Document26

PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

26

Fluid, Electrolyte, and Acid-Base Balance


Body Water Content

•Infants: 73% or more water (low body fat, low bone mass)

•Adult males: ~60% water

•Adult females: ~50% water (higher fat content, less skeletal muscle mass)

•Water content declines to ~45% in old age

Copyright © 2010 Pearson Education, Inc. Figure 26.1

Total body waterVolume = 40 L60% body weight Extracellular fluid (ECF)

Volume = 15 L20% body weight

Intracellular fluid (ICF)Volume = 25 L40% body weight

Interstitial fluid (IF)Volume = 12 L80% of ECF


Composition of Body Fluids

•Water: the universal solvent

• Solvent = substances in which solutes are dissolved

•Solutes:

•Nonelectrolytes

• Electrolytes


Composition of Body Fluid

•Nonelectrolytes: have bonds that do not dissociate in water (no electrical charge)

•most are organic

•e.g., glucose, lipids, creatinine, and urea

• Electrolytes: dissociate into ions in water (have an electrical charge)

•E.g., inorganic salts, inorganic and organic acids and bases, some proteins


Composition of Body Fluids

•Electrolytes

• The most abundant (most numerous) solutes

•Have greater osmotic power than nonelectrolytes because they dissociate and form two molecules, so may contribute to fluid shifts

•E.g., NaCl Na+, Cl- vs. glucose

•Determine the chemical and physical reactions of fluids


Extracellular and Intracellular Fluids

•Each fluid compartment has a distinctive pattern of electrolytes

•ECF (interstitial fluid and plasma)

• Similar compostion except higher protein content of plasma

•Major cation: Na+

•Major anion: Cl–


Extracellular and Intracellular Fluids

•ICF:

• Low Na+ and Cl–

•Major cation: K+

•Major anion HPO42– (hydrogen phosphate)

• K, Mg, phosphate ions are the predominant electrolytes ICF


Na+ Sodium

K+ Potassium

Ca2+ Calcium

Mg2+ Magnesium

HCO3– Bicarbonate

Cl– Chloride

HPO42–

SO42–

Hydrogenphosphate

Sulfate

Blood plasma

Interstitial fluid

Intracellular fluid


Fluid Movement Among Compartments

•Osmotic and hydrostatic pressures regulate the continuous exchange and mixing of body fluids

• Exchange between plasma and IF occur across capillary walls

• Exchanges between the IF and ICF occur across plasma membranes


Lungs

Interstitialfluid

Intracellularfluid in tissue cells

Bloodplasma

O2 CO2 H2O,Ions

Nitrogenouswastes

Nutrients

O2 CO2 H2O Ions Nitrogenouswastes

Nutrients

KidneysGastrointestinaltract

H2O,Ions


Water Balance and ECF Osmolality

•Water intake = water output = 2500 ml/day

•Water intake: beverages, food, and metabolic water

•Water output: urine, insensible water loss (skin and lungs), perspiration, and feces


Feces 4%

Sweat 8%

Insensible lossesvia skin andlungs 28%

Urine 60%

2500 ml

Average outputper day

Average intakeper day

Beverages 60%

Foods 30%

Metabolism 10%

1500 ml

700 ml

200 ml

100 ml

1500 ml

750 ml

250 ml


Regulation of Water Intake

•Thirst mechanism is the driving force for water intake

•The hypothalamic thirst center osmoreceptors are stimulated by

• Increase in plasma osmolality of 2–3%

• Dry mouth

• Substantial decrease in blood volume or pressure


Regulation of Water Intake

•Drinking water creates inhibition of the thirst center

•Inhibitory feedback signals include

•Relief of dry mouth

• Activation of stomach and intestinal stretch receptors

• These signals inhibit the thirst center before water is absorbed to prevent overhydration


(*Minor stimulus)

Granular cellsin kidney

Dry mouth

Renin-angiotensinmechanism

Osmoreceptorsin hypothalamus

Hypothalamicthirst center

Sensation of thirst;person takes a

drink

Water absorbedfrom GI tract

Angiotensin II

Plasma osmolality

Blood pressure

Water moistens mouth, throat;

stretches stomach, intestine

Plasmaosmolality

Initial stimulus

Result

Reduces, inhibits

Increases, stimulates

Physiological response

Plasma volume*

Saliva


Regulation of Water Output: Influence of ADH

•Water reabsorption in collecting ducts is proportional to ADH release

• ADH dilute urine and volume of body fluids

• ADH concentrated urine and volume of body fluids


OsmolalityNa+ concentration

in plasma

Stimulates

Releases

Osmoreceptorsin hypothalamus

Negativefeedbackinhibits

Posterior pituitary

ADH

Inhibits

Stimulates

Baroreceptorsin atrium andlarge vessels

Stimulates Plasma volumeBP (10–15%)

Antidiuretichormone (ADH)

Targets

Effects

Results in

Collecting ductsof kidneys

OsmolalityPlasma volume

Water reabsorption

Scant urine


Disorders of Water Balance: Dehydration

•Negative fluid balance

• ECF water loss due to: hemorrhage, severe burns, prolonged vomiting or diarrhea, profuse sweating, water deprivation, diuretic abuse

• Signs and symptoms: thirst, dry flushed skin, oliguria (less than 400ml output of urine)

•May lead to weight loss, fever, mental confusion, hypovolemic shock, and loss of electrolytes

Copyright © 2010 Pearson Education, Inc. Figure 26.7a

1 2 3 Excessiveloss of H2Ofrom ECF

ECF osmoticpressure rises

Cells loseH2O to ECFby osmosis;cells shrink

(a) Mechanism of dehydration


Disorders of Water Balance: Hypotonic Hydration

•Cellular overhydration, or water intoxication

•Occurs with renal insufficiency or rapid excess water ingestion

•ECF is diluted hyponatremia net osmosis into tissue cells swelling of cells severe metabolic disturbances (nausea, vomiting, muscular cramping, cerebral edema) possible death

Copyright © 2010 Pearson Education, Inc. Figure 26.7b

3 H2O moves into cells by osmosis; cells swell

2 ECF osmoticpressure falls

1 ExcessiveH2O entersthe ECF

(b) Mechanism of hypotonic hydration


Disorders of Water Balance: Edema

•Atypical accumulation of IF fluid tissue swelling

•Due to anything that increases flow of fluid out of the blood or hinders its return

• Blood pressure

• Capillary permeability (usually due to inflammatory chemicals)

• Incompetent venous valves, localized blood vessel blockage

• Congestive heart failure, hypertension, blood volume


Edema

•Hindered fluid return occurs with an imbalance in colloid osmotic (oncotic) pressures, e.g., hypoproteinemia ( plasma proteins)

• Fluids fail to return at the venous ends of capillary beds

•Results from protein malnutrition, liver disease, or glomerulonephritis, PPIs/acid blockers


Edema

•Blocked (or surgically removed) lymph vessels

•Cause leaked proteins to accumulate in IF

• Colloid osmotic (oncotic) pressure of IF draws fluid from the blood

•Results in low blood pressure and severely impaired circulation


Electrolyte Balance


Electrolyte Balance

•Generally refers to salt balance

• Important in controlling fluid movement and provide minerals essential for excitability, secretory activity, and membrane permeability

•Most important: Na

•In ECF, main cation that contributes to osmotic pressure

•REMEMBER: WATER FOLLOWS SALT

• Kidneys regulate balance of Na, K


Regulation of Sodium Balance: Aldosterone

•Na balance is key in blood pressure/volume

•Na+ reabsorption

• 65% is reabsorbed in the proximal tubules

• 25% is reclaimed in the loops of Henle

• Aldosterone active reabsorption of remaining Na+ in DCT and collecting duct

•Water follows Na+

• Through aquaporins if ADH is present

•Or from ICF



•Renin-angiotensin mechanism is the main trigger for aldosterone release

•Granular cells of JGA secrete renin in response to

•Sympathetic nervous system stimulation

• Filtrate osmolality

• Stretch (due to blood pressure)



•Renin catalyzes the production of angiotensin II, which prompts aldosterone release from the adrenal cortex

•Aldosterone release is also triggered by elevated K+ levels in the ECF

•Aldosterone brings about its effects slowly (hours to days)


K+ (or Na+) concentrationin blood plasma*

Stimulates

Releases

Targets

Renin-angiotensinmechanism

Negativefeedbackinhibits

Adrenal cortex

Kidney tubules

Aldosterone

Effects

Restores

Homeostatic plasmalevels of Na+ and K+

Na+ reabsorption K+ secretion


Regulation of Sodium Balance: ANP

•Released by atrial cells in response to stretch ( blood pressure)

•Effects

•Decreases blood pressure and blood volume:

• ADH, renin and aldosterone production

• Excretion of Na+ and water

• Promotes vasodilation directly and also by decreasing production of angiotensin II


Stretch of atriaof heart due to BP

Atrial natriuretic peptide (ANP)

Adrenal cortexHypothalamusand posterior

pituitary


JG apparatusof the kidney

ADH release Aldosterone release

Na+ and H2O reabsorption

Blood volume

Vasodilation

Renin release*

Blood pressure

Releases

Negativefeedback

Targets

Effects

Effects

Inhibits

Effects

Inhibits

Results in

Results in

Angiotensin II


Influence of Other Hormones

•Estrogens: NaCl reabsorption (like aldosterone)

• H2O retention during menstrual cycles and pregnancy

•Progesterone: Na+ reabsorption (blocks aldosterone)

• Promotes Na+ and H2O loss

•Glucocorticoids: Na+ reabsorption and promote edema


Stretch in afferentarterioles

Angiotensinogen(from liver)

Na+ (and H2O) reabsorption

Granular cells of kidneys

Renin

Posterior pituitary

Systemic arterioles

Angiotensin I

Angiotensin II

Systemic arterioles

Vasoconstriction Aldosterone

Blood volume

Blood pressure

Distal kidney tubules

Adrenal cortex

Vasoconstriction

Peripheral resistance

(+)

(+)

(+)

(+)

Peripheral resistance

H2O reabsorption

Inhibits baroreceptorsin blood vessels

Sympatheticnervous system

ADH (antidiuretichormone)


Filtrate NaCl concentration inascending limb of loop of Henle

Causes

Causes

Causes

Causes

Results in

Secretes

Results in

Targets

Results in

Releases

Release

Catalyzes conversion

Converting enzyme (in lungs)

(+)

(+)(+)

(+)

(+)

(+)

(+) stimulates

Renin-angiotensin system

Neural regulation (sympatheticnervous system effects)

ADH release and effects

Systemicblood pressure/volume


Potassium Balance

•Chief intracellular cation

•Required for normal neuromuscular functioning and metabolic activities

•The heart is very sensitive to K balance


Regulation of Potassium Balance

•Importance of potassium:

• Affects RMP in neurons and muscle cells (especially cardiac muscle)

• ECF [K+] RMP depolarization reduced excitability

• ECF [K+] hyperpolarization and nonresponsiveness



•H+ shift in and out of cells

• Leads to corresponding shifts in K+ in the opposite direction to maintain cation balance

• Interferes with activity of excitable cells

• ECF K levels rise with acidosis as K leaves and H+ enters the cell

• ECF K levels fall with alkalosis as K enters the cell and H+ leaves the cell



•Influence of aldosterone

• Stimulates K+ secretion (and Na+ reabsorption) by principal cells

• Increased K+ in the adrenal cortex causes

•Release of aldosterone

•Potassium secretion


Regulation of Calcium

•Ca2+ in ECF is important for

•Neuromuscular excitability

• Blood clotting

•Cell membrane permeability

• Secretory activities


Regulation of Calcium

•Hypocalcemia excitability and muscle tetany

•Hypercalcemia Inhibits neurons and muscle cells, may cause heart arrhythmias

•Calcium balance is controlled by parathyroid hormone (PTH) and calcitonin


Influence of PTH

•Bones are the largest reservoir for Ca2+ and phosphates

•PTH promotes increase in calcium levels by targeting bones, kidneys, and small intestine (indirectly through vitamin D)

•Calcium reabsorption and phosphate excretion go hand in hand


Intestine

Kidney

Bloodstream

Hypocalcemia (low blood Ca2+) stimulatesparathyroid glands to release PTH.

Rising Ca2+ inblood inhibitsPTH release.

1 PTH activatesosteoclasts: Ca2+

and PO43S released

into blood.

2 PTH increasesCa2+ reabsorptionin kidneytubules.

3 PTH promoteskidney’s activation of vitamin D,which increases Ca2+ absorptionfrom food.

Bone

Ca2+ ions

PTH Molecules


Influence of PTH

•Normally 75% of filtered phosphates are actively reabsorbed in the PCT (follows Na)

•PTH inhibits this by decreasing the Tm


Regulation of Anions

•Cl– is the major anion in the ECF

•Helps maintain the osmotic pressure of the blood

• 99% of Cl– is reabsorbed under normal pH conditions

•When acidosis occurs, fewer chloride ions are reabsorbed (more HCO3- reabsorbed to restore blood pH)

•Other anions have transport maximums and excesses are excreted in urine


Acid-Base Balance

•pH affects all functional proteins and biochemical reactions

•Normal pH of body fluids

• Arterial blood: pH 7.4

• Venous blood and IF fluid: pH 7.35

• ICF: pH 7.0

•Alkalosis or alkalemia: arterial blood pH >7.45

•Acidosis or acidemia: arterial pH < 7.35


Acid-Base Balance

•Most H+ is produced by metabolism

• Phosphoric acid from breakdown of phosphorus-containing proteins in ECF

• Lactic acid from anaerobic respiration of glucose

• Fatty acids and ketone bodies from fat metabolism

•H+ liberated when CO2 is converted to HCO3–

in blood


Chemical Buffer Systems

• Chemical buffer: system of one or more compounds that act to resist pH changes when strong acid or base is added

1. Bicarbonate buffer system

2. Phosphate buffer system

3. Protein buffer system


Bicarbonate Buffer System

•Mixture of H2CO3 (weak acid) and salts of HCO3

– (e.g., NaHCO3, a weak base)

•Buffers ICF and ECF

•The only important ECF buffer


Physiological Buffer Systems

•Respiratory and renal systems

• Act more slowly than chemical buffer systems

•Have more capacity than chemical buffer systems


Respiratory Regulation of H+

•Respiratory system eliminates CO2

•A reversible equilibrium exists in the blood:

•CO2 + H2O H2CO3 H+ + HCO3–

•During CO2 unloading the reaction shifts to the left (and H+ is incorporated into H2O)

•During CO2 loading the reaction shifts to the right (and H+ is buffered by proteins)



•Hypercapnia (increased H+) activates medullary chemoreceptors

•Rising plasma H+ activates peripheral chemoreceptors

•More CO2 is removed from the blood

•H+ concentration is reduced



•Alkalosis depresses the respiratory center

•Respiratory rate and depth decrease

•H+ concentration increases

•Respiratory system impairment causes acid-base imbalances

•Hypoventilation respiratory acidosis

•Hyperventilation respiratory alkalosis


Acid-Base Balance

•Chemical buffers cannot eliminate excess acids or bases from the body

• Lungs eliminate volatile carbonic acid by eliminating CO2

• Kidneys eliminate other fixed metabolic acids (phosphoric, uric, and lactic acids and ketones) and prevent metabolic acidosis


Renal Mechanisms of Acid-Base Balance

•Most important renal mechanisms

•Conserving (reabsorbing) or generating new HCO3

–

• Excreting HCO3–

•Generating or reabsorbing one HCO3– is the

same as losing one H+

•Excreting one HCO3– is the same as gaining

one H+


Renal Mechanisms of Acid-Base Balance

•Renal regulation of acid-base balance depends on secretion of H+

•H+ secretion occurs in the PCT and in collecting duct type A intercalated cells:

• The H+ comes from H2CO3 produced in reactions catalyzed by carbonic anhydrase inside the cells

• See Steps 1 and 2 of the following figure


1 CO2 combines with water within the tubule cell, forming H2CO3.

2 H2CO3 is quickly split, forming H+ and bicarbonate ion (HCO3

–).

3a H+ is secreted into the filtrate.

3b For each H+ secreted, a HCO3– enters the

peritubular capillary blood either via symport with Na+ or via antiport with CI–.

4 Secreted H+ combines with HCO3– in the

filtrate, forming carbonic acid (H2CO3). HCO3–

disappears from the filtrate at the same rate that HCO3

– (formed within the tubule cell) enters the peritubular capillary blood.

5 The H2CO3

formed in the filtrate dissociates to release CO2

and H2O.

6 CO2 diffuses into the tubule cell, where it triggers further H+

secretion.

* CA

CO2CO2

+H2O

2K+2K+

*

Na+ Na+

3Na+3Na+

Tight junction

H2CO3H2CO3

PCT cell

NucleusFiltrate intubule lumen

Cl–Cl–HCO3– + Na+

HCO3–

H2O CO2

H+ H+ HCO3–

HCO3–

HCO3–

ATPase

ATPase

Peri-tubular

capillary

1

24

5

6

3a 3b

Primary active transport

Simple diffusion

Secondary active transport

Carbonic anhydrase

Transport protein


Activetransport

Passivetransport

Peri-tubular

capillary

2

4

4

3

31

1 2 43

Filtratein tubulelumen

Transcellular

Paracellular

Paracellular

Tight junction Lateral intercellular space

Capillaryendothelialcell

Luminalmembrane

Solutes

H2O

Tubule cell Interstitialfluid

Transcellular

Basolateralmembranes

1 Transport across the luminal membrane.2 Diffusion through the cytosol.

4 Movement through the interstitial fluid and into the capillary.

3 Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces.)

Movement via thetranscellular route involves:

The paracellular routeinvolves:

• Movement through leaky tight junctions, particularly in the PCT.


Nucleus

PCT tubule cells

Filtrate intubule lumen

Peri-tubularcapillary

NH4+

out in urine

2NH4+

Na+

Na+ Na+ Na+ Na+

3Na+3Na+

Glutamine GlutamineGlutamine

Tight junction

Deamination,oxidation, and acidification(+H+)

2K+2K+

NH4+ HCO3

–2HCO3– HCO3

–

(new)

ATPase

1 PCT cells metabolize glutamine to NH4

+ and HCO3–.

2a This weak acid NH4+ (ammonium) is

secreted into the filtrate, taking the place of H+ on a Na+- H+ antiport carrier.

2b For each NH4+ secreted, a

bicarbonate ion (HCO3–) enters the

peritubular capillary blood via a symport carrier.3 The NH4

+ is excreted in the urine.

Primary active transport

Simple diffusion

Secondary active transport

Transportprotein

1

2a 2b

3


Abnormalities of Acid-Base Balance

•Respiratory acidosis and alkalosis

•Metabolic acidosis and alkalosis


Respiratory Acidosis and Alkalosis

•The most important indicator of adequacy of respiratory function is PCO2

level (normally 35–45

mm Hg)

• PCO2 above 45 mm Hg respiratory acidosis

•Most common cause of acid-base imbalances

•Due to decrease in ventilation or gas exchange

•Characterized by falling blood pH and rising PCO2


Respiratory Acidosis and Alkalosis

•PCO2 below 35 mm Hg respiratory alkalosis

• A common result of hyperventilation due to stress or pain


Metabolic Acidosis and Alkalosis

•Any pH imbalance not caused by abnormal blood CO2 levels

•Indicated by abnormal HCO3– levels



•Causes of metabolic acidosis

• Ingestion of too much alcohol ( acetic acid)

• Excessive loss of HCO3– (e.g., persistent

diarrhea)

• Accumulation of lactic acid, shock, ketosis in diabetic crisis, starvation, and kidney failure



•Metabolic alkalosis is much less common than metabolic acidosis

• Indicated by rising blood pH and HCO3–

•Caused by vomiting of the acid contents of the stomach or by intake of excess base (e.g., antacids)


Effects of Acidosis and Alkalosis

• Blood pH below 7 (acidosis) depression of CNS coma death

• Blood pH above 7.8 (alkalosis) excitation of nervous system muscle tetany, extreme nervousness, convulsions, respiratory arrest


Respiratory and Renal Compensations

•If acid-base imbalance is due to malfunction of a physiological buffer system, the other one compensates

•Respiratory system attempts to correct metabolic acid-base imbalances

• Kidneys attempt to correct respiratory acid-base imbalances


Respiratory Compensation

•In metabolic acidosis

•High H+ levels stimulate the respiratory centers

•Rate and depth of breathing are elevated

• Blood pH is below 7.35 and HCO3– level is low

• As CO2 is eliminated by the respiratory system, PCO2

falls below normal


Respiratory Compensation

•Respiratory compensation for metabolic alkalosis is revealed by:

• Slow, shallow breathing, allowing CO2 accumulation in the blood

•High pH (over 7.45) and elevated HCO3– levels


Renal Compensation

•Hypoventilation causes elevated PCO2

•(respiratory acidosis)

•Renal compensation is indicated by high HCO3

– levels

•Respiratory alkalosis exhibits low PCO2 and

high pH

•Renal compensation is indicated by decreasing HCO3

– levels


QUESTIONS TO TEST WHAT YOU NOW KNOW!!!


The two main fluid compartments within the body are _________ and _________.

A. plasma; interstitial fluid

B. adipose; skeletal muscle

C. intracellular fluid; extracellular fluid

D. blood; cytoplasm


The most abundant cation of the ECF is _______ and the most abundant anion in the ECF is _______.

A. K+; HPO42–

B. Mg2+; HCO3–

C. Ca2+; SO42–

D. Na+; Cl–


Which of the following accounts for the most water loss, second only to urine output?

A. Insensible perspiration

B. Sweating

C. Defecation

D. Tears


Which is the most potent stimulus for thirst?

A. Dry mouth

B. An increase in plasma osmolarity

C. An increase in blood volume

D. The sight of a cold drink


You were thirsty and drank a full glass of water only to have your thirst return an hour later. This is because:A. thirst is continuously communicated to the

brain.

B. the kidneys produced a large volume of urine.

C. distension of the stomach temporarily inhibits the thirst center.

D. the stomach absorbs water slowly.


When ADH levels are low, the kidneys produce _________ urine.

A. dilute

B. concentrated

C. a low volume of

D. isotonic


An overheated marathon runner accepts cups of plain water at each refreshment area. When the race ends, the runner is very disoriented and collapses. What is the best explanation for her condition?A. The runner overexerted herself.

B. The runner needs more water because she is dehydrated.

C. The runner is suffering from hypotonic hydration and her cell fluids are overdiluted.

D. The runner’s ICF is hypotonic to her ECF.


What might be a probable explanation for an intense craving for heavily salted food?A. Diabetes mellitus, which causes excessive

urine output

B. Addison’s disease, in which insufficient aldosterone is available to reabsorb NaCl from the filtrate

C. Diabetes insipidus, which is manifested by hyposecretion of ADH

D. Hypersecretion of aldosterone


Which of the following statements best summarizes the relationship between the sodium content of fluids and water movement?

A. Water follows salt.

B. Salt follows water.

C. Water equals salt.

D. Water solubilizes salt.


Which two hormones are essential for reabsorption of water at the collecting duct?

A. Renin and aldosterone

B. ADH and aquaporin

C. Aldosterone and ADH

D. ADH and renin


Blood sodium levels are indirectly assessed by __________.

A. sodium chemoreceptors

B. chloride chemoreceptors

C. baroreceptors

D. PH receptors


The _______ contains the largest percentage of water in the body.

A. extracellular fluid

B. intracellular fluid

C. blood plasma

D. lymph


You would expect blood levels of ANP to increase when __________.

A. blood pressure is increased

B. blood Na+ is elevated

C. the walls of the atria are stretched

D. all of the above occur


A patient suffering from hyperthyroidism may experience heart malfunction. Consequently, this patient must also tightly regulate his potassium intake. Which of the following is the best explanation for why he must carefully watch dietary potassium?A. Even slight changes in K+ are not detectable by the

heart.

B. Both hyper- and hypokalemia can disrupt electrical conduction in the heart.

C. The kidney is unable to excrete K+ in someone with hyperthyroidism.

D. Dietary intake of K+ causes hyperthyroidism.


PTH affects calcium blood levels via which of the following mechanisms?

A. PTH stimulates osteoclasts to resorb bone.

B. PTH stimulates increased Ca2+ absorption in the intestine.

C. PTH stimulates increased Ca2+ reabsorption by renal tubules.

D. All of the above are ways PTH affects calcium blood levels.


Which of the following is the initial H+ regulatory mechanism in the body?

A. Renal excretion

B. Chemical buffers

C. Brain stem respiratory centers

D. Lactic acid production


If the blood pH lowers, what change would you expect from the respiratory system?

A. The respiration rate would increase.

B. The respiration rate would decrease.

C. The respiration rate would remain unchanged.

D. The respiration rate would be erratic.

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