Chapter 19 - Fluid and Electrolyte Balance
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46 Terms
What is normovolemia?
Normal blood volume
What is hypervolemia?
High blood volume due to positive water balance
What is hypovolemia?
Low blood volume due to negative water balance
What drives water reabsorption in the PCT?
Osmotic gradient created by Na+ active transport
What follows water movement in the PCT?
Urea reabsorption due to concentration gradient
What happens in the descending limb of the nephron loop?
Water is reabsorbed (20%) and the limb is permeable to water
What happens in the ascending limb of the nephron loop?
It is impermeable to water and actively reabsorbs ions
How does medullary osmolarity change?
It increases deeper into the medulla
What is the countercurrent multiplier?
A positive feedback system that establishes the medullary osmotic gradient
What is urea’s role in the medulla?
It contributes 40% of medullary osmolarity and cycles between the collecting duct and ascending limb
What is the function of the vasa recta?
It maintains the medullary gradient through countercurrent exchange
How much water is reabsorbed in the DCT?
20%
How much water is reabsorbed in the collecting duct?
10%
What regulates water permeability in the DCT and collecting duct?
Aquaporins
What is the maximum urine osmolarity?
1400 mOsm
What stimulates ADH release?
High blood osmolarity
What does ADH do?
Inserts aquaporin‑2 channels to increase water reabsorption
How does ADH affect urine?
Produces low‑volume, high‑osmolarity urine
How much Na+ is reabsorbed in the PCT?
67%
What transporters are in the PCT for Na+?
Cotransport with glucose, amino acids, and H+ plus Na+/K+ pump
How much Na+ is reabsorbed in the nephron loop?
25%
What transporter is in DCT1?
Na+/Cl− cotransporter
What transporters are in DCT2?
Na+ channels, Na+/K+ pump, Na+/H+ exchanger, Na+/HCO3− cotransporter
What does angiotensin II do?
Causes vasoconstriction and stimulates aldosterone, ADH, and thirst
What does aldosterone do?
Increases Na+ reabsorption and K+ secretion in the DCT
What does ADH do for Na+ balance?
Increases water reabsorption and affects osmolarity
What does ANP do?
Increases Na+ excretion by increasing GFR and decreasing Na+ channel activity while inhibiting renin and aldosterone
What determines plasma osmolarity?
Sodium concentration
What must be equal for Na+ balance?
Sodium input must equal sodium output
Where is most K+ reabsorbed?
PCT
Where is K+ secreted?
DCT and collecting duct
What hormone increases K+ secretion?
Aldosterone
Where is Ca2+ reabsorbed?
70% in PCT, 20% in nephron loop, 10% in DCT
What does PTH do?
Increases Ca2+ reabsorption and activates vitamin D
What does calcitonin do?
Decreases Ca2+ reabsorption and increases excretion
What is normal blood pH?
7.35 to 7.45
What is the normal HCO3− to CO2 ratio?
20 to 1
What causes respiratory acidosis?
Hypoventilation increasing CO2
What causes respiratory alkalosis?
Hyperventilation decreasing CO2
What causes metabolic acidosis?
High protein or fat diet, exercise, diarrhea, renal dysfunction
What causes metabolic alkalosis?
Vomiting, alkaline ingestion, increased bicarbonate reabsorption
What are the major buffer systems?
Bicarbonate in ECF and phosphate and proteins in ICF
What happens when pH decreases in respiratory compensation?
Hyperventilation decreases CO2 and raises pH
What happens when pH increases in respiratory compensation?
Hypoventilation increases CO2 and lowers pH
What do kidneys do when pH is low?
Increase bicarbonate reabsorption and hydrogen ion secretion
What do kidneys do when pH is high?
Decrease bicarbonate reabsorption and hydrogen ion secretion