Osmolality and diuresis
• Understand the concept of osmolality and types of diuresis e.g. osmotic/ADH deficiency
Osmolality
- Is a measure of how much one substance has dissolved in another substance
- The greater the concentration of the substance dissolved, the higher the osmolality
- There is a raised gradient of osmolality from the cortex to the tip of the medulla.
o The osmolality is isotonic to the plasma, but down the pyramid the osmolality
increases
Diuretics
- When fluid balance is disturbed, if the kidneys are beginning to function less efficiently or in
diabetes, the circulation becomes overfilled, leading to hypertension.
- In these states it is necessary to increase the urine flow with diuretics to reduce the fluid
overload in the circulation.
- Diuretics = medications designed to increase the amount of water and salt expelled from the
body as urine
- These drugs have several sites of action along the nephron, with different mechanisms of
action depending on the processes of water and salt recovery in the given segment of the
nephron
- Most of the water filtered into the nephron must be recovered to preserve homeostasis
- The bulk of this fluid is reabsorbed by the PCT (70-80%), the loops of Henle recover
approximately 10%–20%, leaving the thick ascending loop, the DCT and the CDs to recover
the final 10%
o Only approximately 1 mL/min passes into the bladder as urine.
• Understand the concept of osmolality and types of diuresis e.g. osmotic/ADH deficiency
Osmolality
- Is a measure of how much one substance has dissolved in another substance
- The greater the concentration of the substance dissolved, the higher the osmolality
- There is a raised gradient of osmolality from the cortex to the tip of the medulla.
o The osmolality is isotonic to the plasma, but down the pyramid the osmolality
increases
Diuretics
- When fluid balance is disturbed, if the kidneys are beginning to function less efficiently or in
diabetes, the circulation becomes overfilled, leading to hypertension.
- In these states it is necessary to increase the urine flow with diuretics to reduce the fluid
overload in the circulation.
- Diuretics = medications designed to increase the amount of water and salt expelled from the
body as urine
- These drugs have several sites of action along the nephron, with different mechanisms of
action depending on the processes of water and salt recovery in the given segment of the
nephron
- Most of the water filtered into the nephron must be recovered to preserve homeostasis
- The bulk of this fluid is reabsorbed by the PCT (70-80%), the loops of Henle recover
approximately 10%–20%, leaving the thick ascending loop, the DCT and the CDs to recover
the final 10%
o Only approximately 1 mL/min passes into the bladder as urine.
