31-3 Glands and Their Functions Chapter 31 - Hormones 31-1 What Hormones Do 31-2 How Hormones Work 31-3 Glands and Their Functions

Section 31-1 What Hormones Do A hormone is a chemical signal that is made in one place and delivered to another – usually by the blood. Hormones regulate the body’s activities. Organs that produce most of the hormones in your body are called endocrine glands. The endocrine glands secrete hormones directly into the bloodstream. The hormones travel to a specific tissue or organ called a target. Once it arrives, the hormone will elicit a specific response.

Some hormones speed up the heart Some hormones speed up the heart. Others help digest food and allow the body to use the food as fuel. Without hormones, humans would not grow or mature. Hormones are essential to maintaining homeostasis. Often, two or more hormones work together to produce their effects. Hormones often last and affect you over extended periods of time.

The hypothalamus is part of the brain that regulates body temperature, breathing, hunger, and thirst. Besides being a part of the nervous system, it is also the master switchboard of the endocrine system. It continually checks the conditions inside your body. If your internal environment gets out of balance, the hypothalamus can set everything right again. It can even send out commands in the form of a hormone.

The pituitary gland produces at least six different hormones in response to the hormones sent out by the hypothalamus. Two of these hormones, growth hormone and prolactin, have a direct effect on growth of bone and cartilage. Feedback is a way the body will self-regulate. The amount of hormones already in the body will affect the endocrine system and either more or less of the hormone depending on the body’s needs. A negative feedback will suppress the production of more hormone. Most control is through negative feedback because hormones are rarely turned off or on completely.

If you remember back to Chapter 4, the cell has receptor proteins embedded in the cell membrane. Each receptor has a unique shape. When hormones approach a cell, the cell will be able to respond to the hormone if the shape of the receptor protein matches it. When the activity inside the cell changes, the chemical reactions inside the cell also change.

Glands Adrenal glands – Two almond-shaped glands located on the top of the kidneys. The adrenal medulla produces epinephrine or adrenaline. This produces the “flight or fight” reaction. In a fraction of a second, this hormone can be secreted in response to fear, anger, pain or physical exertion. The adrenal cortex produces a hormone that helps the body deal with long-term stress. It is a steroid called cortisal. When stressful situations continue without relief, the body enters a state of chronic fatigue. Organs malfunction and physical as well as mental burnout may result. Long term exposure to steroid hormones weakens the immune system.

Thyroid gland – located in the neck just below the Adam’s apple. Thyroid hormones are necessary for normal growth and development during childhood and maintaining mental alertness in adults. Too much thyroxine causes Graves’ disease-people have rapid, irregular heart rate, feel very nervous, and lose weight. Treated with radioactive iodine. Low levels of thyroxine causes a condition that combined with a lack of iodine produces a goiter.

Pancreas – located under the liver Has cells that produce insulin that regulate how much glucose is dissolved in the blood, called blood sugar. Insulin plays a role in diabetes – a disease where the person has an abnormally high blood sugar. Type I diabetes-usually childhood form, requires daily injections of insulin. Type II diabetes-(95% of diabetics), usually occurs in adult over 40. Obesity and inactivity contribute to its development. Proper diet and exercise can improve it, but sometimes oral medication is needed.