Chapter 24 (Fluid Balance) Study Guide

Question 1

What are the three types of homeostatic balances as it relates to cellular function?

Answer 1

1) Fluid Balance
2) Electrolyte balance
3) Acid–base balance

Question 2

Maintaining the 3 homeostatic balances requires the collective action of which eight organ systems?

Answer 2

1) Urinary,
2) Respiratory
3) Digestive
4) Integumentary
5) Endocrine
6) Nervous
7) Cardiovascular
8) Lymphatic

Question 3

1) Who would have their body weight at 75% water?
2) Why would a young woman have less body weight as water compared to a young male?Which tissue does a female have more of than a male?

Answer 3

1) A newborn baby’s body weight is about 75% water
2) Young men are 55-60% water. Women have slightly less body weight as water due to the fact that women have more adipose tissue, which is the most dehydrated tissue in the body.

Question 4

Who has the least amount of body weight as water? How much of their weight does water take up?

Answer 4

Obese and elderly people have the least amount of water, with as little as 45% by weight

Question 5

1) What is the largest fluid compartment?
2) The extracellular fluid (ECF) compartment contains what percent of body water?

Answer 5

1) The largest fluid component is intracellular fluid (ICF) which makes up 65% (2/3rds) of body water
2) 35% (1/3rd) of water is found in extracellular fluid (ECF)

Question 6

1) Can you list the three categories of ECF, and what % of them is water?
2) What kinds of fluids would be in the transcellular fluid?

Answer 6

1)
a) Tissue (interstitial) fluid: 25% water
b) Blood plasma and lymphatic fluid: 8% water
c) Transcellular fluid “catch-all” category: 2% water
2) Cerebrospinal, synovial, peritoneal, pleural, and pericardial fluids; humors of eye; bile and fluids of digestive, urinary, and reproductive tracts.

Question 7

1) How are fluids continually exchanged between compartments?
2) What determines in which direction water will move?
3) What are the most abundant electrolytes in the ECF?
4) What are the most abundant electrolytes in the ICF?

Answer 7

1) Osmosis allows for continual fluid exchange
2) Water moves from low osmolarity to high osmolarity
3) Na+ salts are the most abundant in ECF
4) K+ salts are the most abundant in ICF

Question 8

What is fluid balance? How much do we typically gain and lose in a day?

Answer 8

Defined as when daily gains and losses of fluid are equal (about 2,500 mL/day)

Question 9

What are the two sources for gains in fluid volume? Describe them. Which provides the most gains?

Answer 9

1) Preformed water (2,300 mL/day): Ingested in food (700 mL/day) and drink (1,600 mL/day); provides the most gains
2) Metabolic water (200 mL/day): By-product of aerobic metabolism and dehydration synthesis

Question 10

What are the two sources for water loss? Define them. Which specifically, provides the most loss?

Answer 10

1) Sensible water loss is observable; the most loss
-Urine (1,500 mL/day)
-Feces (200 mL/day)
-Sweat (100 mL/day in resting adult)
2) Insensible water loss is unnoticed
-Expired breath (300 mL/day)
-Cutaneous transpiration (400 mL/day)

Question 11

Name the 3 sources of sensible water loss and 2 sources of insensible water loss

Answer 11

1) Urine, feces, and sweat make up sensible water loss
2) Expired breath and cutaneous transpiration make up insensible water loss

Question 12

1) What determines fluid intake? 2) Where is the thirst center located?

Answer 12

1) The thirst center primarily determines your fluid intake
2) The thirst center is in the hypothalamus.

Question 13

1) What happens (to blood volume, blood pressure and blood osmolarity) if a person is dehydrated?
2) What is an osmoreceptor and what organ is it located in? That organ, in response to what stimulus, will release which hormone?

Answer 13

1) Dehydration reduces blood volume and blood pressure and increases blood osmolarity
2) Osmoreceptors in the hypothalamus respond to angiotensin II (produced when BP drops) and also respond to rise in osmolarity of ECF by releasing ADH.

Question 14

Why does ADH slow water output?

Answer 14

The secretion of ADH is triggered by hypothalamic osmoreceptors, and it slows water output because it triggers aquaporins to be synthesized on collecting ducts, allowing more water to be reabsorbed

Question 15

1) Does ADH slowing water output use positive or negative feedback?
2) Would more or less ADH be released if osmolarity rises?
3) Would more or less ADH be released if osmolarity falls or blood volume rises?

Answer 15

1) ADH system is example of negative feedback
2) If osmolarity rises and/or blood volume falls, more ADH is secreted (slows loss of water)
3) If osmolarity falls and/or blood volume rises, ADH release is inhibited, so tubules reabsorb less water, urine output increases, and more water released

Question 16

1) Define fluid deficiency.
2) What are the two kinds of deficiency?

Answer 16

1) Fluid deficiency: an inefficient amount of fluid in the body.
2) Volume depletion (hypovolemia)
and dehydration (negative fluid balance)

Question 17

1) When does volume depletion (hypovolemia) occur?
2) What would cause this?
3) When does dehydration (negative water balance) occur?
4) What would cause this?

Answer 17

1) Volume depletion (hypovolemia) occurs when proportionate amounts of water and sodium are lost (osmolarity remains normal)
2) Hemorrhage, severe burns, chronic vomiting, diarrhea, or Addison disease
3) Dehydration (negative fluid balance) occurs when more water is lost than sodium, so ECF osmolarity rises
4) Lack of drinking water, diabetes mellitus, diabetes insipidus, profuse sweating, overuse of diuretics

Question 18

What are the two kinds of fluid excess? For each, describe:
a) water and sodium retention
b) what happens to the ECF
c) what causes it

Answer 18

1) Volume excess
a) Both Na^+ and water retained
b) ECF remains isotonic
c) Caused by aldosterone hypersecretion or renal failure
2) Hypotonic hydration (water intoxication or positive Fluid Balance)
a) More water than Na^+ retained or ingested
b) ECF becomes hypotonic (can cause cellular swelling)
c) Most severe effects: pulmonary and cerebral edema and death

Question 19

1) What is fluid sequestration?
2) What are its causes?

Answer 19

1) Fluid sequestration is defined as an excess fluid accumulates in a particular location; total body water may be normal, but circulating blood volume too low (may cause circulatory shock)
2) Causes: edema, hemorrhage (blood pooling in tissues), pleural effusion (fluid in pleural cavity)

Question 20

What 4 properties of electrolytes make them important to the body?

Answer 20

1) Chemically reactive and participate in metabolism
2) Determine electrical potential (charge difference) across cell membranes
3) Strongly affect osmolarity of body fluids
4) Affect body’s water content and distribution

Question 21

List the major cations (5) and major anions (3)

Answer 21

1) Major cations: Na+, K+, Ca(2+), Mg(2+), and H+
2) Major anions: Cl−, HCO3− (bicarbonate), and PO4(3−)

Question 22

1) What is the most important extracellular cation?
2) Which hormones increase reabsorption of the most important extracellular cation? (3)
3) Which hormones decrease reabsorption of the most important extracellular cation? (2)

Answer 22

1) Sodium is the most important cation in ECF.
2) Increase sodium reabsorption: Aldosterone, estrogens, glucocorticoids
3) Decrease sodium reabsorption: Atrial natriuretic peptides and progesterone

Question 23

1) What is the most abundant and important intracellular cation?
2) What hormone regulates the most abundant intracellular cation?

Answer 23

1) Potassium is the most abundant and important cation in ICF.
2) Regulated by aldosterone

Question 24

Define hyperkalemia and hypokalemia.
What do the symptoms of hyperkalemia depend on and what are they?
What are the causes and symptoms of hypokalemia?

Answer 24

1) Hyperkalemia: Too much potassium in bloodstream
a) Symptoms: The effects depend on whether the potassium concentration rises quickly or slowly:
b) If concentration rises quickly (crush injury), the sudden increase in extracellular K^+ makes nerve and muscle cells abnormally excitable, which can produce cardiac arrest
c) Slow onset, inactivates voltage-regulated Na^+ channels, nerve and muscle cells become less excitable
2) Hypokalemia: Not enough potassium in bloodstream
a) Causes: sweating, chronic vomiting, diarrhea, excessive laxative use, aldosterone hypersecretion, or alkalosis
b) Symptoms: nerve and muscle cells less excitable, muscle weakness, loss of muscle tone, decreased reflexes, and arrhythmias from irregular electrical activity in the heart

Question 25

1) Which hormones regulate calcium?
2) What symptoms are seen in hypercalcemia
3) What symptoms are seen in hypocalcemia?
4) Which hormone stimulates excretion of phosphate?

Answer 25

1) PTH, calcitonin (weak in adults), and vitamin D regulate calcium
2) Hypercalcemia: Severe cases cause muscular weakness, depressed reflexes, cardiac arrhythmias
3) Hypocalcemia: Severe cases result in tetany and laryngospasm
4) PTH stimulates the excretion of phosphate

Question 26

1) The pH of a solution is determined by what ion?
2) Define acid.
3) Give an example of a strong acid
4) Give an example of a weak acid.

Answer 26

1) pH of a solution is determined solely by its hydrogen ions (𝐇^+)
2) Acid: any chemical that releases H^+ in solution
3) A strong acid such as hydrochloric acid (HCl) ionizes freely and gives up most of its H^+; strongly lowers pH of a solution
4) A weak acid such as carbonic acid (H2CO3) ionizes only slightly and keeps most H^+ chemically bound; does not affect pH much

Question 27

1) Define Base.
2) Give an example of a strong base
3) Give an example of a weak base

Answer 27

1) Base: any chemical that accepts H^+
2) Strong bases, such as the hydroxide ion (OH^−), have a strong tendency to bind H^+, markedly raising pH
3) Weak bases, such as the bicarbonate ion (HCO3^−), bind less of the available H^+ and have less effect on pH

Question 28

1) What is a buffer?
2) What is a physiological buffer? 3) What organ system is best as a physiological buffer and how fast does it work?
4) What other organ system acts as a buffer and how fast does it work?

Answer 28

1) Buffer: Any mechanism that resists changes in pH; converts strong acids or bases to weak ones
2) Physiological buffer: A system that controls pH
3) The urinary system is the best physiological buffer, and buffers the greatest quantity of acid or base, but it takes several hours to days to have an effect.
4) The respiratory system cannot alter pH as much as the urinary system, but buffers within minutes

Question 29

1) Which type of buffers work to normalize pH in fractions of a second?
2) Define buffer system.
3) What are the three major chemical buffer systems of the body?

Answer 29

1) Chemical buffers restore normal pH in fractions of a second
2) Buffer systems are mixtures composed of weak acids and weak bases
3) The 3 major buffer systems are the bicarbonate, phosphate, and protein systems

Question 30

1) What is an important buffer system in the ECF, and how does this system raise or lower pH?
2) Carbonic acid (H2CO3) forms by the hydration of carbon dioxide and then dissociates into __________ (HCO3–) and H+
3) What role do the lungs and kidneys play in this system?

Answer 30

1) The bicarbonate buffer system is an important buffering system in the ECF; lowers pH by releasing H+ and raises it by binding H+.
2) Carbonic acid (H2CO3) forms by the hydration of carbon dioxide and then dissociates into bicarbonate (HCO3–) and H+
3) To lower pH, kidneys excrete HCO_3^−, and to raise pH, kidneys excrete H^+ and lungs excrete CO_2

Question 31

1) What would the kidneys excrete to lower pH?
2) What would the kidneys excrete to raise pH?
3) What would the lungs excrete to raise pH?

Answer 31

1) To lower pH, kidneys excrete HCO3^−
2) To raise pH, kidneys excrete H^+
3) To raise pH, lungs excrete CO2

Question 32

Describe the phosphate buffering system; what is released to decrease pH and what is bound to increase pH

Answer 32

Reactions that proceed to the right (H2PO4^-2 + H+) release H+ and decrease pH, and those to the left (H2PO4) bind H+ and increase pH

Question 33

1) Which buffer system accounts for about three-quarters of all chemical buffering in the body fluids?
2) What is released and from what side group when the pH begins to rise?
3) What is released and from what side group when the pH gets too low?

Answer 33

1) The protein buffering system accounts for about three-quarters of all chemical buffering in the body fluids
2) The proteins’ buffering ability is due to certain side groups of their amino acid residues; carboxyl (−COOH) side groups release H+ when pH begins to rise
3) Other proteins have amino (〖−𝐍𝐇〗_𝟐) side groups that bind H+ when pH gets too low

Question 34

1) Increased ___ and decreased ___ stimulate pulmonary ventilation, while an increased ____ inhibits pulmonary ventilation.
2) Respiratory control of pH is due to its strong buffering capacity; this system can neutralize two or three times as much acid as the _________ buffers can.

Answer 34

1) Increased CO2 and decreased pH stimulate pulmonary ventilation, while an increased pH inhibits pulmonary ventilation.
2) Respiratory control of pH is due to its strong buffering capacity; this system can neutralize two or three times as much acid as the chemical buffers can

Question 35

1) What buffer system is the basis for the strong buffering capacity of the respiratory system?
2) The addition of CO_2 to the body fluids raises and lowers what?

Answer 35

1) Bicarbonate buffer system is the basis
2) Adding CO2 raises the H^+ concentration and lowers pH

Question 36

1) The kidneys can neutralize more acid or base than what 2 other systems?
2) Most of the secreted hydrogen ion binds to what 3 things?

Answer 36

1) Can neutralize more than either the respiratory system or chemical buffers
2) Most hydrogen ions secreted by the renal tubules bind to bicarbonate, ammonia, and phosphate buffers in the tubular fluid.

Question 37

1) In the body, what constitutes acidosis?
2) How does it cause hyperkalemia?
3) What symptoms would be exhibited?

Answer 37

1) Acidosis: A pH of ECF below 7.35
2) It causes hyperkalemia because H^+ diffuses into cells and drives out K^+, elevating K^+ concentration in ECF
3) Symptoms: Causes membrane hyperpolarization, nerve and muscle cells are hard to stimulate; CNS depression may lead to confusion, disorientation, coma, and death

Question 38

1) In the body, what constitutes alkalosis?
2) How does it cause hypokalemia?
3) What symptoms would be exhibited?

Answer 38

1) Alkalosis: pH above 7.45
2) It causes hypokalemia because H^+ diffuses out of cells and K^+ diffuses in
3) Symptoms: Membranes depolarize too easily, nerves are overstimulated, muscles cause spasms, tetany, convulsions, respiratory paralysis

Question 39

If the blood pH is below 7.0 or above 7.7, can a person live for days and why?

Answer 39

No; a person cannot live for more than a few hours if the blood pH is below 7.0 or above 7.7

Question 40

Acid-base imbalances are either ___________ or ____________

Answer 40

Respiratory or metabolic

Question 41

Define respiratory acidosis and respiratory alkalosis and describe their causes

Answer 41

1) Respiratory acidosis: Carbon dioxide accumulates in the ECF and lowers its pH; occurs when rate of alveolar ventilation fails to keep pace with the body’s rate of CO2 production (ex: in emphysema where there is a severe reduction of functional alveoli)
2) Respiratory alkalosis: CO2 eliminated faster than it is produced; results from hyperventilation

Question 42

1) Define metabolic acidosis.
2) What causes metabolic acidosis?
3) What causes metabolic alkalosis?

Answer 42

1) Metabolic acidosis: Increased production of organic acids such as lactic acid in anaerobic fermentation, and ketone bodies seen in alcoholism, and diabetes mellitus
2) Metabolic acidosis can be due to the ingestion of acidic drugs (aspirin) or the loss of base due to chronic diarrhea, laxative overuse
3) Metabolic alkalosis can be due to the overuse of bicarbonates (antacids and IV bicarbonate solutions) or the loss of stomach acid (chronic vomiting)

Question 43

1) What is the rarest type of acid-base imbalance?
2) What happens in compensated acidosis or alkalosis?

Answer 43

1) Metabolic alkalosis
2) Either the kidneys compensate for pH imbalances of respiratory origin, or the respiratory system compensates for pH imbalances of metabolic origin

Question 44

1) In respiratory compensation, changes in what correct the pH of the body fluids by expelling or retaining CO2?
2) What do acidosis and alkalosis cause pulmonary ventilation to do?

Answer 44

1) Changes in pulmonary ventilation to correct changes in pH of body fluids by expelling or retaining CO2
2) Acidosis stimulates pulmonary ventilation eliminating CO2 and allowing pH to rise; alkalosis reduces ventilation which allows CO2 to accumulate and thereby lowering pH

Question 45

1) Renal compensation is an adjustment of pH by changing the rate of what?
2) What do acidosis and alkalosis cause renal compensation to do?
3) When is renal compensation effective and why?

Answer 45

1) Changing the rate of H^+ secretion by renal tubules
2a) In acidosis, renal tubules increase rate of H+ secretion and urine pH may drop to 4.5 due to excess H^+.
2b) In alkalosis, renal tubules decrease rate of H+ secretion (increase rate of 〖HCO3〗^− secretion) and urine pH as can be as high as 8.2 due to excess HCO3 −.
3) Effective at compensating for pH imbalances that last for a few days or longer (NOT for short-term imbalances because it’s slow)

Question 46

1) Why might the pH of urine drop as low as 4.5 in acidosis, and what do the renal tubules increase the rate of in acidosis?
2) Why might the pH of urine rise as high as 8.2 in alkalosis, and what do the renal tubules increase the rate of in alkalosis?

Answer 46

1) Excess H+ caused by an increased rate of H+ secretion at the renal tubules causes pH to drop as low as 4.5 in acidosis.
2) Excess HCO3- caused by an increased rate of HCO3- secretion and decreased rate of H+ secretion at the renal tubules causes pH to rise as high as 8.2 in alkalosis.

Question 47

1) At a pH of 7.6, which direction would this reaction (bicarbonate buffer system) need to run to get within the normal range? CO2 + H2O ⇆ H2CO3 ⇆ HCO3– + H+.
2) At a pH of 7.2, which direction would this reaction need to run to get within the normal range? CO2 + H2O ⇆ H2CO3 ⇆ HCO3– + H+.

Answer 47

1) Right to decrease pH
2) Left to increase pH

Question 48

1) What is the most important buffer system of the ICF?
2) At a pH of 7.6, which direction would this reaction need to run to get within the normal range? H2PO4– ⇆ HPO42– + H+.
3) At a pH of 7.2, which direction would this reaction need to run to get within the normal range? H2PO4– ⇆ HPO42– + H+.

Answer 48

1) Phosphate buffer system
2) Right to lower pH
3) Left to raise pH

Question 49

1) What is the most important buffer system of the ICF?
2) At a pH of 7.6, which direction would this reaction need to run to get within the normal range? H2PO4– ⇆ HPO42– + H+.
3) At a pH of 7.2, which direction would this reaction need to run to get within the normal range? H2PO4– ⇆ HPO42– + H+.

Answer 49

1) Phosphate buffer system
2) Right to lower pH
3) Left to raise pH