Regulation of ECF Volume and NaCl Balance Flashcards
Primary Cation in Plasma
Sodium
Primary Cation in Interstitial Fluid
Sodium
What three factors must be balanced in body?
Osmolarity
Water
NaCl
What is important in regulating ECF volume long term? what will regulating ECF volume help with?
- maintaining salt balance
Regulating ECF volume will help maintaining blood pressure
What is important in regulating ECF osmolarity long term? what will regulating ECF osmolarity help with?
- maintaining water balance
Regulating ECF volume will prevent swelling or shrinking of cells
Effective Circulating Volume
- definition
- is it measurable?
- proportion of body containing ECV
portion of ECF volume that is in arterial system under particular pressure and is effectively perfusing the tissue
- NOT measurable
- NOT a distinct body fluid compartment
about 0.7 L of vascular volume forms ECV
ECV is SENSORY
Congestive Heart Failure
- what do patients present physiologically?
- low effective circulating volume due to decreased cardiac output
- Na and fluid retention-> edema ( venous and capillary hydrostatic pressure increases )
- Na retention-> increase ECF WITHOUT correcting effective circulating volume
How does body counteract decrease in effective circulating volume/edema? (4)
1) Activation of RAAS system
2) stimulation of sympathetic nervous system via barareceptor reflex
3) Increased ADH secretion
4) Increase renal fluid retention via altered Starling’s forces in peritubular capillaries
Osmoreceptors have two functions. What are they?
1) To regulate release of ADH
2) To regulate thirst
ADH secretion is controlled by:
1) Osmoreceptors
- detect changes in body fluid osmolarity
2) Baroreceptors
- which detect changes in blood volume/ blood pressure
- osmoreceptor system more sensitive than baroreceptor system
What happens when blood pressure and blood volume are reduced?
increase ADH secretion
increased fluid reabsorption by kidneys
help to restore blood pressure and blood volume toward normal
How sensitive is ADH secretion to blood pressure?
What about acute rise in BP?
if blood pressure falls by 20%, ADH increases to maintain antidiuresis
small decreases in BP (5-10%) have little effect
Acute rise in BP suppresses ADH secretion
Sensed Volume on osmolality and ADH release
- what happens when there is decreased sensed volume?
it “sensitizes” the system
- smaller changes in osmolality will induce larger amounts of ADH release
Sensed Volume on osmolality and ADH release
- what happens when body senses volume expansion?
higher threshold for release of ADH
less vigorous response to progressive hyperosmolarity
Three types of baroreceptors
1) Arterial baroreceptors
2) Cardiopulmonary baroreceptors
3) Intrarenal baroreceptors
Arterial baroreceptors
- location
- what it deals with (4)
- function
brainstem vasomotor center
- Total peripheral resistance
- Cardiac Performance
- Sympathetic Drive to Kidney
- Venous compliance
- Sense pressures in aorta and carotid arteries
- send afferent information to brainstem vasomotor
- regulates CV and renal processes via autonomic efferents
Cardiopulmonary baroreceptors
- locations
- what it deals with (4)
- function
- what is special about it
brainstem motor center
Hypothalamus
- venous compliance
- sympathetic drive to kidney
- total peripheral resistance
- cardiac performance
- ADH
- sense pressure in cardiac atria and pulmonary arteries
- send afferent information in parallel with arterial baroreceptors
- have more important influence on hypothalamus than arterial baroreceptors ( regulate secretion of ADH)
Intrarenal baroreceptors
- functions
- Renin-angiotensin system
- GFR, salt, and water reabsorption
Regulation of body Na content
- sensed
- sensor
- effector
- affected
ECF volume
- sensed: effective circulating volume
- sensor: arterial and cardiac baroreceptors
- effector: Ang II/aldosteron/ SNS/ ANP
- affected: Urine Na excretion
Regulation of body fluid content
- sensed
- sensor
- effector
- affected
Plasma osmolality
- sensed: plasma osmolality
- sensor: hypothalamic osmoreceptors
- effector: AVP ( arginine vasopressin)
- affected: urine osmolality (H2O output) & thirst
How does ADH responds to changes in plasma osmolality ? ( think Na and ECF)
3 steps
1) changes in Na intake/output that results in changes in total body Na content can cause change in plasma osmolality
2) body alters water intake and renal water absorption to maintain an isotonic ECF
3) Osmolality is maintained at the expense of ECF volume
Effect of decrease in total body Na content
eventual ECF contraction
Effect of gain in total body Na
eventual ECF expansion
Homeostasis steps for increase Na in ECF
1) stimulate osmoreceptors in hypothalamus
2) secretion of ADH restricts water loss and stimulates thirst
- promote additional water consumption
3) Water shifts ICF-> ECF
- lower ECF Na concentration
4) Na levels in ECF fall (homeostasis)
Homeostasis steps for decrease Na in ECF
1) inhibit osmoreceptors in hypothalamus
2) decrease secretion of ADH
- suppress thirst
- water loss in kidneys
3) Water loss reduces ECF volume
- concentrates ions
4) Na levels in ECF rise (homeostasis)
Vascular Volume Sensors
- detect changes in ECFV
- signals to kidneys
- adjustments in NaCl and water excretion
If ECFV is expanded what happens?
renal NaCl and water excretion are excreted
If ECFV is contracted, what happens?
renal NaCl and water excretion are reduced
Four main effector mechanism for volume sensors
1) Renal Sympathetic nerve activity
2) Renin- Angiotensin-aldosterone system
3) Atrial Natriuretic Peptide
4) AVP ( vasopressin)
Renal Sympathetic nerve activity
- function
- effects
reduce NaCl excretion
- reduce GFR
- increase renin secretion
- increase Na reabsorption along nephron
Renin- Angiotensin Aldosterone System
- function
- effects
reduce NaCl excretion
- increases ang II stimulates Na reabsorption along nephron
- increase aldosterone stimulate Na reabsorption in distal tubule and collecting duct and to a lesser degree in thick ascending LOH
- increase angiotensin II stimulates AVP
Natriuretic Peptide
- function
- effects
ANP, BNP, Urodilation
increase NaCl excretion
- increase GFR
- decrease renin secretion
- decrease aldosterone secretion
(indirect via decrease angiotensin II and direct on adrenal gland) - decrease NaCl and water reabsorption by the collecting duct
- decrease AVP secretion and inhibition and AVP action on distal tubule and collecting duct
AVP
- function
- effects
decrease H2O excretion
-increase H2O reabsorption by distal tubule and collecting duct
Mechanisms for secretion of Renin
- 3 and describe
- Net Effect
1) Perfusion Pressure
- low perfusion in afferent arterioles stimulates renin secretion while high perfusion inhibits renin secretion
2) Sympathetic Nerve Activity
- activation of sympathetic nerve fibers in afferent arterioles increases renin secretion
3) NaCl delivery to macula densa
- when NaCl decreased, renin secretion is stimulated
(Tubuloglomerular Feedback)
- stimulate release of renin by juxtaglomerular apparatus
- cleaves angiotensinogen to for angiotensin
Renin-Angiotensin- Aldosterone System Steps (6)
1) Systemic blood pressure decreases-> decrease in GFR
2) JG cells release renin
3) Renin converts angiotensinogen to angiotensin-1
4) ACE converts angiotensin I to the active angiotensin II
5)
- vasoconstriction of efferent arterioles
- vasoconstriction of systemic blood vessel
- reabsorption of Na and Cl from proximal tubule and H2O follows
- promotes aldosterone release, increasing Na+ H2O reabsorption
6) GFR increases and Systemic blood pressure increases
Atrial Natriuretic Peptide
- where it is produced
- what does it produce
- where is it stored
- function
- Loses Na
- lowers BP
- produced in atrial cardiac muscle cells
- produces natriuresis
- stored in granules and released when heart muscle cells are mechanically stretched by an expansion of circulating plasma volume when ECF volume
- responds to increased blood pressure caused by Na+ and H2O retention
- promote natriuresis and diuresis
- decrease plasma volume
- lowers blood pressure
- inhibit Na reabsorption in distal part of nephron
- increase Na excretion
- increase H2O excretion in urine
How does Na excretion increase in urine?
-steps
- by inhibiting RAAS
1) ANP inhibit renin secretion by kidneys and act on adrenal cortex to inhibit aldosterone secretion
2) ANP inhibit the secretion of vasopressin
Regulation for Salt deficit
plasma osmolality low-> water diuresis -> plasma volume and blood pressure decrease -> renin secretion -> increase angiotensin II-> increase aldosterone-> increase Na reabsorption -> salt and water excretion decreases
Regulation of Salt Excess
plasma osmolality high-> increase ADH and thirst pathway -> plasma volume and blood pressure increase ->atrial pressure increase _> increase ANP-> renin inhbition -> inhibit aldosterone-> decrease Na reabsorption -> salt and water excretion increases
Na Excretion with Volume Expansion (5)
- end result
1) Decreased activity of renal sympathetic nerve
2) Increased release of ANP and BNP from the heart and urodilation by the kidneys
3) Inhibition of AVP secretion from the posterior pituitary and decreased AVP action on the collecting duct
4) decreased renin secretion and thus decreased production of angiotensin II
5) reduced angiotensin II-> decreased aldosterone secretion and elevated natriuretic peptide levels
- increase sodium excretion
Na Excretion with Volume Contraction (3)
1) Increased renal sympathetic nerve
2) Increased secretion of renin which results in elevated angiotensin II levels and thus increased secretion of aldosterone by adrenal cortex
3) Stimulation of AVP secretion by posterior pituitary
Hyponatremia
- values
- definition
- clinical presentations
Serum sodium < 135 mEq/L
Serum Osmolality <280 mOsm/Kg
- sodium concentration in plasma is lower than normal
- body fluid diluted
- decreased ECF osmolality
- cell swell
Fluid moves from osmosis from ECF-> ICF
- edema and hypovolemia
ECF volume
- factors that regulate it
- effects on arterial blood pressure when not normal
Regulated by
- salt balance maintenance
- aldosterone
Decrease ECF volume= Decrease arterial blood pressure
increase ICF volume= increase arterial blood pressure
ECF osmolarity
- factors that regulate it
- effects on cell size when not norma
Regulated by
- H2O balance maintenance
- Vasopressin
Increase ECF osmolarity (hypertonicity) -> H2O leaves cells -> cells shrink
Decrease ECF osmolarity (hypotonicity) -> H2O enters the cells-> cells swell
Water balance
- what maintains it? what does that lead to?
ADH maintains water balance
- leads to retention of excess free water
Hyponatremia
In> Out
Hypernatremia
Out> In
Sodium Balance/ ECV
- regulated by what?
- effect when ECV is high? Low?
1) Sympathetic Nervous System
2) RAAS
- ECV low= activated
- ECV high = inhibited
Increase sodium consumption leads to?
- symptoms
ECV expansion
- weight gain
- possible hypertension
Decrease sodium consumption leads to?
- symptoms
ECV contraction
- weight loss
- improvement in hypertension
