Kidney Function and Nephrons Overview

Kidney Function and Regulation

• Kidneys regulate blood composition and volume via excretion and osmoregulation, maintaining homeostasis.
• Excretion removes metabolic waste products; osmoregulation balances water and salt.
• Kidney functions include regulating fluid volume, composition, and pH; removing metabolic waste; controlling red blood cell production (erythropoietin); regulating blood pressure and volume (renin); and activating vitamin D for calcium absorption.

Nephrons: Functional Units of the Kidney

• Nephrons are the functional units of the kidneys.
• The renal corpuscle comprises a glomerulus (capillaries) enclosed in Bowman's capsule.
• Blood enters via the afferent arteriole, flows through glomerular capillaries, and exits through the efferent arteriole to peritubular capillaries.
• Fluid and substances filter from blood into Bowman's space within Bowman's capsule.

Diagnostic Tests for Kidney Function

• Urine analysis (pH, electrolytes, metabolic byproducts) assesses kidney function.
• Urine specific gravity measures urine concentration ability.
• Proteinuria/microalbuminuria tests detect abnormal glomerular filtration or tubule reabsorption.
• Serum creatinine, a muscle metabolism byproduct, is a common GFR (glomerular filtration rate) indicator (freely filtered, not reabsorbed, not secreted).
• BUN (blood urea nitrogen), a liver protein metabolism byproduct, is related to GFR but also affected by protein intake, bleeding, and hydration.

Visualizing Kidney Structures

• Visual inspection/tests
• Cystoscopy and ureteroscopy visualize urethra, bladder, and ureters.
• Ultrasound assesses kidney size.
• Radioisotope imaging evaluates kidney structures.
• Radiological methods (excretory urography) examine renal calyces, pelvis, ureters, and bladder.
• CT scans, MRI, and renal angiography provide further diagnostics.

Renal Clearance

• Renal clearance measures plasma volume cleared of a substance per minute.
• Clearance depends on filtration, reabsorption, and secretion of a substance in the renal tubules.
• Clearance rates vary by substance, always measured in plasma volume per unit time. Calculated by urine concentration multiplied by urine flow rate, divided by plasma concentration of the substance

Aging and the Urinary System

• Kidney function declines with age.
• Functional nephrons decrease by 30-40% between ages 25 and 85.
• Glomerular filtration rate diminishes.
• Water and sodium reabsorption reduces; potassium excretion increases.
• Micturition reflex issues can arise.
• Total body water content and mineral content decrease.
• Increased incidence of disorders affecting other major systems.

Kidney Dysfunction

• Reduced renal activity can result from glomerulonephritis, diabetes, atherosclerosis, or kidney stones and cause:
  • High blood pressure
  • High blood potassium and hydrogen levels
  • Uremia (urea in the blood)
• Patients with uremia may require dialysis.