Renal 7: Regulation of Osmolality

Electrolytes, water

Body fluid balance depends on the relationship between ___ (primarily sodium) and ___.

300

Body fluid osmolality is maintained at ~___ mOsm/L.

1

± _% change in osmolarity is tolerated (more regulated than blood pressure).

ECF water

Control of osmolality always involves changes in ___.

Hypernatremia

High sodium levels

Dogs are sensitive to this condition

Herring bodies

Nerve terminals that ADH is stored in within the posterior pituitary

Osmolality of the body fluids (osmotic), volume and pressure of the vascular system (hemodynamic)

Two primary physiologic regulators of ADH secretion

Angiotensin II, nicotine

Hormones that stimulate ADH secretion

Atrial natriuretic peptide, ethanol

Hormones that inhibit ADH secretion

Set point

Plasma osmolality value at which ADH secretion begins to increase

Varies among individuals and is genetically determined

No ADH is released

What happens below the set point?

ADH is released

What happens above the set point?

Osmoreceptors

Sense changes in body fluid osmolality by either shrinking or swelling

Cell shrinking

Action of osmoreceptors

Activates more channel activity, thereby depolarizing the cell —> Increase action potentials

Cell swelling

Action of osmoreceptors

Inhibits channel activity, thereby hyperpolarizing the cell —> Reduce action potentials

Volume, osmolality

ADH regulates the ___ and ___ of urine.

Feedback loop of osmoregulation

High osmolarity scenario

Stimulation of osmoreceptors in hypothalamus

Increased, increased, dilute

Diuresis:

Decreased ADHplasma —> ___ water loss —> ___ volume of urine —> urine is ___

Decreased, decreased, concentrated

Antidiuresis:

Increased ADHplasma —> ___ water loss —> ___ volume of urine —> urine is ___

Decrease

ADH is stimulated by a [increase or decrease] in blood pressure.

Increases

ADH [increases or decreases] the permeability to water.

Collecting duct

Which part of the nephron does ADH primarily target?

Decreased

Principal cells (DCT and CD):

___ ADH —> No AQP2 —> Impermeable to water

Increased

Principal cells (DCT and CD):

___ ADH —> increased AQP2 in cell surface—> increased permeability to water

Increased, increased

Collecting duct:

Increased ADH —> ___ urea transporters —> ___ reabsorption and recycling of urea —> increased water retention

Iso, hypo, hypo, hyper

Tubule fluid is:

__osmotic in the PCT

__osmotic in the LOH

__ or __osmotic by the end of the CD

Renal medulla

Compartment of the kidney where reabsorption of water occurs