Key Concepts:
Vocabulary: endocrine glands, thyroid gland, parathyroid glands, pancreas, pituitary gland, adrenal glands
The Endocrine System
How the Endocrine System Works
Main Idea: The endocrine system includes various organs that work together to regulate body functions.
Endocrine glands are ductless or tubeless organs or groups of cells that secrete hormones directly into the bloodstream.Hormones are chemical substances that help regulate many of your body’s functions. Carried to their destination in the body through the blood, these chemical messengers influence physical and mental responses.
Hormones produced during puberty trigger physical and emotional changes in the body. Growth is controlled by certain hormones, and abnormally high or low amounts of these hormones may contribute to growth disorders. Factors such as stress, infection, and changes in the balance of fluids and minerals in the blood may affect hormone levels. Hormones work to maintain these balances in the body so that important processes and functions work more efficiently. Figure 16.1 describes the major glands of the endocrine system and the body functions they regulate.
The Pituitary: The Master Gland
Known as the master gland, the pituitary gland has three sections, or lobes: anterior, intermediate, and posterior.
Anterior Lobe The anterior, or front, lobe of the pituitary gland produces these hormones:
Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to produce hormones.
Adrenocorticotropic hormone (ACTH) stimulates production of hormones in the adrenal glands.
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) stimulate production of all other sex hormones. These two hormones are secreted by the anterior lobe of the pituitary gland during adolescence. They control the growth, development, and functions of the gonads, another name for the ovaries and testes.
In females, FSH stimulates cells in the ovary to produce estrogen, a female sex hormone that triggers the development of ova, or egg cells. LH is responsible for ovulation and stimulates ovarian cells to produce progesterone, another female sex hormone. The hormone prolactin stimulates milk production in females who have given birth.
Intermediate Lobe. The intermediate, or middle, lobe of the pituitary secretes melanocyte-stimulating hormone (MSH), which controls the darkening of the pigments in the skin.
Posterior Lobe. The posterior, or rear, lobe of the pituitary secretes antidiuretic hormone (ADH), which regulates the balance of water in the body. ADH also produces oxytocin, which stimulates the smooth muscles in the uterus during pregnancy, causing contractions during the birth of a baby.
The Adrenal Glands
The adrenal glands help the body deal with stress and respond to emergencies. They each have two parts, the adrenal cortex and a smaller, inner region called the adrenal medulla, which controls a variety of body functions.
The adrenal cortex secretes a hormone that inhibits the amount of sodium excreted in urine and maintains blood volume and blood pressure. It also secretes hormones that aid in the metabolism of fats, proteins, and carbohy- drates. These hormones influence the body’s response to stress and play a role in both the immune response and sexual function.
The adrenal medulla is controlled by the hypothalamus and the autonomic nervous system. It secretes the hor- mones epinephrine (also called adrenaline) and norepi- nephrine. Epinephrine increases heartbeat and respiration, raises blood pressure, and suppresses the digestive process during periods of high emotion.
Maintaining Your Endocrine Health
To keep your endocrine system working at its peak, you need to follow sound health practices.
Your endocrine health is directly related to your overall health. Remember to eat balanced meals to ensure that you get the nutrients you need, and use stress-management techniques. Sleep is also important to endocrine health. Teens need 8 1⁄2 to 9 hours of sleep every night. Engage in regular physical activity to keep your body strong. Also, have regular medical checkups. Some hormonal disorders have symptoms you may not notice or recognize. A health care professional can perform tests to determine whether your endocrine function is normal.
Certain endocrine disorders can have lifelong effects on your health. Factors such as stress, infection, and changes in the balance of fluid and minerals in the blood can cause hormone levels to fluctuate. In many cases, these situations will correct themselves. Serious problems, including diabetes mellitus, hypothyroidisim, hyperthyroidism, goiter, or over-production of adrenal hormones may require medication.
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