Exercise Physiology

HEART AND EXERCSE

noreply@blogger.com (Anonymous) — Mon, 05 Nov 2012 08:24:00 +0000

The heart is an organ which pumps blood, which in turns carries oxygen and nutrients to the cells of the body and transports away the waste products such as carbon dioxide, lactic acid etc.

Cardiac Output

CO is defined as the volume of blood pumped by the heart in one minute, and is expressed in liters per minute or milliliters per minute. CO is the product of heart rate times stroke volume (the amount of blood pumped with each beat of the heart). For example if HR equals 72 beats per minute and stroke volume equals 70 ml of blood, then the CO is equal to 5,040 ml/min or 5.04 lts./min (72x70). CO can also be calculated from the amount of oxygen consumed per minute and the amount of oxygen taken up by the blood as it flows through the lungs. These relationships can be expressed by the Fick principle as follows:

For example if the oxygen content of the venous blood entering the lings is 16 volumes percent, that of the arterial blood leaving the lungs is 20 volumes percent and the oxygen consumption of the body 200 ml per minute, the amount of oxygen used per minute equals the amount of oxygen taken up by the lungs per minute. From the above data it can be seen that each 100 ml of blood flowing through the lungs picks up 4 ml of oxygen. Since the total amount of oxygen absorbed into the blood from the lungs each minute is 200 ml, then a total of fifty 100 ml portions of blood must flow through the lungs each minute to absorb this amount of oxygen. Thus the cardiac output is

The blood samples to measure the oxygen content by the Fick's procedure is taken by Cardiac catheterization and the oxygen consumption rate is measure by a respirometer apparatus.

Another method used to measure CO is the dye dilution method. Other methods include the carbon dioxide rebreathing test and radioisotope test.

It should be pointed out that Fick technique is considered most accurate to measure the CO under resting or steady state conditions of exercise, while CO in rapid changing conditions the dye dilution technique is more accurate.

Cardiac Output during rest

At rest in the supine position, the normal cardiac output in adults is approximately 5 liters per minute. This is generally achieved with a heart rate of 70beats per min for the untrained and 45 beats per min for endurance trained person. Since the trained person’s cardiac output at rest is also about 5 lits, then the decrease in heart rate must be offset by an increased in stroke volume if the cardiac output formula, the calculated stroke volume for the untrained person would be around 71.4 ml of blood per beat, whereas the stroke volume for the untrained person would be about 111.1 ml per beat.

Cardiac Output during exercise

During exercise upto 40 to 60 percent of maximal capacity, cardiac output in trained athletes may be increased to 40 lts per min. At this level of work, it is known that this 5-7 fold increase in cardiac output is due to increases in both heart rate and stroke volume. At levels beyond 40 to 60 percent of maximum, increases in cardiac output are mainly a function of heart rate increases. At the same time, it should be emphasized that since heart rate in strenuous exercise increases approximately the same in both athletes and non athletes, the greater changes in cardiac output attained by the trained athletes is due to their greater ability for increasing the stroke volume of the heart. This is more than double the size of the stroke volume for untrained subjects. Again substituting the heart rate values in the cardiac output formula, the calculated stroke values for the untrained person would be around 100 ml of blood per beat, whereas the stroke volume for the trained person would be approximately 200 ml per beat.

The regulation of cardiac output involves the regulation of heart rate and stroke volume.

Heart rate

The impulse that causes the heart to contract rhythmically originates within the heart muscle itself, in the right atrium known as the pacemaker or S-A node. Unlike skeletal muscles, the heart muscle possesses autorhythmicity. However both the nervous and chemical factors are involved in the regulation of the heart rate during rest and exercise.

The autonomic nervous system which supplies the parasympathetic or vagus nerves and the sympathetic nervous system or the accelerator nerves to the S-A node plays an important role in regulating heart rate.

Stimulation of the parasympathetic fibers cause the release of acetylcholine (Ach) from their ends, which slows the rate of impulse formation in the S-A node and also slows the rate of conduction through the A-V bundle which slows the impulse into the ventricles. Such impulses are cardio-inhibitory and the final result is a slower heart rate.

Stimulation of the sympathetic fibers causes the release of norepinephrine from their ends. The norepinephrine speeds up both the S-A node rates and the conduction rates. Such impulses are called cardio-acceleratory which results in a faster and stronger heart rate.

This different effect of the two nerves is referred to as reciprocal innervation of the heart muscle.

The nerves controlling the heart arise from specific areas of the medulla of the brain called cardio-inhibitory and cardio-acceleratory centers, the control of the heart rate is predominantly through reflexes.

The cardio-acceleratory centers are affected by several afferent stimulation sources which are referred to as pressor. They are

(i) proprioceptive reflexes originating in the working muscles and joints to contribute to increases in heart rate.

(ii) impulses arising in the chemoreceptors of the carotid body and the aortic body as a result of decreased pH or increased carbon dioxide results in an increased heart rate.

(iii) impulses arising in the adrenal medulla cause a discharge of norepinephrine and epinephrine hormones into the blood stream and an increase in heart rate.

The cardio inhibitory or depressor afferent sources are from the activity of the stretch receptors in the carotid sinus and the aortic arch. The activities from these receptors tend to slow the heart rate down.

Two other factors that are important are an increase in body temperature and a fall in the blood oxygen content, also play a large role in the increased heart rate.

Heart Rate Response to Exercise

Heart rate increases linearly with increasing oxygen consumption in both the trained and untrained individuals. During exercise the heart rate of a well trained person is consistently lower at any given workload or Vo2 than that of the untrained person

Endurance training also tends to lower maximal HR from about 200 to around 185 to 190 beats per minute. That this rate tends to lower with exercise means that since training also increases work capacity (and max Vo2), maximal HR in trained individuals are obtained at relatively higher workloads and Vo2 levels than in untrained subjects.

Endurance training also tends to lower the resting heart rate (bradycardia). For example the resting HR in highly trained athletes may be as low or lower that 40 to 45 beats per minute. On the other hand in healthy untrained subjects, the resting rates may be high as 90 to 100 beats per minute. Thus the trained is generally categorized as having a lower resting HR and the untrained as having a higher resting heart rate.

The highest attainable HR during performance of strenuous work not only depends upon the state of conditioning but also on age. For instance the maximum HR at the age of 20 is about 200 which is reduced to approximately 155 at the age of 70. This is one of the biological changes which comes with old age.

The type of exercise also influences the increase in HR. For example, the greatest acceleration of the heart occurs in speed exercises like sprint running, whereas the smallest increase takes place in strength exercises such as weight training and throwing. In distance running the increase in HR is somewhere between sprint and strength activities.

Besides exercise and training, other factors which affect the HR are Posture, Sex, Age and Emotion and Environmental factors.

Stroke Volume (SV)

Stroke Volume response to exercise

The following graph clearly indicates that Stroke volume increases progressively from rest to moderate work and then it levels off at about 30 to 40 percent of the maximum aerobic power. The dynamics of adjustment are the same in the trained and the untrained person. However the trained person operates at a higher level.

The trained athletes have a greater capacity for not only pumping more blood by the heart per beat, but they also have a greater capacity for extracting more oxygen from the blood into the muscle tissues than sedentary subjects.

The following figure illustrates the relationship between CO, SV and HR as a function of oxygen uptake. It shows that once SV reaches its maximum level (which is usually at a workload of 30 to 40 percent of maximum aerobic power, or at a heart rate of 110 to 120 beats per minute), any additional increases in CO are obtained only through increases in HR.

It should be noted that during maximum work when the HR may reach values as high as 200 beats per minute, the SV is generally at its maximum, which means that the time available for filling of the ventricles at heart rates up to 200 is sufficient to allow maximal stroke volumes.

At rest and in supine position the stroke volume of an adult untrained man is around 70 to 100 ml per beat depending on body size, while the maximal values may range between 100 to 120 ml per beat.

In trained adult men, the resting SV are around 100 to 120 ml per beat whereas maximal values may come up to 150 to 200 ml per beat.

Hence a relatively slow HR and a relatively large SV is characteristic of a trained person and denotes an efficient circulatory system.

In women due to the smaller size of the heart, their SV is usually 25% lower.

When assuming a sitting or standing position, since under the influence of gravity blood normally pools in the lower portions of the body, resulting in a drop in venous return to the heart, this may result in about 30% reduction in SV.

There is a definite relationship between maximum aerobic work and CO and that SV to a large extent limits CO. Since nearly everyone has about the same maximum HR levels, it is generally agreed among exercise physiologists that SV is the difference between an individual with a large cardiac output and one with only a normal output.

Blood Pressure

noreply@blogger.com (Anonymous) — Tue, 30 Oct 2012 06:58:00 +0000

Blood Pressure is the pressure exerted by the blood at right angles to the walls of the blood vessels. Unless indicated otherwise, blood pressure refers to systemic arterial blood pressure, i.e., the pressure in the large arteries delivering blood to body parts other than the lungs, such as the brachial artery (in the arm). The pressure of the blood in other vessels is lower than the arterial pressure. Blood pressure values are universally stated in millimetres of mercury (mmHg). The systolic pressure is defined as the peak pressure in the arteries during the cardiac cycle; the diastolic pressure is the lowest pressure (at the resting phase of the cardiac cycle). The mean arterial pressure and pulse pressure are other important quantities.

Typical values for a resting, healthy adult human are approximately 120 mmHg systolic and 80 mmHg diastolic (written as 120/80 mmHg), with large individual variations. These measures of blood pressure are not static, but undergo natural variations from one heartbeat to another or throughout the day (in a circadian rhythm); they also change in response to stress, nutritional factors, drugs, or disease.

The function of the heart is to circulate blood around the body. The heart comprises of four chambers:

Right Atrium

Left Atrium

Right Ventricle

Left Ventricle

Functionally the heart comprises of two pumps:

The right atrium receives blood from the body (de-oxygenated blood) and the right ventricle pumps it into the lungs for aeration (removal of carbon dioxide and add oxygen).

The left atrium receives the oxygenated blood from the lungs and the left ventricle pumps it around the body.

Blood Pressure

The cardiac cycle (heart beat) consists of cardiac muscle contraction (systole) and cardiac muscle relaxation (diastole).

Blood pressure represents the force (pressure) exerted by blood against the arterial walls during a cardiac cycle. Systolic blood pressure, the higher of the two pressure measurements, occurs during ventricular contraction (systole) as the heart pumps blood into the aorta.

After systole, the ventricles relax (diastole), arterial pressure declines and the heart refills with blood. The lowest pressure reached during ventricular relaxation represents the diastolic blood pressure.

Normal systolic blood pressure in an adult varies between 110 and 140 mm Hg, and diastolic pressure varies between 60 and 90 mm Hg.

Blood Pressure ClassificationSystolic(mm Hg) Diastolic(mm Hg)

Classification

Heart Rate

The resting heart rate for the average person is between 70 and 90 beats per minute (bpm). The term tachycardia is applied to a rapid heart rate (over 100 bpm) and the term bradycardia indicates a slow heart rate (less than 50 bpm). Endurance athletes may have a resting heart rate of less than 50 bpm.

Cardiac Output

This is the amount of blood pumped from your heart and is calculated by multiplying heart rate by stroke volume (the amount of blood ejected by the heart in each beat). An athlete will have a lower resting heart rate and a larger stroke volume than a non-athlete. The cardiac output for an athlete is approx. 35 litres while that for the non-athlete is 22 litres.

Autonomic Innervation of the Heart and Vasculature

noreply@blogger.com (Anonymous) — Tue, 23 Oct 2012 06:45:00 +0000

The medulla, located in the brainstem above the spinal cord, receives sensory input from different systemic and central receptors (e.g., baroreceptors and chemoreceptors) as well as signals from other brain regions (e.g., hypothalamus). Autonomic outflow from the brainstem is divided principally into sympathetic and parasympathetic (vagal) branches. Efferent fibers of these autonomic nerves travel to the heart and blood vessels where they modulate the activity of these target organs.

The heart is innervated by vagal and sympathetic fibers. The right vagus nerve primarily innervates the SA node, whereas the left vagus innervates the AV node; however, there can be significant overlap in the anatomical distribution. Atrial muscle is also innervated by vagal efferents, whereas the ventricular myocardium is only sparsely innervated by vagal efferents. Sympathetic efferent nerves are present throughout the atria (especially in the SA node) and ventricles, including the conduction system of the heart.

Cardiac function is altered by neural activation. Sympathetic stimulation increases heart rate (positive chronotropy), inotropy and conduction velocity (positive dromotropy), whereas parasympathetic stimulation of the heart has opposite effects. Sympathetic and parasympathetic effects on heart function are mediated by beta-adrenoceptors and muscarinic receptors, respectively.

Sympathetic adrenergic nerves travel along arteries and nerves and are found in the adventitia (outer wall of a blood vessel). Varicosities, which are small enlargements along the nerve fibers, are the site of neurotransmitter release. Capillaries receive no innervation. Activation of vascular sympathetic nerves causes vasoconstriction of arteries and veins mediated by alpha-adrenoceptors.

Parasympathetic fibers are found associated with blood vessels in certain organs such as salivary glands, gastrointestinal glands, and in genital erectile tissue. The release of acetylcholine (ACh) from these parasympathetic nerves has a direct vasodilatory action (coupled to nitric oxide formation and guanylyl cyclase activation). ACh release can stimulate the release of kallikrein from glandular tissue that acts upon kininogen to form kinins (e.g., bradykinin). Kinins cause increased capillary permeability and venous constriction, along with arterial vasodilation in specific organs.

Arterial Pulse Pressure

noreply@blogger.com (Anonymous) — Tue, 16 Oct 2012 06:39:00 +0000

As the left ventricle ejects blood into the aorta, the aortic pressure increases. The greater the stroke volume, the greater the change in pressure during ejection. The maximal change in aortic pressure during systole (from the time the aortic valve opens until the peak aortic pressure is attained (see Cardiac Cycle) represents the aortic pulse pressure, which is defined as the systolic pressure minus the diastolic pressure. For example, if the systolic pressure is 130 mmHg and the diastolic pressure is 85 mmHg, then the pulse pressure is 45 mmHg.

Pulse Pressure = Systolic Pressure ─ Diastolic Pressure

The rise in aortic pressure from its diastolic to systolic value is determined by the compliance of the aorta as well as the ventricular stroke volume. In the arterial system, the aorta has the highest compliance, due in part to a relatively greater proportion of elastin fibers versus smooth muscle and collagen. This serves the important function of dampening the pulsatile output of the left ventricle, thereby reducing the pulse pressure (systolic minus diastolic arterial pressure). If the aorta were a rigid tube, the pulse pressure would be very high. Because the aorta is compliant, as blood is ejected into the aorta, the walls of the aorta expand to accommodate the increase in blood volume. As the aorta expands, the increase in pressure is determined by the compliance of the aorta at that particular range of volumes. The more compliant the aorta, the smaller the pressure change during ventricular ejection (i.e., smaller pulse pressure) (see figure). Therefore, aortic compliance is a major determinant, along with stroke volume, of the pulse pressure.

Summary:

A highly compliant aorta (i.e., less stiff) has a smaller pulse pressure for a given stroke volume into the aorta.

A larger stroke volume (not shown in the figure) produces a larger pulse pressure at any given compliance.

Aortic compliance decreases with age due to structural changes, thereby producing age-dependent increases in pulse pressure.

For a given stroke volume, compliance determines pulse pressure and not mean aortic pressure.

However, because vessels display dynamic compliance, increasing the rate of ventricular ejection (as occurs with increased ventricular inotropy) will increase the pulse pressure compared to the same volume ejected at a lower rate.

Aerobic exercise

noreply@blogger.com (Anonymous) — Tue, 09 Oct 2012 06:33:00 +0000

In physical exercise, aerobic exercise is complementary to anaerobic exercise. Aerobic literally means "with oxygen", and refers to the use of oxygen in muscles' energy-generating process. Aerobic exercise includes any type of exercise, typically those performed at moderate levels of intensity for extended periods of time, that maintains an increased heart rate. In such exercise, oxygen is used to "burn" fats and glucose in order to produce adenosine triphosphate, the basic energy carrier for all cells. Initially during aerobic exercise, glycogen is broken down to produce glucose, but in its absence, fat metabolism is initiated instead. The latter is a slow process, and is accompanied by a decline in performance level. The switch to fat as fuel is a major cause of what marathon runners call "hitting the wall".

Anaerobic exercise, in contrast, refers to the initial phase of exercise, or any short burst of intense exertion, in which the glycogen or sugar is consumed without oxygen, and is a far less efficient process.Operating anaerobically, an untrained 400 meter sprinter may "hit the wall" after only 300 meters.

There are various types of aerobic exercise. In general, aerobic exercise is one performed at a moderately high level of intensity over a long period of time. For example, running a long distance at a moderate pace is an aerobic exercise, but sprinting is not. Playing singles tennis, with near-continuous motion, is generally considered aerobic activity, while golf or doubles tennis, with their more frequent breaks, may not be.

Among the recognized benefits of doing regular aerobic exercise are:

Strengthening the muscles involved in respiration, to facilitate the flow of air in and out of the lungs

Strengthening and enlarging the heart muscle, to improve its pumping efficiency and reduce the resting heart rate

Toning muscles throughout the body, which can improve overall circulation and reduce blood pressure

Increasing the total number of red blood cells in the body, to facilitate transport of oxygen throughout the body

Increased storage of energy molecules such as fats and carbohydrates within the muscles, allowing for increased endurance

Neovascularization of the muscle sarcomeres to increase blood flow through the muscles

Aerobic exercise versus aerobics

"Aerobics" are a particular form of aerobic exercise. Aerobics classes generally involve rapid stepping patterns, performed to music with cues provided by an instructor. This type of aerobic activity became quite popular in the United States after the 1970 publication of The New Aerobics by Dr. Kenneth H. Cooper, and went through a brief period of intense popularity in the 1980s, when many celebrities (such as Jane Fonda and Richard Simmons) produced videos or created television shows promoting this type of aerobic exercise. Group exercise aerobics can be divided into two major types: Freestyle Aerobics and Pre-choreographed Aerobics.

Aerobic capacity

Aerobic capacity'(VO2 max)' describes the functional status of the cardiorespiratory system, (the heart, lungs and blood vessels). Aerobic capacity is defined as the maximum volume of oxygen that can be consumed by one's muscles during exercise. It is a function both of one's cardiorespiratory performance and of the ability of the muscles to extract the oxygen and fuel delivered to them. To measure maximal aerobic capacity, an exercise physiologist or physician typically directs a subject to exercise on a treadmill, first by walking at an easy pace and then, at set time intervals during graded exercise tests, gradually increasing the workload. The higher a cardiorespiratory endurance level, the more oxygen transported to exercising muscles and the longer exercise can be maintained without exhaustion. The higher aerobic capacity, the higher the level of aerobic fitness.

Critiques

When generalized fitness is a professional operational requirement, as for athletes, combat services, police and fire personnel, aerobic exercise alone may not provide a well-balanced exercise program. In particular, muscular strength, especially upper-body muscular strength, is usually neglected. Also, the metabolic pathways involved in anaerobic metabolism (glycolysis and lactic acid fermentation) that generate energy during high intensity, low duration tasks such as sprinting, are not exercised at peak rates. Aerobic exercise is, however, an extremely valuable component of a balanced exercise programme and is good for cardiovascular health.

Some persons suffer repetitive stress injuries with some forms of aerobics and then must choose less injurious "low-impact" forms or lengthen the gap between bouts of aerobic exercise to allow for greater recovery.

Aerobics notably does not increase the resting metabolic rate as much as some forms of weight-training, and may therefore be less effective at reducing obesity. However, this form of exercise also allows for longer, more frequent activity and consumes more energy when the individual is active. In addition, the metabolic activity of an individual is heightened for several hours following a bout of aerobic activity.

Aerobic activity is also used by individuals with anorexia as a means of suppressing appetite, since aerobic exercise increases glucose and fatty acids in the blood by stimulating tissues to release their energy stores.[citation needed] While there is some support for exercising while hungry as a means of tapping into fat stores, most evidence is equivocal. In addition, performance can be impaired by lack of nutrients, which can impair training effects.

Action Potentials

noreply@blogger.com (Anonymous) — Tue, 02 Oct 2012 06:24:00 +0000

Many cells in the body have the ability to undergo a transient depolarization and repolarization that is either triggered by external mechanisms (e.g., motor nerve stimulation of skeletal muscle or cell-to-cell depolarization in the heart) or by intracellular, spontaneous mechanisms (e.g., cardiac pacemaker cells).

There are two general types of cardiac action potentials. Non-pacemaker action potentials, also called fast response action potentials because of their rapid depolarization, are found throughout the heart except for the pacemaker cells. The pacemaker cells generate spontaneous action potentials that are also termed slow response action potentials because of their slower rate of depolarization. These are found in the sinoatrial and atrioventricular nodes of the heart.

Both types of action potentials in the heart differ considerably from action potentials found in neural and skeletal muscle cells. One major difference is in the duration of the action potentials. In a typical nerve, the action potential duration is about 1 ms. In skeletal muscle cells, the action potential duration is approximately 2-5 ms. In contrast, the duration of cardiac action potentials range from 200 to 400 ms. Another difference between cardiac and nerve and muscle action potentials is the role of calcium ions in depolarization.

In nerve and muscle cells, the depolarization phase of the action potential is caused by an opening of sodium channels. This also occurs in non-pacemaker cardiac cells. However, in cardiac pacemaker cells, calcium ions are involved in the initial depolarization phase of the action potential. In non-pacemaker cells, calcium influx prolongs the duration of the action potential and produces a characteristic plateau phase.

Cardiovascular Physiology Concepts

noreply@blogger.com (Anonymous) — Tue, 25 Sep 2012 06:20:00 +0000

Richard E. Klabunde, Ph.D.

Abnormal Rhythms - Definitions

General Terms:

Bradycardia - a heart rate that is lower than normal.

Tachycardia - a heart rate that is higher than normal.

Paroxysmal - an arrhythmia that suddenly begins and ends.

Specific Arrhythmias:

Sinus bradycardia - low sinus rate <60 beats="beats" br="br" min.="min.">
Sinus tachycardia - high sinus rate of 100-180 beats/min as occurs during exercise or other conditions that lead to increased SA nodal firing rate.

Sick sinus syndrome - a disturbance of SA nodal function that results in a markedly variable rhythm (cycles of bradycardia and tachycardia).

Atrial tachycardia - a series of 3 or more consecutive atrial premature beats occurring at a frequency >100/min; usually due to abnormal focus within the atria and paroxysmal in nature. This type of rhythm includes paroxysmal atrial tachycardia (PAT).

Atrial flutter - sinus rate of 250-350 beats/min.

Atrial fibrillation - uncoordinated atrial depolarizations.

Junctional escape rhythm - SA node suppression can result in AV node-generated rhythm of 40-60 beats/min (not preceded by p-wave).

AV nodal blocks - a conduction block within the AV node (or occasionally in the bundle of His) that impairs impulse conduction from the atria to the ventricles.

First-degree AV nodal block - the conduction velocity is slowed so that the P-R interval is increased to greater than 0.2 seconds. Can be caused by enhanced vagal tone, digitalis, beta-blockers, calcium channel blockers, or ischemic damage.

Second-degree AV nodal block - the conduction velocity is slowed to the point where some impulses from the atria cannot pass through the AV node. This can result in p-waves that are not followed by QRS complexes. For example, 1 or 2 p-waves may occur alone before one is followed by a QRS. When the QRS follows the p-wave, the P-R interval is increased. In this type of block, the ventricular rhythm will be less than the sinus rhythm.

Third-decree AV nodal block - conduction through the AV node is completely blocked so that no impulses are able to be transmitted from the atria to the ventricles. QRS complexes will still occur (escape rhythm), but they will originate from within the AV node, bundle of His, or other ventricular regions. Therefore, QRS complexes will not be preceded by p-waves. Furthermore, there will be complete asynchrony between the p-wave and QRS complexes. Atrial rhythm may be completely normal, but ventricular rhythm will be greatly reduced depending upon the location of the site generating the ventricular impulse. Ventricular rate typically range from 30 to 40 beats/min.

Supraventricular tachycardia (SVT) - usually caused by reentry currents within the atria or between ventricles and atria producing high heart rates of 140-250.

Ventricular premature beats (VPBs) - caused by ectopic ventricular foci; characterized by widened QRS.

Ventricular tachycardia (VT) - high ventricular rate caused by aberrant ventricular automaticity or by intraventricular reentry; can be sustained or non-sustained (paroxysmal); characterized by widened QRS; rates of 100 to 200 beats/min; life-threatening.

Ventricular flutter - ventricular depolarizations >200/min.

Ventricular fibrillation - uncoordinated ventricular depolarizations.

Organic Chemistry

noreply@blogger.com (Anonymous) — Tue, 18 Sep 2012 06:03:00 +0000

by Anthony Carpi, Ph.D.

To understand life as we know it, we must first understand a little bit of organic chemistry. Organic molecules contain both carbon and hydrogen. Though many organic chemicals also contain other elements, it is the carbon-hydrogen bond that defines them as organic. Organic chemistry defines life. Just as there are millions of different types of living organisms on this planet, there are millions of different organic molecules, each with different chemical and physical properties. There are organic chemicals that make up your hair, your skin, your fingernails, and so on. The diversity of organic chemicals is due to the versatility of the carbon atom. Why is carbon such a special element? Let's look at its chemistry in a little more detail.

Carbon (C) appears in the second row of the periodic table and has four bonding electrons in its valence shell. Similar to other non-metals, carbon needs eight electrons to satisfy its valence shell. Carbon therefore forms four bonds with other atoms (each bond consisting of one of carbon's electrons and one of the bonding atom's electrons). Every valence electron participates in bonding, thus a carbon atom's bonds will be distributed evenly over the atom's surface. These bonds form a tetrahedron (a pyramid with a spike at the top), as illustrated below:

Organic chemicals get their diversity from the many different ways carbon can bond to other atoms. The simplest organic chemicals, called hydrocarbons, contain only carbon and hydrogen atoms; the simplest hydrocarbon (called methane) contains a single carbon atom bonded to four hydrogen atoms:

But carbon can bond to other carbon atoms in addition to hydrogen, as illustrated in the molecule ethane below:

In fact, the uniqueness of carbon comes from the fact that it can bond to itself in many different ways. Carbon atoms can form long chains:

branched chains:

rings:

There appears to be almost no limit to the number of different structures that carbon can form. To add to the complexity of organic chemistry, neighboring carbon atoms can form double and triple bonds in addition to single carbon-carbon bonds:

Keep in mind that each carbon atom forms four bonds. As the number of bonds between any two carbon atoms increases, the number of hydrogen atoms in the molecule decreases (as can be seen in the figures above).

Simple Hydrocarbons

The simplest hydrocarbons are those that contain only carbon and hydrogen. These simple hydrocarbons come in three varieties depending on the type of carbon-carbon bonds that occur in the molecule. Alkanes are the first class of simple hydrocarbons and contain only carbon-carbon single bonds. The alkanes are named by combining a prefix that describes the number of carbon atoms in the molecule with the root ending "ane". The names and prefixes for the first ten alkanes are given in the following table.

The chemical formula for any alkane is given by the expression CnH2n+2. The structural formula, shown for the first five alkanes in the table, shows each carbon atom and the elements that are attached to it. This structural formula is important when we begin to discuss more complex hydrocarbons. The simple alkanes share many properties in common. All enter into combustion reactions with oxygen to produce carbon dioxide and water vapor. In other words, many alkanes are flammable. This makes them good fuels. For example, methane is the principle component of natural gas, and butane is common lighter fluid.

The second class of simple hydrocarbons, the alkenes, consists of molecules that contain at least one double-bonded carbon pair. Alkenes follow the same naming convention used for alkanes. A prefix (to describe the number of carbon atoms) is combined with the ending "ene" to denote an alkene. Ethene, for example is the two- carbon molecule that contains one double bond. The chemical formula for the simple alkenes follows the expression CnH2n. Because one of the carbon pairs is double bonded, simple alkenes have two fewer hydrogen atoms than alkanes.

Alkynes are the third class of simple hydrocarbons and are molecules that contain at least one triple-bonded carbon pair. Like the alkanes and alkenes, alkynes are named by combining a prefix with the ending "yne" to denote the triple bond. The chemical formula for the simple alkynes follows the expression CnH2n-2.

Isomers

Because carbon can bond in so many different ways, a single molecule can have different bonding configurations. Consider the two molecules illustrated here:

Both molecules have identical chemical formulas (shown in the left column); however, their structural formulas (and thus some chemical properties) are different. These two molecules are called isomers. Isomers are molecules that have the same chemical formula but different structural formulas.

Functional Groups

In addition to carbon and hydrogen, hydrocarbons can also contain other elements. In fact, many common groups of atoms can occur within organic molecules, these groups of atoms are called functional groups. One good example is the hydroxyl functional group. The hydroxyl group consists of a single oxygen atom bound to a single hydrogen atom (-OH). The group of hydrocarbons that contain a hydroxyl functional group is called alcohols. The alcohols are named in a similar fashion to the simple hydrocarbons, a prefix is attached to a root ending (in this case "anol") that designates the alcohol. The existence of the functional group completely changes the chemical properties of the molecule. Ethane, the two-carbon alkane, is a gas at room temperature; ethanol, the two-carbon alcohol, is a liquid.

Ethanol, common drinking alcohol, is the active ingredient in "alcoholic" beverages such as beer and wine.

Nutrition

noreply@blogger.com (Anonymous) — Tue, 11 Sep 2012 05:29:00 +0000

Nutrition deals with the composition of food, its energy content, and slowly (or not at all) synthesized organic molecules. Chemotrophs are organisms (mostly bacteria) deriving their energy from inorganic chemical reactions. Phototrophs convert sunlight energy into sugar or other organic molecules. Heterotrophs eat to obtain energy from the breakdown of organic molecules in their food.

Macronutrients are foods required on a large scale each day. These include carbohydrates, lipids, and amino acids. Water is essential, correct water balance is a must for proper functioning of the body.

About 60% of the diet should be carbohydrates, such as are in milk, meat, vegetables, grains and grain products. The diet should contain at least 100 grams of carbohydrate every day.

Proteins are polymers composed of amino acids. Proteins are found in meat, milk, poultry, fish, cereal grains and beans. They are needed for cellular growth and repair. Twenty amino acids are found in proteins, of which humans can make eleven. The remaining nine are the essential amino acids which must be supplied in the diet. Normally proteins are not used for energy, however during starvation muscle proteins are broken down for energy. Excess protein can be used for energy or converted to fats.

Lipids and fats generate the greatest energy yield, so many plants and animals store energy as fats. Lipids and fats are present in oils, meats, butter, and plants (such as avocado and peanuts). Some fatty acids, such as linoleic acid, are essential and must be included in the diet. When present in the intestine, lipids promote the uptake of vitamins A, D, E, and K.

Vitamins are organic molecules required for metabolic reactions. They usually cannot be made by the body and are needed in trace amounts. Vitamins may act as enzyme cofactors or coenzymes. Some vitamins are soluble in fats, some in water.

Minerals are trace elements required for normal metabolism, as components of cells and tissues, and for nerve conduction and muscle contraction. They can only be obtained from the diet. Iron (for hemoglobin), iodine (for thyroxin), calcium (for bones), and sodium (nerve message transmission) are examples of minerals.

There is a quantitative relationship between nutrients and health. Imbalances can cause disease. Many studies have concluded nutrition is a major factor in cardiovascular disease, hypertension, and cancer.

Fats and Proteins

noreply@blogger.com (Anonymous) — Tue, 04 Sep 2012 05:20:00 +0000

by Anthony Carpi, Ph.D.

In addition to the carbohydrates, fats and proteins are the other two macronutrients required by the human body.

Fats

Fats are a subgroup of compounds known as lipids that are found in the body and have the general property of being hydrophobic (meaning they are insoluble in water). Fats are also known as triglycerides, molecules made from the combination of one molecule of glycerol with three fatty acids, as depicted below:

The main purpose of fats in the body is to serve as a storage system and reserve supply of energy. During periods of low food consumption, fat reserves in the body can be mobilized and broken down to release energy. Fats serve as an insulation material to allow body heat to be conserved and fats line and protect delicate internal organs from physical damage. Fats in the diet can be converted to other lipids that serve as the main structural material in the membranes surrounding our cells. Fats are also used in the manufacture of some steroids and hormones that help regulate proper growth and maintenance of tissue in the body.

Fats can be classified as either saturated or unsaturated depending on the structure of the long carbon-carbon chains in the fatty acids (the R's in the diagram above). Fats that contain no double bonds in their fatty acid chains are referred to as saturated fats. These fats tend to be solid at room temperature, such as butter or animal fat. The consumption of saturated fats carries some health risks in that they have been linked to arteriosclerosis (hardening of the arteries) and heart disease. Unsaturated fats contain some number of double bonds in their structure. These fats are generally liquid at room temperature (fats that are liquid at room temperature are referred to as oils). Unsaturated fats can be either polyunsaturated (many double bonds) or monounsaturated fats (one or few double bonds). Recent research suggests that the healthiest of the fats in the human diet are the monounsaturated fats, such as olive oil and canola oil, because they appear to be beneficial in the fight against heart disease.

Proteins

Proteins are polymers of amino acids. Though there are hundreds of thousands of different proteins that exist in nature, they are all made up of different combinations of amino acids. Proteins are large molecules that may consist of hundreds, or even thousands, of amino acids. Amino acids all have the general structure:

The R in the diagram represents a functional group that varies depending on the specific amino acid in question. For example, R can be simply an H atom, as in the amino acid glycine, or a more complex organic group. When two amino acids bond together, the two ends of nearby amino acids (shown in red) are released and the carbon (called a carboxyl) end of one amino acid bonds to the nitrogen end of the adjacent one forming a peptide bond, as illustrated below:

When many amino acids bond together to create long chains, the structure is called a protein (it is also called a polypeptide because it contains many peptide bonds). Proteins serve two broad purposes in the human body. Structural proteins form most of the solid material in the human body. For example, the structural proteins keratin and collagen are the main component of your hair, muscles, tendons and skin. Functional proteins help carry out activities and functions in the human body. For example, hemoglobin is a functional protein that occurs in the red blood cells and helps to transport oxygen in the body. Myosin is a protein that occurs in muscle tissue and is responsible for the ability of muscles to contract. Insulin is a functional protein that helps regulate the storage of the sugar glucose in the human body. A subclass of the functional proteins is the group of polypeptides referred to as enzymes. Enzymes help to carry out specific chemical reactions in the body. For example, amylase is an enzyme that occurs both in human saliva and in the intestines that helps to break apart the glucose-glucose bonds in the carbohydrate starch, thus allowing your body to absorb the glucose and use it for energy.

There are an estimated 100,000 different proteins in the human body alone, and each of them is made up of a combination of different combinations of only twenty amino acids. Each protein has a different structure and performs a different function in the body. When we eat protein-containing foods (such as meat, fish, beans, eggs, cheese, etc.) the polypeptide chains are generally broken down in the digestive tract and the individual amino acids are absorbed into our bodies. These amino acids are then recombined into proteins specific to each individual person in a process called protein synthesis.

In order to carry out these very precise jobs in the body, each individual protein has to be unique and specific to the job in question. Three aspects of a protein's structure are specific to the job the protein does in the body. The first aspect of a protein's structure is called the primary structure (1°). The primary structure of a protein is the sequence of amino acids in the protein. The number of amino acids in a protein can vary from the hundreds to the thousands, and the sequence in which those twenty different amino acids just mentioned occur (obviously one amino acid can occur in a protein many times) is specific to the individual protein, just as the sequence of numbers in your phone number is specific to your phone. The secondary structure (2°) of a protein is defined by the way the long strands of amino acids coil about themselves. Just as a phone cord wraps around itself to form a coil, a protein will also wrap around itself, and the degree and tightness of the coil is specific to the protein in question. Once a protein is coiled, the protein will begin to fold onto itself (similar to the way a phone cord tangles around itself); this folding is specific to the protein's function and is called the protein's tertiary structure (3°).

What type of surgery can repair AC Joint problems?

noreply@blogger.com (Anonymous) — Thu, 30 Aug 2012 13:27:00 +0000

The simplest type of surgery for AC joint injury involves resection or removal of the end of the clavicle using arthroscopic (mini-surgical) techniques (called a Mumford procedure). If the joint becomes painful because of DCO (weightlifter's shoulder) or arthritis, or the separation is only minor, this technique can be very satisfactory. When the joint is severely displaced, then a more complex procedure is needed to restore the position of the clavicle. Usually this operation, called a Weaver-Dunn procedure, is done using a two-inch incision over the joint. The end of the clavicle is removed, and ligament is transferred from the underside of the acromion into the cut end of the clavicle to replace the ligaments torn during the dislocation. Soon an arthroscopic procedure should be available to restore the position of the joint, but at this point, only open surgery techniques are available.

When and why is surgery necessary for AC Joint separations?

noreply@blogger.com (Anonymous) — Tue, 28 Aug 2012 13:22:00 +0000

Usually surgery is reserved for those cases where there is residual pain or unacceptable deformity in the joint after several months of conservative treatment. The pain can occur with direct pressure on the joint, such as with straps from underwear or work clothing. Sometimes there will be catching, clicking, or pain with overhead activities, such as lifting, throwing, or reaching. Finally, in some people with very thin skin and very little muscular and soft tissue padding above their shoulders, the prominent clavicle after the separation may be considered unattractive, since the shoulder can appear to be unbalanced.

What is the proper treatment for a sprained AC Joint?

noreply@blogger.com (Anonymous) — Sun, 26 Aug 2012 13:20:00 +0000

When a joint is first sprained, conservative treatment is certainly the best. Applying ice directly to the point of the shoulder is helpful to inhibit swelling and relieve pain. The arm can be supported with a sling which also relieves some of the weight from the shoulder. Gentle motion of the arm can be allowed to prevent stiffness, and exercise putty is very helpful to improve function of the elbow, wrist, and hand, but any attempts at vigorous shoulder mobilization early on will probably lead to more swelling and pain.

How is the AC Joint usually injured?

noreply@blogger.com (Anonymous) — Fri, 24 Aug 2012 13:16:00 +0000

shoulder1_1001 (Photo credit: Ce nest pas un JB.)

The AC joint is injured most often when one falls directly on the point of the shoulder. The trauma will separate the acromion away from the clavicle, causing a sprain or a true AC joint dislocation. In a mild injury, the ligaments which support the AC joint are simply stretched (Grade I), but with more severe injury, the ligaments can partially tear (Grade II) or completely tear (Grade III). In the most severe injury, the end of the clavicle protrudes beneath the skin and is visible as a prominent bump.

What is the AC Joint in the shoulder?

noreply@blogger.com (Anonymous) — Wed, 22 Aug 2012 13:11:00 +0000

clavicle (Photo credit: msklibrary)

The top of the wing bone or scapula is the acromion. The joint formed where the acromion connects to the collar bone or clavicle is the AC joint. Usually there is a protuberance or bump in this area, which can be quite large in some people normally. This joint, like most joints in the body, has a cartilage disk or meniscus inside and the ends of the bones are covered with cartilage. The joint is held together by a capsule, and the clavicle is held in the proper position by two heavy ligaments called coracoclavicular ligaments.

How successful is rotator cuff surgery?

noreply@blogger.com (Anonymous) — Mon, 20 Aug 2012 13:02:00 +0000

Again, every case is unique. In the young, healthy person with a minor rotator cuff impingement, surgery is predictably successful. As the injury becomes more severe, such as with a large bone spur and fragmentation of the tendon, then a perfect result cannot be expected. Since it is necessary to trim back the unhealthy tendon before reattaching it to the bone, a decreased range of motion of the shoulder will often result. Despite this, pain relief and return of strength are usually well worth the minor decreased mobility. The final outcome often depends on the willingness and ability of an individual patient to work on their postoperative physical therapy program.

What is the rehabilitation program after rotator cuff surgery?

noreply@blogger.com (Anonymous) — Sat, 18 Aug 2012 12:59:00 +0000

Depending on the type of surgery performed, the program will allow a period of time for healing of the soft tissues followed by time to regain range of motion and then strengthen the shoulder muscles, but particularly the rotator cuff. In minor tendinitis and impingement syndrome, the program takes approximately two to three months. If the rotator cuff tendon has been completely torn, it may take six months or more before the atrophied muscles can resume their function and the range of motion of the arm is restored. Frequently, pain relief is much quicker and return to daily activities is often possible by two to three months.

How is my shoulder treated after surgery?

noreply@blogger.com (Anonymous) — Thu, 16 Aug 2012 12:56:00 +0000

In a minor operation for impingement, the shoulder is placed in a simple sling. If a full thickness tear of the rotator cuff was present and repaired, then the shoulder will be supported by an UltraSling or a SCOI postoperative brace. The brace is very helpful because it will allow exercise of the elbow, wrist, and hand at all times, and places the arm in a position that promotes better blood circulation and relieves stress on the repaired rotator cuff tissues. In addition, the shoulder can be exercised in the brace much easier than when it is at the side in an immobilizer.

How is a major injury to the rotator cuff tendon repaired surgically?

noreply@blogger.com (Anonymous) — Wed, 15 Aug 2012 12:51:00 +0000

The arthroscope is extremely helpful when repairing rotator cuff tendons, but sometimes it is necessary to add a "mini-open" procedure if the tendon is completely torn. Using the arthroscope at the beginning of the case allows visualization of the interior of the joint to facilitate trimming and removal of fragments of torn cuff tendon and biceps tendon. The next step utilizes the arthroscope to visualize the spur and thickened ligament beneath the acromial bone, while they are removed with miniature cutting and grinding instruments. If it is necessary to suture a rotator cuff tear which has pulled off the bone, a two-inch incision can be made directly over the tear that has been visualized and localized using the arthroscope. The deltoid muscle fibers can be spread apart so that strong stitches can attach the rotator cuff tendon back to the bone. If the tear is minimally retracted, small suture screw anchors may be used arthroscopically or open.

What will happen if the rotator cuff is not repaired?

noreply@blogger.com (Anonymous) — Wed, 15 Aug 2012 12:47:00 +0000

In some situations, the bursa overlying the rotator cuff may form a patch to close the defect in the tendon. Although this is not true tendon healing, it may decrease the pain to an acceptable level. If the tendon edges become fragmented and severely worn, and the muscle contracts and atrophies, repair at that point may not be possible. Sometimes in this situation, the only beneficial surgical procedure would be an arthroscopic operation to remove bone spurs and fragments of torn tissue that catch when the arm is rotated. This certainly will not restore normal power or strength to the shoulder, but often will relieve pain.

If the rotator cuff is already torn, what are the options?

noreply@blogger.com (Anonymous) — Tue, 31 Jul 2012 07:43:00 +0000

When the tendon of the rotator cuff has a complete tear, the tendon often must be repaired using surgical techniques. The choice of surgery, of course, depends on the severity of the symptoms, the health of the patient, and the functional requirements for that shoulder. In young working individuals, repair of the tendon is most often suggested. In some older individuals who do not require significant overhead lifting ability, surgical repair may not be as important. If chronic pain and disability are present at any age, consideration for repair of the rotator cuff should be given.

What is the second line of treatment if the rotator cuff pain and weakness persist?

noreply@blogger.com (Anonymous) — Tue, 31 Jul 2012 07:42:00 +0000

If there is a thickened acromion or acromial bone spur causing impingement, it can be removed with a burr using arthroscopic visualization. This procedure can often be performed on an outpatient basis, and at the same time, any minor damage and fraying to the rotator cuff tendon and scarred bursal tissue can be removed. Often this will completely cure the impingement and prevent progressive rotator cuff injury

What is the initial treatment for rotator cuff disease and impingement?

noreply@blogger.com (Anonymous) — Tue, 31 Jul 2012 07:41:00 +0000

If minor impingement or rotator cuff tendinitis is diagnosed, a period of rest coupled with medicines taken by mouth, and physical therapy will frequently decrease the inflammation and restore the tone to the atrophied muscles. Activities causing the pain should be slowly resumed only when the pain is gone. Sometimes a cortisone injection into the bursal space above the rotator cuff tendon is helpful to relieve swelling and inflammation. Application of ice to the tender area three or four times a day for 15 minutes is also helpful.

How is the diagnosis of rotator cuff disease proven?

noreply@blogger.com (Anonymous) — Tue, 31 Jul 2012 07:40:00 +0000

The diagnosis of rotator cuff tendon disease includes a careful history taken and reviewed by the physician, an x-ray to visualize the anatomy of the bones of the shoulder, specifically looking for acromial spur, and a physical examination. Atrophy may be present, along with weakness, if the rotator cuff tendons are injured, and special impingement tests can suggest that impingement syndrome is involved. An MRI (magnetic resonance imaging) scan frequently gives the final proof of the status of the rotator cuff tendon. Although none of these tests is guaranteed accurate, most rotator cuff injuries can be diagnosed using this combination of exams.

What kind of symptoms does a patient have when the rotator cuff is injured?

noreply@blogger.com (Anonymous) — Tue, 31 Jul 2012 07:39:00 +0000

The most common complaint is aching located in the top and front of the shoulder, or on the outer side of the upper arm (deltoid area). The pain is usually increased when the arm is lifted to the overhead position. Frequently, the pain seems to be worse at night, and often interrupts sleep. Depending on the severity of the injury, there may also be weakness in the arm and, with some complete rotator cuff tears, the arm cannot be lifted in the forward or outward direction at all.