1. Water, Electrolyte, and Acid-Base Balance

2. Water, Electrolyte, and Acid-Base Balance
Of the 40 liters of water in the body of an average adult male, about two-thirds is intracellular, and one-third is extracellular
25L Intra
15L Extra
3L Plasma
12L IF

3. Water Normal amount of water in the human body
Young adult females – 50%
Young adult males – 60%
Babies – 75%
Old age – 45%
Water is necessary for many body functions and levels must be maintained

4. Fluid Compartments

6. Blood plasma Interstitial fluid Intracellular fluid Na+ Sodium K+
Potassium
Ca2+
Calcium
Mg2+
Magnesium
HCO3–
Bicarbonate
Cl–
Chloride
HPO42–
Hydrogen
phosphate
SO42–
Sulfate
Figure 26.2

7. Movement of Fluids Between Compartments
Net movements of fluids between compartments result from differences in hydrostatic and osmotic pressures
21-5

8. Nitrogenous wastes Nitrogenous wastes
Lungs
Gastrointestinal
tract
Kidneys
Blood
plasma O2
CO2
Nutrients
H2O,
Ions
H2O,
Ions
Nitrogenous
wastes O2
CO2
Nutrients
H2O
Ions
Nitrogenous
wastes
Interstitial
fluid
Intracellular
fluid in tissue cells
Figure 26.3

9. Maintaining Water Water intake must equal water output
Sources for water intake
Ingested foods and fluids
Water produced from metabolic processes
Sources for water output
Vaporization out of the lungs
Lost in perspiration
Leaves the body in the feces
Urine production

10. 100 ml Feces 4% Metabolism 10% 250 ml Sweat 8% 200 ml
Insensible losses
via skin and
lungs 28%
Foods 30%
750 ml
700 ml
2500 ml
Urine 60%
1500 ml
Beverages 60%
1500 ml
Average intake
per day
Average output
per day
Figure 26.4

11. 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

12. 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

13. Regulation of Water Output Got to Pee???
Dehydration
osmotic pressure increases in extracellular fluids
osmoreceptors in hypothalamus stimulated
hypothalamus signals posterior pituitary to release ADH
urine output decreases
Excess Water Intake
osmotic pressure decreases in extracellular fluids
osmoreceptors stimulated in hypothalamus
hypothalamus signals posterior pituitary to decrease ADH output
urine output increases

15. (a) Mechanism of dehydration
Excessive
loss of H2O
from ECF 1
ECF osmotic
pressure rises 2 3
Cells lose
H2O to ECF
by osmosis;
cells shrink
(a) Mechanism of dehydration
Figure 26.7a

16. (b) Mechanism of hypotonic hydration
Excessive
H2O enters
the ECF 1
ECF osmotic
pressure falls 2
H2O moves
into cells by
osmosis; cells swell 3
(b) Mechanism of hypotonic hydration
Figure 26.7b

17. Electrolyte Balance Electrolytes are salts, acids, and bases
Electrolyte balance usually refers only to salt balance
Salts enter the body by ingestion and are lost via perspiration, feces, and urine

18. Electrolyte Balance Importance of salts Controlling fluid movements
Excitability
Secretory activity
Membrane permeability

19. 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

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

21. Potassium and Sodium Balance

22. 1 2 3 Hypocalcemia (low blood Ca2+) stimulates
parathyroid glands to release PTH.
Rising Ca2+ in
blood inhibits
PTH release.
Bone
PTH activates
osteoclasts: Ca2+
and PO43S released
into blood. 1 2
PTH increases
Ca2+ reabsorption
in kidney
tubules.
Kidney
PTH promotes
kidney’s activation of vitamin D,
which increases Ca2+ absorption
from food. 3
Intestine
Ca2+ ions
Bloodstream
PTH Molecules
Figure 16.12

23. 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

24. Maintaining Acid-Base Balance
Blood pH must remain between 7.35 and 7.45 to maintain homeostasis
Alkalosis – pH above 7.45
Acidosis – pH below 7.35
Most ions originate as byproducts of cellular metabolism
Most acid-base balance is maintained by the kidneys
Other acid-base controlling systems
Blood buffers
Respiration

25. Sources of Hydrogen Ions (Acid)
aerobic respiration of glucose produces carbonic acid
anaerobic respiration of glucose produces lactic acid
incomplete oxidation of fatty acids produces acidic ketone bodies
oxidation of amino acids containing sulfur produces sulfuric acid
breakdown of phosphoproteins and nucleic acids produces phosphoric acid
some hydrogen ions are absorbed through digestive tract
By products of Metabolism!!!!!

26. Strengths of Acids and Bases
Strong acids release more H+
Weak acids release fewer H+
Strong bases release more OH-
Weak bases release fewer OH-

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

28. Regulation of Hydrogen Ion Concentration
acid-base buffer systems
respiratory excretion of carbon dioxide
renal excretion of hydrogen ions

29. Acid-Base Buffer Systems
Bicarbonate System
the bicarbonate ion converts a strong acid to a weak acid
carbonic acid converts a strong base to a weak base
Phosphate System
the monohydrogen phosphate ion converts a strong acid to a weak acid
the dihydrogen phosphate ion converts a strong base to a weak base
H+ + HPO4-2  H2PO4-  H+ + HPO4-2

30. Acid-Base Buffer Systems
Protein Buffer System
NH3+ group releases hydrogen ions in the presence of excess base
COO- group accepts hydrogen ions in the presence of excess acid

31. Respiratory Excretion of Carbon Dioxide

32. Renal Excretion of Hydrogen Ions

33. Summary of Acid-Base Balance

34. Respiratory Acidosis and Alkalosis
The most important indicator of adequacy 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
PCO2 below 35 mm Hg  respiratory alkalosis
A common result of hyperventilation due to stress or pain

35. Clinical Application Acid-Base Imbalances
If the pH of arterial blood drops to 6.8 or rises to 8.0 for more than a few hours, the person usually cannot survive

36. Factors that Lead to Respiratory Acidosis

37. Metabolic acidosis

38. Respiratory alkalosis

39. Metabolic alkalosis