Urinary System Lecture Notes

Introduction

• Overview of the urinary system components:
  • Kidneys: Filter blood, remove waste, convert filtrate into urine.
  • Ureters, Urinary Bladder, Urethra: Covered in lab sessions.

Functions of the Kidneys

1. Elimination of Metabolic Wastes
   • Primarily nitrogenous wastes from protein and nucleic acid digestion (urea, uric acid).
2. Regulation of Ion Levels
   • Electrolytes: Sodium, potassium, calcium.
3. Regulation of Acid-Base Balance
   • Hydrogen ions and bicarbonate ions.
4. Regulation of Blood Pressure
   • Long-term regulation via kidneys.
5. Elimination of Biologically Active Molecules
   • Drugs, hormones.
6. Formation of Calcitriol
   • Active vitamin D (calcitriol) from inactive form.
7. Production and Release of Erythropoietin
   • Stimulates red blood cell production in response to low blood oxygen (hypoxia).
8. Gluconeogenesis
   • Producing glucose from non-carbohydrate sources during starvation.

Kidney Structure and Issues

• Kidney Ptosis: Sagging, blocking ureter, leading to hydronephrosis or kidney failure.
• Variations: Location differences, horseshoe kidneys, additional kidneys.

Nephron: Functional Unit of the Kidney

• Microscopic functional filtration unit.
• Composed of:
  • Renal Corpuscle: Contains glomerulus and glomerular capsule.
  • Renal Tubule: Includes proximal convoluted tubule, nephron loop (Loop of Henle), distal convoluted tubule.

Parts of the Nephron

• Renal Corpuscle:
  • Glomerulus: Tangle of capillary loops.
  • Glomerular Capsule: Two layers (visceral and parietal).
  • Filtration: Occurs in the capsule, filtrate enters capsular space.
• Renal Tubule:
  • Proximal Convoluted Tubule: Major site of reabsorption, rich in microvilli.
  • Nephron Loop: Descending (thin) and ascending (thick) limbs.
  • Distal Convoluted Tubule: Further reabsorption.

Types of Nephrons

• Cortical Nephrons: Short loops, 85% of nephrons.
• Juxtamedullary Nephrons: Long loops, regulate urine concentration.

Collecting System

• Collecting Tubules and Ducts: Receive urine from nephrons, adjust water and sodium levels.
• Principal Cells: Responsive to hormones (aldosterone, ADH).
• Intercalated Cells: Regulate pH.

Blood Supply to the Nephrons

• Afferent Arterioles: Bring blood to glomerulus.
• Efferent Arterioles: Branch into peritubular capillaries or vasa recta.
• Vasa Recta: Associated with juxtamedullary nephrons, important for concentrating urine.

Juxtaglomerular Apparatus

• Granular Cells (JG cells): Release renin, regulate blood pressure.
• Macula Densa: Detect sodium chloride concentration, signal renin release.
• Mesangial Cells: Support glomerular structure, unclear full function.

Additional Notes

• Filtration Process: Blood filtered at glomerulus, filtrate becomes urine.
• Lab and Histology: Important to examine tissue slides for proximal and distal tubules.

These notes summarize the key points of the urinary system lecture, providing an overview of kidney functions, nephron structure, and related anatomical and physiological aspects. Use these as a reference for understanding the urinary system's roles and processes.