Endocrine System
Endocrine System:
I. ANATOMY AND PHYSIOLOGY OF ENDOCRINE GLANDS
A. Functions
1. Maintenance and regulation of vital functions
2. Response to stress and injury
3. Growth and development
4. Energy metabolism
5. Reproduction
6. Fluid, electrolyte, and acid-base balance
B. Risk factors
C. Hypothalamus
1. Portion of the diencephalon of the brain,
forming the floor and part of the lateral wall of the third ventricle
forming the floor and part of the lateral wall of the third ventricle
2. Activates, controls, and integrates the
peripheral autonomic nervous system, endocrine processes, and many somatic
functions, such as body temperature, sleep, and appetite
peripheral autonomic nervous system, endocrine processes, and many somatic
functions, such as body temperature, sleep, and appetite
D. Pituitary gland
1. The master gland; located at the base of the brain
2. Influenced by the hypothalamus; directly affects the function of the other endocrine glands
3. Promotes growth of body tissue, influences water absorption by the kidney, and controls sexual development and function.
E. Adrenal gland
1. One adrenal gland is on top of each kidney.
2. Regulates sodium and electrolyte balance; affects carbohydrate, fat, and protein metabolism; influences the development of sexual characteristics; and sustains the fight-or-flight response
3. Adrenal cortex
a. The cortex is the outer shell of the adrenal gland.
b. The cortex synthesizes glucocorticoids and mineralocorticoids and secretes small amounts of sex hormones (androgens, estrogens;
4. Adrenal medulla
a. The medulla is the inner core of the adrenal gland.
b. The medulla works as part of the sympathetic nervous system and produces epinephrine and norepinephrine.
F. Thyroid gland
1. Located in the anterior part of the neck
2. Controls the rate of body metabolism and growth and produces thyroxine (T4), triiodothyronine (T3), and thyrocalcitonin
G. Parathyroid glands
1. Located on the thyroid gland
2. Control calcium and phosphorus metabolism; produce parathyroid hormone
H. Pancreas
1. Located posteriorly to the stomach
2. Influences carbohydrate metabolism, indirectly influences fat and protein metabolism, and produces insulin and glucagon
I. Ovaries and testes
1. The ovaries are located in the pelvic cavity and produce estrogen and progesterone.
2. The testes are located in the scrotum, control the development of the secondary sex characteristics, and produce testosterone.
J. Negative-feedback loop
1. Regulates hormone secretion by the hypothalamus and pituitary gland
2. Increased amounts of target gland hormones in the bloodstream decrease secretion of the same hormone and other hormones that stimulate its release.
II. DIAGNOSTIC TESTS
A. Stimulation and suppression tests
1. Stimulation testing
a. In the client with suspected underactivity of an endocrine gland, a stimulus may be provided to determine whether the gland is capable of normal hormone production.
b. Measured amounts of selected hormones or substances are administered to stimulate the target gland to produce its hormone.
c. Hormone levels produced by the target gland are measured.
d. Failure of the hormone level to increase with stimulation indicates hypofunction.
2. Suppression tests
a. Suppression tests are used when hormone levels are high or in the upper range of normal.
b. Agents that normally induce a suppressed response are administered to determine whether normal negative feedback is intact.
c. Failure of hormone production to be suppressed during standardized testing indicates hyperfunction.
B. Radioactive iodine uptake
1. This thyroid function test measures the absorption of the iodine isotope to determine how the thyroid gland is
functioning.
functioning.
2. A small dose of radioactive iodine is given bymouth or intravenously; the amount of radioactivity is measured in 2 to 4
hours and again at 24 hours.
hours and again at 24 hours.
3. Normal values are 3% to 10% at 2 to 4 hours, and 5% to 30% in 24 hours.
4. Elevated values indicate hyperthyroidism, decreased iodine intake, or increased iodine excretion.
5. Decreased values indicate a low T4 level, the use of antithyroid medications, thyroiditis, myxedema, or hypothyroidism.
6. The test is contraindicated in pregnancy.
C. T3 and T4 resin uptake test
1. Blood tests are used to diagnose thyroid disorders.
2. T3 and T4 regulate thyroid-stimulating hormone.
3. Normal values (normal findings vary between laboratory settings)
a. T3: 80 to 230 ng/dL
b. T4: 5 to 12 mcg/dL
c. Thyroxine, free (FT4): 0.8 to 2.4 ng/dL
4. The T3 level is elevated in hyperthyroidism, decreases with the aging process, and may be decreased in hypothyroidism.
5. The T4 level is elevated in hyperthyroidism and decreased in hypothyroidism.
D. Thyroid-stimulating hormone
1. Blood test is used to differentiate the diagnosis of primary hypothyroidism.
2. Normal value is 0.2 to 5.4 microunits/mL (normal findings vary among laboratories).
3. Elevated values indicate primary hypothyroidism.
4. Decreased values indicate hyperthyroidism or secondary hypothyroidism.
E. Thyroid scan
1. A thyroid scan is performed to identify nodules or growths in the thyroid gland.
2. A radioisotope of iodine or technetium is administered before scanning the thyroid gland.
3. Reassure the client that the level of radioactive medication is not dangerous to self or others.
4. Determine whether the client has received radiographic contrast agents within the past 3 months, because these may invalidate the scan.
5. Check with the physician regarding discontinuingmedications containing iodine for 14 days before the test and the need to discontinue thyroid medication before the test.
6. Instruct the client to maintain an NPOstatus after midnight on the day before the test; if iodine is used, the client will fast for an additional 45 minutes after ingestion of the oral isotope and the scan will be performed in 24 hours.
7. If technetium is used, it is administered by the intravenous (IV) route 30 minutes before the scan.