PHIS 206 Lecture Notes - Lecture 20: Peritubular Capillaries, Tubular Fluid, Nephron
2 May 2018
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Lecture 20: Filtration, Reabsorption, and Secretion
Vocabulary
• Lumen = the inside of any tube or hollow space
• Filtration = passive movement of water and dissolved solute from blood (glomerular
capillaries) into tubule → relatively indiscriminant
• Reabsorption = active process of moving already filtered substances from the tubule back
into the blood (peritubular capillaries) → only reabsorb what we filtrate that we need
• Secretion = active process of moving substances from blood (peritubular capillaries) into
the tubule
• Urine = everything in your blood that you don’t want
• Kidney is like a collection of tubes
•
Three Processes
• Focus question:
o Name two ways that substances can enter the tubule (tubular fluid)
o Name two ways that substances can leave the tubule (tubular fluid)
• Explain using the vocab we just learned**also know the answers to this
• Glomerular filtration (GF) - non discriminant filtration of a protein-free plasma from the
glomerulus into Bowman’s capsule
• Tubular Reabsorption - selective movement of filtered substances from the tubular lumen
into the peritubular capillaries
• Tubular secretion - selective movement of non filtered substances from the peritubular
capillaries into the tubular lumen
Different Types of Nephrons
• Juxtamedullary Nephrons
o 20% of nephrons
o Long loops of Henle
• Cortical Nephrons
o 80% of nephrons
o Larger role in reabsorption and secretion
• Some of them have big loops of henle → play a role to help concentrate your urine
(longer the loop, the more concentrated)
The Glomerulus
• Filtration → from blood into the tubule
• Forms the filtrate or ultrafiltrate
• Remember, A before E (afferent before efferent)
Spaghetti Strainer
• What can be filtered?
o Anything small dissolved in the plasma and H20
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Document Summary
The glomerulus: filtration from blood into the tubule, forms the filtrate or ultrafiltrate, remember, a before e (afferent before efferent) Spaghetti strainer: what can be filtered, anything small dissolved in the plasma and h20, examples: glucose, na+, bicarbonate, what cannot, rbcs, large proteins, other cells of the blood, should not have blood in your urine. Other pressures: overall the pressures typically add up so that pressures favoring filtration exceed pressures opposing filtration, remember, osmotic pressures pull , proteins in your blood trying to hold on to fluid, osmotic pressure opposes filtration. If your full of urine, it won"t make anymore. What adjusts gfr: double arterioles, how is gfr affected by , constriction of , afferent arteriole, efferent arteriole, dilation of , afferent arteriole, efferent arteriole. 100: remember the goal here - remove nasties, hold on to goodies. 100: 20% of everything that can be filtered, will be filtered.
