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24-1
WATER, ELECTROLYTE,
AND ACID-BASE
BALANCE
24-2
Water, Electrolyte
and Acid-Base Balance
24-3
Water Balance
• Total body water for 150 lb. male = 40L
• Fluid compartments
– 65% ICF
– 35% ECF
• 25% tissue fluid
• 8% blood plasma, lymph
• 2% transcellular fluid (CSF, synovial fluid)
24-4
Water Movement in Fluid Compartments
• Electrolytes play principle role in water
distribution and total water content
24-5
Water Gain
• Preformed water
– ingested in food and drink
• Metabolic water
– by-product of aerobic metabolism and
dehydration synthesis
24-6
Water Loss
• Routes of loss
– urine, feces, expired breath, sweat, cutaneous
transpiration
• Loss varies greatly with environment and
activity
– respiratory loss ↑: with cold, dry air or heavy work
– perspiration loss ↑: with hot, humid air or heavy work
• Insensible water loss
– breath and cutaneous transpiration
• Obligatory water loss
– breath, cutaneous transpiration, sweat, feces,
minimum urine output (400 ml/day)
24-7
Fluid Balance
24-8
Regulation of Fluid Intake
• Dehydration
↓ blood volume and pressure
↑ blood osmolarity
• Thirst mechanisms
– stimulation of thirst center (in hypothalamus)
• angiotensin II: produced in response to ↓ BP
• ADH: produced in response to ↑ blood osmolarity
• hypothalamic osmoreceptors: signal in response to
↑ ECF osmolarity
– inhibition of salivation
• thirst center sends sympathetic signals to salivary
glands
24-9
Satiation Mechanisms
• Short term (30 to 45 min), fast acting
– cooling and moistening of mouth
– distension of stomach and intestine
• Long term inhibition of thirst
– rehydration of blood (↓ blood osmolarity)
• stops osmoreceptor response, ↑ capillary filtration,
↑ saliva
24-10
Dehydration, Thirst, and Rehydration
24-11
Regulation of Output
• Controlling Na+
reabsorption (changes volume)
– as Na+
is reabsorbed or excreted, water follows
• Action of ADH (changes concentration of urine)
– ADH secretion (as well as thirst center) stimulated by
hypothalamic osmoreceptors in response to
dehydration
– aquaporins synthesized in response to ADH
• membrane proteins in renal collecting ducts to channel water
back into renal medulla, Na+
is still excreted
– effects: slows ↓ in water volume and ↑ osmolarity
24-12
Secretion and Effects of ADH
24-13
Disorders of Water Balance
• Fluid deficiency
– volume depletion (hypovolemia)
• total body water ↓, osmolarity normal
• hemorrhage, severe burns, chronic vomiting or diarrhea
– dehydration
• total body water ↓, osmolarity rises
• lack of drinking water, diabetes, profuse sweating, diuretics
• infants more vulnerable
– high metabolic rate demands high urine excretion, kidneys
cannot concentrate urine effectively, greater ratio of body
surface to mass
• affects all fluid compartments
– most serious effects
• circulatory shock, neurological dysfunction, infant mortality
24-14
Water Loss & Fluid Balance
1) profuse sweating
2) produced by
capillary filtration
3) blood volume and
pressure drop,
osmolarity rises
4) blood absorbs
tissue fluid to
replace loss
5) fluid pulled from
ICF
24-15
Fluid Excess
• Volume excess
– both Na+
and water retained, ECF isotonic
– aldosterone hypersecretion
• Hypotonic hydration
– more water than Na+
retained or ingested, ECF
hypotonic - can cause cellular swelling
• Most serious effects
– pulmonary and cerebral edema
24-16
Blood Volume & Fluid Intake
Kidneys compensate
very well for excessive
fluid intake, but not for
inadequate intake
24-17
Fluid Sequestration
• Excess fluid in a particular location
• Most common form: edema
– accumulation in the interstitial spaces
• Hematomas
– hemorrhage into tissues; blood is lost to circulation
• Pleural effusions
– several liters of fluid may accumulate in some lung
infections
24-18
Electrolytes
• Function
– chemically reactive in metabolism
– determine cell membrane potentials
– affect osmolarity of body fluids
– affect body’s water content and distribution
• Major cations
– Na+
, K+
, Ca2+
, H+
• Major anions
– Cl-
, HCO3
-
, PO4
3-
24-19
Sodium - Functions
• Membrane potentials
• Accounts for 90 - 95% of osmolarity of ECF
• Na+
- K+
pump
– exchanges intracellular Na+
for extracellular K+
– creates gradient for cotransport of other
solutes (glucose)
– generates heat
• NaHCO3 has major role in buffering pH
24-20
Sodium - Homeostasis
• Primary concern - excretion of dietary excess
– 0.5 g/day needed, typical diet has 3 to 7 g/day
• Aldosterone - “salt retaining hormone”
↑ # of renal Na+
/K+
pumps, ↑ Na+ and ↓ K+
reabsorbed
– hypernatremia/hypokalemia inhibits release
• ADH - ↑ blood Na+
levels stimulate ADH release
– kidneys reabsorb more water (without retaining more Na+
)
• ANP (atrial natriuretic peptide) – from stretched
atria
– kidneys excrete more Na+
and H2O, thus ↓ BP/volume
• Others - estrogen retains water during pregnancy
– progesterone has diuretic effect
24-21
Sodium - Imbalances
• Hypernatremia
– plasma sodium > 145 mEq/L
• from IV saline
– water retension, hypertension and edema
• Hyponatremia
– plasma sodium < 130 mEq/L
– result of excess body water, quickly corrected
by excretion of excess water
24-22
Potassium - Functions
• Most abundant cation of ICF
• Determines intracellular osmolarity
• Membrane potentials (with sodium)
• Na+
-K+
pump
24-23
Potassium - Homeostasis
• 90% of K+
in glomerular filtrate is
reabsorbed by the PCT
• DCT and cortical portion of collecting duct
secrete K+
in response to blood levels
• Aldosterone stimulates renal secretion of
K+
24-24
Secretion and Effects of Aldosterone
24-25
Potassium - Imbalances
• Most dangerous imbalances of electrolytes
• Hyperkalemia-effects depend on rate of
imbalance
– if concentration rises quickly, (crush injury) the
sudden increase in extracellular K+
makes nerve and
muscle cells abnormally excitable
– slow onset, inactivates voltage-gated Na+
channels,
nerve and muscle cells become less excitable
• Hypokalemia
– from sweating, chronic vomiting or diarrhea
– nerve and muscle cells less excitable
• muscle weakness, loss of muscle tone, ↓ reflexes, arrthymias
24-26
Potassium & Membrane Potentials
24-27
Chloride - Functions
• ECF osmolarity
– most abundant anions in ECF
• Stomach acid
– required in formation of HCl
• Chloride shift
– CO2 loading and unloading in RBC’s
• pH
– major role in regulating pH
24-28
Chloride - Homeostasis
• Strong attraction to Na+
, K+
and Ca2+
, which
it passively follows
• Primary homeostasis achieved as an
effect of Na+
homeostasis
24-29
Chloride - Imbalances
• Hyperchloremia
– result of dietary excess or IV saline
• Hypochloremia
– result of hyponatremia
• Primary effects
– pH imbalance
24-30
Calcium - Functions
• Skeletal mineralization
• Muscle contraction
• Second messenger
• Exocytosis
• Blood clotting
24-31
Calcium - Homeostasis
• PTH
• Calcitriol (vitamin D)
• Calcitonin (in children)
– these hormones affect bone deposition and
resorption, intestinal absorption and urinary
excretion
• Cells maintain very low intracellular Ca2+
levels
– to prevent calcium phosphate crystal
precipitation
• phosphate levels are high in the ICF
24-32
Calcium - Imbalances
• Hypercalcemia
– alkalosis, hyperparathyroidism, hypothyroidism
↓ membrane Na+
permeability, inhibits depolarization
– concentrations > 12 mEq/L causes muscular
weakness, depressed reflexes, cardiac arrhythmias
• Hypocalcemia
– vitamin D ↓, diarrhea, pregnancy, acidosis, lactation,
hypoparathyroidism, hyperthyroidism
↑ membrane Na+
permeability, causing nervous and
muscular systems to be abnormally excitable
– very low levels result in tetanus, laryngospasm, death
24-33
Phosphates - Functions
• Concentrated in ICF as
– phosphate (PO4
3-
), monohydrogen phosphate (HPO4
2-
),
and dihydrogen phosphate (H2PO4
-
)
• Components of
– nucleic acids, phospholipids, ATP, GTP, cAMP,
creatine phosphate
• Activates metabolic pathways by
phosphorylating enzymes
• Buffers pH
24-34
Phosphates - Homeostasis
• Renal control
– if plasma concentration drops, renal tubules
reabsorb all filtered phosphate
• Parathyroid hormone
↑ excretion of phosphate
S
• Imbalances not as critical
– body can tolerate broad variations in
concentration of phosphate
24-35
Acid-Base Balance
• Important part of homeostasis
– metabolism depends on enzymes, and
enzymes are sensitive to Ph
• Normal pH range of ECF is 7.35 to 7.45
• Challenges to acid-base balance
– metabolism produces lactic acids, phosphoric
acids, fatty acids, ketones and carbonic acids
24-36
Acids and Bases
• Acids
– strong acids ionize freely, markedly lower pH
– weak acids ionize only slightly
• Bases
– strong bases ionize freely, markedly raise pH
– weak bases ionize only slightly
24-37
Buffers
• Resist changes in pH
– convert strong acids or bases to weak ones
• Physiological buffer
– system that controls output of acids, bases or CO2
• urinary system buffers greatest quantity, takes several hours
• respiratory system buffers within minutes, limited quantity
• Chemical buffer systems
– restore normal pH in fractions of a second
– bicarbonate, phosphate and protein systems bind H+
and transport H+
to an exit (kidney/lung)
24-38
Bicarbonate Buffer System
• Solution of carbonic acid and bicarbonate ions
– CO2 + H2O ↔ H2CO3 ↔ HCO3
-
+ H+
• Reversible reaction important in ECF
– CO2 + H2O → H2CO3 → HCO3
-
+ H+
• lowers pH by releasing H+
– CO2 + H2O ← H2CO3 ← HCO3
-
+ H+
• raises pH by binding H+
• Functions with respiratory and urinary systems
– to lower pH, kidneys excrete HCO3
-
+
24-39
Phosphate Buffer System
• H2PO4
-
↔ HPO4
2-
+ H+
– as in the bicarbonate system, reactions that
proceed to the right release H+
and ↓ pH, and
those to the left ↑pH
• Important in the ICF and renal tubules
– where phosphates are more concentrated and
function closer to their optimum pH of 6.8
• constant production of metabolic acids creates pH
values from 4.5 to 7.4 in the ICF, avg. 7.0
24-40
Protein Buffer System
• More concentrated than bicarbonate or
phosphate systems especially in the ICF
• Acidic side groups can release H+
• Amino side groups can bind H+
24-41
Respiratory Control of pH
• Neutralizes 2 to 3 times as much acid as
chemical buffers
• Collaborates with bicarbonate system
– CO2 + H2O → H2CO3 → HCO3
-
+ H+
• lowers pH by releasing H+
– CO2(expired) + H2O ← H2CO3 ← HCO3
-
+ H+
• raises pH by binding H+
∀↑ CO2 and ↓ pH stimulate pulmonary
ventilation, while an ↑ pH inhibits
pulmonary ventilation
24-42
Renal Control of pH
• Most powerful buffer system (but slow
response)
• Renal tubules secrete H+
into tubular fluid,
then excreted in urine
24-43
H+
Secretion and Excretion in Kidney
24-44
Limiting pH
• Tubular secretion of H+
(step 7)
– continues only with a concentration gradient of H+
between tubule cells and tubular fluid
– if H+
concentration ↑ in tubular fluid, lowering pH to
4.5, secretion of H+
stops
• This is prevented by buffers in tubular fluid
– bicarbonate system
– phosphate system
• Na2HPO4 + H+
→ NaH2PO4 + Na+
– ammonia (NH3),from amino acid catabolism
• NH3 + H+
and Cl-
→ NH4Cl (ammonium chloride)
24-45
Buffering Mechanisms in Urine
24-46
Acid-Base Balance
24-47
Acid-Base & Potassium Imbalances
• Acidosis
– H+
diffuses into cells and drives out K+
,
elevating K+
concentration in ECF
• H+
buffered by protein in ICF, causes membrane
hyperpolarization, nerve and muscle cells are hard
to stimulate; CNS depression may lead to death
24-48
Acid-Base & Potassium Imbalances
• Alkalosis
– H+
diffuses out of cells and K+
diffuses in,
membranes depolarized, nerves overstimulate
muscles causing spasms, tetany, convulsions,
respiratory paralysis
24-49
Disorders of Acid-Base Balances
• Respiratory acidosis (emphysema)
– rate of alveolar ventilation falls behind CO2 production
• Respiratory alkalosis (hyperventilation)
– CO2 eliminated faster than it is produced
• Metabolic acidosis
↑ production of organic acids (lactic acid, ketones
seen in alcoholism, diabetes)
– ingestion of acidic drugs (aspirin)
– loss of base (chronic diarrhea, laxative overuse)
• Metabolic alkalosis (rare)
– overuse of bicarbonates (antacids)
– loss of acid (chronic vomiting)
24-50
Compensation for pH Imbalances
• Respiratory system adjusts ventilation
(fast, limited compensation)
– hypercapnia (↑ CO2) stimulates pulmonary
ventilation
– hypocapnia reduces it
• Renal compensation (slow, powerful
compensation)
– effective for imbalances of a few days or
longer
– acidosis causes ↑ in H+
secretion
– alkalosis causes bicarbonate secretion

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Water, Electrolyte, And Acid-Base Balance

  • 3. 24-3 Water Balance • Total body water for 150 lb. male = 40L • Fluid compartments – 65% ICF – 35% ECF • 25% tissue fluid • 8% blood plasma, lymph • 2% transcellular fluid (CSF, synovial fluid)
  • 4. 24-4 Water Movement in Fluid Compartments • Electrolytes play principle role in water distribution and total water content
  • 5. 24-5 Water Gain • Preformed water – ingested in food and drink • Metabolic water – by-product of aerobic metabolism and dehydration synthesis
  • 6. 24-6 Water Loss • Routes of loss – urine, feces, expired breath, sweat, cutaneous transpiration • Loss varies greatly with environment and activity – respiratory loss ↑: with cold, dry air or heavy work – perspiration loss ↑: with hot, humid air or heavy work • Insensible water loss – breath and cutaneous transpiration • Obligatory water loss – breath, cutaneous transpiration, sweat, feces, minimum urine output (400 ml/day)
  • 8. 24-8 Regulation of Fluid Intake • Dehydration ↓ blood volume and pressure ↑ blood osmolarity • Thirst mechanisms – stimulation of thirst center (in hypothalamus) • angiotensin II: produced in response to ↓ BP • ADH: produced in response to ↑ blood osmolarity • hypothalamic osmoreceptors: signal in response to ↑ ECF osmolarity – inhibition of salivation • thirst center sends sympathetic signals to salivary glands
  • 9. 24-9 Satiation Mechanisms • Short term (30 to 45 min), fast acting – cooling and moistening of mouth – distension of stomach and intestine • Long term inhibition of thirst – rehydration of blood (↓ blood osmolarity) • stops osmoreceptor response, ↑ capillary filtration, ↑ saliva
  • 11. 24-11 Regulation of Output • Controlling Na+ reabsorption (changes volume) – as Na+ is reabsorbed or excreted, water follows • Action of ADH (changes concentration of urine) – ADH secretion (as well as thirst center) stimulated by hypothalamic osmoreceptors in response to dehydration – aquaporins synthesized in response to ADH • membrane proteins in renal collecting ducts to channel water back into renal medulla, Na+ is still excreted – effects: slows ↓ in water volume and ↑ osmolarity
  • 13. 24-13 Disorders of Water Balance • Fluid deficiency – volume depletion (hypovolemia) • total body water ↓, osmolarity normal • hemorrhage, severe burns, chronic vomiting or diarrhea – dehydration • total body water ↓, osmolarity rises • lack of drinking water, diabetes, profuse sweating, diuretics • infants more vulnerable – high metabolic rate demands high urine excretion, kidneys cannot concentrate urine effectively, greater ratio of body surface to mass • affects all fluid compartments – most serious effects • circulatory shock, neurological dysfunction, infant mortality
  • 14. 24-14 Water Loss & Fluid Balance 1) profuse sweating 2) produced by capillary filtration 3) blood volume and pressure drop, osmolarity rises 4) blood absorbs tissue fluid to replace loss 5) fluid pulled from ICF
  • 15. 24-15 Fluid Excess • Volume excess – both Na+ and water retained, ECF isotonic – aldosterone hypersecretion • Hypotonic hydration – more water than Na+ retained or ingested, ECF hypotonic - can cause cellular swelling • Most serious effects – pulmonary and cerebral edema
  • 16. 24-16 Blood Volume & Fluid Intake Kidneys compensate very well for excessive fluid intake, but not for inadequate intake
  • 17. 24-17 Fluid Sequestration • Excess fluid in a particular location • Most common form: edema – accumulation in the interstitial spaces • Hematomas – hemorrhage into tissues; blood is lost to circulation • Pleural effusions – several liters of fluid may accumulate in some lung infections
  • 18. 24-18 Electrolytes • Function – chemically reactive in metabolism – determine cell membrane potentials – affect osmolarity of body fluids – affect body’s water content and distribution • Major cations – Na+ , K+ , Ca2+ , H+ • Major anions – Cl- , HCO3 - , PO4 3-
  • 19. 24-19 Sodium - Functions • Membrane potentials • Accounts for 90 - 95% of osmolarity of ECF • Na+ - K+ pump – exchanges intracellular Na+ for extracellular K+ – creates gradient for cotransport of other solutes (glucose) – generates heat • NaHCO3 has major role in buffering pH
  • 20. 24-20 Sodium - Homeostasis • Primary concern - excretion of dietary excess – 0.5 g/day needed, typical diet has 3 to 7 g/day • Aldosterone - “salt retaining hormone” ↑ # of renal Na+ /K+ pumps, ↑ Na+ and ↓ K+ reabsorbed – hypernatremia/hypokalemia inhibits release • ADH - ↑ blood Na+ levels stimulate ADH release – kidneys reabsorb more water (without retaining more Na+ ) • ANP (atrial natriuretic peptide) – from stretched atria – kidneys excrete more Na+ and H2O, thus ↓ BP/volume • Others - estrogen retains water during pregnancy – progesterone has diuretic effect
  • 21. 24-21 Sodium - Imbalances • Hypernatremia – plasma sodium > 145 mEq/L • from IV saline – water retension, hypertension and edema • Hyponatremia – plasma sodium < 130 mEq/L – result of excess body water, quickly corrected by excretion of excess water
  • 22. 24-22 Potassium - Functions • Most abundant cation of ICF • Determines intracellular osmolarity • Membrane potentials (with sodium) • Na+ -K+ pump
  • 23. 24-23 Potassium - Homeostasis • 90% of K+ in glomerular filtrate is reabsorbed by the PCT • DCT and cortical portion of collecting duct secrete K+ in response to blood levels • Aldosterone stimulates renal secretion of K+
  • 24. 24-24 Secretion and Effects of Aldosterone
  • 25. 24-25 Potassium - Imbalances • Most dangerous imbalances of electrolytes • Hyperkalemia-effects depend on rate of imbalance – if concentration rises quickly, (crush injury) the sudden increase in extracellular K+ makes nerve and muscle cells abnormally excitable – slow onset, inactivates voltage-gated Na+ channels, nerve and muscle cells become less excitable • Hypokalemia – from sweating, chronic vomiting or diarrhea – nerve and muscle cells less excitable • muscle weakness, loss of muscle tone, ↓ reflexes, arrthymias
  • 27. 24-27 Chloride - Functions • ECF osmolarity – most abundant anions in ECF • Stomach acid – required in formation of HCl • Chloride shift – CO2 loading and unloading in RBC’s • pH – major role in regulating pH
  • 28. 24-28 Chloride - Homeostasis • Strong attraction to Na+ , K+ and Ca2+ , which it passively follows • Primary homeostasis achieved as an effect of Na+ homeostasis
  • 29. 24-29 Chloride - Imbalances • Hyperchloremia – result of dietary excess or IV saline • Hypochloremia – result of hyponatremia • Primary effects – pH imbalance
  • 30. 24-30 Calcium - Functions • Skeletal mineralization • Muscle contraction • Second messenger • Exocytosis • Blood clotting
  • 31. 24-31 Calcium - Homeostasis • PTH • Calcitriol (vitamin D) • Calcitonin (in children) – these hormones affect bone deposition and resorption, intestinal absorption and urinary excretion • Cells maintain very low intracellular Ca2+ levels – to prevent calcium phosphate crystal precipitation • phosphate levels are high in the ICF
  • 32. 24-32 Calcium - Imbalances • Hypercalcemia – alkalosis, hyperparathyroidism, hypothyroidism ↓ membrane Na+ permeability, inhibits depolarization – concentrations > 12 mEq/L causes muscular weakness, depressed reflexes, cardiac arrhythmias • Hypocalcemia – vitamin D ↓, diarrhea, pregnancy, acidosis, lactation, hypoparathyroidism, hyperthyroidism ↑ membrane Na+ permeability, causing nervous and muscular systems to be abnormally excitable – very low levels result in tetanus, laryngospasm, death
  • 33. 24-33 Phosphates - Functions • Concentrated in ICF as – phosphate (PO4 3- ), monohydrogen phosphate (HPO4 2- ), and dihydrogen phosphate (H2PO4 - ) • Components of – nucleic acids, phospholipids, ATP, GTP, cAMP, creatine phosphate • Activates metabolic pathways by phosphorylating enzymes • Buffers pH
  • 34. 24-34 Phosphates - Homeostasis • Renal control – if plasma concentration drops, renal tubules reabsorb all filtered phosphate • Parathyroid hormone ↑ excretion of phosphate S • Imbalances not as critical – body can tolerate broad variations in concentration of phosphate
  • 35. 24-35 Acid-Base Balance • Important part of homeostasis – metabolism depends on enzymes, and enzymes are sensitive to Ph • Normal pH range of ECF is 7.35 to 7.45 • Challenges to acid-base balance – metabolism produces lactic acids, phosphoric acids, fatty acids, ketones and carbonic acids
  • 36. 24-36 Acids and Bases • Acids – strong acids ionize freely, markedly lower pH – weak acids ionize only slightly • Bases – strong bases ionize freely, markedly raise pH – weak bases ionize only slightly
  • 37. 24-37 Buffers • Resist changes in pH – convert strong acids or bases to weak ones • Physiological buffer – system that controls output of acids, bases or CO2 • urinary system buffers greatest quantity, takes several hours • respiratory system buffers within minutes, limited quantity • Chemical buffer systems – restore normal pH in fractions of a second – bicarbonate, phosphate and protein systems bind H+ and transport H+ to an exit (kidney/lung)
  • 38. 24-38 Bicarbonate Buffer System • Solution of carbonic acid and bicarbonate ions – CO2 + H2O ↔ H2CO3 ↔ HCO3 - + H+ • Reversible reaction important in ECF – CO2 + H2O → H2CO3 → HCO3 - + H+ • lowers pH by releasing H+ – CO2 + H2O ← H2CO3 ← HCO3 - + H+ • raises pH by binding H+ • Functions with respiratory and urinary systems – to lower pH, kidneys excrete HCO3 - +
  • 39. 24-39 Phosphate Buffer System • H2PO4 - ↔ HPO4 2- + H+ – as in the bicarbonate system, reactions that proceed to the right release H+ and ↓ pH, and those to the left ↑pH • Important in the ICF and renal tubules – where phosphates are more concentrated and function closer to their optimum pH of 6.8 • constant production of metabolic acids creates pH values from 4.5 to 7.4 in the ICF, avg. 7.0
  • 40. 24-40 Protein Buffer System • More concentrated than bicarbonate or phosphate systems especially in the ICF • Acidic side groups can release H+ • Amino side groups can bind H+
  • 41. 24-41 Respiratory Control of pH • Neutralizes 2 to 3 times as much acid as chemical buffers • Collaborates with bicarbonate system – CO2 + H2O → H2CO3 → HCO3 - + H+ • lowers pH by releasing H+ – CO2(expired) + H2O ← H2CO3 ← HCO3 - + H+ • raises pH by binding H+ ∀↑ CO2 and ↓ pH stimulate pulmonary ventilation, while an ↑ pH inhibits pulmonary ventilation
  • 42. 24-42 Renal Control of pH • Most powerful buffer system (but slow response) • Renal tubules secrete H+ into tubular fluid, then excreted in urine
  • 44. 24-44 Limiting pH • Tubular secretion of H+ (step 7) – continues only with a concentration gradient of H+ between tubule cells and tubular fluid – if H+ concentration ↑ in tubular fluid, lowering pH to 4.5, secretion of H+ stops • This is prevented by buffers in tubular fluid – bicarbonate system – phosphate system • Na2HPO4 + H+ → NaH2PO4 + Na+ – ammonia (NH3),from amino acid catabolism • NH3 + H+ and Cl- → NH4Cl (ammonium chloride)
  • 47. 24-47 Acid-Base & Potassium Imbalances • Acidosis – H+ diffuses into cells and drives out K+ , elevating K+ concentration in ECF • H+ buffered by protein in ICF, causes membrane hyperpolarization, nerve and muscle cells are hard to stimulate; CNS depression may lead to death
  • 48. 24-48 Acid-Base & Potassium Imbalances • Alkalosis – H+ diffuses out of cells and K+ diffuses in, membranes depolarized, nerves overstimulate muscles causing spasms, tetany, convulsions, respiratory paralysis
  • 49. 24-49 Disorders of Acid-Base Balances • Respiratory acidosis (emphysema) – rate of alveolar ventilation falls behind CO2 production • Respiratory alkalosis (hyperventilation) – CO2 eliminated faster than it is produced • Metabolic acidosis ↑ production of organic acids (lactic acid, ketones seen in alcoholism, diabetes) – ingestion of acidic drugs (aspirin) – loss of base (chronic diarrhea, laxative overuse) • Metabolic alkalosis (rare) – overuse of bicarbonates (antacids) – loss of acid (chronic vomiting)
  • 50. 24-50 Compensation for pH Imbalances • Respiratory system adjusts ventilation (fast, limited compensation) – hypercapnia (↑ CO2) stimulates pulmonary ventilation – hypocapnia reduces it • Renal compensation (slow, powerful compensation) – effective for imbalances of a few days or longer – acidosis causes ↑ in H+ secretion – alkalosis causes bicarbonate secretion