出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/11/07 15:36:15」(JST)
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| Parathyroid glands | |
|---|---|
| Endocrine system. (Parathyroid gland not pictured, but are present on surface of thyroid gland, as shown below.) | |
| Thyroid and parathyroid. | |
| Latin | glandula parathyroidea inferior, glandula parathyroidea superior |
| Gray's | subject #273 1271 |
| System | Endocrine |
| Artery | superior thyroid artery, inferior thyroid artery, |
| Vein | superior thyroid vein, middle thyroid vein, inferior thyroid vein, |
| Nerve | middle cervical ganglion, inferior cervical ganglion |
| Lymph | pretracheal, prelaryngeal, jugulo-diagastric,and lympahtics of thymus |
| Precursor | neural crest mesenchyme and third and fourth pharyngeal pouch endoderm |
| MeSH | Parathyroid+Glands |
The parathyroid glands are small endocrine glands in the neck that produce parathyroid hormone. Humans usually have four parathyroid glands, which are usually located on the rear surface of the thyroid gland, or, in rare cases, within the thyroid gland itself or in the chest. Parathyroid glands control the amount of calcium in the blood and within the bones.
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The parathyroid glands are four or more small glands, about the size of a grain of rice, located on the posterior surface (back side) of the thyroid gland. The parathyroid glands usually weigh between 25 mg and 40 mg in humans. There are typically two, one above the other, on the left lobe of the thyroid and similarly on the right. The two parathyroid glands on each side which are positioned higher (closer to the head) are called the superior parathyroid glands, while the lower two are called the inferior parathyroid glands. Occasionally, some individuals may have six, eight, or even more parathyroid glands.
The parathyroid glands are named for their proximity to the thyroid but serve a completely different role than the thyroid gland. The parathyroid glands are quite easily recognizable from the thyroid as they have densely packed cells, in contrast with the follicle structure of the thyroid.[1] However, at surgery, they are harder to differentiate from the thyroid or fat.
Because the inferior thyroid arteries provide the primary blood supply to the posterior aspect of the thyroid gland where the parathyroid glands are located, branches of these arteries usually supply the parathyroid glands. However they may also be supplied by the branches of the superior thyroid arteries. thyroid ima artey or the laryngeal, tracheal or esopahgeal artery.[clarification needed] Parathyroid veins drain into thyroid plexus of veins of the thyroid gland.
Lymphatic vessels from the parathyroid glands drain into deep cervical lymph nodes and paratracheal lymph nodes.
In the histological sense, they distinguish themselves from the thyroid gland, as they contain two types of cells:[2]
| Name | Staining | Quantity | Size | Function |
| parathyroid chief cells | darker | many | smaller | manufacture PTH (see below). |
| oxyphil cells | lighter | few | larger | function unknown.[3] |
The parathyroid glands were first discovered in the Indian Rhinoceros by Richard Owen in 1850.[4] The glands were first discovered in humans by Ivar Viktor Sandström (1852-1889), a Swedish medical student, in 1880.[5] It is the last major organ to be recognized in humans so far.
The major function of the parathyroid glands is to maintain the body's calcium level within a very narrow range, so that the nervous and muscular systems can function properly.
Parathyroid hormone (PTH, also known as parathormone) is a small protein that takes part in the control of calcium and phosphate homeostasis, as well as bone physiology. Parathyroid hormone has effects antagonistic to those of calcitonin.
Calcium
PTH increases blood calcium levels by stimulating osteoclasts to break down bone and release calcium. PTH also increases gastrointestinal calcium absorption by activating vitamin D, and promotes calcium conservation (reabsorption) by the kidneys.
Phosphate
PTH is the major regulator of serum phosphate concentrations via actions on the kidney. It is an inhibitor of proximal and also distal tubular reabsorption of phosphorus.
Through activation of Vitamin D the absorbtion of Phosphate is increased.
Many conditions are associated with disorders of parathyroid function. These can be divided into those causing hyperparathyroidism, and those causing hypoparathyroidism.
The parathyroid glands originate from the interaction of neural crest mesenchyme and third and fourth branchial pouch endoderm.
Eya-1 (transcripitonal co-activator), Six-1 (a homeobox transcription factor), and Gcm-2 (a transcription factor) have been associated with the development of the parathyroid gland, and alterations in these genes alters parathyroid gland development.
The superior parathyroids arise from the fourth pharyngeal pouch, and the inferior parathyroids arise from the third pharyngeal pouch. They are vertically transposed during embryogenesis. This is significant in function-preserving parathyroidectomy, because both the superior and the inferior parathyroids are supplied by the inferior thyroid artery. If the surgeon is to leave a single functional parathyroid for the patient, he/she must preserve the appropriate blood supply.
Parathyroid glands are found in all adult tetrapods, although they vary in their number, and in their exact position. Mammals typically have four parathyroids, while other groups typically have six.
Fish do not possess parathyroid glands, although the ultimobranchial glands, which are found close to the oesophagus, may have a similar function and could even be homologous with the tetrapod parathyroids. Even these glands are absent in the most primitive vertebrates, the jawless fish, but as these species have no bone in their skeletons, only cartilage, it may be that they have less need to regulate calcium metabolism.
The conserved homology of genes and calcium-sensing receptors in fish gills with those in the parathryroid glands of birds and mammals is recognized by evolutionary developmental biology as evolution-using genes and gene networks in novel ways to generate new structures with some similar functions and novel functions.
High magnification micrograph of a parathyroid gland. H&E stain.
Intermediate magnification micrograph of a parathyroid gland. H&E stain.
Low magnification micrograph of a parathyroid gland and parathyroid adenoma (bottom left). H&E stain.
Scheme showing development of branchial epithelial bodies. I, II, III, IV. Branchial pouches.
Human parathyroid glands
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| リンク元 | 「鰓弓」「副甲状腺」 |
| 関連記事 | 「parathyroid」 |
| # | 鰓弓 | 神経 | 筋 | 骨格 | 動脈* |
| 1 | 顎弓(上顎隆起、下顎隆起) | CN V 三叉神経: 上顎枝、下顎枝(第一鰓弓の筋を支配) |
咀嚼筋(側頭筋、咬筋、内側翼突筋・外側翼突筋)、顎舌骨筋、顎二腹筋前腹、口蓋帆張筋と鼓膜張筋 | 上顎突起(顎前骨、上顎骨、頬骨、側頭骨の一部)、メッケル軟骨(下顎骨、キヌタ骨、ツチ骨、前ツチ骨靱帯、蝶下顎靱帯) | 消失し一部残存(顎動脈) |
| 2 | 舌骨弓 | CN VII 顔面神経 |
顔面表情筋(頬筋、耳介筋、前頭筋、広頚筋、口輪筋および眼輪筋)、顎二腹筋後腹、茎突舌骨筋、アブミ骨筋 | アブミ骨、茎状突起、茎突舌骨靱帯、舌骨小角と舌骨体の上部 | 消失し一部残存(舌骨動脈、アブミ骨動脈) |
| 3 | CN IX 舌咽神経 |
茎突咽頭筋 | 舌骨大角と舌骨体の下部 | 総頚動脈、内頚動脈の基部。外頚動脈が出芽 | |
| 4 | CN X 迷走神経 |
輪状甲状筋、口蓋帆挙筋 | 喉頭軟骨(甲状軟骨、輪状軟骨、披裂軟骨、小角軟骨、および楔状軟骨 | 大動脈弓の一部 | |
| 5 | 上喉頭神経(第四鰓弓支配神経) | 咽頭収縮筋 | 消失 | ||
| 6 | 反回神経(下喉頭神経)(第六鰓弓支配神経) | 喉頭内の筋 | 動脈管と肺動脈の基部 |
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