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Hormones that Affect Metabolism. Section 8.3 Page 384. Recall. Hormones send chemical messages in the body Endocrine glands produce, store, and release hormones

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Hormones that Affect Metabolism

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Hormones that affect metabolism

Hormones that Affect Metabolism

Section 8.3

Page 384



  • 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

Hormones affecting metabolism

Hormones affecting metabolism

The thyroid gland

The thyroid gland

  • One of the largest endocrine glands in the body

  • Located in the neck

Thyroid hormones

Thyroid hormones

  • Calcitonin

  • Triiodothyroxine (aka T3)

  • Thyroxine (aka T4)



  • Lowers calcium levels in the blood

  • Acts on bone cells to limit resorption of calcium

  • Also acts on intestines to limit absorption of calcium

Triiodothyronine t3 and thyroxine t4

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

Control of t3 and t4 secretion

Control of T3 and T4 secretion

Control of t3 and t4 secretion1

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.



This signaling pathway will be a recurring theme:

Hyperthroidism excessive secretion of thyroid hormones

Hyperthroidism = Excessive secretion of thyroid hormones

  • elevated metabolism

  • high body temperature

  • high heart rate, blood pressure

  • weight loss

  • irritability

  • goiter

Hypothyroidism low secretion of thyroid hormones

Hypothyroidism = Low secretion of thyroid hormones

  • muscle weakness

  • cold intolerance

  • dry skin and hair

  • weight gain

  • low blood pressure and heart rate

Iodine and thyroid hormones

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




Parathyroid glands

Parathyroid glands

  • Four of them

  • Located behind, or within, the thyroid gland

  • Produce parathyroidhormone (PTH)

Hormones that affect metabolism

Unique feature:

  • Do not require neural or hormonal input from hypothalamus.

  • They respond directly to environmental conditions.

Parathyroid hormone pth

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

Anterior pituitary

Anterior pituitary

  • Growth hormone (somatotropin)

  • Effects:

    • Promotes elongation of long bones

    • Increases utilization of fat stores for energy

    • Promotes protein synthesis (builds muscle)

Growth hormone abnormalities

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



  • Copy Table 1, page 387, into notes

  • Pg. 387 #3, 5-8

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