Biol 226 Final

• Nephron


  The functional unit of the kidney

  
• Parts of the nephron

  • Glomerulus
  • Bowman's capsule
  • PCT
  • Loop of Henle
  • DCT
  • Collecting duct
• Glomerulus


  • Fenestrated capillary bed, site of filtration
  • Afferent arteriole brings blood to the glomerulus
  • Efferent arteriole brings blood away from the glomerulus
• Bowman's Capsule


  • Contains specialized cells called podocytes that have filtration slits where fluid filters out of the glomerulus and into renal tubules

  
• Filtration Membrane


  • Fenestrated capillary epithelium (glomerulus + basement membrane) + podocytes of Bowman's Capsule

  
• PCT (Proximal Convoluted Tubule)


  Major site of reabsorption (glucose, amino acids, vitamins, ions, urea, water) and secretion (ions, toxins, neurotransmitters, drugs, bile)

  
• Loop of Henle


  Site of reabsorption (water, ions) and secretion (urea)
• DCT (Distal Convoluted Tubule)


  Site of reabsorption (ions) and secretion (ions)
• Collecting Duct


  Site of reabsorption (water, urea, ions) and secretion (ions)
• Filtration is a passive process that moves materials across the filtration membrane due to pressure differences
• Reabsorption is the movement of materials from the filtrate back into the bloodstream, which may be passive or active
• Secretion is the active transport of additional materials from the blood into the kidney nephron

  
• Juxtaglomerular Apparatus (JGA)


  • Composed of granular cells and macula densa
  • Granular cells detect blood pressure changes and release renin
  • Macula densa detect osmolarity of filtrate

  
• When blood pressure is low


  Renin is released by JG cells, triggering the renin-angiotensin system which increases blood pressure and decreases urine volume
• When blood pressure is high


  Afferent arteriole constricts, decreasing blood flow to the glomerulus and decreasing urine volume
• When blood pressure is low


  Afferent arteriole dilates, increasing blood flow to the glomerulus and increasing urine volume
• Net Filtration Pressure (NFP)


  The pressure that drives filtration in the glomerulus, calculated as the difference between the hydrostatic pressure in the glomerular capillaries and the sum of the hydrostatic pressure in Bowman's capsule and the osmotic pressure of the plasma proteins
• Normal Glomerular Filtration Rate is 125 ml/min or 200 L/day, but 99% is reabsorbed so only ~2 L/day is excreted as urine
• Percentage of filtrate reabsorbed


  • 65% in PCT
  • 15% in Loop of Henle
  • 19% in Collecting Duct (if ADH is secreted)
• Aldosterone


  Increases Na+ and H2O reabsorption, K+ secretion, leading to increased blood volume, blood pressure and decreased urine volume
• Angiotensin II


  Causes vasoconstriction, increases blood pressure, stimulates aldosterone and ADH release, and stimulates thirst, leading to increased blood volume and decreased urine volume
• ADH (Antidiuretic Hormone)


  Increases permeability of collecting duct to water, leading to increased water reabsorption, increased blood volume, increased blood pressure, and decreased urine volume
• Atrial Natriuretic Peptide (ANP)


  Inhibits ADH, aldosterone, and renin release, leading to decreased water reabsorption in collecting duct, increased urine volume, decreased blood volume, and decreased blood pressure
• Sympathetic nervous system stimulation constricts the afferent arteriole, decreasing blood flow to the glomerulus and decreasing urine volume
• Diuretics


  Agents that prevent water reabsorption, resulting in high urine volume
• Osmotic diuretics


  Substances not reabsorbed, so water remains in the urine (e.g. high glucose in diabetic patients)
• Dialysis


  Artificial filtration of blood
• Micturition Reflex


  Stimulated when stretch receptors in the bladder detect distension, controlled by external (voluntary) and internal (involuntary) sphincters