Topic 15.3 Hormones that Affect Metabolism (this covers 3 glands)

1) Thyroid Gland  the thyroid gland helps regulate metabolism  individuals who secrete high levels of thyroid hormone oxidize sugar and nutrients faster than other individuals  do you know someone like this – with a fast metabolism?

 The thyroid gland sits at the base of the neck in front of the trachea  It produces 2 hormones that regulate metabolism, growth and differentiation of tissues 1)Thyroxine (T4) – 65% 2)Triiodothyronine (T3) - 35%, contains 3 iodine atoms

 It also produces a hormone called calcitonin that lowers calcium levels in the blood

Negative Feedback of Thyroid Hormones  When the metabolic rate decreases receptors in the hypothalamus are activated  Nerve cells in the hypothalamus secrete thyroid-releasing hormone (TRH) which cause the pituitary to release thyroid-stimulating hormone (TSH)

 THS is carried by the blood to the thyroid which then releases T3 and T4  Responses to increased T3 and T4 1)Raises metabolism – causes cells to take in sugar 2)High levels of T3 and T4 turn off the pathway by inhibiting the release of TRH

Draw figure 2 on page 486

Importance of Iodine  Iodine is an important part of T3 and T4  When there is not enough iodine in the diet the thyroid enlarges and makes a goiter

 Iodine is an important part of the negative feedback loop by aiding in the creation of T3 and T4  When T3 and T4 never are in excess then the hypothalamus continues to create TRH and the hypothalamus is constantly stimulated by TSH  How is this solved?  (Iodine is often added to salt)

Thyroid Problems  Hyperthyroidism – overproduction of thyroxine (T4)  This initiates the fast oxidation of nutrients to which causes weight loss, high body temp and nervous behaviour – Graves’ disease  Hypothyroidism – low thyroid secretions – may cause weight gain

2) Parathyroid Glands  4 small glands hidden in the thyroid gland  Respond to chemical changes in their immediate environment  Help keeps calcium levels in homeostasis  Tetanus occurs if these glands are removed – nerves become easily excited

How the Parathyroid Glands Work 1)Low calcium levels stimulate the release of parathyroid hormone (PTH) from the parathyroid and inhibits the release of calcitonin from the thyroid 2)a rise in PTH causes calcium levels to rise in the blood and phosphate levels to decrease

3) PTH acts on three organs a)Kidneys – reabsorb calcium b)Intestines – absorb calcium c)Bones – release calcium by allowing breakdown of bone cells - Phosphate is excreted in the urine Result – calcium in the blood rises

To return to homeostasis… 1)Higher calcium levels stops the release of PTH from the parathyroid 2)AND high calcium levels causes the thyroid glad to release calcitonin 3)The calcitonin acts on three things

3a) kidneys – reabsorb less calcium b) Intestines – absorb less calcium c) Bones – deposit calcium 4) Return to homeostasis

Issues with Calcium and PTH 1)High levels of calcium in collect in blood vessels or create kidney stones 2) PTH helps activates vitamin D and with low levels of vitamin D a disease called rickets can occur

3) Anterior Pituitary Gland and hGH (human growth hormone)  hGH stimulates the elongation of the skeleton  Hyposecretion in children causes dwarfism  Hypersecretion in children causes gigantism  The effect is most pronounced in the cartilage and bone cells

hGH regulates growth  Cells of soft tissue and bone begin to grow by the number (hyperplasia) and size (hypertrophy) from hGH  hGH stimulates growth in cells by increasing the uptake of amino acids by cells and inhibits protein breakdown

hGH helps maintain homeostasis  It increases fatty acid levels in the blood by promoting the breakdown of fats  Muscles begin to use fatty acids instead of glucose for fuel  Necessary during times of fasting  Why?

To Do:  Go through questions 1-8 on page 489  Make flash cards of glands and hormones on page 489  Note: you must know all of the hormones, where they are made and their target organs