Now for the real stuff. An examination of the lungs and respiratory system is the focus of this month's Newsletter. In addition, the discussion of plyometrics, begun in last month's issue as a response to a reader's question, is completed this month.
Breathing, or respiration, involves four processes: 1) pulmonary ventilation is moving air in and out of the lungs, 2) external respiration is the exchange of oxygen for carbon dioxide, which is occurs between the blood and air, in the lungs, 3) transport of respiratory gases, which is done by the blood, and 4) internal respiration, which is the exchange of gases (oxygen and carbon dioxide) between the blood and tissue cells, in the capillaries. Whew, I didn't know it would be so complicated to describe a body function that we all perform routinely - without thought - everyday of our lives.
The respiratory system is composed of the nose and nasal cavity, the larynx, the trachea, the bronchi, and the lungs. Its main function is to keep adequate oxygen available to the body, and to remove carbon dioxide (CO2).
This body system is functionally divided into the respiratory and conducting zones. The respiratory zone is where gas exchanges are actually made in the lungs. The conducting zone is the passageways by which air reaches the respiratory zone. Other conducting zone functions are to filter, humidify, and warm incoming air.
It all starts here. It provides: 1) access for air to the lungs, 2) moisturizes and warms incoming air, 3) filters inhaled air and cleanses it of foreign particles, 4) is a resonating chamber for speech, and 5) houses the olfactory (smell) receptors.
Noses come in all shapes and sizes, but this discussion only deals with the inside - the nasal cavity (an area behind the exterior nose and above the roof of the mouth) . If we wanted to get technical now, we would talk about the hard and soft palates, the vestibule, and the vibrissae (nose hairs), but we don't, and we won't. But we will talk about two types of lining in the nasal cavity: 1) the olfactory mucosa, which resides near the roof of the nasal cavity, and houses the receptors for smell, and 2) the respiratory mucosa, which lines most of the nasal cavity, and contains both. serous and mucous cells . Mucous cells secrete, obviously, mucous; and serous cells secrete a sticky, watery fluid containing digestive enzymes (see Note 1). Daily, about a quart of lysozyme, an enzyme that digests bacteria, is secreted. This sticky mucous traps dust, pollen, bacteria, viruses, etc. from incoming air. This trapped "junk" is carried by the mucous, which is continuously moving, into the pharynx, swallowed, and then destroyed in the digestive juices in the stomach. Presumably, serous cells are what run out of your nose on a cold day, or when you eat something hot.
______________________________
Note 1 - An enzyme is a protein, secreted by cells, that acts as a catalyst to induce chemical changes in other substances, but without itself being changed.
______________________________
This is the passageway from the nose and mouth to the larynx (air) and esophagus (food), and is commonly called the throat. What amounts to a flap of skin, called the uvula, serves to prevent food from getting in the nasal cavity. At times this valvelike "thing" fails, and we choke - "I'm okay, it just went down the wrong pipe."
This anatomical gadget, commonly called the "voice box," has three main functions: 1) to provide an open airway, 2) a "switch" to route food and air to their proper destinations, and 3) voice production. The larynx is constructed of cartilage, which includes the Adam's apple - prominent in men because of the stimulation by male sex hormones during puberty. The epiglottis forms the top of the larynx, and is anchored to the back of the tongue. During swallowing, the epiglottis is tipped so that it covers the laryngeal inlet to prevent food from getting into the lower respiratory tubes. Anything other than air that enters the larynx triggers the cough reflex to expel it before it can reach the lungs. Incidentally, this reflex doesn't work in an unconscious body, so fluids should not be given in an attempt to revive an unconscious person.
The location of the larynx is a compromise - it is so low that during swallowing, the epiglottis is sometimes "defeated," and food goes where it isn't supposed to - and we choke. Lucky for us, humans are the only animals that can choke to death, but the low position and long length of the larynx permits speech. The larynx is a resonating chamber for the sounds of speech.
Near the top of the larynx is the cuneiform cartilages, to which the vocal cords are anchored. A boy's larynx, during puberty, enlarges, causing his laryngeal prominence (Adam's apple), which lengthens the vocal cords. Longer vocal cords vibrate more slowly, which deepens the voice. Loss of speech, as with laryngitis, is from swelling of the vocal cords (inflammation), which interferes with their vibration; which can change the tone of the voice, cause hoarseness, or even stop speech altogether (anything above a whisper, normally).
The trachea (windpipe) runs from the larynx down through the neck to where it branches into the right and left bronchial tubes just before entering the lungs. The trachea is another cartilage structure - it has to be fairly rigid to keep from collapsing during breathing, but, at the same time, it is flexible enough to move some (like - expansion when food moves toward the stomach). In addition, it can twist and elongate, while stiff enough to keep the passageway open.
The bronchi (or air tubes) consist of a conducting zone, and a respiratory zone. At the bottom of the trachea, the conducting zone begins as trachea branches into the right and left bronchi, which then enter the lungs. The lungs are divided into lobes (more about that later) - three on the right side and two on the left. Likewise, the bronchi branch in the same manner, to serve the lobes . As they move through the lungs they ramify into many smallerandsmaller bronchi. As their diameter shrinks, they are called bronchioles and terminal bronchioles, which can be microscopic in size. This network is called a bronchial (or respiratory) tree. As the tubes get smaller, the cartilage becomes less rigid. In fact, smooth muscle takes over in the smallest tubes. It contracts or expands to meet the air demands of the moment.
The respiratory zone begins where the terminal bronchioles meet the respiratory bronchioles within the lungs. The respiratory bronchioles are "studded" with alveoli (clusters of which are called alveolar sacs). There are estimated to be 300 million of these sacs, which are the major part of lung volume, and provide an enormous area for gas exchange (oxygen for carbon dioxide) - about 1500 square feet. The alveoli are densely covered by a network of pulmonary capillaries. The thin capillary and alveolar walls are separated by an extremely thin membrane known as the airblood barrier, through which gas exchange takes place.
They occupy the largest part of the thorax (chest cavity), but share it with other anatomical "stuff," mainly the heart. The left lung is slightly smaller than the right one because of the heart - remember its lean to the left - causing its apex to be a little to the left of center. That impinges on the left lung's space, and accounts for the left lung having only two lobes, as opposed to the right lung's three lobes. The apex of a lung (at the top, unlike the heart) is at the level of the clavicle (collar bone), and sits on the diaphragm. The lungs are bounded on their sides, front, and rear by the ribs. The inside of the thoracic cavity is lined by what is called a pleura, which also forms an outer lining of the lungs. It secretes a lubricating fluid which allows the lungs to slide on the inner thoracic cavity walls as they expand and contract during breathing. The pleura also compartmentalize the lungs and heart; that is, it keeps them from interfering with each other during their modest movement during breathing.
A disease - pleurisy (or pleuritis) - is an inflammation of the pleura, often resulting from lung infections, like pneumonia. The rubbing of inflamed pleurae can be very painful. Inflamed pleura can also secrete enough pleural fluid to put pressure on the lungs, and restrict breathing.
Ventilation is the "heart" of lung function - breathing, which is accomplished by inspiration and respiration.
Quiet expiration is primarily passive. The relaxing inspiratory muscles drop the rib cage under the force of gravity, the diaphragm moves up, and elastic fibers in the lungs recoil, which decreases the size of the chest cavity and the lungs - forcing air out.
On the other hand, forced expiration is caused mainly by contraction of the abdominal muscles transversus abdominis and obliques. These contractions decrease chest cavity volume, and out goes the air. Concurrent contraction of the intercostal, quadratus lumborum (sides of waist), and the latisimus dorsi (back) muscles assist with forced expiration.
Neural control of ventilation (for normal breathing) is in the hands of the pons and medulla in the brain stem (lower brain, near where the spinal cord connects at the base of the skull). The dorsal respiratory group (DRG) located in the medulla oblongata, sends out nerve impulses to produce the normal rhythmic breathing pattern (1215 breaths per minute) The pons affects the medullary actions by smoothing transitions between inspiration and expiration (both ways). A unique pons breathing function is to limit inspiration, thereby preventing over inflation of the lungs. Another pons function is to cause breath holding.
Receptors in the medulla, called chemoreceptors, monitor blood chemistry - oxygen, carbon dioxide, and acidity levels. They send out messages to increase the depth and rate of breathing to restore chemical levels to normal, when they get outofwhack.
Higher brain centers can influence respiration, as when the body is under conditions of pain or emotional stress.
Breathing is normally automatically controlled, but we can, of course, modify it, temporarily; as when you hold your breath, or take an exceptionally deep breath. But you can't completely control breathing. Breathholding, for instance, is limited. When a critical level of carbon dioxide is detected, the medulla takes over to try to rectify the imbalance.
Respiratory system diseases are relatively common because of its being open to airborne "stuff." The most serious of these diseases is lung cancer, followed by chronic obstructive pulmonary disease (COPD), like chronic emphysema, and chronic bronchitis. All are highly correlated to cigarette smoking.
Lung cancer is a major killer; 90% of lung cancer victims were smokers. The 5year survival rate for lung cancer sufferers is a paltry 7%. And secondhand smoke is a problem because the carbon dioxide from a smoker isn't evacuated from the scene of the crime until 45 hours after the perp leaves. "Passive smokers" suffer from respiratory irritations and lung cancer just like a smoker. The normal "air cleaners" in the respiratory system are overwhelmed by cigarette smoke, and eventually become dysfunctional. It is the tobacco tars (many are carcinogens) that lead to lung disease.
It is estimated that smokers are 20 times more likely than nonsmokers to get lung cancer, but for smokers that quit at least 15 years ago, the ratio drops to 2 to 1.
Obstructive emphysema is characterized by permanent expansion of the alveoli with a concomitant deterioration of their walls. The lungs become chronically inflamed, causing scar tissue, which causes the lungs to become less elastic - hence expiration becomes more difficult and exhausting. Ending up on a respirator is not an unlikely event.
Chronic bronchitis is a condition where inhaled irritants (like cigarette smoke or air pollution) lead to inflammation and fibrosis (formation of fibrous material) which obstructs airways and impairs ventilation and gas exchange. blood reoxygenation is retarded as a result. It is speculated that this disease would be nearly nonexistent if not for cigarette smoking.
Here is part 2 of the plyometric exercise discussion begun in last month's Newsletter. As was previously stated, it is a system of exercises designed to increase power and speed, and almost by default, strength. Leg training is primarily done through jumping and hopping drills, while upper body work is done primarily using a medicine ball (or plyoball, a medicine ball of varying sizes and weights, and covered in polyurethane). Leg training via jump drills can be very stressful, and plyometric training should only be done after establishing a solid, general fitness level - a good program of flexibility, cardiovascular endurance, and general muscular conditioning.
Some exercises are:
Q I have recently heard that stress may not be the cause of ulcers, as we have been told for years. Do you know anything about this?
W.W., Hershey, P
A Yes. An article in the February 1996 issue of Scientific American says that it has been discovered that most stomach ulcer patients have a high number of a bacteria called H. pylori (Helicobactor pylori), and now consider bacteria to be the main cause of gastric ulcers, and not stress, as was once strongly promoted. The theory was that stress caused excess acidity in the stomach, which, in turn, caused ulcers. But there seems to be no high quality relationship of stress to the stomach, but there is a high H. pilori relationship. NSAIDs, a class of drugs - aspirin is one - can also cause ulcers; but it is thought that H. pylori is, by far, the major culprit. H. pylori seems to affect gastritis, peptic ulcers, and gastric cancer.
Q Is there any legitimacy attached to the calorierestrictionslowsdown aging theory?
Old Dude, S.F., CA
A There seems to be, although the studies that I have seen on this topic were done on mice - none on humans, that I have heard of. Studies on longevity that feature calorierestricted diets have reported increasing longevity by up to 33%. Successful calorierestricted diets require an adequate supply of nutrients - this is essential. Typical aging effects - serious disease, loss of mass, slower thinking processes, loss of flexibility, ad nauseam - are delayed in properly nourished, but lowcalorie dieters.
[Anecdotally, this matches findings in humans.]
It seems to be calorie restriction in general, not just fat (or some other nonspecified part of a diet) that causes the aging slowdown.
Both average and maximum lifespans are extended. One theory suggests that the aging process is the result of freeradical buildup in the body. The freeradicals are formed in the mitochondria when oxygen and nutrients are turned into ATP, which is the final source of energy in mitochondria (the energy storehouse in cells).
Freeradical damage to mitochondria leads to impaired production of ATP, and more freeradicals are created. The result of less ATP is that cells function less efficiently, and overall body functions become impaired. Mitochondrial damage means less energy is produced, and mitochondrial DNA is part of the wreckage. That may be why degeneration of the heart and nervous system are so common in the elderly. It may also account for why muscles lose size and strength with age. Freeradicals lead to cell breakdown and ensuing functional breakdown throughout the body.
To date, tests on primates indicate that a restrictivecalorie diet improves blood pressure, reduces percentage of body fat, lowers triglyceride levels, and more - all good stuff.
On the downside, calorierestricted diets are inappropriate for children - retards growth, might cause osteoporosis, may retard resistance to physical stress (like temperature), and ??
This kind of diet needs more study before being recommended across the board.
Q What is a PUFA? I was reading some nutrition information, and "PUFA" came up repeatedly, but I don't know what it is.
Y.F., Las Vegas, NV
A PUFA is an acronym for polyunsaturated fatty acids. It is somewhat ironic that this question came up, since it is somewhat related to the previous question on calorierestricted diets, as well as the current lowfat diets that are so popular. Since it was specifically stated that a restrictedcalorie diet should be nutritionally complete, this discussion will deal only with lowfat diets. A letter published in the March 6, 1996 issue of JAMA (Journal of the American Medical Association), stated that a lowfat diet can lead to increased risk of heart problems, especially for those with low HDL levels, and high triglyceride levels; or even as a maintenance diet for the general population. Essential Fatty Acids (EFAs) (see Note 2) seem to be, well_ _ _ essential, to maintaining proper HDL levels. Omega3 PUFAs at low levels may increase risk of cardiac arrest. People who eat lowfat diets for more than 3 months, without losing weight , may be at risk of unfavorable cholesterol levels. [There was no explanation of this statement.] Lowfat diets low in PUFAs, may be deadly (heart disease).
Generally speaking, PUFA deficiencies may include:
Q I have seen articles that have brought bystander administered CPR under some criticism. It seems that some (mainly the press) claim that it does more harm than good. Does that mean that I should just stand and watch someone die?
C.J., Potlatch, ID
A No, although some reports would have us believe so. As one doctor said: some CPR is better than none. Speed is of the essence. Get help, but do what you can do for the victim.
Q What type of aerobic machine is best, and don't tell me the one that you'll use.
N.F, Las Vegas, NV
A A recent study of aerobic exercise machines, including rowers, steppers, treadmills, and exercise bicycles, determined that the most effective was the treadmill - in terms of energy expenditure, as measured by RPE (Rate of Perceived Exertion, a scale by which one subjectively rates exercise intensity, and has been found to be reasonably accurate in cases where some practice with using the scale is provided). There was a pretest period for the test subjects to get used to the machines, and the RPE scale. However, the test was run using young, fit subjects; therefore the conclusions may not apply to all populations (initial fitness level, age, etc.). But, the conclusion was not unexpected because treadmills are more weightbearing than the other machines.
Q What is a phospholipid? I know it is a type of fat, but what exactly is it?
D.F., Palo Alto, CA
_______________________________
For questions, call (408) 739-0501, or write to:
MAF, 964 Ponderosa Ave., Suite 25, Sunnyvale, CA 94086-8931.
Yearly mailed subscriptions are $12.00, payable to M.A. Fenner.
Email to Mike_Fenner@netcom.com
Click here to send an email to the author, Mike Fenner