Renal L2: from blood plasma to urine (Reabsorption and secretion) Flashcards
_____% of plasma entering kidneys is filtered
20%
_____ml of filtrate/min; ____ L/day; Average plasma volume = _____ L
125; 180; 2.75
Plasma is filtered __ times per day!
65
Without reabsorption total plasma volume lost in ____min!!!!
30
What is reabsorption? Why is it important?
selective movement of substances from tubules back into blood
Filtrate (same contents as plasma without protein) contains substances we want to keep (eg. Water, electrolytes & nutrients)
Reabsorbed substances travel back into the ____system via _____ capillaries
venous; peritubular
Out of the 180 L/day plasma filtered, ____ L/day is reabsorbed! Why produce excessive filtrate and then reabsorb most of it?!
178.5 allows control; can get various toxics, drugs into filtrate–> doesn’t always have a specific receptor
Which tubule is where most of the filtrate is reabsorbed? What is specifically reabsorbed in this tubule?
Proximal tubule (60-70%)
Approx. all organic nutrients (glucose & amino acids) –60-70% Na+& Cl-+ other ions –60-70% water
What is reabsorbed in the Loop of Henle?
25% water and Na+reabsorption very specific role (abililty to be [urine]- dilute or concentrated)
What is reabsorbed in the distal tubule and collecting duct?
Hormonally controlled reabsorption of water and Na+ important for maintaining blood volume
How does reabsorption occur?
Molecules must move from the tubule lumen to the interstitial fluid & capillaries
- Transepithelial transport (1)
- Paracellular pathway (2)
What is the Transepithelial transport?
More common; through cell
What is the Paracellular pathway?
between the cells (2)
Movement can be _____ and ______.
Passive; Active
What does passive movement mean?
No steps require ATP
What does active movement mean?
at least one step requires ATP`
What are the 5 barriers that must be crossed during transepithelial transport?
- Na+is reabsorbed by active transport to produce concentration & electrical gradients
- Movement of Na+produces an electrical gradient that favours the movement of anions into the ECF (eg. Cl-) (-ve ions pass passively into ECF)
- Movement of Na+and anions increasesthe solute concentration in the ECF and water follows via osmosis
- Movement of water into the ECF concentratesthe remaining solutes in the lumen allowing passive diffusion of solutes into the ECF (eg. Urea) (NA+ re-absorption is important for initiating the process)
What is the process of reabsorption in terms of Na+?
- Na+transport across the basolateral membrane is active (Na+-K+pump) and produces a Na+concentration gradient(low in cell, high in the interstitial fluid) 2)
- Transport across the luminal membrane is passive and down the concentration gradient
How does Na+ concentration gradient aid the reabsorption of other essential molecules (eg. glucose)? What does each of the steps require in terms of active or passive diffusion?
- Secondary active transport
- Facilitated diffusion
- Primary active transport
What is the transport maximum (Tm)? What does this mean?
Transport maximum (Tm) = transport rate when carriers are saturated
no longer transportation is available
What is the renal threshold?
Renal threshold = plasma concentration at which Tm is reached and molecule (eg. Glucose) first appears in the urine
Why are some substances secreted form the plasma into the filtrate?
use for substances that that are too high in conc.
Reduce their concentration in the blood
How is K+ secreted?
Na+/K+ pump
Where is the Na+/K+ pump found?
basolateral membrane- to regulate Na+ and K+
