20130123_Body Fluids 4-5
What is a quick way to measure serum osmolality?
"A quick estimate of serum osmolality can be made by simply measuring the amount of sodium, urea, and glucose in the serum. "
High plasma potassium directly stimulates aldosterone secretion by the adrenal glands. What effect does this have?
"Aldosterone has the effect in the kidney to increase potassium secretion (the opposite of what happens to sodium). The end result is an increase in potassium excretion by the kidney. The mechanisms of aldosterone action in the kidney will be discussed in the kidney section."
The direct effects of high concentrations of potassium or low concentrations of sodium in the plasma occur in the adrenal gland and are thought to be results of what?
"Changes in membrane potentials caused by the differences in sodium and potassium currents across the cell membranes.
Increased plasma osmolality often means that plasma sodium is high and thus_____ aldosterone is needed. Thus, high plasma osmolality has the effect to partially _____ aldosterone release. The reverse is also true, low plasma osmolality______ aldosterone release. "
"Increased plasma osmolality often means that plasma sodium is high and thus less aldosterone is needed. Thus, high plasma osmolality has the effect to partially inhibit aldosterone release. The reverse is also true, low plasma osmolality ______ aldosterone release. "
Renin release from the kidney is controlled to some extent by the level of ______ entering the kidney
"It is interesting to note that renin release from the kidney is controlled to some extent by the level of sodium entering the kidney
What does angiotensin II do?
"It stimulates aldosterone production and release from the adrenal cortex. Aldosterone causes the kidneys to save sodium and excrete potassium.
What factors control release of aldosterone from the adrenal glands?
"Listed in order or importance: angiotensin II plasma potassium concentration blood sodium concentration Several other things have minor roles to influence adrenal aldosterone release-heart can release ANP, ACTH
Low plasma volume results in what and what does this lead to? "
"Low plasma volume results in low blood flow and low kidney filtration of fluid. This leads to release of renin by the kidney and the production of angiotensin II. In turn, the high angiotensin II causes stimulation of aldosterone production and release by the adrenal glands. The aldosterone circulates to the kidneys and acts on the distal tubules and collecting ducts in the kidney to increase reabsorption of sodium (saves sodium) so that sodium excretion is reduced
What is the role of the sympathetic nervous system play in the renin-angiotensin-aldosterone system?
"The Sympathetic Nervous System (SNS) has an important role to stimulate renin release from the kidneys. Increased SNS stimulation to the kidneys means increased renin release from the kidneys."
What happens to the adrenal response to a given amount of ACTH?
"The change in responses to ACTH is minimal (the slope of the line is relatively flat) because ACTH is not a true regulator of aldosterone. On an absolute scale, the response to Angiotenin II > K+ > ACTH.
Describe the renin-angiotensin-aldosterone system
"The liver makes and releases angiotensinogen into the circulating blood. When the kidney is stimulated to release renin (by low sodium or low kidney blood flow or high sympathetic nerve stimulation to the kidneys), renin acts to convert angiotensinogen to angiotensin I which is quickly converted to angiotensin II by converting enzyme (also called angiotensin converting enzyme or ACE) which is already in the blood. Angiotensin II travels in the blood stream to the adrenal glands and stimulates increased aldosterone production and release. Then, aldosterone travels in the blood stream to the kidneys and causes the kidneys to save more sodium and excrete more potassium. "
Stretch receptors (also called baroreceptors or pressure receptors) are neurons located in the heart atria, aorta and carotid arteries. What do these do?"
"These neurons send action potentials to the cardiovascular centers in the brain to influence both: 1) heart and blood vessel function and thus blood pressure, and 2) they also help control ADH release from the pituitary.
What happens to the adrenal response to a given amount of angiotensin II when osmolality is low? What about when the osmolality is high? "
"When osmolality is low (-20 mOsm) the adrenal response to a given amount of Angiotensin II is almost 10 fold higher (much more aldosterone released). The reverse is also true, when plasma osmolality is high (+20 mOsm), the response to a given amount of Angiotenisn II is nearly 10-fold less. The same is true for the adrenal response to potassium. "
What happens when osmolality is low? What happens when osmolality is high?"
"When osmolality is low, the action of angiotensin II is greatest at the adrenal gland increasing almost 10-fold. When osmolality is high, angiotensin II has a lesser effect. This makes sense. At low osmolality, water is relatively abundant, sodium is relatively low, and the need to conserve sodium is great. Therefore the action of angiotensin II at the adrenal gland is to release larger amounts of aldosterone that stimulate the kidney, to save or retain sodium."
When renal SNS stimulation is high, what happens?"
"When renal SNS stimulation is high, renin release is high and thus adrenal aldosterone production (via the action of Angiotensin II) is increased. "
What can low sodium mean in the body?
"low plasma concentration of sodium Low blood pressure low blood flow a combination of circumstances that would present low amounts of blood flow or sodium to the kidneys.
What 2 hormones control body fluid water and sodium?
1) ADH (antidiuretic hormone) and 2) aldosterone
What does adrenocorticotropic hormone do?
ACTH (adrenocorticotropic hormone) from the pituitary gland incidentally causes minor release of aldosterone from the adrenal cortex
Where is ADH synthesized and stored?
ADH (also named vasopressin or arginine vasopressin called AVP) is synthesized in the hypothalamus and stored in neuron axons that descend into the posterior pituitary gland.
Aldosterone acts on the kidney distal tubules and collecting tubules to stimulate ______ retention (by reabsorption from the urinary fluid) and _____ loss (by secretion into the urine).
Aldosterone acts on the kidney distal tubules and collecting tubules to stimulate sodium retention (by reabsorption from the urinary fluid) and potassium loss (by secretion into the urine).
Where does aldosterone come from?
Aldosterone comes from the adrenal glands (adrenal cortex)
When is angiotensin II made?
Angiotensin II is made when renin is released by the kidneys in response to low sodium or to low blood flow or to increased renal sympathetic nerve stimulation
Both _____ volume and _____ volume are signals used to control ADH release.
Both blood volume and cell volume are signals used to control ADH release.
Excess tonic solutes in the extracellular fluid will cause cells to ______ while excess non-tonic solutes in body fluids will ____ _____ cell volumes.
Excess tonic solutes in the extracellular fluid will cause cells to shrink while excess non-tonic solutes in body fluids will not change cell volumes.
For aldosterone, both ___ and kidney ___ and ______ concentrations are used as signals to control aldosterone release.
For aldosterone, both blood and kidney sodium and potassium concentrations are used as signals to control aldosterone release.
How does plasma potassium concentration effect aldosterone release?
High blood potassium concentration stimulates more aldosterone release from the adrenal glands "How does blood sodium concentration effect aldosterone release? " Low sodium concentration in the blood directly stimulates more aldosterone release from the adrenal glands as well as stimulates renin release by the kidneys"
High potassium______ aldosterone while high sodium has the _______ effect and vice versa.
High potassium increases aldosterone while high sodium has the opposite effect and vice versa.
When 1000 ml of hypertonic saline is put into the body, what is the fluid breakdown in fractions? What happens to the water in the cells"
Hypertonic saline causes cells to shrink. The extracellular space gets all the infused water that is in hypertonic saline plus additional water is drawn osmotically from the cells into the interstitium and plasma. Cells shrink and the ECF (interstitium and plasma) greatly expands.
if pure ethanol is put into the body, will the volume of cells increase?"
NO!
"Osmoreceptors are neurons located in the ______ that continually send action potentials to the pituitary to cause the release of _____.
Osmoreceptors are neurons located in the hypothalamus that continually send action potentials to the pituitary to cause the release of ADH.
What controls release of ADH?
Release of ADH is controlled by osmoreceptors and stretch receptors which monitor cell and blood volume (or blood pressure) respectively.
What controls the release of aldosterone?
Release of aldosterone is controlled mainly by kidney release of the enzyme renin to cause formation of angiotensin II, a hormone that stimulates adrenal cortex production of aldosterone.
What does ADH cause the kidneys to do?
Released ADH circulates in the blood stream to the kidneys and acts to cause the kidneys to save water (make less urine)
True or False? The osmolality of ECF and ICF will always change together?"
TRUE!
What is the action of aldosterone?
The action of aldosterone at the kidney is to induce the kidney to reabsorb (or save) sodium and lose potassium. This retains sodium in the body and reduces sodium excretion in the urine.
What is the effect of plasma osmolality?
The effect of plasma osmolality is to alter the adrenal response to both Angiotenisn II and potassium.
What does atrial natriuretic peptide do?
The heart can release ANP (atrial natriuretic peptide) which mildly inhibits aldosterone release
The osmoreceptor essentially monitors ____ _____ and the stretch receptor essentially monitors ____ ____ and ____ _____.
The osmoreceptor essentially monitors cell volume and the stretch receptor essentially monitors blood volume and blood pressure
If the measured value for actual osmolality is higher than the calculated value (from sodium x 2 + urea and glucose) what does this mean?
There is an unknown (unmeasured) solute in your serum.
When stretch receptors are increasingly stretched due to high blood pressure or high blood volume what happens?
They send increasing numbers of action potentials to the brain hypothalamus to reduce (partially inhibit) ADH release.
What is happening in this picture?
This example shows shrinking of an osmoreceptor and the subsequent increased release of ADH from the pituitary.
In this patient case, a young girl drank antifreeze. She subsequently was treated by stomach aspiration and with ethanol infusion (to reduce toxicity of absorbed antifreeze), and sent to the hospital where serum values for sodium, urea, glucose, ethanol, and serum osmolality were measured. The calculation of serum osmolality (based on the known measured solutes) was 327 mOsm/L. The measured serum osmolality was 373 mOsm/L. What does this indicate?"
This indicates that there is still (373-327) 46 mOsm/L of antifreeze in this little girl's body fluids
When osmoreceptor neurons _____ (lose water) they fire _______ numbers of action potentials that signal ______ ADH release from the pituitary.
When osmoreceptor neurons shrink (lose water) they fire increasing numbers of action potentials that signal increased ADH release from the pituitary.
increased body fluid osmolality ______ the effect of angiotensin II's action to stimulate aldosterone secretion by the adrenal gland
increased body fluid osmolality reduces the effect of angiotensin II's action to stimulate aldosterone secretion by the adrenal gland