Fluid Balance and Electrolytes

Fluid balance and electrolytes are important in two ways. First is they are used by the cells in various ways. Second is having the right concentrations in the right places is essential to being able to move substances from one place to another. If the balance of any electrolytes or fluid is off by too much seizurecomadeath.

Fluid Balance
So after struggeling with this I think I know why it's so hard to understand. Since tonic is the liquid part then if something is hypertonic it should have more liquid. But dehydration is hypertonic meaning there is less liquid. It's the opposite of what the term hypertonic should mean if you think it through. Just remember hypertonic means less liquid in the blood, relative to what's inside cells, and hypotonic means more. Fluid and electrolytes will move from an area of higher concentration to one of lower concentration because of diffusion. So when you are dehydrated and hypertonic fluid moves from inside the cells, there's a lot there, to the outside. Ask if you have any questions.

Glossary

ECF - Extracellular fluid. Includes blood, lymph system, interstitial spaces and body cavities like CSF. 1/3 of all body fluids.

ICF - Intracellular fluid. 2/3 kept inside cells.

Solute - The solid part of a fluid. In blood electrolytes are solutes.

Tonic - The fluid part of a liquid. In blood this is plasma.

Hypotonic - Liquid has more solvent (fluid) than solutes/solids.

Isotonic - Fluid and tonic concentrations are equal.

Hypertonic - Liquid has more solvent (fluid) than solids/solutes. In blood this means more plasma.

Difussion - Important to know. The different levels of tonicity between ECF and ICF will cause fluid and solids to shift from one to the other. This happens because difussion causes solids to move from an area of high concentration to one of lower concentration until an isotonic state is achieved.

General Types of Fluid Imbalances

Hypotonic - Hypo means less tonic means fluid. If plasma is hypotonic that means it has more water than the cell. This is counterintuitive when considering what is above but true. Since more water is in plamsa water will enter cells and electrolytes will leave if the solution given or plasma is hypotonic. Water in plasma is greater than in cells, water enters cells they expand.

Isotonic - State of equilibrium minimal movement between cell and plasma.

Hypertonic - More fluid in the cell than out. '''In a hypertonic solution or plasma fluid will leave the cells and electrolytes will enter. '''Dehydration. Cells shrink.

Specific Imbalances

Hypovolemia - Isotonic ECF loss. H2O and electrolytes both go down so body reamins isotonic. Caused by vomiting, diarrhea, internal fluid shift (burns), decreased intake.

Dehydration - Hypertonic ECF decifit. H2O is lost from plasma but not from cells. H2O leaves cells. Caused by fever, reduced ADH, hyperglycemia.

Hypotonic - This is water intoxication. Too much fluid in the plasma. Cells grow and can burst.

Isotonic Excess - Happens with CHF. Only the ECF volume is increased. Does not affect cellular size.

Electrolytes And Their Functions
These are the three electrolytes discussed for this section. This is not meant to be a comprehensive review of these electrolytes but will focus on their function during cellular action potential. what endocrine disorders can alter them, and some of the more well known manifestations of imbalances.

Calcium

Calcium is responsible for a number of functions in the body. Bone formation is the most well known. Aside from this it also has a calming function on cells when they fire, is used for cardiac function (helps regulate B/P), plays a role in muscle movement and in the brain for memory and mood.

Calcium is controled by the parathyroids. Imbalances are usually due to removal or overactive parathyroid glands. Thiazides may elevate Ca+ and Lasix may lower it. Pituitary tumore or removal will also cause imbalances. Increased phosphate levels will lower Ca+ levels.

Hypercalcemia will result in cells that do not fire often enough as it will take longer for the cells to repolarize and reach a resting state where they can again fire. This manifests as weakness, lethargy, and slowed reflexes. In cardiac funciton there will by dysrhythmias as the electrical signals will try and make cells fire before they have recovered. Cognitively it will manifest as poor memory and confusion.

Hypocalcemia will result in a shorter plateau during the action potential of a cell meaning it will fire more often. This is fatiguing for the cell and is generally seen in how it manifests. Muscles will tire easily due to increased action (chovstok (cheek) and trousseau (B/P cuff)), cramps, tetany, seizures, hyperreflexia. The heart will be tachycardiac. Mentally the person will be depressed, anxious and confused.

Sodium

Sodium has two main functions related to this section. One is to maintain fluid balance between ECF and ICF as well as being used to regulate blood pressure. Blood pressure is regulated mainly by the kidneys, Na+ plays a role here as where sodium goes water follows so by increasing or decreasing sodium excretion the kidneys can control the volume of plasma which directly affects B/P. On the cellular level Na+ is the most abuntant ECF ion. It is a conductor of electricity and during a cells action potential sodium moves from the outside of a cell to the inside which polarizes the cell causing it to fire.

Na+ levels are controlled by the kidneys. Excretion is increased or decreased mainly in response to aldosterone and antidiuretic hormone. Diabetes Mellitus, diabetes insipidus, aldosteronism, pituitary tumors, Cushing's and Addison's can all alter  sodium balance.

Hypernatremia will generally present as headache restlessness, agitation, twitching, exhaustion, polydipsia seizurecomadeath. There may also be weight gain. HTN, and pulmonary and peripheral edema if ECF volume is normal and Na+ is high.

Hyponatremia presents with irritability, personality changes, confusion, seizurecomadeath. This is water intoxication. Other signs are hypotension and tachycardia, nausea, vomiting.

Potassium

Relative to this section potassium (K+), along with sodium, plays a major role in the action potential of nerve cells. It is also involved in diabetic ketoacidosis see 241 test 1 for a link and description of potassium's role in DKA. In addition to action potential potassium is very important to cardiac conduction.

Potassium levels are controlled by the kidneys and usually move in the opposite direction of sodium. Conditions that affect sodium retention will likely have the opposite effect on potassium retention.

The function of K+ in cells is normally excitatory. Hyperkalemia will manifest as anxiety, irritability, abdominal cramps, parasthesia (tingling), diarrhea, irregular pulse and MI if high enough.

Hypokalemia will manifest as weakness, fatigue, weak pulse, bradycardia, leg cramps, polyuria and hyperglycemia (why).

The text says that as insulin is given potassium moves into cells. Important to know I think.