Uncontrolled high blood pressure, hypertension, is one of the leading causes of
disability or death due to stroke, heart attack, heart failure and kidney
failure. High blood pressure has been described as "the silent killer"
because it often occurs without symptoms. Headaches, blurred vision, nosebleeds,
or dizziness may occur, but these symptoms are not specific to high blood
pressure. Everybody has, and needs blood pressure. Without it, blood cannot
circulate through the body. And without circulating blood, vital organs cannot
get the oxygen and food that they need to work. So it's important to know the
role of blood pressure, and the organs and systems that help regulate it. The
explanation of blood pressure begins with the cardiovascular system, the system
responsible for circulating blood through the heart and blood vessels. When the
heart beats, a surge of blood is released from the left ventricle, which is the
heart’s main pumping chamber, into an intricate web of blood vessels that
spread throughout the body. The arteries are the blood vessels that carry
nutrients and oxygenated blood from the heart to the body’s tissues and
organs. The largest artery, aorta, is connected to the left ventricle and serves
as the main channel for blood leaving the heart. The aorta branches off into
smaller arteries, which turn into even smaller arteries, called arterioles. (1)
Within the body’s tissues and organs are microscopic blood vessels called
capillaries. The capillaries exchange nutrients and fresh oxygen from the
arterioles for carbon dioxide and other waste products produced by our cells.
This "used" blood is sent back to the heart through a system of blood
vessels called veins. When it reaches the heart, blood from the veins is routed
to the lungs, where it releases carbon dioxide and picks up a new supply of
oxygen. This freshly oxygenated blood is sent back to the heart, ready to begin
a new journey. Other waste products are removed as blood passes through the
kidneys. (1) To keep this process working and all of the 11 pints of blood in
our body moving, a certain amount of pressure is required. Blood pressure is the
force that’s exerted on the artery walls as blood passes through. This force
helps keep blood in the arteries flowing smoothly. Several factors help control
blood pressure and keep it from increasing too high or decreasing too low. They
include three major organs; heart, arteries, and kidneys. When the heart
releases blood into the aorta, a certain amount of force is created by the
pumping action of the heart muscle. The harder the heart muscle has to work to
release blood, the greater the force exerted on the arteries. To assist the
surge of blood coming from the heart, the arteries are lined with smooth muscles
that allow them to expand and contract as blood flows through. The more
"elastic" the arteries are, the less resistant they are to the flow of
blood and the less force exerted on their walls. When arteries lose their
"elasticity" or become narrowed, resistance to blood flow increases
and additional force is needed to push blood through the vessels. (1) The
kidneys regulate the volume of water circulating in the body and the amount of
sodium the body contains. More sodium in the body means that more water is
retained in the circulation and may cause an increase in blood pressure. More
sodium in the body also may increase the tendency for blood vessels to narrow.
The central nervous system, hormones, and enzymes are other factors that also
influence blood pressure. Within the walls of the heart and several blood
vessels, are tiny structures called baroreceptors. The baroreceptors’ job is
to monitor the pressure of blood through the arteries and veins. If a change is
noticed, the baroreceptors send signals to the brain; to slow down or speed up
the heart rate, or to widen or narrow the arteries to keep the blood pressure
within a normal range. (1) The brain reacts on the messages from the
baroreceptors, by signaling the release of hormones and enzymes that affect the
functioning of the heart, blood vessels, and kidneys. Epinephrine, adrenaline,
is one of the most significant hormones to affect blood pressure. Epinephrine is
released during high periods of stress or tension. The release of Epinephrine,
causes the arteries to narrow and heart contractions become stronger and rapid,
increasing the pressure on the arteries. Blood pressure is the measure of the
force generated by the heart against the artery walls. This force is expressed
as two numbers, such as 110 over 80 mm Hg (millimeters of mercury). The first
number, the "systolic" blood pressure, represents the amount of force
used by the heart to initially fill the blood vessel circuit; the second number,
the "diastolic" blood pressure, is a measure of the resistance to that
force. Combined, these numbers give a picture of how hard the heart is working
to get blood to the tissues in the body. High blood pressure, is blood pressure
that consistently reads above 140 over 90 mm Hg. There are 3 separate stages of
high blood pressure, based on increased severity. They are simple referred to as
stages 1, 2, and 3. Among people whose blood pressure is uncontrolled, about 75
percent, have stage 1 high blood pressure. About 20 percent of people have stage
2, and about 5 percent have stage 3 high blood pressure. (2) High blood pressure
causes undue stress to the circulation of key organs, particularly the brain,
heart and kidneys. This leads to increased risk of stroke, heart attack and
kidney failure. High blood pressure also can cause an aneurysm, a small
balloon-like weakening of the artery wall, which can be life-threatening. Nearly
one-third of the people affected by high blood pressure do not even know they
have it. They may go for years without knowing it. Among people who are aware of
their condition, only about half are being treated. And even fewer, only about
one-quarter of the people with high blood pressure, have their blood pressure
under control. High blood pressure can occur in children or adults, but is
particularly prevalent in blacks, middle-aged and elderly people, obese people,
heavy drinkers and individuals who are taking oral contraceptives. Hypertension
can be especially hard to manage when combined with other disorders, such as
diabetes or obesity. The more you know about blood pressure, hopefully, the more
willing you will be to take the necessary steps to lower your blood pressure and
keep it under control.

Bibliography

1. Sheldon G. Sheps, M.D. Mayo Clinic on High Blood Pressure; 1999 Mayo Clinic
Research and Development



2. American Heart Association, About High Blood
Pressure; 1999