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Renal Function
Aka: Renal Function, Kidney Function
- See Also
- Sodium and Water Homeostasis
- Acid-Base Homeostasis
- Renin-Angiotensin System
- Blood Pressure Physiology
- Fluids and Electrolytes in Critical Care
- Electrolyte
- Acute Kidney Injury
- Chronic Kidney Disease
- Free Water Clearance
- Physiology: Renal Function
- Background: Core Renal Functions
- Sodium and Water Homeostasis
- Acid-Base Homeostasis
- Blood Pressure Physiology (including Renin-Angiotensin System)
- Metabolic Waste Product Excretion
- Urea (from amino acid metabolism)
- Creatinine (from muscle breakdown)
- Uric Acid (nucleic acid breakdown)
- Conjugated Bilirubin as Urobilinogen (from Hemoglobin breakdown)
- Synthetic function (e.g. Erythropoietin, Vitamin D, Glucose)
- Renal Filtration (Glomerulus)
- Glomerular Membrane (3 layers)
- Capillary endothelium (outer layer)
- Glomerular Basement Membrane
- Main barrier to leakage of proteins and other large molecules
- Openings within basement membrane are much smaller than those in capillary endothelium or podocytes
- Openings within the basement membrane are negatively charged
- Repels moderate to large proteins which are typically negatively charged
- Podocytes (epithelial foot processes, inner layer adjacent to bowman's space)
- Mesangial Cells
- Modulates glomerular filtration (when contracted, reduces glomerular surface area and filtration)
- Contract in response to Norepinephrine, Epinephrine, Angiotensin II (decreases filtration)
- Relax in response to atrial natriuretic factor (increases filtration)
- Renal Reabsorption (Renal Tubule)
- Non-charged molecules (non-polar) are more easily reabsorbed
- Sodium reabsorption (active transport) occurs primarily in the proximal tubule
- Carrier molecules facilitate reabsorption of various molecules (e.g. amino acids)
- Other molecule reabsorption (Active co-transport with Sodium)
- Water
- Glucose, Lactic Acid and Ketones
- Water soluble Vitamins
- Amino Acids (see below)
- Renal Secretion (Peritubular Capillary)
- Peritubular capillary secretion of molecules (e.g. ammonia, Hydrogen Ion, Potassium) into the renal tubules
- Renal Synthesis
- Erythropoetin (stimulates erythrocyte production)
- Renin
- Vitamin D
- Prostaglandins (e.g. PGE2)
- Glucose
- Bicarbonate
- Ammonia
- Labs: Chemistry Measures of Renal Function
- Serum Creatinine (Cr)
- Creatinine is a muscle breakdown product
- Typically filtered by the normal Kidney at a constant rate, and rises with renal dysfunction
- However varies with muscle mass and muscle activity
- Blood Urea Nitrogen (BUN)
- Protein breakdown product
- Increases in renal dysfunction, but also with increased protein ingestion or tissue breakdown
- BUN to Serum Creatinine Ratio
- Prerenal Failure: Ratio >20:1
- Glomerular Filtration Rate (GFR, Creatinine Clearance)
- More accurate Renal Function measure than either Serum Creatinine or BUN alone
- Rate of fluid filtered through glomerular membrane
- GFR = uCr/sCr * uVol/t
- where uCr = Urine Creatinine concentration (excreted Creatinine concentration)
- where sCr = Serum Creatinine concentration (equal to filtered Creatinine concentration)
- where uVol/t = volume of urine collected over measured time period (rate of urine production)
- Fractional Excretion of Sodium (FENa)
- Labs: Other changes in the absence of Renal Function
- Serum Potassium increases 0.3-0.5 mEq/L/day
- Serum Bicarbonate decreases 1-2 meq/L/day
- Serum Calcium decreases
- Serum Phosphorus increases
- Serum Magnesium increases
- Complete Blood Count changes in chronic insufficiency
- Anemia
- Platelet Dysfunction
- References
- Goldberg (2014) Clinical Physiology, Medmaster, p. 21-23, 33-4
- Guyton and Hall (2006) Medical Physiology, Elsevier, p. 307-47