What are Stem Cells?

For many years, stem cells have been suggested as the ideal vehicle for mending or replacing tissues damaged by disease. Experimentation has been severely hampered by the technological problems of producing and obtaining genetically compatible stem cells. In addition, potential ethical issues surround obtaining and using stem cells derived from embryos.

This issue of embryonic stem cells and their use in medicine has caused considerable public controversy. Recently, however, a technique using the fully differentiated skin-cell nucleus, injected into an unfertilized ovum, may get around the concern of using embryonic cells. Moreover, this technique would make it possible to match the stem-cell genetics with the recipient’s genome. In actual practice, the process would be very expensive, and it is many years from being clinically applicable. Still, this is a medical break-through.

What are stem cells?  Stem cells are cells with a full complement of genetic material that are able to differentiate into different types of cells with different functions.

In this definition, I’ve used words and phrases that are not part of standard vocabulary but are well understood by biologists. Full complement of genetic material means a cell has all the genetic material necessary for a whole organism; in the case of humans and most other animals, this means a diploid cell, or a cell that has chromosomes (and genes) from two parents. Differentiate is a verb that means to transform from one, rather general functional state to another, more specialized function. This involves permanently turning off some genes and turning on others. Different kinds of cells means cells with different functions, such as liver cells compared with cells of the pancreas. Most cells in the body are not stem cells because they are already fully differentiated or specialized. And most differentiated cells rarely divide or reproduce themselves.

Stem cells may be “pluripotent,” that is, they may be able to differentiate into many different cell types. This sort of stem cell is plentiful in embryos and is rare in adult individuals. Other stem cells may be partially differentiated; for example, they may be able to develop into one type of blood cell or another type of blood cell, but they cannot produce a skin cell. The signals for cellular differentiation come from the surrounding environment. Chemical signals may arrive through the blood stream, but more often they come from surrounding cells. Physical signals such as stretch and pressure can also play a role. Thus, if you transplant a pluripotent stem cell into a tissue, it will receive instructions from surrounding cells, and these form a sort of cellular cultural milieu, telling the stem cell what traits it should develop.

The ethical issue seems to center around the question: “Are human stem cells actually micro-humans?” The answer to this question has to be an unequivocal “NO.” Only a developed human being is actually a human, with the rights and privileges (and ethical consideration) due to a person. A cell is not a person. Our bodies contain many stem cells, but we do not thereby believe that we are several persons in one body.

It is an absurdity and a failure of our educational system that so many Americans think a single cell—or even a group of cells—should be equated with a fully developed human being.

How Does the Body Repair Itself? Cellular repair.

Perhaps the most amazing feature of living beings (organisms) is that they are often able to repair injuries inflicted by the environment. That’s lucky for us, because our bodies sustain a lot of damage as we move through life, and the body needs to last a lifetime.

Living organisms exist in a non-living environment, which is basically hostile and can easily do harm. Fortunately, every life form is endowed with protective strategies against invasion from outside; in humans, the most obvious protective shield would be the skin. But protective strategies do not always work, and all organisms are subject to damage.

Damage can be lethal, or an organism may survive the damage. If it survives, an it must repair itself in order to be able to function. How does repair happen? There are two levels of biological repair: 1) cellular repair and 2) tissue repair. These two types of repair take place through different mechanisms.

Cells are the basic building blocks of living things. They are tiny, microscopic units surrounded by membranes, which separate what’s inside from the surroundings. Cells contain even tinier organelles that carry out the work of keeping each cell alive. Human cells are surrounded by extracellular fluid, mostly coming from blood.

Cells can be damaged by chemicals or by radiation, or they may be invaded by viruses. Cellular damage occurs even during normal, everyday activity. For one thing, cells need oxygen to fuel the process of energy production, but oxygen is really a toxic molecule. It tends to react with other molecules, causing them to change structure and lose function. Special cellular organelles, called peroxisomes, help minimize oxygen damage to cells. Many other kinds of molecules can also cause cellular damage, including toxins in food we eat and in the air we breathe. Examples include alcohol, smoke, pesticides, and many medicines.

Thus, the survival time of most cellular proteins is shorter than you might think – ranging from about half an hour to a day or so. A few proteins, well protected inside cellular organelles, can last longer, perhaps a few weeks.

During the repair process, a cell must clear out damaged proteins and produce new functional molecules. Special organelles, called lysosomes, contain enzymes capable of breaking down biological molecules. The small subunits are then re-used to produce new molecules in a fine example of cellular recycling.

New proteins are constantly being manufactured by cells—in part to replace damaged proteins, and in part to perform new functions that a cell may be called on to perform. This process takes place through gene expression, which involves using information from a gene to manufacture proteins. These complicated biochemical processes occur continually in all cells except red blood cells.

So, the bottom line is: many cells are able to survive for a long time because they can  repair moderate damage and produce new molecules–if they have adequate nutrition and energy. Important exceptions include cells of the skin and digestive tract, which are damaged by friction, bacterial invasion, chemicals and enzymes in the gut. Thus, their lifetimes are measured in days or weeks rather than months.

The topic for the next entry will be tissue repair, the other major strategy for fixing the body when it has been damaged.

See Your Doctor If…

The body is an almost miraculous, self-healing being, and if cared for properly, it will usually last for a good, long lifetime. If you have survived the ills of childhood and have reached the age of 25 without incurring serious, long-term illnesses, your body is probably able to take care of potential assaults from the outside, including most micro-organisms and trauma from minor accidents. However, the body, like any reliable vehicle, must be carefully maintained. If you lead a healthy lifestyle, you can trust your body to heal itself most of the time without having to visit a physician for simple sniffles or coughs or stomach upsets, or after minor damage from cuts and bruises.

However, a few warning signals should not be ignored, even in a healthy person. If you experience any of the following signs, a physician should be consulted immediately.

  • Bleeding from any orifice. If blood comes from the eyes, nose, ears, mouth or anus, this is usually a sign of trouble inside the body.
  • Fever above 103 degrees Fahrenheit indicates that the body is trying to fight a very serious infection.
  • Loss of consciousness, other than during normal sleep, indicates a problem in the brain or in its blood supply. This can also be signaled by sudden and lasting confusion, loss of vision, or loss of ability to control movement.
  • Stabbing pain in any area of the body, but particularly in the chest or abdomen, can signal heart disease or serious gastrointestinal problems, such as appendicitis or intestinal blockage These can have deadly consequences.
  • Serious difficulty with breathing can signal a potentially deadly acute allergic reaction that may even result in anaphylactic shock (loss of blood fluid volume because of a systemic allergic reaction) or possibly a blood clot in the lungs. Asthmatics usually know the symptoms of an asthmatic attack, and  these should also be treated quickly, but may or may not require a doctor’s visit.
  • A severe blow to the head, particularly in the region of the temples—even without loss of consciousness—can lead to a delayed, life-threatening build-up of pressure on the brain. It is important to verify that there has been no internal bleeding.

In the absence of symptoms such as those listed above, probably the best long-term strategy for maintaining health is:

  • eat a healthy diet,
  • get adequate sleep and exercise, and
  • allow the body to heal itself if you experience normal communicable diseases such as colds, flu, occasional stomach upsets, or headaches.

If you go to a physician for diseases that are temporary and not life-threatening, the doctor will probably prescribe medicine, thinking you expect it, and the medicine could do more harm than good.

Many studies now indicate that doing nothing (or taking a placebo) for ordinary illnesses may have better outcomes than seeking medical help. This is clearly understood by physicians, who tend to go to doctors less frequently than the general public. Because doctors know the potential danger signals, they understand when a physical problem is serious and when it is likely to go away on its own. Homeopathic medicine may be “effective” in many cases simply because the patient is receiving essentially no medication, and the body is allowed to heal itself. If you talk to those who have lived very long lives, one of the things they will say is that they rarely go to the doctor, and they seldom take medicine, other than coffee, tea, or a little wine. Do they not go to doctors because they are so healthy, or are they healthy because they don’t often visit doctors?

Did You Know? Diabetes

Did you know that there are actually three general types of diabetes? Diabetes comes from a Greek word that simply means excessive urine. It was recognized as a specific disease millennia ago by Egyptian and Greek physicians. All three forms of diabetes involve problems with hormones: the two most common forms involve the hormone insulin and the third involves a hormone called ADH or vasopressin.

Diabetes mellitus (“sweet urine”) results from excessive sugar in the blood, specifically glucose, which passes into the kidney tubules and is insufficiently reabsorbed into the blood. This high urine glucose concentration draws extra water along with it into the bladder, causing it to fill more rapidly. The two types of diabetes mellitus are Type I (or juvenile-onset) diabetes, and Type II (or maturity-onset) diabetes.

Type I diabetes is caused by loss or destruction of insulin-secreting cells (beta cells) of the endocrine pancreas. The reasons for loss of these cells are not clear, but it usually occurs in childhood. This condition may result from viral infection followed by an auto-immune reaction. There may be a genetic component to the susceptibility to this type of diabetes. Type I diabetes is less common than Type II diabetes. Insulin is the key hormone that promotes uptake of sugar into muscle and fat, and many other tissues, although the brain can use glucose without insulin. If insulin is not produced by the endocrine pancreas (islet cells), then blood glucose is not taken up into most tissues, and blood sugar levels rise.

Type II diabetes is usually a result of decreased insulin receptors on cell surface membranes. A receptor is a molecule that binds to a hormone (or to some other communication molecule) and that brokers its effects on a target. Type II diabetes normally occurs in older, overweight individuals, but with the onset of the obesity epidemic in America, even younger children are suffering from this form of diabetes. Again, causes of the disease are not entirely clear, but there is definitely a genetic component involved, which is made worse by obesity and stress.

Diabetes insipidus is a third type of diabetes, which is much rarer than diabetes mellitus and does not involve sugar in the urine. Diabetes insipidus is caused by a decrease or loss in the production of a pituitary hormone known as anti-diuretic hormone (ADH) or vasopressin. This small molecule is secreted by the posterior pituitary gland. It is a major hormone involved in the regulation of body fluid volume and blood pressure. Vasopressin acts on kidney tubules to promote water reuptake into the blood from the urine.

This type of diabetes is rare, but it can occur following a blow to the head, or with blood loss to the lower part of the brain, or damageof the pituatary stalk with a brain tumor. The secretion of ADH/vasopressin is inhibited by alcohol, and thus alcohol consumption also increases urine output, but its effects are reversible.

The Large and Small of It

Let’s begin with an overview of the body as we will view it in this blog-site.

The human body is an extremely complex, self-repairing organism that consists of trillions of specialized, interdependent cells. The body remains alive so long as its cells are able to metabolize (chemically transform molecules and energy) sufficiently well to sustain the body’s homeostasis (maintenance of an internal environment optimum for cellular metabolizm). So each one of us is an enormous ecosystem that is both sturdy and fragile.

Our cells and our bodies are products of both genetic and environmental influences. Genetic information comes mostly from our parents at the moment of conception. That genetic information changes only rarely as we develop, mature and age. Outside–environmental–influences affect the way that genetic informtion is expressed from the time of conception until death. Such outside influences include what we eat, how much we exercise, other organisms we’re exposed to, the psychological stresses we endure, as well as physical and chemical assaults.

So our body’s structure and function are a result of what we are and what we do. What we do, the habits we develop, strongly influence our body’s ability to repair and maintain us into a long, satisfying older age. This blog will focus on the underlying biology of the major body systems in the hope that understanding will influence habits of health that can sustain those systems over the long run.

Good Health to You!

Welcome to Caring for Your Body, devoted to helping you, the reader, develop HABITS OF HEALTH. You own your own body, it’s yours for the long run, and you can’t trade it in, so you may as well take care of it!

This site offers information on human anatomy, physiology and pathology, in the belief that understanding can motivate behavior and promote health and wellness. The information presented here is in no way intended to substitute for medical care and/or advice.