The document outlines chapters and sections from a biology textbook covering cell biology topics. Specifically, it discusses Section 5.3 from Chapter 5 on metabolism, energy, and enzymes. This section describes the roles of the thyroid and parathyroid glands in regulating metabolic rate and blood calcium levels. The thyroid gland produces hormones that increase metabolic rate and regulates blood calcium. The parathyroid gland produces a hormone that increases blood calcium when it falls too low. Together these glands maintain appropriate calcium levels and metabolic rates in the body.

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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