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Biology 12 - Thyroid and Parathyroid Glands - Section 5-3
1.
2. UNIT A: Cell Biology
Chapter 2: The Molecules of Cells
Chapter 3: Cell Structure and Function
Chapter 4: DNA Structure and Gene
Expression
Chapter 5: Metabolism: Energy and
Enzymes: Section 5.3
Chapter 6: Cellular Respiration
Chapter 7: Photosynthesis
3. UNIT A Chapter 5: Metabolism: Energy and Enzymes
Chapter 5: Metabolism: Energy
In this chapter you will learn about the numerous chemical reactions
in our bodies involved in breaking down food to produce essential
biological molecules and energy.
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and Enzymes
What is the role of
an enzyme?
What factors
influence the rate of
enzyme activity?
4. UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3
5.3 Metabolic Rate and the Thyroid and
Parathyroid Glands
The thyroid gland is a large gland in the neck.
•It produces triiodothyronine (T3) and thyroxine (T4)
hormones, using high levels of iodine acquired from the
bloodstream. Iodine in the bloodstream comes from food that
has been consumed; iodized salt is the primary source.
•T3 and T4 increase metabolic rate by stimulating cells to break
down more glucose and use more energy.
•The thyroid also produces the hormone calcitonin. Calcitonin
is released when blood calcium levels rise. This promotes the
deposit of calcium in bones.
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5. UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3
Parathyroid Glands
The parathyroid glands are embedded behind the thyroid
gland.
•They produce parathyroid hormone (PTH)
•PTH causes blood levels of phosphate to decrease
•PTH also increases blood calcium levels by promoting
release of calcium from bones, reabsorption of calcium in
the kidneys, and calcium absorption in the intestine
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6. UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3
Regulation of Blood Calcium
Figure 5.8 Regulation of blood calcium level.
Top: When the blood calcium (Ca2+) level is high,
the thyroid gland secretes calcitonin. Calcitonin
promotes the uptake of Ca2+ by the bones, and
therefore the blood Ca2+ level returns to normal.
Bottom: When the blood Ca2+ level is low, the
parathyroid glands release parathyroid hormone
(PTH). PTH causes the bones to release Ca2+ and
the kidneys to reabsorb Ca2+ and activate vitamin D.
Thereafter, the intestines absorb Ca2+. Therefore,
the blood Ca2+ level returns to normal.
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7. UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3
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Check Your Progress
1. Predict the effects of the removal of the thyroid gland.
2. List the two hormones produced by the thyroid gland.
8. UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3
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Editor's Notes
Presentation title slide
Chapter opener background notes
Are you lactose intolerant? Do you know someone who is? As much as three-quarters of the world's population has some difficulty digesting lactose. Digesting a piece of cheese pizza can be very uncomfortable for those who are lactose intolerant because cheese and other dairy products contain lactose. What causes lactose intolerance?
Lactose is a disaccharide sugar that must be broken down chemically into its two smaller building blocks (galactose and glucose) before it can be absorbed into the bloodstream and used for energy. If it is not broken down, lactose remains in the digestive tract and can cause uncomfortable digestive symptoms. The breakdown of lactose requires an enzyme called lactase. People who are lactose intolerant do not produce enough lactase. A lactose intolerant person who wants to consume dairy products without discomfort must consume products that have been specially treated with enzymes or a lactase enzyme supplement with the dairy in their meal. Yogurt and buttermilk can often be tolerated by those with lactose intolerance because they contain bacterial cultures that aid in the digestion of lactose.
Why is it that some people can easily digest lactose when so many other people cannot? After young mammals are weaned, milk becomes a smaller component of the diet. In most mammals, lactase activity decreases and lactose intolerance usually begins. However, some humans have developed what is called lactase persistency. These individuals continue to produce lactase. Factors that contribute to lactase persistency include diet, culture, and genetics.
The breakdown of lactose is just one of myriad chemical reactions that occur in the human body. Almost every reaction that takes place in our bodies requires a specific enzyme. In this chapter, you will learn about the characteristics of enzymes and how enzymes function in the flow of energy and metabolism.
thyroid gland: a large gland in the neck that produces several important hormones, including triiodothyronine, thyroxine, and calcitonin
triiodothyronine (T3): a hormone produced by the thyroid gland that increases metabolic rate
thyroxine (T4): a hormone produced by the thyroid gland that increases metabolic rate
calcitonin: a hormone produced by the thyroid gland that helps control blood calcium levels
parathyroid glands: glands embedded behind the thyroid gland; produce parathyroid hormones
parathyroid hormone (PTH): hormone produced by the parathyroid glands; causes the blood phosphate level to decrease and the blood calcium level to increase
Answers
1. Removal of the thyroid gland would mean that there would be a decrease in associated hormones, T3 ,T4, and calcitonin. Since T3 and T4 aid in the metabolism of glucose, this process would decrease. Likewise, if there was a decrease in calcitonin production from the thyroid gland, there would be a decrease in calcium uptake in the bones from the bloodstream.
2. Hormones produced by the thyroid gland are T3 and T4. Calcitonin is also produced by the thryoid.