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Chapter 26: Fluid, Electrolyte, and Acid- Base Balance
Terms in this set (77)
What are solutes?
-Substances dissolved in water
What are the two types of solutes?
What are nonelectrolyes?
Do not dissociate in water (glucose, lipids, creatinine, and urea)
What are electrolytes?
-Dissociate into ions in water; inorganic salts, all acids and bases, some proteins (ions conduct electrical current)
-Greater osmotic power than nonelectrolytes (greatest ability to cause fluid shifts)
What are the two types of fluids compartments in the body?
-Extracellular fluid (ECF)
-Intracellular fluid (ICF)
What electrolytes are in the extracellular fluid?
-Major cation: Na+
-Major anion: Cl-
What electrolytes are in the intracellular fluid?
-Low Na+ and Cl-
-Major cation: K+
-Major anion HPO42-
-More soluble proteins than in plasma
What regulates the continuous exchange and mixing of fluids?
How does fluid move between plasma and interstitial fluid capillary walls?
-Fluid leaks from arteriolar end of capillary, reabsorbed at venule end; lymphatics pick up remaining and return to blood
How does fluid move between interstitial fluid and intracellular fluid across cell membrane?
-Two-way osmotic flow of water
-Ions move selectively; nutrients, wastes, gases unidirectional
What occurs when there is a rise in the osmolarity?
What occurs when there is a decrease in the osmolarity?
How does water get into the body?
How does water leave the body?
-Insensible water loss (lost through skin and lungs)
What governs the regulation of thirst?
-Hypothalamic thirst center
How is the hypothalamic thirst center activated?
-↑ Plasma osmolality of 1 - 2%
-Decreased blood volume or pressure
-Angiotensin II or baroreceptor input
What is the mechanism that is the driving force for water intake?
What inhibits the thirst center?
What are the inhibitory feedback signals?
-Relief of dry mouth
-Activation of stomach and intestinal stretch receptors
What occurs if there is an decrease in ADH?
-Dilute urine and ↓ volume of body fluids
What occurs if there is a increase in ADH?
-Concentrated urine; reabsorption of water → ↑ volume of body fluids
What regulates ADH?
-Hypothalamic osmoreceptors sense ECF solute concentration
What are other factors that trigger the release of ADH?
-↓ BP → ↑ ADH release due to blood vessel baroreceptors and renin-angiotensin-aldosterone mechanism
-Factors lowering blood volume: intense sweating, vomiting, or diarrhea; severe blood loss; traumatic burns; and prolonged fever
What is dehydration?
-Negative fluid balance
How is dehydration caused?
-ECF water loss due to: hemorrhage, severe burns, prolonged vomiting or diarrhea, profuse sweating, water deprivation, diuretic abuse, endocrine disturbances
What are some symptoms of dehydration?
-"cottony" oral mucosa, thirst, dry flushed skin, oliguria
-May lead to weight loss, fever, mental confusion, hypovolemic shock, and loss of electrolytes
What is hypotonic hydration?
-Cellular overhydration, or water intoxication
How is hypotonic hydration caused?
-Occurs with renal insufficiency or rapid excess water ingestion
What happens during hypotonic hydration?
-ECF osmolality ↓ → hyponatremia → net osmosis into tissue cells → swelling of cells → severe metabolic disturbances (nausea, vomiting, muscular cramping, cerebral edema) → possible death
How is hypotonic hydration treated?
What are types of electrolytes?
What are the functions of salts in the body?
-Control fluid movements
-Provide minerals for excitability, secretory activity, membrane permeability
How does salt enter the body?
How does salt leave the body?
What is Na+- water linked to?
-Blood pressure and blood volume control mechanisms
What does sodium move back a forth from?
-Extracellular fluid and body secretions
What is coupled with the renal acid-base control mechanisms?
-Sodium ion transport
What is the importance of potassium?
-Affects resting membrane potential (RMP) in neurons and muscle cells (especially cardiac muscle)
-↑ ECF [K+] → ↓RMP → depolarization → reduced excitability
-↓ ECF [K+] → hyperpolarization and nonresponsiveness
What is hyperkalemia?
-Too much K+
What is hypokalemia?
-Too little K+
What is the function of K+?
-H+ shifts in and out of cells in opposite direction of K+ to maintain cation balance
-ECF K+ levels rise with acidosis
-ECF K+ levels fall with alkalosis (Interferes with activity of excitable cells)
What occurs when K+ is low?
-Kidneys have a low retention rate
-Principal cells reduce secretion and excretion of K+; type A intercalated cells reabsorb some K+ left in filtrate
How does aldosterone influence K+?
-Stimulates K+ secretions by principle cell
-Adrenal cortical cells directly sensitive to K+ content of ECF (Release of aldosterone causes K+ secretions)
Where is 99% of the calcium in the body?
What are the functions of calcium?
-Cell membrane permeability
-Neuromuscular excitability - most important
What is hypercalcemia?
-↑ excitability and muscle tetany
What is hypocalcemia?
-Inhibits neurons and muscle cells, may cause heart arrhythmias
How is calcium regulated?
-Controlled by parathyroid hormone (PTH) from parathyroid gland
-Rarely deviates from normal limits
What is the acid-base balance system?
-pH affects all functional proteins and biochemical reactions, so closely regulated
What are the normal pH levels of the body fluids?
-Arterial blood: pH 7.4
-Venous blood and IF fluid: pH 7.35
-ICF: pH 7.0
-Alkalosis or alkalemia: arterial pH >7.45
-Acidosis or acidemia: arterial pH <7.35
How is H+ produced?
-Phosphorus-containing protein breakdown releases -phosphoric acid into ECF
-Lactic acid from anaerobic respiration of glucose
-Fatty acids and ketone bodies from fat metabolism
-H+ liberated when CO2 converted to HCO3- in blood
How is the concentration of hydrogen ions regulated?
-Chemical buffer systems to resist pH changes when a strong acid or base is added: rapid; first line of defense
What are the buffer systems if the pH rises?
1). Bicarbonate buffer system
2). Phosphate buffer system
3). Protein buffer system
What are renal mechanisms?
-Most potent, but require hours to days to effect pH changes
What is the bicarbonate buffer system?
-Mixture of H2CO3 (weak acid) and salts of HCO3- (e.g., NaHCO3, a weak base)
What is the function of the bicarbonate buffer system?
-Buffers ICF and ECF (only important ECF buffer)
What does the bicarbonate buffer system do when there is a strong acid added?
-HCO3- ties up H+ and forms H2CO3 (HCl + NaHCO3 → H2CO3 + NaCl)
-pH decreases only slightly, unless all available HCO3- (alkaline reserve) used up
-HCO3- concentration closely regulated by kidneys
What does the bicarbonate buffer system do where there is a strong base added?
-It causes H2CO3 to dissociate and donate H+
-H+ ties up the base (e.g. OH-)
NaOH + H2CO3 → NaHCO3 + H2O
-pH rises only slightly
-H2CO3 supply is almost limitless (from CO2 released by respiration) and subject to respiratory controls
What is the function of the phosphate buffer system?
-Action nearly identical to bicarbonate buffer
-Effective buffer in urine and ICF, where phosphate concentrations are high
What are the salts in the phosphate buffer system?
-Dihydrogen phosphate (H2PO4-), a weak acid
-Monohydrogen phosphate (HPO42-), a weak base
What is the function of the protein buffer system?
-When pH rises, organic acid or carboxyl (COOH) groups release H+
-When pH falls, NH2 groups bind H+
-Hemoglobin functions as intracellular buffer
What are the basic functions of the acid-base balance system?
-Lungs eliminate volatile carbonic acid by eliminating CO2
-Kidneys eliminate nonvolatile (fixed) acids produced by cellular metabolism (phosphoric, uric, and lactic acids and ketones) to prevent metabolic acidosis
-Kidneys also regulate blood levels of alkaline substances; renew chemical buffers
What are the classes of acid-balance?
-Respiratory acidosis and alkalosis
-Metabolic acidosis and alkalosis
What is respiratory acidosis and alkalosis?
-Caused by failure of respiratory system to perform pH-balancing role
-Single most important indicator is blood PCO2
What is metabolic acidosis and alkalosis?
-All abnormalities other than those caused by PCO2 levels in blood; indicated by abnormal HCO3- levels
How does the acid-base system compensate if there is a malfunction in the one of the systems?
-Respiratory system attempts to correct metabolic acid-base imbalances
-Kidneys attempt to correct respiratory acid-base imbalances
What is respiratory alkalosis and how is it caused?
-PCO2 below 35 mm Hg
-Common result of hyperventilation often due to stress or pain (CO2 eliminated faster than produced)
What is respiratory acidosis and how is it caused?
-PCO2 above 45 mm Hg
-Common cause of acid-base imbalances
-Due to decrease in ventilation or gas exchange
-CO2 accumulates in blood
-Characterized by falling blood pH and rising PCO2
What does respiratory alkalosis do to the respiratory system?
-Depresses respiratory center
-Respiratory rate and depth decrease
-H+ concentration increases
How is respiratory acidosis caused?
How is respiratory alkalosis caused?
What is metabolic acidosis?
-Low blood pH and HCO3-
What is the cause of metabolic acidosis?
-Ingestion of too much alcohol (→ acetic acid)
-Excessive loss of HCO3- (e.g., persistent diarrhea)
-Accumulation of lactic acid (exercise or shock)
-Ketosis in diabetic crisis, starvation, and kidney failure
What occurs if blood pH gets too low?
-Blood pH below 6.8 → depression of CNS → coma → death
What is metabolic alkalosis?
-High blood pH and HCO3-
How is metabolic alkalosis caused?
-Vomiting of acid contents of stomach or by intake of excess base (e.g., antacids)
What occurs if the blood pH gets too high?
-Blood pH above 7.8 → excitation of nervous system → muscle tetany, extreme nervousness, convulsions, death often from respiratory arrest
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