L22 - Renal physiology

• What percentage of resting cardiac output is delivered to the kidney?

  ~25%
• What does filtrate contain?

  Almost everything found in plasma except proteins
• What is urine?

  Processed filtrate containing unneeded substances
• How much filtrate is formed per day?

  Roughly 180 L
• How much urine leaves the body daily?

  Less than 1% (1.5 L)
• What percentage of filtrate is reabsorbed?

  More than 99%
• What are the three processes for urine formation?

  1. Glomerular filtration
  2. Tubular reabsorption
  3. Tubular secretion
• What is glomerular filtration?

  Produces cell- and protein-free filtrate
• What occurs during tubular reabsorption?

  Returns 99% of substances from filtrate to blood
• What is tubular secretion?

  Moves substances from blood to filtrate
• What is the primary force in glomerular filtration?

  Glomerular hydrostatic pressure (HPgc)
• What does the filtration membrane prevent?

  Filtration of blood cells and large proteins
• What is the net filtration pressure (NFP) formula?

  NFP = outward pressures - inward pressures
• If HPgc is 55 mm Hg, OPgc is 30 mm Hg, and HPcs is 15 mm Hg, what is NFP?

  $10 \text{ mm Hg}$
• What is the typical glomerular filtration rate (GFR)?

  120-125 ml/min
• What factors is GFR directly proportional to?

  Net filtration pressure, surface area, permeability
• How does afferent arteriole diameter affect GFR?

  Wider diameter increases GFR, narrower decreases
• What are the intrinsic controls of GFR regulation?

  • Myogenic mechanism
  • Tubuloglomerular feedback
• What happens during the myogenic mechanism?

  Afferent arteriole constricts with increased blood pressure
• What do macula densa cells respond to?

  Filtrate NaCl concentration
• What is the response to high filtrate NaCl?

  Release of vasoconstrictor chemicals
• What is the role of the juxtaglomerular apparatus (JGA)?

  Regulates glomerular filtration rate
• What are the extrinsic controls of GFR regulation?

  • Sympathetic nervous system
  • Renin-angiotensin-aldosterone mechanism
• How does the sympathetic nervous system affect GFR?

  Increases vasoconstriction, decreasing GFR
• What triggers the renin-angiotensin-aldosterone mechanism?

  Decrease in systemic blood pressure or volume
• What is the ultimate goal of the renin-angiotensin-aldosterone mechanism?

  Increase systemic blood pressure
• What does aldosterone do in this mechanism?

  Increases Na+ and H2O reabsorption
• What does angiotensin II cause?

  Peripheral vasoconstriction
• What increases sympathetic activity in the body?

  Norepinephrine and epinephrine
• What do norepinephrine and epinephrine activate?

  Adrenergic receptors (⍺1-type)
• What is the effect of adrenergic receptor activation on systemic arterioles?

  Causes vasoconstriction
• What happens to total peripheral resistance when vasoconstriction occurs?

  Total peripheral resistance increases
• How does vasoconstriction affect systemic blood pressure (BP)?

  It increases systemic BP
• What is the effect of vasoconstriction on afferent arterioles in the kidneys?

  It decreases blood flow to nephron
• What is the result of decreased blood flow to the nephron?

  Decreased glomerular filtration rate (GFR)
• How does decreased GFR affect urine output?

  It decreases urine output
• What is the purpose of redirecting blood flow to vital organs?

  To maintain organ function during low BP
• What is the renin-angiotensin-aldosterone mechanism?

  • Sequence of hormones released due to low BP
  • Increases systemic BP by:
  • Increasing Na+ and H2O reabsorption (aldosterone)
  • Causing peripheral vasoconstriction (angiotensin II)
• What triggers the release of renin from juxtaglomerular cells?

  Low systemic BP or blood volume
• What are the three pathways that activate juxtaglomerular cells to release renin?

  Sympathetic nervous system, macula densa cells, reduced stretch