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HUMAN DISEASES (Part 2 of 7)   Leave a comment

What Happens When Immunity Backfires

Paradoxically, a person’s immunity system can backfire and develop auto-antibodies against his own body tissue. In many diseases of unknown cause, doctors have found many unusual antibodies in the blood serum of patients.

Rheumatoid arthritis (RA), chronic disease of the connective tissue, causing painful sensations in joints and muscles.

Doctors think the patients become sensitive to something made by their own bodies. Only a slight change in certain proteins in normal body tissue is necessary for them to become antigens. Most diseases marked by the production of auto-antibodies cannot be traced to infection or drug allergy. In rheumatoid arthritis, for example, the rheumatoid factor is the presence of auto-antibodies in the victim’s blood. These auto-antibodies may stick to the membranes lining the bone joints and cause a reaction that destroys tissue in the joints. In other disorders associated with reversed immunity, auto-antibodies strike red blood cells, tissues surrounding small blood vessels, or other target areas. Ulcerative colitis, a disorder marked by an inflamed portion of the intestine, often with ulcers, is also believed to be an autoimmune disease.

In some cases, lymphocyte defects or discrepancies in antibody production lead to an immune deficiency. The victim is then helpless against recurring infections. A simple head cold can soon become pneumonia. Antibiotics or serums with antibody-rich gamma globulin offer temporary relief in such cases.

1796: Inoculation against disease. The simple medical procedure known as vaccination first came into use in about 1713 as a means of preventing smallpox. Such inoculation sometimes proved dangerous, because individuals sometimes caught a severe case of the disease instead of a mild one. This problem was solved by Edward Jenner, a British physician, in 1796. He realized that individuals inoculated with the much milder cowpox virus became immune to smallpox. Jenner tested his theory in May 1796.

This kind of inoculation earned the name vaccine, from the Latin word vaccinus, meaning “from cows.” Since Jenner’s day vaccines have been developed to fight polio, diphtheria, whooping cough, measles, typhoid fever, cholera, tetanus, and other diseases.

1928: Penicillin. In 1928 the Scottish bacteriologist Alexander Fleming was doing research on the Staphyloccus bacteria when he noticed that a growth of mould Penicillium notatium was contaminating the culture. There was no bacteria where the mould was present. Following up on this fact, Fleming found there was something in the mould that prevented bacterial growth. He named this substance penicillin.

By continued experiment Fleming learned that penicillin is capable of killing many common disease-causing bacteria. His discovery proved to be one of the first and most useful antibiotics used in medicine today. By 1940 penicillin had been turned into an injectable medicine. Its use grew dramatically during World War II as an infection-preventing agent.

HOW DRUGS FIGHT DISEASE

With the advent of drug therapy in the 20th century, doctors began to use lifesaving drugs to fight disease. The clinical use of sulphanilamide, the predecessor of sulphur drugs, in the 1930s and the mass production of penicillin, the first antibiotic, in the 1940s gave physicians extremely powerful tools with which to fight infection. A disease-fighting drug never acts by itself. It always works in conjunction with the body’s immunity system. Vaccines have also become available for the prevention of certain diseases.

How Certain Drugs Quell Infection

Such antibiotics as penicillin, streptomycin, and tetracycline are very effective against bacterial infections. The name “antibiotic” comes from antibiosis, or the use of substances made by one living thing to kill another. Antibiotics are made by bacteria and moulds that are specially cultured in commercial drug laboratories.

Antibiotics kill bacteria and other disease organisms in various ways. Some destroy the cell walls of bacteria. Others interfere with bacterial multiplication or fatally alter the way bacteria make vital proteins. Still others mix up the genetic blueprints of the bacteria.

Ordinarily, an antibiotic tricks bacteria into using the antibiotic’s chemicals instead of closely related ones that the organisms really need for making the key enzymes required for their growth and reproduction. With the antibiotic assimilated into their systems instead of the vital chemicals, an essential activity or structure of the pathogens is lacking and they die.

Sulphur drugs act in a somewhat similar but less effective way. Weakened but not killed by the sulphur drugs, the pathogens fall easy prey to the body’s scavenger cells. Drugs are also available against parasitic worms, infectious amoeba, and other pathogenic organisms.

Antibiotics are not very effective against viruses because the drugs cannot get into the body cells where viruses hide and multiply. However, the body produces a protein called interferon that inhibits viral reproduction.

A drug is sometimes recognized by the body’s immunity system as an antigen. It then triggers a severe reaction. In some cases, a person can suffer anaphylaxis, or extreme sensitivity, to penicillin after repeated injections. Without quick medical aid, severe cases of anaphylactic shock can be fatal.

How Bacteria Become Drug Resistant

Once in every several hundred million cell divisions a mutation makes a bacterium immune to an antibiotic drug. The mutation alters the bacterium’s genetic code and thus its ability to use certain chemicals for its life activities. Mutations can be caused by the radiations from outer space that stream into the Earth’s atmosphere, as well as by some atmospheric chemicals. As a result of the mutation, all bacteria that stem from the immune germ will be resistant to the drug unless any of them undergoes a mutation that makes the strain susceptible again. Hence, whenever a new antibiotic is developed, there will be a chance that bacteria will develop an immunity against it. But because mutations are fairly rare, doctors have a good chance of fighting a bacterial disease with the new drug before future strains become resistant.

Some members of a bacterial strain are resistant to certain drugs naturally. In the course of time they can eventually become selected through evolutionary forces to become the dominant drug-resistant forms of a pathogenic strain.

More importantly, some bacteria can pass on their drug resistance to bacteria of another strain by “infection.” Since the passing of resistance factors does not depend upon the lengthy process of mutation, it poses a much greater problem of drug immunity. As a consequence, doctors often must prescribe more than one antibiotic to fight certain diseases in the hope that this will slow bacterial resistance.

Use of Vaccines and Hormones

A person can become artificially immune to some diseases by means of a vaccine. Vaccines contain antigens that stimulate the production of protective antibodies. Immunity to smallpox, polio, measles, rabies, and certain other diseases, is induced by injecting a person with vaccines containing living but attenuated, or weakened, disease organisms.

A vaccine containing only dead organisms protects against typhoid fever and whooping cough, as well as against measles and polio. Vaccines containing toxins, or poisons, are used to prevent diphtheria and tetanus. When injected into a person, they trigger the production of special antibodies called antitoxins.

Some body disorders are caused by too much or too little hormone production. Hormones are body chemicals that influence many vital biochemical reactions. When someone suffers a hormone deficiency, a doctor usually can treat the deficiency with hormone shots.

1347: Black Death. The plague is one of the most devastating diseases that has ever afflicted mankind. It is a highly contagious fever caused by the bacillus Yersinia pestis, which is carried by fleas that infest rats.

The plague, commonly called bubonic plague or the Black Death, has been known since ancient times, but the best documented instance was its deadly appearance in Europe in 1347. It raged throughout all of Europe, killing at least one-fourth of the population probably 25 million people. Without understanding how it is spread, people had no defence against the disease. Poor sanitary conditions and the disruption of war only worsened the epidemic.

In Europe the epidemic started in Sicily and was spread by shipboard rats to other Mediterranean ports. It moved to North Africa, Italy, Spain, England, and France. By 1349 it made its way to Austria, Germany, Switzerland, and the Low Countries. By 1350 it reached Scandinavia and the Baltic states.

In general, the population of Europe did not recover to its size before the plague until the 16th century, and some towns never recovered. The immediate results of the plague a general collapse of economies, a breakdown of class relationships, and a halt to wartime hostilities forced a massive restructuring of society. It has had a lasting impact on art, literature, and religious thought.

INFECTIOUS DISEASES

Infectious diseases can be transmitted in many ways. They can be spread in droplets through the air when infected persons sneeze or cough. Whoever inhales the droplets can then become infected. Some diseases can be passed through contaminated eating or drinking utensils. Some can be spread through sexual activity. Others can even be spread in the course of medical or surgical treatment, or through the use of dirty injection equipment, especially by drug abusers.

Cold (also called common cold, or coryza), illness, acute inflammation of upper respiratory tract.

Once an infectious organism gains a foothold in the body, it begins to thrive and multiply. Its success is slow or fast, depending upon the nature of the pathogen. The symptoms of the common cold, for example, appear within a few days of infection. However, the symptoms of kuru, an uncommon disease of the nervous system, often appear three years or longer after infection.

Incubation period, length of time before the symptoms of a disease appear.

Every infectious disease has an incubation period. This is the length of time between the pathogen’s gaining a foothold in the body and the appearance of the first symptoms of the disease.

Several factors also determine whether a person will become the victim of a disease after being infected. The number of invading germs the dose of the infection influences the outbreak of disease. So does the virulence of the pathogens; that is, their power to do harm. In addition, the condition of the body’s immunological defences also affects the probability of catching a disease.

Contagious Disease

A great many infectious diseases are contagious; that is, they can easily be passed between people. To acquire certain contagious diseases someone need only be in the presence of someone with it, or come in contact with an infected part of the body, or eat or drink from contaminated utensils.

Someone can be a carrier of a contagious disease in several ways. He can be an asymptomatic carrier, or have a disease without ever developing its symptoms. He can be an incubationary carrier and pass on the pathogens at any time during the “silent” incubation period. He can be a convalescent carrier and transmit some of the infectious organisms remaining in the body even after recovery. Of course, anyone suffering the frank symptoms of a contagious disease can pass it on to others while the disease is running its course.

HEART AND BLOOD SYSTEM DISEASES

Disease of the heart or of the blood vessels, called cardiovascular disease, is the leading cause of death in the United States and Canada. It claims more than a million lives each year in the United States; more than 70,000 each year in Canada.

The heart is a muscular pump. When its own tissue or blood vessels become diseased, serious and sometimes fatal harm can follow.

Coronary Artery Disease

Disease of the coronary arteries that supply oxygen and nutrients to the heart is the most common heart ailment. Coronary artery disease accounts for more than a third of all deaths among males in the United States between the ages of 35 and 55. It also strikes many women past the age of 50. Hypertension (high blood pressure), overweight, cigarette smoking, diabetes mellitus, excess cholesterol, triglycerides and other fats in the blood, and probably lack of regular exercise contribute to the chance of getting coronary artery disease.

Coronary artery disease is characterized by an atheroma, a fatty deposit of cholesterol beneath the inner lining of the artery. The atheroma obstructs the passage of blood, thereby reducing the flow of nourishing blood to the heart muscle. It also sets up conditions for a blood clot in the coronary artery. Atheroma formation seems to run in families. Eating foods rich in saturated animal fat and cholesterol is also thought to contribute to atheroma formation.

Many persons with coronary artery disease do not experience symptoms. If the obstruction is bad enough, however, it may cause angina pectoris, myocardial infarction, or heart enlargement and failure.

Angina pectoris, brief paroxysm of severe chest pain with feeling of suffocation.

Angina pectoris is a chest pain that feels like something is squeezing or pressing the chest during periods of physical exertion. It takes place when the heart’s oxygen needs cannot be met because of a blocked coronary artery. Rest will relieve the pain. Some persons have angina pectoris for years and still live active lives.

Myocardial infarction is commonly called heart attack. Tissue death that results from a lack of blood is called infarction. When the coronary artery becomes so obstructed that the myocardium, or heart muscle, does not receive oxygen, it dies.

Heart attack (also called myocardial infarction, or coronary occlusion), an acute episode of heart disease.

Once, it was believed that a blood clot occluded the coronary artery and caused the infarction. This is why a heart attack is sometimes called a coronary occlusion. However, it now appears that most clots form in the artery after the infarction.

The first few hours after a heart attack are the most critical because abnormal heart rhythms may develop. Ventricular fibrillation is the most dangerous. The ventricles of the heart contract so fast that the pumping action is baulked Death follows in three or four minutes. Heart attack patients are usually treated in the coronary care unit of a hospital for a few days to enable electronic monitoring of the heart rate and rhythm.

Heart failure, condition that develops when repeated heart attacks occur.

Heart failure can occur when repeated heart attacks put too much strain on the remaining healthy heart muscle. As attacks destroy more and more heart muscle, the remaining muscle hypertrophies, or enlarges, to maintain effective pumping. Pressure builds up in a weakened heart, however, and causes fluid backup in the lungs. As a result, the heart output cannot keep pace with the body’s oxygen demands.

HUMAN DISEASES (Part 5 of 7)   Leave a comment

Non-infectious Nerve Disorders

Neuritis, disease of the nerves causing pain, abnormal circulation, and reflex action; differs from neuralgia because of inflammation; treatment includes heat, proper nutrition, physical therapy, and medication.

Neuritis is the degeneration of one or more nerves. It is often marked by a pins-and-needles feeling, a burning sensation, or a stabbing pain. Neuritis can result from infection, especially of the facial nerve, hard body blows, or bone fracture causing nerve injury. Everyday hard grasping of tools and activities requiring cramped body positions can also trigger neuritis.

Neuralgia, severe, stabbing pain along course of nerve; not associated with nerve damage; attacks often triggered by infection, malnutrition, chilling, or fatigue; sometimes is symptom of organic disease; trigeminal neuralgia, popularly called tic douloureux, affects main sensory nerve of face and is treated by local anaesthetic or cutting of nerve roots.

Neuralgia is often confused with neuritis but is a distinct problem. Neuralgia is characterized by sudden, sharp bursts of pain along any of the sensory nerves near the body surface.

Sciatica is severe leg pain resulting from an inflamed sciatic nerve or its branches. A ruptured, or “slipped,” disk one of the pads between the vertebra of the spine often causes sciatica.

Tics are usually habitual muscle twitches in the face or neck that seem to serve no purpose. A tic is generally intensified by an emotional situation or by fatigue.

Vertigo, a severe form of dizziness resulting from the inability of the body to adapt to abrupt or unexpected motion.

Vertigo is a dizziness or disorientation that occurs when something is wrong with the body’s balancing system, part of which is located in the inner ear. The sufferer feels as though he is falling through space.

Parkinson’s disease (or paralysis agitans, or Parkinsonism), chronic disorder of nervous system, manifest by tremors and muscle weakness, accompanied by changes in pigmented cells of brain stem; strikes in middle or late life; treated with drugs and sometimes by brain surgery; named for James Parkinson (1755-1824), British physician who identified it in 1817.

Parkinsonism, or Parkinson’s disease, is thought to stem from changes in brain chemistry. Victims of the disorder walk with a slow, shuffling gait, have a wide-eyed, unblinking facial look, and experience muscle tremors, or shakes. They also have trouble speaking and swallowing. Parkinsonism can be treated with a drug called levodopa, or L-dopa.

Multiple sclerosis (MS), chronic disease of the nervous system; cause unknown; leads to disturbances of vision, speech, coordination, and bodily functions.

Multiple sclerosis is a slow-developing disease that eventually involves the entire brain and spinal cord. Its cause is not yet known, but the disease eats away the fatty myelin sheath around many nerves. As a result, it interferes with proper nerve-signal transmission to muscles and organs. Muscle control, vision, mental abilities, and many other body functions are eventually impaired. Physical therapy is often required because the limbs of victims become weak and they are easily tired doing ordinary tasks.

Stroke

Stroke (or cardiovascular accident), common term for cerebral thrombosis (a blood clot that interrupts the blood supply of the brain) and for cerebral haemorrhage (a rupture in a blood vessel that allows blood to escape into the brain tissue); both can cause brain damage with resulting paralysis or death.

A stroke, or cardiovascular accident, occurs when blood can no longer nourish brain tissue and key nerve cells are thereby destroyed. A blood clot in one of the brain’s blood vessels, haemorrhage from a broken blood vessel there, or hardening of a brain artery can cause a stroke.

Depending upon the brain area affected, a stroke can culminate in loss of limb use particularly the arms speech difficulties, and partial blindness. In time, victims of relatively non severe strokes often regain most or all of the impaired body functions. In more severe cases, extensive physical or speech therapy is needed for partial rehabilitation of the stroke victim.

Epilepsy

Epilepsy, disease of the nervous system, frequently from subtle brain damage, less often from injury; characterized by sudden, recurrent seizures with loss of consciousness and severe convulsions (grand mal), or in mild form by brief blackouts and fainting spells (petit mal).

Epilepsy is a brain disorder in which nerve signals “fire” abnormally and cause convulsive seizures, or alternating muscle contractions and relaxations. Scar tissue in the brain can provoke some seizures. In many cases, however, doctors cannot pinpoint the reason for an epileptic attack. Someone might have a seizure once and never again. If someone has more than one seizure, the second and any that may follow are officially called epileptic attacks.

Doctors generally recognize several types of epilepsy, including grand mal, petit mal, and infantile spasms. A grand mal attack is usually marked by rigidly contracted muscles, loss of consciousness, and collapse. The attack may last from two to five minutes, followed by deep sleep.

A petit mal attack usually comes as a lapse of awareness for less than a minute. The victim then resumes whatever activity he was engaged in before the attack without realizing anything out of the ordinary took place. Infants under the age of three sometimes have infantile spasms during which sharp muscle contractions force the body to jackknife for a few seconds. Anti convulsive drugs are used to treat and prevent all such attacks.

METABOLIC AND DEFICIENCY DISEASES

Disease can sometimes follow from alterations in normal body metabolism caused by deficiencies in diet, hormones, and vitamins. It can also stem from malfunctions in the body’s immunity system.

Malnutrition and Vitamin Deficiencies

Malnutrition can be either over nutrition or under nutrition Obesity resulting from overeating can lead to high blood pressure, heart disease, and diabetes. Under eating can stifle the development of body and mind.

Marasmus is the condition that results when a child’s diet lacks both total calories and protein. A child with marasmus is always hungry and wastes away. Kwashiorkor is a protein deficiency that saps a child’s strength even though his diet contains enough calories. A child with kwashiorkor lacks an appetite and is sullen. Both conditions occur in underdeveloped nations.

Vitamin deficiencies are uncommon among people in the world’s richer nations, except in the cases of pregnant women and those who breast-feed their babies. Since ample vitamins are in the general diet in those lands, there is no medical justification for daily doses of multivitamins to stimulate vigour or prevent colds or infections.

Iron, silver-grey, hard, brittle, fusible element that is the cheapest and most used of all metals. In pure form it is very reactive chemically and rapidly corrodes in moist air and warm temperatures. Iron is often alloyed with other metals to make it tough yet malleable. Pig iron is used to produce steel. The use of iron is prehistoric

Properties of Iron

Symbol Fe

Atomic number 26

Atomic weight 55.8

Group in periodic table VIII

Boiling point 4,982 F (2,750 C)

Melting point 2,795 F (1,535 C)

Specific gravity 7.874

Mineral deficiencies can also produce body disorders. Iron is indispensable for the prevention of anaemia Magnesium is a cofactor in many enzymes. Deficiency of it causes dizziness, weakness, and convulsions. Iodine is a major part of the thyroid hormones. Without it a person can develop a goitre Fluorine is not considered essential, but it plays a great part in minimizing dental caries, or cavities. Trace elements, such as chromium, cobalt, and manganese are also needed for a healthy body.

Hormone Deficiencies

The body’s endocrine system produces a variety of hormones. When the endocrine glands are not working properly, certain disease processes can begin.

Abnormal output of growth hormone from the pituitary gland early in life can result in one of two disorders dwarfism if there is too little or gigantism if there is too much. Abnormal output of certain hormones from the adrenal glands causes irregular regulation of the body’s water balance and disturbs the normal retention and excretion of salts. Malfunction in sex hormone production can stem sexual activity, as well as produce excessive hair growth and distribution. Malfunction of the thyroid gland affects the rate at which food is burned for energy, causing the metabolic rate to run too fast or too slow for everyday needs. When part of the pancreas breaks down, diabetes develops.

1921: Insulin found to treat diabetes. In 1921, at the University of Toronto, Frederick Grant Banting and Charles H. Best conducted experiments that successfully isolated the hormone insulin. This hormone is used to control the disease diabetes. The name of the hormone is derived from the Latin word for island, insula, because the hormone is produced in the part of the pancreas called the Islets of Langerhans.

Although it had been known for some time that the pancreas made the enzymes responsible for digesting proteins, it had not been possible to isolate insulin. Insulin is a protein and is digested by the enzymes. Banting and Best used animal experiments to extract insulin and demonstrated that it stopped symptoms of diabetes. Commercial production of insulin uses pigs, oxen, and sheep as sources for the hormone.

Diabetes Mellitus

Diabetes mellitus, a fairly common disease, is caused by lack of biologically active insulin, a hormone secreted by the pancreas. Without insulin the body cannot use sugars and starches in the food. It must then rely upon its stored fat for energy. This storehouse is soon exhausted, however, because without insulin the body can no longer make and store fat. In addition, protein is no longer manufactured and the muscle mass of the body dwindles. The effect of growth hormone is reduced too. All this adds up to a rise in the level of blood sugar and increased urination, which, in turn, dehydrates the body and makes the diabetic thirsty. The sufferer loses weight, experiences muscle cramps, and has an itchy skin. If diabetes is not treated, sodium and potassium are lost in the urine and the products of fat breakdown, called ketones, build up in dangerous proportions in the blood. The blood also becomes increasingly acid and body dehydration reaches a dangerous level. Finally, the untreated diabetic goes into a potentially fatal coma.

Diabetes is treated by limiting the patient’s diet and injecting him with insulin derived from cattle or hog pancreases. This treatment was pioneered by the Canadian physicians Frederick G. Banting and Charles H. Best in the 1920s.

Recently, an oral medication has proved capable of lowering the blood sugar of diabetics who develop a mild form of the disease after they reach adulthood. These tablets do not contain insulin but are helpful as long as the pancreas of the diabetic still produces some insulin.

Long-term diabetes is often associated with blood vessel degeneration. When this complication occurs, the diabetic can suffer heart disease, stroke, eye haemorrhage and blindness, kidney failure, gangrene of the feet, and serious neuritis.

The normal blood-sugar level ranges between 60 and 100 milligrams per 100 cubic centimetres of blood. It rises slightly higher after a meal. When the level falls below normal, a person has hypoglycaemia and may develop headache, irritability, sweatiness, and other symptoms. Later, the patient has trouble keeping balance, speaks incoherently, and may even become violent or act listless and withdrawn. Finally, the hypoglycaemic person falls into a coma and may have convulsions.

A diabetic may experience hypoglycaemia when he gets an excessive dose of insulin or oral medication. Hypoglycaemia can also result from diseases of the adrenal, pituitary, and pancreas glands, as well as from starvation, liver damage, and alcohol intake. Moreover, some otherwise healthy persons, especially those under too much stress, can suffer mild hypoglycaemia In an emergency, a health care provider may administer sugar, either orally or by intravenous injection. Glucagon, a pancreatic hormone that raises the blood-sugar level, can also be injected. Long-range treatment involves correcting the disorder engendering the low blood sugar. People suffering from hypoglycaemia often respond very favourably to a change in diet that balances sugar and other nutrients.

GENETIC ENGINEERING (Part 2 of 2)   Leave a comment

Genetic engineering had its origins during the late 1960s and early 1970s in experiments with bacteria, viruses, and small, free-floating rings of deoxyribonucleic acid (DNA) called plasmids, found in bacteria. While investigating how these viruses and plasmids move from cell to cell, recombine, and reproduce themselves, scientists discovered that bacteria make enzymes, called restriction enzymes, that cut DNA chains at specific sites. The 1978 Nobel prize for physiology or medicine was shared by the discoverer of restriction enzymes, Hamilton O. Smith, and the first people to use these tools to analyse the genetic material of a virus, Daniel Nathans and Werner Arber.

The action of restriction enzymes is the crux of genetic engineering. DNA is made up of two long intertwined helices. The backbone of each helix is constructed from a chain of organic compounds called nucleotides. DNA is the carrier of genetic information; it achieves its effect by directing the synthesis of proteins. DNA is composed of four different nucleotides, repeated in specific sequences that form the basis of heredity. Restriction enzymes recognize particular stretches of nucleotides arranged in a specific order and cut the DNA in those regions only. Each restriction enzyme recognizes a different nucleotide sequence. Thus, restriction enzymes form a molecular tool kit that allows scientists to cut the chromosome into various desired lengths, depending on how many different restriction enzymes are used. Each time a particular restriction enzyme or set of restriction enzymes is used, the DNA is cut into the same number of pieces of the same length and composition. At least 80 restriction enzymes are now known.

When restriction enzymes are used along with other enzymes that tie together loose ends of DNA, it becomes possible to remove a bit of DNA from one organism’s chromosome and to insert it into another organism’s chromosome. This allows scientists to produce new combinations of genes that may not exist in nature. For example, a human gene can be inserted into a bacterium or a bacterial gene into a plant.

So far, however, there are limits to this ability. Scientists are unable to start with only test tubes full of nucleotides to create a whole new organism. They must start with the complete genetic material of an already existing organism. Thus, genetic engineering allows the addition of only one or a small number of new characteristics to an organism that remains essentially the same. In addition, only characteristics that are determined by one or a few genes can be transferred. The technology of genetic engineering does not enable scientists to transfer behavioural traits, such as intelligence, that are a complex mixture of many genes and the effects of cultural conditioning.

In practice, genes to be inserted into bacteria are first recombined into a plasmid, which replicates and travels independently from its bacterial host. The modified plasmid is then inserted into another bacterium.

At the time that these methods became available, it was not known whether DNA could be replicated and expressed in a foreign organism. Experiments done in the mid-1970s with these techniques, however, showed clearly that a human gene could be reproduced by a bacterium along with its own genetic material and that the bacterium could make the protein coded for by the human gene. This opened the way to making large amounts of human hormones and other significant human substances in the laboratory, a much easier route than isolating these substances from blood or cadaver glands.

One of the first areas in which genetic engineering exerted an influence was the medical field. Genetic engineering techniques allowed the production of large amounts of many medically useful substances, particularly the class of biological compounds called peptides. Peptides are short proteins. Many of the most important chemical messengers in the body are peptides. These include hormones such as insulin, nervous system messengers such as the endorphins, and regulatory messengers from the hypothalamus that control production of hormones by the pituitary gland, the gonads, and the thyroid gland, among others.

Several biologically useful peptides were made and tested in clinical trials during the late 1970s and early 1980s. The first genetically engineered product to be approved for human use was human insulin made in bacteria. Insertion of the human insulin gene into bacteria was accomplished by the pioneer genetic engineering company Genentech. Testing, approval for medical use, and large-scale production of genetically engineered human insulin were carried out, and the first diabetic patient in the world was injected with human insulin made in bacteria in December 1980, making this the first genetically engineered product to enter medical practice. (Genetically engineered products are often identified by the prefix r, for “recombinant.” Thus, genetically engineered insulin is sometimes written, r-insulin.)

The interferons are another medically important group of peptides that became available in abundance only after the development of genetic engineering techniques. Interferon was useful for treating viral infections, and there were strong indications that it might be effective against some cancers. Before the advent of genetic engineering techniques, it took laborious processing of thousands of units of human blood to obtain enough interferon to treat a few patients. And this interferon was not very pure. With the insertion of the interferon gene into bacteria, large amounts of very pure interferon became available. This supply allowed trials of interferon in the early 1980s against more than ten different cancers, including the particularly virulent form of Kaposi’s sarcoma often found in persons with acquired immunodeficiency syndrome (AIDS). The human body makes more than 50 different varieties of interferon. It is thought that some types of interferon may be more effective against cancer than others.

Other medically useful human peptides that have been made widely available because of genetic engineering are human growth hormone, which is used to treat persons with congenital dwarfism and was formerly obtained from cadaver pituitary glands, and tissue-type plasminogen activator (t-PA), which is a promising new treatment for persons who suffer a heart attack.

Vaccines

Genetic engineering techniques have also been investigated as a means to produce safer new vaccines. The first step is to identify the gene in a disease-causing virus that stimulates protective immunity. That gene is isolated and inserted into a harmless virus, such as vaccinia, the virus used to immunize against smallpox. The recombinant vaccinia virus is used as a vaccine, producing immunity without exposing people to the disease-causing virus. In the case of viruses about which little is known, such as the AIDS virus, this extra margin of safety is crucial.

Recombinant techniques may be useful in making vaccines against organisms for which no vaccines could be made by traditional methods. These include possible vaccines against the tropical parasites that cause schistosomiasis and malaria.

Diagnosis, Therapy, and Research

Genetic engineering is also being used in the prenatal diagnosis of inherited diseases. Restriction enzymes are used to cut apart the DNA of parents who may carry a gene for a congenital disorder, and the DNA pattern of cells from the fetus is compared. In many situations the disease status of the fetus can be determined. Currently this technique is applicable to thalassemias, Huntington’s disease, cystic fibrosis, and Duchenne’s muscular dystrophy.

A future medical use of genetic engineering is for gene therapy. Persons who are born with a congenital disorder resulting from a defective gene could have a sound gene inserted into their cells, preventing the manifestations of the disease. The era of gene therapy began on Sept. 14, 1990, when the first therapeutic, genetically engineered cells were infused into a 4-year-old girl with adenosine deaminase (ADA) deficiency, an inherited life-threatening immune deficiency. The infused cells were lymphocytes from the girl’s own blood, into which researchers had inserted copies of a missing gene that directs production of ADA. On Jan. 29, 1991, gene therapy was used for the first time to treat cancer, when two patients with advanced skin cancer were infused with their own white blood cells after the cells had been genetically altered to produce a tumour-killing protein. Many obstacles must be overcome to achieve the promise of gene therapy, but its value could be immense.

Ribozymes, RNA molecules that act like enzymes to cut and splice themselves.

Genetic engineering has allowed discoveries that could not have been made any other way. One of the most important is the discovery of oncogenes, specific genes that play an important part in causing some cancers. The identification and isolation of oncogenes depended on being able to cut cancer-causing DNA into manageable segments and finding the specific segments that were responsible for transforming normal cells into cancer cells. Discovery of ribozymes RNA molecules that act like enzymes to cut and splice themselves gave scientists hope for a new way of destroying the expression of unwanted genes. (RNA, along with DNA, is a carrier of genetic information.)

Agricultural advances are also expected from genetic engineering. Some of the earliest recombinant organisms made were a soil bacterium that was induced to make a toxin against a worm that destroys corn roots, a bacterium engineered to make potato and strawberry crops more frost-resistant, and a tobacco plant bearing a bacterial gene that protects against herbicides. Work on agricultural applications of genetic engineering proceeds slowly because recombinant organisms must be released outdoors in test fields to find whether they work. They cannot be tested only in a contained laboratory. Government regulatory agencies and ecological scientists are wary of the possible adverse consequences of releasing recombinant organisms, particularly fast-reproducing bacteria, into a field plot. No one knows how likely it is that such organisms may escape the field, grow in some situation in which they are not wanted, and cause unexpected effects.

National Institutes of Health, established 1887 at Marine Hospital, New York, N.Y.; present name from 1948.

Public debate about the safety of recombinant organisms began in the 1970s. Government bodies were set up to screen proposed experiments and institute safety guidelines. Chief among them was the Recombinant Advisory Committee of the National Institutes of Health. For many years the public was concerned about the safety of laboratory research with recombinant organisms. As research has continued and no safety hazards have become evident, public concern has abated somewhat.

Assisted by William A. Check.

Posted 2012/02/25 by Stelios in Education

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ANIMAL BEHAVIOUR (Part 2 of 3)   Leave a comment

Orienting Behaviour

An animal orients by adjusting its posture and position in space. It does so in relation to the source of different forms of energy in its environment. These forms include light, heat, and chemicals in the air or water, pressure, electric current, air or water currents, gravity, radiation, and magnetic fields.

Tropism, involuntary turning of a cell or organism in response to a stimulus.

Orienting behaviour may take the form of a tropism an action in which the animal simply orients its body toward or away from the source of energy without changing location. Plants can also respond in this way. However, the orienting response may take the form of a taxis a movement toward or away from the source of energy by swimming, flying, or locomotion. As a rule, only animals are capable of such responses. Still another type of orienting response is called a kinesics an increase or decrease in an animal’s activity, but in no particular direction.

Prefixes are usually added to the root words tropism, taxis, and kinesics to indicate the kind of energy to which the organism is responding. For example, geotropism is response to gravity; photo taxis, response to light. Prefixes may also indicate the type of response made. Thus klinokinesis refers to turning activities. In addition, the direction or intensity of a response may be described as positive, if directed toward a stimulus, or negative, if directed away from it.

Orientation makes it possible for an animal to feed, to exhibit social behaviour, and to avoid obstacles and barriers. Some organisms, such as the bat, use sonar reflected sound to locate prey and to avoid obstacles. Some fish can navigate through tight crevices by detecting changes in their electric field. Electronic instruments enable researchers to detect and record the sound frequencies and electricity emitted by different species.

When foraging for food, the honeybee orients to the odour of flowers and the polarization of light. It also responds to cues from the sun’s position off the horizon. This type of activity is called sun compass orientation. On returning to the hive the bee performs certain “dances” a variety of motor patterns that vary with the distance and direction of the food. These dances stimulate the other bees to travel the path of the returning bee.

Fish and birds also exhibit compass orientation when homing or migrating. However, scientists are not sure that animals navigate in the same way as man. When humans navigate, they use such instruments as the sextant to find the altitude of the sun and stars and a chronometer for timekeeping. It has not yet been demonstrated that homing and migrating animals can “shoot an azimuth” and “tell time.”

Some animals are known to return to the areas where they were born or spawned. The salmon, for example, upon reaching sexual maturity responds to the chemical characteristics of the stream in which it was spawned. The hormonal changes associated with sexual maturity are a cause of this new sensitivity. The stickleback moves from salty to brackish water to reproduce. Its behaviour is related to endocrine gland responses to seasonal fluctuations in light. Similar hormonal changes in birds lead to migration and reproduction. These cyclic changes in behaviour due to hormonal regulation are considered evidence of a chronometer that might enable migrating or homing animals to correlate changes in visual cues during compass orientation with changes in internal rhythms and thus make navigation possible.

Social Behaviour

All living things relate to other members of their species. In an amoeba, the relationship occurs only during the short time it takes the animal to split into two animals. In other species, such as the social insects, the relationship is so necessary that they cannot survive as individuals. This is true also of humans, who are dependent on others until they reach maturity. Social organization of some kind is common to all animals. However, the type of organization varies with the nervous system of the species. And in true social organization, animals of the same species react to each other.

Con-specifics, or animals of the same species, may at times be close to each other without exhibiting social behaviour For example, mollusc larvae may respond to changes in the intensity of light by swimming to the water surface. The resultant grouping, called an aggregation, stems from a common response to a physical aspect of the environment. But a response is truly social only when it is a response to visual, chemical, auditory, or other stimuli emanating from a con-specific As a result of such stimuli, animals may approach each other to form a bond or to fight. Although dissimilar, both reactions are examples of social behaviour

Goby, any of numerous, widely distributed, spiny-finned fishes constituting family Gobiidae, having wide, flat head, large mouth, and ventral fins often united in funnel-shaped disk.

The type of bond formed by con-specifics is a measure of their nervous and hormonal systems. Organisms with relatively simple systems may respond to each other only as long as they give off attractive or offensive stimuli. For example, a worm will approach another worm during the reproductive state because certain chemicals are released. Once mating has occurred, they have nothing further to do with each other. A goby will remain near its eggs only as long as the hormonal state of the fish and the chemical and visual features of the eggs remain the same. Once the fry, or young, hatch, the fish responds to them as it would toward any small fish and tries to eat them. The goby does not recognize the fry as its own offspring.

Although orientation, changing hormonal levels, and other processes play a part, social bonding depends primarily on a mutual exchange of stimulation and food between animals. The give-and-take stimulation of a pair or a group is fundamental to the organization of social groups.

The Army Ant Colony – An Example of a Social Group

An army ant colony consists of many thousands of workers and a queen. The queen is capable of laying large batches of infertile eggs when she is fed sufficiently. These eggs hatch into workers, females incapable of sexual reproduction. However, at a certain stage of the queen’s development she produces a brood of males and females capable of reproducing and starting new colonies.

The colony has a two-phase cycle of activity. The nomadic phase lasts about 18 days. By late afternoon or early evening, the larger workers cluster and leave the bivouac area where they spent the previous night. They move out over many yards in the area around the bivouac. As they crawl, they lay a chemical trail. Other ants in the colony travel over the trail, and as the trail becomes more frequently travelled the concentration of chemical stimuli on it becomes stronger. The entire colony, queen and all, eventually move out from the bivouac along the trail. The ants range over large areas, preying on other insects and their young.

Army ants take in considerable food during the nomadic phase. The queen receives a good deal of it. She does not usually forage but is able to feed on the food brought back by medium-size workers. They return to the bivouac to lick the queen for the highly attractive chemicals she exudes. Chemicals that attract or repel con-specifics and heterospecifics (members of other species) are called pheromones. The exchanges of food and secretions between the queen and the workers produce a strong social bond that aids in keeping the colony together. The queen’s increased food intake enables her to lay a batch of eggs. However, this affects her relationship with the workers. She becomes less stimulating to them, and their foraging, therefore, begins to decrease. Now the colony enters the other phase of its cycle the statuary phase. The number, frequency, distance, and area of foraging decreases considerably. The level of the entire colony’s activity drops to a minimum.

After about 21 days the eggs hatch, and the larvae emerge. These squirming, active young are an intense source of stimulation to the workers. The workers are driven out of the bivouac and the nomadic phase starts again. They are now attracted by the pheromones of the larvae and the queen. When the workers return from foraging, they drop their food and feel and handle the larvae with their antennae and legs. As a result of this excitation, the number and frequency of raids again increase. The colony travels great distances, the larvae are fed, and the queen is overfed. At this point, the colony consists of the queen, workers, and larvae.

About 18 days after the eggs have hatched, the larvae enclose themselves in cocoons and become pupae. At about the same time, the queen lays her next batch of eggs. Now the colony consists of the queen, workers, pupae, and developing eggs. However, the pupae and the eggs offer little stimulation for the workers, and the statuary slowdown begins. But the queen continues to secrete pheromones that socially bind the colony.

Dominance

In communities of certain animals the ruling, or dominant, animal is the largest, strongest, or most aggressive and thereby exerts the most influence on the other animals in the group. The dominant animal enjoys the greatest and most preferential access to members of the opposite sex and control of the best territory for feeding and breeding. Many groups of animals, most notably baboons, birds, foxes, lions, and crocodiles, establish dominance hierarchies. The best-known example is the pecking order of chickens. Flock members are arranged on the “rungs” of a social ladder, with each chicken superior to those below and subordinate to those above. The top animal has primary access to the necessities of life, such as the best food, mates, and living quarters. Submissive animals are left with less-desirable food, mates, and living quarters. Such animals may even be expected to groom dominant members and to help care for the offspring of more dominant animals, because subordinates are often prevented from having offspring of their own.

In other animal groups, dominance hierarchies are more complicated. Wolf packs, for example, are led by two dominants who have three subclasses of subordinates below them. Other animals have only one dominant leader with all other animals below him or her being exactly equal. Once an animal has established dominance, challenges to the order are rarely made from within the group, since animals are reluctant to fight other animals that are bigger, stronger, or more aggressive than they are themselves. Sometimes, however, animals from outside the group can successfully challenge and overthrow a long-time leader, but this is rare.

In more intelligent species, such as baboons, factors beyond mere size and strength determine the dominance hierarchy. Age seniority, hormonal condition, maternal lineage, and personality are sometimes factors that affect dominance in more intelligent animals. In baboon groups, furthermore, hierarchies are often elaborate. Adult males are dominant over less mature males and females; yet a fully mature female can be dominant over a less mature male. A dominant baboon displays its superiority with rapid “fencing” manoeuvres, open-jaw displays, and hitting.

Close Bonds Among Animals

Animals with complex nervous systems, ranging from some fish to mammals, may form monogamous bonds. The mates of such species stay together for a breeding season or even for a lifetime. Their social ties are not restricted by the time-bound, immediate stimulation that simpler animals need. However, monogamous pairs must be able to identify their mates from other con-specifics This requires the intricate action of an advanced nervous system.

Some birds and many mammals band in large groups, such as herds and families. These groups include adult males and females and offspring of different ages. The offspring in most mammalian groups remain with the group until they reach sexual maturity. The females frequently remain until the group splits up. Some socially bonded groups of mammals consist of an older male, a number of younger males, many females, and immature offspring. Among the howler monkeys and some other mammals, the younger males band together into a marginal bachelor group until each establishes himself as the older male in a new social group.

Not all mammals maintain elaborate group arrangements. Many live fairly solitary lives, coming together only for mating. Afterwards, the female remains with the litter until the young become juveniles or are sexually mature. In some instances, the mating pair stay together until the young are born. Beavers behave in this way. In other instances, the male and the female separate immediately after mating. This is true of many other rodents.