2. Regulation of Sodium and Water Balance Flashcards
What is the major cause of hyponatremia?
gain of water. Concentration of Na remains the same but there is more water to dilute
What controls the amount of total body Na content?
the kidneys
The amount in is not regulated but the amount needed to be removed is by urinary Na excretion
Where does the bullk of reabsorption of filtered Na occur?
Proximal tubule.
If there is an increase in ECF volume, what does the body do to decrease the volume?
Increase Na excretion
How much Na reabsorption occurs in the TAL?
25%
How much Na reabsorption occurs in the DT and CCD?
DT - fine tuning; 4%
CDD - 3%
What are factors that promote Na reabsorption?
Hypovolemia..
activation of renal sympathetic nerves
Activation of renin/angiotensin system
Secretion of aldosterone
What are factors that promote Na excretion?
Hypervolemia
Release of ANP and BNP
release of urodilatin (intrarenal local hormone)
Intrarenal prostaglandins - vasodilation, maintain renal blood flow
If there is hypovolemia, why does the sympathetic nervous system clamp down on afferent arterial when ultimately GFR needs to be maintain in order to fix the hypovolemia
Because by clamping down on the afferent, there is a decrease rate of fluid delivery to the macula densa which triggers even more release of renin. Renin will then lead to the vasoconstriction of efferent to maintain GFR and also more reabsorption of Na and thus water
What stimulates the renal sympathetic system?
Fall in perfusion pressure through the cardiopulmonary baroreceptors
How does the renal sympathetic system directly stimulate renin secretion?
Via B1 receptor activation in JG apparatus
In the tubuloglomerular feedback system, what causes the macula densa to trigger increase renin secretion?
decreased delivery of NaCl to macula densa
Where is the intrarenal baroreceptor and what does it detect?
wall of afferent arteriole
It is part of the myogenic response. Detects high BP
Due to high BP it tries to prevent damage to kidneys and afferent arterial vasoconstrict
If the intrarenal baroreceptor is firing, what is secreted and why?
Renin is secreted because the afferent arteriole is constricted and thus GFR decreases. Renin is released to maintain GFR by constricting efferent arteriole
What effect would loop diuretics have on renin secretion?
Increase renin secretion to retain fluids
List what angiotensin II stimulates
- systemic arteriolar constriction
- renal arteriolar constriction (efferent moreso)
- Na reabsorption: PCT > TAL, CCD
- Thirst
- ADH secretion from posterior pituitary
- Aldosterone secretion from adrenal cortex
What are the actions of aldosterone in the late distal convoluted tubule and collecting duct?
Stimulates sodium reabsorption (inserts transporters)
Stimulates potassium secretion by principal cells
Stimulates H secretion in principle cells
Stimulates H secretion in intercalated cells
Aldosterone leads to Sodium reabsorption which causes a large lumen-negative potential difference. How is the electroneutrallity maintained in the lumen?
Passive Cl- reabsorption (slow bc of tight junctions)
And K/H secretion
What would happen to K and H excretion in a patient with hyperaldosteronism?
Hypokalemia and metabolic alkalosis
What primarily controls aldosterone secretion?
K concentration
What are the factors that control aldosterone secretion?
K concentration, ACTH concentration and volume
ANP increases GFR how?
afferent arteriolar dilation, efferent arteriolar constriction
ANP inhibits Na reabsorption in _________ collecting duct
medullary
ANP suppresses secretion of what?
Renin, aldosterone and AVP
ANP is a systemic _________
Vasodilator
Urodilatin is secreted by what? In response to what?
DCT, collecting duct
In response to increased arterial pressure and ECF volume
What does urodilatin do?
Suppresses Na and water reabsorption by medullary collecting duct but has no effect on systemic circulation
How does prostaglandins increase Na excretion?
increasing GFR by dilating (afferent) renal arterioles and suppresses Na reabsorption in TAL and CCD
What effect with prostaglandins have on the solute concentration in the renal medullary tissue?
Decrease osmolarity, will not be able to concentrate urine
Where is AVP synthesized?
Hypothalamus
What are the two major stimuli for ADH release?
hyperosmolality (osmoreceptors) and volume depletion (baroreceptors)
Which osmoreceptors are more important?
Hypothalamic osmoreceptors are more important than hepatic osmoreceptors
Normal osmolality is around 300 mosm/kg H2O. If your osmolality increases anymore, why is there not a significant increase in the amount of ADH secreted?
Because at the normal osmolality, there is almost maximal secretion of ADH already.
If there is maximal secretion of ADH, what is triggered to help the body recover from high osmolality?
thirst
Which system is not as sensitive in triggering the release of ADH? Osmolality or blood volume?
blood volume. It takes 10-15% of blood volume lost before there is a significant increase in ADH release. Baroreceptors are not as sensitive
Which system is more rapid and strong? Osmolality or blood volume sensors?
Blood volume sensors
If there is low osmolality and also a decrease in volume, will ADH be secreted at higher or lower amounts compared to normal osmolality and volume levels?
Higher. Despite the osmolality being lower, it is more important to maintain volume so that there is enough perfusion to tissues.
What is the renal response to increased NaCl intake? Why?
increased urinary NaCl excretion by suppressing RAAS by ANP and decreasing sympathetic outflow to kidney .
Increased NaCl causes an increase in ECF volume
Sympathetic outflow to kidney directly stimulates reabsorption of NaCl where?
proximal tubular
Too much water = ?
hyponatremia, impaired water regulation
Too little water = ?
hypernatremia, impaired water regulation
Too much Na =
edema
Too little Na = ?
volume depletion
Water is directly related to what?
Sodium concentration in the plasma
Na is directly related to what?
ECF compartment volume
What reflexes cause the activity of the renal sympathetic nerves to increase?
Carotid sinus and aortic arch reflexes sensing decrease in arterial blood pressure
_______ Na is regulated primarily by changes in water balance
plasma
What situations causes an increases in renin secretion?
- high blood pressure, myogenic feedback ->intrarenal baroreceptor -> afferent vasoconstriction -> decrease pressure at JG cells and thus renin secretion
- Sympathetic discharge due to fall in perfusion pressure through cardio pulmonary baroreceptors
- tubuloglomerular feedback, decrease in NaCl in DCT sensed by macula densa
What acts to fine ttune Na levels in principal cells of LDCT and CD?
aldosterone
