24.1 Fluid Balance

Question 1

fluid compartments

Answer 1

areas of the body separated by selectively permeable membranes and differing from each other in chemical composition: 65% ICF, 35% ECF, 25% interstitial fluid, 8% blood plasma + lymph, 2% transcellular fluid

Question 2

fluid balance

Answer 2

a state in which average daily water gains (by intake and synthesis) equal water losses (2,500 mL/day), and water is properly distributed among the body’s fluid compartments

Question 3

metabolic water

Answer 3

water produced as a byproduct of dehydration synthesis reactions and aerobic respiration (200 mL/day)

Question 4

preformed water

Answer 4

water ingested in food (700 mL/day) and drink (1,600 mL/day)

Question 5

cutaneous transpiration

Answer 5

water that diffuses through the epidermis and evaporates

Question 6

insensible water loss

Answer 6

water output through the breath and cutaneous transpiration

Question 7

sensible water loss

Answer 7

noticeable water output through the urine and sweating

Question 8

obligatory water loss

Answer 8

water output that is relatively unavoidable through expired air, cutaneous transpiration, sweat, fecal moisture, and minimum urine output (400 mL/day)

Question 9

osmoreceptors

Answer 9

groups of neurons in the hypothalamus that respond to angiotensin II and rising osmolarity of the ECF

Question 10

transcellular fluid

Answer 10

cerebrospinal, synovial, peritoneal, pleural, and pericardial fluids; vitreous and aqueous humors of the eye; bile; fluid in the digestive, urinary, and respiratory tracts

Question 11

fast-acting thirst relief stimuli

Answer 11

cooling and moisturizing of the mouth, distention of the stomach and small intestine

Question 12

antidiuretic hormone (ADH)

Answer 12

a hormone that controls water output independently of sodium

Question 13

fluid deficiency

Answer 13

the state that arises when fluid output exceeds fluid intake over time

Question 14

volume depletion (hypovolemia)

Answer 14

fluid deficiency that occurs when proportionate amounts of water and sodium are lost without replacement; total body water declines but osmolarity remains normal; e.g. hemorrhage, severe burns, chronic vomiting and diarrhea, aldosterone hyposecretion

Question 15

dehydration (negative water balance)

Answer 15

fluid deficiency that occurs when the body eliminates significantly more water than sodium, so the ECF osmolarity rises; e.g. lack of drinking water, diabetes mellitus, ADH hyposecretion (diabetes insipidus), profuse sweating, overuse of diuretics

Question 16

three reasons infants are vulnerable to dehydration

Answer 16

1) high metabolic rate –> excretion of more water to eliminate toxic metabolites; 2) immature kidneys –> slower urine concentration; 3) greater ratio of body surface to volume –> more water loss by evaporation

Question 17

fluid excess

Answer 17

the state that arises when fluid intake exceeds fluid output over time

Question 18

volume excess

Answer 18

fluid excess in which both water and sodium are retained and the ECF remains isotonic; e.g. aldosterone hypersecretion or renal failure

Question 19

hypotonic hydration (water intoxication and positive water balance)

Answer 19

fluid excess in which more water than sodium is retained or ingested and the ECF becomes hypotonic; e.g. losing water and salt through urine and sweat and replacing it with only plain water, ADH hypersecretion

Question 20

serious effects of fluid excess

Answer 20

pulmonary and cerebral edema and death

Question 21

fluid sequestration

Answer 21

a condition in which excess fluid accumulates in a particular location; e.g. edema

Question 22

edema

Answer 22

the abnormal accumulation of fluid in the interstitial spaces

Question 23

pleural effusion

Answer 23

the accumulation of several liters of fluid in the pleural cavity