Notes on Renal Processes
Rahul's Noteblog
Notes on Nephrology
Notes on Renal Processes
General notes:
• Amount excreted = (amount filtered - amount reabsorbed) + amount secreted.
• Excretion = disposed in urine.
• Filtration = 100% blood is filtered through glomerular capillaries into the Bowman's capsule, and most is reabsorbed back into blood through the peritubular capillaries through to the renal vein; an energy requiring process.
• Tubular secretion = amount that is excreted directly through the peritubular capillaries without being filtered through. Eg., H+ ions for pH balance.
Factors that affect filtration:
Hydrostatic pressure of glomerular capillaries:
• Promotes filtration.
Oncotic pressure of plasma:
• Opposes filtration.
Hydrostatic pressure in Bowman's Capsule:
• Opposes filtration.
Protein or oncotic pressure in capsule:
• This is zero.
The filtering membrane is negatively charged; this inhibits the filtering of anions (negative). Protein is filtered if this charge is removed.
Concentrate entering the Bowman's capsule has the same concentration as plasma minus proteins.
20% of substance that enters the kidney is freely filtered.
Filtration fraction = FF = GFR/(Renal Plasma Flow).
GFR is determined by the glomerular capillary pressure; direct proportionality.
FF determined by renal plasma flow; direct proportionality.
Sympathetic NS: vasoconstriction; decreased GFR; increased FF; increased reabsorption.
Angiotensin II: no effect on GFR; maybe minimal decrease.
Glucose filtration dynamics:
• At low plasma levels, glucose filtration = glucose reabsorption.
• As glucose plasma concentration rises in plasma to ~ 2mg/ml, glucose excretion curve enters the region of splay and begins to increase.
• As glucose plasma concentration rises in plasma to ~ 2mg/ml, glucose absorption curve enters the region of splay and begins level off.
Transport Maximum (Tm) Systems:
• Entire filtered load is reabsorbed until carriers are saturated; the excess is then excreted.
• Eg., Glucose.
Time-gradient system:
• Eg., Sodium.
• A constant percentage of sodium is actively absorbed, that is, 2/3rd of all filtered sodium is reabsorbed.
• Oxygen consumption in the kidney is directly proportional to Na reabsorption and GFR.
• Na reabsorption is the main metabolic process in the kidney.
p-Aminohippuric Acid (PAH):
• Transport maximum system.
• Most is excreted through peritubular capillaries (80%) without being filtered through glomerular capillaries (20%).
• There is no reabsorption.
• Secretion = 4x greater than filtration.
• 80% continues to be secreted until nephron carriers become saturated.
Filtration = excretion:
• Insulin, mannitol.
Filtration greater than excretion:
• Glucose, sodium, urea.
Filtration less than excretion:
• PAH, creatinine.
Additional Reading:
Basic Nephrology
1. Renal Control in Acid-Base Balance
2. Renal Processes
3. Renal Clearance
4. Regional Transport
Related Topics
1. Kidney Disorders
2. Histology of the Urinary System
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Page accessed on: July 29, 2010, 11:08 am.