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MLAB 2401: Clinical Chemistry Keri Brophy-Martinez

MLAB 2401: Clinical Chemistry Keri Brophy-Martinez. Renal Unit :Overview. Kidney physiology. Renal Physiology. Three renal processes Glomerular filtration Tubular reabsorption Tubular secretion. Glomerular Filtration. Glomerulus filters incoming blood How?

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MLAB 2401: Clinical Chemistry Keri Brophy-Martinez

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  1. MLAB 2401: Clinical Chemistry Keri Brophy-Martinez Renal Unit :Overview

  2. Kidney physiology

  3. Renal Physiology • Three renal processes • Glomerular filtration • Tubular reabsorption • Tubular secretion

  4. Glomerular Filtration • Glomerulus filters incoming blood • How? • High pressure in the glomerular capillaries sets up a pressure difference • Semipermeable glomerular basement membrane allows small dissolved solutes, which have a positive charge to pass • Glomerular filtrate, which is cell-free, protein free is made and can be measured by the GFR( glomerular filtration rate)

  5. Tubular Reabsorption • Substance movement from tubular lumen to peritubular capillary plasma for regulation of concentration • Assists in conservation of nutrients • Prevents electrolyte loss • Assists in acid-base imbalance • Occurs by Active and Passive transport • Active Transport • Tubular epithelial cells use energy to bind and transport substances across plasma membrane to blood • Transports Glucose, Amino acids, Proteins, Electrolytes • Maintains the sodium pump to prevent the cells from swelling up • Passive Transport • No energy requirement • Substances, such as water and urea, move from higher concentrations to lower concentrations

  6. Tubular Reabsorption • Occurs in proximal convoluted tubule • Receives the glomerular filtrate • Return the bulk of substances back to blood circulation • Proteins, glucose completely reabsorbed • Sodium, chloride partially reabsorbed • Creatinine no reabsorption • Secretes products of kidney tubular metabolism, such as hydrogen ions and drug

  7. Tubular Secretion • Occurs in the proximal convoluted tubule • How is this used? • Movement of substances from peritubular capillary plasma to tubular lumen that were not previously eliminated • Secretion of products from tubule cell cellular metabolism into filtrate, such as hydrogen

  8. Distal Convoluted Tubule • Most of reabsorption complete • Function • Make small adjustments to benefit electrolyte and acid-base balance • Adjustments occur under control of ADH (antidiuretic hormone) and aldosterone

  9. Functions of the Kidney • Urine formation • Fluid and electrolyte balance • Regulation of acid-base balance • Excretion of waste products of protein metabolism • Excretion of drugs and toxins • Secretion of hormones

  10. Water Balance • Kidney assists with water balance through water loss or water conservation • Water balance regulated by ADH/AVP • Secretion of ADH • Increased plasma osmolality or decreased intravascular volume • Action of ADH • ADH increases the permeability of the distal convoluted tubules and collecting ducts to water • Results in water reabsorption and concentration of urine • Activates thirst mechanism

  11. How does it work?

  12. Aldosterone • Origin • Adrenal cortex • Influenced by renin-angiotension system • Secretion • Decreased blood flow or blood pressure • Decreased plasma sodium • Action • Stimulates sodium reabsorption in distal tubules and potassium and hydrogen ion secretion • Increases water retention • Raises blood pressure

  13. Acid-Base Balance • Renal system assists with constant control of overall pH • Conserve bicarbonate ions • Secretes H+ ions attached to phosphate • Secretes H+ ions attached to ammonia

  14. Elimination of Nonprotein Nitrogen Compounds • Waste products formed by degradative metabolism of proteins, amino acids and nucleic acids • Main players are urea, creatinine and uric acid • Urea • 75% of the nonprotein nitrogens excreted daily • By product of ammonia breakdown • 40-60% reabsorbed • Creatinine • Formed from creatine, which is found in muscle • Not reabsorbed by the tubules • Uric acid • Waste product of purine metabolism (nucleic acid) • Ammonia • Product of amino acid and protein catabolism

  15. Endocrine Functions • Produces hormones • Renin • Erythropoietin • 1,25- dihydroxy vitamin D 3 • Prostaglandins • Target for certain hormones produced by other endocrine glands

  16. Hormones: Renin • Released by juxtaglomerular cells • Stimulated by decreases in fluid volume or blood pressure • Effect of: • Promote sodium reabsorption and water conservation • Promotes secretion of aldosterone • Bottom line: Increase blood pressure

  17. Hormones: Erythropoietin • Made by kidney • Production regulated by blood oxygen levels (hypoxia) • Effect of: • Stimulate RBC production

  18. Hormones: 1,25-Dihydroxy Vitamin D3 • Made in the kidneys • Active form of vitamin D • Determines phosphate and calcium balance and bone calcification in the human body

  19. Hormones: Prostaglandins • Fatty acids formed from dietary fatty acids • Produced in the kidney • Function • Increase renal blood flow (vasodilator) • Sodium and water excretion • Antagonistic to renin release

  20. References • Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins. • Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson .

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