CH. 19 Urinary System: Fluid and Electrolyte Balance Flashcards
What needs to occur for balance to occur?
input + production = utilization + output
What is the function of the kidneys?
regulate solute and water content which also determines volume
- regulate acid-base balance
What is a positive solute or water balance?
solute or water enters plasma faster than it exits
- quantity increases
What is a positive solute or water balance?
solute or water enters plasma faster than it exits
- quantity increases
What is a negative solute or water balance?
solute or water exits plasma faster than it enters
- quantity decreases
What cells in the late distal tubules and collecting ducts regulate balance?
principal cells
- water electrolytes
intercalated cells
- acid-base balance
What accounts for water intake?
gastrointestinal tract and metabolism (generating water as anything is synthesized
What accounts for water output?
- insensible loss
- sweating
- gastrointestinal tract
- kidneys
What is normovolemia, hypervolemia, and hypovolemia?
Normovolemia: normal blood volume
Hypervolemia: high blood volume due to positive water balance (more than 42L)
Hypovolemia: low blood volume due to negative water balance
In which direction does water move in regard to solute concentration?
water moves from area of low solute concentration to area of high solute concentration
What is the osmolarity of body fluids?
300 mOsm (300 mOsm of solute per liter of plasma
How do kidneys compensate for changes in osmolarity of ECF?
regulating water reabsorption
What is it that regulates water reabsorption in the distal tubules and collecting ducts?
ADH (vasopressin) secreted by posterior pituitary gland
What is the primary solute in which water reabsorption follows?
sodium; establishes an osmotic gradient for water reabsorption when transported across basolateral membrane
What level of osmolarity of interstitial fluid can be found at the cortex vs. renal pelvis of the renal medulla?
lower osmolarity near cortex
greater osmolarity near renal pelvis
What establishes the osmotic gradient?
countercurrent multiplier: currents go in opposite direction
- ascending limb vs. descending limb
What are the differences between the ascending limb and the descending limb?
Ascending limb:
- impermeable to water
- active transport of sodium, chlorine, and potassium
Descending limb:
- permeable to water
- no transport of sodium, chlorine, or potassium
In order to set up the countercurrent multiplier, what needs to be established first?
ascending limb
How does urea contribute approximately 40% of the osmolarity of the gradient?
transport of urea through UTA from filtrate to peritubular fluid
What is the role of the vasa recta in the establishment of the medullary osmotic gradient?
anatomical arrangement of vasa recta capillaries prevent the diffusion of water and solutes from dissipating the medullary osmotic gradient
What occurs in the descending limb of the vasa recta? and what is its milliosmolarity?
water leaves capillaries by osmosis and solutes enter by diffusion through their ion channels
- 300 mOsm
What occurs in the ascending limb of the vasa recta? and what is its milliosmolarity?
water moves into plasma and solutes move into interstitial fluid
- 325 mOsm; higher due to lack of urea transporters
What is water permeability dependent on?
water channels
- aquaporin-3: present in basolateral membrane always
- aquaporin-2: present in apical membrane only when ADH present in blood
What occurs when the membrane of the late distal tubule and collecting duct is impermeable to water?
- water cannot leave the tubules
- no water reabsorption
- more water is excreted in urine
What does the maximum amount of water reabsorbed depend on?
length of loop of Henle
What does ADH stimulate in the distal tubule and collecting duct?
the insertion of water channels (aquaporin-2) into apical membrane
What is an effect that ADH has on water reabsorption?
- regulates permeability of late distal tubules and collecting ducts
Where is ADH released?
released from terminals in the posterior pituitary from cell bodies originating in the hypothalamus
What two receptors is ADH affected by?
baroreceptors and osmoreceptors
What occurs when blood pressure drops to less than 80 mmHg?
- decrease in GFR
- decrease in water filtered
- decrease in water excretion
What occurs when blood pressure increases to more than 180 mmHg?
- increase in GFR
- increase in water filtered
- increase in water excretion
- occurs only in pathological circumstances
What is hypernatremia and hyponatremia?
hyper: high plasma sodium
hypo: low plasma sodium
What is the primary solute in ECF and what is it critical for?
sodium
- critical for normal osmotic pressure
- critical to function of excitable cells.
What does freely filtered refer to?
100% of substance is moved from glomerulus to bowman’s capsule
What regulates sodium reabsorption and where does it occur?
aldosterone and ANP
- regulated at principal cells of distal tubules and collecting ducts
What is the effect of aldosterone and what secretes it?
increases sodium reabsorption and secreted from adrenal cortex
- increase number of sodium/potassium pumps on basolateral membrane
- increases number of open sodium and potassium channels on apical membrane
What 3 ways is renin release stimulated?
- decreased pressure in afferent arteriole
- renal sympathetic nerve activity
- decreases in sodium and chlorine in distal tubule filtrate
How does atrial natriuretic peptide increase GFR?
dilation of afferent arteriole and constriction of efferent arteriole
How does ANP decrease sodium reabsorption?
closing sodium channels in apical membrane; increased sodium excretion
What is hyperkalemia and hypokalemia?
hyper: high plasma potassium
hypo: low plasma potassium
What does potassium in plasma directly stimulate?
aldosterone release; potassium increase leads to more aldosterone release
What is hypercalcemia and hypocalcemia?
hypercalcemia: high plasma calcium
hypo: low plasma calcium
Why is calcium balance critical?
- triggers exocytosis in neurons
- triggers secretion
- triggers muscle contraction
- increases contractility of cardiac and smooth muscle
Where is reabsorption of calcium regulated?
in loops of henle and distal tubules
What is considered acidosis and alkalosis?
acidosis: pH < 7.35
alkalosis: pH > 7.45
What 5 complications can lead to an acid-base disturbance?
- conformation change in protein structure
- changes in excitability of neurons
- changes in potassium balance
- cardiac arrhythmias
- vasodilation
What can lead to metabolic acidosis?
- high protein diet
- high fat diet
- heavy exercise
- severe diarrhea
- renal dysfunction
What can lead to metabolic alkalosis?
- excessive vomiting
- consumption of alkaline products
- renal dysfunction
What are the three lines of defense against acid-base disturbances?
- buffering of hydrogen ions
- respiratory compensation
- renal compensation
What is the quickest defense against changes in pH?
buffering
How does respiratory compensation work in acting against acid-base disturbances?
increased ventilation -> decreased carbon dioxide
decreased ventilation -> increased carbon dioxide
How does renal handling of hydrogen and bicarbonate ions occur in the proximal tubule and distal tubule and collecting duct?
proximal tubule: bicarbonate reabsorption coupled to hydrogen ion secretion
distal tubule and collecting duct: secretion of hydrogen ions coupled to synthesis of new bicarbonate ions
When does glutamine come into play in acid-base disturbances?
severe acidosis; glutamine metabolism produces new bicarbonate and secretes hydrogen in the form of ammonium
