The adrenal glands are two in number, one right and one left, they are each located near the upper pole of the kidney match. Their average size is 3 inches high, 2 cm wide, 1 cm in thickness, weighs 4 to 6 g, consistency soft buff yellow coloring.
When cut, the adrenals show will consist of two entirely different areas, that difference is reflected in their function. These two areas are:
- the cortex or adrenal cortex, located at the periphery of the gland, the color yellow. It is formed by three layers of glandular cells, these three layers of cells bearing the names of areas glomerular, fascicular and reticular;
- medulla or the adrenal medulla, looking brown-red occupies the center of the gland. It is composed of polygonal cells in cords, stuffed enclaves stain; these enclaves can be highlighted by a special chemical reaction, the chromaffin reaction.
Numerous experiments ablation of adrenal glands in animals performed since Brown-Sequard in 1856 showed that the adrenal cortex is essential to life while the medulla is not.
The removal of the adrenal cortex in animals, as do humans, causes death in 1 to 5 days in a table involving digestive disorders, a cardiovascular collapse and prostration leading to coma. The biological tests show serious disturbances on the equilibrium and metabolism of water and on the balance of electrolytes (sodium and potassium in particular).
The administration of adrenal extracts in adrenalectomized animals corrects these problems.
The cortex secretes many hormones whose chemical composition is now well defined and their manufacture in the adrenal (biosynthesis) and their metabolism in the body. The physiological action of some compounds is however still unknown.
All adrenal hormones can now be synthesized and it makes even artificial products endowed with hormonal activity but radically different structure of natural hormones (called steroid synthesis).
All the hormones of the adrenal cortex is known as the General corticosteroids or steroids.
All these hormones have in common the same core chemical sterol nucleus and the same synthetic pathway, ie manufactured from cholesterol; different hormones differ only by elements fixed on the nucleus;
The hormones of the adrenal cortex may, depending on their biological role, be classified into three major groups: mineralocorticoids, glucocorticoids and androgens.
These are the hormones of water and salt. They regulate the body effect in the balance of water and electrolytes by acting on the disposal of this material by the kidney. The hormone essential for this group is called aldosterone, it reduces the renal elimination of sodium and water and increases the contrary the elimination by the body, potassium, and the point of impact hormone is the distal renal tubule: it increases at this level, the reabsorption of sodium and water and increases the secretion of potassium. Adrenalectomy causes so because of the suppression of secretion of aldosterone an increased urinary excretion of sodium and water retention and potassium: these disturbances result clinically by polyuria, dehydration, hypotension and biologically by lower blood levels of sodium, chlorine, alkali reserve and elevated potassium. Conversely, an excessive secretion of aldosterone has been demonstrated in some adrenal tumors (hyperaldosteronism or Conn’s syndrome), then there is high blood pressure, fatigue, muscle weakness, tetanic seizures, and biologically, a decrease of blood potassium (hypokalemia), elevated blood sodium (hypernatremia), reserve alkaline (metabolic alkalosis), blood volume (blood volume), increased urinary excretion of potassium (hyperkaliurie ), a decrease of sodium (hyponatriurie). Other hormones of this group have a lower action than aldosterone, these are: the deoxycorticosterone and 17 hydroxy 11 deoxycorticosterone. At its action on metabolism hydromineral that the adrenal is vital functions.
These hormones affect the metabolism of carbohydrates and proteins: they promote, in effect, making the body, carbohydrates, food energy from protein, plastic food, such production is called neo-glycogen; they promotes the synthesis of glycogen in the liver. Steroids were hyperglycaemic action and can run in excess, lead to diabetes (diabetes Steroid). These hormones also act on lipid metabolism: they inhibit lipolysis and alters the distribution of adipose tissue. In addition, corticosteroids act on cells and inhibit the production of antibodies, so they are used to prevent and treat rejection of organ transplants, because of this action, they have an anti-inflammatory.
The essential hormone of this group is cortisol or hydrocortisone which the average production in humans is 15 to 20 mg per 24 hours. The adrenal produces little cortisol, the hormone group and the action of the adrenal glucocorticoid in humans is attributed almost entirely to cortisol.
Glucocorticoids have also, but to a lesser degree of mineralocorticoid properties. This dual action of cortisol is the most active cortical hormones as its single administration is sufficient to keep alive the animal or human adrenalectomized. The discovery of cortisol allowed to practice in humans total adrenalectomy (shown for example in some cancers) and survival to maintain patients whose adrenal glands are destroyed (Addison’s disease).
The hydrocortisone replacement therapy of choice in case of failure of normal hormonal secretion.
The hormone androgen or 17 ketosteroids.
These are hormones whose chemical formula is very close to that of the male genital hormones produced by the testis. The most important of these is the hormone dehydroepiandrosterone DHA The physiological role of adrenal androgens seems low in light of testicular androgens and especially testosterone, which provides the bulk of this function.
The adrenal finally draw a small amount of estrogen (female sex hormones).
These three categories of hormones are inactivated in the liver and then eliminated by the kidneys. The dosages of these various constituents in the urine are of fundamental importance in the study of adrenal disease.
The differentiation of the three areas of the cortex is not only histological but also functional.
- Mineralocorticoids are produced in the zona glomerulosa and this activity is independent of pituitary activity including the secretion of ACTH;
- the glucorticoides are developed in the zone fasciculata and this secretion is under the control of pituitary ACTH;
- androgens are produced in the zona reticularis.
The cortical obey a regulatory complex
The anterior pituitary secretes a hormone stimulating the corticostimuline or AC T. H. (Adreno-cortico-Trophin-Hormon) (or syn ene ACTH) injection which increases the adrenocortical secretion. Secretion KT T. H. is controlled by the hypothalamus: it develops a hormone called CRF, which stimulates the secretion of pituitary ACTH secretion FIU is itself determined by the rate of circulating adrenal hormones. L ‘ AC T .H. KT T. H. acts exclusively on the secretion of metabolic hormones (glucocorticoids).
A control antibody: the latter mechanism occurs only for the secretion of aldosterone in dependence on the renin angiotensin system:
The circulating blood volume and blood pressure: the increase in blood volume inhibits the secretion of aldosterone, its decrease stimulates (via the juxtaglomerular apparatus) is in fact angiotensin (formed by the action of renin developed by the kidney) that directly triggers the secretion of aldosterone. All incentives cause so exciting at first secretion of renin which triggers the secretion of aldosterone. Incentives freinatrices have the opposite effect.
The nervous system is involved in the secretion of aldosterone: any stimulation of the sympathetic nervous system triggers the release of catecholamines. The nerve endings and adrenal medulla. The release of catecholamines causes the secretion of renin (and therefore aldosterone).
Adrenal diseases common
The adrenal insufficiency occurs during the illness of Addison, linked to impairment of cortico-adrenal. The use of etomidate (hypnotic) can also cause adrenal insufficiency.
The cortico-adrenal hyperfunction or hypercortisolism may occur in tumors or hypertrophy of these glands: hypersecretion of aldosterone causes a condition called Conn’s syndrome, hypersecretion of cortisol causes Cushing’s disease, the hypersecretion of sex hormones leads to phenomena of virilization or feminization.
The exploration of the adrenal cortical function is the determination of cortico-steroids or their metabolites in blood and urine.
The adrenal medulla secretes two hormones: epinephrine and norepinephrine. These hormones are designated under the broader term of catecholamines.
Secretion under physiological conditions, consists of approximately 90% of adrenaline and noradrenaline 10%.
These two compounds are chemically related but their biological action is similar.
Norepinephrine causes: vasoconstriction except in the coronary vessels; (alpha exclusive positive action)
Adrenaline causes inotropism, bathmotropisme, chronotropic and dromotropic increased and therefore a rise in cardiac output, but also a systemic vasocontriction (action alpha and beta agonists + +) (may be vasodilator in low doses). These two hormones may well lead to hypertension and pressure if it is poorly secreted.
The action on glucose metabolism results in hyperglycemia due to mobilization of liver glycogen, and increased carbohydrate catabolism in all cells but especially muscle cells. Adrenaline is here 4 to 5 times more active than norepinephrine.
The action on 1st lipid metabolism leads to mobilization of fat reserves.
All these metabolic actions involved in the fight against the cold, muscular exertion (increase in muscle performance, delay the onset of fatigue).
Catecholamines cause relaxation of smooth muscle and thereby cause: bronchial dilatation (actiion B2 agonist), decreased gastric peristalsis, and bowel.
The action of catecholamines is comparable to that of the sympathetic. This reflects the fact that norepinephrine is not only a hormone but also the medullary chemical mediator of sympathetic fibers. The sympathetic system and adrenal medulla act so closely connected: the gland is really nice integrated system and can be considered the equivalent of nerve cells postganglionic.
The medulla has a low but constant secretion reacts rapidly to emergency situations by increased secretion of catecholamines.
The events that trigger secretion are: hypotension (hemorrhage, shock), muscle power, cold, emotions, pain, hypoglycemia, in short, all circumstances represent an assault on the body or which increase sharply its metabolic needs.
These factors act on the centers of the hypothalamus and medulla stimulation borrows from there ways sympathetic nerve (splanchnic nerve) and is triggered by pre-ganglionic fibers of the sympathetic through their chemical mediator the acetylcholine. The onset of adrenal medullary secretion during attacks carried out by so nervous exclusive and primarily through sympathetic. This reflects a common embryological origin of the sympathetic nervous system and adrenal medulla.
The hyperfunction of the adrenal medulla occurs in cases of pheochromocytoma (tumor). It produces in excess of noradrenaline and adrenaline and results in a paroxysmal hypertension and hyperglycemia.
The exploration of the adrenal medulla secretion, justified if pheochromocytoma is made by measurement of catecholamines and their metabolites in blood and urine.