1470001     3.7               1470002        3.8                  1470003      3.6            1470004        3.7

1470005     3.6                1470007       3.5                  1470008      3.2             1470056       4.3

1470057     4.7                1470058       3.5                  1470059      3.9             1470063       3.7

1470064     3.6                1470066       4.0

GOD BLESS YOU!

1480942     3.6                  1480990       3.6                1480991     3.0            1481004       3.5

1481023     3.9                  1481024       4.0                1481025     4.2            1481029        3.0

1481030     3.1                  1481033       3.2                1481034     3.1            1481035        4.2

1481036     3.4                  1481037       3.7                1481039     3.9             1481040       3.4

1481044     3.8                  1481046       3.6                 1481048    3.5             1481049       3.2

1481031     3.6              NO ESTAN EN LISTA        NIÑO RONDON   3.6        VERGARA  MARIN     3.6

GOD BLES YOU!!

Yvette C. Terrie , BSPharm, RPh

Pathophysiology

Although the exact etiology of AD still is unknown, research suggests that it can be attributed to both inherited and environmental factors. The 3 standard neuropathologic features of AD include amyloid plaques; neurofibrillary tangles; and a third factor, which has been described only in the last 3 decades—synaptic and neuronal cell death that involves a progressive or gradual loss of connections between neurons.^6,8,9 As the death of the neurons progresses and spreads through the brain, brain atrophy occurs in the affected areas.⁹ Whereas researchers have known about these features of AD for several years, they are still learning more about them and their roles in the development and progression of AD. The progression of AD often is unpredictable, and the severity varies from patient to patient.

There are 2 distinct forms of AD: (1) familial and (2) sporadic.¹⁰ Familial AD is considered very rare and typically occurs before the age of 60. It also is referred to as early-onset AD. Less than 5% of the cases are early-onset, and this form is believed to be caused by gene mutations on chromosomes 1, 14, and 21.^10,11

As for sporadic AD, genes may not be the direct cause of the disease but may influence the risk of developing it. Sporadic AD also is referred to as lateonset AD, because many cases occur in individuals after the age of 60, with the vast majority in their 70s and 80s.^10,11 There are, however, exceptions to thegeneral observations regarding age at onset.

The apolipoprotein E (apo E) gene, which is found on chromosome 19, is the best studied susceptibility gene in sporadic AD.¹⁰ The apo E gene is responsible for the manufacturing of a protein that moves cholesterol and other fats throughout the body.¹⁰ It is postulated that this protein may be involved in the structure and function of the fatty membrane that surrounds a brain cell.¹⁰ The apo E gene occurs in many forms or alleles. The 3 forms that occur most frequently are apo E-II, apo E-III, and apo EIV.^10-12 Furthermore, the apo E-IV gene may increase an individual’s chance of developing late-onset AD. It is estimated that between 35% and 50% of individuals with AD carry some form of the apo E-IV gene.¹⁰

Risk Factors

Current research indicates that AD may be triggered by several factors, including age, genetics, serious head injuries, and inflammation of the brain, as well as environmental factors. Age is the most well-documented risk factor. Other possible risk factors include the following^13-15:

• Down’s syndrome
• Head injury
• Diabetes mellitus
• Hypertension
• Hypercholesterolemia
• Hyperglycemia
• Family history
• Sedentary lifestyle
• Diets high in saturated fat

Signs and Symptoms

Recognizing the warning signs associated with the development of AD is crucial in order to initiate early intervention, as well as to differentiate AD from other forms of dementia. In many cases, an individual’s symptoms may progress gradually over time and may not be obvious initially. Patients may exhibit cognitive or intellectual symptoms, such as acalculia (inability to perform simple mathematical calculations), aphasia (inability to communicate effectively), apraxia (inability to perform daily activities such as brushing teeth or combing hair), amnesia, and agnosia (loss of the ability to interpret sensory stimuli) as the disease progresses. Behavioral signs and symptoms—such as depression, apathy, and anxiety—typically are present in the early stages, and delusions, hallucinations, and psychosis are prevalent during the latter stages.^16,17 In the advanced stages, individuals also may present with extrapyramidal symptoms, such as gait disturbance, myoclonus, tremor, and urinary incontinence.¹⁶

Potential Warning Signs

Some warning signs of AD are as follows¹⁶:

• Memory loss that may affect job performance
• Difficulty in performing routine, familiar tasks
• Difficulty or problems with speech
• Decrease in judgment skills
• Difficulty with abstract thinking
• Disorientation as to time and place
• Difficulty in finding objects or misplacing items
• Changes in mood, personality, or behavior, such as agitation, aggression, and hallucinations
• Loss of initiative or motivation
• Impaired memory or thinking
• Impaired visual or spatial skills

Stages

Because AD progresses in severity over time, the disease generally is characterized by the following stages: mild, moderate, and severe. During the mild stage, the individual may start to experience some memory loss, which may be insignificant enough that others may not notice a problem. Short-term memory usually is affected first.

As the disease progresses from mild to moderate, the signs may become more noticeable to family and friends, because the patient may exhibit difficulty in self-care and in accomplishing everyday tasks. At this stage, some behavioral changes often are noted, such as frustration, anger, and anxiety. Usually at this stage, the need for caregiver assistance may become essential for the safety of the individual.

In the severe stage of AD, individuals typically are characterized as being solely dependent on the caregiver. Some patients in this stage may experience loss of bladder and bowel control and episodes of aggression. Table 1 lists, for each stage of AD, behavioral and cognitive changes as well as how the disease may affect the individual’s daily routine.

The Role of the Pharmacist

In almost every area of pharmacy practice, pharmacists are very likely to encounter a patient with AD and/or a caregiver. Therefore, it is imperative for pharmacists to keep abreast of new developments in research and pharmacologic therapies regarding the disease.

Pharmacists can be a vital resource for both patients and their caregivers, thereby improving quality of life. A comprehensive understanding of the etiology, pathophysiology, and stages of AD, as well as pharmacologic therapy, is imperative to provide effective care to the patient.

Pharmacists can assist patients with AD through monitoring drug regimens for potential drug interactions as well as possible contraindications. More importantly, pharmacists always should try to demonstrate empathy toward patients with AD and their caregivers, keeping them informed about new developments in the fight against this condition and suggesting resources of information for them.

Caring for a patient with AD involves more than drug treatment. Caregivers should be encouraged to join a local support group and to take care of themselves and seek assistance when warranted.

During counseling, pharmacists can provide patients and their caregivers with various suggestions for techniques that may aid in the management of AD, such as the use of memory aids or schedules. Examples of memory aids include a list of daily routines, important telephone numbers in case of an emergency, and instructions on how to perform various tasks. In addition, pharmacists can make recommendations for creating a safe environment and establishing an exercise routine, if appropriate.⁴⁴

El “Present Continuous” (Presente Continuo) lo utilizamos cuando queremos hablar de acciones que están ocurriendo “ahora” o, en un tiempo cercano a “ahora” o, que no han terminado.
Por ejemplo: Estoy comiendo (I’m eating) o, estoy leyendo un libro (I’m reading a book). En este último caso, te refieres a una acción inacabada, no a que estás leyendo el libro en el momento en que hablas.

Ejemplo 1: I am (I’m) working . Yo estoy trabajando.

Ejemplo 2: She is (She’s)studying . Ella está estudiando.

Ejemplo 3. It is (It’s) working . Está funcionando.

Ejemplo 4: They are (They’re) looking . Ellos/Ellas están mirando.

Problemas que presenta el Present Continuous: En teoría es un tiempo muy sencillo de dominar. No obstante, dado que a veces en español utilizamos el “Presente” para hablar de algo que ocurre en el momento en que hablamos, en inglés cometemos el error de utilizar el “Presente” cuando deberíamos utilizar el “Present Continuous”.

Por ejemplo, decimos: “She comes” , cuando deberíamos decir: “She’s coming” . (Ella viene). Es verdad que en inglés hay algunos verbos que no se conjugan en “Present Continuous”, por ejemplo, “want”  (querer), pero son pocos.

¿Cómo se pregunta con el “Present Continuous”?

Estructura preguntas: Verbo + sujeto + verbo principal terminado en “ing”+?

Ejemplo: Is she working?  ¿Está ella trabajando

¿Cómo se niega con el “Present Continuous?

Estructura negación: Sujeto + verbo “to be” en presente + not + verbo principal terminado en “ing”.

Ejemplo: She is not (isn´t)working . Ella no está trabajando.
Repaso de las estructuras:

Positivo	Sujeto+ Verbo”to be” en presente+VP terminado en “ing”. You are (You’re)working.
Negativo	Sujeto + Verbo “to be”en presente +not+VP terminado en“ing”. You are not (aren’t) working.
Pregunta	Verbo “to be” en presente+ Sujeto+ VP terminado en “ing”+?Are you working?

FORM[am/is/are + present participle]

Examples:

• You are watching TV.
• Are you watching TV?
• You are not watching TV.  

USE 1 Now

 Use the Present Continuous with Normal Verbs to express the idea that something is happening now, at this very moment. It can also be used to show that something is not happening now.

USE 2 Longer Actions in Progress Now

In English, “now” can mean: this second, today, this month, this year, this century, and so on. Sometimes, we use the Present Continuous to say that we are in the process of doing a longer action which is in progress; however, we might not be doing it at this exact second.

USE 3 Near Future

Sometimes, speakers use the Present Continuous to indicate that something will or will not happen in the near future.

USE 4 Repetition and Irritation with “Always”

The Present Continuous with words such as “always” or “constantly” expresses the idea that something irritating or shocking often happens. Notice that the meaning is like Simple Present, but with negative emotion. Remember to put the words “always” or “constantly” between “be” and “verb+ing.”

REMEMBER Non-Continuous Verbs/ Mixed Verbs

It is important to remember that Non-Continuous Verbs cannot be used in any continuous tenses. Also, certain non-continuous meanings for Mixed Verbs cannot be used in continuous tenses. Instead of using Present Continuous with these verbs, you must use Simple Present.

ADVERB PLACEMENT

The examples below show the placement for grammar adverbs such as: always, only, never, ever, still, just, etc.

ACTIVE / PASSIVE

Examples:

ACTIVITY

Simple Present / Present Continuous

3. Shhhhh! Be quiet! John (sleep)________ .

4. Don’t forget to take your umbrella. It (rain)________ .

5. I hate living in Seattle because it (rain, always)_________ .

6. I’m sorry I can’t hear what you (say)______ because everybody (talk)______ so loudly.

7. Justin (write, currently)_____________ a book about his adventures in Tibet. I hope he can find a good publisher when he is finished.

8. Jim: Do you want to come over for dinner tonight?
Denise: Oh, I’m sorry, I can’t. I (go)_______ to a movie tonight with some friends.

9. The business cards (be, normally )________ printed by a company in New York. Their prices (be) ______inexpensive, yet the quality of their work is quite good.

10. This delicious chocolate (be)_________ made by a small chocolatier in Zurich, Switzerland.

Are We Speaking the Same Language?

Michael J. Gaunt, PharmD

Dr. Gaunt is a medication safety analyst and the editor of ISMP Medication Safety Alert! Community/Ambulatory Care Edition.

electr-images1

You might have been wondering how electrons can continuously flow in a uniform direction through wires without the benefit of these hypothetical electron Sources and Destinations. In order for the Source-and-Destination scheme to work, both would have to have an infinite capacity for electrons in order to sustain a continuous flow! Using the marble-and-tube analogy, the marble source and marble destination buckets would have to be infinitely large to contain enough marble capacity for a “flow” of marbles to be sustained.

The answer to this paradox is found in the concept of a circuit: a never-ending looped pathway for electrons. If we take a wire, or many wires joined end-to-end, and loop it around so that it forms a continuous pathway, we have the means to support a uniform flow of electrons without having to resort to infinite Sources and Destinations:

each electron advancing clockwise in this circuit pushes on the one in front of it, which pushes on the one in front of it, and so on, and so on, just like a hula-hoop filled with marbles. Now, we have the capability of supporting a continuous flow of electrons indefinitely without the need for infinite electron supplies and dumps. All we need to maintain this flow is a continuous means of motivation for those electrons, which we’ll address in the next section of this chapter.

It must be realized that continuity is just as important in a circuit as it is in a straight piece of wire. Just as in the example with the straight piece of wire between the electron Source and Destination, any break in this circuit will prevent electrons from flowing through it:

An important principle to realize here is that it doesn’t matter where the break occurs. Any discontinuity in the circuit will prevent electron flow throughout the entire circuit. Unless there is a continuous, unbroken loop of conductive material for electrons to flow through, a sustained flow simply cannot be maintained.

·         REVIEW:

·         A circuit is an unbroken loop of conductive material that allows electrons to flow through continuously without beginning or end.

·         If a circuit is “broken,” that means it’s conductive elements no longer form a complete path, and continuous electron flow cannot occur in it.

·         The location of a break in a circuit is irrelevant to its inability to sustain continuous electron flow. Any break, anywhere in a circuit prevents electron flow throughout the circuit.

Voltage and current in a practical circuit

Because it takes energy to force electrons to flow against the opposition of a resistance, there will be voltage manifested (or “dropped”) between any points in a circuit with resistance between them. It is important to note that although the amount of current (the quantity of electrons moving past a given point every second) is uniform in a simple circuit, the amount of voltage (potential energy per unit charge) between different sets of points in a single circuit may vary considerably:

Take this circuit as an example. If we label four points in this circuit with the numbers 1, 2, 3, and 4, we will find that the amount of current conducted through the wire between points 1 and 2 is exactly the same as the amount of current conducted through the lamp (between points 2 and 3). This same quantity of current passes through the wire between points 3 and 4, and through the battery (between points 1 and 4).

However, we will find the voltage appearing between any two of these points to be directly proportional to the resistance within the conductive path between those two points, given that the amount of current along any part of the circuit’s path is the same (which, for this simple circuit, it is). In a normal lamp circuit, the resistance of a lamp will be much greater than the resistance of the connecting wires, so we should expect to see a substantial amount of voltage between points 2 and 3, with very little between points 1 and 2, or between 3 and 4. The voltage between points 1 and 4, of course, will be the full amount of “force” offered by the battery, which will be only slightly greater than the voltage across the lamp (between points 2 and 3).

This, again, is analogous to the water reservoir system:

Between points 2 and 3, where the falling water is releasing energy at the water-wheel, there is a difference of pressure between the two points, reflecting the opposition to the flow of water through the water-wheel. From point 1 to point 2, or from point 3 to point 4, where water is flowing freely through reservoirs with little opposition, there is little or no difference of pressure (no potential energy). However, the rate of water flow in this continuous system is the same everywhere (assuming the water levels in both pond and reservoir are unchanging): through the pump, through the water-wheel, and through all the pipes. So it is with simple electric circuits: the rate of electron flow is the same at every point in the circuit, although voltages may differ between different sets of points.

Basic Electrical Concepts

Charge

 Electricity is a rather multi-faceted subject and a good understanding of the basics is important. We begin with a “SCI200″ review of charge. Charge is a basic property possessed by electrons and protons. Charge comes in two types, negative (the type on an electron) and positive (the type on a proton.) Opposite charges attract and like charges repel one another. Atoms are formed by light, negatively-charged electrons orbiting around positively-charged protons in the much heavier nucleus. In general, matter has equal numbers of protons and electrons and is neutral overall. An object becomes charged only when electrons are added to or stripped away from the object.

Current

Generally, a current is any movement or flow of charge. In household applications, it is specifically the movement of electrons through wires and electrical devices. There are several factors that determine the flow of current. First, we classify all substances into two broad categories, according to how well current can flow through them.

Insulators are substances in which all the electrons in the atoms of the substance are tightly bound. The electrons do not easily move from one atom to the next. It is very difficult to get current to flow through insulators. Examples of insulators include: ceramics, rubber, plastic, and surprisingly, pure water.

Conductors are those substances in which the outer electrons (typically only one or two in each atom) can move freely from one atom to the next. Current flows easily through conductors. Examples of conductors include: metals such as copper, iron, aluminum, and water‹that contains a lot of dissolved minerals.

Although most substances are easily classified as one or the other, there is no absolute dividing line between insulators and conductors. There are substances which lie somewhere in between. Semi-conductors, important for electronics, are an important example. The glowing filaments in light bulbs and toasters are often classified as conductors, but they are actually not very good conductors. As we will see below, they shouldn’t be. The electrical wiring in the walls of your home and the power cords for electrical devices, such as lamps and refrigerators, are much better conductors.

Consider the diagram of a conducting wire, in which a few of the outer electrons are shown. A current (denoted I) exists in the wire as the electrons move along the wire. (Note that the wire stays neutral as current flows. As one electron jumps to a neigboring atom, another moves in to take its place.) The more charge that passes per unit time, the greater the current. The idea is simple. Current is a measure of the number of electrons that flow past any point along the wire during any time interval, divided by that time interval.

I    =    ^charge / _time

The units of current are amperes or just amps (denoted A). One amp represents a flow of about 6 x 10¹⁸ electrons per second! Is one amp a lot of current? Despite the incredible number of electrons per second, one ampere is roughly the amount of current that flows in the common household 100 Watt incandescent light bulb. It is also roughly the amount of current that flows in small flashlight. Are you surprised? There’s more to learn.

Electric Potential

Electric potential is what drives current. You may know electric potential by another term that we will use … voltage. This name comes from the unit of potential, which is the volt (denoted V). When you buy an AA battery, you are buying a device that provides a potential of 1.5 V between its positive and negative terminals. Your car battery maintains about 12 V between its terminals. And the potential between the two slots in a household electrical outlet is about 120 V. (Although not important here, the different nature of the potential of the outlet will be considered in the AC section.) You are probably already familiar with a basic truth about electric potential. All other things being equal, a greater potential will create a greater current. But what is electric potential?

 Water can provide a good analogy (although far from perfect!) for both current and potential. Consider a pipe that comes out of the bottom of a large tank of water, such as shown above. You open the spigot and water flows. The flow rate of the water is analogous to current. Common sense tells you that the higher the water level in the tank, the higher the flow rate in the pipe. (We will investigate this further in the Plumbing module!) The height of the water level is analagous to electric potential. A greater potential will cause a greater current.

Where this analogy fails is with the battery. The tank stores water and as the height slowly decreases, so does the water flow. A battery does not store charge! It is always electrically neutral and for whatever amount of charge leaves one terminal, an equal amount must come into the other. (As we will see in the next section, a complete circuit is required for this to happen.) A battery is more analogous to the water pump shown in Figure 1-3. A battery, therefore, is an electron pump! It has the ability to push electrons directly proportional to its voltage rating. And, it does this through a chemical reaction. The battery becomes “discharged,” (an unfortunately misleading term), when the chemicals in the battery are used up. Most batteries maintain a fixed potential until near the end of their life. The 120 V potential of a household outlet is produced in a very different way. There will be more on this topic in an upcoming section.

Resistance

How much current flows when a given potential is present? That depends upon the resistance to the flow of charge. For a given potential, low resistance results in a higher current and high resistance results in a lower current. The resistance of an object depends upon both the material used and it’s shape. A good conducting material has lower resistance while an insulating material has higher resistance. A long wire has more resistance than a short one. A thick wire (having a large cross section) has less resistance than a skinny one.  Resistance (R) is actually defined by the ratio of potential (V) to current (I).

R    =    ^V / _I

The unit for resistance is the volt/amp, called an ohm, and is denoted by the greek symbol omega (W). Associated with this definition is Ohm’s Law, which is represented by the same equation, but usually written as V = IR. We will use Ohm’s Law in the next section on circuits.

Resistance and Heat Energy

 Resistance in a material arises from the collision of electrons with the atoms and with each other as they move. The collisions produce heat, increasing the temperature of the material. Consider the ordinary toaster shown* in Figure1-4. Current flows through the wires of the power cord and through the toaster’s filament (the glowing wire you see inside). The same current must flow in the power cord as flows through the filament. The cord has very little resistance, while the filament has considerably more. Since the filament has a much higher resistance than the cord, it produces much more heat. That’s as it should be. You want the heat for your toast, but you do not want the power cord getting hot! The standard incandescent light bulb is another example. The filament in the light bulb glows white hot (hence, the word “incandescent”) to produce light and a lot of heat as well. But, the low-resistance power cord stays cool.

Toasters and light bulbs are called resistive devices. They convert electrical energy into heat and light energy. Electrical devices with motors, such as refrigerators or blenders, are more complicated than simple resistive devices. They are designed to convert elecrical energy into mechanical energy. (We will study this in more detail later.) Nevertheless, they have an effective resistance. In general, the power cords and electrical wiring in your home should have much less resistance than the devices to which they supply current. Power cords and electrical wiring are rated by the maximum current they can carry without significant heating. That brings us to another important concept.

Power

How much energy does your toaster use? That depends upon how many pieces of bread you toast. Devices are not rated by the energy they consume, but by the rate at which they consume energy, the power.

Power is energy per time. The standard unit used in electricity is the Watt (W) = 1 Joule / second. (Need a review of energy?) A 100 W light bulb will consume 100 joules of energy every second that it is in operation. Batteries (and WAPA) supply power, while electrical devices such as light bulbs and refrigerators consume power. There is a simple relationship between power and all the other quantities we have discussed so far. For all electrical devices, the power that they supply or consume is the product of the potential across the device and the current that flows through the device.

P = I V   all devicesIf a device has a well-defined resistance such as a light bulb or resistor (a device purposely designed to limit current), we can also use our expression V = I R to get

P = I² R   resistorsIn this form, we can see more clearly the importance of the current in power consumption. If we were to double the potential across a resistor, the current would also double (V = I R). But the power consumption of the resistor would increase by a factor of 4! We’ll see the importance of this later when we consider energy losses in high voltage powerlines

High Blood Pressure: Getting the Most Out of Home Monitoring

Victor J. Lewis, PharmD, and Robert Lee Page II, PharmD, FASCP, CGP, BCPS

Dr. Lewis is a pharmacy practice resident at University of Colorado (UC) Hospital. Dr. Page is an associate professor of clinical pharmacy and physical medicine and a clinical specialist, Division of Cardiology, UC Health Sciences Center, Schools of Pharmacy and Medicine.

Conductors, insulators, and electron flow

The electrons of different types of atoms have different degrees of freedom to move around. With some types of materials, such as metals, the outermost electrons in the atoms are so loosely bound that they chaotically move in the space between the atoms of that material by nothing more than the influence of room-temperature heat energy. Because these virtually unbound electrons are free to leave their respective atoms and float around in the space between adjacent atoms, they are often called free electrons.

In other types of materials such as glass, the atoms’ electrons have very little freedom to move around. While external forces such as physical rubbing can force some of these electrons to leave their respective atoms and transfer to the atoms of another material, they do not move between atoms within that material very easily.

This relative mobility of electrons within a material is known as electric conductivity. Conductivity is determined by the types of atoms in a material (the number of protons in each atom’s nucleus, determining its chemical identity) and how the atoms are linked together with one another. Materials with high electron mobility (many free electrons) are called conductors, while materials with low electron mobility (few or no free electrons) are called insulators.

Here are a few common examples of conductors and insulators:

• Conductors:
• silver
• copper
• gold
• aluminum
• iron
• steel
• brass
• bronze
• mercury
• graphite
• dirty water
• concrete

• Insulators:
• glass
• rubber
• oil
• asphalt
• fiberglass
• porcelain
• ceramic
• quartz
• (dry) cotton
• (dry) paper
• (dry) wood
• plastic
• air
• diamond
• pure water

It must be understood that not all conductive materials have the same level of conductivity, and not all insulators are equally resistant to electron motion. Electrical conductivity is analogous to the transparency of certain materials to light: materials that easily “conduct” light are called “transparent,” while those that don’t are called “opaque.” However, not all transparent materials are equally conductive to light. Window glass is better than most plastics, and certainly better than “clear” fiberglass. So it is with electrical conductors, some being better than others.

For instance, silver is the best conductor in the “conductors” list, offering easier passage for electrons than any other material cited. Dirty water and concrete are also listed as conductors, but these materials are substantially less conductive than any metal.

Physical dimension also impacts conductivity. For instance, if we take two strips of the same conductive material — one thin and the other thick — the thick strip will prove to be a better conductor than the thin for the same length. If we take another pair of strips — this time both with the same thickness but one shorter than the other — the shorter one will offer easier passage to electrons than the long one. This is analogous to water flow in a pipe: a fat pipe offers easier passage than a skinny pipe, and a short pipe is easier for water to move through than a long pipe, all other dimensions being equal.

It should also be understood that some materials experience changes in their electrical properties under different conditions. Glass, for instance, is a very good insulator at room temperature, but becomes a conductor when heated to a very high temperature. Gases such as air, normally insulating materials, also become conductive if heated to very high temperatures. Most metals become poorer conductors when heated, and better conductors when cooled. Many conductive materials become perfectly conductive (this is called superconductivity) at extremely low temperatures.

While the normal motion of “free” electrons in a conductor is random, with no particular direction or speed, electrons can be influenced to move in a coordinated fashion through a conductive material. This uniform motion of electrons is what we call electricity, or electric current. To be more precise, it could be called dynamic electricity in contrast to static electricity, which is an unmoving accumulation of electric charge. Just like water flowing through the emptiness of a pipe, electrons are able to move within the empty space within and between the atoms of a conductor. The conductor may appear to be solid to our eyes, but any material composed of atoms is mostly empty space! The liquid-flow analogy is so fitting that the motion of electrons through a conductor is often referred to as a “flow.”

A noteworthy observation may be made here. As each electron moves uniformly through a conductor, it pushes on the one ahead of it, such that all the electrons move together as a group. The starting and stopping of electron flow through the length of a conductive path is virtually instantaneous from one end of a conductor to the other, even though the motion of each electron may be very slow. An approximate analogy is that of a tube filled end-to-end with marbles:

The tube is full of marbles, just as a conductor is full of free electrons ready to be moved by an outside influence. If a single marble is suddenly inserted into this full tube on the left-hand side, another marble will immediately try to exit the tube on the right. Even though each marble only traveled a short distance, the transfer of motion through the tube is virtually instantaneous from the left end to the right end, no matter how long the tube is. With electricity, the overall effect from one end of a conductor to the other happens at the speed of light: a swift 186,000 miles per second!!! Each individual electron, though, travels through the conductor at a much slower pace.

If we want electrons to flow in a certain direction to a certain place, we must provide the proper path for them to move, just as a plumber must install piping to get water to flow where he or she wants it to flow. To facilitate this, wires are made of highly conductive metals such as copper or aluminum in a wide variety of sizes.

Remember that electrons can flow only when they have the opportunity to move in the space between the atoms of a material. This means that there can be electric current only where there exists a continuous path of conductive material providing a conduit for electrons to travel through. In the marble analogy, marbles can flow into the left-hand side of the tube (and, consequently, through the tube) if and only if the tube is open on the right-hand side for marbles to flow out. If the tube is blocked on the right-hand side, the marbles will just “pile up” inside the tube, and marble “flow” will not occur. The same holds true for electric current: the continuous flow of electrons requires there be an unbroken path to permit that flow. Let’s look at a diagram to illustrate how this works:

A thin, solid line (as shown above) is the conventional symbol for a continuous piece of wire. Since the wire is made of a conductive material, such as copper, its constituent atoms have many free electrons which can easily move through the wire. However, there will never be a continuous or uniform flow of electrons within this wire unless they have a place to come from and a place to go. Let’s add an hypothetical electron “Source” and “Destination:”

Now, with the Electron Source pushing new electrons into the wire on the left-hand side, electron flow through the wire can occur (as indicated by the arrows pointing from left to right). However, the flow will be interrupted if the conductive path formed by the wire is broken:

Since air is an insulating material, and an air gap separates the two pieces of wire, the once-continuous path has now been broken, and electrons cannot flow from Source to Destination. This is like cutting a water pipe in two and capping off the broken ends of the pipe: water can’t flow if there’s no exit out of the pipe. In electrical terms, we had a condition of electrical continuity when the wire was in one piece, and now that continuity is broken with the wire cut and separated.

If we were to take another piece of wire leading to the Destination and simply make physical contact with the wire leading to the Source, we would once again have a continuous path for electrons to flow. The two dots in the diagram indicate physical (metal-to-metal) contact between the wire pieces:

Now, we have continuity from the Source, to the newly-made connection, down, to the right, and up to the Destination. This is analogous to putting a “tee” fitting in one of the capped-off pipes and directing water through a new segment of pipe to its destination. Please take note that the broken segment of wire on the right hand side has no electrons flowing through it, because it is no longer part of a complete path from Source to Destination.

It is interesting to note that no “wear” occurs within wires due to this electric current, unlike water-carrying pipes which are eventually corroded and worn by prolonged flows. Electrons do encounter some degree of friction as they move, however, and this friction can generate heat in a conductor. This is a topic we’ll explore in much greater detail later.

• REVIEW:
• In conductive materials, the outer electrons in each atom can easily come or go, and are called free electrons.
• In insulating materials, the outer electrons are not so free to move.
• All metals are electrically conductive.
• Dynamic electricity, or electric current, is the uniform motion of electrons through a conductor.
• Static electricity is an unmoving (if on an insulator), accumulated charge formed by either an excess or deficiency of electrons in an object. It is typically formed by charge separation by contact and separation of dissimilar materials.
• For electrons to flow continuously (indefinitely) through a conductor, there must be a complete, unbroken path for them to move both into and out of that conductor.

Understanding Cholesterol: Do You Know Your Numbers?

Guido R. Zanni, PhD

What Is Cholesterol?

Cholesterol is a fat-like substance in the blood. The body’s cells need cholesterol, but too much of it creates problems. Approximately two thirds of the body’s cholesterol is made and stored in the liver; the remaining cholesterol comes from diet, especially from meat, chicken, fish, and dairy products. A simple blood test measures cholesterol, and laboratory tests report 3 values: low-density lipoprotein cholesterol, called LDL; high-density lipoprotein cholesterol, called HDL; and total cholesterol, which is the sum of LDL and HDL.

LDL and HDL have very different functions, and problems occur when patients have either too much LDL or too little HDL. Think of LDL as the carriers taking cholesterol from the liver to cells. Once the cells have what they need, they refuse delivery. The carriers do not know what to do with the extra cholesterol, so they dump it in the bloodstream and return to the liver for another batch.

Now think of HDL as the clean-up crew; they travel the bloodstream hauling away the excess, but if there are too few HDL workers, they cannot clean up all the excess. This excess cholesterol then clogs arteries and causes heart damage. This is why LDL is called bad cholesterol and HDL good cholesterol. Ideally, patients should have a low LDL number (fewer carriers) and a high HDL number (more clean-up crew). Of the 2 cholesterol types, elevated LDL levels are considered especially unhealthy.

Cholesterol levels are reported in units of measurement called milligrams per deciliter of blood (mg/dL). Generally, providers refer to the numbers without saying the units. All 3 cholesterol values are required to determine if a person is in a healthy or unhealthy range. Table 1 summarizes the various ranges.

Triglycerides

Along with cholesterol levels, doctors also monitor another type of fat in the bloodstream—triglycerides. The body needs triglycerides, but excess triglycerides leads to heart disease and swelling of the pancreas. Less than 150 is considered normal, 150 to 199 is borderline high, 200 to 499 is high, and greater than 500 is considered very high.

What Is an Ideal Cholesterol Level?

The numbers in Table 1 provide general ranges, but they may not reflect a person’s ideal cholesterol level, especially for LDL. To determine your ideal LDL level, doctors assess risk for coronary disease based on such factors as diabetes and hypertension, age, tobacco use, weight, lack of exercise, elevated triglycerides, and family history of heart disease. Recommended LDL levels are based on these risk factors (Table 2).

Treatment

To lower cholesterol levels, your doctor may first recommend lifestyle changes. These include the following:

Because the body manufactures cholesterol, exercise and diet may not be enough to lower cholesterol levels, and medication may be necessary. Most medications will decrease cholesterol levels 30% to 40%. Some patients require more than 1 medication. This is especially true if triglycerides are high.

All medications have side effects, though not all people may experience them. Side effects associated with cholesterol- and triglyceride-lowering drugs include intestinal problems, constipation, flushing, gout, gallstones, liver and kidney problems, nausea, muscle weakness, and cramps. Your doctor will monitor for these side effects, but if you experience any of them, call your doctor. He or she may ask you to come in for blood work and/or change your medication.

Take-away Message

Elevated cholesterol is called a silent killer because people rarely have symptoms until heart disease strikes. For this reason, it is important to know your numbers!