Hydraulic hormones are hormones involved in the regulation of blood pressure.
“Devote an entire Chapter to a single symptom? – surprised now some readers. – Well, that’s out of the question.…»
In what, in what… in those the most.
The change in blood pressure, mainly-its increase, it is not a symptom, but a separate disease, a formidable complication of other diseases and, if you want with pathos, the true scourge of the XXI century, the most hypodynamic [28] period in the history of mankind.
“Yes we all already know! other readers will say. – Adrenaline narrows blood vessels, so at the time of stress, the pressure rises, cortisol does the same, but glucagon in large doses lowers blood pressure.”
Yes, everything is so – adrenaline and cortisol increase blood pressure, and large doses of glucagon lower it, as they have a relaxing effect on the muscles of the walls of blood vessels.
All right, but said in no way creates an idea of hormonal regulation of blood pressure. It’s like saying, ” Russia is a country where people live and trees grow.” Will you get a full impression of Russia from such a correct explanation? That’s right.
However, if anyone is not interested, you can immediately move on to the next Chapter. You are reading this book for your own pleasure, and not preparing for the exam in endocrinology.
And with those who are interested, let’s look at the causes of high blood pressure.
The first reason is narrowing of blood vessels. Everybody knows that. But what kind of vessels are narrowed, not everyone knows. If the aorta is narrowed? Whether narrowed veins?
No, neither the aorta nor the veins constrict. Narrowing of the aorta, the main and largest blood vessel, is not a disease, but a real disaster for the body. As, however, and narrowing any arteries of – a major or relatively a major blood vessel. And the increase in blood pressure due to the narrowing of peripheral blood vessels (the key word – peripheral) was originally conceived by nature as an adaptive reaction, and not for the sake of disaster. There are cases in life when a sharp increase in blood pressure brings a healthy body benefits. For example – under stress because what is happening redistribution of blood flow (recall that “vasoconstrictor” adrenaline dilates blood vessels of the brain) contributes to the blood supply of the brain. And in General in any hydraulic system regulation of peripheral resistance is important.
Most arteries are generally incapable of either significantly narrowing due to muscle contraction, or subsiding because their walls are thick and elastic.
Vienna is also not taper – not those they have the muscle to do so “sharp” movement. The muscle layer in the walls of the veins is present, but it is very poorly developed. From the point of view of muscular development, veins are real dystrophy.
If someone of the readers thinks that constricts capillaries, something very wrong. Capillary walls are generally devoid of muscle layer, otherwise they could not penetrate any substance, because muscle cells would create a dense impenetrable barrier to ions and molecules.
Narrowed arterioles-small arteries immediately preceding the capillaries. In the walls of arterioles, the muscular layer is developed remarkably, and in General the structure of these walls is such that arterioles can actively change the size of their lumen.
Also narrow (although to a lesser extent than arterioles) small veins, called venules, but the capillaries, as already mentioned, this can not do practically. Therefore, the established expression “narrowing of peripheral blood vessels” is essentially incorrect, since capillaries, along with arterioles and veins belonging to peripheral vessels, are not able to narrow. It would be more correct to speak about narrowing of arterioles and venules, but for some reason in a lexicon including in scientific, peripheral vessels were fixed. Please bear this in mind.
Vessels constrict – resistance in the system increases-pressure rises.
Vessels expand – resistance in the system decreases-pressure decreases.
The second reason is an increase in cardiac output (the so-called minute volume of blood circulation-the amount of blood that the heart pumps per minute). Note that we are talking about the cardiac output, not the heart rate, because in addition to the frequency also matters and the amount of blood emitted by the heart with each contraction. It may be that the heart contracts frequently, but “pumps” blood in small volumes.
The more powerful the pump, the greater the volume of liquid pumped by it, the higher the pressure. That is-blood pressure depends not only on arterioles, but also on the heart. However, an increase in cardiac output is important for increasing blood pressure only in the initial stages of hypertension. The further the disease progresses, the greater the role of peripheral vascular resistance. Over time, hypertension cardiac output even decreases, but the course of the disease is not affected, because it is determined by a greatly increased peripheral resistance.
And now let’s get acquainted with the main “hydraulics” of our body – renin and angiotensin-2.
Renin is a protein that is mainly produced by the special secretory cells of the kidneys. To be more precise, these cells are in the walls of the arterioles of the renal glomeruli (remember, we talked about them). Renin is also produced in other blood vessels, in the brain, in the adrenal glands, in the ovaries, in adipose tissue and in the heart.
Noble don Renino no luck. Quibblers-scientists deny him the right to be called “hormone”, despite the fact that by its origin and nature of action renin is a hormone – produced in one place, enters the blood and is transferred to the place of action. Only here the acts of the renin’t on target cells, and another protein found in blood called “angiotensinogen”. As a result, renin is deprived of the high title of “hormone” and is forced to be called an enzyme. It’s a shame, of course, but nothing can be done about it. But in fact by releasing it into the blood renin can still be attributed to hormones. And the best thing would be to create for him and some of his “relatives”, which we will not touch, a special group of”hormones-enzymes”. Wishing to eliminate injustice can launch in Network appropriate a petition, and we will continue that with renin.
Renin is a very important hormone, and therefore its production is regulated simultaneously by four mechanisms.
The first mechanism – in the renal arterioles there are receptors that detect changes in blood pressure and send signals to the cells that produce renin. Lowering the pressure stimulates the production of renin.
The second mechanism is a change in the concentration of sodium and chlorine ions in the renal tubules. Lowering the concentration of these ions stimulates the production of renin.
The third mechanism is stimulation of renin production by nerves.
The fourth mechanism is the mechanism of negative feedback, in which the angiotensin-2 contained in the blood directly affects the cells that produce renin, inhibiting their function.
Angiotensin-2 is an active hormone that constricts blood vessels and stimulates the production of the hormone aldosterone in the adrenal glands. Angiotensin-2 is formed from the blood glycoprotein angiotensinogen. With the participation of renin, angiotensinogen is converted into angiotensin-1, which, in turn, under the action of a special angiotensin converting enzyme is converted into angiotensin-2.
Here angiotensin-2 no one denies the right to be called a “hormone” because it acts on the cell receptors of the muscles of the walls of arterioles and venules, causing their contraction, that is, narrowing of blood vessels.
But this is not enough for our active angiotensin-2. Along the way, it stimulates the production of aldosterone, which retains sodium ions in the body, that is – increases their concentration in the blood and stimulates the excretion of potassium ions in the urine. It would seem-what nonsense, just two types of ions, two types of substances. But if we remember that sodium ions “attract” water into the blood, increasing the volume of blood and thereby contributing to high blood pressure, the “hypertensive” action of angiotensin-2 will appear before us in all its greatness. Not only does this hormone constrict peripheral vessels, but it also increases blood volume. To increase the pressure on all cylinders, with all available properties!
Aldosterone – is the third hormone-Gidravlik, which can be called the “grandson” of renin and the” son ” of angiotensin-2. I must say that if there were no “kinship” between angiotensin-2 and aldosterone, that is, if angiotensin-2 did not stimulate aldosterone production, the course of hypertension would be milder. But, that have-the have and with those live.
Three hormones-hydraulics conditionally combined into a single renin-angiotensin-aldosterone system (RAAS), regulating blood pressure and the volume of circulating blood in our body.
Here’s another favorite examiner’s question :” is there pressure in the veins?”Constantly and everywhere mentioned blood pressure, so it is likely that the student will answer:” There is no pressure in the veins.” In fact, in the veins, too, there is a certain blood pressure, but it is much smaller than the arterial, strongly depends on the position of the body and physical activity, and its fluctuations do not have such a pathogenic effect on the body, as an increase in blood pressure.
High blood pressure is not just a headache, as some people think. This is a factor that disrupts the work of all organs and can cause strokes, heart attacks, the development of heart and kidney failure.
Acting on the renin-angiotensin-aldosterone system, you can reduce blood pressure. For example, ACE inhibitors widely used nowadays [30] inhibit the action of angiotensin converting enzyme (ACE), thereby suppressing the conversion of biologically inactive angiotensin-1 into a very active angiotensin-2.
Direct stimulating effect on cardiac output by increasing the heart rate have adrenal hormones-adrenaline and norepinephrine, as well as thyroid hormones. Pituitary hormones that stimulate the production of hormones in the adrenal and thyroid glands (thyroid-stimulating and adrenocorticotropic) have an indirect effect on the heart rate (cardiac output).
Adrenaline and norepinephrine also have a vasoconstrictive effect. The same effect is produced in the hypothalamus vasopressin… And you can remember that cortisol increases the sensitivity of vascular receptors to norepinephrine and stimulates the reabsorption of sodium ions into the blood in the kidneys.
The group of hormones, so that there is “group”, say so right – the whole crowd is involved in raising blood pressure.
Who’s in charge of his demotion?
No one?
No, of course not. There is whom and expand vessels, without this cannot be. Vasodilating effect have some prostaglandins, biologically active fat-like substances that are produced in many organs. In the submandibular and pancreatic glands, in the lungs and some other organs, as well as in the blood plasma, a vasodilator of the protein nature bradykinin is produced.
And these are just two examples, vasodilators in our body produces a lot (let’s remember about glucagon). But, unfortunately, their strength is not enough to physiologically prevent the development of hypertension. The ” hydraulics “that increase blood pressure are stronger than the” hydraulics ” that lower it. Unfortunately. The reason for this “inequality” is rooted in the distant primitive past. The fact is that the increase in blood pressure has a mobilizing effect on the body, and the decrease in blood pressure weakens the body – dizzy, weak muscles, and fainting can happen. That’s natural selection, and walked in the direction of increasing pressure. Roughly speaking, individuals prone to its decline, survived less than those who had a tendency to increase. And now humanity would be happy to get rid of such an evolutionary gift, but it is impossible.
Summary
Causes of high blood pressure are narrowing of blood vessels and an increase in cardiac output or minute volume of blood circulation.
Three hormones-renin, angiotensin and aldosterone-are conventionally combined into a single renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and the volume of circulating blood in our body.
Renin is a protein that is mainly produced by special secretory cells located in the walls of the arterioles of the renal glomeruli. Renin is also produced in other blood vessels, in the brain, in the adrenal glands, in the ovaries, in adipose tissue and in the heart. Since renin does not act on target cells, but on another protein contained in the blood and called “angiotensinogen”, it is formally attributed not to hormones, but to enzymes.
With the participation of renin, angiotensinogen is converted into angiotensin-1, which, in turn, under the action of a special angiotensin converting enzyme is converted into angiotensin-2, an active hormone that narrows blood vessels and stimulates the production of the hormone aldosterone in the adrenal glands.
Aldosterone retains sodium ions in the body, that is-increases their concentration in the blood and stimulates the excretion of potassium ions in the urine. Sodium ions “attract” water into the blood, increasing the volume of blood and thereby increasing blood pressure.
Direct stimulating effect on cardiac output by increasing the heart rate have adrenal hormones-adrenaline and norepinephrine, as well as thyroid hormones. Pituitary hormones that stimulate the production of hormones in the adrenal and thyroid glands (thyroid and adrenocorticotropic) have an indirect effect on heart rate (cardiac output). Adrenaline and norepinephrine also have a vasoconstrictive effect. The same effect has produced in the hypothalamus vasopressin.
Vasodilating effect have some prostaglandins, biologically active fat-like substances that are produced in many organs. In the submandibular and pancreatic glands, in the lungs and some other organs, as well as in the blood plasma, a vasodilator of the protein nature bradykinin is produced.
Our body produces other vasodilators. But, unfortunately, their strength is not enough to physiologically prevent the development of hypertension. The ” hydraulics “that increase blood pressure are stronger than the” hydraulics ” that lower it. The reason for this “inequality” is rooted in the distant primitive past. The fact is that the increase in blood pressure has a mobilizing effect on the body, and the decrease in blood pressure weakens the body – dizzy, weak muscles, and fainting can happen. That’s natural selection, and walked in the direction of increasing pressure.