Renal System Review

Agenda

• Overview of renal system functions
• Anatomy of the kidneys
• Structure of the nephron
  • Renal corpuscle
  • Proximal convoluted tubules
  • Loop of Henle
  • Collecting ducts
• Extra renal systems and vascular supply
• Medical applications

Functions of the Kidney

• Removal of nitrogenous waste from protein metabolism (urea, uric acid, ammonia)
• Regulation of fluid and electrolyte balance
• Blood pressure regulation
• Hormone production (e.g., erythropoietin for blood cell formation)

Gross Anatomy of the Kidneys

• Covered by a tough outer capsule of connective tissue
• Superior (cephalic) pole and inferior (caudal) pole
• Divided into cortex and medulla
• Major vessels enter and leave through renal hilum
• Retroperitoneal organ: not suspended by mesentery
• Renal pelvis: urine drains from minor and major calyces to the ureter
• Renal pyramids and lobes
• Vascular supply via renal artery and vein

Structure of the Nephron

• Cortical nephrons: mostly in the cortex
• Juxtamedullary nephrons: loops extend into the medulla, better at urine concentration
• Components:
  • Renal corpuscle: Bowman's capsule and glomerulus
  • Proximal convoluted tubule: ion and water reabsorption, glucose, amino acids
  • Loop of Henle: thin descending limb permeable to water, thick ascending limb for ion pumping (countercurrent exchange)
  • Distal convoluted tubule: ion transport, hormone-regulated (aldosterone)
  • Collecting duct: water reabsorption regulated by ADH (vasopressin)

Renal Corpuscle

• Blood filtration via blood hydrostatic pressure
• Specialized capillaries: glomerulus, with fenestrated endothelium
• Filtration barrier: trilaminar basal lamina, podocytes with filtration slits
• Diseases: Goodpasture syndrome, glomerulonephritis

Juxtaglomerular Apparatus

• Macula densa: sensitive to sodium and chloride
• Juxtaglomerular cells: release renin in response to low blood pressure
• Renin-angiotensin-aldosterone system:
  • Renin converts angiotensinogen to angiotensin I
  • Angiotensin-converting enzyme (ACE) converts it to angiotensin II
  • Angiotensin II acts as a vasoconstrictor and stimulates aldosterone release

Medical Applications

• ACE inhibitors (e.g., Captopril)
• Angiotensin receptor blockers (ARBs, e.g., Valsartan)

Collecting Ducts and Urinary Tract

• Collecting ducts transport urine to renal pelvis
• Consist of principal and intercalated cells
• Regulated by aldosterone and ADH
• Urinary tract: begins with calyces to ureter and bladder
• Transitional epithelium allows for stretching
• Specializations: apical plaques in bladder for stretch resilience

These notes provide a comprehensive overview of the renal system's anatomy and function, focusing on the nephron's structure and its role in processing and filtering blood to form urine. They highlight the hormonal regulation mechanisms and their medical implications, particularly in treating hypertension.