Glomerular

• Nephron

  The functional unit of the kidney responsible for filtering blood
• Glomerular Filtration Rate (GFR)

  The amount of filtrate that is formed per minute, a measure of kidney function
• Unfiltered blood enters the kidney through the renal artery. Filtered blood leaves through the renal vein.
• Cortical nephron

  Have short loops of Henle, make up 80% of nephrons, play a role in reabsorption
• Juxtamedullary nephron

  Have long loops of Henle that travel deep into the renal medulla, make up 20% of nephrons, play a critical role in controlling urine concentration
• Organ system arranged in series

  Blood flow occurs in a specific order
• Organ system arranged in parallel

  Blood flow is split into different pathways and delivered to several organ systems at the same time
• Components that prevent cells and proteins from leaving the glomerular capillaries

  • Fenestrated capillaries
  • Basement membrane
  • Podocytes
• Ions, water, small molecules (glucose, amino acids, drugs, inulin, creatinine) are filtered through the glomerular capillaries
• Vasodilation of the afferent arteriole

  GFR increases
• Vasoconstriction of the efferent arteriole

  GFR increases
• Vasoconstriction of the afferent arteriole

  GFR decreases
• Vasodilation of the efferent arteriole

  GFR decreases
• Autoregulation

  An intrinsic mechanism that regulates GFR to keep it within a set point following changes in MAP
• Mean arterial pressure decreases

  Afferent arteriole vasodilates to increase PGC and bring GFR back up to set point
• Juxtaglomerular cells are responsible for detecting changes in pressure
• Extrinsic factors that regulate blood pressure

  • Norepinephrine (quick)
  • Angiotensin II (slow)
• Tasks necessary to produce urine

  • Glomerular filtration
  • Tubular reabsorption
  • Tubular secretion
• Paracellular reabsorption of water

  Water moves through tight junctions between renal epithelial cells into the blood
• Transcellular reabsorption of water

  Water moves down its concentration gradient through aquaporins (osmosis)
• Major functions of proximal tubule

  • Isoosmotic reabsorption of solutes, water, organic solutes, bicarbonate
  • Secretion of acid and drugs
• If clearance of a substance is greater than its GFR, it means the substance is secreted
• If clearance of a substance is less than its GFR, it means the substance is reabsorbed
• GFR

  Measures how much filtrate is formed
• Clearance of a substance is greater than its GFR

  Substance is secreted
• Clearance of a substance is less than its GFR

  Substance is reabsorbed
• Inulin

  Freely filtered and not reabsorbed or secreted, considered the gold standard for measuring GFR
• Creatinine

  Freely filtered, not reabsorbed and very slightly secreted, used as a measure for GFR
• Substances typically reabsorbed

  • Glucose
  • Amino acids
  • Sodium
  • Bicarbonate
  • Water
• Substances typically secreted

  • H+
  • Drugs
  • Toxins
• Juxtamedullary nephrons

  Play a major role in regulating water balance
• Concentration of urine as it travels through the loop of Henle

  Increases
• Descending limb of Henle

  Permeable to water, water moves through aquaporins
• Thick ascending loop of Henle

  Contains Na+/K+/Cl- symporter which leads to reabsorption of certain ions
• No ADH

  Urine would be very dilute, patients would urinate more frequently
• Alcohol inhibits ADH production

  Decreased water reabsorption, higher urine volume, more frequent urination
• Renin-angiotensin-aldosterone system (RAAS)

  Hormonal mechanism that changes blood pressure by regulating blood volume and salt concentrations
• Two special types of cells found at the juxtaglomerular apparatus

  • Macula Densa Cells (sense ions)
  • Juxtaglomerular Cells (sense changes in pressure)
• pH regulation in proximal tubule

  Bicarbonate reabsorbed, H+ secreted
• pH regulation in distal tubule

  H+ secretion within the intercalated cells