Chapter 16 Electrolytes

Question 1

Define intracellular fluid (ICF).

Answer 1

The fluid inside the cells and accounts for about two-thirds of total body water.

Question 2

Define extracellular fluid (ECF).

Answer 2

Accounts for one-third of total body water and includes intravascular ECF (plasma) and interstitial cell fluid (surrounds the cells in tissue).

Question 3

Plasma is about 93% water, what is the remaining volume made up of?

Answer 3

Lipids and proteins.

Question 4

Define active transport.

Answer 4

A mechanism that requires energy to move ions across cellular membranes.

Question 5

Define diffusion.

Answer 5

The passive movement of ions (no energy consumed) across a membrane; depends on size and charge.

Question 6

Define osmolality.

Answer 6

A physical property of a solution that is based on the concentration of solutes per kilogram of solvent (w/w).

Question 7

Osmolality is related to several changes in the properties of a solution relative to pure water, what are those changes?

Answer 7

Freezing point depression and decrease in vapor pressure.

Question 8

Why is the measurement of osmolarity inaccurate to use in the clinical setting?

Answer 8

Hyperlipidemia, hyperproteinemia, urine specimens, and certain osmotically active substances can cause inaccurate results.

Question 9

Which hormone is stimulated and secreted by the hypothalamus in response to an increased osmolality of blood?

Answer 9

Arginine Vasopressin Hormone (AVP); also termed the Antidiuretic Hormone (ADH).

Question 10

Which ion(s) accounts for approximately 90% of the osmotic activity in plasma?

Answer 10

Sodium

Question 11

How is AVP effected as a result of excess water intake?

Answer 11

AVP is suppressed.

Question 12

How does diabetes insipidus effect AVP production?

Answer 12

There is either no AVP production or no ability to respond to the AVP in circulation.

Question 13

The renin-angiotensin-aldosterone hormone system primarily to a decrease in what?

Answer 13

Blood volume.

Question 14

Renin is secreted in response to decrease renal blood flow. Where is it secreted?

Answer 14

By the renal glomeruli.

Question 15

Renin coverts the hormone ___ to ___, which then becomes ___.

Answer 15

Renin converts the hormone angiotensinogen to angiotensin I, which then becomes angiotensin II.

Question 16

Angiotensin II causes what to happen to quickly increase blood pressure?

Answer 16

Vasoconstriction

Question 17

What is atrial natriuretic peptide’s (ANP) role in affecting blood volume?

Answer 17

Promotes sodium excretion in the kidney.

Question 18

Volume receptors independent of osmolality stimulate what hormone?

Answer 18

AVP, conserves water by renal absorption.

Question 19

How does the glomerular filtration rate affect blood volume?

Answer 19

Increases with volume expansion and decreases with volume depletion.

Question 20

What kind of samples may be measured for osmolality testing?

Answer 20

Serum or Urine.

Question 21

Why can’t plasma be used for osmolality testing?

Answer 21

Substances may be introduced into the specimen from the anticoagulant.

Question 22

Which cation is the most abundant in the ECF?

Answer 22

Sodium

Question 23

The Na/K ATPase ion pump moves how many sodium ions for every two potassium ions?

Answer 23

Three.

Question 24

The plasma sodium concentration depends greatly on what?

Answer 24

The intake and excretion of water.

Question 25

Define hyponatremia.

Answer 25

A serum/plasma level less than 135 mmol/L.

Question 26

What would be the major causes for decreased levels of sodium?

Answer 26

Increased sodium loss, increased water retention, or water imbalance.

Question 27

Increased sodium loss in the urine can occur with decreased what?

Answer 27

Aldosterone production, diuretics, and/or ketonuria (Na lost with ketones).

Question 28

When serum potassium levels are low, how does that affect sodium levels?

Answer 28

The renal tubules will conserve potassium and excrete sodium in exchange for the loss of the monovalent cation.

Question 29

Pseudohyponatremia can occur when sodium is measured using indurect ion-selective electrodes (ISEs) in a patient who is what?

Answer 29

Hyperproteinemic or Hyperlipidemic.

Question 30

Serum sodium levels below 120 mmol/L are considered what?

Answer 30

A medical emergency.

Question 31

What type of specimen is acceptable for sodium measurements?

Answer 31

Serum, plasma, and urine.

Question 32

What is the principle for ion-selective electrode (ISE) for electrolyte measurements?

Answer 32

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.

Question 33

Describe direct measurement ISE.

Answer 33

Provides and undiluted sample to interact with the ISE membrane.

Question 34

Describe indirect measurement ISE.

Answer 34

A diluted sample is used for measurement.

Question 35

What is one source of error with ISEs?

Answer 35

Protein buildup on the membrane through continuous use.

Question 36

What is the major intracellular cation in the body?

Answer 36

Potassium,

Question 37

What are some functions of potassium within the body?

Answer 37

Regulation of neuromuscular excitability, contraction of the heart, ICF volume, and H+ concentration.

Question 38

What are three factors that influence the distribution of potassium?

Answer 38

(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.

Question 39

How does hyperosmolality effect potassium activity?

Answer 39

Causes water to diffuse from the cells, carrying potassium with the water; leads to gradual depletion of K+ if kidney function is normal.

Question 40

What are some important things to keep in mind when collect for potassium measurement?

Answer 40

(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.