My reason in writing this article is to present the structures of Adrenal Cortex and the different laboratory tests that are used in determining the hormones vital in our body. Through the used of the knowledge that I gain from different references, I want to share some important facts that can be useful not only for medical students but also for those who has concern about their health.
What comes to your mind when you heard these words: Adrenal glands, Adrenal Cortex, and hormones? Do you know that there are present laboratory tests in determining if your hormones function well or if your body is capable of responding in stress? For us to well understand my topic, let us discuss the answers for these questions.
What is an Adrenal Gland?
When you heard Adrenal Glands (also known as suprarenal glands or adrenals, we might think about stress. And yes, we are correct. Adrenal glands secretes hormones that are capable of preparing our body when it encounters stressful situation and also, in maintaining our blood pressure.
The Adrenal gland has two parts; the outer part which is the Cortex, and the inner part which is the Medulla. And as one of the purpose of this discussion, the structure of adrenal cortex which is divided in three regions and the hormones they secrete are presented in the succeeding paragraph.
Adrenal cortex and its hormones
Adrenal cortex, as part of adrenal gland, is divided in three regions: Zona glomerulosa, Zona fasciculata, and Zona reticularis. Each of which produces different groups of hormones
First region
Zona glomerulosa or the G-zone is the thin and outer zone of the cortex that composed of cells which are closely packed and arranged in spherical clusters and arched columns. They secrete hormones called mineralcorticoids and they affect mineral homeostasis. Aldosterone is the major mineralcorticoid. It acts to conserve sodium ions and water in the body.
What will happen if your aldosterone gets high or low?
When aldosterone gets too high, your blood pressure also gets too high and your potassium levels become too low. You can have muscle cramps, muscle weakness, and numbness or tingling in your extremities.
But when it gets too low, your kidneys will excrete too much salt, and it leads to low blood pressure, low blood volume, a high pulse and/or palpitations, dizziness and or lightheadedness when you stand.Symptoms of low aldosterone can also include frequent urination, sweating, a slightly higher body temperature, and a feeling of thirst, besides the craving of salt. Potassium can at first rise too high, then fall, as well.
Second region
Zona fasciculata or the F-zone is the middle zone and the widest of the three zones and consists of cells arranged in long, straight columns. They secrete hormones called glucocorticoids and they affect glucose homeostasis. Cortisol is the main glucocorticoid which increases blood glucose levels and resistance to stress.
Carrying out metabolism of fat, carbohydrates and proteins, and suppressing the immune system are the important function of cortisol to increase the blood glucose level in our body. Cortisol is also being released in response to feeling of stress and because of its function you may have elevated cortisol if you are under stress. This isn’t in favor for us. Experts say that overexposure to stress has a cumulative affect, leading to heart disease, sleep issues, digestive issues, obesity, depression and worsening of skin conditions. So to fight the adverse effect of having elevated cortisol level, try to have enough sleep. Do not oblige yourself in doing things that doesn’t make sense. Take a few minutes in concentrating on your breathing.
Third region
Zona reticularis or the R-zone is the inner most cortical layer in which the cells are arranged in branching cords. It produces androgens.
After puberty in males, the androgen testosterone is also released in much greater quantity by the testes. In females, however, adrenal androgens play important roles. They promote libido (sex drive) and are converted into estrogens (feminizing sex steroids) by other body tissues. Adrenal androgens also stimulate growth of axillary and pubic hair in boys and girls and contribute to the prepubertal growth spurt.
After having the structure of adrenal cortex and the hormones it secretes, the answers for the second question is next to be discussed which refers to laboratory tests specifically for hormones that being secreted in adrenal cortex.
Laboratory Evaluation of Adrenal function
We have a lot of different laboratory tests for hormones but I am only presenting three specific tests. As you will read the description and procedure for each test, you will notice that it is expensive to have at least one of these tests.
Porter-Silber chromogen test is the first reliable method for measuring glucocorticoid levels. This fluorometric test measures cortisol and cortisone levels in the plasma, or their urinary metabolites, 17-OH corticosteroids (17-OHCS), by the intensity of a color change that occurs when the urine or plasma reacts with phenylhydrazine.
Plasma Adrenocorticotropic Hormone Radioimmunoassays
Plasma levels of endogenous ACTH can be measured by radioimmunoassay. ACTH is secreted in a pulsatile fashion, and its circadian rhythm is responsible for the circadian rhythm of cortisol secretion. Clinically, ACTH radioimmunoassays may measure not only the native 39-amino-acid ACTH molecule, but also structurally related POMC products (Howlett and Besser, 1985). In normal, unstressed subjects, the level of ACTH late in the evening generally is less than 20 pg/ml, and morning values are in the range of 10–80 pg/ml (Horrocks and London, 1982). The plasma ACTH level can be helpful in determining the etiology of adrenocortical insufficiency (Wand and Ney, 1985).
Adrenocorticotropic Hormone Stimulation Tests
The response of the adrenal gland to exogenous ACTH may be helpful from a diagnostic standpoint. In general, the synthetic ACTH analog cosyntropin, which consists of the 24 N-terminal amino acids of the native peptide, is used for testing purposes. The degree of response depends not only on the physiologic integrity of the gland but also on the degree of prior stimulation. This test is used to diagnose adrenocortical insufficiency by measuring cortisol levels or to diagnose CAH by measuring androgen precursor levels.
For the rapid ACTH test, one or two blood samples are collected to determine basal levels of plasma cortisol, followed by intravenous injection of 250 μg cosyntropin. Plasma may be sampled 30, 45, or 60 minutes after ACTH administration (Nelson and Tindall, 1978). With a normal response to stimulation, the plasma cortisol level will exceed 15 μg/dl and will exhibit an incremental rise of 5–7 μg/dl or more. A normal response excludes primary adrenocortical insufficiency.
Here ends my presentation about the structure of adrenal cortex and the laboratory evaluation for adrenal function. Thank you for reading my article.
References:
· Tortora, Gerard J., Derrickson, Bryan H., Principles of Anatomy and Physiology 12 edition, Vol.1
· Howlett TA, Rees LH, Besser GM: Cushing's syndrome. Clin Endocrinol Metab 14: 911, 1985
· Horrocks PM, London DR
· Wand GS, Ney RL: Disorders of the hypothalamic-pituitary-adrenal axis. Clin Endocrinol Metab 14: 33, 1985
· Nelson JC, Tindall DJ: A comparison of the adrenal responses to hypoglycemia, metyrapone and ACTH. Indian J Med Sci 275: 165, 1978
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