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BIOL*235 Final Exam > Ch. 27: Fluid, Electrolyte and Acid-Base Homeostasis > Flashcards

Ch. 27: Fluid, Electrolyte and Acid-Base Homeostasis Flashcards

1
Q

Body fluids constitute ____ of total body mass in females and males.

A

55-60%

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2
Q

Intracellular fluid.

A

2/3rd of body fluid. Within cells.

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3
Q

Extracellular fluid.

A

1/3rd of body fluid. Outside cells.

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4
Q

Describe the 2 different kinds of extracellular fluid.

A

1) Interstitial fluid: 80%, microscopic spaces between tissue cells.

2) Blood plasma: 20%.

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5
Q

Two barriers separate intracellular fluid, interstitial fluid, and blood plasma.

A

1) Plasma membrane: PM of individual cells separates intracellular fluid from the surrounding interstitial fluid. Active transport pumps work to maintain different concentrations of certain ions in the cytosol and interstitial fluid.

2) Blood vessel walls: Divide interstitial fluid from blood plasma. Only in capillaries are the walls thin and leaky enough to permit the exchange of water and solutes between blood plasma and interstitial fluid.

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6
Q

Water makes up ____ of total body mass. Why is this such a big range?

A

45-75%.
Infants have 75% of water, and then this number decreases until 2 years old.
Until puberty, water accounts for 60% of total body mass.
In lean adult males, water accounts for 60% of total body mass.
In lean adult females, water accounts for 55% of total body mass (more subcutaneous fat).

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7
Q

Skeletal muscle tissue is ___ water.

A

65%

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8
Q

Why would obese people have less water than lean people?

A

Water comprises under 20% of the mass of adipose tissue.

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9
Q

Fluid balance is closely related to ____ balance.

A

Electrolyte.

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10
Q

How does the body gain water?

A

Ingestion (liquids, moist foods) and metabolic synthesis (when electrons are accepted by oxygen during aerobic respiration).

Daily water gain = 2500 mL.

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11
Q

How does the body lose water?

A

Kidneys (excretion), skin (evaporation), lungs (exhalation) and GI tract (elimination in feces).

Daily water loss = 2500 mL.

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12
Q

The volume of metabolic water formed in the body depends on the level of…

A

Aerobic respiration, which reflects the demand for ATP. When more ATP is produced, more water is formed.

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13
Q

Thirst center.

A

Hypothalamus.
Water loss is greater than water gain –> dehydration -> decrease in blood volume –> decrease in blood pressure –> increased blood osmolarity –> increased activity of osmoreceptors in hypothalamus –> thirst center is stimulated.
Other signals that stimulate thirst center come from volume receptors in atria that detect decreased blood volume, baroreceptors in blood vessels that detect decreased blood pressure, angiotensin II that is formed in RAA activation by decreased blood pressure, and neurons in the mouth that detect dryness.

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14
Q

What is the main factor that determines body water loss in urine?

A

Urinary salt (NaCl).

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15
Q

What is the main factor that determines body fluid osmolarity?

A

Urinary water loss.

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16
Q

What is the major hormone that regulates water loss?

A

ADH. Produced by neurosecretory cells in hypothalamus. Stored in posterior pituitary. ADH is released when blood osmolarity increases, and osmoreceptors in hypothalamus are activated. ADH promotes insertion of aquaporin-2 into apical membranes of principal cells in late DCT and CD to increase water permeability –> water than moves by osmosis from renal tubular fluid into cells and then blood to decrease blood osmolarity and increased blood volume and blood pressure.

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17
Q

Other than increased blood osmolarity, what other stimuli cause ADH release?

A

Decreased blood volume sensed by atria volume receptors. Decreased blood pressure sensed by baroreceptors. Pain, nausea and stress.

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18
Q

What inhibits ADH secretion?

A

Alcohol. Without ADH, more water is lost in urine.

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19
Q

Which hormones regulate urinary loss of Na+?

A

Aldosterone: Decreased BP or Na+ plasma deficiency –> kidneys release renin –> RAA pathway –> aldosterone –> increased Na+ reabsorption in late DCT and CD –> ADH is also released, so water reabsorption accompanies Na+ reabsorption via osmosis.

ANP: Increased blood volume stretches atria –> ANP release –> promotes natriuresis –> loss of more water in urine –> decreases blood volume and BP.
*Increased blood volume also slows renin release, less aldosterone is formed, and reabsorption of Na+ is slowed.

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20
Q

Natriuresis.

A

Elevated urinary loss of Na+.

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21
Q

Changes in which body fluid causes fluid imbalances?

A

Extracellular fluid.
If ECF becomes hypertonic, water moves from cells into ECF by osmosis, causing cells to shrink.
If ECF becomes hypotonic, water moves from ECF into cells by osmosis, causing cells to swell.

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22
Q

An increase in the osmolarity of ECF occurs after you…

A

Eat a salty meal. Increased intake of NaCl produces increased Na+ and Cl- in ECF. Osmolarity of ECF increases, causing water to move from cells into the ECF, and these cells shrink. Corrective measures usually kick in shortly to increase body water volume.

If neurons remain in this state for a significant period of time, mental confusion, convulsions, coma and death can occur.

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23
Q

A decrease in the osmolarity of ECF occurs after you…

A

Drink a large volume of water. When Na+ and Cl- concentrations in ECF decrease, osmolarity of ECF decreases. Water moves from ECF into cells, and these cells swell. Corrective measures usually kick in shortly to decrease body water volume.

When osmolarity of ECF decreases, ADH is inhibited, and kidneys excrete a large volume of water.

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24
Q

Water intoxication.

A

When a person steadily consumes water faster than the kidneys can excrete it or when renal functional is poor. Causes body cells to swell dangerously. Swelling of neurons can cause mental confusion, seizures, coma and death.

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25
Q

The ions formed when electrolytes dissolve and dissociate serve 4 functions:

A

1) Ions are confined to particular fluid compartments and are more numerous than non electrolytes, so certain ions control the osmosis of water between fluid compartments.
2) Ions help maintain acid-base balance required for normal cellular activities.
3) Ions carry electrical current, which allows production of APs and GPs.
4) Ions serve as cofactors as needed for enzyme activity.

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26
Q

What is the unit of concentration of ions?

A

mEq/L

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27
Q

Blood plasma contains many _______ , while interstitial fluid contains very few.

A

Protein anions. Because capillary membranes are impermeable to proteins, only a few plasma proteins leak out of blood vessels into the interstitial fluid. This difference in protein concentration is responsible for the blood colloid osmotic pressure exerted by blood plasma.

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28
Q

In ECF, what is the most abundant cation and anion?

A

Na+, Cl-.

29
Q

In ICF, what is the most abundant cation and anion?

A

K+, proteins and phosphates.

30
Q

Na+ ions.

A

Account for 90% of ECF cations. Normal blood plasma concentration of Na+ is 136-148 mEq/L. Blood level of Na+ is controlled by aldosterone, ADH, and ANP.

Hyponatremia = blood plasma concentration of Na+ < 135 mEq/L, ADH release stops, more water is lost in urine.

Hypernatremia = blood plasma concentration of Na+ > 148 mEq/L, ANP increases Na+ excretion.

31
Q

Cl- ions.

A

Normal blood plasma concentration of Cl- is 95-105 mEq/L. Moves easily between ECF and ICF because most plasma membranes contain many Cl- leakage channels and antiporters. Cl- balance is regulated by ADH.

32
Q

Chloride shift.

A

Occurs between RBCs and blood plasma as the blood level of CO2 increases or decreases. The antiporter exchange of Cl- for HCO3- maintains the correct balance of anions between ECF and ICF.

33
Q

K+ ions.

A

Normal blood plasma concentration of K+ is 4.5-5.0 mEq/L. Establishes resting membrane potential and depolarization phase of action potentials. Maintains normal ICF volume. Regulates pH of body fluids since it is exchanged for H+ when moving into or out of cells. K+ balance is regulated by aldosterone (high blood K+ –> aldosterone release –> principal cells secrete K+ so excess K+ is lost in urine).

Abnormal K+ levels can be lethal.

34
Q

HCO3- ions.

A

Normal blood plasma concentration of HCO3- is 22-26 mEq/L in arterial blood, and 23-27 mEq/L in venous blood. Second most prevalent anion in ECF.

35
Q

The exchange of ____ and ____ maintains the correct balance of anions in ECF and ICF.

A

Cl-, HCO3-.

36
Q

Why would HCO3- concentration increase as blood flows through systemic capillaries as opposed to pulmonary capillaries?

A

Because CO2 released by metabolically active cells combines with water to form carbonic acid, which dissociates into H+ and HCO3-.

37
Q

Ca2+ ions.

A

Normal blood plasma concentration of Ca2+ is 4.5-5.5 mEq/L. Mainly in ECF. Contributes to hardness of bone and teeth. Involved in blood clotting, NT release, muscle tone maintenance, and excitability of nervous and muscle tissue.

38
Q

Most abundant mineral in the body.

A

Calcium.

39
Q

What is the most important regulator of Ca2+ concentration in blood plasma?

A

PTH.
Low Ca2+ –> PTH release –> osteoclasts increase bone resorption to release Ca2+ from bone ECM / Ca2+ reabsorption is increased from glomerular filtrate / calcitriol is produced which increases Ca2+ absorption from GI tract.

40
Q

Calicitonin.

A

Inhibits osteoclasts. Accelerates Ca2+ deposition into bones. Lowers blood Ca2+ levels.

Opposite of calcitriol

41
Q

Phosphate.

A

Normal blood plasma concentration of ionized phosphate is 1.7-2.6 mEq/L. Most phosphate ions are covalently bound to organic molecules.

42
Q

Where is 85% and 15% of the phosphate in the body?

A

85%: Calcium phosphate salts.
15%: Ionized.

43
Q

Which 3 phosphate ions are important intracellular anions, and which one is the most prevalent form?

A

H2PO4-, HPO4(2-), PO4(3-).
Most prevalent: HPO4(2-), which is an important buffer of H+ in body fluids and urine.

44
Q

How is HPO4(2-) concentration regulated in the blood?

A

PTH: Low phosphate –> osteoclasts are stimulated –> release phosphate and calcium into blood. High phosphate –> PTH inhibits reabsorption of phosphate while stimulating reabsorption of calcium in kidneys to increase phosphate excretion.

Calcitriol: Promotes absorption of phosphates and calcium from GI tract when levels are low.

FGF 23: Polypeptide paracrine. Decreases phosphate levels by increasing kidney excretion and decreasing GI absorption.

45
Q

Mg2+ ions.

A

Normal blood plasma concentration is 1.3-2.1 mEq/L. Cofactor for enzymes needed for metabolism of CHOs and proteins. Also needed for Na-K pump. Essential for neuromuscular activity, synaptic transmission, and myocardial functioning.

46
Q

___ of total body magnesium is part of _____ as magnesium salts.

A

54%, bone matrix.

Remaining 45% in ICF, and 1% in ECF.

47
Q

Secretion of PTH depends on which ion?

A

Mg2+.

48
Q

How does protein acidify the blood?

A

When large amounts of protein are ingested, cellular metabolism produces more acids and bases.

49
Q

The removal of H+ from body fluids and its elimination from the body depend on:

A

1) Buffer systems.
2) CO2 exhalation.
3) Kidney excretion of H+.

50
Q

Buffer systems.

A

Temporarily bind H+ to remove excess H+ from solution and raise pH. Prevent rapid drastic changes in pH of body fluids by converting strong acids and bases into weak acids and bases within seconds.

51
Q

Protein buffer system.

A

Most abundant buffer in ICF and blood plasma. Proteins can buffer acids and bases.

Blood flows through systemic capillaries –> CO2 passes from tissue cells to RBCs –> CO2 combines with water to form carbonic acid –> dissociates into H+ and HCO3- –> Hb-O2 gives up its O2 to tissue cells –> reduced Hg picks up H+.

52
Q

Functional component of protein buffer system.

A

Amine group of protein.

53
Q

What is a good buffer within RBCs, and what is a good buffer in blood plasma?

A

RBCs: Hemoglobin.
Plasma: Albumin.

54
Q

Carbonic acid-bicarbonate buffer system.

A

Weak base: bicarbonate ion.
Weak acid: carbonic acid.

Excess H+ –> HCO3- removes H+ –> H2CO3 dissociates into H2O and CO2 –> CO2 is exhaled.

Deficient H+ –> H2CO3- provides H+.

55
Q

Phosphate buffer system.

A

Regulator of pH in cytosol.
Excess H+ in renal tubular fluid –> HPO4- combines with H+ to form H2PO4- –> excreted in urine.

56
Q

Exhalation of CO2.

A

Increase of CO2 increases H+ in blood. Rate and depth of breathing increases –> within minutes carbonic acid in blood decreases –> raises blood pH.

57
Q

Volatile acid.

A

Carbonic acid; H2CO3.

58
Q

Describe the negative feedback between pH of body fluids and the rate and depth of breathing.

A

pH decreases –> detected by central chemoreceptors in medulla oblongata and peripheral chemoreceptors in aortic and carotid bodies –> stimulate dorsal respiratory group in medulla oblongata –> diaphragm and respiratory muscles contract more forcefully and frequently –> more CO2 is exhaled –> less H2CO3 forms –> lower H+ in blood –> pH increases.

pH increases –> respiratory center is inhibited –> rate and depth of breathing decrease –> CO2 accumulates –> H+ rises –> pH decreases.

59
Q

Kidney excretion of H+.

A

Slowest mechanism. Only way to eliminate acids from the body, other than H2CO3. Two types of intercalated cells maintain the pH of body fluids by excreting excess H+ when pH of body fluids is too low, and by excreting excess HCO3- when pH is too high.

60
Q

What is the most plentiful buffer in the tubular fluid of collecting ducts?

A

HPO4(2-), and a small amount of NH3.
H+ combines with HPO4(2-) to form H2PO4-, and with NH3 to form NH4+. These ions cannot diffuse back into tubule cells, so they are excreted in urine.

61
Q

Normal pH range of systemic arterial blood.

A

7.35 to 7.45.

62
Q

Acidosis.

A

Blood pH is below 7.35. Results in CNS and synaptic transmission depression.
If blood pH is below 7, depression of nervous system is so severe that the individual becomes disoriented –> comatose –> death.

63
Q

Alkalosis.

A

Blood pH is above 7.45. Results in CNS and peripheral nerve over excitability. neurons will conduct impulses repetitively, and even when not stimulated by normal stimuli. Nervousness, muscle spasms, convulsions, death.

64
Q

A change in blood pH that leads to acidosis or alkalosis may be countered by…

A

Compensation. Physiological response to an acid-base imbalance that acts to normalize arterial blood pH. May be complete, if pH is brought within the normal range, or partial, if pH is still outside normal range.

Respiratory compensation: hyperventilation or hypoventilation.

Renal compensation: changes in H+ and HCO3- secretion and reabsorption.

65
Q

Respiratory acidosis.

A

High P(CO2) in systemic arterial blood above 45 mmHg. Inadequate CO2 exhalation causes blood pH to drop due to buildup of H2CO3 and H+. If the respiratory problem is not too severe, the kidneys can help raise blood pH to normal range by increasing excretion of H+ and reabsorption of HCO3-.

66
Q

Respiratory alkalosis.

A

Low P(CO2) in systemic arterial blood below 35 mmHg. Caused by hyperventilation (occurs in conditions that stimulate dorsal respiratory group in brainstem), high altitude, pulmonary disease, stroke, severe anxiety. Renal compensation may bring blood pH to normal if kidneys are able to decrease excretion of H+ and reabsorption of HCO3-.

67
Q

Metabolic acidosis.

A

Low systemic arterial blood HCO3- level below 22 mEq/L. Caused by loss of HCO3- by severe diarrhea or renal dysfunction, accumulation of an acid other than carbonic acid as may occur in ketosis, or failure of kidneys to excrete H+ from metabolism of proteins. Hyperventilation can bring blood pH to normal range.

68
Q

Metabolic alkalosis.

A

High systemic arterial blood HCO3- level above 26 mEq/L. Caused by excessive intake of alkaline drugs, non-respiratory loss of acid, excessive vomiting (most common), gastric suctioning, diuretics, endocrine disorders, severe dehydration. Hypoventilation can bring blood pH to normal range.

BIOL*235 Final Exam (10 decks)

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