Lecture on Kidney Function and Filtration

Key Concepts:

• Glomerular Filtration
• Nephron Function
• Reabsorption and Secretion
• Regulatory Mechanisms of Filtration

Glomerular Filtration

• Over 1000 mL of blood flows through the glomeruli per minute
• Filters 120-125 mL/min; about 10% of the fluid is removed
• Kidney tubules process 180 liters of fluid daily, yet only about 1.5 liters are excreted as urine
• Filtration occurs in the renal corpuscle

Nephrons

• Nephrons are metabolically active, requiring a lot of oxygen
• Filtration is passive, does not require ATP
• Main energy expense in reabsorption and secretion

Structure and Function

• Filtration membrane involves:
  • Epithelial cells of glomerular capillaries
  • Podocyte foot processes
  • Basement membrane
• Allows molecules < 3 nanometers to pass (e.g., water, glucose, amino acids, urea)
• Large molecules and proteins remain in the blood, maintaining osmotic pressure

Filtration Dynamics

• Hydrostatic pressure in glomerular capillaries: high (about 55 mm Hg)
• Osmotic pressure in capsular space is negligible (treated as zero)
• Net filtration pressure determines glomerular filtration rate (GFR)

Regulatory Mechanisms

• Intrinsic Controls:
  • Renal autoregulation via myogenic mechanism and tubuloglomerular feedback
  • Myogenic mechanism: Smooth muscle responds to stretch, maintaining steady GFR
  • Tubuloglomerular feedback: Involves macula densa cells sensing ion concentration
• Extrinsic Controls:
  • Sympathetic nervous system response to low blood pressure
  • Hormonal mechanisms involving renin-angiotensin-aldosterone system

GFR and Blood Pressure

• High GFR results in more urine, decreased blood volume
• Low GFR can lead to accumulation of waste and toxins
• Regulation involves maintaining balance to avoid excessive urine output or retention of toxins

Important Questions:

• How do changes in blood pressure affect GFR and filtration dynamics?
• What role does diabetes mellitus play in affecting kidney function?

Conclusion:

• Understanding kidney filtration and regulation is crucial for maintaining homeostasis
• The balance between filtration and reabsorption is vital to body function
• Regulatory mechanisms are in place to adjust filtration in response to physiological needs