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98 Cards in this Set
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Balance
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a state of equilibrium
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Levels of water & electrolytes in the body remain
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relatively stable at all times
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Water balance & electrolyte balance are interdependent because
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electrolytes are dissolved in the water of body fluids
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Anything that alters the concentrations of electrolytes will alter
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concentration of the water by adding solutes to it or by removing solutes from it.
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Body fluids occur
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in compartments of different volumes that contain fluids of varying compositions
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The movement of water & electrolytes between compartments is regulated
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to stabilize their distribution & the composition of body fluids
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The body of an average adult female is about ___ % water by weight, & that of an average male is about ____% water
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52, 63
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The differences of water content between the sexes are due to
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the fact that females generally have more adipose tissue, which has little water
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The two major fluid compartments of the body are
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intracellular & extracellular
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The intracellular compartment includes
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all the water & electrolytes that cell membranes enclose
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Intracellular fluid
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represents about 63% by volume of total body water
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The extracellular fluid compartment includes
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all the fluid outside the cells
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Transcellular fluid
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is cerebrospinal fluid, aqueous & vitreous humors of the eyes, synovial fluids, serous fluids, & secretions of exocrine glands
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The fluids of the extracellular compartment constitute about
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37% by volume of the total body water.
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Extracellular fluids have high concentrations of
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sodium, chloride, calcium & bicarbonate ions
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Extracellular fluids have low concentrations of
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potassium, magnesium, phosphate, & sulfate ions
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The blood plasma fraction of extracellular fluid
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contains considerably more protein than interstitial fluid or lymph
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Intracellular fluid has high concentrations of
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potassium, phosphate, & magnesium ions
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Intracellular fluid has lesser concentrations of
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sodium, chloride, & bicarbonate ions
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Intracellular fluid has a higher concentration of ______ than _______
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protein, plasma
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The two major factors that influence the movement of water & electrolytes from one fluid compartment to another are
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hydrostatic pressure & osmotic pressure
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Any net fluid movement between cells & interstitial fluid is most likely due to changes in
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osmotic pressure, because hydrostatic pressure within the cells & surrounding interstitial fluid is ordinarily equal & remains stable
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Osmotic pressure is due to
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impermeant solutes on one side of a cell membrane
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A decrease in extracellular sodium ion concentration causes a net movement of water from the
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extracellular compartment into the intracellular compartment by osmosis
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An increase in extracellular sodium ion concentration causes cells to
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shrink as they lose water
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Water balance exists when
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water intake equals water output
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Maintenance of the internal environment depends on
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thirst centers in the brain & the kidneys’ ability to vary water output
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Most water is obtained
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through beverages, Water is also obtained through food & metabolic reactions
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Water of metabolism
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is water generated in chemical reactions in the body
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The primary regulator of water intake is
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thirst
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The feeling of thirst derives from
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the osmotic pressure of extracellular fluids & a thirst center
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The thirst center is located in the
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hypothalamus
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Osmoreceptors detect
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osmotic pressure changes in extracellular fluids
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The thirst mechanism is usually triggered
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when the total body water decreases by as little as 1%
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The thirst mechanism is inhibited by
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the act of drinking water & the resulting distension of the stomach.
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Water leaves the body through
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urine, feces, sweat, & breathing
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Most water is lost through
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urine
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The primary means of regulating water output is
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control of urine production
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The distal convoluted tubules & collecting ducts
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regulate the volume of water excreted in the urine
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When ADH is present
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the linings of the renal tubules become more permeable to water
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Osmoreceptors in the hypothalamus are stimulated by
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the increased osmotic pressure of blood
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When osmotic pressure of body fluids increases
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the hypothalamus signals the posterior pituitary to release ADH
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ADH causes
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distal convoluted tubules & collecting ducts to become more permeable to water
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If a person drinks too much water
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ADH release is inhibited so the distal convoluted tubules & collecting ducts become more impermeable to water & urine output increases.
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The electrolytes
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provide cellular function by releasing sodium, potassium, calcium, magnesium, chloride, sulfate, phosphate, bicarbonate, & hydrogen ions
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Electrolytes are primarily obtained by
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food but they may also be obtained by fluids & metabolic reactions
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A person normally obtains sufficient electrolytes by
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responding to hunger & thirst
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A severe electrolyte deficiency may cause
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a salt craving
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The body loses electrolytes through
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sweat, feces, & urine
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The greatest electrolyte output occurs
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as a result of kidney function & urine production
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Most important electrolytes
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concentrations of sodium, potassium, & calcium are particularly important
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Potassium ions
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maintain the resting potential of nerve & cardiac muscle cells
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Sodium ions concentrations are primarily regulated by
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the hormone aldosterone & the kidneys
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Besides sodium, aldosterone also regulates
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potassium ions
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A rising potassium level triggers
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aldosterone secretion
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Parathyroid hormone regulates
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calcium concentrations by increasing the activity of osteoclasts when calcium levels are too low
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Negatively charged ions are controlled by
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the regulatory mechanisms that control positively charged ions.
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Acids
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electrolytes that release hydrogen ions in water
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Bases
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substances that combine with hydrogen ions
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Regulation of hydrogen ion concentration is very important because
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slight changes in hydrogen ion concentration can alter the rate of enzyme controlled metabolic reactions, shift the distribution of other ions, or modify hormone actions.
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The major metabolic sources of hydrogen ions are
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aerobic respiration of glucose, anaerobic respiration of glucose, incomplete oxidation of fatty acids, oxidation of amino acids containing sulfur, & breakdown of phosphoproteins & nucleic acids
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The acids resulting from metabolism
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vary in strength
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Strong acids
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ionize more completely
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Weak acids
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ionize less completely
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An example of a strong acid is
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hydrochloric acid
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An example of a weak acid is
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carbonic acid
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Strong bases dissociate to
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release more hydroxyl ions or its equivalent than do weak bases
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An example of a strong base is
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sodium hydroxide.
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The maintenance of acid base balance
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usually entails elimination of acid
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Acids are eliminated by
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the following three ways: acid
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base buffer systems, respiratory excretion of carbon dioxide, & renal excretion of hydrogen ions
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Acid base buffer systems are
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in all body fluids & are based on chemicals that combine with excess acids or bases
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Buffers are
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substances that stabilize the pH of a solution, despite the addition of an acid of a base
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Chemical components of a buffer system can
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combine with strong acids to convert them to weak bases.
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The three most important buffer systems in the body are
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bicarbonate buffer system, phosphate buffer system, & protein buffer system
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The bicarbonate buffer system
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is present in both intracellular & extracellular fluids
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Bicarbonate buffer system
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the bicarbonate ion is the weak base & carbonic acid is the weak acid
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In the presence of excess hydrogen ions, bicarbonate ions
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combine with hydrogen ions to form carbonic acid
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If conditions are basic, carbonic acid
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dissociates to release a bicarbonate ion & hydrogen ion
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The phosphate buffer system is in
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both intracellular & extracellular fluids
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In the phosphate buffer system, monohydrogen phosphate is
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the weak base
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In the phosphate buffer system
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dihydrogen phosphate is the weak acid
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In the presence of excess hydrogen ions, monohydrogen phosphate
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combines with hydrogen ions to form dihydrogen phosphate
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The protein acid base buffer system consists of
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plasma proteins
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If the hydrogen ion concentration drops
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a carboxyl group of an amino acid can become ionized releasing a hydrogen ion
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In the presence of excess hydrogen ions
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the COO
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portions of the protein molecules can accept hydrogen ions
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In the presence of excess hydroxyl ions
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the NH3+ groups within proteins give up hydrogen ions & become NH2 groups again
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Hemoglobin
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is an important protein that buffers hydrogen ions.
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The respiratory center helps
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regulate hydrogen ion concentrations is body fluids by controlling
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If body cells increase their production of carbon dioxide
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carbonic acid production increases
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An increase of carbon dioxide & subsequently hydrogen ions in cerebrospinal fluid stimulates
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chemosensitive areas within the respiratory center
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When the respiratory center increases rate & depth of breathing, the lungs
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excrete more carbon dioxide
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Nephrons
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regulate hydrogen ion concentration by excreting hydrogen ions in the urine
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The tubular secretion of hydrogen ions is linked to
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tubular reabsorption of bicarbonate ions
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A diet high in proteins may trigger
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excess acid formation
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Phosphate ions
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buffer hydrogen ions in urine
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Ammonia produced by renal cells help
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transport hydrogen ions to the outside of the body
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The body’s first line of defense against shifts in pH are
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chemical buffer systems
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The secondary defenses against shifts in pH are
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physiological buffer systems such as respiratory & renal mechanisms
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