L30: Electrolyte Renal Functions pt. 1

how many mL is in 1 kg about?

1000 mL

total body water makes up _____% of body weight.

60

why is the ECF often the focus?

typically where blood samples are drawn from

what mechanism dominates the control of blood volume and ECF volume?

the effect of blood volume on arterial pressure

the interplay of what two systems is critical in controlling blood volume?

kidneys and cardiovascular system

osmotic pressure

the pressure required to stop the diffusion of pure water through a semi permeable membrane under a concentration gradient

osmolarity

total number of moles dissolved in molecules or ions in 1L of solution

tonicity

osmotic pressure of a solution on a cell to gain or lose water based on the concentration of nonpenetrating solutes

isotonic solution

no change in cell volume

hypertonic solution

solution has increased number of solutes that draws water out of the cell causing the cell to shrink

hypotonic solution

solution has decreased number of solutes (outside the cell) causing water to be drawn into the cell = cell swelling

what happens if fluid intake falls below normal in the pressure natriuresis and pressure diuresis fluid feedback?

1. decrease in blood pressure

2. decrease in blood volume

3. large decrease in urine output

what compensatory mechanisms will be activated when fluid intake falls below normal?

1. baroreceptors

2. RAAS

3. aldosterone

4. ADH

what does aldosterone do when fluid intake falls below normal?

increases absorption of water and salts to try and maintain fluid volume in the blood

what does RAAS do when fluid intake falls below normal?

angiotensin 2 will be released to cause vasoconstriction and increase blood pressure

A 7-year-old, 20 kg labrador presents with lethargy, weakness, and a history of decreased water intake. Bloodwork reveals mild hypernatremia and elevated plasma osmolarity. You suspect a compensatory hormonal response to address the dehydration and sodium imbalance.

What is the most likely mechanism through which angiotensin II contributes to restoring plasma volume and osmolarity in this dog?

induction of aldosterone release from the adrenal cortex to promote sodium and water reabsorption

What is the function of Atrial Natriuretic Peptide (ANP) in regulating body fluids?

1. promotes natriuresis and diuresis (increases Na+ and water excretion)

2. inhibits ADH and the renin–angiotensin–aldosterone pathways.

volume expansion leads to…

1. decreased renal sympathetic nerve activity

2. increased release of ANP

3. inhibition of ADH

4. decreased renin

5. decreased aldosterone

what happens to cells in dehydration?

osmolarity increases and cells shrink

what hormones are released in dehydration?

1. ADH released to maximize water retention and thirst

2. aldosterone leads to sodium and water retention during hypovolemia

what might cause hypertonic dehydration?

extensive hyperventilation and hyperthermia

How does antidiuretic hormone (ADH) influence water balance during dehydration?

promotes water reabsorption in collecting ducts and stimulates thirst to restore ECF osmolarity

How does extracellular hypertonicity trigger ADH release at the cellular level?

1. Hypertonicity causes neuron shrinkage

2. activates nonselective cation channels (NSCCs)

3. depolarization increases AVP/ADH release

4. hypotonic states inhibit NSCCs and reduce ADH release from axon terminals

5. promotion of diuresis

what happens to GFR during dehydration?

GFR decreases

what occurs in the body during dehydration?

1. GFR decreases

2. Na+ reabsorption by proximal tubule and loop of henle increases

3. Na+ reabsorption by the distal tubule and collecting duct enhanced

4. reduced urinary water and Na+ excretion

What hormonal changes occur during volume expansion related to the RAAS system?

Renin secretion decreases → lower angiotensin II → lower aldosterone; natriuretic peptides promote excretion, opposing RAAS

What happens when extracellular fluid expands beyond the normal range to the interstitial space?

The interstitial space can overflow, leading to edema when ECF expands roughly 30–50% above normal.