Water, Electrolytes, And Acid-Base Balance

8/14/2019 Water, Electrolytes, And Acid-Base Balance

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Water, Electrolytes, andAcid-Base Balance


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Body Fluids

Intracellular

All fluids inside cells of body

About 40% of total body weight

Extracellular

All fluids outside cells

About 20% of total body weight

Subcompartments

Interstitial fluid and plasma; lymph, CSF, synovial

fluid


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Water Content Regulation

Content regulated sototal volume of water in

body remains constant

Kidneys primary

regulator of waterexcretion

Regulation processes Osmosis

Osmolality

Baroreceptors

Learned behavior

Sources of water Ingestion

Cellular metabolism

Routes of water loss

Urine

Evaporation

Perspiration Respiratory passages

Feces


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Extracellular Fluid Osmolality

Osmolality

Adding or removing

water from a solutionchanges this

Increased osmolality

Triggers thirst andADH secretion

Decreased osmolality

Inhibits thirst and

ADH secretion


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Hormonal Regulation of

Blood Osmolality


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Regulation of ECF Volume

Mechanisms

Neural

Renin-angiotensin-aldosterone

Atrial natriuretic

hormone (ANH)

Antidiuretic hormone(ADH)

Increased ECF results in Decreased aldosterone secretion

Increased ANH secretion

Decreased ADH secretion

Decreased sympathetic stimulation

Decreased ECF results in Increased aldosterone secretion

Decreased ANH secretion

Increased ADH secretion Increased sympathetic stimulation


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Blood Volume


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Blood Volume


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Regulation of ECF Volume


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Regulation of ICF and ECF


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Regulation of Electrolytes in ECF

Electrolytes

Molecules or ions with

an electrical charge

Water ingestion adds

electrolytes to body

Kidneys, liver, skin,

lungs remove from

body

Concentration changes

only when growing,

gaining or losing

weight

Na+

Ions Dominant ECF cations Responsible for 90-95% of

osmotic pressure

Regulation of Na+ ions Kidneys major route of

excretion

Small quantities lost insweat

Terms Hypernatremia

Hyponatremia


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Mechanisms Regulating Blood Sodium


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Mechanisms Regulating Blood Sodium


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Abnormal Plasma Levels of

Sodium Ions


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Regulation of Chloride,

Potassium, Magnesium Ions

Chloride ions Predominant anions in

ECF

Magnesium ions Capacity of kidney to

reabsorb is limited

Excess lost in urine

Decreased extracellular

magnesium results ingreater degree ofreabsorption

Potassium ions

Maintained in narrow

range

Affect resting membrane

potentials

Aldosterone increases

amount secreted

Terms

Hyperkalemia

Hypokalemia


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Potassium Ion Regulation in ECF


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Abnormal Concentration of Potassium

Ions


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Abnormal Plasma Levels of

Magnesium Ions


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Regulation of Blood Magnesium


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Regulation of Calcium Ions

Regulated withinnarrow range Elevated extracellular

levels prevent

membranedepolarization

Decreased levels leadto spontaneous action

potential generation

Terms Hypocalcemia

Hypercalcemia

PTH increases Ca2+ extracellular levels and

decreases extracellular

phosphate levels

Vitamin D stimulatesCa2+ uptake in intestines

Calcitonin decreases

extracellular Ca2+ levels


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Regulation of Calcium Ions


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Regulation of Phosphate Ions

Under normal conditions, reabsorption of phosphate occurs

at maximum rate in the nephron An increase in plasma phosphate increases amount of

phosphate in nephron beyond that which can be reabsorbed;

excess is lost in urine


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Regulation of Blood Phosphate

A id d B


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Acids and Bases

and Buffers

Acids

Release H+ into

solution Bases

Remove H+ from

solution

Acids and bases Grouped as strong or

weak

Buffers: Resist changes inpH When H+ added, buffer

removes When H+ removed, buffer

replaces

Types of buffer systems

Carbonic acid/bicarbonate Protein

Phosphate


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Regulation of Acid-Base Balance


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Buffer Systems

R i t R l ti f


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Respiratory Regulation of

Acid-Base Balance

Respiratory regulation of pH is achieved

through carbonic acid/bicarbonate buffer

system

As carbon dioxide levels increase, pH decreases

As carbon dioxide levels decrease, pH increases

Carbon dioxide levels and pH affect respiratory

centers

Hypoventilation increases blood carbon dioxide levels

Hyperventilation decreases blood carbon dioxide levels

R i t R l ti f


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Respiratory Regulation of

Acid-Base Balance

R l R l ti f A id B


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Renal Regulation of Acid-Base

Balance

Secretion of H+ into filtrate and reabsorption of

HCO3

- into ECF cause extracellular pH to

increase HCO

3

- in filtrate reabsorbed

Rate of H+ secretion increases as body fluid pH

decreases or as aldosterone levels increase Secretion of H+ inhibited when urine pH falls

below 4.5

Kid R l ti f


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Kidney Regulation of

Acid-Base Balance


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Hydrogen Ion Buffering


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Acidosis and Alkalosis

Acidosis: pH body fluids below 7.35Respiratory: Caused by inadequate ventilation

Metabolic: Results from all conditions other

than respiratory that decrease pH Alkalosis: pH body fluids above 7.45

Respiratory: Caused by hyperventilation

Metabolic: Results from all conditions otherthan respiratory that increase pH

Compensatory mechanisms


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Acidosis and Alkalosis

Water, Electrolytes, And Acid-Base Balance

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