Chapter 21- Electrolyte-Water Balance

Balance

levels of water and electrolytes in the body remain relatively stable at all times

Water-Electrolyte dependence

change in electrolyte quantity will change water concentration

increased electrolytes decrease water concentration and vice versa

Body Fluids

found in different volumes and concentrations throughout the body in compartments

Intracellular Fluid Compartment

all the water and electrolytes that cell membranes enclose accounts for 63% of the total body water

Extracellular Fluid Compartment

all the fluid outside cells

interstitial fluid

interstitial fluid of brain / spinal cord

cerebrospinal fluid

interstitial fluid of plasma

blood cells

interstitial fluid of lymph

lymphatic vessels

Sodium and Potassium

cell membranes are impermeable to these ions, which are important in maintaining the water balance between intracellular and extracellular fluid

Extracellular Sodium Levels

Fall: water moves from outside of cell to inside, intracellular fluid will contain more ions and less water concentration

Rise: water moves out of cell

Water Balance

water intake = water output

Water Intake

water is obtained from drinking (60 %)

moist foods (30%)

metabolism (10%)

Osmoreceptors

detect increased solute concentrations and stimulate the body to feel thirst

Water output

waters lost through urine, feces, sweat, evaporation from skin, breathing

body has greatest control over water lost through urination

water reabsorption can increase the collecting ducts if water concentrations are low (ADH)

Water Balance Disorders

Dehydration

Water Intoxication

Edema

Dehydration

water output exceeds water intake

strenuous exercise, diarrhea, vomiting

Hypothermia

results from decreased sweating and confusion, delirium, and coma result from increase body temperature and waste accumulation in the blood

Water Intoxication

excessive fluid intake decreases levels of electrolytes in the body

Edema

abnormal accumulation of extracellular fluid in the interstitial spaces

causes decreased plasma protein levels, obstructions in lymphatic vessels, increased venous pressure, and increased capillary permeability (inflammation)

Electrolyte Intake / Output

person obtains sufficient electrolytes from diet

electrolyte deficiency causes strong salt craving

body loses electrolytes through sweat, feces, and urine

Regulation of Electrolyte Output

sodium accounts for 90% of the positively charged ions in extracellular fluid

Low Sodium Levels

aldosterone released from adrenal glands

sodium ions reabsorbed from distal convoluted tubule of nephron

Parathyroid hormone PTH

glands of the neck release PTH when calcium levels are low to increase rate of calcium absorption from the intestines, kidneys, and bones

Concentrations of Ions

Sodium: Na+

Potassium: K+

Calcium: Ca+2

appropriate concentration vital for nerve impulse conduction, muscle fiber contraction, and cell membrane permeability

changes are life threatening, causing cardiac arrythmias and impaired neural function

Acid-Base Balance

regulation of hydrogen ion concentration of body fluid

changes in hydrogen ion concentrations alter the rate of enzyme-controlled metabolic reactions

internal environment is between pH 7.35-7.45

deviation is deadly

Regulation of Hydrogen Ion Concentration

Three ways to eliminate waste from body

1. acid-base buffer systems

2. respiratory excretion of CO2

   1. Renal Excretion of H+

Acid-Base Buffer System

resists changes in pH by neutralizing added acids or bases

Buffers

substances that stabilize the pH of a solution (preventing increase in acid and base)

Bicarbonate Buffer System

carbonic acid is produced in body fluids when CO2 reacts with water

Carbonic Acid H2CO3

weak acid that acts as a buffer

more acidic: carbonic acid gives H+

Bicarbonate HCO3−H

more basic: bicarbonate takes H+

Protein Buffer System

amino acids have acidic and basic groups on their structure

plasma proteins (albumin and hemoglobin) can take up excess H+ or donate H+ when needed