Group 4 Presentation14 May 2014

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+?

Present the Na+ clearance for your test subjects. (Table format)• Control subject had a general

decrease in Na+ clearance over time.

• Hypotonic subject had a general increase in Na+ clearance over time.

• Isotonic subject had a general decrease in Na+ clearance over time.

• Alkalosis subject had a general decrease in Na+ clearance over time.

Time (min) 0 30 60 90 120

Control0.556 0.667 0.326 0.264 0.371

Hypotonic 0.009 0.161 0.171 0.192 0.247

Isotonic0.221 0.084 0.068 0.057 0.047

Alkalosis 0.418 0.342 0.256 0.177 0.144

Present the Na+ clearance for your test subjects. (Graph format)

Control Hypotonic Isotonic Alkalosis0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

T = 0 minT = 30 minT = 60 minT = 90 minT = 120 min

Subject Category

Na+

cle

ara

nce

in m

L/m

in

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.

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.

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.

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.

How can you determine whether Na+ was secreted or absorbed?• This is the difference

between the filtration rate and the excretion rate.• Values greater than 0 indicate

secretion.

• Values lesser than 0 indicate absorption.

• A value of 0 indicates no secretion or absorption.

• All values in this case are greater than 0.

• Na+ was secreted in all cases.

Glomerular

filtration rate.

(~125 mL/min)

Na+ clearance

rate.

>0 = secretion

<0 = absorption0 = neither

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.

Homeostasis System1. 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.

Click icon to add picture