Function of metabolic rate in the human body

Biology

Function of the Metabolic Rate in the Human Body

Metabolism consists of the total of all chemical transformations that take place in a cell or the body of an organism. It can be broken down into two subdivisions: catabolism and anabolism. Catabolism consists of all the reactions in which large molecules are broken down into smaller ones, with a discharge of energy from their chemical bonds. Instances of this include the incorporation of a protein into amino acids in which the body can absorb and use in its own metabolism, and the breakdown of stored glycogen in the liver to provide energy between meals. These breakdown procedures are known chemically as oxidation reactions. Anabolism consists of all the reactions that bring together small molecules into larger ones and store energy in the newly formed chemical bonds. Examples of this comprise the meeting of amino acids into muscle proteins and the synthesis of glycogen and fat for energy storage. These synthetic processes are known chemically as reduction responses (Metabolism, Human, 2010).

Metabolism is a process by which the body converts what one eats and drinks into energy. During this intricate biochemical process, calories in food and beverages are mixed with oxygen in order to release the energy that the body needs in order to function. Even when a person is at rest, the body still needs energy for all its unseen functions that include such things as breathing, circulating blood, adjusting hormone levels, and growing and repairing cells. The amount of calories that the body uses to carry out these basic functions is known as the basal metabolic rate (BMR). Several factors help to determine a person's basal metabolic rate:

Body size and composition -- people's bodies that are larger or have more muscle burn up more calories, even at rest.

Gender - men typically have less body fat and more muscle than women do of the same age and weight, and thus need more calories.

Age - as one gets older, the amount of muscle tends to decrease and fat accounts for more of a person's weight, which slows down calorie burning.

Energy needs for a body's basic functions stays fairly consistent and aren't easily altered. A person's basal metabolic rate accounts for about 60 to 75% of the calories that they burn every day. In addition to the basal metabolic rate, two other factors determine how many calories one burns each day:

Food processing (thermogenesis) - digesting, absorbing, transporting and storing the food you consume also takes calories. This explains about 10% of the calories that are used each day. Essentially, a person's body's energy requirement to process food stays relatively steady and isn't easily changed.

Physical activity - physical activity and exercise account for the rest of the calories that a person's body burns up every day (Metabolism and weight loss: How you burn calories, 2010).

The body also has a group of organs that are known as the endocrine system. This systems primary function is to produce hormones that regulate the function of other organs. For example, the thyroid gland produces thyroid hormone, which controls the metabolic rate (the speed at which the body's chemical functions proceed); the pancreas produces insulin, which controls the use of sugar; and the adrenal glands produce epinephrine, which stimulates many organs to prepare the body for stress (Organ Systems, 2006).

Metabolic rate refers to the quantity of chemical energy that is released in the body per unit of time. Chemical energy is calculated in calories of water by one degree Celsius. Because a calorie is so small it is more practical to think of them in terms of kilocalories (kcal). One kilocalorie is equal to 1,000 calories. Metabolic rate is usually articulated in kcal/hour or kcal/day. A person's metabolic rate can be anticipated by having a person breathe from a spirometer. This is a device that measures a person's rate of oxygen consumption. Every liter of oxygen consumed represents the release of approximately 4.82 kcal of energy from organic compounds such as fat and glycogen. This ratio differs depending on what type of energy-storage molecules that a person is oxidizing at the instance of measurement (Metabolism, Human, 2010).

A person's metabolic rate depends on such things as physical activity, mental state, fed or fasting status, and hormone levels, especially one's thyroid hormone. The basal metabolic rate (BMR) is a standard of comparison that diminishes these variables. It is figured when a person has not eaten for twelve to fourteen hours and is awake, relaxed, and at a comfortable temperature. This is not considered to be the minimum rate that is needed in order to keep a person alive. The metabolic rate is lower than the BMR when a person is sleeping. Total metabolic rate (TMR) is the BMR plus the additional energy expenditure for movement and other activities. A person's metabolic rate goes up when they are engaged in physical activity. It also increased when they are eating, experiencing anxiety, have a fever or are pregnant. Factors that lessen the TMR below normal include depression, apathy, and prolonged starvation (Metabolism, Human, 2010).

TMR is often higher in children than it is in adults. As a result, as people approach middle age, they often gain weight even if they have had no change in food intake. Weight-loss diets are often frustrating because most of the initial weight loss is water, which is then quickly regained. They are also frustrating because TMR often declines over time. The average young adult male has a BMR of 2,000 to 2,500 kcal/day. The average female has a slightly lower rate. A person must consume this many calories every day just to be able to sustain such essential processes as the heartbeat, respiration, brain activity, muscle tone, renal function, and active transport through cell membranes. The central nervous system is made up of about 40% of the BMR and the muscular system about 20 to 30%. Even if a person has a fairly sedentary lifestyle they will need another 500 kcal/day, and hard physical labor, may require up to 5,000 kcal/day more (Metabolism, Human, 2010).

Basal Metabolic Rate (BMR) can be explained as minimum amount of calories required to sustain the body's functions and processes, when the body rests. It is responsible for consumption of about 70% of total calories that are used up by the body. BMR is regulated by a hormone called thyroxin. This hormone is produced by thyroid gland, which helps to control the body's metabolic activities. Thyroxin has an affect on the heart rate, body weight, muscle strength and blood cholesterol levels (Basal Metabolic Rate, 2010).

BMR generally goes down with age. BMR is affected by certain body functions such as respiration, circulation and maintenance of constant body temperature. Exercise, calorie use and lean body tissue can also affect this rate. Body weight, height and environmental temperature also play a major role in increasing a persons BMR. If BMR is increased, then there would be steady consumption of calories. It results in burning excess fats and remarkable weight loss. An increase in BMR offers a number of health benefits. These reduce the risk of developing heart disease, stroke, heart attack and diabetes. An average BMR for adults ranges between 1200 and 1800 kcal (Basal Metabolic Rate, 2010).

A decrease of metabolic rate causes a reduced energy levels and cognitive capacity independent of other factors. A reduced metabolic rate can be an indication of mitochondrial dysfunction, hypothyroidism, hypocortisolism or another factor influencing metabolic rate. Respiratory quotient is also shown to correlate positively with fatigue severity. Respiratory quotient is the ratio of carbon dioxide produced to oxygen consumed. Respiratory quotient is an indicator of macronutrient utilization. A Higher RQ often proposes that there is an increase in fat oxidation and less carbohydrate oxidation which is consistent with higher levels of fatigue (Graham, 2005).

BMR for an individual person is usually defined as the amount of energy expressed in kilocalories or megajoules expended when the person is al complete rest, both physical and psychological. It can also be articulated as kilocalories per hour or per kilogram of weight. BMR provides the energy that is needed by the body for maintenance of body temperature. It also supplies for the work of body organs such as the beating heart and the muscles working for normal, at rest, breathing and for the functioning of other organs such as the liver, kidneys and brain (Basic Nutrition, n.d.).

BMR varies from individual to individual. Important universal factors that influence BMR include a person's weight, gender, age and state of health. BMR can also be influenced by a person's body make up. An example can be seen in the quantity of muscle and adipose tissue and therefore the amounts of protein and fat in the body. Bigger people with more muscle and larger body organs have a higher BMR than smaller people do. Elderly people tend to have lower BMR than they had when they were young, and females tend to have lower BMR than males even on a per kilogram body weight basis (Basic Nutrition, n.d.).

The primary organ that is accountable for regulating metabolism is the hypothalamus. The hypothalamus is situated on the brain stem and forms the floor and part of the lateral walls of the third ventricle of the cerebrum. The main functions of the hypothalamus is to control and integrate activities of the autonomic nervous system (ANS), production and regulation of feelings of rage and aggression, regulation of body temperature and regulation of food intake (Graham, 2005).