Chapter 16 Electrolytes Flashcards
Define intracellular fluid (ICF).
The fluid inside the cells and accounts for about two-thirds of total body water.
Define extracellular fluid (ECF).
Accounts for one-third of total body water and includes intravascular ECF (plasma) and interstitial cell fluid (surrounds the cells in tissue).
Plasma is about 93% water, what is the remaining volume made up of?
Lipids and proteins.
Define active transport.
A mechanism that requires energy to move ions across cellular membranes.
Define diffusion.
The passive movement of ions (no energy consumed) across a membrane; depends on size and charge.
Define osmolality.
A physical property of a solution that is based on the concentration of solutes per kilogram of solvent (w/w).
Osmolality is related to several changes in the properties of a solution relative to pure water, what are those changes?
Freezing point depression and decrease in vapor pressure.
Why is the measurement of osmolarity inaccurate to use in the clinical setting?
Hyperlipidemia, hyperproteinemia, urine specimens, and certain osmotically active substances can cause inaccurate results.
Which hormone is stimulated and secreted by the hypothalamus in response to an increased osmolality of blood?
Arginine Vasopressin Hormone (AVP); also termed the Antidiuretic Hormone (ADH).
Which ion(s) accounts for approximately 90% of the osmotic activity in plasma?
Sodium
How is AVP effected as a result of excess water intake?
AVP is suppressed.
How does diabetes insipidus effect AVP production?
There is either no AVP production or no ability to respond to the AVP in circulation.
The renin-angiotensin-aldosterone hormone system primarily to a decrease in what?
Blood volume.
Renin is secreted in response to decrease renal blood flow. Where is it secreted?
By the renal glomeruli.
Renin coverts the hormone ___ to ___, which then becomes ___.
Renin converts the hormone angiotensinogen to angiotensin I, which then becomes angiotensin II.
Angiotensin II causes what to happen to quickly increase blood pressure?
Vasoconstriction
What is atrial natriuretic peptide’s (ANP) role in affecting blood volume?
Promotes sodium excretion in the kidney.
Volume receptors independent of osmolality stimulate what hormone?
AVP, conserves water by renal absorption.
How does the glomerular filtration rate affect blood volume?
Increases with volume expansion and decreases with volume depletion.
What kind of samples may be measured for osmolality testing?
Serum or Urine.
Why can’t plasma be used for osmolality testing?
Substances may be introduced into the specimen from the anticoagulant.
Which cation is the most abundant in the ECF?
Sodium
The Na/K ATPase ion pump moves how many sodium ions for every two potassium ions?
Three.
The plasma sodium concentration depends greatly on what?
The intake and excretion of water.
Define hyponatremia.
A serum/plasma level less than 135 mmol/L.
What would be the major causes for decreased levels of sodium?
Increased sodium loss, increased water retention, or water imbalance.
Increased sodium loss in the urine can occur with decreased what?
Aldosterone production, diuretics, and/or ketonuria (Na lost with ketones).
When serum potassium levels are low, how does that affect sodium levels?
The renal tubules will conserve potassium and excrete sodium in exchange for the loss of the monovalent cation.
Pseudohyponatremia can occur when sodium is measured using indurect ion-selective electrodes (ISEs) in a patient who is what?
Hyperproteinemic or Hyperlipidemic.
Serum sodium levels below 120 mmol/L are considered what?
A medical emergency.
What type of specimen is acceptable for sodium measurements?
Serum, plasma, and urine.
What is the principle for ion-selective electrode (ISE) for electrolyte measurements?
One electrode has a constant potential (reference electrode), and the difference in potential between the reference and measuring electrodes can be used to calculate the “concentration” of the ion in solution.
Describe direct measurement ISE.
Provides and undiluted sample to interact with the ISE membrane.
Describe indirect measurement ISE.
A diluted sample is used for measurement.
What is one source of error with ISEs?
Protein buildup on the membrane through continuous use.
What is the major intracellular cation in the body?
Potassium,
What are some functions of potassium within the body?
Regulation of neuromuscular excitability, contraction of the heart, ICF volume, and H+ concentration.
What are three factors that influence the distribution of potassium?
(1) Na/K-ATPase pump inhibitor
(2) Insulin promoting acute ensure of K+ into the skeletal muscle and liver by increasing Na/K-ATPase activity
(3) Beta-blockers (epinephrine) promote cellular entry of potassium.
How does hyperosmolality effect potassium activity?
Causes water to diffuse from the cells, carrying potassium with the water; leads to gradual depletion of K+ if kidney function is normal.
What are some important things to keep in mind when collect for potassium measurement?
(1) If the patient’s platelet count is elevated, the potassium value may be elevated.
(2) If a tourniquet is left on the arm, or excessive hand-squeezing, potassium may escape into the plasma.
(3) Always store at room temperature.
(4) Hemolysis can cause falsely elevated results.
