3. Regulation of ECF and Sodium Balance Flashcards
H2O, Na, and Osm has to be kept in balance at all times. ECF volume must be closely regulated to maintain BP. Maintaining salt balance is the primary importance in longer term regulation of ECF volume. ECF osmolarity must be regulated to prevent?
swelling and shrinking of cells… maintaining water balance is of primary importance in regulating ECF osmolarity
What is a portion of the ECF volume that is in the arterial system under particular pressure and is effectively perfusing the tissues? (it is not a measurable/distinct body fluid compartment)
Effective circulatory volume (ECV)
What percent of the vascular volume forms the ECV?
20% of the plasma of the ECF = 5% ecf or 1.7%TBW or 1% of body weight
Patients with congestive heart failure have low ECV d/t decreased cardiac output. Na/fluid retention results in edema where hydrostatic pressure increases. Patients retain Na, increasing ECFV without correcting the ECV. What are the 4 ways decrease in ECV is counteracted?
- RAAS
- Sympathetics via baroreceptors
- Increased ADH
- Increased renal fluid retention via Starling forces
The osmosreceptors located in the supraoptic and paraventricular areas of the posterior hypothalamus detect changes in the plasma osmolality and function to do what? (2)
- regulate release of ADH
2. Regulate thirst sense
What are the two different ways ADH is controlled and which is more sensitive?
- Osmoreceptors, more sensitive, detect changes in body fluid osmolality
- Baroreceptors detect changes in BP/BV/stretch
Small decreases in blood pressure have little affect in activating the baroreceptors.. but IF the blood pressure falls by 20%, what occurs?
ADH rises to levels beyond what is needed to maintain antidiuresis
(if an acute rise in BP then ADH secretion is supressed)
When there is volume contraction (hypovolemia), there is more of a response to release ADH in comparison to?
when there is a volume expansion (hypervolemia), = inc in h2o = decrease in secretion of ADH to excrete extra h2o
Arterial baroreceptors sense pressure in the aorta/carotid and send to brainstem vasomotor which regulates CV and renal processes. Cardiopulmonary baroreceptors sense what and do what?
pressure in the cardiac atria and pumlonary arteries, which send afferent information with arterial baroreceptors (ADH)
The cardiopulmonary baroreceptors have a important influence on the hypothalamus which regules secretion of ADH… The intrarenal receptors have a major role in?
RAAS system
Sodium balance problems manifest as altered ECFV (body Na content), sensed ECV via arterial and cardiac baroreceptors, turings on the RAAS, which affects?
Urine Na excretion
Water balance problems manifest as altered plasma osmolality (body water content), which is reflected in an alteration in plasma Na. So plasma osmolality decrease is sensed via hypothalamus, and AVP/ADH is released to do?
increase urine osmolality, reuptake H2o and activate thirst
When there are changes in Na uptake or output that results in changes in total body Na content causes a change in plasma osmolarity. What is the process when Na levels in ECF rise? (4)
- Stimulates osmoreceptors in hypothalamus
- ADH secretion increases to reabsorb water from urine to bring to blood to BRING DOWN high blood osmo, also promotes thirst
- Since ECF osmo increases, water moves from ICF to ECF increasing ECF volume and lowering ECF [Na]
- Restored homeostasis
A decrease in total body Na content would lead to what in the ECF?
ECF contraction
An increase in total body Na content would lead to what in the ECF?
ECF expansion
If ECFV is expanded , NaCl and water excretion are increased, if ECFV is contracted, then NaCl and water excretion are reduced. What are the four effector mechanisms that work with the vascular volume senesors that detect theses changes?
- Sympathetics to renal
- RAAS
- ANP
- ADH/AVP
how do renal sympathetic nerves respond to increased activity?
Increased activity means decreased GFR, which leads to Renin secretion and an increase in Na reabsorption
How does the RAAS respond to decreased BP?
Increases AGTII (nephron) and Aldosterone (DCT/CD) which stimulate Na reabsorption, AGTII stimulates ADH secretion
How does ANP/BNP work when there is a increase in BP?
Decreases renin secretion, decreased aldosterone, decreased Na/H20 reabsorption in the CD, decrease ADH secretion
How does AVP/ADH work?
increase h20 absorption by the DCT and CD to decrease plasma osmolality
What are the three major mechanisms for the secretion of renin?
Low Perfusion pressure
sympathetic nerve activity
low NaCl delivery to macula densa-tubuloglomerular feedback
When there is an increase in NaCl, ECFV, or atrial BP, ANP, atrial natriuretic protein, is released which works opposite of ADH. ANP promotes diuresis to lower BP. How does it do so? (2)
- Directly inhibits Na reabsorption in the distal nephron, increasing Na excretion and H2O follows
- Inhibits RAAS, inhibits renin in the kidneys and aldosterone from the adrenal cortex, also inhibits AVP secretion
When there is a volume expansion (excess Na) more Na and H20 need to be excreted. So what mostly will occur?
Decrease in sympathetics, Increase in ANP and BNP which inhibits renin, agt2, and aldosterone secretion, which results in increased excretion
When there is a volume contraction (salt deficit) more Na and H20 need to be reabsorbed. How is this done?
A volume contraction leads to decrease BP which activates sympathetics and renin release, along with AGT2 conversion and activation of ADH and aldosterone to reabsorb NaCl/H2O, ANP/BNP is decreased
Hyponatremia is when there is a lower sodium concentration in the ECF compared to ICF. So water shifts into the cells causing swelling and less Blood volume in vessels = hypovolemia…What about hypernatremia?
Hypernatremia is when there is a higher concentration in the ICF than the ECF
ECF volume is mainly maintained by salt balance since water follows salt (aldosterone). While ECF osmolarity is maintained by water balance via?
ADH/Vasopressin/AVP
