Physiology of renal and proximal and distal convoluted tubules , essential physiology of renal system, and affect of hormones on renal function, as reabsorption and excretion

1. Essentials of Human Physiology
Seventh Edition
Dr l Saleh-Aljammal
Renal system
9/2/2023.Lecture (9)
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2. Diuresis
Means increase in rate of urine output
1- Water diuresis:
Produced by drinking large amounts of water or hypotonic fluid. The diuresis begins
15 minute after water ingestion and reaches its maximum after 40 minutes.
Mechanism: increase in water intake leads to decrease in plasma osmolality which
inhibits ADH secretion decrease permeability of CD to water
decrease in water reabsorption in collecting ducts decrease facultative water
reabsorption excretion of large volume of hypotonic urine. Alcohol causes
water diuresis because it inhibits ADH secretion.
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3. Water intoxication
The maximal urine flow produced during water
diuresis is 16 ml/min. If water is ingested at a
higher rate cause swelling of cells because ECF
becomes hypotonic so water comes from ECF to
ICF leads to swelling of cell. In brain causes
convulsion, coma and death (water intoxication)
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4. 2- Osmotic diuresis (solute diuresis)
Produced by administration of osmotically active substances which are not
absorbed, in renal tubules mainly proximal tubules. The osmotic effect of such
compounds holds water within proximal tubules, causing decrease in obligatory
water reabsorption increasing urine volume.
a- Diabetes mellitus:
large quantities of unabsorbed glucose remaining in tubular fluid, osmotically
drags water with it, water absorption in proximal tubules is decreased leading
to increase urine volume in diabetics (urine contains glucose).
b- Administration of compounds that are filtered but not reabsorbed.
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6. Difference between water and osmotic diuresis
Osmotic diuresis
Water diuresis
- Amount of water reabsorbed in
proximal tubules is decreased .
Both obligatory and facultative water
reabsorption are decreased .
- Much more urine volume is
produced .
- ADH normal or increased .
- Urine is iso- or hypertonic due to
presence of solutes .
- Amount of water reabsorbed in
proximal tubules is normal .
- Maximum , urine volume produced is
16 ml / min . (23 L day ) .
- Decrease ADH due to decreased
plasma osmolarity .
- Urine is diluted ( hypotonic ) .
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7. 3)Pressure diuresis:
Increase in arterial blood pressure leads to:
a. GFR .
b. Inhibition of RAS renin and angiotensin II production .
c. hydrostatic pressure in glomerular capillaries which
increase Na+ and H2O excretion.
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8. 4) Diuretics: these drugs are used to increase rate of urine production.
i- Carbonic anhydrase inhibitors = acetazolamide (Diamox).
it inhibits carbonic anhydrase enzyme decrease H+ secretion decrease
Na+ and HCO3
- reabsorption in PCT and increase K+ secretion in DCT increase
Na +, HCO3
- and K+ excretion in urine.
ii. Loop diuretics = furosemide (Lasix )
Blocking Na+ - K+ -2Cl- co-transporter in thick ascending limb of LH decrease
reabsorption of these solutes in thick ascending limb of LH.
excretion of Na+ , solute concentration in MI
K+ and Cl- in urine osmolarity of MI
H2O reabsorption from CD
marked diuresis
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9. iii. Thiazide diuretics = chlorothiazide (esidrex). It inhibits reabsorption of Na+ in
early portion of DCT .
iv. Potassium –sparing diuretics ( aldosterone inhibitors ) spironolactone
(aldactone) it blocks action of aldosterone in late DCT and CD .
Na+ reabsorption K+ secretion
Na+ loss in urine k+ excretion
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