Fluids & Electrolytes

Anatomy & Physiology

• Necessary to maintain health and function in all body systems. 
• Vital to life and adequate balance is imperative to maintain healthy funcitoning of the body.
• Maintains homeostasis

• Transports nutrients to cells and waste from cells.
• Transports hormones, enzymes, blood platelets, and red and white blood cells throughout the body.
• Facilitates cellular metabolism and proper cellular chemical functioning.
• Acts as a solvent for electrolytes and nonelectrolytes.
• Helps maintain body temperature.
• Failitates digestion and promotes elimination.
• Acts as a tissue lubricant.

Intracellular Fluid (ICF): Fluid within the cells.

Extracellur Fluid: Fluid outside the cells.

Extracellular Fluid (ECF) has 2 major areas: The intravascular and the intersitial compartments

A minor area: The transcellular fluids

Definitions:

1. Major area: Intravascular fluid, or Plasma, is the liquid component of blood (Fluid found within the vascular system) (4% of body weight)
2. Major area: Interstitial fluid is fluid that surrounds cells and includes lymph. (16% of body weight)
3. Minor area: Trancellular Fluids include cerebrospinal, pericardial, synovial, intraocular, and pleural fluids, as well as sweat and digestive secretions.

Normal fluid range is 50% to 60% of the body's weight depending on such factors as the person's age, body fat, and gender.

Examples:

• Infants have more total body fluid and ECF than adults. ECG is more easily lost from the body than ICF. Infants are more prone to fluid volume deficits.
• Fat cells contain little water. The more obese a person is the smaller the percentage of total body water when compared to body weight. 
• Women have more body fat than men do, also have less body fluid than men.

• Obtains water from several sources: Ingested liquids, food, and as a by-product of metabolism.

Metabolism: water is an end product of the oxidation that occurs during the metabolism of food substances, specifically carbohydrates, fats, and proteins.

The thirst mechanism located within the hypothalamus.

The thirst control center is stimulated by intracellular dehydration and decreased blood volume.

Fluid is lost from the body through sensible and insensible losses.

Definitions:

1. Sensible losses can be measured and include fluid lost during urination, defecation, and wounds.
2. Insensible losses can't be measured or seen and incluid fluid lost during evaporation through the skin and as a water vapor from the lungs during respiration.

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Kidneys (Urine Output):

• Regulates ECF volume and osmolality by selective retention and excretion of body fluids. 
• Regulates electrolyte levels in the ECF by selective retention of needed substances and excretion of unneeded substances. 
• Regulates pH of ECF by excretion or retention of hydrogen ions.
• Excrete metabolic wastes (Primarily acids) and toxic substances.

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Heart & Blood Vessels (Moves Fluids):

• Responsible for pumping and carrying nutrients and water throughout the body.
• Circulates blood through the kidneys under sufficient pressure for urine to form (Pumping action of the heart)

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Lungs (Maintains pH):

• Expires 400mL/day
• Regulates O2 and CO2 levels of the blood. Regulation of the CO2 is crucial in maintaing acid-base balance. 
• Acts promptly to correct metabolic acid-base disturbances; regualtes hydrogen ion concentration (pH) by controlling the level of CO2 in the ECF as follows:

1. Metabolic Alkalosis causes hypoventilation, resulting in CO2 retention (Increases acidity of the ECF)
2. Metabolic Acidosis causes hyperventilation, resulting in CO2 excretion (Decreases acidity of the ECF)

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Adrenal Glands (secretes aldosterone-located on top of kidneys):

• Regulates blood volume and sodium and potassium balance by secreting aldosterone, a mineral corticoid secreted by the adrenal cortex. 

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Pituitary Gland:

(p. 1419)

• Stores and releases the antidiuretic hormone, ADH, which makes the body retain water; functions of ADH include:

1. Maintains osmotic pressure of the cells by controlling renal water retention or excretion.
• When osmotic pressure of the ECF is greater than that of the cells (hypernatermia-excess sodium-or hyperglycemia), ADH secretion is increased, causing renal retention of water.
1. Controls blood volume (less influential than aldosterone)
• When blood volume is decreased, an increased secretion of ADH results in water conservation.

Neurons, called Osmoreceptors, are sensitive to changes in the concentration of ECF, sending impulses to the pituitary gland to release ADH or inhibit its release to mainain ECF volume concentration.

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Nervous System (Regulates Fluids/Electrolytes):

• Inhibits and stimulates mechanisms influencing fluid balance; acts chiefly to regulate sodium and water intake and excretion.
• Regulates oral intake by sensing ICF dehydration, which triggers thirst. *ADH from the hypothalmus stimulates thirst.

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Parathyroid Glands (Causes excretion of Phosphates):

• Regulates calcium and phosphate balance by means of parathyroid hormone (PTH).
• PTH draws calcium into the blood from the bones, kidneys, and intestines. It also facilitates the mvmt of phosphorous from the blood to the kidneys, where it's excreted in the urine.

Organs of Homeostasis that Maintains Normal Volume of body Fluids

Thyroxine:

• Released by the Thyroid gland.
• Increases blood flow in the body, leading to increased renal circulation and resulting in increased glomerular filtration and urinary output. 

Organs of Homeostasis that Maintains Normal Volume of body Fluids

GI Tract:

• Absorbs water and nutrients that enter the body through this route. 
• 100-200mL is lost in normal circumstances. Diarrhea can increase the output.

Substances that are capable of breaking into particles called ions. An ion is an atom or molecule carrying an electrical charge. 

*Molecules in the body that remain intact, without a charge, are called nonelectrolytes. Examples: Urea and glucose

• Positive charged ion.
• Major Cations in the body fluid: Sodium, potassium, calcium, hydrogen, magnesium

• Negative Charge
• Major Anions in body fluid: Chloride, bicarbonate, phosphate

Liquids that hold a substance in solution

Water is the primary solvent in the body.

Substances that are dissolved in a solution.

Solutes are electrolytes and nonelectrolytes.

Electrolytes

ICF vs ECF Values

 Intracelluar Fluid

• Na 10
• K 150
• Mg 40
• Bicarbonate 10
• Phosphate 40
• Proteinate 40 

Electrolytes

ICF vs ECF Values

Extracellular Fluid

• Na 142
• K 5
• Ca 5
• Mg 2
• Cl 103
• Bicarbonate 26
• Phosphate 17
• Sulfate 1
• Org Acids 5
• Proteinate 17

• The unit of measure the describes the chemical activity of electrolytes. 
• One mEq of either a cation or an anion is chemically equivalent to the activity of 1mg of H. Therefore, 1 mEq of any cation is equivalent to 1 mEq of any anion.
• The total cations in the body are normally equal to the the total # of anions, maintaining homeostasis.
• **When electrolytes aren't balanced, the person is at risk for alterations in health.

Major Electrolytes: 

Sodium:

• Chief electrolyte of ECF; primarily influence outside cell
• Normal Range: 135-145 mEq/L
• Controls and regulates ECF volume
• Important in regulation of acid-base balace as sodium bicarbonate. *Bicarbonate-main buffer in body. W/out it we die.
• Transported out of the cell by the sodium potassium pump.
• **where sodium goes water follows.

Major Electrolyes

Potassium

• Major cation of ICF; primarily influence inside cell
• Normal serum concentration: 3.5-5.0 mEq/L
• Assists in regulationof acid-base balance by cellular exchange with H.
• Regulated by aldosterone.

Major Electrolytes

Calcium

• Most abundant electrolyte in the body; major component of bones and teeth
• Major role in transmitting nerve impulses (heart)
• Role in blood coagulation
• Activates enzymes that stimulate essential chemical reactions in the body.

Major Electrolytes

Magnesium:

• Second most abundant ICF cation after potasium
• Normal serum concentration: 1.3-2.3 mEq/L
• Is important for the metabolism of carbohydrates and proteins.

Major Electrolytes

Chloride:

• Major ECF anion.
• Acts with sodium to maintain the osmotic pressure.

Major Electrolytes

Bicarbonate:

Major Electrolytes

Phosphate:

• A major ICF anion
• A buffer anion in both ICF & ECF
• Helps maintain the body's acid-base balance as a hydrogen buffer.

• Major method of transporting body fluids.
• Movement of water from lower solute concentration to a higher solute concentration to equalize concentrations on both sides of the semi permeable membrane
• Depends upon:Temp of solution, Electrical charge, Difference of osmotic pressure

Isotonic

(neutral/ balanced)

A solution that has the same concentration of particles, or osmolarity, as plasma (b/t 275 & 295 mOsm/l). 

Remains in the intravascular compartment without any net flow accross the semipermeable membrane.

Hypertonic

(talking abt outside cell-H2O from inside cell to outside-causing cell to shrink)

Has greater osmolarity than plasma (>295 mOsm/L).

Because it has a greater osmolarity, water moves out of the cells and is drawn into the intravascular compartment, causing the cells to shrink.

Hypotonic

(talking abt outside cell-H20 moves into cell-causing to swell)

Has less osmolarity than plasma (<275 mOsm/L).

Because of a lower osmolarity, a hypotonic solution in the intravascular space moves out of the intravascular space and into intracellular fluid, causing the cells to swell & possibly burst.

Diffusion

("Coasting downhill")

• Mvmt of solute in solution across semipermeable membrane.
• Moves from an area of higher concentration to an area of lower concentration until equilibrium is established.
• Diffusion occurs in the lungs b/t O2 and CO2. 

Active Transport

("Pumping uphill")

• A process that requires energy for the mvmt of substances through a cell membrane from an area of lesser solute concentration to an area of higher solute concentration.
• Adenosine triphosphate or ATP, stored in cells, supplies energy for solute mvmt in & out of the cell.
• The energy requirements for active transport are affected by characteristics of the cell membrane, specific enzymes, & concentration of ions. 
• Glucose uses insulin to transport across the cell membrane.

• The passage of fluid through a permeable membrane.
• Passage from an area of high pressure to low pressure.
• Ex: Capillary filtration results from the force of blood "pushing" against the walls of the capillaries. 
• "Pushing force" is called Hydrostatic pressure. When the hydrostatic pressure inside the capillary exceeds the surrounding interstital space, fluids & solutes are forced out of the capillary wall into the intersitial space. In contrast, when the pressure inside the capillary is less than the pressure in the intersitial space, the fluids & solutes will move back into the capillary.

Filtration (Cont.)

Colloid Osmotic Pressure

(Oncotic Pressure)

• Plasma proteins, particularly albumin, concentrated in the intravascular space or plasma facilitate the reabsorption process by "pulling" the fluid back into the capillaries.