Download Second lecture – continue The number of calories a person burns in

Second lecture – continue
The number of calories a person burns in a day is affected by how much that person
exercises, the amount of fat and muscle in his or her body, and the person's basal
metabolic rate. The basal metabolic rate, or BMR, is a measure of the rate at which a
person's body "burns" energy, in the form of calories, while at rest. The BMR can play a
role in a person's tendency to gain weight. For example, a person with a low BMR (who
therefore burns fewer calories while at rest or sleeping) will tend to gain more pounds of
body fat over time, compared with a similar-sized person with an average BMR who eats
the same amount of food and gets the same amount of exercise.
What factors influence a person's BMR? To a certain extent, a person's basal metabolic
rate is inherited - passed on through the genes a person gets from his or her parents.
Sometimes health problems can affect a person's BMR. But people can actually change
their BMR in certain ways. For example, exercising more will not only cause a person to
burn more calories directly from the extra activity itself, but becoming more physically fit
will increase BMR as well. BMR is also influenced by body composition - people with
more muscle and less fat generally have higher BMRs.
Things That Can Go Wrong With Metabolism:
 In a broad sense, a metabolic disorder is any disease that is caused by an abnormal
chemical reaction in the body's cells. Most disorders of metabolism involve either
abnormal levels of enzymes of hormones or problems with the functioning of those
enzymes or hormones. When the metabolism of body chemicals is blocked or defective,
it can cause a buildup of toxic substances in the body or a deficiency of substances
needed for normal body function, either of which can lead to serious symptoms.
 Some metabolic diseases are inherited. These conditions are called inborn errors of
metabolism. When babies are born, they're tested for many of these metabolic diseases in
a newborn screening test. Many of these inborn errors of metabolism can lead to serious
complications or even death if they're not controlled with diet or medication from an
early age.
Examples of metabolic disorders and conditions include:
G6PD deficiency:
 Glucose-6-phosphate dehydrogenase, or G6PD, is just one of the many enzymes that play
a role in cell metabolism. G6PD is produced by red blood cells and helps the body
metabolize carbohydrates. Without enough normal G6PD to help red blood cells handle
certain harmful substances, red blood cells can be damaged or destroyed, leading to a
condition known as hemolytic anemia. In a process called hemolysis red blood cells are
destroyed prematurely, and the bone marrow (the soft, spongy part of the bone that
produces new blood cells) may not be able to keep up with the body's need to produce
more new red blood cells. Kids with G6PD deficiency may be pale and tired and have a
rapid heartbeat and breathing. They may also have an enlarged spleen or jaundice - a
yellowing of the skin and eyes. G6PD deficiency is usually treated by discontinuing
medications or treating the illness or infection causing the stress on the red blood cells.
How humans (and other animals) do it?.
Humans are heterotrophs. We are totally dependent on ingested preformed organic
molecules to meet all our energy needs. We are also dependent on preformed organic
molecules as the building blocks to meet our anabolic needs.
Ingestion: taking food within the body (although as the figure shows, it is still
topologically in the external world, not the internal).
Digestion.
The enzyme-catalyzed hydrolysis of
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polysaccharides (e.g., starch) to sugars.
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proteins to amino acids .
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fats to fatty acids and glycerol.
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nucleic acids to nucleotides .
Absorption into the body and transport to the cells.