How many grams of salt per liter of water must a person ingest to maintain an isosmotic ECF?
9 grams of NaCl per liter of water.
Which solute accounts for over 90% of ECF cations?
Sodium.
How will dehydration affect ECF osmolarity?
The concentration of Na+ in the ECF will increase, thus raising osmolarity.
What center of the body recognizes an increase/decrease in ECF osmolarity?
Osmoreceptors in the supraoptic and paraventricular nuclei of the hypothalamus, and in the 3rd ventricle.
True or False?
Sensing an increasing in [Na+]ECF, osmoreceptors stimulate ADH release from the anterior pituitary.
False.
ADH is released from the posterior pituitary.
True or False?
An increase in [Na+]ECF will ultimately result in increased permeability to water in the LDT and collecting ducts?
True.
Water will be retained in response to ADH release.
How will reabsorption of water without solutes in the latter portions of the nephron affect ECF osmolarity?
ECF osmolarity will decrease.
In a response to ECF osmolarity that calls for concentrating urine, why doesn't Na+ follow water out of the tubule as it is reabsorbed?
The high osmolarity of the renal medulla attracts water but not solutes.
List 4 types of extracellular fluid.
1.) Abdominal
2.) Interstitium
3.) Plasma
4.) Cerebro-spinal fluid (in equillibrium with plasma)
Where are osmoreceptors located? How do they sense changes in ECF osmolarity?
1.) Osmoreceptors line the 3rd ventricle, and are located in the supraoptic nuclie and paraventricular nuclei
2.) These cells shrink when [Na+]ECF is too high and swell when it is too low. Tonic firing is altered in response to these changes.
True or False?
The pituitary gland is covered by the blood brain barrier.
False.
In order to release hormones directly into vascular circulation, no BBB can exist here.
Where is ADH synthesized?
The hypothalamus.
It is stored in the anterior pituitary.
True or False?
Behavoirs are required to add H2O and salt to the body?
True.
The kidneys can conserve salt and water, but cannot create it.
An increase in ECF fluid volume will result in __________ ECF osmolarity. In response, ADH production will _________, and _________ urine will be excreted.
1.) Decreased / Low
2.) Decrease
3.) Dilute
Which feedback system is more sensitive, ECF osmolarity or blood pressure?
ECF osmolarity is a far more sensitive system, needing a change of only 1-2% to cause a change in ADH. Blood volume must change by 10% in order to elicit a response.
True or False?
ECF osmolarity and blood volume are equal stimuli in regards to ADH release.
False.
What 3 stimuli control ADH secretion?
1.) ECF osmolarity
2.) Blood volume
3.) Blood pressure
Alcohol is an ADH inhibitor and therefore leads to (concentrated / dilute) urine.
Dilute.
Caffeine intake leads to dilute urine. Explain.
Caffein is a vasoconstrictor.
1.) Increased MAP
2.) Autoregulation of GFR leads to increased PPC 3.) Decreased reabsorption of water
4.) Increased urine output
*Also, the caffeine came in with fluid but no salt, causing a decrease in ECF osmolarity and therefore a decrease in ADH release.
True or False?
Thirst is a behavoir that is independent of ADH release.
False.
ADH can stimulate thirst.
List the 6 stimuli that signal "thirst."
1.) ADH
2.) Increased ECF osmolarity
3.) Decreased blood volume
4.) Decreased blood pressure
5.) Angiotensin II
6.) Dry mouth
The ADH system can correct ______ - osmolarity.
Thirst can correct ______ - osmolarity.
Salt appetite can correct ______ - osmolarity.
1.) Hyper- and hypo-
2.) Hyper-
3.) Hypo-
True or False?
Plasma-sodium concentrations change significantly in response to fluctuations in daily sodium intake.
False.
The ADH/Thirst/Salt appetite system keeps [sodium]plasma fairly constant.
True or False?
The body corrects changes in osmolarity first, in all situations.
True.
What term describes increased urine output in response to increased blood pressure?
Pressure diuresis.
Which process more closely returns blood pressure to normal?
1.) Water retention with ADH in response to low BP
2.) Water excretion with absence of ADH in response to high BP
Water excretion is more accurate. Complete water retention cannot occur since some must be lost to carry excreted solutes and wastes.
True or False?
Small changes in MAP can be fixed by small changes in urine output.
False.
Small changes in MAP result in big changes in urine output.
What term describes a pathophysiological condition where water accumulates in the interstitium?
Edema.
Edema is caused by adverse changes in the ___________ of the capillaries.
Starling forces.
A change in which starling force is usually the cause of edema?
