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Chapter 15 Section 15.3 Hormones that Affect Metabolism

Endocrine Glands Three glands of the endocrine system are responsible for maintaining metabolism: 1. Thyroid Gland - located at the base of the neck, immediately in front of trachea (windpipe) 2. Parathyroid Glands - 4 parathyroid glands - located inside the thyroid gland 3. Anterior Pituitary - front of pituitary in the brain - REMEMBER = makes it’s own hormones

Endocrine Glands Thyroid Gland

Produces 3 hormones: 1. Thyroxine (T4) – increases metabolism and regulates growth. 2. Triiodothyronine (T3) – increases metabolisms and regulates growth; contains 3 iodine atoms. 3. Calcitonin – lowers calcium levels in the blood.

Feedback System for the Thyroid Metabolic rate decreases. Receptors in the hypothalamus are activated. Nerve cells in the hypothalamus secrete thyroid releasing hormone (TRH). TRH stimulates the pituitary to release thyroid stimulating hormone (TSH).

TSH is carried by the blood to the thyroid gland. Thyroid gland releases T3 and T4. T3 and T4 raise metabolism by stimulating increased use of sugar by cells. High levels of T3 and T4 cause the pathway to be turned off by inhibiting the release of TRH from the hypothalamus.

Hypothalamus Anterior Pituitary TRH TSH Thyroid T3T4 Diagram of Thyroid Feedback System = turns off Feedback Loop #5

Goiters and the Importance of Iodine Iodine is normally actively transported out of the blood into the follicle cells of the thyroid. This iodine enables the thyroid to produce it’s hormones (3 iodine atoms are needed to make T3). Problems arise when iodine levels begin to fall.

When inadequate amounts of iodine are obtained from the diet, the thyroid enlarges, producing a goiter.

Parathyroid Glands Parathyroid does not respond to nerve or hormone regulation. It responds directly to chemical changes in their immediate surroundings. Produces 1 hormone: Parathyroid Hormone (PTH) – increases calcium levels in the blood and lowers the phosphate levels

Feedback System for the Parathyroid Blood calcium levels fall. Parathyroid glands release PTH. Calcitonin is inhibited. PTH acts on 3 organs: 1. Kidneys – reabsorb more Ca 2+ before excreting waste. 2. Intestines – absorb more Ca 2+ from food. 3. Bones – release Ca 2+ into blood.

Blood calcium levels rise. Thyroid gland releases calcitonin. Calcitonin acts on the same 3 organs: 1. Kidneys – reabsorb less Ca 2+ before excreting waste. 2. Intestines – absorb less Ca 2+ from food. 3. Bones – deposit Ca 2+. Blood calcium levels fall and the cycle begins again.

Diagram of Thyroid Feedback System Feedback Loop #6

Anterior Pituitary Gland Produces : 1. Human Growth Hormone (hGH) – stimulates elongation of skeleton. Mainly affects the cartilage and bone cells. Problems arise when the body produces too much (hypersecretion) or too little (hyposecretion).

Childhood Hyposecretion of hGH during childhood can result in dwarfism. Hypersectration of hGH during childhood can result in giantism.

Growth Hormone (GH, hGH, or somatotropin) GH promotes protein synthesis and fat metabolism in a wide variety of target cells. Excess GH in a young person can result in gigantism (acromegaly) whereas a lack of GH can cause dwarfism.

Adulthood Hypersecretion in adulthood can cause acromegaly, an abnormal bone growth in the hands, feet and head.

What does hGH do? Under the influence of hGH, cells of soft tissues and bone begin to grow by increasing the number of cells (hyperplasia) and increasing the size of cells (hypertrophy). Increases cell size in muscle cells and connective tissue by promoting protein synthesis and inhibiting protein breakdown.

hGH also plays a role in homeostasis. It increases fatty acid levels in the blood by promoting the breakdown of fats. Muscles use these fatty acids for fuel instead of glucose. This helps to maintain blood glucose levels. Feedback Loop #7

Summary GlandHormoneEffect on Metabolism ThyroidThyroxine (T4)and Triiodothyronine (T3) - Regulates the rate at which glucose is oxidized within the body cells ThyroidCalcitonin- Lowers calcium levels in the blood Parathyroid Glands Parathyroid Hormone (PTH) - Raises calcium levels in the blood Anterior Pituitary Growth Hormone (hGH) - Promotes protein synthesis by increasing uptake of amino acids by cells - Causes a switch in fuels  glucose to fatty acids