BIOL 373: Unit 4d (Fluid and Electrolyte
Balance)
1.1L - correct answer ✔✔The kidneys are responsible for most salt (Na) excretion, however, if the
kidneys weren't clearing any salt, we would need to take in _____ extra water per day just to maintain
normal Na+ in ECF.
False: loss of salt through sweat is normally very minimal, the only exception to this is HEAVY sweating. -
correct answer ✔✔T or F: A substantial amount of salt is lost through sweat
True: Cl- normally follows Na+ via the electrochemical gradient and via NKCC or NaCL symporters -
correct answer ✔✔T or F: Na+ is regulated, but not Cl-
Vasopressin and thirst - correct answer ✔✔Increased osmolarity is a strong stimulus for?
False: No change in volume (purely hyperosmolarity response). Although there is no actual issue with
being short on water, the increase in osmolarity causes thirst, so more water intake will increase, and
this messes up the homeostatic extracellular volume of water (water balance). - correct answer ✔✔T or
F: when extra NaCl is ingested, osmolarity and volume increase.
baroreceptor reflex - correct answer ✔✔The primary reflex pathway for homeostatic control of blood
pressure
Baroreceptors constantly monitor how much blood you have in your blood vessels and their pressure.
When your blood pressure needs to change, your baroreceptors will tell your brain, which signals your
heart and blood vessels to take action.
With increased blood volume, the blood vessels stretch, and the baroreceptors will sense this stretch.
This message of the increased firing rate of baroreceptors goes to the brain. The response is activated via
the parasympathetic system, while the sympathetic system is inhibited. Blood pressure decreases by
vasodilation and decreased heart rate.
In the absence of this stretch (decreased BP), and decreased firing rate of baroreceptors, the
sympathetic system is activated and the parasympathetic system inhibited. BP is increased by
,vasoconstriction and increasing heart rate. - correct answer ✔✔What do baroreceptors do? How does
the baroreceptor reflex work?
Increased water intake leads to increased ECF volume and blood pressure, and this problem is fixed by
the rapid response of the cardiovascular system and the slow response of the kidneys. In a baroreceptor
response, cardiovascular reflexes lower blood pressure rapidly, while the kidneys slowly excrete salt and
water, helping the volume and blood pressure to return to normal. - correct answer ✔✔When extra NaCl
is ingested, this lead to an increased water intake because of thirst. However, this disrupts the water
balance in the body. How is this problem solved?
With salt ingestion, there is no change in volume, but increased osmolarity. Vasopressin is secreted and
another response includes thirst, which increases water intake. This and the increase in aquaporin
expression due to VP causes an increase in renal water reabsorption, and the extracellular volume of
water, as well as blood pressure, increases. While the kidneys have been successful in conserving water,
the ECF volume and blood pressure need to be returned to homeostasis. To do this, the kidneys slowly
excrete salt and water. With this, and the increased water intake, osmolarity returns to normal. The
cardiovascular system reduces cardiac output and relaxes blood vessels rapidly, lowering blood pressure.
Both the excretion of salt and water by the kidneys and the cardiovascular reflexes bring volume and
blood pressure back to normal. - correct answer ✔✔Describe all homeostatic responses to salt ingestion.
Hypo-osmotic; 90 - correct answer ✔✔The fluid leaving the ascending loop of Henle is ________ relative
to plasma. At this point, ___% of the original filtrate has been reabsored.
True - correct answer ✔✔T or F: the proximal tubule is always permeable to water
False: Water is reabsorbed at the descending limb, but this is not regulated. The descending limb is
always permeable to water.
Remember, the reabsorption of water is only regulated (by VP) with the insertion of aquaporins at the
distal tubule and collecting duct (distal nephron). - correct answer ✔✔T or F: Water is reabsorbed at the
descending limb, which is regulated by the expression of aquaporins.
NKCC - correct answer ✔✔Na+ is reabsorbed at the ascending limb via _______
Aldosterone - correct answer ✔✔Na+ is regulated at the distal nephron via ___________ hormone.
, Mineralocorticoids (aldosterone)
- "mineral" - involved with Na+ and K+
- "corticoid" - produced in adrenal cortex - correct answer ✔✔Promote reabsorption of Na+ and
excretion of K+ in kidneys
True - correct answer ✔✔T or F: Aldosterone is a steroid hormone
False: Aldosterone is lipid soluble, so it cannot be stored in membrane-bound vesicles because it would
just float out. Therefore, aldosterone is synthesized on demand in the adrenal cortex. - correct answer
✔✔T or F: Aldosterone is stored in membrane-bound vesicles
False: Replace "extracellular" with "intracellular" to make this statement true. - correct answer ✔✔T or
F: Aldosterone acts via extracellular receptors; ligand-activated transcription factors.
True - correct answer ✔✔T or F: new proteins that modulate existing pumps/channels, as well as new
pumps/channels, are synthesized by upstream aldosterone response elements, which are expressed by
genes driven by aldosterone steroid hormone.
Apical; basolateral - correct answer ✔✔On which side of the epithelial membrane is Na+ import and K+
export occurring by the action of aldosterone? On which side of the epithelial membrane is the Na/K-
ATPase located?
Principal cells (P cells) - correct answer ✔✔primary target cells of aldosterone located within the
epithelium of the distal nephron
1) Aldosterone arrives in the blood and crosses into the interstitial fluid to bind to the cytoplasmic
aldosterone receptor, which is a transcription factor that needs to be activated by ligand-binding.
2) The hormone-receptor complex drives the expression of aldosterone-regulated genes, which
transcribe new pumps/channels and also modulate existing pumps/channels, such as the basolateral
Na+-K+ pump.
3) Result is increased Na+ reabsorption and K+ secretion. - correct answer ✔✔Describe, in steps, how
the action of the aldosterone steroid hormone results in increased Na+ reabsorption and K+ secretion.
Balance)
1.1L - correct answer ✔✔The kidneys are responsible for most salt (Na) excretion, however, if the
kidneys weren't clearing any salt, we would need to take in _____ extra water per day just to maintain
normal Na+ in ECF.
False: loss of salt through sweat is normally very minimal, the only exception to this is HEAVY sweating. -
correct answer ✔✔T or F: A substantial amount of salt is lost through sweat
True: Cl- normally follows Na+ via the electrochemical gradient and via NKCC or NaCL symporters -
correct answer ✔✔T or F: Na+ is regulated, but not Cl-
Vasopressin and thirst - correct answer ✔✔Increased osmolarity is a strong stimulus for?
False: No change in volume (purely hyperosmolarity response). Although there is no actual issue with
being short on water, the increase in osmolarity causes thirst, so more water intake will increase, and
this messes up the homeostatic extracellular volume of water (water balance). - correct answer ✔✔T or
F: when extra NaCl is ingested, osmolarity and volume increase.
baroreceptor reflex - correct answer ✔✔The primary reflex pathway for homeostatic control of blood
pressure
Baroreceptors constantly monitor how much blood you have in your blood vessels and their pressure.
When your blood pressure needs to change, your baroreceptors will tell your brain, which signals your
heart and blood vessels to take action.
With increased blood volume, the blood vessels stretch, and the baroreceptors will sense this stretch.
This message of the increased firing rate of baroreceptors goes to the brain. The response is activated via
the parasympathetic system, while the sympathetic system is inhibited. Blood pressure decreases by
vasodilation and decreased heart rate.
In the absence of this stretch (decreased BP), and decreased firing rate of baroreceptors, the
sympathetic system is activated and the parasympathetic system inhibited. BP is increased by
,vasoconstriction and increasing heart rate. - correct answer ✔✔What do baroreceptors do? How does
the baroreceptor reflex work?
Increased water intake leads to increased ECF volume and blood pressure, and this problem is fixed by
the rapid response of the cardiovascular system and the slow response of the kidneys. In a baroreceptor
response, cardiovascular reflexes lower blood pressure rapidly, while the kidneys slowly excrete salt and
water, helping the volume and blood pressure to return to normal. - correct answer ✔✔When extra NaCl
is ingested, this lead to an increased water intake because of thirst. However, this disrupts the water
balance in the body. How is this problem solved?
With salt ingestion, there is no change in volume, but increased osmolarity. Vasopressin is secreted and
another response includes thirst, which increases water intake. This and the increase in aquaporin
expression due to VP causes an increase in renal water reabsorption, and the extracellular volume of
water, as well as blood pressure, increases. While the kidneys have been successful in conserving water,
the ECF volume and blood pressure need to be returned to homeostasis. To do this, the kidneys slowly
excrete salt and water. With this, and the increased water intake, osmolarity returns to normal. The
cardiovascular system reduces cardiac output and relaxes blood vessels rapidly, lowering blood pressure.
Both the excretion of salt and water by the kidneys and the cardiovascular reflexes bring volume and
blood pressure back to normal. - correct answer ✔✔Describe all homeostatic responses to salt ingestion.
Hypo-osmotic; 90 - correct answer ✔✔The fluid leaving the ascending loop of Henle is ________ relative
to plasma. At this point, ___% of the original filtrate has been reabsored.
True - correct answer ✔✔T or F: the proximal tubule is always permeable to water
False: Water is reabsorbed at the descending limb, but this is not regulated. The descending limb is
always permeable to water.
Remember, the reabsorption of water is only regulated (by VP) with the insertion of aquaporins at the
distal tubule and collecting duct (distal nephron). - correct answer ✔✔T or F: Water is reabsorbed at the
descending limb, which is regulated by the expression of aquaporins.
NKCC - correct answer ✔✔Na+ is reabsorbed at the ascending limb via _______
Aldosterone - correct answer ✔✔Na+ is regulated at the distal nephron via ___________ hormone.
, Mineralocorticoids (aldosterone)
- "mineral" - involved with Na+ and K+
- "corticoid" - produced in adrenal cortex - correct answer ✔✔Promote reabsorption of Na+ and
excretion of K+ in kidneys
True - correct answer ✔✔T or F: Aldosterone is a steroid hormone
False: Aldosterone is lipid soluble, so it cannot be stored in membrane-bound vesicles because it would
just float out. Therefore, aldosterone is synthesized on demand in the adrenal cortex. - correct answer
✔✔T or F: Aldosterone is stored in membrane-bound vesicles
False: Replace "extracellular" with "intracellular" to make this statement true. - correct answer ✔✔T or
F: Aldosterone acts via extracellular receptors; ligand-activated transcription factors.
True - correct answer ✔✔T or F: new proteins that modulate existing pumps/channels, as well as new
pumps/channels, are synthesized by upstream aldosterone response elements, which are expressed by
genes driven by aldosterone steroid hormone.
Apical; basolateral - correct answer ✔✔On which side of the epithelial membrane is Na+ import and K+
export occurring by the action of aldosterone? On which side of the epithelial membrane is the Na/K-
ATPase located?
Principal cells (P cells) - correct answer ✔✔primary target cells of aldosterone located within the
epithelium of the distal nephron
1) Aldosterone arrives in the blood and crosses into the interstitial fluid to bind to the cytoplasmic
aldosterone receptor, which is a transcription factor that needs to be activated by ligand-binding.
2) The hormone-receptor complex drives the expression of aldosterone-regulated genes, which
transcribe new pumps/channels and also modulate existing pumps/channels, such as the basolateral
Na+-K+ pump.
3) Result is increased Na+ reabsorption and K+ secretion. - correct answer ✔✔Describe, in steps, how
the action of the aldosterone steroid hormone results in increased Na+ reabsorption and K+ secretion.
