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

10. 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

11. 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

12. How does it work?

13. 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

14. 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

15. 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

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

17. 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

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

19. 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

20. 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

21. 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 .