Metabolism

Metabolism refers to all of the chemical processes that take place in an organism when it obtains and uses energy. Metabolism can be divided into two major phases in which substances are broken down and other substances are made. All organisms conduct both phases constantly.

If the body of a living thing is thought of as a machine, then its metabolism is similar to a running motor. In an organism, however, the motor is not only never turned off, but it is able to monitor itself and make adjustments according to internal and external changes that are always taking place. The job of the entire organism, just like the job of every living cell, is to conduct metabolic reactions continuously. These reactions all center around the processing and use of energy. Such reactions are needed by cells and the entire organism to constantly fuel itself, repair itself, and grow. The entire range of these chemical reactions make up an organism's metabolism.

TYPES OF METABOLISM

Metabolism can be divided into two phases or categories: catabolic metabolism (catabolism) and anabolic metabolism (anabolism). Catabolism is also known as destructive metabolism. It involves the breaking down of the molecules in nutrients taken in and the release of the energy they contain. Through catabolic processes, complex compounds like fats, carbohydrates, and proteins, are degraded (broken down) into simple molecules so their energy can be released. Catabolism takes place in the body when food is digested. However, if the system needs energy and no food is available, catabolism can also break down the body's stored fat and protein.

Anabolism is also called biosynthesis or constructive metabolism and can be considered the reverse of catabolism. By its different names, it is apparent that these types of chemical reactions involve the synthesis or the making of essential, complex molecules from simpler components. Anabolism is the body's building-up phase in which it uses the complex substances it has just formed for growth and overall body maintenance. For instance, by combining amino acids (the building blocks of protein molecules), the body's cells can form structural proteins and use them to repair and replace worn-out tissues. It can also form functional proteins such as enzymes to speed up chemical reactions, antibodies to fight disease, and hormones to regulate body processes.

The remarkable thing about an organism's metabolism is that its two phases of chemical reactions are going on constantly, stopping only when the organism dies. This constant and highly complex level of chemical activity has built-in control mechanisms that regularly monitor and adjust to all sorts of changing conditions. Hormones control metabolism, and thyroxine, which is secreted by the thyroid gland, determines the rate of metabolism (meaning the rate at which the body uses up energy to perform a certain metabolic function). The pancreas determines whether anabolism or catabolism is being performed, and then releases either insulin or glucagon. Since eating causes the level of glucose in the blood to rise, the pancreas responds by releasing insulin which, in turn, starts the process of anabolism. If the glucose level is low, the pancreas releases the hormone glucagon, which triggers the catabolic processes.

THE BASAL METABOLISM RATE (BMR)

A person's metabolic rate, or the rate at which it releases energy, is influenced by a number of factors, such as an individual's age, sex, level of activity, general health, and hormone levels. Because an individual's metabolic rate can provide a doctor with a great deal of information, it often needs to be measured. Since almost all of the energy used by the body is eventually converted to heat, the metabolic rate is usually calculated by measuring the amount of heat loss an individual displays during basal (resting) conditions. A person's Basal Metabolism Rate (BMR), therefore, measures the amount of energy the body consumes in performing its maintenance operations, like normal breathing, heart beating, and minor movements while it is at rest (but not asleep). A person's BMR is then judged to be normal or abnormal by comparing it to standardized rates or rates that reflect the average BMR of healthy individuals of various ages.

Typically, the BMR of males is higher than that of females, and both sexes have a lower BMR as they age. A recent discovery relates metabolism to the aging process, since animal studies suggest that there is some connection between substantially reducing calorie intake and living longer. It has yet to be determined what role metabolism plays in this phenomenon.

SANTORIO SANTORIO

Italian physiologist Santorio Santorio (1561–1636) founded the modern study of animal metabolism (all of the chemical processes that take place in an organism when it obtains and uses energy). He introduced the idea of quantification (number or quantity of) and measurement into the study of human physiology (the study of how different processes in living things work) and used mathematics and experimentation as his tools. He was an original thinker who was far ahead of his time.

As part of a tradition that was not unusual for Italy, Santorio was given the same first name as his last. Even when he became well-known and his name was Latinized as Sanctorius Sanctorius, it was still the same double name. He was born in Capodistria (what is now Croatia), and his father was an official in the Republic of Venice. Santorio was soon sent to Venice where he was educated by tutors. He began the study of philosophy and medicine at the age of fourteen, and obtained his medical degree from the University of Padua in 1582. For the next decade or so, it is unclear whether he spent time in Poland working as a physician for the king. Biographers disagree, but it is known that he was often in Venice during this period. In 1611, however, he was appointed professor of theoretical medicine at the University of Padua on the strength of a medical book he had written in 1602. At Padua he was a very popular lecturer, and students came from all over Europe to attend.

It was in this 1602 medical book that he first began writing about how important it was to measure things exactly when doing physiology. He also stressed that close and careful observation was equally important. Ten years later he published another medical book based on his more extensive research, and in it he described his use of a type of thermometer, probably invented by Italian physicist and astronomer Galileo Galilei (1564–1642), which he adapted to measure the warmth of the body. He was thus the first physician to use a thermometer on a person and to write about it. This could be said to be the first clinical thermometer. In yet another book written in 1614, Santorio described his experiment weighing a human being every day to determine the influence of everything that went into and came out of a body, including perspiration. He even designed an apparatus that had a chair built onto a large scale and was able to prove with this that people lost weight by the evaporation of their perspiration. His ability to measure all things related to the body was further improved when he invented a device to measure a person's pulse rate. For more than twenty-five years, Santorio performed experiments on more than 10,000 subjects, using scales and similar measuring instruments. This led modern biologists to call him "the father of the science of metabolism." If metabolism can be described as all of the chemical processes that take place in a living thing, then metabolism is indeed what Santorio was pioneering.

However, his work did not have any great impact on the science of his era, and many scientists believe it is because he was simply too far ahead of his time. Nonetheless, as science progressed, his modern ideas came to be more understood and appreciated. Santorio always stressed the importance of measurement, facts, and solid information, and regularly argued against such unscientific practices as astrology (the use of stars and planets to predict their influence on human affairs). He was in favor of applying all the new tools and instruments that science had in its possession to the study of the human body. Although he did not know the word for what he was doing, he was studying what is now called human metabolism.

Finally, since enzymes and hormones play such a key role in every metabolic process, a glandular problem or a genetic fault that affects the production of an enzyme can result in major metabolism problems. Such conditions as diabetes and Addison's disease throw a person's metabolism off severely, while other people simply cannot tolerate or process certain foods, like milk.