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Lesson 6-04 Endocrine Glands

Page history last edited by Chai Nakpiban 10 years, 8 months ago

 

Lesson 6.04 – Endocrine Glands

Standard: B9.b Students know how the nervous system mediates communication between different parts of the body and the body’s interactions with the environment.

 

 

INTRODUCTION

The endocrine glands are scattered throughout the body. Generally, they do not have direct connections to one another. Like signals that are beamed throughout the country from a broadcast station, the hormones released from the endocrine glands into the bloodstream travel throughout the body, reaching almost every cell.

 

 

The human endocrine system regulates a wide variety of activities. Any improper functioning of an endocrine gland may result in a disease or a disorder. The major glands of the endocrine system include the pituitary gland, the hypothalamus, the thyroid gland, the parathyroid glands, the adrenal glands, the pancreas, and the reproductive glands.

INSTRUCTION

Pituitary Gland

The pituitary gland is a bean-sized structure that dangles on a slender stalk of tissue at the base of the skull. As you can see in the figure at right, the gland is divided into two parts: the anterior pituitary and the posterior pituitary.  The pituitary gland secretes nine hormones that directly regulate many body functions and controls the actions of several other endocrine glands.

 

 

Normal function of the pituitary gland is essential to good health. For example, if the pituitary gland produces too much growth hormone (GH) during childhood, the body grows too quickly and a condition called gigantism results. Too little GH during childhood causes a condition known as pituitary dwarfism, which can be treated by administering growth hormone. Growth hormone used to be in short supply. Today, however, genetically engineered bacteria are able to produce GH in large quantities.

Hypothalamus

The hypothalamus is the part of the brain above and attached to the posterior pituitary.  The hypothalamus controls the secretions of the pituitary gland. The activity of the hypothalamus is influenced by the levels of hormones in the blood and by sensory information collected by other parts of the central nervous system. Interactions between the nervous system and the endocrine system take place at the hypothalamus.

 

 

The close connection between the hypothalamus and the pituitary gland means that the nervous and endocrine systems can act together to help coordinate body activities

 

 

Thyroid Gland

If you look at the figure at the left, you can see that the thyroid gland is located at the base of the neck and wraps around the upper part of the trachea.  The thyroid gland has the major role in regulating the body's metabolism. Cells in the thyroid gland produce thyroxine, which is made up of the amino acid tyrosine and the mineral iodine.

 

 

Remember that thyroxine affects nearly all of the cells of the body by regulating their metabolic rates. Thyroxine increases the rate of protein, carbohydrate, and fat metabolism as well as the rate of cellular respiration, which means that the cells release more heat and energy. Decreased levels of thyroxine can decrease the rate of cellular respiration and the amount of heat and energy released.

 

 

Thyroid and Parathyroid Glands  

Hormones produced by the thyroid gland and the parathyroid glands maintain the level of calcium in the blood. The thyroid gland wraps around the trachea.

The homeostatic activities of the thyroid gland are so well controlled that you may never become aware of them. However, if the thyroid gland produces too much thyroxine, a condition called hyperthyroidism occurs.

 

 

Hyperthyroidism results in nervousness, elevated body temperature, increased metabolic rate, increased blood pressure, and weight loss. Too little thyroxine causes a condition called hypothyroidism. Lower metabolic rates and body temperature, lack of energy, and weight gain are characteristics of this condition. In some cases, hypothyroidism can cause a goiter, an enlargement of the thyroid gland.

 

 

Parathyroid Glands

The four parathyroid glands are found on the back surface of the thyroid gland.  Hormones from the thyroid gland and the parathyroid glands act to maintain homeostasis of calcium levels in the blood. Parathyroid glands secrete parathyroid hormone (PTH). Recall that PTH and calcitonin have opposite effects on the body. PTH regulates the calcium levels in the blood by increasing the reabsorption of calcium in the kidneys and by increasing the uptake of calcium from the digestive system. Parathyroid hormone also affects other organ systems, promoting proper nerve and muscle function and bone structure.

 

 

Adrenal Glands

The adrenal glands are two pyramid-shaped structures that sit on top of the kidneys, one gland on each kidney, as shown in the figure at right.  The adrenal glands release hormones that help the body prepare for and deal with stress. An adrenal gland has an outer part called the adrenal cortex and an inner part called the adrenal medulla. These parts contain different types of tissues.

 

 

They also stimulate the release of extra glucose into the blood to help produce a sudden burst of energy. The result of all these actions is a general increase in body activity, which can serve as preparation for intense physical activity. If your heart rate speeds up and your hands begin to perspire when you take a test, you are feeling the effects of your adrenal glands!

 

 

Pancreas

The pancreas is a digestive gland whose enzyme secretions help to break down food. These secretions are released into the blood and flow into the small intestine.

 

 

The hormone-producing portion of the pancreas consists of clusters of cells that resemble islands. These clusters of cells are called islets of Langerhans after their discoverer, the German anatomist Paul Langerhans. Each islet includes beta cells, which secrete a hormone called insulin, and alpha cells, which secrete another hormone called glucagon.  Insulin and glucagon help to keep the level of glucose in the blood stable. Insulin stimulates cells in the liver and muscles to remove sugar from the blood and store it as glycogen or fat. Glucagon stimulates the liver to break down glycogen and release glucose back into the blood. It also stimulates the release of fatty acids from stored fats.

 

 

Diabetes Mellitus 

When the pancreas fails to produce or properly use insulin, a condition known as diabetes mellitus occurs. In diabetes mellitus, the amount of glucose in the blood may rise so high that the kidneys actually excrete glucose in the urine. Very high blood glucose levels can damage almost every system and cell in the body, including the coronary arteries.

 

 

There are two types of diabetes mellitus. Type I diabetes is an autoimmune disorder that usually develops in people before the age of 15. In this type of diabetes, there is little or no secretion of insulin. People with this type of diabetes must follow a strict diet and get daily injections of insulin to keep their blood glucose levels under control.

 

 

The second type of diabetes, Type II, most commonly develops in people after the age of 40. People with Type II diabetes produce low to normal amounts of insulin. However, their cells are unable to properly respond to the hormone because the interaction of the insulin receptors and the insulin is inefficient. In its early stages, Type II diabetes can often be controlled through diet and exercise. A diet high in complex carbohydrates and low in saturated fat and sugar can prevent blood sugar fluctuations.

Unfortunately, many people with Type II diabetes eventually require medication, as well. If the body stops producing insulin, the person will also need to have daily insulin injections.

 

 

Reproductive Glands

The gonads are the body's reproductive glands.  The gonads serve two important functions: the production of gametes and the secretion of sex hormones. The female gonads—the ovaries—produce eggs (ova; singular: ovum). The male gonads—the testes (singular: testis)—produce sperm. The gonads also produce sex hormones.

 

 

The ovaries produce the female sex hormones, estrogen and progesterone. Estrogen is required for the development of eggs and for the formation of the physical characteristics associated with the female body.  The testes produce testosterone (tes-TAHS-tuh-rohn). Testosterone is required for normal sperm production and the development of physical characteristics associated with the male body.

 

 

PRACTICE

  1. Click here (http://videos.howstuffworks.com/hsw/12690-the-endocrine-system-regulating-the-bodys-hormones-video.htm) to watch a video about endocrine glands.

 

 

  1. Take notes on the above information.

 

 

ASSESSMENT

  1. Turn in your notes.
  2. Take the 6.04 Quiz.

 

 

 

 


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