Lecture notes
human physiology year 1
- Module
- Physiology (BY1HP1)
- Institution
- Aston University, Birmingham (Aston)
Lecture notes of 8 pages for the course Physiology at Aston
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Urinary 3Urine excretion and plasma clearance
Plasma clearance is the volume of plasma cleared of a particular substance per minute
o Plasma clearance rate for a substance filtered but not reabsorbed or secreted (same as rate
of glomerular filtration)
o Plasma clearance rate for a substance filtered and reabsorbed (lower than glomerular
filtration rate)
o Clearance rate for a substance filtered and secreted (greater than glomerular filtration rate)
, Plasma clearance
Clearance rates for inulin (a carbohydrate) and PAH (polyamino-hippuric acid) can be used to
determine the filtration fraction:
o Filtration fraction = GFR (plasma insulin clearance)/ renal plasma flow (plasma PAH
clearance)
Urine excretion and long Henle’s loops
the kidneys can excrete urine of varying concentrations depending on body needs
o the extracellular fluid osmolarity depends on the relative amount of H2O compared to solute
establish the vertical osmotic gradient by counter current multiplication
o descending and ascending limbs of a long Henle’s loop
o counter current multiplication
1.
1. The active salt pump in the ascending limb establishes a 200 mOsm/L gradient at each horizontal
level
2. As the fluid flows forward several ‘frames’, a mass of 200mOsm/L fluid exists into the distal tubule
and a new mass of 300mOsm/L fluid enters from the proximal tubule
3. The ascending limb pump and descending limb passive fluxes re-establish the 200mOsm/L gradient
at each horizontal level
4. Once again, the fluid flows forward several ‘frames’
5. The 200mOsm/L gradient at each horizontal level is established once again
6. The final vertical osmotic gradient is established and maintained by the ongoing counter current
multiplication of the long loops of Henle
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