Module 7 Short Summary

EFFECTS OF AGING ON RENAL FUNCTION

Notes from Chapter 58, "Aging Changes in Renal Function" by L.H. Beck in Principles of Geriatric Medicine and Gerontology (4^th Edition) by Hazzard, Blass, Ettinger, Halter and Ouslander, 1999, pgs. 767-776.

 With advancing the kidneys progressively shrink, accompanied by decreased renal blood flow and glomerular filtration rate. The ability to respond to internal and external stresses becomes less robust.

1. Anatomic changes.
1. Decreased renal size- 10% per decade after age 20.
2. Increased number of sclerotic glomeruli.
3. Decreased tubular mass.
4. Sclerosis of pre-and postglomerular arterioles.

2. Physiologic changes.
   1. Glomerular filtration rate:
      1. 30% decrease in creatinine clearance by age 80.
      2. No changes in serum creatinine concentration due to a parallel decrease in creatinine production because of decreased muscle mass.
2. Renal blood flow: decrease of 10% per decade after age 20.
3. Renal tubular function. May not be a specific defect in transport but rather the total capacity decreases as the number of nephrons decreases with age.
4. Sodium homeostasis: slow response to sodium deprivation.
5. Potassium homeostasis: decreased tubular mass limits rate of potassium excretion.
6. Acid-base parameters: decreased rate of response to an acid load.
7. Water homeostasis:
   1. Total body water decreases with age- tendency for dehydration in elderly.
   2. Decreased maximal urinary osmolality.
   3. Decreased thirst response to hyperosmolality.
   4. Slow renal excretion of a water load.
      
      
3. Clinical consequences of physiologic changes.
   1. Functional changes of the aging kidney do not, of themselves, lead to disease.
   2. Elderly are vulnerable to environmental, disease-related, & drug-induced stresses.
   3. Disorders of salt (sodium) metabolism:
      1. Deficiency of sodium results in hypovolemia.
      2. Because of slow response to volume depletion, organ hypoperfusion is dangerous to the elderly patient.
   4. Disorders of water metabolism. Hypernatremic dehydration is a very common fluid- electrolyte disorder in older individuals and patients.
   5. Disorders of potassium metabolism.
      1. Hyperkalemia frequently occurs in the elderly due to treatment with drugs that interfere with potassium excretion, e.g., potassium-sparing diuretics.
      2. Hypokalemia is also common in elderly- can lead to tachyarrhythmia.