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

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.

UNIT A Chapter 5: Metabolism: Energy and Enzymes

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Chapter 5: Metabolism: Energy and Enzymes

What is the role of an enzyme?

What factors influence the rate of enzyme activity?

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.

UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3

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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

UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3

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Regulation of Blood Calcium

UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3

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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, theparathyroid 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.

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.

UNIT A Chapter 5: Metabolism: Energy and Enzymes Section 5.3

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