T he integumentary system consists of the skin, sweat glands, oil glands, hair, and nails. This isn't necessarily the most glamorous body system to discuss, but you have to admit that it is important.
The skin is made up of two layers: the epidermis, and the dermis. There is a third layer-the hypodermis, which isn't technically part of the skin, but we will treat it as such anyway.
This outer layer is basically a cover for the body. The epidermal layer is constructed of the same kind of tissue that covers internal organs.
Our skin functions to cushion and insulate deeper body organs, protects us from cuts and bumps, thermal damage, harmful chemicals, and invading bacteria. It also provides an outlet for urea, salts, and water. It also offers some protection against the sun, synthesizes vitamin D from the sun, and "houses" sensory receptors that sense pressure, temperature, and pain. They make our inner body aware of its outside environment.
The epidermal layer is made of four separate types of cells, two of which are discussed - we won't go too deep into the gory details. Keratinocytes, the first cells to be discussed, produce keratin, which is a tough, fibrous protein that gives the epidermis its protective qualities. These keratinocytes, filled with keratin, are constantly dying and rising up to the skin surface, where they are rubbed off. It turns out that the epidermis is "brand new" every 35-45 days, as new cells are produced at the same rate that the old ones die.
The second type of skin cells to be discussed is melanocytes (melanin cells). They make melanin, which gives pigment to the skin to protect against UV rays from the sun. In Caucasians, the melanin is essentially eaten up early in its trip up toward the surface, whereas, in blacks, no such activity occurs, allowing melanin to spread throughout the epidermis.
The epidermis is layered - four layers over most of the body, five in thick skin, as on the palms and soles. The layers provide things like waterproofing - so we can go swimming without becoming waterlogged, and so we can retain water; and help protect against lacerations, for instance.
Underlying the epidermis is the dermis, which is a strong, flexible connective tissue. It is "stuffed" with blood vessels (both the dermis and the epidermis are supplied with blood from capillaries in the dermis) and nerve fibers. The skin contains up to 5% of the body's blood supply. It can be diverted for use in active muscles. It is engorged during hot days to help cooling by radiating heat from the body.
The dermis is made up of two layers. In the upper, or superficial, layer are located what are called "dermal ridges," which push up on the overlaying epidermis, thereby creating fingerprints and footprints. Their real purpose, in addition to crime fighting, is to aid gripping ability.
The deepest layer is made up of collagen fibers that give skin its strength and resiliency.
This layer just below the skin (sometimes called subcutaneous layer, or superficial fascia), and not technically part of the integumentary system, is well known for fat storage (the infamous subcutaneous fat layer). The hypodermis also attaches the skin to the underlying 'stuff' - mainly muscles - and allows the skin to slide on underlying structures, and, therefore, many blows bounce off us - just ask any self-respecting pugilist.
Severe stretching of the skin, as from pregnancy or obesity, can result in tears in the dermis. The scar tissue that results from the heeling of dermal tears is what is commonly called "stretch marks."
Before moving on to the organs of the skin, we will briefly discuss some ramifications of skin color. It has been theorized that human skin colors are adaptations to UV rays from the sun. UV rays are somewhat of a dichotomy - both good and bad, in that too much can cause skin cancer, and too little disrupts the essential process of producing (in the deep epidermis) vitamin D, which the body needs for calcium absorption. In tropical areas, thick dark skin evolved - skin cancer is almost unknown in these areas, but vitamin D can still be manufactured. In northern Europe, where there is frequently very little sunlight, the skin is very light to allow sufficient penetration for vitamin D production. For those in intermediate latitudes, the skin is kind of in-between, to allow vitamin D production, but also to minimize cancer (skin tanning helps). This theory is just conjecture, but that's the best we've got right now.
This sounds like warts or something, but it refers to hair follicles, hair, sebaceous glands, sweat glands, and nails.
Hair Follicles are, in essence, "tubes" from which hairs grow.
Hair for most mammals serves to provide warmth. Human body hair, or so says one theory, is mainly to sense insects before they sting us. [Yeah. Right.] Hair on the head helps us conserve heat, and helps protect the head from the sun. The purpose of eyelashes is obvious. Nose hair helps keep bugs out - and other larger particles that we might breathe in.
Hair is made of keratin, like in other body cells, but it is harder, so it doesn't flake off like skin.
A hair's shape dictates whether it is straight or curly. A hair that is flat (cross section) is kinky; if it's oval it is wavy; and if round, it is straight.
Hair is constantly being recycled. A little falls out daily, and is replaced by new growth. Permanent loss comes with old age - in both men and women. This loss due to age can better be described as hair thinning.
Permanent loss - baldness - is normally a response in males to a genetic "trigger" that usually goes off after about age 40. Permanent loss may also occur from chemotherapy (not necessarily permanent), or exposure to excessive radiation (likely to be permanent). In the case of permanent loss, replacement hair "dies" before it gets out of its follicle.
There are essentially two types of hair: 1) vellus hair, and 2) terminal hair. Vellus hair is short and fine - the normal body hair for women and children. Terminal hair is coarser - like axillary (armpit) hair. As both sexes age, normal hair is often replaced by vellus hair, which accounts for hair thinning.
In some cases hair loss can be reversed by the drug minoxidil, which was actually designed to be an anti-hypertension drug. It was discovered that a side-effect was stimulation of hair growth.
Sebaceous Glands are oil glands in the skin. They secrete an oily substance called sebum, which softens hair and skin, and prevents the epidermis from cracking. It also works to slow water loss, and it does some extermination of bacteria.
Some teenagers have a problem of secreting large amounts of sebum, which blocks sebaceous glands, which often become infected by bacteria - hence, acne. The problem isn't dirt, or diet; and typically disappears as the body matures.
Sweat Glands are located on most surfaces of the human body - about 2.5 million of them. Some sweat (excuse me, perspiration) is produced daily, but intense activity on a hot day can produce over three gallons. Sweating is the body's main cooling system. Humans are better adapted to working in heat than any other mammal. That seems to be why we don't have much body hair, which would interfere with water (sweat) evaporating from our skin. Most of us should notice that sweating begins on the forehead (this is exercise sweat, not nervous sweat) to cool the brain.
Some interesting trivia: ear wax comes from modified sweat glands, and mammary glands are actually modified sweat glands as well. Just a bit of information for your next Jeopardy appearance.
Nails are a scale-like modification of the epidermis. This part of the integumentary system isn't very interesting, so let's just say that nails help us pickup small objects, and scratch ourselves. Enough said.
Carbohydrates are divided into simple carbohydrates (sugars), and complex carbohydrates (starch and fiber).
Simple Carbohydrates, or sugars, are compounds constructed of carbon, hydrogen, and oxygen atoms (as are all carbohydrates). There are six of them: fructose (fruit sugar) and maltose; which can easily be broken down to glucose; which is eminently important, as it lends itself to easy breakdown for energy; sucrose (common table sugar); and galactose and lactose (milk sugars).
Simple sugars and sugar substitutes are rife in our diets. They fall under the names: brown sugar, corn syrup, invert sugar, corn sugar, sorbitol, levulose, fructose, dextrose, honey, and "natural sweeteners." [An aside: honey is no more "natural" or no healthier than sucrose. The chemical components are identical.]
There are a number of artificial sweeteners with few or no calories, like: saccharine, aspartame (Nutrasweet), Equal, and acesulfame (Sunette). Some of these products contain some calories, but only minute amounts are needed to produce the same sweetness as sucrose. A paradoxical side to the use of artificial sweeteners is that, in excess, they may lead to increased calorie intake above that of regular sweeteners.
Complex Carbohydrates (starch and fiber) are found in corn, grains - as in bread, spaghetti (pasta), cereal - legumes, potatoes, and in a variety of fruits and vegetables.
Fiber makes up the structural part of plant cell walls, and is found in leaves, stems, roots, seeds, and edible skins and peels of fruits and veggies. Cellulose, a common form of fiber, is contained in the outer layer of whole grains. (This is the part of grain that is milled out in the refining process. That's why something like 100% whole wheat bread is typically a healthy product - less processing.)
Dietary fiber is not technically a nutrient, but it is an important component of one's diet, as you know from all the fiber hype in the past few years. I think everyone is aware of its value, so I won't go into any "stool" talk.
The recommended intake is 20-35 grams, daily. Soluble fiber (as in oats, peas, carrots, and fruits) should be at about a ratio of 1:3 to insoluble fiber (as in brown rice, corn, and wheat bran), and should preferably come from real food - not Metamucil, or other commercial fiber products. It is interesting that a chart that I am looking at as I write this, lists freeze-dried parsley as the number one food in terms of fiber content (almost three times as high as the next food; of course we don't ordinarily eat gobs of parsley, whether it's fresh or freeze-dried. Maybe we should.
Of course there is a downside to nearly everything. Too much dietary fiber leads to GI problems, and decreases absorption of calcium, iron, zinc, magnesium, and phosphorous. So don't go "high fiber" with religious fervor - ease into it.
It is recommended that one's daily diet should include about 60% carbohydrates - more for active people up to about 70%. Obviously, if you eat more carbs than you can burn or store, the excess is converted to fat, and stored as such; but that is true of all the macronutrients - carbs, fats, or proteins. Excess fat is ---- well, you know. And even protein can be converted to fat. Beyond its job of repairing/building cells, some can be used for energy, some is converted and stored as fat, and the rest is eliminated as just another body waste.
Carbs as an energy source begin as food is eaten. As it moves through the digestive system, it is broken down to sugar molecules and dumped into the blood stream, and transported to body cells. In the cells, it (glucose) can be used to form energy, or it can be converted to glycogen for later use. If carbs aren't supplied regularly, the stored glycogen is returned to its glucose form.
After carbohydrate ingestion, insulin is released to help ferry glucose into cells. When there is sufficient glucose, and the glycogen stores are full, the sugar molecules are converted to fat, and stored. In the absense of sufficient glycogen, protein is broken down, mainly into glucose. Hence, carbohydrates are a "protein sparer," in addition to being a major energy source.
As has been mentioned, ingested carbohydrates are primarily used as an energy source, either as glucose for immediate use, or as glycogen for future use. [Let's just ignore the conversion of excess carbohydrates to fat for now.] The blood normally contains a standard amount of glucose. At this normal level, we are said to be in a normoglycemic state. After a meal, insulin is released to help move glucose into cells. Any excess is stored in the liver and muscles as glycogen, but there is a limit to how much can be stored. Beyond that limit, any excess is converted to, and stored as, fat (triglycerides). [Sorry, I couldn't help it.]
In the absence of adequate glycogen, muscle protein is used to create more glucose. This process is called gluconeogenesis (for those of you who care), and results in a decrease in lean body mass, and over-works the kidneys, which must excrete the "garbage" resulting from protein breakdown.
Another important job of carbohydrates is to assist in fat metabolism. [You may have heard the phrase: fat burns in a carbohydrate fire.] Without adequate carbohydrate stores, the body wants to use its normally plentiful fat stores for energy, but only incomplete metabolism can occur, resulting in the release of acid by-products called ketones. They can upset the acid/base balance in the body, causing a potentially dangerous condition called ketosis.
The brain needs glucose. When the blood sugar level falls below normoglycemic, the body becomes hypoglycemic. Some symptoms are hunger, dizziness, tachycardia (sewing machine heart beat), weakness, excessive sweating, and impaired exercise performance (as in hitting the wall in a marathon). Hypoglycemia can result from starvation, a weird diet-like low carbs-high fat, or long duration exercise. This highlights the need for a constant supply of carbohydrates - whether it comes in the form of snacks, a meal, or even a sports drink, isn't important. But, that they are in constant supply is important.
A third condition, hyperglycemia, is a result of a too-high blood sugar level; as can result from diabetes (characterized by insufficient levels of, or ineffective use of, insulin). Death is the most extreme, though very possible, result of this condition.
In summary, there are four basic functions of carbohydrates:
1 - an energy source
2 - a protein sparer
3 - an aid to fat metabolism
4 - CNS fuel (brain food)
Heartburn (also called dyspepsia) is the sensation of burning just at the tip of the sternum, or upward into the center of the chest. In addition to other causes previously mentioned in an earlier issue of this newsletter, it may be a result of a hiatal hernia.
Hiatal hernia is the name of the condition where a portion of the stomach protrudes through a hole in the diaphragm, into the chest cavity. The diaphragm, a muscle that assists breathing, separates the chest cavity from the abdominal cavity. There are holes in the diaphragm to allow "stuff." like nerves and blood vessels, to pass from the chest to the abdomen. One of these holes is called the hiatus, which allows the esophagus to connect to the stomach. If this hole gets too big, part of the stomach can slip through it into the chest cavity - called a "sliding" hernia, or esophageal hernia, or diaphragmatic hernia. This is an intermittent problem. When you are standing, everything is okay, but when you are lying down, the "sliding" occurs. Two common causes are pregnancy and obesity. If one has stored excess abdominal fat, it can create pressure (as would a baby, or even intestinal gas), and force the stomach through the hiatus. The bottom line is that abdominal pressure, regardless of the source, can cause a hiatal hernia.
In addition to a hiatal hernia, heartburn can be caused by ulcers, or inflammation from things like citrus fruit or juices, tomato products, coffee, or alcohol. Heartburn symptoms may also be caused by fats (which delay stomach emptying), chocolate, peppermint, or spearmint. Of course, eating late meals is a contributor to heartburn. Another cause of heartburn stems from the fact that some digestive system nerves come through the spine, and affect involuntary muscles, like those of the digestive system, which is, end-to-end, one long tube made of involuntary muscles. Here are some rules to follow if you have heartburn, regardless of the source :
L et's finish off the fiber topic for this month's Newsletter. We hear about fiber, dietary fiber, soluble fiber, and insoluble fiber. What's the difference? We defined fiber earlier, in our carbohydrate section. An oak tree is stuffed full of fiber, but most of us wouldn't eat it. We prefer fiber in vegetables, fruits, breads, cereals, grains, and legumes. Fiber that we actually eat is "dietary fiber."
Soluble fiber is fiber that can be dissolved in water. There are high concentrations of soluble fiber in oats, barley, and legumes, for example. It delays emptying of the stomach, and the ensuing transit of semi-digested food from the stomach to the intestines. It tends to lower blood cholesterol, but maybe only because it tends to replace other food which includes cholesterol (like when a person changes to a more vegetarian type diet, from more of a meat-eating diet). Anyway, whatever the reason, eating more fiber does lower cholesterol.
Insoluble fiber is not dissolvable in water, and is found in high concentrations in veggies, wheat, and cereals, for example.
Obviously, fiber comes from plants only, and plants all contain a mixture of soluble and insoluble fiber. Eat a plant, get some fiber. Of course, the more processed it is, the less fiber it contains. So a prudent shopper will look for things like 100% whole wheat bread, and brown rice; and a prudent eater will go for things like fresh fruit and vegetables, as much as possible.
This is sort of an afterthought, but another benefit of eating plenty of fiber (other than cholesterol lowering and the bowl stuff) is that it is calorie-free, since it is indigestible; but it helps give a "full" feeling - so you will eat less; therefore, it can be a weight control factor.
(Q) What is the best [aerobic] exercise?
N.M.K.F., Los Vegas, NV
(A) That question begs for a subjective answer, so that's what I'll give you. A glib answer is: "the one you will do." But I'll try to do a little better. Although, actually, you may have just gotten the absolute best answer. But,. you probably want to hear something more substantive. Your personal fitness goals have some bearing on this, but my personal favorites are: 1) walking, 2) a recumbent bicycle, and 3) swimming.
Walking ranks high for convenience, and weight control. You can do it pretty much anytime, anywhere. The only equipment needed is a pair of shoes, and that isn't even always a requirement. There is no joint-stress, to speak of; and choosing a pace that makes walking an effective 'fat-burner' is almost a non-choice. Low to moderate intensity exercise uses a higher percent of fats than carbohydrates as its fuel source. Walking can even improve cardiopulmonary fitness. If there is a drawback to walking for fitness, it is that a significant time investment is required, unless you're not in a hurry for progress. But it is safe and effective.
Pumping away on a recumbent exercise bike is my own personal favorite aerobic exercise (when I can't run, that is). The seat and seat-back provide excellent support. You can work toward cardio pulmonary fitness, leg muscle endurance, weight control - you can maximize your efforts toward whatever your goal might be, without an intrusive seat between your legs.
Swimming may be the best of all, except for people like me who don't like to swim, or don't have full-time access to a pool. But, for those who do, you get super benefits. It can improve cardiopulmonary fitness, and muscle strength and tone; without weight bearing stress.
On the downside is the potential for shoulder injury, and, seemingly, no significant fat loss. The jury is still out on this very significant fitness factor. Many studies have shown no significant weight loss, but some researchers believe that too little intensity, or too-cold water may be the problem - not the exercise mode.
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