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Thread: Thyroid and Parathyroid Glands picture - Endocrine Histology Atlas

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    Default Thyroid and Parathyroid Glands picture - Endocrine Histology Atlas

    Thyroid and Parathyroid Glands
    The thyroid gland and parathyroid glands are a group of endocrine glands located in the base of the neck. These glands play a vital role in maintaining the body’s homeostasis by producing hormones that regulate the body’s metabolism and free calcium levels. Variations in thyroid hormones can lead to drastic changes in energy level, growth, development, and reproduction. Calcium plays a critical role in maintaining healthy bones and teeth as well as stimulation of neurons and muscle cells vital to the nervous, muscular, and cardiovascular systems.

    [Continued from above] . . . It wraps around the anterior portion of the trachea and expands significantly on the lateral sides of the trachea and larynx. The lateral masses are known as the left and right lateral lobes, while the narrower medial region is known as the isthmus.

    The parathyroid glands are a collection of four round glands around the size of a grain of rice. These glands are attached to the posterior surface of the lateral lobes of the thyroid gland. Two parathyroid glands (right superior and right inferior) are attached one above the other to the right lateral lobe of the thyroid, while the other two glands (left superior and left inferior) are found on the left lobe.

    The thyroid gland produces two vital metabolic hormones – triiodothyronine (T3) and thyroxine (T4). T3 and T4 are produced using iodine, with T3 containing three iodine atoms and T4 containing four. Both T3 and T4 are used to regulate the body’s metabolism by turning on practically every cell in the body and inducing them to produce proteins. The result of the increase in cellular metabolism leads to many physiological effects, including increased heart rate, tissue growth and development, body heat production, and energy consumption.

    Calcitonin is also produced by the thyroid gland and works as an antagonist to the only hormone produced by the parathyroid glands, parathyroid hormone (PTH). These two hormones work together to maintain the vital homeostatic balance of calcium ions in the blood, which is essential to the proper function of muscle and nervous tissue as well as bone health. Calcium deficiency may cause twitching, spasms, convulsions and even death, while too much calcium can lead to a weakening of muscle tone and kidney stones. Calcitonin reduces the level of free calcium ions in the blood by reducing the absorption of calcium from food in the intestines; increasing the excretion of calcium ions in the kidneys; and decreasing the activity of osteoclast cells that break down bone matrix to release calcium ions. PTH raises calcium ion levels by increasing calcium absorption in the intestine; decreasing calcium excretion in the kidneys; and increasing the activity of osteoclasts in bones.
    Thyroid Parathyroid Glands picture Endocrine attachment.php?s=a1c1415b27e4fbcaa560f28798d5a872&attachmentid=1311&d=1439059114

    Where is the thyroid found?

    The thyroid gland is found in the front part of your neck, just below the large cartilage tissue in your neck (your Adam's apple). It is made up of two lobes - the right and the left lobes. These two lobes are joined by a small bridge of thyroid tissue called the isthmus. The two lobes lie on either side of your trachea (windpipe).

    What does the thyroid do?
    The thyroid makes three hormones that it secretes into the bloodstream. Two of these hormones, called thyroxine (T4) and triiodothyronine (T3), increase your body's metabolic rate. Essentially, the body's metabolic rate is how quickly the cells in your body use the energy stored within them. Thyroid hormones make cells use more energy. By controlling how much energy our cells use, thyroid hormones also help to regulate our body temperature. Heat is released when energy is used, increasing our body temperature. Thyroid hormones also play a role in making proteins, the building blocks of the body's cells. They also increase the use of the body's fat and glucose stores.

    In order to make T3 and T4, the thyroid gland needs iodine, a substance found in the food we eat. T4 is called this because it contains four atoms of iodine. T3 contains three atoms of iodine. In the cells and tissues of the body most T4 is converted to T3. T3 is the more active hormone, it influences the activity of all the cells and tissues of your body.

    The other hormone that the thyroid makes is called calcitonin. This helps to control the levels of calcium and phosphorus in the blood. These minerals are needed, among other things, to keep bones strong and healthy.

    How does the thyroid work?
    The main job of the thyroid gland is to produce hormones T4 and T3. To do this the thyroid gland has to take a form of iodine from the bloodstream into the thyroid gland itself. This substance then undergoes a number of different chemical reactions which result in the production of T3 and T4.

    The activity of the thyroid is controlled by hormones produced by two parts of the brain, the hypothalamus and the pituitary. The hypothalamus receives input from the body about the state of many different bodily functions. When the hypothalamus senses that levels of T3 and T4 are low, or that the body's metabolic rate is low, it releases a hormone called thyrotropin-releasing hormone (TRH). TRH travels to the pituitary via the connecting blood vessels. TRH stimulates the pituitary to secrete thyroid-stimulating hormone (TSH).

    TSH is released from the pituitary into the bloodstream and travels to the thyroid gland. Here, TSH causes cells within the thyroid to make more T3 and T4. T3 and T4 are then released into the bloodstream where they increase metabolic activity in the body's cells. High levels of T3 stop the hypothalamus and pituitary from secreting more of their hormones. In turn this stops the thyroid producing T3 and T4. This system ensures that T3 and T4 should only be made when their levels are too low.

    Calcitonin is released by the thyroid gland if the amount of calcium in the bloodstream is high. Calcitonin decreases the amount of calcium and phosphorus in the blood. It does this by slowing the activity of cells found in bone, called osteoclasts. These cells cause calcium to be released as they 'clean' bone. Calcitonin also accelerates the amount of calcium and phosphorus taken up by bone. Calcitonin works with parathyroid hormone to regulate calcium levels (see below for full explanation).

    References:
    The Thyroid and Parathyroid Glands. Thyroid disorders; info | Patient
    Thyroid and Parathyroid Glands - Anatomy Pictures and Information











    Last edited by Medical Photos; 08-08-2015 at 06:38 PM.

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