Renal Phys 2

• 20% of plasma is:


  filtered
• 80% of plasma continues into the:


  efferent arteriole
• excretion (urine composition) =

  F + S - R

  filtration + secretion - reabsorption
• does secretion equal excretion?

  no
• freely filtered, 100% secreted


  ex: drugs, toxins

  
• freely filtered, partially reabsorbed


  ex: Na+, Cl-, water

  
• freely filtered, 100% reabsorbed


  ex: glucose, amino acids

  
• where does glomerular filtration occur?

  renal corpuscle
• outer capsule of Bowman's capsule


  parietal layer
• inner capsule that is tightly wrapped around glomerular capillaries in Bowman's capsule

  visceral layer (podocyte)
• three layers composing the filtration barrier

  1.) capillary endothelium

  2.) basement membrane

  3.) Bowman's epithelium
• fenestrated = more exchange


  capillary endothelium
• negatively charged matrix that surrounds capillaries

  basement membrane
• podocytes and filtration slits

  Bowman's epithelium
• blood flows into the glomerulus through the afferent arterioles and leaves the glomerulus through the efferent arterioles. the proximal tubule exits the Bowman's capsule.
• podocytes of Bowman's capsule surround the capillaries. filtration slits between the podocytes allow fluid to pass into Bowman's capsule. the glomerulus is composed of capillary endothelium that is fenestrated. surrounding the endothelial cells is a basement membrane.
• fenestration ________ exchange

  increases
• substances in the blood are filtered through capillary pores between endothelial cells (single layer). the filtrate then passes across the basement membrane and through filtration slit between the foot processes (also called pedicels) and enters the capsular space. from here, the filtrate is transported to the lumen of the proximal convoluted tubule.
• what solutes are too big for filtration?

  plasma proteins and cells
• negatively charged membranes also exclude ______ proteins

  plasma
• filtrate =

  blood plasma except for RBCs and proteins
• filtrate gathers in Bowman's space and then goes into ________ tubule

  proximal
• blood cells, plasma proteins, large anions, protein-bound minerals and hormones, most molecules > 8 nm in diameter


  can't be filtered out of the bloodstream
• water, electrolytes, glucose, amino acids, fatty acids, vitamins, urea, uric acid, creatinine


  can be filtered out of the bloodstream
• Glomerular Filtration Rate (GFR) =


  125 mL/min (180 L/day)
• name the starling force that favors filtration and the 2 starling forces that oppose filtration

  favors filtration: P(GC)

  opposes filtration: P(BS) & pi(GC)

  
• P(GC) is normally

  60 mmHg
• renal arterioles can regulate P(GC) from neural, hormonal, or local inputs
• 15 mmHg


  P(BS)
• 29 mmHg


  pi(GC)
• opposes filtration and is determines by plasma proteins


  pi(GC)
• why doesn't pi(BS) usually exist?

  because there are no proteins in Bowman's space
• if P(GC) > P(BS) + pi(GC), then...

  filtration into Bowman's space occurs (this is normal)
• constriction of afferent arteriole or dilation of efferent arteriole


  decreased GFR

  
• constriction of efferent arteriole or dilation of afferent arteriole


  increased GFR

  
• net glomerular filtration pressure =

  P(GC) - P(BS) - pi(GC)
• which starling force will be changed by a urinary tract blockage, such as a kidney stone?

  increased P(BS)
• what happens to the net glomerular filtration pressure if a kidney stone is present?

  decreases
• comparison between F, S, and R


  image:

  
• filtered load (mg/min) = 


  GFR (mL/min) x [P]s (mg/mL)