Fluid, Electrolyte, and Acid-Base Fluid, Electrolyte, and Acid-Base HomeostasisHomeostasis

A. Fluid compartments and fluid balanceA. Fluid compartments and fluid balanceB. WaterB. Water 1. Regulation of fluid intake (gain)1. Regulation of fluid intake (gain) 2. Regulation of fluid output (loss)2. Regulation of fluid output (loss)C. ElectrolytesC. Electrolytes 1. Distribution1. DistributionD. Movement of body fluidsD. Movement of body fluids 1. Exchange between plasma and interstitial fluid1. Exchange between plasma and interstitial fluid 2. Exchange between interstitial and intracellular fluids2. Exchange between interstitial and intracellular fluidsE. Acid-base balanceE. Acid-base balance 1. Buffer systems1. Buffer systems 2. Exhalation of carbon dioxide2. Exhalation of carbon dioxide 3. Kidney excretion of H+3. Kidney excretion of H+

Body Fluid CompartmentsBody Fluid Compartments

11. intracellular fluid (67%). intracellular fluid (67%)

2. extracellular fluid (33%2. extracellular fluid (33%

a. interstitial fluid (80%)a. interstitial fluid (80%)

b. plasma (20%)b. plasma (20%)

c. other fluidsc. other fluids

SelectivelySelectively permeablepermeable cellcell membranesmembranes separate body fluids into the fluid separate body fluids into the fluid

compartments. Which cells do this?compartments. Which cells do this?

plasma

endothelium

tissue cells

arteriolar end

filtrationreabsorption

venularend

interstitial fluid

osmosis

Fluids are in constant motion between the three compartments.

Water is the main component of Water is the main component of all body fluids.all body fluids.

1. What does the term fluid balance mean?1. What does the term fluid balance mean?

2. What is the primary mechanism by which 2. What is the primary mechanism by which water moves from one compartment to the water moves from one compartment to the next? next?

3. What controls osmosis and therefore fluid 3. What controls osmosis and therefore fluid balance?balance?

4. Fluid balance, then, means water balance, 4. Fluid balance, then, means water balance, but it implies electrolyte balance as well; the but it implies electrolyte balance as well; the two are inseparable in this regard.two are inseparable in this regard.

Water makes up 45 - 75% of total body Water makes up 45 - 75% of total body weight. The exact percentage is weight. The exact percentage is

dependent upon:dependent upon:

Age- Age- newborn = 75%, lean adult man = 60%, old age = 45%

Body Size- Body Size- obese = as little as 45%, very lean as much as 75%

Gender- Gender- lean adult man = 60%, lean adult women = 50%

Water gain and lossWater gain and loss(2,500 ml/day)(2,500 ml/day)

1. water gain1. water gain

a. preformed a. preformed vsvs

b. metabolicb. metabolic

2. water loss2. water loss

sensible vs. insensiblesensible vs. insensible

Dehydration, Thirst, and RehydrationDehydration, Thirst, and Rehydration

Regulation of fluid intake (Thirst)Regulation of fluid intake (Thirst)

decreased salivation

decreased blood volume

increased blood osmotic pressure

dry mouth and throat

decreased blood pressure

stimulation of hypothalamic

osmoreceptors

conscious awareness of thirst

increased water intake

stimulation of tactile receptors

increased angiotensin

II

stimulation of hypothalamic thirst center

Regulation of Fluid Output

(adjusted by 3 hormones)

dehydration

ANTIDIURETIC HORMONE

increased blood osmolarity

stimulation of hypothalamic

osmoreceptors

rehydration

secretion of ADH from posterior pituitary gland

increased water reabsorption

increased thirst

ALDOSTERONE

dehydration

rehydration

increased water reabsorption

increased Na+ reabsorption

increased aldosterone

increased angiotensin II

ATRIAL NATRIURETIC PEPTIDE

increased blood volume

decreased Na+ reabsorption

decreased water reabsorption

decreased blood volume

stretch of right atrium

secretion of ANP

Electrolytes versus Non-electrolytesElectrolytes versus Non-electrolytes

Electrolytes have a greater effect on osmosis than do Electrolytes have a greater effect on osmosis than do nonelectrolytes. Consider the following:nonelectrolytes. Consider the following:

CC66HH1212OO66 in water = C in water = C66HH1212OO66

NaCl in water = Na+ and Cl-NaCl in water = Na+ and Cl- CaClCaCl22 in water = Ca++ and Cl- and Cl- in water = Ca++ and Cl- and Cl-

Which of these three compounds will exert the greater Which of these three compounds will exert the greater effect on osmosis?effect on osmosis?

Just as important, once the electrolyte dissociates, its Just as important, once the electrolyte dissociates, its ions can attract other ions of the opposite charge, ions can attract other ions of the opposite charge, creating an electrochemical gradient.creating an electrochemical gradient.

Electrolyte DistributionElectrolyte Distribution

Electrolytes serve four Electrolytes serve four general functions:general functions:

1. essential minerals1. essential minerals

2. exert a greater effect on osmosis2. exert a greater effect on osmosis

3. help maintain acid-base balance3. help maintain acid-base balance

4. carry electrical current4. carry electrical current

Exchange of body fluids between plasma and Exchange of body fluids between plasma and interstitial fluid occurs across capillary interstitial fluid occurs across capillary

membranes in what three ways?membranes in what three ways?

1. diffusion1. diffusion2. vesicular transport2. vesicular transport3. bulk flow 3. bulk flow

Bulk flow is dependent on what four pressures that Bulk flow is dependent on what four pressures that determine the net filtration pressure?determine the net filtration pressure?

NFP = (BHP + IFOP) - (BCOP + IFHP)NFP = (BHP + IFOP) - (BCOP + IFHP) = +10 mm Hg (net filtration)= +10 mm Hg (net filtration) = - 9 mm Hg (net reabsorption)= - 9 mm Hg (net reabsorption)

Exchange between ICF and Exchange between ICF and interstitial fluidinterstitial fluid

1. based on osmosis1. based on osmosis

2. different ionic compositions2. different ionic compositions

3. net flow = 03. net flow = 0

4. Na+ and K+ most important4. Na+ and K+ most important

5. example -- decreased [Na+]5. example -- decreased [Na+]

Relationship Between Sodium Relationship Between Sodium Balance and Water BalanceBalance and Water Balance

intake of plain water

RELATIONSHIP BETWEEN SODIUM BALANCE AND WATER BALANCE

decreased interstitial sodium decreased interstitial osmotic pressure

excessive sweating, vomiting, diarrhea

net flow of water into cells from interstitial space

decreased blood volume

increased filtration from blood capillaries

+

overhydration of cells

convulsions coma

decreased blood pressure

DEATH

circulatory shock

Acid-base balanceAcid-base balance

Normal body fluid pH is 7.35 - 7.45. Normal body fluid pH is 7.35 - 7.45.

This range is maintained by three major This range is maintained by three major mechanisms:mechanisms:1. buffer systems1. buffer systems2. exhalation of carbon dioxide2. exhalation of carbon dioxide

(respiratory compensation)(respiratory compensation)3. kidney excretion of H+3. kidney excretion of H+

(renal compensation)(renal compensation)

Metabolic acidosis vs. respiratory acidosisMetabolic alkalosis vs. respiratory alkalosis

In a buffer system, a strong acid is converted In a buffer system, a strong acid is converted to a weaker one, using a weak base, or, a to a weaker one, using a weak base, or, a

strong base is converted to a weaker one using strong base is converted to a weaker one using a weak acid.a weak acid.

The carbonic acid-bicarbonate system:The carbonic acid-bicarbonate system:HH22COCO33 HCO HCO33

-- + H + H++

HCO3- (bicarbonate ion acts as a weak base.)HCO3- (bicarbonate ion acts as a weak base.)H2CO3 (carbonic acid acts as a weak acid.)H2CO3 (carbonic acid acts as a weak acid.)

H+ + HCO3- H2CO3H+ + HCO3- H2CO3 (Used if there is an excess of H+.)(Used if there is an excess of H+.)

H2CO3 H+ + HCO3-H2CO3 H+ + HCO3- (Used if there is a shortage of H+)(Used if there is a shortage of H+)

The phosphate buffer system is an The phosphate buffer system is an important regulator of pH in the important regulator of pH in the

intracellular fluid.intracellular fluid.

H2PO4- HPO42- + H+

H2PO4- (dihydrogen phosphate acts as a weak acid)HPO4

2- (monohydrogen phosphate acts as a weak base)OH- + H2PO4- H2O + HPO4

2- (used as a weak acid to buffer strong bases)

H+ + HPO42- H2PO4-

(used as a weak base to buffer a strong acid)

The protein buffer system is the most abundant The protein buffer system is the most abundant buffer in cells and plasma. Proteins act as buffer in cells and plasma. Proteins act as both acidic and basic buffers because they both acidic and basic buffers because they have a free carboxyl group and a free amine have a free carboxyl group and a free amine

group.group.

NH2 C COOH

H

R

NH2 C

R

COO- H+

H

+

+COOH C

R

H

NH2 COOHH+ C

R

H

NH3+

Inside red blood cells, hemoglobin is an especially Inside red blood cells, hemoglobin is an especially good buffer. In the tissues, the Bohr effect ensures good buffer. In the tissues, the Bohr effect ensures that oxygen is delivered to the tissues as hydrogen that oxygen is delivered to the tissues as hydrogen

ions are buffered.ions are buffered.

HbO

O2

Hb- H++ HbH

H2CO3

H+ HCO3++

H2O CO2+

Exhalation of Carbon DioxideExhalation of Carbon Dioxide

What would be the net effect of hyperventilation?What would be the net effect of hyperventilation?

reaction shifts to the left

increased H+ used to reform carbonic acid used to reform CO2

pH increases

increased CO2 lost from the body

What would be the net effect of hypoventilation?What would be the net effect of hypoventilation?

reaction shifts to the right as CO2 accumulates in the body

H+ accumulate in the body

pH decreases

CO2 + H2O H2CO3 H+ + HCO3-

CO2 + H2O H2CO3 H+ + HCO3-

Kidney excretion of hydrogen ionsKidney excretion of hydrogen ions

pH is adjusted by changing the rate of pH is adjusted by changing the rate of H+ secretion by the renal tubules. H+ secretion by the renal tubules.

Kidneys slow to respond to imbalancesKidneys slow to respond to imbalances

Imbalances need to last for a few days Imbalances need to last for a few days or longer or longer

More permanentMore permanent

Respiratory Acidosis/Alkalosis versus Respiratory Acidosis/Alkalosis versus Metabolic acidosis/alkalosisMetabolic acidosis/alkalosis