2. Question 4
• Present the Na+ clearance for your test subjects.
• What changes in Na+ clearance would you expect to see for each of these
subjects?
• How can you determine whether Na+ was secreted or absorbed?
• How does the body compensate for reduced body Na+?
• How does the body compensate for elevated Na+?
3.
4.
5. What changes in Na+ clearance would you
expect to see for each of these subjects?
• CONTROL SUBJECT
• Consumed no liquids during the lab.
• Results in no change to plasma volume.
• Results in no change to plasma osmolarity.
• Na+ clearance should remain constant or slightly decrease over time.
• No receptors are intensely activated.
• A slight decrease may be observed as the subject continues urinating without
rehydrating, resulting in mild decrease of blood plasma volume and subsequent brief
activation of volume receptors.
• This causes slightly more renin production, thus slightly more aldosterone production and
ultimately a slightly higher level of Na+ reabsorption.
6. What changes in Na+ clearance would you
expect to see for each of these subjects?
• HYPOTONIC SUBJECT
• Consumed 14 mL of water per kilogram of body mass.
• Results in plasma volume increase.
• Results in plasma osmolarity decrease.
• Na+ clearance should increase greatly over time.
• Increase should be highest among all the subjects.
• Osmoreceptors and volume receptors both activated in response to change in osmotic
pressure and fluid balance, respectively.
• Osmoreceptors will decrease vasopressin release from the posterior pituitary gland, resulting in
less water retention.
• Volume receptors will decrease renin production, which decreases aldosterone production, which
results in a decrease in Na+ reabsorption.
7. What changes in Na+ clearance would you
expect to see for each of these subjects?
• ISOTONIC SUBJECT
• Consumed 14 mL of isotonic saline solution per kilogram of body mass.
• Results in plasma volume increase.
• Results in no change to plasma osmolarity.
• Na+ clearance should increase over time.
• Only volume receptor is affected in this subject, not osmoreceptors.
• This subject’s blood plasma has the same osmolarity as the solution.
• Volume receptor will decrease production of renin, which decreases production of
aldosterone, which results in less Na+ reabsorption.
• Vasopressin levels decrease only due to volume receptors.
• Magnitude of effect is not as intense as the hypotonic subject.
• Water reabsorption does decrease, but not as much.
8. What changes in Na+ clearance would you
expect to see for each of these subjects?
• ALKALOSIS SUBJECT
• Consumed 2 mL of sodium bicarbonate solution per kilogram of body mass.
• Results in plasma volume increase.
• Results in no change to plasma osmolarity.
• Na+ clearance should increase over time.
• Similar receptor response as the isotonic subject.
9.
10. How does the body compensate…
..for reduced body Na+?
• Hyponatremia (<135 mEq/L)
• Renin-Angiotension-Aldosterone
complex reduces production of
vasopressin and induces
production of aldosterone, leading
to increased Na+ reabsorption.
• Decreases plasma volume and
increases Na+ concentration to
normal range.
…for elevated body Na+?
• Hypernatremia (>145 mEq/L)
• Angiotensin II induces production
of vasopressin and increases
water reabsorption.
• This increases plasma volume and
restores Na+ concentration to
normal range.
• Also causes feeling of thirst to
increase water in the body.
11. Homeostasis
System
1. Perfusion changes in
juxtaglomerular apparatus of the
kidney causes renin release.
2. Renin cleaves angiotensinogen into
angiotensin I.
3. Angiotensin-converting enzyme
converts angiotensin I to II.
4. Angiotensin II induces aldosterone
release and increased Na+
reabsorption/vasopressin and
sensation of thirst.
