Essential hypertension
Encyclopedia
Essential hypertension is the form of hypertension
that by definition, has no identifiable cause. It is the most common type of hypertension, affecting 95% of hypertensive patients, it tends to be familial and is likely to be the consequence of an interaction between environmental
and genetic
factors. Prevalence
of essential hypertension increases with age
, and individuals with relatively high blood pressure
at younger ages are at increased risk for the subsequent development of hypertension.
Hypertension can increase the risk of cerebral, cardiac, and renal events.
A recent classification recommends blood pressure criteria for defining normal blood pressure, prehypertension
, hypertension (stages I and II), and isolated systolic hypertension, which is a common occurrence among the elderly. These readings are based on the average of seated blood pressure readings that were properly measured during 2 or more office visits. In individuals older than 50 years, hypertension is considered to be present when a person's blood pressure is consistently at least 140 mmHg systolic or 90 mmHg diastolic. Patients with blood pressures over 130/80 mmHg along with Type 1
or Type 2
diabetes
, or kidney disease
require further treatment.
Resistant hypertension is defined as the failure to reduce blood pressure to the appropriate level after taking a three-drug regimen. Guidelines for treating resistant hypertension have been published in the UK, and US.
s have been identified.
Hypertension may be secondary to other diseases but over 95% of patients have
essential hypertension which is of unknown origin. It is observed though that:
More than 50 genes have been examined in association studies with hypertension, and the number is constantly growing. One of these genes is the angiotensinogen (AGT) gene, studied extensively by Kim et al. They showed that increasing the number of AGT increases the blood pressure and hence this may cause hypertension. Twins have been included in studies measuring ambulatory blood pressure; from these studies it has been suggested that essential hypertension contains a large genetic influence. Supporting data has emerged from animal studies as well as clinical studies in human populations. The majority of these studies support the concept that the inheritance is probably multifactorial or that a number of different genetic defects each has an elevated blood pressure as one of its phenotypic expressions. However, the genetic influence upon hypertension is not fully understood at the moment. It is believed that linking hypertension-related phenotypes with specific variations of the genome may yield definitive evidence of heritability. Another view is that hypertension can be caused by mutations in single genes, inherited on a Mendelian basis.
Hypertension can also be age related, and if this is the case, it is likely to be multifactorial. One possible mechanism involves a reduction in vascular compliance due to the stiffening of the arteries. This can build up due to isolated systolic hypertension with a widened pulse pressure. A decrease in glomerular filtration rate is related to aging and this results in decreasing efficiency of sodium excretion. The developing of certain diseases such as renal microvascular disease and capillary rarefaction may relate to this decrease in efficiency of sodium excretion. There is experimental evidence that suggests that renal microvascular disease is an important mechanism for inducing salt-sensitive hypertension.
Obesity
can increase the risk of hypertension to fivefold as compared with normal weight, and up to two-thirds of hypertension cases can be attributed to excess weight. More than 85% of cases occur in those with a Body mass index
greater than 25. A definitive link between obesity and hypertension has been found using animal and clinical studies; from these it has been realized that many mechanisms are potential causes of obesity-induced hypertension. These mechanisms include the activation of the sympathetic nervous system as well as the activation of the renin–angiotensin-aldosterone system.
Another risk factor is salt (sodium) sensitivity which is an environmental factor that has received the greatest attention. Approximately one third of the essential hypertensive population is responsive to sodium intake. When sodium intake exceeds the capacity of the body to excrete it through the kidneys, vascular volume expands secondary to movement of fluids into the intra-vascular compartment. This causes the arterial pressure to rise as the cardiac output increases. Local autoregulatory mechanisms counteract this by increasing vascular resistance to maintain normotension in local vascular beds. As arterial pressure increases in response to high sodium chloride
intake, urinary sodium excretion increases and the excretion of salt is maintained at expense of increased vascular pressures. The increased sodium ion concentration stimulates ADH
and thirst mechanisms, leading to increased reabsorption of water in the kidneys, concentrated urine
, and thirst with higher intake of water. Also, the water movement between cells and the interstitium plays a minor role compared to this.
The relationship between sodium intake and blood pressure is controversial. Reducing sodium intake does reduce blood pressure, but the magnitude of the effect is insufficient to recommend a general reduction in salt intake.
Renin
elevation is another risk factor. Renin is an enzyme
secreted by the juxtaglomerular apparatus
of the kidney and linked with aldosterone
in a negative feedback loop. In consequence, some hypertensive patients have been defined as having low-renin and others as having essential hypertension. Low-renin hypertension is more common in African American
s than white American
s, and may explain why African Americans tend to respond better to diuretic therapy than drugs that interfere with the Renin-angiotensin system
.
High renin levels predispose to hypertension by causing sodium retention through the following mechanism: Increased renin → Increased angiotensin II → Increased vasoconstriction
, thirst/ADH
and aldosterone
→ Increased sodium
reabsorption in the kidney
s (DCT and CD) → Increased blood pressure.
Hypertension can also be caused by Insulin resistance
and/or hyperinsulinemia
, which are components of syndrome X
, or the metabolic syndrome
. Insulin
is a polypeptide hormone
secreted by cells in the islets of Langerhans
, which are contained throughout the pancreas
. Its main purpose is to regulate the levels of glucose
in the body antagonistically
with glucagon
through negative feedback
loops. Insulin also exhibits vasodilatory properties. In normotensive individuals, insulin may stimulate sympathetic activity without elevating mean arterial pressure. However, in more extreme conditions such as that of the metabolic syndrome
, the increased sympathetic neural activity may over-ride the vasodilatory effects of insulin.
It has been suggested that vitamin D deficiency
is associated with cardiovascular risk factors. It has been observed that individuals with a vitamin D deficiency have higher systolic and diastolic blood pressures than average. Vitamin D inhibits renin secretion and its activity, it therefore acts as a "negative endocrine regulator of the renin-angiotensin system". Hence a deficiency in vitamin D leads to an increase in renin secretion. This is one possible mechanism of explaining the observed link between hypertension and vitamin D levels in the blood plasma
.
Also, some authorities claim that potassium might both prevent and treat hypertension.
Recent studies claims that obesity is a risk factor for hypertension because of activation of the renin-angiotensin system
(RAS) in adipose tissue
, and also linked renin-angiotensin system
with insulin resistance
, and claims that any one can cause the other.
Cigarette smoking, a known risk factor for other cardiovascular disease, may also be a risk factor for the development of hypertension.
Cardiac output
and peripheral resistance
are the two determinants of arterial pressure. and so blood pressure
is normally dependent on the balance between
cardiac output and peripheral resistance. Cardiac output is determined by stroke volume
and heart rate
; stroke volume is related to myocardial contractility
and to the size of the vascular compartment
. Peripheral resistance is determined by functional and anatomic changes in small arteries and arterioles.
The pathophysiology of essential hypertension is an area of research, and until now remains not well understood, but many theories have been proposed to explain this.
What is known is that cardiac output
is raised early in the disease course, with total peripheral resistance
(TPR) normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:
It is also known that hypertension is highly heritable and polygenic (caused by more than one gene) and a few candidate genes
have been postulated in the etiology of this condition.
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
that by definition, has no identifiable cause. It is the most common type of hypertension, affecting 95% of hypertensive patients, it tends to be familial and is likely to be the consequence of an interaction between environmental
Environment (biophysical)
The biophysical environment is the combined modeling of the physical environment and the biological life forms within the environment, and includes all variables, parameters as well as conditions and modes inside the Earth's biosphere. The biophysical environment can be divided into two categories:...
and genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
factors. Prevalence
Prevalence
In epidemiology, the prevalence of a health-related state in a statistical population is defined as the total number of cases of the risk factor in the population at a given time, or the total number of cases in the population, divided by the number of individuals in the population...
of essential hypertension increases with age
Ageing
Ageing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...
, and individuals with relatively high blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
at younger ages are at increased risk for the subsequent development of hypertension.
Hypertension can increase the risk of cerebral, cardiac, and renal events.
Classification
Prehypertension
Prehypertension is an American classification for cases where a person's blood pressure is elevated above normal but not to the level considered to be hypertension . The seventh report of the Joint National Committee proposed a new definition of blood pressure values below 140/90 mm Hg...
, hypertension (stages I and II), and isolated systolic hypertension, which is a common occurrence among the elderly. These readings are based on the average of seated blood pressure readings that were properly measured during 2 or more office visits. In individuals older than 50 years, hypertension is considered to be present when a person's blood pressure is consistently at least 140 mmHg systolic or 90 mmHg diastolic. Patients with blood pressures over 130/80 mmHg along with Type 1
Diabetes mellitus type 1
Diabetes mellitus type 1 is a form of diabetes mellitus that results from autoimmune destruction of insulin-producing beta cells of the pancreas. The subsequent lack of insulin leads to increased blood and urine glucose...
or Type 2
Diabetes mellitus type 2
Diabetes mellitus type 2formerly non-insulin-dependent diabetes mellitus or adult-onset diabetesis a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. Diabetes is often initially managed by increasing exercise and...
diabetes
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
, or kidney disease
Nephropathy
Nephropathy refers to damage to or disease of the kidney. An older term for this is nephrosis.-Causes:Causes of nephropathy include administration of analgesics, xanthine oxidase deficiency, and long-term exposure to lead or its salts...
require further treatment.
| Classification | Systolic pressure | Diastolic pressure | ||
|---|---|---|---|---|
| mmHg | kPa Pascal (unit) The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre... (kN/m2) |
mmHg | kPa (kN/m2) | |
| Normal | 90–119 | 12–15.9 | 60–79 | 8.0–10.5 |
| Prehypertension | 120–139 | 16.1–18.5 | 81–89 | 10.8–11.9 |
| Stage 1 | 140–159 | 18.7–21.2 | 90–99 | 12.0–13.2 |
| Stage 2 | ≥160 | ≥21.3 | ≥100 | ≥13.3 |
| Isolated systolic hypertension |
≥140 | ≥18.7 | <90 | <12.0 |
| Source: American Heart Association (2003). | ||||
Resistant hypertension is defined as the failure to reduce blood pressure to the appropriate level after taking a three-drug regimen. Guidelines for treating resistant hypertension have been published in the UK, and US.
Risk factors
Hypertension is one of the most common complex disorders. The etiology of hypertension differs widely amongst individuals within a large population. And by definition, essential hypertension has no identifiable cause. However, several risk factorRisk factor
In epidemiology, a risk factor is a variable associated with an increased risk of disease or infection. Sometimes, determinant is also used, being a variable associated with either increased or decreased risk.-Correlation vs causation:...
s have been identified.
Hypertension may be secondary to other diseases but over 95% of patients have
essential hypertension which is of unknown origin. It is observed though that:
- Having a personal family history of hypertension increases the likelihood that an individual develops HPT.
- Essential hypertension is four times more common in black than white people, accelerates more rapidly and is often more severe with higher mortality in black patients.
More than 50 genes have been examined in association studies with hypertension, and the number is constantly growing. One of these genes is the angiotensinogen (AGT) gene, studied extensively by Kim et al. They showed that increasing the number of AGT increases the blood pressure and hence this may cause hypertension. Twins have been included in studies measuring ambulatory blood pressure; from these studies it has been suggested that essential hypertension contains a large genetic influence. Supporting data has emerged from animal studies as well as clinical studies in human populations. The majority of these studies support the concept that the inheritance is probably multifactorial or that a number of different genetic defects each has an elevated blood pressure as one of its phenotypic expressions. However, the genetic influence upon hypertension is not fully understood at the moment. It is believed that linking hypertension-related phenotypes with specific variations of the genome may yield definitive evidence of heritability. Another view is that hypertension can be caused by mutations in single genes, inherited on a Mendelian basis.
Hypertension can also be age related, and if this is the case, it is likely to be multifactorial. One possible mechanism involves a reduction in vascular compliance due to the stiffening of the arteries. This can build up due to isolated systolic hypertension with a widened pulse pressure. A decrease in glomerular filtration rate is related to aging and this results in decreasing efficiency of sodium excretion. The developing of certain diseases such as renal microvascular disease and capillary rarefaction may relate to this decrease in efficiency of sodium excretion. There is experimental evidence that suggests that renal microvascular disease is an important mechanism for inducing salt-sensitive hypertension.
Obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
can increase the risk of hypertension to fivefold as compared with normal weight, and up to two-thirds of hypertension cases can be attributed to excess weight. More than 85% of cases occur in those with a Body mass index
Body mass index
The body mass index , or Quetelet index, is a heuristic proxy for human body fat based on an individual's weight and height. BMI does not actually measure the percentage of body fat. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing...
greater than 25. A definitive link between obesity and hypertension has been found using animal and clinical studies; from these it has been realized that many mechanisms are potential causes of obesity-induced hypertension. These mechanisms include the activation of the sympathetic nervous system as well as the activation of the renin–angiotensin-aldosterone system.
Another risk factor is salt (sodium) sensitivity which is an environmental factor that has received the greatest attention. Approximately one third of the essential hypertensive population is responsive to sodium intake. When sodium intake exceeds the capacity of the body to excrete it through the kidneys, vascular volume expands secondary to movement of fluids into the intra-vascular compartment. This causes the arterial pressure to rise as the cardiac output increases. Local autoregulatory mechanisms counteract this by increasing vascular resistance to maintain normotension in local vascular beds. As arterial pressure increases in response to high sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
intake, urinary sodium excretion increases and the excretion of salt is maintained at expense of increased vascular pressures. The increased sodium ion concentration stimulates ADH
Vasopressin
Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
and thirst mechanisms, leading to increased reabsorption of water in the kidneys, concentrated urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
, and thirst with higher intake of water. Also, the water movement between cells and the interstitium plays a minor role compared to this.
The relationship between sodium intake and blood pressure is controversial. Reducing sodium intake does reduce blood pressure, but the magnitude of the effect is insufficient to recommend a general reduction in salt intake.
Renin
Renin
Renin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...
elevation is another risk factor. Renin is an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
secreted by the juxtaglomerular apparatus
Juxtaglomerular apparatus
The juxtaglomerular apparatus is a microscopic structure in the kidney, which regulates the function of each nephron. The juxtaglomerular apparatus is named for its proximity to the glomerulus: it is found between the vascular pole of the renal corpuscle and the returning distal convoluted tubule...
of the kidney and linked with aldosterone
Aldosterone
Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
in a negative feedback loop. In consequence, some hypertensive patients have been defined as having low-renin and others as having essential hypertension. Low-renin hypertension is more common in African American
African American
African Americans are citizens or residents of the United States who have at least partial ancestry from any of the native populations of Sub-Saharan Africa and are the direct descendants of enslaved Africans within the boundaries of the present United States...
s than white American
White American
White Americans are people of the United States who are considered or consider themselves White. The United States Census Bureau defines White people as those "having origins in any of the original peoples of Europe, the Middle East, or North Africa...
s, and may explain why African Americans tend to respond better to diuretic therapy than drugs that interfere with the Renin-angiotensin system
Renin-angiotensin system
The renin-angiotensin system or the renin-angiotensin-aldosterone system is a hormone system that regulates blood pressure and water balance....
.
High renin levels predispose to hypertension by causing sodium retention through the following mechanism: Increased renin → Increased angiotensin II → Increased vasoconstriction
Vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
, thirst/ADH
Vasopressin
Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
and aldosterone
Aldosterone
Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
→ Increased sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
reabsorption in the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
s (DCT and CD) → Increased blood pressure.
Hypertension can also be caused by Insulin resistance
Insulin resistance
Insulin resistance is a physiological condition where the natural hormone insulin becomes less effective at lowering blood sugars. The resulting increase in blood glucose may raise levels outside the normal range and cause adverse health effects, depending on dietary conditions. Certain cell types...
and/or hyperinsulinemia
Hyperinsulinemia
Hyperinsulinemia, or hyperinsulinaemiais a condition which there is excess levels of insulin circulating in the blood than expected relative to the level of glucose. While it is often mistaken for diabetes or hypoglycaemia, hyperinsulinemia can result from a variety of metabolic diseases and...
, which are components of syndrome X
Metabolic syndrome
Metabolic syndrome is a combination of medical disorders that, when occurring together, increase the risk of developing cardiovascular disease and diabetes. It affects one in five people in the United States and prevalence increases with age...
, or the metabolic syndrome
Metabolic syndrome
Metabolic syndrome is a combination of medical disorders that, when occurring together, increase the risk of developing cardiovascular disease and diabetes. It affects one in five people in the United States and prevalence increases with age...
. Insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
is a polypeptide hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
secreted by cells in the islets of Langerhans
Islets of Langerhans
The islets of Langerhans are the regions of the pancreas that contain its endocrine cells. Discovered in 1869 by German pathological anatomist Paul Langerhans at the age of 22, the islets of Langerhans constitute approximately 1 to 2% of the mass of the pancreas...
, which are contained throughout the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
. Its main purpose is to regulate the levels of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
in the body antagonistically
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...
with glucagon
Glucagon
Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...
through negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
loops. Insulin also exhibits vasodilatory properties. In normotensive individuals, insulin may stimulate sympathetic activity without elevating mean arterial pressure. However, in more extreme conditions such as that of the metabolic syndrome
Metabolic syndrome
Metabolic syndrome is a combination of medical disorders that, when occurring together, increase the risk of developing cardiovascular disease and diabetes. It affects one in five people in the United States and prevalence increases with age...
, the increased sympathetic neural activity may over-ride the vasodilatory effects of insulin.
It has been suggested that vitamin D deficiency
Hypovitaminosis D
Hypovitaminosis D is a deficiency of Vitamin D. It can result from: inadequate nutritional intake of vitamin D coupled with inadequate sunlight exposure , disorders that limit vitamin D absorption, and conditions that impair the conversion of vitamin D into active metabolites including certain...
is associated with cardiovascular risk factors. It has been observed that individuals with a vitamin D deficiency have higher systolic and diastolic blood pressures than average. Vitamin D inhibits renin secretion and its activity, it therefore acts as a "negative endocrine regulator of the renin-angiotensin system". Hence a deficiency in vitamin D leads to an increase in renin secretion. This is one possible mechanism of explaining the observed link between hypertension and vitamin D levels in the blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
.
Also, some authorities claim that potassium might both prevent and treat hypertension.
Recent studies claims that obesity is a risk factor for hypertension because of activation of the renin-angiotensin system
Renin-angiotensin system
The renin-angiotensin system or the renin-angiotensin-aldosterone system is a hormone system that regulates blood pressure and water balance....
(RAS) in adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
, and also linked renin-angiotensin system
Renin-angiotensin system
The renin-angiotensin system or the renin-angiotensin-aldosterone system is a hormone system that regulates blood pressure and water balance....
with insulin resistance
Insulin resistance
Insulin resistance is a physiological condition where the natural hormone insulin becomes less effective at lowering blood sugars. The resulting increase in blood glucose may raise levels outside the normal range and cause adverse health effects, depending on dietary conditions. Certain cell types...
, and claims that any one can cause the other.
Cigarette smoking, a known risk factor for other cardiovascular disease, may also be a risk factor for the development of hypertension.
Pathophysiology
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
and peripheral resistance
Total peripheral resistance
Vasculature throughout the entire body can be thought of as two separate circuits - one is the systemic circulation, while the other is the pulmonary circulation. Total peripheral resistance is the sum of the resistance of all peripheral vasculature in the systemic circulation...
are the two determinants of arterial pressure. and so blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
is normally dependent on the balance between
cardiac output and peripheral resistance. Cardiac output is determined by stroke volume
Stroke volume
In cardiovascular physiology, stroke volume is the volume of blood pumped from one ventricle of the heart with each beat. SV is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood in the ventricle at the end of a beat from the volume...
and heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
; stroke volume is related to myocardial contractility
Contractility
Myocardial contractility is the intrinsic ability of the heart to contract independent of preload and afterload. Changes in the ability to produce force during contraction result from different degrees of binding between myosin and actin filaments...
and to the size of the vascular compartment
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
. Peripheral resistance is determined by functional and anatomic changes in small arteries and arterioles.
The pathophysiology of essential hypertension is an area of research, and until now remains not well understood, but many theories have been proposed to explain this.
What is known is that cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
is raised early in the disease course, with total peripheral resistance
Total peripheral resistance
Vasculature throughout the entire body can be thought of as two separate circuits - one is the systemic circulation, while the other is the pulmonary circulation. Total peripheral resistance is the sum of the resistance of all peripheral vasculature in the systemic circulation...
(TPR) normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:
- An overactive Renin-angiotensin systemRenin-angiotensin systemThe renin-angiotensin system or the renin-angiotensin-aldosterone system is a hormone system that regulates blood pressure and water balance....
leads to vasoconstrictionVasoconstrictionVasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
and retention of sodium and water. The increase in blood volume leads to hypertension. - An overactive sympathetic nervous systemSympathetic nervous systemThe sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
, leading to increased stress responses.
It is also known that hypertension is highly heritable and polygenic (caused by more than one gene) and a few candidate genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
have been postulated in the etiology of this condition.