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Chapter 26: Fluid, Electrolyte, and Acid-base Balance

What is the body water content of infants?
73% or more so more than adults
Which holds more water; fat cells or muscle tissue?
More muscle mass more body water so lean or muscular individuals have more water.
What is the body water content of females?
About 50% water, lower than males (higher fat content, less skeletal muscle mass).
Water accounts for how much of the body weight?
About 45 - 75% of body weight
What is the ICF?
The intracellular fluid. Location of 2/3 of metabolic water (25L adult male)
What is ECF?
The fluid located outside the cell. Location of 1/3 of metabolic water (15L adult males).
How is ECF further divided into?
Blood plasma within blood vessels and the microscopic spaced between cells called interstitial fluid.
What is the universal solvent?
Water is the universal solvent because a variety of solutes can be dissolved.
What are solvents?
Polar charges that attract their opposite charges, H+2O- will attract Cl- and Na+, so it dissolves solutes (dissociate into Ions).
What are non-electrolytes?
Non-conducting particles (no charge) will be created when they are dissolved in water.
Glucose and some proteins mostly organic molecules.
What are electrolytes?
Charged particles (conduct a current) and proteins (Na+, K+, Cl-, Ca++, Mg++, HCO3-, HPO42-, SO42-)
Ions: (Salts; ionic compounds that result from neutralized reactions of an acid and a base, i.e. Na+Cl-), acids (water splits the hydrogen ion H(+) can combine with negatively charged elements to form acids) and bases (molecules that can split apart in water and release hydroxide ion, i.e.NaOH)
Why do electrolytes have a greater osmotic power than non-electrolytes?
The electrolyte molecule dissociates into at least 2 ions. NaCl -> Na+ and Cl-, MgCl2 -> Mg++ and 2Cl-
Why do electrolytes have a greater ability to cause fluid shifts?
Regardless of the solute particle (electrolyte), water moves according to osmolality (from areas of lesser gradient to areas of greater gradient).
What are the distinctive pattern of electrolytes in ECF?
Major Positive charge: Na+(sodium), Negative charge: Cl- (chloride) with an abundance of HCO3-(bicarbinate)(helps to maintain pH balance) with plasma carrying the proteins.
What are the distinctive pattern of electrolytes in ICF?
Positive charge: K+, Negative charge: HPO42- (hydrogen phosphate) with large amounts of soluble proteins (carry a surface charge) about 3x more than plasma (ECF).
What in extra- and intracellular fluids are nearly opposites?
Sodium and potassium concentrations.
Why are sodium and potassium nearly opposite in ECF and ICF?
Reflects the activity of cellular ATP- dependent sodium -potassium pumps which keeps the IC concentration of Na+ low and the K+ concentration high.
What are the main compartments of fluid movement?
body barriers (Lungs, GI tract, Kidneys) -> Blood plasma -> interstitial fluid -> intracellular fluid (there is no jumping from area to area, solutes must flow from one to the other)
How does the first exchange occur between the body barriers and the blood plasma?
Happens continuously with the gases, solutes and water which alter the plasma composition and volume.
How does the second exchange occur between the blood plasma and interstitial fluid?
Compensating continually with the blood plasma the exchange occurs at the capillary membranes by hydrostatic pressure of the blood.
What is hydrostatic pressure?
The force exerted by a fluid against the capillary wall (pushing force) into the interstitial space.
What is colloid osmotic pressure?
It reabsorbs the filtered fluid into the bloodstream by the plasma proteins (filtrates).
How will fluid flow in the capillaries?
Fluid will leave the capillary if hydrostatic > oncotic pressure
Fluid will enter the capillary if hydrostatic < oncotic pressure
How does the third exchange occur between the interstitial fluid and the intracellular fluid?
It occurs across plasma membranes and depends on the membranes' complex permeability properties.
What are the permeability properties of plasma membranes?
1. two way osmotic water flow is substantial 2. ions move selectively by active transport and by channels by size or charge 3. Movements of nutrients, respiratory gases and metabolic waste are unidirectional. 4. Water always follows solutes.
What are sources of water?
ingested foods, ingested fluids and metabolic water (water oxidation)
What are sources of water loss?
1. insensible loss: By the lungs (exhale), diffused through the skin (perspiration) 2. obvious sweat and feces 3. sensible loss: the rest (60%) through urine
A rise in plasma osmolality triggers?
Thirst - prompts us to drink, the release of antidiuretic hormone (ADH) in the pituitary - causes the kidneys to conserve water (nearly all the water is reabsorbed) and a small volume of concentrated urine is excreted.
What is the driving force for water intake?
Thirst in the hypothalamic thirst center.
What are the thirst mechanism?
Increased plasma osmolality or a substantial decrease in blood volume (pressure) with the result being a decrease plasma osmolality.
What are the inhibitory feedback signals of water intake?
Water moistens mouth, throat, stomach distends and intestines stretch.
Why is thirst quenched before water hits the bloodstream?
The premature quenching of thirst prevents us from drinking more than we need and over diluting our body fluids and allows time for the osmotic changes to come into play as regulatory factors.
What is obligatory water loss?
Skin, lungs, feces and urine. The loss in urine reflects that the kidneys must flush 600mmol per day of urine solutes out of the body in water = 500ml per day.
What are the principle abnormalities of water balance?
Dehydration, hypotonic hydration and edema
What is dehydration?
When water output exceeds intake = body is in negative fluid balance.
What are the signs and symptoms of dehydration?
Thirst, dry flushed skin, oliguria (decreased production of urine).
What is hypovolemic shock?
The inadequate blood volume to maintain normal circulation.
What are the mechanisms of dehydration?
Excessive loss of water from extracellular fluid => Extracellular fluid osmatic pressure to rises =>cells to loss water to ECF by osmosis,so cells shrink
What is hypotonic hydration?
Cellular overhydration, or water intoxication (a dramatically greater water intake)
What are the mechanisms of hypotonic hydration?
Excessive water to extracellular fluid => Extracellular fluid osmatic pressure to drop => Water moves into cell by osmosis, so cells swell.
What happens if the ECF is diluted?
Hyponatremia (low Na+ concentrations in the ECF).
What can hypotonic hydration lead to?
Cerebral Edema - tissue swelling of the brain
What is edema?
Atypical accumulation of fluid in the interstitial space - tissue swelling (not cell swelling).
What is the result of accelerated fluid loss from the blood?
The abnormally high capillary hydrostatic pressure intensifies filtration at the capillary beds. (results in impaired blood circulation)
What is the impaired blood circulation due too?
Usually an ongoing inflammatory response
What does electrolyte balance usually refer too?
Only salt balance.
What are salts important for?
Neuromuscular excitability, secretory activity, membrane permeability, controlling fluid movements.
How do salts (electrolytes) enter the body?
Obtained from foods and fluids usually in huge excess of the body's needs.
How are salts (electrolytes) loss from the body?
Through perspiration, feces and urine.
What do sodium salts (NaHCO3 & NaCl) account for in solutes of the ECF?
90 - 95% in the ECF of all solutes
What are some of Na+ roles?
Exerts significant (ECF) osmotic pressure, water volume control and water distribution.
What is the rule about salt?
Water follows salt
What is important about Na+ concentrations?
its ECF concentrations normally remain stable
Na+ renal transport is influenced by and helps regulate?
K+, Cl-, HCO3-, H+ in the ECF
How are Na+ levels regulated?
Through the link to blood pressure and blood volume. With nearly all Na+ being reabsorbed through feedback loops.
What does aldosterone do?
Promotes Na+ re absorption and water conservation
What is the trigger for aldosterone?
Renin -> Angiotensin II (vasocontrition) mechanism mediated by the JGA
What can also trigger the release of Aldosterone?
Elevated K+ levels in the ECF.
What are the principle effects of aldosterone?
Diminish urinary output and increase blood volume.
What is the influence of ANP (atrial natriuretic peptide)?
It reduces blood pressure and blood volume by inhibiting nearly all events that promote vasoconstriction and Na+ and water retention.
What is ANP and how is it released?
It is a hormone, and it is release by atria heart cells when they are stretched by high blood pressure or blood volume.
What are its effects on JGA?
Decreases Renin -> Angiotensin II which causes smooth muscle to relax (vasodialator), the result being a decrease in blood pressure
What are the effects of hypothalmus and pituitary?
Decreases ADH release which inhibits the kidneys so Na+ and water are reabsorbed with the result of a decrease in blood volume and blood pressure
What are the effects on the adrenal cortex?
Decreases the Aldosterone release which inhibits the kidneys so Na+ and water are reabsorbed with the result of a decrease in blood volume and blood pressure.
How does regulation of Na+ effect the female sex hormones?
Estrogens are chemically similar to aldosterone so they enhance NaCl reabsorption. (water weight gain). Progesterone decreases Na+ reabsorption so it is a diuretic (water loss). Glucocorticoids enhance reabsorption of Na+ (water gain)
How much of K+ is reabsorbed?
90% by the nephrons
What is the purpose in kidney (renal) regulation of K+?
To excrete K+ excess
What controls the regulation of Ca++?
The parathyroid hormone.
Where does PTH draw calcium from?
Targets Bones, Intestine, and Kidneys.
Where is Ca++ stored?
In the bone matrix.
How does calcitonin effect the calcium levels?
Is thought as a calcium lowering hormone.
What is Calcium ion Ca2+ in ECF important for?
Neuromuscular excitability, blood clotting, cell membrane permeability, secretory activities.
How are the phosphate ions regulated?
The phosphate ions (H2PO4-,HPO4- -, PO4- - -) are reabsorbed in the PCT by active transport.
What are anions?
The negatively charged electrolyte ions.
Why is Cl- regulated with Na+?
Their bond attraction so Cl- helps to maintain the osmotic pressure of the blood and when pH levels are normal nearly all the Cl- is reabsorbed.
What happens when the pH is low?
The Cl- is replaced by HCO3- to be reabsorbed to restore pH balance.
What does pH affect?
All functional proteins (enzymes, hemoglobin, cytochromes) because of their hydrogen bonds. Remember proteins have hydrogen in their base structures.
What is the normal pH of water?
What is normal blood pH range?
7.35 - 7.45
What are the extremes ranges of pH for life?
7.0 - 7.8
What is a H+ proton donor?
< 7, strong acids dissociate in water (free all their H+)
What is a H+ proton acceptor?
> 7, strong bases dissociate in water (tie up H+)
Where do most H+ originate?
Some foods and metabolism: Phosphorous-containing proteins (phosphoric acid), anaerobic respiration of glucose (lactic acid), fat metabolism (fatty acids and ketones)
What is the concentration of hydrogen ions regulated by?
Chemical buffer systems, brain stem respiratory centers, and renal mechanisms.
Acid + base ->? HCL + NaOH ->?
salt + water = NaCl + H2O
How are acids and bases balanced?
Through chemical buffers
What is a chemical buffer?
Resist pH changes when strong acid or base is added.
What is the chemical buffer systems?
bicarbonate (HCO3-), phosphate (PO4- -) and protein buffer system
What are the most plentiful and powerful buffers?
Intracellular proteins.
What are the most important renal mechanisms?
Conserving (reabsoring) or generating new HC03-, Excreting HC03-.
What is the respiratory regulation of acid?
It eliminates CO2 (an acid) from the blood through breathing.
What is the equation of respiratory regulation of breathing?
Co2 + H2O <=> H2CO3 <=> H+ & HCO3- OR carbonic anhydrase <=> carbonic acid <=> bicarbonate ion
What is hyperventilation?
It causes a net elimination of CO2 which eliminated H2CO3 (carbonic acid)
What are the ultimate acid-base regulatory organs?
The Kidneys for slow but surely balancing of acid-base levels.
The kidneys eliminate what acids?
The metabolism acids: lactic, uric, phosphoric and ketone bodies.
What are the important renal mechanisms?
1. reabsorbing or generating new HCO3- 2. excreting HCO3-
How do the kidneys reabsorb or excrete HCO3?
By secreting one H+ or retaining one H+