water, electrolyte, pH balance

1. EC questions
• What does ICF stand for?
• a chemical compound that dissociates into
ions in water is called an______.
• is sodium concentration higher in the ECF or
ICF?
• a sensation of thirst causes us to:
1

2. Describe the major fluid
compartments including intracellular,
extracellular, intravascular and
interstitial.

3. Total body water
Volume = 40 L
60% body weight Extracellular fluid (ECF)
Volume = 15 L
20% body weight
Intracellular fluid (ICF) Interstitial fluid (IF)
Volume = 25 L Volume = 12 L
40% body weight 80% of ECF
Figure 26.1

4. • Describe the regulation of water intake and
output

5. Regulation of Water Intake
• Thirst mechanism is the driving force for
water intake
• The hypothalamic thirst center
osmoreceptors are stimulated by
– Plasma osmolality of 2–3%
–Angiotensin II or baroreceptor input
–Dry mouth
–Substantial decrease in blood volume or
pressure

6. Regulation of Water Intake
• Drinking water creates inhibition of the
thirst center
• Inhibitory feedback signals include
–Relief of dry mouth
–Activation of stomach and intestinal
stretch receptors

7. • Most of the body’s water is
1. Intracellular
2. Intravascular
3. interstitial
7

8. Regulation of Water Output
• Obligatory water losses
–Insensible water loss: from lungs, skin,
Feces
–Minimum daily sensible water loss of
500 ml in urine to excrete wastes
• Body water and Na+ content are regulated
in tandem by mechanisms that maintain
cardiovascular function and blood
pressure

9. Regulation of Water Output: Influence
of ADH
• Water reabsorption in collecting ducts is
proportional to ADH release
• ADH dilute urine and volume of body
fluids
• ADH concentrated urine
• Hypothalamic osmoreceptors trigger or
inhibit ADH release

10. • Which of the following would stimulate thirst
center osmoreceptors?
1. Plasma osmolality of 2–3%
2. Angiotensin II or baroreceptor input
3. Dry mouth
4. Substantial decrease in blood volume
or pressure
5. All of these
10

11. • Which of the following is an electrolyte?
1. sodium chloride
2. Hydrochloric acid
3. Sodium hydroxide
4. glucose
5. 1,2, and 3
6. All of these
11

12. • Describe the regulation of the major
electrolytes- salts, acids and bases

13. Central Role of Sodium
• Most abundant cation in the ECF
• Sodium salts in the ECF contribute 280 mOsm
of the total 300 mOsm ECF solute
concentration
• Na+ leaks into cells and is pumped out against
its electrochemical gradient
• ECF Na+ concentration remains stable due to
osmosis

14. Central Role of Sodium
• Changes in plasma sodium levels affect
– Plasma volume, blood pressure
– ICF and IF volumes
• Renal acid-base control mechanisms are
coupled to sodium ion transport
• No receptors are known that monitor Na+
levels in body fluids

15. Regulation of Sodium Balance:
Aldosterone
• Na+-water balance is linked to blood pressure
and blood volume control mechanisms
• Na+ reabsorption
– 65% is reabsorbed in the proximal tubules
– 25% is reclaimed in the loops of Henle
• Aldosterone active reabsorption of
remaining Na+
• Water follows Na+ if ADH is present

16. Regulation of Sodium Balance:
Aldosterone
• Renin-angiotensin mechanism is the main
trigger for aldosterone release
–Granular cells of JGA secrete renin in
response to
• Sympathetic nervous system
stimulation
• Filtrate osmolality
• Stretch (due to blood pressure)

17. Regulation of Sodium Balance:
Aldosterone
• Renin catalyzes the production of angiotensin
II, which prompts aldosterone release from the
adrenal cortex
• Aldosterone release is also triggered by
elevated K+ levels in the ECF
• Aldosterone brings about its effects slowly
(hours to days)

18. K+ (or Na+) concentration Renin-angiotensin
in blood plasma* mechanism
Stimulates
Adrenal cortex
Negative
Releases
feedback
inhibits
Aldosterone
Targets
Kidney tubules
Effects
Na+ reabsorption K+ secretion
Restores
Homeostatic plasma
levels of Na+ and K+
Figure 26.8

19. Regulation of Sodium Balance: ANP
• Released by atrial cells in response to stretch
( blood pressure)
• Effects
• Decreases blood pressure and blood volume:
– ADH, renin and aldosterone production
– Excretion of Na+ and water
– Promotes vasodilation directly and also by
decreasing production of angiotensin II

20. Influence of Other Hormones
• Estrogens: NaCl reabsorption (like
aldosterone)
– H2O retention during menstrual cycles and
pregnancy
• Progesterone: Na+ reabsorption (blocks
aldosterone)
– Promotes Na+ and H2O loss

21. • The most abundant cation in the ECF is:
1. Sodium
2. Potassium
3. Calcium
4. chloride
21

22. • Changes in sodium ion concentration effect:
1. Blood Plasma volume
2. blood pressure
3. ICF volume
4. IF volume
5. All of these
22

23. Cardiovascular System Baroreceptors
• Baroreceptors alert the brain of increases in
blood volume and pressure
– Sympathetic nervous system impulses to the
kidneys decline
– Afferent arterioles dilate
– GFR increases
– Na+ and water output increase

24. Regulation of Potassium Balance
• Importance of potassium:
– Affects RMP in neurons and muscle cells
(especially cardiac muscle)
• ECF [K+] RMP depolarization
reduced excitability
• ECF [K+] hyperpolarization and
nonresponsiveness

25. Regulation of Potassium Balance
• H+ shift in and out of cells
– Leads to corresponding shifts in K+ in the opposite
direction to maintain cation balance
– Interferes with activity of excitable cells

26. Regulation of Potassium Balance
• K+ balance is controlled in the cortical
collecting ducts by changing the amount of
potassium secreted into filtrate
• High K+ content of ECF favors tubule cell
secretion of K+
• When K+ levels are low, cells reabsorb some K+
left in the filtrate

27. Regulation of Potassium Balance
• Influence of aldosterone
–Increased K+ in the adrenal cortex
causes
• Release of aldosterone
• Potassium secretion

28. Regulation of Calcium
• Ca2+ in ECF is important for
–Neuromuscular excitability
–Blood clotting
–Cell membrane permeability
–Secretory activities

29. Regulation of Calcium
• Hypocalcemia- excitability and muscle tetany
• Hypercalcemia- Inhibits neurons and muscle
cells, may cause heart arrhythmias
• Calcium balance is controlled by parathyroid
hormone (PTH) and calcitonin

30. Influence of PTH
• Bones are the largest reservoir for Ca2+ and
phosphates
• PTH promotes increase in calcium levels by
targeting bones, kidneys, and small intestine
(indirectly through vitamin D)

31. Hypocalcemia (low blood Ca2+) stimulates
parathyroid glands to release PTH.
Rising Ca2+ in
blood inhibits
PTH release.
Bone
1 PTH activates
osteoclasts: Ca2+
and PO43S released
into blood.
2 PTH increases Kidney
Ca 2+ reabsorption
in kidney
tubules.
3 PTH promotes
kidney’s activation of vitamin D,
which increases Ca2+ absorption
from food.
Intestine
Ca2+ ions
PTH Molecules Bloodstream
Figure 16.12

32. Regulation of Anions
• Cl– is the major anion in the ECF
– Helps maintain the osmotic pressure of the blood
– 99% of Cl– is reabsorbed under normal pH
conditions
• When acidosis occurs, fewer chloride ions are
reabsorbed
• Other anions have transport maximums and
excesses are excreted in urine

33. • Which ion moves in and out of cells to
maintain cation balance in response to
hydrogen ion shifts?
1. Sodium
2. Potassium
3. Calcium
4. chloride
33

34. • Which hormone will increase sodium
reabsorption?
1. PTH
2. ADH
3. Aldosterone
4. Estrogen
5. Progesterone
6. 3 and 4
34

35. • Describe buffer systems and their role in
acid/base balance. what is a buffer?

36. Acid-Base Balance
• pH affects all functional proteins and
biochemical reactions
• Normal pH of body fluids
– Arterial blood: pH 7.4
– Venous blood and IF fluid: pH 7.35
– ICF: pH 7.0
• Alkalosis or alkalemia: arterial blood pH >7.45
• Acidosis or acidemia: arterial pH < 7.35

37. Acid-Base Balance
• Most H+ is produced by metabolism
–Lactic acid from anaerobic respiration
of glucose
–Fatty acids and ketone bodies from fat
metabolism
–H+ liberated when CO2 is converted to
HCO3– in blood

38. Acid-Base Balance
• Concentration of hydrogen ions is regulated
sequentially by
–Chemical buffer systems: rapid; first line
of defense
–Brain stem respiratory centers: act within
1–3 min
–Renal mechanisms: most potent, but
require hours to days to effect pH changes

39. Acid-Base Balance
• Strong acids dissociate completely in water;
can dramatically affect pH
• Weak acids dissociate partially in water; are
efficient at preventing pH changes
• Strong bases dissociate easily in water; quickly
tie up H+
• Weak bases accept H+ more slowly

40. HCI H2CO3
(a) A strong acid such as (b) A weak acid such as
HCI dissociates H2CO3 does not
completely into its ions. dissociate completely.
Figure 26.11

41. • Something that resists changes in pH is a
1. Strong acid
2. Electrolyte
3. Buffer
4. hormone
41

42. • Which of the following dissociates completely
in water?
1. Strong acid
2. Weak acid
3. Weak base
4. All of these
42

43. Bicarbonate Buffer System
• Mixture of H2CO3 (weak acid) and salts of
HCO3– (e.g., NaHCO3, a weak base)
• Buffers ICF and ECF
• The only important ECF buffer

44. Bicarbonate Buffer System
• If strong acid is added:
– HCO3– ties up H+ and forms H2CO3
• HCl + NaHCO3 H2CO3 + NaCl
– pH decreases only slightly, unless all
available HCO3– (alkaline reserve) is used up
– HCO3– concentration is closely regulated by
the kidneys

45. Bicarbonate Buffer System
• If strong base is 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 is subject to respiratory
controls

46. Phosphate Buffer System
• Action is nearly identical to the bicarbonate
buffer
• Components are sodium salts of:
– Dihydrogen phosphate (H2PO4–), a weak acid
– Monohydrogen phosphate (HPO42–), a weak base
• Effective buffer in urine and ICF, where
phosphate concentrations are high

47. Protein Buffer System
• Intracellular proteins are the
most plentiful and powerful
buffers; plasma proteins are also
important
• Protein molecules are
amphoteric (can function as
both a weak acid and a weak
base)
– When pH rises, organic acid or
carboxyl (COOH) groups release H+
– When pH falls, NH2 groups bind H+

48. • The most important ECF buffer system is:
1. bicarbonate
2. Phosphate
3. Protein
4. plasma
48

49. • The phosphate buffer system functions in:
1. ECF
2. ICF
3. Urine
4. 2 and 3
5. All of these
49

50. Describe the role of the respiratory system in
acid/base balance.
Describe the role of the urinary system in
acid/base balance.

51. Physiological Buffer Systems
• Respiratory and renal systems
– Act more slowly than chemical buffer systems
– Have more capacity than chemical buffer systems

52. Acid-Base Balance
• Chemical buffers cannot eliminate excess acids
or bases from the body
– Lungs eliminate volatile carbonic acid by
eliminating CO2
– Kidneys eliminate other fixed metabolic acids
(phosphoric, uric, and lactic acids and ketones) and
prevent metabolic acidosis

53. Respiratory Regulation of H+
• Respiratory system eliminates CO2
• A reversible equilibrium exists in the blood:
– CO2 + H2O H2CO3 H+ + HCO3–
• During CO2 unloading the reaction shifts to the
left (and H+ is incorporated into H2O)
• During CO2 loading the reaction shifts to the
right (and H+ is buffered by proteins)

54. 54

55. Respiratory Regulation of H+
• Hypercapnia activates medullary
chemoreceptors
• Rising plasma H+ activates peripheral
chemoreceptors- breathing rate increases
–More CO2 is removed from the blood
–H+ concentration is reduced
–CO2 + H2O H2CO3 H+ + HCO3–

56. Respiratory Regulation of H+
• Alkalosis depresses the respiratory center
– Respiratory rate and depth decrease
– H+ concentration increases
• Respiratory system impairment causes acid-
base imbalances
– Hypoventilation respiratory acidosis
– Hyperventilation respiratory alkalosis
– CO2 + H2O H2CO3 H+ + HCO3–

57. • The advantage of chemical buffer systems is
1. They have a very high capacity
2. Their effects are long lasting
3. Their effects are rapid
4. All of these
57

58. 2/3 of the body’s fluid is located where?
1. ECF
2. ICF
3. IVF
4. IF
58

59. Where is the thirst center?
1. mouth
2. hypothalamus
3. cerebellum
4. medulla
59

60. • What hormone regulates water balance
1. Aldosterone
2. PTH
3. ADH
4. Secretin
5. aquaporin
60

61. • What hormone regulates calcium balance
1. Aldosterone
2. PTH
3. ADH
4. Secretin
5. aquaporin
61

62. • What hormone regulates sodium balance
1. Aldosterone
2. PTH
3. ADH
4. Secretin
5. aquaporin
62

63. • How do the lungs eliminate carbonic acid?
1. Excreting it directly
2. Eliminating carbon dioxide
3. They don’t
4. Sending hormones to the kidneys, which
cause the kidneys to excrete it
63

64. • The advantage of physiological buffer systems
is
1. They have a very high capacity
2. Their effects are short term
3. Their effects are instantaneous
4. All of these
64

65. • Rising plasma H+ concentration will do
what to breathing rate?
1. Increase
2. Decrease
3. Not change
65

66. Renal Mechanisms of Acid-Base Balance
• Most important renal mechanisms
–Conserving (reabsorbing) or generating
new HCO3–
–Excreting HCO3–
• Generating or reabsorbing one HCO3– is
the same as losing one H+
• Excreting one HCO3– is the same as
gaining one H+

67. Renal Mechanisms of Acid-Base Balance
• Renal regulation of acid-base balance
depends on secretion of H+
• H+ secretion occurs in the PCT and in the
collecting duct:
–The H+ comes from H2CO3 produced in
reactions catalyzed by carbonic
anhydrase inside the renal tubule cells

68. Peri-
PCT cell tubular
capillary
2K+ 2K+
ATPase
3Na+ 3Na+
HCO3– + Na+ Cl– Cl–
HCO3–
H+ 3a H+ HCO3– 3b
HCO3–
2
HCO3–
4
ATPase
H2CO3
H2CO3 Na+ Na+
5 * 1
6
H2O CO2 CO2
+ CO2
H2O
Tight junction
68

69. Reabsorption of Bicarbonate
• Tubule cell luminal membranes are
impermeable to HCO3–
– CO2 combines with water in PCT cells,
forming H2CO3, which dissociates
– H+ is secreted, and HCO3– is reabsorbed into
capillary blood
– Secreted H+ unites with HCO3– to form H2CO3
in filtrate, which generates CO2 and H2O
• HCO3– disappears from filtrate at the same rate
that it enters the peritubular capillary blood

70. Peri-
PCT cell tubular
capillary
2K+ 2K+
ATPase
3Na+ 3Na+
HCO3– + Na+ Cl– Cl–
HCO3–
H+ 3a H+ HCO3– 3b
HCO3–
2
HCO3–
4
ATPase
H2CO3
H2CO3 Na+ Na+
5 * 1 CA
6
H2O CO2 CO2
+ CO2
H2O
Tight junction
70

71. Bicarbonate Ion Secretion
• When the body is in alkalosis, renal tubule cells
– Secrete HCO3–
– Reclaim H+ and acidify the blood

72. Abnormalities of Acid-Base Balance
• Respiratory acidosis and alkalosis
• Metabolic acidosis and alkalosis

73. Respiratory Acidosis and Alkalosis
The most important indicator of respiratory
function is PCO2 level (normally 35–45 mm Hg)
– PCO2 above 45 mm Hg respiratory acidosis
• Most common cause of acid-base imbalances
• Due to decrease in ventilation or gas
exchange
• Characterized by falling blood pH and rising
PCO2

74. Respiratory Acidosis and Alkalosis
• PCO2 below 35 mm Hg respiratory
alkalosis
–A common result of hyperventilation
due to stress or pain

75. Metabolic Acidosis and Alkalosis
• Any pH imbalance not caused by
abnormal blood CO2 levels
• Indicated by abnormal HCO3– levels

76. Metabolic Acidosis and Alkalosis
• Causes of metabolic acidosis
–Ingestion of too much alcohol
( acetic acid)
–Excessive loss of HCO3– (e.g., persistent
diarrhea)
–Accumulation of lactic acid, shock, ketosis
in diabetic crisis, starvation, and kidney
failure

77. Metabolic Acidosis and Alkalosis
• Metabolic alkalosis is much less common
than metabolic acidosis
–Indicated by rising blood pH and HCO3–
–Caused by vomiting of the acid contents
of the stomach or by intake of excess
base (e.g., antacids)

78. Effects of Acidosis and Alkalosis
• Blood pH below 7 depression of CNS
coma death
• Blood pH above 7.8 excitation of
nervous system muscle tetany, extreme
nervousness, convulsions, respiratory
arrest death

79. Respiratory and Renal Compensations
• If acid-base imbalance is due to
malfunction of a physiological buffer
system, the other one compensates
–Respiratory system attempts to correct
metabolic acid-base imbalances
–Kidneys attempt to correct respiratory
acid-base imbalances

80. Respiratory Compensation
In metabolic acidosis
–Blood pH is below 7.35 and HCO3– level is low
–High H+ levels stimulate the respiratory
centers
–Rate and depth of breathing are increased
–As CO2 is eliminated by the respiratory
system, PCO2 falls below normal

81. Respiratory Compensation
• Respiratory compensation for metabolic
alkalosis is revealed by:
–Slow, shallow breathing, allowing CO2
accumulation in the blood
–High pH (over 7.45) and elevated HCO3–
levels

82. Renal Compensation
• Hypoventilation causes elevated PCO2
• (respiratory acidosis)
–Renal compensation is indicated by high
HCO3– levels
• Respiratory alkalosis exhibits low PCO2 and high
pH
–Renal compensation is indicated by
decreasing HCO3– levels

83. • The respiratory system compensates for
metabolic acidosis by
1. Increasing breathing rate
2. Decreasing breathing rate
CO2 + H2O H2CO3 H+ + HCO3–
83

84. • The renal system compensates for respiratory
acidosis by
1. absorbing or generating bicarbonate
2. Secreting more bicarbonate
CO2 + H2O H2CO3 H+ + HCO3–
84