Parathyroid Gland

-
Parathyroid Gland is any of a group of glandular cell aggregations located in the neck region close to the thyroid gland in lizards, some birds, and most mammals. In humans, four such clumps are usually present as distinct, yellowish-brown, encapsulated organs, each about 6 mm (‚ in) long. The combined weight of these glands is no more than 560 mg (1/50 oz). They are located beneath the thyroid gland; one or more of them are occasionally embedded in the thyroid tissue. Sometimes they may appear in association with the thymus, or anywhere between the thyroid and thymus, or even elsewhere in the neck or upper anterior chest. Such glands, which may be present in addition to four normally placed ones, are known as accessory parathyroid tissue.

The parathyroid glands secrete a hormone known as parathormone, which controls the concentration of calcium (calcium ion) and phosphorus (phosphate) in the blood. Calcium and phosphorus normally have a relationship to each other that the body keeps fairly constant. Parathyroid hormone acts to increase the excretion of phosphorus by the kidneys (which tends to lower blood phosphorus levels) and to increase the rate of resorption of calcium from bone (which tends to raise the level of blood calcium). Deficiency of parathormone, which rarely occurs spontaneously and which is sometimes caused by accidental removal of the parathyroid glands during surgical excision of the thyroid, results in reduction of blood calcium, increase of blood phosphorus, and increased nervous excitability leading to rapid involuntary contractions of the muscles, a condition known as tetany. The accessory parathyroid tissue is occasionally sufficient to prevent severe deficiency symptoms when the essential four clumps are removed.

Comments

Post a Comment

Popular posts from this blog

Cellular Respiration

-
Cellular Respiration, process in which cells produce the energy they need to survive. In cellular respiration, cells use oxygen to break down the sugar glucose and store its energy in molecules of adenosine triphosphate (ATP). Cellular respiration is critical for the survival of most organisms because the energy in glucose cannot be used by cells until it is stored in ATP. Cells use ATP to power virtually all of their activities—to grow, divide, replace worn out cell parts, and execute many other tasks. Cellular respiration provides the energy required for an amoeba to glide toward food, the Venus fly trap to capture its prey, or the ballet dancer to execute stunning leaps. Cellular respiration occurs within a cell constantly, day and night, and if it ceases, the cell—and ultimately the organism—dies. Two critical ingredients required for cellular respiration are glucose and oxygen. The glucose used in cellular respiration enters cells in a variety of ways. Plants, algae, and cer...
Read more

Respiratory System

-
. Respiratory System, in anatomy and physiology, organs that deliver oxygen to the circulatory system for transport to all body cells. Oxygen is essential for cells, which use this vital substance to liberate the energy needed for cellular activities. In addition to supplying oxygen, the respiratory system aids in removing of carbon dioxide, preventing the lethal buildup of this waste product in body tissues. Day-in and day-out, without the prompt of conscious thought, the respiratory system carries out its life-sustaining activities. If the respiratory system’s tasks are interrupted for more than a few minutes, serious, irreversible damage to tissues occurs, followed by the failure of all body systems, and ultimately, death. While the intake of oxygen and removal of carbon dioxide are the primary functions of the respiratory system, it plays other important roles in the body. The respiratory system helps regulate the balance of acid and base in tissues, a process crucial for the norma...
Read more

Fertilization

-
Fertilization is the process in which gametes —a male's sperm and a female's egg or ovum—fuse together, producing a single cell that develops into an adult organism. Fertilization occurs in both plants and animals that reproduce sexually—that is, when a male and a female are needed to produce an offspring (see Reproduction ). Fertilization is a precise period in the reproductive process. It begins when the sperm contacts the outer surface of the egg and it ends when the sperm's nucleus fuses with the egg's nucleus. Fertilization is not instantaneous—it may take 30 minutes in sea urchins and up to several hours in mammals. After nuclear fusion, the fertilized egg is called a zygote. When the zygote divides to a two-cell stage, it is called an embryo. Fertilization is necessary to produce a single cell that contains a full complement of genes. When a cell undergoes meiosis , gametes are formed—a sperm cell or an egg cell. Each gamete contains only half the genetic materia...
Read more