1. Fluids, Electrolytes, and Acid Base Balance
Chapter 25
Fluids, Electrolytes, and Acid Base Balance 1 1

2. Fluids -- Electrolytes -- Acid-base
Three types of homeostatic balance
water balance - Body fluids homeostasis is essential to life
55%- 75% of body weight based on gender, body mass, age
newborn baby’s body weight 75% water
2/3 of body fluids are inside cells:
1/3 of body fluids is outside cells: extracellular fluid (ECFobese and elderly people as little as 45% by weight
electrolyte balance -conduct electrical current in solution
3. acid-base balance -production and loss of hydrogen ions (pH)
Water intake: preformed water (2,500 mL/day)
ingested in food (1000 mL/day) and drink (1200 mL/day)
metabolically generated (300 mL/day) in cells
Water eliminated
Sensible: urination and heavy perspiration, feces
Insensible: cutaneous transpiration, respiration.

3. Fluid Movements
OSMOSIS responsible for water movement between body cells, interstitium, and blood. Osmosis determined by the RELATIVE CONCENTRATIONS OF SOLUTES in each compartment
Fluid will MOVE TO higher concentration of SOLUTES
Electrolytes – play the principal role in governing the body’s water distribution and total water content
Homeostatic mechanisms that monitor and adjust body fluid composition respond to changes in the EXTRACELLULAR FLUID (ECF), not in the INTRACELLUALR FLUID (ICF)
Cells cannot move water molecules by active transport
ECF osmotic concentration INCREASES - more solutes to fluid
ECF becomes HYPERTONIC to ICF - H2O from Cells to ECF
ECF osmotic concentration DECREASES -less solutes to fluid
ECF becomes HYPOTONIC to ICF - H2O from ECF to Cells

4. Mouse = MORE solid substances
HYPERTONIC
CELL
solids
water
solids
solids
solids
water
solids
solids
solids
Cat = water
Mouse = MORE solid substances

5. Mouse = LESS solid substances
HYPOTONIC
CELL
water
water
water
water
water
solids
solids
water
water
Cat = water
Mouse = LESS solid substances

6. Disorders of Water Balance
FLUID DEFICIENCY fluid output exceeds intake over long time
volume depletion (hypovolemia) H20 & Na+ lost w/o replacement
hemorrhage, severe burns, chronic vomiting, or diarrhea
dehydration (negative water balance) more H20 than (Na+)
Infants vulnerable to dehydration- high metabolic rate; high urine excretion, immature kidneys cannot concentrate urine, diarrhea
Elderly dehydration = depend on others to provide fluid intake
FLUID EXCESSES
volume excess = both Na+ and water retained
(water intoxication) more H20 than (Na+) ingested- water drinking contests or from long bouts of exercise- high water consumption
FLUID SEQUESTRATION –EXCESS fluid accumulates in a PARTICULAR LOCATIONS. Total body water may be normal
edema - abnormal accumulation of fluid in the INTERSTIUM
lymphedema -Edema caused by blockage of LYMPH drainage
hemorrhage - BLOOD pools in the tissues is lost to circulation
pleural effusion –fluid accumulates in the pleural cavity
caused by some LUNG infections 6

7. Electrolytes
Electrolytes are any substance containing free ions that make the
substance electrically conductive.
strongly affect osmolarity of body fluids (they are solutes)
determine electrical potential (charge difference) across cell membranes
Cations are positively charged: Na+, Ca2+, K+, Mg2+ , H+.
Anions are negatively charged: HCO3- , Cl-, PO43- (phosphate)
Electrolyte depletion can occur through excessive perspiring, vomiting, dehydration
Very important to maintain electrolyte balance. EX: if you lose 500 mg of Na+ in the urine you need to replenish the loss by food and drink intake to restore balance.

8. Sodium / Chloride / Potassium Ions
SODIUM (Na+) ions are the dominant ECF cations.
DeterminesTOTAL H20 volume and water distribution body wide; promotes osmotic pressure; electrical / resting membrane potentials
Accounts for 90%- 95% of fluid osmolarity
Regulation of Na+ ions:ANP, Aldosterone, ADH
CHLORIDE (Cl-) ions are the most abundant anions in the ECF.
help maintain the resting membrane potential of the cell.
Component of bicarbonate ions during the chloride shift.
Gastric glands utilize to make hydrochloric acid in the stomach.
POTASSIUM (K+) ions - 98% found inside cells
Resting membrane potentials; repolarization; hyperpolarization
Hyperkalemia: Lowers action potential threshold in nerve and muscle cells ABNORMALLY EXCITABLE
Hypokalemia: Causes hyperpolarization; nerve and muscle cells LESS EXCITABLE
Both conditions may affect cardiac function, blood pressure, and neuromuscular interaction.
KCl used as lethal injection in high doses 1st induces sleep, 2nd respiratory failure, finally fibrillation and cardiac arrest

9. Hyperkalemia= MORE K+ in the blood.
With more K+ outside the cell more will move into the cell down the electro chemical gradient which will decrease cellular negativity and lower the threshold for action potential.
Hypokalemia= LESS K+ in the blood. With less K+ outside the cell, less will move into the cell causing an increase in the cellular negativity. The result is a higher threshold (more negative) for action potential.

10. Bicarbonate / Phosphate Ions
BICARBONATE (HCO3-) ions are the main buffer in the ECF.
HCO3- is the main form of transport of CO2 in blood plasma:
CO2 + H2O  H2CO3  HCO3- + H+
CHLORIDE SHIFT- exchange of bicarbonate (HCO3−) and chloride (Cl−) across the membrane of red blood cells (RBCs)
PHOSPHATE (PO43-) Ions
PO43- ions are found in bone, DNA, phospholipids, ATP associated to Ca2+ ions.
(HPO42−) and phosphoric acid H3PO4) act as buffers to stabilize the pH of body fluids
renal control – phosphate continually lost by glomerular filtration
parathyroid hormone
increases excretion of phosphate in urine occurs by reducing reabsorption in kidney tubule
Calcium and phosphate have an inverse relationship

11. CHLORIDE SHIFT exchange of bicarbonate (HCO3−) and chloride (Cl−) across the membrane of red blood cells (RBCs

12. Calcium (Ca2+) ions
Calcium - Ca2+most abundant ion in body; 99% of Ca2+ stored in bones as calcium phosphate; 50% bound to plasma proteins albumin
Inverse relationship between Ca and P ratio of is 2-to-1; careful balance.; as Ca2+ rises PO43- declines.
Excess amounts inside cells can results in crystallization
Structural role in bones; blood clotting, release of neurotransmitter, muscle contraction, nerve and muscle function.
Controlled by PTH and Calcitonin
calcium BLOCKS sodium channels and inhibits depolarization of nerve and muscle fibers
Hypocalcemia: Chronic renal failure; vitamin D deficiency
Lowers threshold potential for depolarization. Action potential more easily obtained resulting in OVER EXCITEMENT of nervous and muscular systems. SIMILAR TO POTASSIUM (K+)
Hypercalcemia: Due to over secretion of PTH
increased calcium RAISES the threshold (hyperpolarization) causing muscle weakness by SLOWING THE STIMULUS to muscles. A higher threshold takes longer to reach depolarization.
High levels of Ca2+ can increase secretions of gastrin. This would stimulate HCl production possibly leading to peptic ulcers

13. Acid Base Balance One of the most important aspects of homeostasis
Acid base balance achieved by controlling H+ in body fluids.
H+ homeostasis is absolutely necessary for protein structure, and blood pH (Blood pH range: 7.35 to 7.45)
pH CNS DEPRESSED –person goes into coma
pH CNS OVERSTIMULATION of respiratory muscles impairs breathing–death results from respiratory arrest.
Acids release H+ into solution; Bases remove H+ from solution
Challenges to acid-base balance:
metabolism constantly produces acid
lactic acids from anaerobic fermentation
phosphoric acid from nucleic acid catabolism
fatty acids and ketones from fat catabolism
carbonic acid from carbon dioxide
The 3 types of pH regulation:
Buffer regulation; Respiratory regulation; Renal regulation

14. Buffer Systems Buffer = Mechanism that resists changes in pH
When H+ is added, buffer removes it
When H+ is removed, buffer replaces it
Types of buffer systems
Physiological buffer- body control
urinary system- MOST EFFECTIVE but VERY SLOW respiratory system –FAST buffers within minutes but not as effective as urinary system; release in expiration or chloride shift
Chemical buffer- bind or release of H+
Protein buffer
Carbonic acid / bicarbonate ion
Phosphate buffer

15. Protein Buffer Systems
Intracellular and plasma proteins bind or release H+
Provide about 75% of the buffer capacity of the body.
Hemoglobin act as a buffer in erythrocytes.
Albumin act as a buffer in blood plasma.
Amino acids of individual proteins produce buffering capacity
pH rises [too alkaline]- the carboxyl group of amino acid releases a H+
pH drops [too acidic]- Carboxylate ion (RCOO-) and amino group accepts H+ (NH3 ammonia)
The amino group binds H+ when pH gets too low (acidic)

16. Carbonic acid / bicarbonate ion / Phosphate
Carbonic acid (H2CO3) is a weak acid: slight release of H+
Bicarbonate ion (HCO3−) is a weak base: BINDS LESS H+ forming carbonic acid, resulting in a smaller net increase in acidity ( H2CO3 = H+ + HCO3- )
Not as powerful as the protein buffer, but important for the maintenance of blood pH
Phosphate buffer system consists of anion H2PO4– (a weak acid); slight release of H+
Important buffer in renal tubules (urine).
Consists of di-hydrogen phosphate ions - (H2PO4-) as H+ donor (acid) and hydrogen phosphate ions (HPO42-) as H+ acceptor (base)
H2PO H+ + HPO42-
Provide only temporary solution to acid–base imbalance
Does not eliminate H+ ions

17. Respiratory / Renal Regulation
Neutralizes 2x to 3x as much acid as chemical buffers
RESPIRATORY regulation of pH is achieved through carbonic acid/bicarbonate buffer system
CO2 levels increase, pH decreases (acidic)
CO2 levels decrease, pH increases (basic)
Increased CO2 and decreased pH stimulate pulmonary ventilation- Hypoventilation
Increased pH inhibits pulmonary ventilation- Hyperventilation
KIDNEYS neutralize MORE ACID OR BASE THAN EITHER the respiratory system or chemical buffers by changing the rate of H+ secretion in the renal tubules

18. Acidosis Alkalosis
Respiratory acidosis pH below 7.35 to 7.45 caused by inadequate ventilation
CO2 accumulates in the ECF and lowers its pH
Respiratory alkalosis - plasma pH above 7.45
hyperventilation or CO2 eliminated faster than it is produced
Metabolic acidosis results of all conditions other than respiratory that DECREASE pH; build up of acid compounds
increased lactic acid, ketone bodies (ketoacidosis) seen in alcoholism, and diabetes mellitus
loss of base due to chronic diarrhea, laxative overuse
chronic renal insufficiency/failure- inability to remove H+
Metabolic alkalosis is the results of all conditions other than respiratory that increase pH= Rarely occurs
overuse of bicarbonates (antacids and IV bicarbonate solutions)
loss of stomach acid (chronic vomiting)