1. Hormones that Affect Metabolism Section 8.3 Page 384

2. Recall... • Hormones send chemical messages in the body • Endocrineglands produce, store, and release hormones • Metabolism is the series of reactions that make life possible – it comprises both the breakdown and construction of organic molecules

3. Hormones affecting metabolism

4. The thyroid gland • One of the largest endocrine glands in the body • Located in the neck

5. Thyroid hormones • Calcitonin • Triiodothyroxine (aka T3) • Thyroxine (aka T4)

6. Calcitonin • Lowers calcium levels in the blood • Acts on bone cells to limit resorption of calcium • Also acts on intestines to limit absorption of calcium

7. Triiodothyronine (T3) and thyroxine (T4) • Same function: • Increases cellular rate of metabolism • Normal rate of metabolism: Glucose is oxidized through cellular respiration • 60% is utilized right away; heat is released as a result • 40% is stored as ATP • T3 and T4 increase cellular utilization of glucose

8. Control of T3 and T4 secretion

9. Control of T3 and T4 secretion • Drop in metabolic rate is sensed • Hypothalamus releases thyroid-releasinghormone (TRH) • TRH signals anterior pituitary to release thyroid-stimulatinghormone (TSH) • TSH signals thyroid to release T3 and T4 Negative feedback • High levels of T4 inhibit the hypothalamus from releasing further TRH, which in turn inhibits TSH release by the pituitary.

10. IMPORTANT!! This signaling pathway will be a recurring theme:

11. Hyperthroidism = Excessive secretion of thyroid hormones • elevated metabolism • high body temperature • high heart rate, blood pressure • weight loss • irritability • goiter

12. Hypothyroidism = Low secretion of thyroid hormones • muscle weakness • cold intolerance • dry skin and hair • weight gain • low blood pressure and heart rate

13. Iodine and thyroid hormones • Iodine is required for thyroxine production • Without adequate iodine, thyroxine is not produced • TRH and TSH are not inhibited • TSH continues to stimulate the thyroid's follicular cells • Thyroid enlarges → goiter forms • This is why iodine is added to table salt TSH

14. Goiter

15. Parathyroid glands • Four of them • Located behind, or within, the thyroid gland • Produce parathyroidhormone (PTH)

16. Unique feature: • Do not require neural or hormonal input from hypothalamus. • They respond directly to environmental conditions.

17. Parathyroid hormone (PTH) • Raises levels of calcium in the blood (works antagonistically with calcitonin) • Stimulated by low calcium levels • Effects: • Kidneys: Increase Ca2+reabsorption • Intestines: Absorb more Ca2+ • Bones: Release Ca2+ Negative feedback • High levels of calcium inhibit PTH release

19. Anterior pituitary • Growth hormone (somatotropin) • Effects: • Promotes elongation of long bones • Increases utilization of fat stores for energy • Promotes protein synthesis (builds muscle)

20. Growth hormone abnormalities: • Low secretion in childhood can lead to dwarfism • High secretion in childhood can lead to gigantism • Continued high secretion can lead to acromegaly – broadening of facial features and other bones

21. Homework • Copy Table 1, page 387, into notes • Pg. 387 #3, 5-8