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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

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

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 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)

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