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OSMOREGULATION (Renal clearance
ability of a kidney to remove substance…
OSMOREGULATION
What is osmoregulation?
The maintenance of constant osmotic pressure in the fluid of an organism by the control of water and salt concentration
Osmolarity
the concentration of a solution expressed as the total number of solute particles per liter.
Osmoregulator
Organisms that actively maintain their internal osmolarity without taking into account external environment
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Osmoregulation of Kidney function
Osmolarity of urine regulated by nervous system
Control of water & urine reabsorption by kidney
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Primary regulatory mechanism : ADH
Hypothalamus ->influeces thirst -> water uptake -> osmolarity reduces
Hypothalamus -> releases ADH -> homeostasis-> increases osmolarity -> Hypothalamus
Secondary regulatory mechanism : RAAS
Dehydration -> BP/BV decreases -> juxtaglomerular apparatus triggers secretion of renin -> angiotensinogen -> angiotensin I -> angiotensin II -> increases BP & BV -> urine decreases -> aldosteron released
Aldosterone - increases water & sodium reabsorption
Countercurrent Mechanism
osmotic gradient created with utilization of energy
Descending limb of loop of Henle permeable to water
Ascending loop is
permeable to solute but impermeable to water
:red_flag:osmolarity gradient created due to the less osmolarity in tubular fluid compared to the higher osmolarity in peritubular fluid
Renal clearance
ability of a kidney to remove substance from plasma
Ux V
Cx = -------
Px
measures
a) glomerular filtration rate
b) renal plasma flow
c) renal blood flow
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Creatinine clearance
to measure GFR
Free creatinine are not reused and excreted
Creatinine Clearance (ml / min) = (Urine Creatinine / Serum Creatinine) x (Urine Volume (ml) / [ time (hr) x 60 ] )* ( 1.73 / Body Surface Area)
• BSA (m2) = 0.0235 x Height (cm)0.42246 x Weight (kg)0.51456 (The Gehan and George formula)
Transport maximum
maximum rate for reabsoprtion of substance
- reached when carriers for reabsorption are saturated and nephrons are at their maximum capacity
Renal threshold
Amount of filtration exceeded = substance appears in urine
Glucose regulation
As reabsorption reaches maximum tubular capacity, glucose appears in urine
Glycosuric threshold - plasma glucose conc at given GFR
Glucose & Diabetes Mellitus
high glucose conc in plasma & urine due to lack of sufficient insuline
Kidney failure requires dialysis
Fresh water fish
- gills actively absorbs salt
- larger glomerulus
Salt water fish
- chloride cell actively expels chlorine ion & passively removes sodium ion
- reduce/no glomerulus
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