Renal 3: Osmoreg. and ADH Flashcards
Define tonicity
The osmotic pressure created by solutes: either hypotonic, isotonic, or hypertonic
What is osmolarity, what is it’s unit, and what is the difference between molarity and osmolarity?
Osmolarity is the concentration of dissolved particles: mol solute/L
An Osmole (Osm or osmol) defines the # of mols of solute that contribute to osmotic pressure.
Molarity refers to the concentration of a compound.
What is Hypertonicity?
Refers to a high level of solute in solution.
What impact does extracellular Hypertonicity have on cell size? Hypotonicity?
EC hypertonicity will shrink/shrivel a cell because the water in the cell will follow the higher concentration of salt outside of the cell.
EC hypotonicity will enlarge the cell for the same reason - water from the EC is being drawn too the salt inside the cell.
What is typical blood osmolarity?
300 mOs
How is osmoregulation a true feedback loop?
Excess dietary salt intake > excess osmolarity in blood (hypertonic?) > physiological and behavioral mechanisms dilute blood back to normal (300 mOsm)
Physiological: tubular reabsorption of water via medullary hypertonicity, calyceal compression, and ADH minimize further water loss
Behavioral: thirst - drinking water provides sufficient extra water to dilute salt
How does the interstitial region of the medullary pyramid become hypertonic?
Urea (from the collecting duct) and NaCl ( passively, from thin ascending loop, and actively from thick ascending loop) accumulate in interstitium causing the region to become hypertonic. The solutes and water are suspended in a gel of albumin and hyaluronic acid.
How is hypertonic medullary interstitium protected by the vasa recta?
The entirety of the vasa recta is highly permeable to water and solutes
Loops of the vasa recta absorb solutes in the inner medulla but release them into outer medulla
(vasa recta don’t undo osmotic gradient)
What is ADH and what does it do?
Anti-diuretic hormone regulates water permeability in collecting tubules by up reg aquaporins.
Stimulates water reabsorption from collecting ducts by increasing permeability, then capillaries rapidly reabsorb water preventing dilution of osmolarity in interstitium.
Where is ADH synthesized?
In paraventricular (PV) and supraoptic (SO) neurons, then transported along axons and secreted into circulation from posterior pituitary.
Where and what are the osmoreceptors?
Osmoreceptors are in the anterior hypothalamus. They project to the SO and PV nuclei to trigger release of ADH.
Also project to thirst and drinking regions of the limbic system.
When we consume dietary salt, raising our plasma Na+, what happens to our osmoreceptor cells?
They shrink, triggering an AP and increased ADH release; water is reabsorbed.
What happens to our osmoreceptor cells when we drink a lot of water, resulting in decreased plasma Na+?
Our osmoreceptors expand, decreasing ADH release; water is excreted.
When does ADH peak?
At night.
In daylight, suprachiasmatic (SCN) nucleus presynaptically inhibits osmoreceptor activation of SO and PV neurons, reducing ADH levels.
At night low levels of light do not inhibit ADH, preserving body water levels.
Describe the 3 ways that excess blood osmolarity (salt) is diluted to normal levels by the kidney.
- Osmotic water reabsorption
- Physical pressure on tubules and interstitium by minor calyces: reabsorption
- Increased water permeability via ADH in collecting ducts
