997399 adrenal-glands

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  • 1. www.Examville.com Online practice tests, live classes, tutoring, study guides Q&A, premium content and more .
  • 2. THE ADRENAL GLANDS
  • 3. They lie at the superior poles of the two kidneys. Each gland is composed of two distinct parts:
        • 1. Adrenal Cortex – 80%
    • 2. Adrenal Medulla- 20%
  • 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
  • 5. LAYERS OF ADRENAL CORTEX AND SECRETION
  • 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.
    • 2. Zona Fasciculata
    • - constitutes about 75% of the adrenal cortex
    • - middle and widest layer
    • - secretes the glucocorticoids cortisol and corticosterone and small amounts of adrenal androgens and estrogens
    • - secretion is controlled by hypothalamic- pituitary axis via adrenocorticotropic hormone (ACTH )
  • 8.
    • 3. Zona Reticularis
    • - secretes the adrenal androgen hydroepiandrosterone (DHEA) and androstenedione and small amounts of estrogen and some glucocorticoids
    • - secretion is regulated by ACTH and other factor such as cortical androgen-stimulating hormone from the pituitary
  • 9.  
  • 10. More Important Glucocorticoid Hormones including Synthetic ones:
    • 1. Mineralocorticoids
    • - Aldosterone ( very potent , accounts for 90% of all mineralocorticoid activity
    • - Desoxycorticosterone ( 1/30 as potent as aldosterone, but very small quantities secreted
    • - Corticosterone ( slight minralocorticoid activity )
    • - 9a-Fluococortisol ( synthetic , slightly more potent than aldosterone)
    • - Cortisol (very slight mineralocorticoid activity, but large quantity secreted
    • - Cortisone ( synthetic , slight mineralocorticoid activity)
  • 11.
    • 2. Glucocorticoid
    • - Cortisol ( very potent , accounts for about 95% of all glucocorticoid activity
    • - Corticosterone (provides 4% of total glucocorticoid) activity, much less potent than cortisol)
    • - Cortisone ( synthetic , almost as potent as cortisol)
    • - Prednisone ( synthetic , four times as potent as cortisol)
    • - Methyprednisone ( synthetic, five tmes as potent as cortisol)
    • - D examethasone ( synthetic , 30 times as potent as cortisol)
  • 12. The Intense Glucocorticoid Activity of Dexamethasone, has almost zero mineralocorticoid activity, thus is important drug for stimulating specific glucocorticoid activity
  • 13. FUNCTIONS OF MINERALOCORTICOID – Aldosterone
    • 1 . Renal and Circulatory Effects of Aldosterone
    • 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
    • b. Excess Aldosterone Increases ECF Volume and Arterial Pressure but Has Only a Small Effect on Plasma Sodium Concentration
    • c. Excess Aldosterone Causes Hypokalemia and Muscle Weakness; Too little Aldosterone Causes Hyperkalemia and Cardiac Toxicity
  • 14.
        • 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
        • Deficient Aldosterone – results to cardiac toxicity , including weakness of heart contraction and development of arrhythmia
  • 15.
    • C. Excess Aldosterone Increases Tubular Hydrogen Ion
    • Secretion with Resultant Mild Alkalosis
        • - secretion hydrogen ion in exchange for sodium in the intercalated cells of the cortical collecting tubules
        • 2. Aldosterone Stimulates sodium and Potassium Transport in Sweat Glands, Salivary Glands and Intestinal Epithelial Cells
          • - same effects as it has on the renal tubules
  • 16. Cellular Mechanism of Aldosterone Action
    • 1. Aldosterone diffuses readily to the interior of the tubular epithelial cells
    • 2. In the cytoplasm of the tubular cells, aldosterone combines with specific cytoplasmic receptor protein
    • 3. Aldosterone-receptor complex diffuses into the nucleus, inducing RNA to form messenger RNA
    • 4. The mRNA diffuses back into the cytoplasm operating in conjunction with the ribosomes causes protein formation
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