About bones - we will address bone function, types of bones, and bone growth and maintenance.
A long bone, or any type, consists of an outer layer (smooth and solid looking) called smooth bone. Inside the outer layer is spongy bone, which is structured in a honeycomb fashion, where the solid parts are called trabeculae. The open spaces are the actual homes of bone marrow.
Now, on to long bone structure. Each bone has a shaft (a tubular structure called a diaphysis. Each end of the bone, called epiphyses:, which are covered with a thin layer of cartilage, for cushioning. During childhood the epiphyses are soft, which allows for lengthening to accommodate growth. The soft ends slowly ossify (solidify) and thereby lengthen the bone - while the soft end just moves out farther. After complete maturation, the epiphyses are solid bone.
This is a slight diversion, but an infant begins life with many more bones than an adult has - a result of ossification (e.g., an infant's skull consists of five separate bony plates - the frontal, two temporal, a parietal, and an occipital plate. These flat bones are held together by a cartilage-like material, which ossifies as part of physical maturation; and we end up with one bone (like a helmet (We are purposely ignoring the face and jaw.). The same thing happens with the hip girdle: in an infant it consists of an ilium, pubis, and ishium. All are joined together after cessation of growth.
Long bones are well-supplied with blood, which is supplied by arteries that enter through holes in the diaphysis (holes in bones for blood vessels and nerves are called foramen.). Anyway, the blood enters bone to nourish the bone marrow, and both spongy and compact bone.
As we arrive at the center of a long bone, we discover an open cavity (medullary cavity, or marrow cavity), which is filled with yellow bone marrow. This is just another storage depot in addition to between the trabeculae of spongy bone.
Long bones have an exterior covering, except on their articular cartilage surfaces ("articulate" is anatomyese for "touch;" i.e., some ribs articulate with the sternum (breastbone)), called the periosteum, which is attached to bones by a thick mass of collagen (see Note 1). One of its functions is to provide a surface to which tendons and ligaments can attach. At its deepest layer are some interesting characters - osteoblasts and osteoclasts. These guys scour bones - osteoclasts look for old or damaged bone, and dig it out - destroy it. Osteoblasts follow along, and when they find a pot hole, they fill it (i.e., they deposit new bone). This is part of the body's renewing itself - skin flakes off and is replaced; blood cells come and go; and, similarly, bone is continually being renewed. In one sense, we aren't today what we were yesterday.
In addition to the outer surface of bones being covered, the inner surfaces have their own thin covering - endosteum - which also contains osteoblasts and osteoclasts .
Irregular, short, and flat bones are very similar to long bones in that they have a periosteum covering the outside of compact bone, and endosteum covering the inside of spongy bone; but, they have no diaphysis or epiphysis. and they do contain bone marrow, but there is no marrow cavity.
______________________________
Note 1 - Colagen is the major protein component of the white fibers of connective tissue, cartilage, and bone.
The stress is very often unbalanced, or off-center; which results in the bones bending. As a bone bends, it compresses on one side, and stretches on the opposite side. These forces are strongest at the bone surfaces, which may appear to be why the designer put compact bone on the outside; while the inside contains spongy bone - perfectly adequate for the lower internal forces. Even the medullar cavity in long bones (making them essentially hollow) is up to handling normal stress. The internal space makes bones much lighter - we probably couldn't move very well with solid ones.
The trabeculae in spongy bone are aligned to provide maximum strength for the relatively light bones - a very efficient overall design.
The lengthening of bones has been mentioned - ossification of cartilage (using a long bone as an example, again) at the epiphyses, and further extension of cartilage until the epiphyseal plates (in a word" "bone-ends") close and growth ceases (roughly, at age 18 in females; and age 21 in males). In other words, what happens here is that the epiphyses and diaphysis grow together, or fuse. But, in addition to bones lengthening, they have to widen as well. How do they do that, you ask. Well, I just happen to have an answer for that question, and it involves action from our old friends, osteoblasts and osteoclasts. Osteoblasts add bone to the exterior of the diaphysis; and osteoclasts, more-or-less simultaneously, remove it from the interior surfaces. Note that in most cases long bone growth has been used as an example. The other bone types grow in slightly different ways, but are not sufficiently different to be described here.
The organic/inorganic mix makes bone as strong as steel, as far as resisting tension goes. Another way to say this is that without the mineral salts, our skeletons, consisting only of the rubbery collagen to hold the bones together, would collapse.
This gets us back to osteoclasts and osteoblasts again. These two cell types come in a series of "packets," which are "remodeling units." Their digging/filling jobs have been previously described. Early in life, bone mass stays relatively constant because they work equally. All bones (or even bone parts) aren't remodeled at the same rate, although all are remodeled to some degree. An example is the femur (thigh bone) - the bottom end is renewed every five or six months, but the diaphysis is remodeled much more slowly.
Q There is a product sold here in Oregon, and elsewhere, called Blue Green Algae, which the manufacturers claim will cure or help AIDS, Altzheimer's, herpes, among other diseases; and will detoxify your body, purify your blood, boost your energy, help you lose weight, or maybe even boost your immune system. Have you heard anything about this drug, food - whatever it is?
P.E., Oakland, OR
A Yes, I am familiar with the product - pond scum, actually. It contains some protein, vitamins, and other nutrients; but there is nothing special about this stuff, except maybe the price. They (the manufacturers) claim that American soil is so deleted of nutrients that we need to buy their product. If that were true, we would all be seriously debilitated, or dead, by now. According to the Jan 1997, Berkeley Wellness Letter, some of the claims are supported by testimonials, but by no published evidence, except that this pond scum contains some nutrients. So if you don't eat vegetables, maybe you should eat this stuff, but there are some side effects - frequently nausea and diarrhea. To sum up: Dr Varro Tyler, Professor of Pharmacognosy (scientific study of herbs) at Purdue University says: "It contains minimal amounts of protein, and it's not a particularly good source of nutrients. It doesn't even taste good. It has never been proven useful. I'd rather eat a carrot."
Q I consider myself to be a fashionable woman, and wish to try a little cigar smoking. If it's good enough for Demi Moore and Goldie Hawn, I just have to try it; but, are there any drawbacks; I won't inhale.
B.B., Hollywood, CA
A For starters, they stink; but more significantly, although they result in less lung cancer than cigarettes, cigars are hardly risk-free. They increase a woman's chance of getting lung cancer by three times. They also boost the risk of getting heart disease and cancer of the mouth/lips. Smoking cigars causes from four to ten times as much oral cancer in women, compared to those who don't smoke.
Also, cigars produce more pollutants than cigarettes. For example, they produce three times more carbon monoxide than a cigarette. And second-hand smoke presents similar problems to that of cigarettes.
Oral cancers have been mainly a male problem, but women seem to be trying to catch up as they strive for sexual equality.
Q Is a stiff-legged deadlift a low back or a hamstring exercise? I have heard both.
D.F., Palo Alto, CA
A I have also heard it both ways, and I think it can be incorporated into a workout either way. Think about what happens. You start standing, arms extended, while holding a barbell across your thighs. Now you lean forward, and lower the bar toward the floor (the bar is over your feet, that is, close to your body). Your back is "flat" (e.g., no big hump in your back, but maintain the normal, modest inward curve in your lower back (lumbar spine)). As you lower the weight, your hamstrings (and glutes) are seriously contracted (isometrically), so it is a leg exercise; but the only significant movement throughout this exercise is in the lower back (erector spinae muscles) as you bend forward and then straighten up again. So it's a back exercise. I use it as a back exercise; you do what you want.
A word of caution. You will frequently see people in gyms standing on a bench so they can lower the weight below their feet. Don't do that! The lower one goes, the greater the risk of back injury, as the "big hump" inevitably creeps in at this point. In point of fact, I have rarely seen anyone perched on a bench who actually lowered the weight below the level of the top of the bench; in-other-words, the exercise could have been done while standing on the floor, without risking a fall, and without sacrificing ROM. And remember to keep your neck in-line-with-your-spine. When you are erect, you should be facing forward; and when you are bent over, you should be facing the floor.
Q Is there anything to the currently popular high-protein, high-fat, low-carb diets, as espoused by Barry Sears, Dr. Adkins, Michael and Mary Eade, and Rachel and Richard Heller? They make some pretty fantastic claims.
J.L., Boston, MA
A Yes they do, and there seems to be only anecdotal evidence on their side. The scientific community seems to be in agreement that these diets are nothing more than a rehash of similar diets proposed decades ago. There is agreement that weight loss is an almost inevitable result of these diets because they are low calorie, but that there are some potential dangers associated with them; and that the rest of the claims are a pipedream.
The diets proposed are supposed to cut out bread, grain, pasta, and fruit. All are associated with unhealthy fat gain, they say. It's the resulting excessive insulin that makes us fat, they say. Researchers say, not because of excess carbs, but because of too little activity - not enough exercise. And more protein isn't the answer. Many sources, including researcher Edward A. Mascioli at Harvard Medical School, say that the average diet in the U.S. already includes twice as much protein as is needed. According to the January 1997, Harvard Health Letter (the source of the bulk of this information on low-carbohydrate diets), there have been numerous studies that have linked high-protein/high-fat diets to many health problems. It can increase the risk of cardiovascular disease and cancer. And many of these low carbohydrate diets include warnings to avoid foods like fruit, vegetables, grains, and low-fat dairy products; which are attributed by mainstream dietitians/doctors to have proven health benefits.
Books like Sears' The Zone, claim that a high fat/protein diet fights cancer, among other things. Michael Thun of the American Cancer Society, scoffs at that idea. Saying instead that, in the absence of any supporting evidence for that claim, he recommends a diet high in fruits and vegetables and fruits, and lower in fat and maybe protein as well [15% may be a good number].
High fat/high protein foods are associated with a third of the 500,000 cancer deaths per year in the U.S. In September of 1996, the American Cancer Society recommended eating very little meat [Red meat, I presume.] and, instead, eat more plant foods.
Most people already know that the way to control their weight is through controlling caloric intake and exercising. And, as much as we wish otherwise, there is still no "magic pill."
_______________________________
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