Control of Fluid balance Flashcards
What mechanisms contribute to water loss?
Insensible
Sweat
Feces
Urine
What are the three local mechanisms of renal function?
Autoregulation (Myogenic and tubuloglomerular feedback)
Pressure Diuresis
Pressure Naturesis
Why dosn’t the metabolic response affect the kidneys?
Renal autoregulation serves to keep GFR constant, whereas in other tissues auto regulation matches blood flow for metabolic needs
What is the sensor and response in the tubuloglomerurlar feedback mechanism?
High/Low Na sensed by the macula densa cells, NO to afferent arteriole, angiotensin II to efferent arteriole and a decrease in tonic release of adenosine
What is the mechanism of pressure diuresis and natriuresis?
Increased renal arterial pressure increases peritubular capillary hydrostatic pressure, increases renal interstitial fluid hydrostatic pressure Na and water in interstitial fluid leak back into tubular lumen AND decreased aldosterone less Na reabsorption water follows
What type of receptors are the macula densa cells?
Stretch receptors, shrink or swell depending on sodium concentration (similar to Cosmo receptors)
What three mechanisms are part of the neural regulation of renal function?
Cardiovascular reflexes
Renal sympathetic nerve
Osmoreceptors
What is the neural response to low pressure/volume by the baroreceptors and volume receptors?
ADH secretion
ANG II
thirst promotion
Where does the renal sympathetic nerve innervate?
The afferent and efferent arteriole
What are the effects of renal sympathetic nerve stimulation?
Renal arteriole constriction, increased sodium reabsorption and increased ANG II (activation reduces sodium and water loss)
Where are the osmoreceptors located?
Neurons in the AV3V region, they lack a BBB in order to sample ECF osmolarity
What is the sensor and response of the osmoreceptors?
Swell shrink based on osmolarity and ADH inhibition/excretion
Where are the thirst and salt appetite centers of the brain?
AV3V region
What receptors are responsible to triggering thirst and salt appetite?
Osmoreceptors Baroreceptors and volume receptors (project to AV3V) THIRST ONLY Increased ANG II Dry mouth
What inhibits the thirst response?
Distended stomach
Receptors in the mouth
What is the most powerful regulator of ECF osmolarity and sodium concentration?
ADH-thirst
What is the importance of aldosterone to salt and water retention?
Stimulates the Na/K ATP pump on tubular epithelial cell basolateral membrane (Na retention and K secretion)
MORE IMPORTANT K REGULATOR
What hormone is considered the master of body fluid balance?
ANG II, most important hormone for Na retention (stimulates aldosterone secretion and ATP pump)
What causes the release of ANP?
Increased atrial stretch, causes naturesis and water reabsorption is inhibited
How does parathyroid hormone affect tubular reabsorption?
Increases tubular reabsorption of Ca at the distal tubules, inhibits phos (proximal) and promotes mag reabsorption (loop)
Where is angiotensigenogen produced?
The liver
Where is ACE produced?
Lungs (supply in kidney and brain for local RAAS system)
What are other factors that can promote the release of ADH?
Nausea Nicotine Morphine Alcohol Haloperidol
Which has a greater effect on body fluid balance salt intake or water intake?
Salt, special channels and pumps are required to move Na across membranes
When there is an acute change in b/p what is the first mechanism to respond?
Neural: Chemoreceptors, baroreceptors, CNS ischemic response, activation of SNS
What is the purpose of increasing TPR if you have a decrease in blood volume?
Shunt blood away from the periphery to the core
When there is an acute change in b/p what mechanisms respond after minutes to the change?
RAS
Capillary fluid shift: ISF -> blood
Stress relaxation (NOT auto regulation)
What is the mechanism behind the stress relaxation response?
When there is an increase in pressure followed by a decrease in pressure from changes in the orientation of elastic tissue fibers in smooth muscle of vessel or organ
When there is an acute change in b/p what mechanisms respond after hours/days to the change?
Renal body fluid mechanisms: Aldosterone Diminishing baroreceptor (resets) Capillary fluid shift contribution
Does RAAS affect salt appetite or thirst?
Yes, on a local level the brain’s RAAS system stimulates SFO neurons
How does the RAAS move arterial pressure regulation to a new set point?
Change in salt/water output (renin)
Change in salt/water intake (thirst salt)
Why are ACE inhibitors an effective treatment for most HTN patients?
The origin of most HTN is an overactive RAAS system
