Chapter 19 - fluid and electrolyte balance

Question 1

what is the concept of balance

Answer 1

to maintain homeostasis, what comes in the body must be used or excreted to be in balance. input + production = utilization + output

Question 2

how do kidneys function in balance

Answer 2

they regulate fluid and electrolyte composition of plasma and regulate acid-base balance

Question 3

describe factors affecting the plasma composition

Answer 3

kidneys regulate solute and water content, which also determines volume. composition is also affected by exchange between different compartments of body: cells, connective tissue, gastrointestinal tract, sweating, and respiration

Question 4

compare non-regulated vs regulated in relation to input vs output

Answer 4

non-regulated generally results in net input while regulated results in net output

Question 5

describe plasma balance vs positive balance vs negative balance

Answer 5

balance is when solutes and water enter and exit plasma at the same rate so quantity stays the same. positive balance is when solute or water enters plasma faster than exiting so quantity increases. negative balance is when solute or water exits plasma faster than it enters so quantity decreases

Question 6

name two cells in late distal tubule and collecting duct that regulate balance

Answer 6

principal cells regulate water and electrolytes while intercalated cells regulate acid-base balance

Question 7

describe water balance

Answer 7

water intake + metabolically produced water = water output + water used

Question 8

name 2 water intakes

Answer 8

gastrointestinal tract and metabolism

Question 9

name 4 water outputs

Answer 9

insensible loss, sweating, gastrointestinal tract, and kidneys

Question 10

what is normovolemia

Answer 10

normal blood volume

Question 11

what is hypervolemia

Answer 11

high blood volume due to positive water balance

Question 12

what is hypovolemia

Answer 12

low blood volume due to negative water balance

Question 13

describe osmosis

Answer 13

water diffuses down concentration gradient. water moves from area of low solute concentration to area of high solute concentration. water reabsorption follows solute reabsorption

Question 14

describe the osmolarity of body fluids

Answer 14

300 mOsm (300 milliosmoles of solute per liter of plasma). no osmotic force for water to move between fluid compartments. kidneys compensate for changes in osmolarity of ECF by regulating water reabsorption. water reabsorption is a passive process based on osmotic gradient

Question 15

describe water reabsorption in proximal tubules and distal tubules and collecting ducts

Answer 15

proximal tubules: 70% of filtered water is reabsorbed this is not regulated. distal tubules and collecting ducts: most remaining water is reabsorbed. regulated by ADH (vasopressin)

Question 16

what does water reabsorption follow and was is primary solute

Answer 16

water reabsorption follows solute reabsorption. the primary solute is sodium

Question 17

describe sodium reabsorption

Answer 17

Na is actively transported (pumped) across basolateral membrane; this establishes an osmotic gradient for water reabsorption

Question 18

describe water reabsorption

Answer 18

water follows actively transported solute: Na, X, and Y. and urea follows water

Question 19

describe medullary osmotic gradient

Answer 19

osmolarity of interstitial fluid of renal medulla varies with depth: lower osmolarity near cortex and greater osmolarity near renal papilla (deep in medulla). gradient is critical for water reabsorption from collecting duct

Question 20

describe counter-current multiplier in the loop of Henle

Answer 20

osmotic gradient is established by countercurrent multiplier that is dependent on loop of Henle. the ascending limb is impermeable to water and has active transport of Na/Cl/K out of tubules. while the descending limb is permeable to water and there is no transport of Na, Cl, or K

Question 21

describe results of countercurrent multiplier

Answer 21

fluid in proximal tube = 300 mOsm (same as interstitial fluid in cortex). fluid in discending limb: osmolarity increases as it descends so osmolarity = interstitial fluid of medulla. fluid in ascending limb: osmolarity decreases as it ascends so osmolarity < interstitial fluid, descending limb. the fluid in distal tubule = 100 mOsm

Question 22

describe the change in tubule fluid through loop of henle

Answer 22

tubule fluid is iso-osmotic in the proximal tubule, becomes dilute in the loop of Henle, and then either remains dilute or becomes concentrated at the end of collecting duct - subject to hormonal regulation

Question 23

describe role of urea in the medullary osmotic gradient

Answer 23

urea is generate by liver. it is nitrogen elimination. extremely water soluble. requires urea transporters (UT). renal handling of urea is complex, transport of urea from filtrate to peritubular fluid contributes the osmolarity of the gradient

Question 24

how does vasa recta prevent washout of medulla gradient

Answer 24

anatomical arrangement of vasa recta capillaries allows diffusion of water and solutes across capillary walls without disturbing the medullary osmotic gradient. descending limb of vasa recta: as it descends, water leaves capillaries and solutes enter. ascending limb of vasa recta: process is reversed as it ascends water moves into capillaries and solutes exit into interstitial fluid

Question 25

what would happen if vasa recta did not have a countercurent flow

Answer 25

plasma leaves kidneys at 1375 mOsm