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98 Cards in this Set

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