Lecture Notes: Chapter 19 - The Kidneys

Overview

• Focus on kidney functionality
• Skipping detailed kidney anatomy

Functions of the Kidneys

• Regulation of Blood Volume and Pressure
  • Increased blood volume -> increased blood pressure
  • Kidneys release excess fluid to reduce pressure
• Osmolarity Regulation
  • Excretion or retention of water
  • Ion balance maintenance (sodium, potassium, calcium)
• pH Regulation
  • Excretes hydrogen or bicarbonate ions
• Waste Excretion
  • Removes metabolic waste, xenobiotics, hormones
• Hormone Production
  • Synthesizes erythropoietin, enzyme renin
  • Converts vitamin D3 to calcitriol

Urinary System Components

• Urinary System: Ureters, urinary bladder, urethra, kidneys
  • Function: Filter blood, modify filtrate, produce urine
  • Pathway: Kidneys -> Ureters -> Bladder -> Urethra

Blood Flow and Nephrons

• Blood Flow: 20-25% cardiac output to kidneys
• Nephrons: Functional unit of the kidney
  • Components: Renal corpuscle, renal tubule
  • Types: Cortical nephrons, juxtamedullary nephrons

Nephron Structure

• Portal System
  • Afferent arteriole -> Glomerulus -> Efferent arteriole -> Peritubular capillaries/vasa recta
• Renal Corpuscle: Glomerulus and glomerular capsule
• Renal Tubule: Proximal convoluted tubule, nephron loop (Loop of Henle), distal convoluted tubule

Kidney Processes

• Filtration
  • Movement of fluid/solutes from blood to capsular space
  • Filtrate: Water and solutes in capsular space
• Reabsorption
  • Movement of substances from filtrate back into the body
  • Important for reclaiming glucose, sodium, etc.
• Secretion
  • Transfer of materials from blood to filtrate
  • More selective than filtration

Filtration Rate

• Glomerular Filtration Rate (GFR)
  • Volume of filtrate produced per time unit
  • Average GFR: 180 liters/day
  • Factors: Net filtration pressure, filtration coefficient

Reabsorption Details

• Processes: Active and passive transport
• Sodium Reabsorption: Transcellular (through cells)
• Water Movement: Follows ions by osmosis
• Transport Maximum and Renal Threshold
  • Saturation point where transport proteins are fully occupied

Secretion and Clearance

• Secretion: Movement of materials into filtrate
• Clearance: Rate solute disappears from blood
  • Used to estimate GFR
  • Substances like inulin and creatinine used for measurement

Regulation of GFR

• Local Regulation: Smooth muscle reaction to pressure
• Juxtaglomerular Complex: Monitors sodium/chloride concentration
• Long-Distance Reflexes: Sympathetic signals, hormones

Chapter 20 - Integrative Physiology 2

Water and Electrolyte Balance

• Water Balance: Intake vs. loss
• Kidney Role: Conserves water, adjusts GFR
• Osmolarity in Medulla: Concentration gradient aids water reabsorption

Hormonal Regulation

• ADH (Antidiuretic Hormone)
  • Controls water permeability in collecting system
• Aldosterone
  • Stimulates sodium reabsorption

Renin-Angiotensin System

• Role: Regulates blood pressure/volume
• Process: Renin -> Angiotensinogen -> Angiotensin I -> ACE -> Angiotensin II
• Effects: Increases ADH, thirst, vasoconstriction, sympathetic signaling

Conclusion

• Regulation of Blood Pressure and Osmolarity
• Effects of Dehydration: Increased osmolarity, decreased pressure
  • Hormonal responses to maintain balance

Additional Notes

• Office Hours: Tuesdays 12:30-1:30 PM
• Study Guide and Homework available on Moodle
• Final Exam: Next Friday, prep using provided resources