1. Thyroid Glands Located at the base of the neck, in front of the trachea There are two important thyroid hormones ▫1. Thyroxine (T4) ▫2. Triiodothyronine (T3) Regulate body metabolism and the growth and differentiation of tissues.
Thyroxine (T4) Individuals who secrete high levels of T 4 oxidize sugars and nutrients at a faster rate 60% of oxidized glucose is released as heat 40% transferred to ATP This added energy reserve is usually consumed during activity Result? Lack of weight gain
Thyroxine (T4) Individuals who secrete low levels of T 4 cannot break down sugars and nutrients as easily Excess blood sugar converted into liver and muscle glycogen Once the glycogen stores are filled converted to fat Low levels of T 4 leads to muscle weakness, cold intolerance and dry skin
The Feedback System If the metabolic rate decreases receptors in the hypothalamus are activated Nerves secrete TRH (thyroid-releasing hormone) The release of TRH signals pituitary to release TSH (thyroid-stimulating hormone) TSH is carried by blood to thyroid gland which releases T4 T4 increases metabolism or increased sugar utilization
The Feedback System Figure 3. page 385 nerves blood
Decrease in metabolic rate TRH TSH Thyroxine (T4) Increased utilization of sugar
Thyroid Disorders Iodine is an important component of both thyroid hormones (T3 and T4) When iodine levels begin to decline, the production and secretion of T4 drops The level of TSH increases and cells of the thyroid continue to develop The thyroid enlarges goiter or the swelling of the neck area Figure 4. page 385
2. Parathyroid Glands 4 small parathyroid glands exist in the thyroid gland Usually hormones or nerves regulate endocrine glands parathyroid is the exception Respond to chemical changes in surrounding environment
Parathyroid Gland and Calcium Low calcium levels release parathyroid hormone (PTH) PTH causes calcium levels to increase and phosphate levels to decrease PTH acts on 3 different organs: the kidneys, the intestines and the bones
Parathyroid Gland and Calcium PTH causes: 1.The kidneys and gut to retain calcium 2.Calcium release from the bones Bone cells break down calcium is separated from phosphate ions Calcium is reabsorbed, phosphate is excreted in the urine.
Parathyroid Gland and Calcium After calcium levels increase, the release of PTH is inhibited to ensure calcium levels are not too high. If calcium levels increase beyond demand: 1.The prolonged break down of bone 2.High levels of calcium could collect in blood vessels and form stone-like structures
Growth Hormone (GH) Also known as somatotropin Created by the anterior pituitary Low levels of GH dwarfism High levels of GH gigantism Affects most cells in the body, especially cartilage and bone cells Increases # of cells (hyperplasia) Increases size of cells (hypertrophy)
Growth Hormone (GH) Promotes protein synthesis while inhibiting protein degradation Stimulates ribosomes to follow the genetic instructions for protein synthesis Promotes the elongation of long bones Causes a switch in cellular fuels from glucose to fatty acids As you get older, GH decreases
Anabolic steroids: Designed to build excessive muscle and mimics the traits of the sex hormone testosterone Can provide greater lean muscle development and increased strength Prematurely fuse growth plates in the long bones Can cause mood swings and feelings of rage
Anabolic steroids don’t: Provide increased agility or skill level Enhance the ability of cardiovascular system to deliver oxygen
What are the side effects of prolonged use of anabolic steroids?