to restore the balance of the internal environment. Most of the time, the nervous system (which acts through nerve impulses) and the endocrine system (which acts through hormones), together or independently, implement measures to restore this internal balance, having a connection inthe hypothalamus-hypopysarian axis. These systems are called feedback systems.
Feedback systems
Our body regulates the internal environment through many feedback systems. A feedback system is a cycle of phenomena in which the state of a certain body condition is controlled, evaluated and supervised (controlled condition). Any alteration that causes a change in a controlled condition is called stimulus. There are three basic components in the feedback system.
In the first place is the receiver that consists of a structure of the body that is responsible for detecting changes in the controlled condition and sending information to a control center, such as the brain. This route is called afferent, since the information flows to the control center. Generally, the afferent path is produced in the form of nerve impulses or chemical signals.
Another component is the control center, which establishes the range of values within which a controlled condition must be maintained. This is responsible for evaluating the signals you receive and generate signals when needed. In general, the output or efferent pathway is produced in the form of nerve impulses, hormones or other chemical signals. It is called that since the information leaves the control center.
Finally is the effector that is the structure of the body that is responsible for receiving the efferent signs of the center causing an answer or effect, which will produce a modification in the controlled condition. Most organs or tissues of the human body can function as effectors, causing a response to certain stimuli.
There are two types of feedback systems: negative and positive.
- Negative feedback invests the direction of the initial condition. The body reaction counteracts stress with the aim of reestablishing homeostasis. It is said that it is stimulatory-infection. An example of negative feedback is the regulation of blood pressure. When receptors that detect pressure on the wall of blood vessels detect an increase, they send a message to the brain, which in turn sends messages to effectors, heart and blood vessels. As a result, the frequency of the heart decreases and blood vessels increase its diameter, which causes blood pressure to fall to a value within the interval around the reference value. The same happens if blood pressure decreases, since receptors send a message to the brain, which causes the frequency of the heart to increase and blood vessels decreases in diameter.
- Positive feedback, on the other hand, intensifies the stimulus of the reaction by itself. It is said that it is stimulatory-stimulatory. An example of positive feedback is in the situation where a woman is in labor, but is not producing enough oxytocin. Therefore, oxytocin is provided intravenously, and this stimulates the secretion of this hormone, which allows birth to be carried out.
In the human body, almost all feedback systems are negative, and there are only a few positive feedback systems that are beneficial (such as the one mentioned above).
Homeostatic imbalances
As we said previously homeostasis is a condition in which the internal environment of the organism remains relatively stable.
The body’s ability to maintain homeostasis allows you to cure and resist abuse. The physiological processes responsible for maintaining homeostasis are both responsible for good health. Some of the main health factors are the medium and how it behaves, how genetics and air that breathes, the food it consumes and even its thoughts is formed.
The way of living can favor or interfere negatively with the body’s ability to maintain homeostasis and recover from inevitable stress factors.
There are many diseases that are the result of many years of bad habits that interfere with the natural impulse of the organism to maintain homeostasis. For example, smoking tobacco exposes to the lung tissue sensitive to chemical agents that cause cancer and damage the ability to self-repair the lung. While all the controlled conditions of the body are maintained within the limits, homeostasis will be maintained and the body will be healthy. If the homeostatic imbalance is moderate, a disorder or disease can occur.
A disorder is any abnormality of structure or function, while a disease is a specific term that designates a condition characterized by a recognizable series of signs and symptoms. If it is local it affects a limited region of the body and if it is systematic it affects the entire body or several parts of it.
Any person suffering from a disease can present symptoms, which are subjective changes in bodily functions that are not evident to the observer. The objective changes that a doctor can observe and measure are called signs. The signs of a disease can be anatomical or physiological.
Hypothalamus-hypophysis axis
The hypothalamus-hypophysis axis is made up of the hypothalamus and the pituitary. It is the place where the nervous system is connected to the endocrine system, both anatomically and physiologically.
The pituitary glands has two lobes, a posterior lobe and an anterior lobe (there is an intermediate lobe, but it is not developed in the human being).
Neurohypophysis is the posterior lobe, it is formed by nervous tissue, glies and blood vessels. In the hypothalamus, the large secretory neurons are located in two nuclei called supraoptic and paraventricular, which are endocrine since they secrete hormones. These hormones, which are oxytocin and vasopressin (neurohormones, because they are segregated by neurons) go down the axons and go to neurohypophysis. From there they go to the blood and are transported to the white organs. Oxytocin will perform in the smooth muscles of the hollow organs, and vasopressin or antidiuretic will act in blood vessels and kidneys (controlling blood pressure and diuresis).
The main anatomical relationship between the hypothalamus and the neurohypophysis is that the axons of the great secretory neurons reach the neurohypophysis, through the pituitary stem.
The physiological relationship between these two structures is that hormones (oxytocin and antidiuretic) are synthesized in the hypothalamus by large secretory neurons, and released in neurohypophysis, where they turn to the internal environment to reach the Diana organs.
Adenohypophysis is the anterior lobe, it is formed by epithelial tissue, which is secretory tissue. His cells are very together and does not have blood vessels. Therefore, it has a very vascularized underlying conjunctive fabric to nurture the epithelium. There are chromophobic epithelial cells (which do not secrete) and chromophiles (which secrete hormones).
There are secretory neurons located in the hypothalamus that secrete hypothalamic neurohormones, which are liberating factors and inhibitory factors. These hormones reach adenohypophysis through a portal system (set of venous vessels), which crosses the pituitary stem and will act in the adenohypophysis, stimulating (in case of being liberating factors) or inhibiting (in case of being inhibitors) theHormone secretion in adenohypophysis: growth hormone, prolactin, thyroid stimulant, adrenal cortex stimulant and two gonad stimulants.
The anatomical relationship between the hypothalamus and the adenohypophysis is the Porta system and the pituitary stem.
The physiological relationship between them is that through the Porta the neurohormon system of the hypothalamus they communicate with the epithelial cells of the anterior lobe of the pituitary and stimulate or inhibit them to secrete. These will then go to the capillaries of the secondary plexus of the Porta system, and towards the general circulation. They travel to white tissues.
Control and regulation of homeostasis
Both the nervous system and the endocrine system are responsible for regulating body homeostasis, that is, trying to counteract stress situations.
The nervous system acts through nerve impulses, quickly and immediately. On the other hand, the endocrine system acts through hormones, and has a slow and lasting action. These two are complemented, and are related to the hypothalamus-hydrophysarian axis (previously mentioned).
Hormonal Action Mechanism
The hormonal mechanism, that is, the way of acting of hormones in the white organs, is linked to the presence of receptors and their chemical nature. Depending on these two factors, there are two mechanisms of action.
Mechanism per second messenger
If the hormone is protein nature, it does not cross the white cell membrane.
The hormone, the first messenger, is segregated by an endocrine gland and turns to the internal environment through blood vessels. When the receiver in the membrane captures the hormone, adenylciclase is released, an enzyme that accelerates the process in which ATP degrades to AMPC. The AMPC is the second messenger, a chemical that causes the changes as a result of the arrival of the hormone to the white cell.
GENE ACTIVATION MECHANISM
The mechanism by gene activation is carried out by circulating hormones of a lipid nature. These can cross the cell membrane from their white cells, therefore their receptors are inside (either in the nucleus or in the cytoplasm).
The hormone is segregated by an endocrine gland and turns to the internal environment through blood vessels. When it reaches the white cell, it crosses the membrane. The receiving protein, associated with a DNA molecule, captures the hormone and causes the activation of one or more genes that in turn causes the output of the Nucleus RNA for protein synthesis.
Stress response steps
Stressing stimuli make the body react and that response is physiological. A stress situation triggers these physiological reactions that mean the activation of the vegetative nervous system and the pituitary axisosuprarenal. This aforementioned axis (HSP) is where the nervous system and endocrine system are linked and is composed of the hypothalamus, which is a nervous structure that is at the base of the brain, the pituitary gland, a gland that is located under the brainand by the adrenal glands, which are located at the top of the kidneys, one in each. They are composed of cortex and marrow. The cortex of these glands has three zones, the average is the fascicular zone and segregated glucocorticoids. This hormone in stress situations favors the increase in circulating glucose so that there is energy to solve these situations. Prevents the body from griping and letting it circulate so that it is on hand to combat stress.
With respect to the vegetative nervous system (SNV), this is a set of nerve structures that is responsible for regulating the functioning of internal organs and controls some of their functions involuntarily and unconscious.
These two systems control and produce the release of hormones, which are made by the glands and move through the blood exciting, inhibiting or regulating the activity of the organs.
Stress phases: General Adaptation Syndrome
In different situations when the balance of the organism is affected, it seeks to issue an answer in order to try to adapt. This phenomenon is called the set of physiological reactions triggered by any requirement exerted on the body, due to the incidence of any harmful agent that is called Stressor. It can be defined as the physical and specific response of the organism to any demand or aggression, which can be both physical and psychological. When the organism begins to perform the acceptance process, the phases of alarm, adaptation and exhaustion can be distinguished.
Alarm phase
In a danger situation an alarm reaction occurs in which the resistance low below normal. It is important to note that all the processes that are produced are reactions that prepare the agency for the action of facing a task or effort. It is a short duration phase and is not harmful when the agency has time to recover.
In the first phase the activation of the pituitary axis is given;There is an instant and automatic reaction that consists of a series of symptoms equal but from greater to lower intensity. These are the increase in heart rate, the production of a mobilization of the body’s defenses, the contraction of the spleen (releases numerous red blood cells), the redistribution of blood (abandons the least important points to go to action zones),Increased respiratory capacity, pupil dilation, increased blood coagulation and increased lymphocytes. A psychological activation is also generated, increasing the capacity for attention and concentration.
Resistance or adaptation phase
This phase is called resistance and that is where the body seeks to adapt thanks to the homeostasis process. It is where the body tries to overcome, adapt or face those factors that it perceives as a threat or as a harmful agent. In this phase the following reactions occur, corticosteroid levels are normalized and a disappearance of symptomatology takes place.
Exhaustion phase
This phase occurs when the aggression is repeated frequently or is long -lasting, and when the person’s resources to achieve an adaptation level are not enough, and therefore enters the exhaustion phase. Here a tissue alteration occurs and the pathology called psychosomatic can appear.
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