10. ESSENTIAL HYPERTENSION (EH) Flashcards
ESSENTIAL HYPERTENSION (EH) definition?
This is the most common form of hypertension.
Most of the theories which try to explain the pathogenesis do agree on that there is an disorder in
the blood pressure regulation (this disturbance may probably affect any parts of the regulating
chain), that is due to some internal (endogenous) or external (exogenous) factors. The endogenic
factors are multifactorial, including genetic ones. The exogenous factors are the realizators of the
genetic propensity, and they include primarily a high salt intake, high energy provision and some
psychogenic factors.
Genetic and familiar factors?
It is known, that hypertension usually affects more than one member of the family. The decisive factor yet is considered to be the inheritance of those factors that have some importance in the etiology and the pathogenesis of the
essential hypertension.
can be
noticed also in still healthy normotensive members of hypertensive families:
*There might be some genetically conditioned changes of the metabolism and the release of
catecholamines.
*Fast release of (NE) noradrenalin from the thrombocytes, can be one of the genetic markers (the
place of NE storage are even the thrombocytes).
*Low contents of kalikrein (a depressor factor) was found in some children of hypertensive families.
*Apart from the discovered high systolic and diastolic blood pressure as well as the body weight in
children of the hypertensive families, the have also a significantly low level of plasma aldosterone.
*There is also a genetically based high sensitivity to Na+ expected in the essential hypertensive
people.
*There might be a genetic factor that is expressed even due to stress (e.g. the normotensive people
react differently to various psychogenic stimuli by increasing the blood pressure and a long lasting
increment of the BP.
*Meanwhile there is an intensive study about some enzyme transport systems, mainly for Na+, K+,
Ca2+ (in the kidneys and the vascular wall, in erythrocytes, leukocytes, and lymphocytes).
As markers blood and serum groups are being studied before all. Meanwhile it is the HLA system and
other systems that influence the immunity. For hypertension they are important only for its familiar
predilection and also for prognosis of atherosclerosis development and its complications.
Factors of the external environment
(Salt)?
prevalence of hypertension is
directly related to the amount of salt intake. And partly due to some clinical studies, that refer to that
lowering the blood pressure is parallel with decreasing the extra cellular fluid that may be
accomplished by diet containing markedly low quantities of salt or by continuous diuretic therapy.
Increasing the salt intake will result in increasing the volume of extra cellular fluid. This fact results in
a larger venous return to the heart, that will consequently cause an increase the cardiac output and
due to autoregulation peripheral vessel resistance will be secondarily increased.
During an abnormally high
sodium intake there will be an increase of sodium concentration in the muscle cells of the vascular
wall that will consequently result in the retention of more Ca2+ ions leading to higher vascular wall
sensitivity to vasoconstricting agents.
Factors of the external environment
(Potassium (K+)?
There is a lot of evidence that a high K+ intake is protective against hypertension and
maybe even against other hurtful effects of high sodium intake. High potassium intake results in drop
of the blood pressure.
The combination of low Na+ intake and higher K+ intake is more effective than low Na+ intake alone.
There are many possibilities of the hypotensive effect of potassium:
1. It causes diuresis and hence lowers the plasma volume
2. In patients treated with K+ there is a drop in the body weight and there is a decrease of Na+
content in the organism
3. It inhibits the plasma renin activity
4. It can cause vasodilatation due to a direct effect on the arteriolar smooth muscle.
Factors of the external environment
(Magnesium (Mg2+))?
It was found that adding Mg2+ (in the form aspartate hydrochloride) increases
the depressor effect of the diuretics. Any disturbance of Mg2+ metabolism may result in generalized
muscular contraction and hence affecting the blood pressure. Mg2+ is Na+–K+ ATPase activator and
it is Ca2+ antagonist. When the level of Mg2+ is low it causes an increase of the intracellular Ca2+
concentration and hence promotes vasoconstriction.
Insulin Resistance, Obesity, and the Metabolic Syndrome?
Recent research has suggested that the
hormone insulin may play a role in the development of EH. In many people with hypertension,
especially those who are obese or have type 2 diabetes, there is impaired insulin–dependent
transport of glucose into many tissues (termed insulin resistance).
As a result, serum glucose levels rise, stimulating the pancreas to release additional insulin. Elevated
insulin levels may contribute to hypertension via increased sympathetic activation or by stimulation
of vascular smooth muscle cell hypertrophy, which increases vascular resistance. Smooth muscle cell
hypertrophy may be caused by a direct mitogenic effect of insulin or through enhanced sensitivity to
platelet-derived growth factor.
Obesity itself has been directly associated with hypertension. Possible explanations for this
relationship include (1) the release of angiotensinogen from adipocytes as substrate for the renin–
angiotensin system, (2) augmented blood volume related to increased body mass, and (3) increased
blood viscosity caused by adipocyte release of profibrinogen and plasminogen activator inhibitor 1.
Psychoemotional stress?
In the interaction with other mechanisms the neurovegetative system also
takes part in the regulation of blood pressure. Also its function arises from the basic circulatory
functions – in any case to ensure the supply of oxygenated blood under the required blood pressure
to all organs and tissues according to their actual needs. The CNS reacts to exogenous stressor
factors (stressors of the outside environment) actually via a dual efferent stereotype which affects
also the blood pressure:
1. Activating the sympathetic system that leads to the release of catecholamines from the
adrenal medulla and this is characterized by some known reactions. (a) fight (associated with
vasodilatation in all limbs) (b) flight (vasodilatation only in lower limbs)
2. Activating of the adenohypophysis and via the adrenocorticotropic hormone the stimulation
of the adrenal cortex.
In the initial phase of stress?
In the initial phase of stress there will be an activation of antidiuretic hormone (ADH) that is formed
in the hypothalamus. After its release from the neurohypophysis (where it is only stored) into the
circulation, it acts on the distal and the collecting tubules of the kidneys. Its action lies in enhancing
the reabsorption of water. Apart from this it shares in the modulation of blood pressure. In the
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beginning of the stress situation and as a result of the peripheral vasoconstriction there will be a
lowered renal perfusion that leads to the activation of the rennin – angiotensin I, II, III – aldosterone
system. Aldosterone increases the volume of body fluids by the reabsorption of Na+ and hence water
in the distal tubules. Angiotensin II is a pressor factor. It stimulates vasoconstriction via a direct
mechanism. It enhances the synthesis and the release of noradrenalin from the nerve endings and it
also blocks its uptake by the nerve terminals. Apart from this it stimulates adrenaline and
aldosterone release from the adrenals as well as the vasopressin from the neurohypophysis, what
will consequently lead into increasing the vascular susceptibility to vasoconstricting agents. Along
with the stimulation of the sympathetic nervous system and the adrenal medulla, there will be also
the release of hormones of the anterior lobe of the pituitary (adenohypophysis), from which the
most important one in the stressor situations is the adrenocorticotropic hormone (ACTH). The
accepted fact meanwhile is that a high blood pressure is associated with certain personality
characters as well as with the type of occupation. Apart from this in about 30 % of hypertensive
people we are dealing with a hypertension that is only present at work (white coat office
hypertension). From this point of view there are some interesting studies that classify people
according to their behavior and reactivity into two types: type A and type B. Type A people – who are
predisposed to hypertension are characterized by high agility, ambition, psychological instability that
might turn into aggressively and impulsive behavior, the person is despotic and egocentric. People of
type B are characterized as phlegmatic, psychologically stable, with no personal ambitions.
Hemodynamic changes in essential hypertension?
During the initial stage of the essential hypertension the cardiac output is increased and tachycardia
is present. The causes are due to an increased sympathetico-adrenal activity. It acts directly on
the heart and the vascular structure.
Narrowing the venous field will increase the preload and
could be the primary cause of the increased cardiac output. But more marked hemodynamic changes
can be seen in people with the essential hypertension during the physical activity. During the early
stages of the hypertension there will already be a drop in the cardiac output due to the drop of the
systolic output. However, the resistance of arteries increases.
In patients with long lasting hypertension the high blood pressure is the result of a high
peripheral resistance in case of a low functioning myocardium, or a marked cardiac insufficiency. The
first change occurring in the vessels can be a functional vasoconstriction or some structural changes
in the vascular wall. During vasoconstriction that is caused by a high sympathetic tonus,
concentration of Na+, Ca2+ and water content in the vascular wall also increase. Later on there will
be some structural changes in the wall of the vessels. A thickening due to the hypertrophy of the
media and a hyperplasia of the collagen fibers.
The narrowing of the lumen alone can increase the
peripheral resistance.
The arteriolar vasoconstriction and the vascular resistance do not occur in all the organs equally in the essential
hypertension. The most affected are vessels of the skin and kidneys, whereas the skeletal muscles
are perfused normally.
