7_HST110 Sodium Balance and Disorders of ECV 2017 Flashcards
(X) is the main extracellular cation and is responsible for most of the osmotic driving force that maintains the size of the (Y) volume
X = Na+ Y = extracellular fluid (ECF)
The total amount of Na+ in the ECF is the major determinant of the (X) of the ECF volume
X = size
If the total amount of Na+ in the ECF increases, ECF volume increases
If the total amount of Na+ in the ECF decreases, ECF volume decreases
Changes in Na+ balance result in changes to (X)
Regulation of Na+ balance translates into regulation of (X)
The kidneys regulate Na+ balance by adjusting urinary Na+ excretion to match input
X = extracellular fluid volume
(X) and body volume are tightly associated, therefore regulation of (X) is tightly associated with regulation of volume
X = blood pressure
What is the portion of the ECF volume that is in the arterial system and effectively perfuses the tissues?
Effective Circulating Volume (ECV)
ECV is the volume (or pressure) that is “sensed” by baroreceptors in the carotid sinus, aortic arch, atria, and afferent arteriole and regulated
ECV usually varies directly with ECF volume and is proportional to total body Na+ content
Maintenance of ECV and regulation of Na+ balance are closely related
However, in some settings, ECV may be independent of ECF volume
Name 2 such scenarios
Congestive heart failure: ECV decreases while ECF volume increases
Hepatic cirrhosis: ECV decreases while ECF volume increases
Name 2 steps with which the body responds to variations in the ECV
- Changes are “sensed” by volume receptors, which actually sense pressure (stretch)
- These receptors activate a series of effector systems that restore euvolemia by:
- Adjusting vascular resistance
- Adjusting NaCl and water excretion by the kidneys
What are the 4 effector systems that regulate ECV?
- Renin-Angiotensin-Aldosterone System
- Natriuretic Peptides (ANP, BNP)
- Sympathetic Nervous System
- ADH
Renin-Angiotensin-Aldosterone System is activated when the body senses a (X) in ECV
X = decrease
Renin: A proteolytic enzyme synthesized, stored, and released by (X) (granular cells) in the afferent arterioles. Catalyzes the conversion of (Y) to angiotensin I
X = juxtaglomerular cells Y = angiotensinogen (liver)
What are 3 stimuli for renin secretion?
↓ afferent arteriolar stretch
↓ NaCl delivery to macula densa
↑ sympathetic nerve activity to afferent arterioles
Angiotensin I is converted to angiotensin II by (X) found in (Y)
X = angiotensin- converting enzyme (ACE) Y = endothelial cells
What are the effects of Angiotensin II?
- Vasoconstriction
- Na+ and water reabsorption (mainly proximal tubule)
- Stimulate aldosterone release
- Stimulate ADH release
What are 2 ways to inhibit the activity of angiotensin II?
ACE inhibitors and angiotensin receptor blockers (ARBs), used to treat hypertension
What is Aldosterone?
A mineralocorticoid (steroid hormone) produced in the zona glomerulosa of the adrenal cortex. Secreted in response to angiotensin II and increased plasma K+
What is the primary site of action and what are the effects of Aldosterone?
Primary site of action is in the principal cells of the cortical collecting duct
Increases apical epithelial Na+ channels (ENaC)
Increases Na+-K+-ATPase at the basolateral membrane
Stimulates NaCl reabsorption and K+ secretion
Natriuretic Peptides are activated when the body senses an (X) in ECV
X = increase
What are the net results of ANP release?
↓ Renin ↓ Aldosterone ↓ ADH ↓ NaCl reabsorption (CCD) ↑ GFR
Systemic vasodilation
Increased NaCl and water excretion
Counter-regulatory system for the R-A-S system
SNS intervention is activated when the body senses an (X) in ECV
X = decrease
Steps of SNS intervention
- Baroreceptors sense decrease in ECV
- ↑ Sympathetic nervous system activity to the kidney
(arterioles, tubules) - ↑ Renin secretion
↑ NaCl reabsorption
↓ GFR
Net Result of SNS activation
Systemic vasoconstriction
Increased NaCl and water reabsorption
Note: When baroreceptors sense an increase in ECV, SNS activity is decreased and the opposite happens
ADH effects in ECV regulation
Modest changes in ECV regulate ADH secretion from the posterior pituitary
Increased levels of ADH result in increased water reabsorption by the kidneys and vice versa
Classic syndromes of ECF volume (Congestive heart failure, Cirrhosis, Nephrotic syndrome) are characterized by what 2 ECV effects?
Increased ECF volume (total body volume overload)
Decreased ECV (effective circulating volume depletion)
What is a common feature of disorders of ECF volume?
Edema
ECF Volume Disorders are disorders of (X)
X = sodium balance
Edema is characterized by palpable swelling produced by expansion of the (X)
X = interstitial fluid volume
Two basic steps required for edema formation are…
A change in capillary hemodynamics (Starling forces) that promotes movement of fluid out of capillaries into the interstitium
Retention of dietary Na+ and water by the kidneys that expands the ECF volume
Development of edema requires a large change in one or more of Starling’s forces that favors net (X)
- Increased capillary (Y) pressure (most common)
- Increased capillary (Z)
- Decreased plasma oncotic pressure (e.g. hypoalbuminemia)
X = filtration Y = hydrostatic Z = permeability
Edema and Na+/Water retention. 2 basic mechanisms
Kidney is defective and unable to excrete dietary Na+ and water
-Usually seen in the setting of kidney disease (advanced kidney disease, nephrotic syndrome, or acute glomerulonephritis). May result from renal resistance to the actions of ANP
Kidney is appropriately compensating in response to ECV depletion
-More common cause. Typically seen in CHF and cirrhosis. Urine [Na+] often is very low (<15 mEq/L)
How is ECV sensed?
Signals from both low and high pressure sensors are transmitted to the (X) (brainstem) via (Y) (CN IX) and vagus (CN X) nerves.
X = medulla oblongata Y = glossopharyngeal
Osmoregulation vs. Volume Regulation: What is being sensed?
Osmo: Plasma osmolarity
Volume: ECV
Osmoregulation vs. Volume Regulation: What are the sensors?
Osmo: Hypothalamic osmoreceptors
Volume: Carotid sinus, afferent arteriole, atria
Osmoregulation vs. Volume Regulation: What are the effectors?
Osmo: ADH, thirst
Volume: RAS, SNS, ANP, Pressure Natriuresis, ADH
Osmoregulation vs. Volume Regulation: What is affected?
Osmo: Water excretion, Water intake (via thirst)
Volume: Urine sodium excretion
