cause of hyperkalemia is kidney dysfunction in
which the KIDNEYSretain excessive potassium in
the blood. Such dysfunction may develop as a
consequence of RENAL FAILUREor due to endocrine
disorders such as ADRENAL INSUFFICIENCY. Hyper-
kalemia may develop in people who have poorly
controlled DIABETESas a consequence of chroni-
cally elevated blood GLUCOSElevels, which dam-
ages kidney function. Sometimes potassium-
sparing diuretic medications, which doctors may
prescribe to treat HEART FAILURE or HYPERTENSION
(high BLOOD PRESSURE), can result in hyperkalemia.
Moderate to severe hyperkalemia causes ARRHYTH-
MIA(disturbance of the heartbeat).
Weakness and tiredness are the most common
symptoms. The diagnostic path includes blood
tests to measure the level of potassium and other
electrolytes in the blood and ELECTROCARDIOGRAM
(ECG) to evaluate the HEART’S electrical activity.
Treatment consists of appropriate methods to
reduce potassium levels according to the underly-
ing cause. Such methods may include changing
medications or doses for diuretics, HORMONE THER-
APYto supplement adrenal function, reducing con-
sumption of foods high in potassium (such as
bananas, green leafy vegetables, and raisins), or
therapies to improve kidney function. Most people
who have uncomplicated hyperkalemia fully
recover with appropriate treatment.
See also ADRENAL GLANDS; ALDOSTERONE; HYPERAL-
DOSTERONISM.
hypernatremia A circumstance of elevated
sodium in the BLOODcirculation. The most com-
mon cause of hypernatremia is DEHYDRATIONthat
results from prolonged NAUSEA and VOMITING.
Rarely, hypernatremia results from DIABETES
INSIPIDUSor other dysfunctions of ANTIDIURETIC HOR-
MONE(ADH) release from the HYPOTHALAMUSor PITU-
ITARY GLANDthat causes the KIDNEYSto increase the
amount of water they pass from the body. The
concentration of sodium in the blood correspond-
ingly rises.
The primary symptom of hypernatremia is
extreme thirst. As the concentration of sodium
increases symptoms become neurologic and
include confusion and seizures. The diagnostic
path starts with blood tests to measure sodium
and other electrolyte levels in the blood and may
include a water-deprivation test, which measures
the body’s endocrine responses (such as increased
ADH release) to the shift in electrolyte concentra-
tions. Treatment is increased fluid to restore the
appropriate water–sodium balance in the blood.
When the cause is diabetes insipidus or other
ADH-related insufficiency (such as pituitary dys-
function), treatment typically incorporates HOR-
MONE THERAPYwith ADH supplement.
See also ADENOMA; HYPERCALCEMIA; HYPOKALEMIA.hyperparathyroidism A condition in which the
PARATHYROID GLANDSsecrete an excessive amount of
PARATHYROID HORMONE. The four tiny parathyroid
glands are on the back of the THYROID GLAND.
Parathyroid hormone regulates the balance of cal-
cium and phosphorus in the BLOOD. Excessive
parathyroid hormone results in too much calcium
pulled from the bones and absorbed from the gas-
trointestinal tract into the BLOOD circulation
(HYPERCALCEMIA). At the same time blood levels of
phosphorus drop (hypophosphatemia). Phospho-
rus helps retain calcium in the bones and is
important for BONE STRENGTH. Calcium is also
essential for the conduction of NERVEimpulses and
for MUSCLEcontraction. Excessive calcium in the
blood disrupts neuromuscular functions.
The most common cause of hyperparathy-
roidism is an ADENOMA(noncancerous tumor) of a
parathyroid gland. Sometimes the parathyroid
glands enlarge (parathyroid HYPERPLASIA) without
apparent cause. Either circumstance results in
increased secretion of parathyroid hormone.
Symptoms of hyperparathyroidism tend to be
nonspecific and include- weakness and rapid tiring with physical exer-
tion - loss of APPETITE
- lethargy and fatigue
- generalized aches and discomforts
OSTEOPOROSIS may be the first indication of
hyperparathyroidism in many people. Sometimes
conditions such as HYPERTENSION(high BLOOD PRES-
SURE), a consequence of calcium’s actions, or kidney
stones (NEPHROLITHIASIS) reveal the underlying
cause to be hyperparathyroidism. The diagnostic
path includes blood tests to measure the levels of138 The Endocrine System