Chapter 27 Fluid, Electrolyte, and Acid-Base Balance

Describe the distribution of fluids among fluid compartments in the human body

Intracellular fluid (ICF) - 2/3 of total body water   

·  Extracellular fluid (ECF) - 1/3 of total body water   

·  Interstitial fluid - 80% of ECF   

·  Plasma - 20% of ECF

Describe the distribution of electrolytes in the human body by completing the table below

Know this

What is the percent composition of solids and liquids in males

• 60% water

• 40% solid components

What is the percent composition of solids and liquids in females

• 50% water

• 50% solid components

Homeostatic mechanisms regulate the ________ ONLY

ECF

Water moves by ____ transport ONLY

Passive

How does ADH regulate fluid and electrolyte balance

Increases H2​O conservation at the kidneys; stimulates thirst center of the hypothalamus

How does aldosterone regulate fluid and electrolyte balance

Increases conservation of Na+ (H2​O follows) and elimination of K+ at the kidneys

How does ANP regulate fluid and electrolyte balance

peptides (ANP and BNP): Promotes diuresis by opposing RAAS and inhibiting thirs

List sources of water gain

Water content of food, water consumed as liquid, metabolic generation   

List sources of water loseses

Urination, evaporation at skin, evaporation at lungs, loss in fece

What is the difference between osmolarity and tonicity

Osmolarity: Concentration of a solution; total particles per liter   

·  Tonicity: Behavior of a solution; non-penetrating particles

Given the tonicity of a solution, predict how cell volume changes

·  Isotonic - no net movement of H2​O

·  Hypotonic - net intracellular shift of H2​O

·  Hypertonic - net extracellular shift of H2​O

Predict changes in fluid balance that occur due to dehydration

Fluid shifts extracellularly, total body water decreases, osmolarity increases

Predict changes in fluid balance that occur due to hyper hydration

Fluid shifts intracellularly, total body water increases, osmolarity decreases

Determine the tonicity of fluids administered to dehydrated patients

Hypotonic fluids

Determine the tonicity of fluids administered to hyper hydrated patients

Hypertonic fluids

Over time, the ECF and ICF equilibrate and become isosmotic due to the free movement of ____. Thus, by directly monitoring and regulating the ECF, we can indirectly regulate the ICF

H2O

The concentration of an electrolyte solution is measured in units of ___

mEq/L

Convert between units of osmolarity (mmol/L) and equivalency (mEq/L)

a.      2 mmol Na⁺ is dissolved in 1 L of water. Concentration is ________

2

Convert between units of osmolarity (mmol/L) and equivalency (mEq/L)

3 mmol of Ca²⁺ is dissolved in 2 L of water. Concentration solution is ________

6

What are [Na⁺]_{ECF for normal}

135-145 mEq/L

What are [Na⁺]_{ECF for hypernatremia}

Above 145 mEq/L

What are [Na⁺]_{ECF for hyponatremia}

Bloew 135 mEq/L

Which physiological functions are affected by [Na⁺]_ECF

Membrane potential and fluid homeostasis

How does the body regulate (i) Na⁺ balance and (ii) ECF volume

·  (i) Changes in [Na+]ECF​   

· (ii) Changes in ECF volume

What are [K⁺]_ECF for normal

3.5-5.0 mEq/L

What are [K⁺]_ECF for hyperkalemia

Above 5.0 mEq/L

What are [K⁺]_ECF for hypokalemia

Below 3.5 mEq/L

Which physiological functions are affected by [K⁺]_ECF

Membrane potential and pH homeostasis

How do (i) acute and (ii) chronic hyperkalemia affect membrane excitability

Increase membrane excitability

How does hypokalemia, regardless of chronic or acute, affect membrane excitability

Decreases membrane excitability

How do (i) acidemia and (ii) alkalemia affect K⁺ balance

·  Acidemia increases K+ concentration in ECF

·  Alkalemia decreases K+ concentration in ECF

How does the body regulate K⁺ balance

Changes in [K+]ECF​, changes in pH, aldosterone

What are [Ca²⁺]_ECF for normal,

4.3 to 5.3 mEq/L

What are [Ca²⁺]_ECF for hypercalcemia

Above 5.3 mEq/L

What are [Ca²⁺]_ECF for hypocalcemia

Below 4.3 mEq/L

1.     Which physiological functions are affected by [Ca²⁺]_ECF?

• Neuromuscular excitability,

• blood clotting,

• second messenger systems,

• integrity of bones and teeth

How do (i) hypercalcemia and (ii) hypocalcemia affect membrane excitability

·  Hypercalcemia decreases membrane excitability

·  Hypocalcemia increases membrane excitability

How does the body regulate Ca²⁺ balance

PTH

What are [Mg²⁺]_ECF for normal

1.4 to 2.0 mEq/L

What are [Mg²⁺]_ECF for hypermagnesium

Above 2.0 mEq/L

What are [Mg²⁺]_ECF for hypomagnesium

Below 1.4 mEq/L

Which physiological functions are affected by [Mg²⁺]_ECF

Glucose phosphorylation within cells, use of ATP by contracting muscle fibers

Phosphate (PO₄^3-)

What are [PO₄^3-]_ECF for normal

1.8 to 3.0 mEq/L

What are [PO₄^3-]_ECF for hyperphosphatemia

Above 3.0 mEq/L

What are [PO₄^3-]_ECF for hypophosphatemia

Below 1.8 mEq/L

Which physiological functions are affected by [PO₄^3-]_ECF

Mineralization of bone, formation of high-energy compounds (like ATP), activation of enzymes through phosphorylation, synthesis of nucleic acids

What are [Cl^-]_ECF for normal

100-108 mEq/L

What are [Cl^-]_ECF for hyperchloremia

Above 108 mEq/L

What are [Cl^-]_ECF for hypochloremia

Below 100 mEq/L

Which physiological functions are affected by [Cl^-]_ECF

Fluid homeostasis, acid-base balance   

What is pH for normal

7

What is normal pH for acidic

Below 7

What is pH for alkaline

Above 7

Describe the relationships between pH, [H⁺]_ECF, and P_CO2

·  pH = -log[H+]   

· PCO2​ is a measure of the amount of CO2​, which is related to H+ concentration via the bicarbonate buffer system

The normal pH range of extracellular fluid is

7.35 to 7.45

For each change in pH by 1, [H⁺] changes by a factor of

10

As pH changes from 7 to 6, [H⁺] [increases by a factor of

10

As pH changes from 7 to 11, [H⁺] decreases] by a factor of

10,000

Define acid in terms of proton transfer

Causes a decrease in pH, typically by releasing H+   

Define base in terms of proton transfer

Causes an increase in pH, typically by accepting H+ or releasing OH−

Define acidosis in terms of pH

Conditions resulting in acidemia (pH of ECF below 7.35)   

Define alkalosis in terms of pH

Conditions resulting in alkalemia (pH of ECF > 7.45) 

What is the function of buffers

Resist changes in pH

What is the mechanism of buffers

Neutralizing acids or bases

Which two organs play very important roles in acid-base balance

Lungs and kidneys

What are the differences between volatile and non-volatile acids

·  Volatile acids can leave solution and are excreted by the lungs, while non-volatile acids cannot leave solution and are excreted by the kidneys.

What is the only volatile acid produced in the body

Carbonic acid (H2​CO3​)  

Describe mechanism and site of action for phosphate buffer system

·       (i) Mechanism: The dissociation of disodium phosphate provides additional monohydrogen phosphate for use by the buffer.   

(ii) Site of action: ICF and urine   

Describe mechanism and site of action for protein buffer system

·       (i) Mechanism: Amino acids (the building blocks of protein) are amphoteric   

·       (ii) Site of action: ICF and ECF; hemoglobin buffer system in RBCs   

Describe mechanism and site of action for carbonic acid/bicarbonate system

·      ( i) Mechanism: Sources of bicarbonate include the bicarbonate reserve and the renal deamination of Glu.   

·       (ii) Site of action: ECF 

What are limitations of the carbonic acid-bicarbonate buffer system? What can it NOT buffer

It cannot protect the ECF from changes in pH that result from increased or decreased levels of CO2​

pH imbalances are temporarily managed by

Buffer system

pH imbalances are permanently managed by

Lungs and kidneys

The lungs regulate pH by controlling

Controlling ventilation

The kidneys regulated pH by controlling

H+ sectretion

Acid-base disorders of respiratory origin are caused by

Abnormal handling of volatile acids (CO2)

Acid-base disorders of metabolic origin are caused by

abnormal handling of non-volatile acids (not CO2)

Compensation for acid-base disorders will NEVER

Fully correct the pH to the normal range

Respiratory compensation occurs at the

lungs

Renal compensation occurs at the

Kidneys

Respiratory compensation can compensate for acid-base disorders of

Metabolic origin

Renal compensation can compensate for acid-base disorders of (blank) origin

Respiratory and metabolic

Lung damage may cause

Respiratory acidosis

Kidney damage may cause

Metabolic acidosis

Hyperventilation causes

Respiratory alkalosis

Hypoventilation may cause

Respiratory acidosis

Ascent to high altitudes may cause

respiratory alkalosis

Prolonged exercise may cause

metabolic acidosis

Excessive diarrhea may cause

Metabolic acidosis

Overeating may cause

Metabolic alkalosis

Excessive vomitting may cause

Metabolic alkalosis

Respiratory compensation for respiratory acidosis

Does not occure

Respiratory compensation for respiratory alkalosis

Does not occur

Respiratory compensation for metabolic acidosis

Increase ventilation

Respiratory compensation for metabolic alkalosis

Decrease ventilation

Renal compensation for respiratory acidosis

Increase H+ secretion, Increases HCO3- reabsorption

Renal compensation for respiratory alkalosis

Increase H+ reabsorption, Increase HCO3- secretion

Renal compensation for metabolic acidosis

Increase H+ secretion, Increase HCO3- reabsorption