and internal carotid arteries. The chemoreceptors have a dual purpose in that they help
to regulate blood pressure in addition to the regulation of blood pressure. The change
in blood pressure they produce is due mainly to the change in heart rate. Working in
conjunction with the chemoreceptors is a mechanism known as the CNS ischemic
response. The CNS ischemic response senses an increase in carbon dioxide and lactic
acid (both waste products of metabolism) in the blood and reacts to increase or
decrease heart rate to maintain these products within normal amounts. The CNS
ischemic response generally decreases the heart rate so that blood spends a longer
time in the lungs thereby allowing for an increased exchange of oxygen and carbon
dioxide.
c. Correction of Blood Pressure. Blood pressure is corrected by changing
blood vessel tone and cardiac output. The baroreceptors eventually adapt to whatever
pressure level to which they are exposed. Therefore, prolonged regulation of arterial
pressure requires other control systems. Kidney malfunctions, fluid shifts, and
electrolyte imbalances will eventually occur if this condition is not corrected. These are
also known as long term regulators.
d. Renal Fluid-Volume Mechanism. The renal fluid-volume mechanism is one
of the long-term regulators located in the kidneys. This mechanism works by causing
changes in the amount of water reabsorbed by the kidneys. An increase in water
reabsorption leads to an increase in blood pressure and a decrease in water
reabsorption leads to a corresponding decrease in the blood pressure. The secretion of
certain hormones also affects blood pressure. Aldosterone, a hormone secreted by the
adrenal cortex, leads to an increase in sodium retention. This increase in sodium
retention leads to a corresponding increase in water retention with an overall effect of
higher blood pressure.
2-10.
ABNORMAL BLOOD PRESSURE
a. Hypertension. Hypertension is characterized by a persistent increase in
blood pressure. It should be noted that there are always periodic increases in blood
pressure due to times of stress or physical exertion. However, if the blood pressure
remains at these high levels serious complications could result. Some of the effects of
hypertension on the body are frequent nosebleeds, strokes, hypertrophy of the
myocardium, and arteriosclerosis. Hypertension is one of the easiest disorders to treat
if it is detected early. Drug therapy consists of diuretics and other antihypertensives. It
is essential for the patient who has controlled his blood pressure by the use of
medication to continue to take that medication even after the outward signs and
symptoms subside.
b. Hypotension. Hypotension is defined as persistent and abnormal low
blood pressure. This condition is not usually fatal in itself; however, the hypotensive
patient is much more susceptible to shock in case of a rapid loss of blood. Many times
low blood pressure is observed in persons who exercise a great deal. When
hypotension becomes serious, it can be treated by drug therapy. Effects of hypotension
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