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Endocrine System

Introduction to this section:

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Figure 1: Glands of the Endocrine System

Video 1: The Endocrine System (13:47)

Video 2: Diabetes and the body (8:44)

Study Guide (Transcripts/Summaries):
Glands of the endocrine system are located throughout body. These glands produce steroid hormones, and peptide hormones. Steroid hormones are lipids, and many are derived from cholesterol, and can diffuse through a cell's membrane, and bind to internal receptors. Peptide hormones are derived from amino acids, and include amines, peptides, and proteins. Hormones derived from amino acids bind to receptors at the cell's surface, and signal to the cell through secondary messengers. Hormones only affect cells that have receptors for the particular hormone. Variations in receptor location, and quantity affect how tissues respond to a hormone.

The pineal gland is located in the brain and secretes melatonin that allows us to tell time of day, and seasons. This allows us to set up our circadian rhythm. The hypothalamus is a part of the brain that forms a connection between the brain, and the endocrine system. It influences the pituitary gland located in the brain. The pituitary has two lobes, the posterior, and anterior. The anterior pituitary gives off several hormones including growth hormone. Growth hormone flows through the body influencing cell growth. The posterior pituitary produces antidiuretic hormone that travels to the kidneys and causes reduced urine output. The thyroid gland is located in the neck and regulates metabolism. It gives off T3 and T4 hormones that contain iodine. It also secretes calcitonin that plays a role in reducing blood calcium. The parathyroid gland is within the thyroid gland and secretes parathyroid hormone that has a role in raising blood calcium. The thyroid and parathyroid work together to keep blood calcium levels correct. The adrenal glands sit on top of the kidneys. They have two parts, the adrenal cortex, and the adrenal medulla. The adrenal cortex is the outer layer that secretes glucocorticoids that are anti-inflammatories. The adrenal medulla secretes epinephrine or adrenaline that goes throughout the body, and is responsible for the fight or flight response. The testes in males, and the ovaries in females are the sex glands. The testes secrete testosterone, and the ovaries secrete estrogen. These are the hormones that are responsible for primary male, and female sex characteristics. The pancreas sits behind the stomach, and secretes enzymes into the small intestine, but it also has cells on its surface that secrete insulin and glucagon. Insulin is secreted to lower blood sugar by helping cells to take in glucose. Glucagon will be secreted if we need to raise the blood sugar. Normally, there’s a cycle in the body that balances out the glucose and insulin levels achieved by the food you eat, the pancreas, and the liver. In some people the system doesn’t work properly, and they develop diabetes. There are two main types of diabetes, Type 1 and Type 2. In Type 1 diabetes the body doesn’t make any insulin at all because of an autoimmune response whereby the body has destroyed the insulin producing cells in the pancreas. Because no insulin is being produced, the glucose can’t get into the cells and the level in the blood rises. In Type 2 diabetes, either the body is not producing enough insulin, or the insulin it is producing isn’t working properly to move the glucose into the cells. Symptoms for both Type 1 and Type 2 diabetes are similar. They result from there being too much glucose in the blood and from the kidneys trying to remove it from the body.

Sources:
Figure 1: Glands of the Endocrine System from: CK-12 Biology (say thanks), http://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/, Figure 13.46
Video 1: The Endocrine System, https://www.youtube.com/watch?v=-S_vQZDH9hY
Video 2: Diabetes UK - animation about diabetes and the body UPDATW, https://www.youtube.com/watch?v=X9ivR4y03DE