Adrenal Glands


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Adrenal Glands

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  3. 3. They lie at the superior poles of the two kidneys. Each gland is composed of two distinct parts: <ul><ul><ul><li>1. Adrenal Cortex – 80% </li></ul></ul></ul><ul><li>2. Adrenal Medulla- 20% </li></ul>
  4. 4. CORTICOSTERIODS – group of hormones secreted by the adrenal cortex. These are synthesized from the steroid Cholesterol . The following are the ADRENOCORTICAL HORMONES: 1. Mineralocorticoids – affect electrolytes of the ECF – Sodium and Potassium 2. Glucocorticoids – Exhibit an important effect in increasing blood glucose concentration 3. Androgenic hormones ALDOSTERONE – principal mineralocorticoid CORTISOL – principal glucocorticoid
  6. 6. 1. Zona Glomerulosa - constitutes about 15% of the adrenal cortex - cells are the only ones secreting Aldosterone - they contain enzyne aldosterone synthase necessary for synthesis of aldosterone - secretion is controlled by ECF conc. of Angiotensin II and Potassium
  7. 7. <ul><li>2. Zona Fasciculata </li></ul><ul><li>- constitutes about 75% of the adrenal cortex </li></ul><ul><li>- middle and widest layer </li></ul><ul><li>- secretes the glucocorticoids cortisol and corticosterone and small amounts of adrenal androgens and estrogens </li></ul><ul><li>- secretion is controlled by hypothalamic- pituitary axis via adrenocorticotropic hormone (ACTH ) </li></ul>
  8. 8. <ul><li>3. Zona Reticularis </li></ul><ul><li>- secretes the adrenal androgen hydroepiandrosterone (DHEA) and androstenedione and small amounts of estrogen and some glucocorticoids </li></ul><ul><li>- secretion is regulated by ACTH and other factor such as cortical androgen-stimulating hormone from the pituitary </li></ul>
  9. 10. More Important Glucocorticoid Hormones including Synthetic ones: <ul><li>1. Mineralocorticoids </li></ul><ul><li>- Aldosterone ( very potent , accounts for 90% of all mineralocorticoid activity </li></ul><ul><li>- Desoxycorticosterone ( 1/30 as potent as aldosterone, but very small quantities secreted </li></ul><ul><li>- Corticosterone ( slight minralocorticoid activity ) </li></ul><ul><li>- 9a-Fluococortisol ( synthetic , slightly more potent than aldosterone) </li></ul><ul><li>- Cortisol (very slight mineralocorticoid activity, but large quantity secreted </li></ul><ul><li>- Cortisone ( synthetic , slight mineralocorticoid activity) </li></ul>
  10. 11. <ul><li>2. Glucocorticoid </li></ul><ul><li>- Cortisol ( very potent , accounts for about 95% of all glucocorticoid activity </li></ul><ul><li>- Corticosterone (provides 4% of total glucocorticoid) activity, much less potent than cortisol) </li></ul><ul><li>- Cortisone ( synthetic , almost as potent as cortisol) </li></ul><ul><li>- Prednisone ( synthetic , four times as potent as cortisol) </li></ul><ul><li>- Methyprednisone ( synthetic, five tmes as potent as cortisol) </li></ul><ul><li>- D examethasone ( synthetic , 30 times as potent as cortisol) </li></ul>
  11. 12. The Intense Glucocorticoid Activity of Dexamethasone, has almost zero mineralocorticoid activity, thus is important drug for stimulating specific glucocorticoid activity
  12. 13. FUNCTIONS OF MINERALOCORTICOID – Aldosterone <ul><li>1 . Renal and Circulatory Effects of Aldosterone </li></ul><ul><li>a. Aldosterone Increases Renal Tubular Reabsorption of Sodium and Secretion of Potassium – especially in the principal cells of the collecting tubules , and to lesser extent in the distal tubules and collecting ducts </li></ul><ul><li>b. Excess Aldosterone Increases ECF Volume and Arterial Pressure but Has Only a Small Effect on Plasma Sodium Concentration </li></ul><ul><li>c. Excess Aldosterone Causes Hypokalemia and Muscle Weakness; Too little Aldosterone Causes Hyperkalemia and Cardiac Toxicity </li></ul>
  13. 14. <ul><ul><ul><li>Hypokalemia causes severe muscle weakness caused by alteration of the electrical excitability of the nerve and muscle fiber membranes which prevents transmission of normal action potential </li></ul></ul></ul><ul><ul><ul><li>Deficient Aldosterone – results to cardiac toxicity , including weakness of heart contraction and development of arrhythmia </li></ul></ul></ul>
  14. 15. <ul><li>C. Excess Aldosterone Increases Tubular Hydrogen Ion </li></ul><ul><li>Secretion with Resultant Mild Alkalosis </li></ul><ul><ul><ul><li>- secretion hydrogen ion in exchange for sodium in the intercalated cells of the cortical collecting tubules </li></ul></ul></ul><ul><ul><ul><li>2. Aldosterone Stimulates sodium and Potassium Transport in Sweat Glands, Salivary Glands and Intestinal Epithelial Cells </li></ul></ul></ul><ul><ul><ul><ul><li>- same effects as it has on the renal tubules </li></ul></ul></ul></ul>
  15. 16. Cellular Mechanism of Aldosterone Action <ul><li>1. Aldosterone diffuses readily to the interior of the tubular epithelial cells </li></ul><ul><li>2. In the cytoplasm of the tubular cells, aldosterone combines with specific cytoplasmic receptor protein </li></ul><ul><li>3. Aldosterone-receptor complex diffuses into the nucleus, inducing RNA to form messenger RNA </li></ul><ul><li>4. The mRNA diffuses back into the cytoplasm operating in conjunction with the ribosomes causes protein formation </li></ul>
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