parathyroid gland

Information about parathyroid gland



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
	subject #273 1271
Artery	superior thyroid artery, inferior thyroid artery,
Vein	superior thyroid vein, middle thyroid vein, inferior thyroid vein, thyreoidea ima
Nerve	middle cervical ganglion, inferior cervical ganglion
Precursor	neural crest mesenchyme and third and fourth pharyngeal pouch endoderm
MeSH	Parathyroid+Glands
Dorlands/Elsevier	g_06/

The parathyroid glands are small endocrine glands in the neck, usually located behind the thyroid gland, which produce parathyroid hormone. In rare cases the parathyroid glands are located within the thyroid glands. Most often there are four parathyroid glands, but some people have six or even eight.

Anatomy

The parathyroid glands are four or more small glands located on the posterior surface of the thyroid gland. Histologically they 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.

They distinguish themselves from the thyroid gland histologically as they contain two types of cells:^[2]

Name	Staining	Quantity	Size	Function
parathyroid chief cells	darker	many^[3]	smaller	manufacture PTH (see below).
oxyphil cells	lighter	few	larger	function unknown.^[4]^[5]

History

The parathyroid glands were discovered by Ivar Sandstrom, a Swedish medical student, in 1880. ^[6] It was the last major organ to be recognized in humans.

Physiology

The sole 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.

When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood.

Parathyroid hormone (PTH, also known as parathormone) is a small protein that takes part in the control of calcium and phosphorus homeostasis, as well as bone physiology. Parathyroid hormone has effects antagonistic to those of calcitonin. It increases blood calcium levels by stimulating osteoclasts to break down bone and release calcium. It also increases gastrointestinal calcium absorption by activating vitamin D, and promotes calcium uptake by the kidneys.

Role in disease

Hyperparathyroidism and related conditions

The single major disease of parathyroid glands is overactivity of one or more of the parathyroid lobes, which make too much parathyroid hormone causing a potentially serious calcium imbalance. This is called hyperparathyroidism; it leads to hypercalcemia and osteitis fibrosa cystica. Since hyperparathyroidism was first described in 1925, the symptoms have become known as "moans, groans, stones, and bones." The primary treatment for this disease is the surgical removal of the faulty gland.

Modern high frequency ultrasound can see parathyroid masses, even before they cause high calcium. They are called parathyroid incidentalomas. If a patient has elevated calcium, the ultrasound can be used to locate the abnormal glands. The use of ultrasound guided FNA, and parathyroid hormone washings can confirm the abnormal glands. A blood calcium 15-30 minutes after the biopsy can help determine if the disease is caused by a single abnormal gland or multiple glands.

A drop in serum calcium suggests a single source, and no drop suggests multiple glands. This, with a non-localizing Sestamibi scan would point toward a neck exploration, rather than a minimally invasive method aimed a single gland disease.

A Sestamibi scan is often used to determine which parathyroid gland(s) are responsible for overproduction of parathyroid hormone.

Another related condition is called secondary hyperparathyroidism (high-per-pair-uh-THIGH-royd-izm), or secondary HPT - common in patients with chronic kidney disease on dialysis. In secondary HPT, the parathyroid glands make too much parathyroid hormone (PTH), and the kidneys do not produce enough vitamin D, and calcium and phosphorus are out of balance. Even though one may not have any symptoms, treating secondary HPT is important. Cinacalcet (Sensipar®) is a medicine that can help treat such dialysis patients and is available by prescription only.

Hypoparathyroidism and related conditions

Hypoparathyroidism
Pseudohypoparathyroidism
Pseudopseudohypoparathyroidism
Disorders of the parathyroid hormone receptor have been associated with Jansen's metaphyseal chondroplasia and Blomstrand's chondroplasia.

Embryology and Evolution

The parathyroid glands originate from the interaction of neural crest mesenchyme and third and fourth pharyngeal pouch endoderm.

Genetically, 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 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.

Additional images

Scheme showing development of branchial epithelial bodies. I, II, III, IV. Branchial pouches.

Human parathyroid glands

References

1. ^ Histology at BU 15001ooa
2. ^ Histology at BU 15002loa
3. ^ Histology at USC end/c_28
4. ^ Histology at OU 40_06
5. ^ Histology at USC end/c_34
6. ^ Eknoyan G.. (1995). "A history of the parathyroid glands". Am J Kidney Dis 26 (5): 801-7. PMID 7485136.

External links

• • [ e] Human anatomy, endocrine system: endocrine glands
Hypothalamic/pituitary axes	Adrenal axis (Adrenal gland) • Thyroid axis (Thyroid gland, Parathyroid gland) • Gonadal axis (Testes, Ovaries, Corpus luteum)
Other	Pineal gland • Islets of pancreas

Latin}}}
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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Arteries are muscular blood vessels that carry blood away from the heart.^[1] All arteries, with the exception of the pulmonary and umbilical arteries, carry oxygenated blood.

The circulatory system is extremely important for sustaining life.
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The superior thyroid artery arises from the external carotid artery just below the level of the greater cornu of the hyoid bone and ends in the thyroid gland.

Relations

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The inferior thyroid artery passes upward, in front of the vertebral artery and Longus colli; then turns medialward behind the carotid sheath and its contents, and also behind the sympathetic trunk, the middle cervical ganglion resting upon the vessel.
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vein is a blood vessel that carries blood toward the heart. The majority of veins in the body carry low-oxygen blood from the tissues back to the heart; the exceptions being the pulmonary and umbilical veins which both carry oxygenated blood.
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The superior thyroid vein begins in the substance and on the surface of the thyroid gland, by tributaries corresponding with the branches of the superior thyroid artery, and ends in the upper part of the internal jugular vein.
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The middle thyroid vein collects the blood from the lower part of the thyroid gland, and after being joined by some veins from the larynx and trachea, ends in the lower part of the internal jugular vein.
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The inferior thyroid veins two, frequently three or four, in number, arise in the venous plexus on the thyroid gland, communicating with the middle and superior thyroid veins.

They form a plexus in front of the trachea, behind the Sternothyreoidei.
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The thyroidea ima ascends in front of the trachea to the lower part of the thyroid gland, which it supplies.

It varies greatly in size, and appears to compensate for deficiency or absence of one of the other thyroid vessels.
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A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron). Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the glial cells that
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The middle cervical ganglion is the smallest of the three cervical ganglia, and is occasionally absent.

It is placed opposite the sixth cervical vertebra, usually in front of, or close to, the inferior thyroid artery.
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The inferior cervical ganglion is situated between the base of the transverse process of the last cervical vertebra and the neck of the first rib, on the medial side of the costocervical artery.
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Embryology is the study of the development of an embryo. An embryo is defined as any vertebrate in a stage before birth or hatching. Embryology refers to the development of the egg cell (zygote) after fertilization and the differentiation of cells into tissues and organs.
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The neural crest, a transient component of the ectoderm, is located in between the neural tube and the epidermis (or the free margins of the neural folds) of an embryo during neural tube formation.
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Mesenchyme (also known as embryonic connective tissue) is the mass of tissue that develops mainly from the mesoderm (the middle layer of the trilaminar germ disc) of an embryo. Viscous in consistency, mesenchyme contains collagen bundles and fibroblasts.
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pharyngeal pouch is a pathological pulsion diverticulum of the pharyngeal mucosa through Killian's dehiscence. Killian's dehiscence (also known as Killian's triangle) is a triangular area in the wall of the pharynx between the inferior constrictor muscle and the cricopharyngeus
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Endoderm is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm.

The endoderm consists at first of flattened cells, which subsequently become columnar.
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Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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1. Pineal gland 2. Pituitary gland 3. Thyroid gland 4. Thymus 5. Adrenal gland 6. Pancreas 7. Ovary 8. Testes]]

The endocrine system
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gland is an organ in an animal's body that synthesizes a substance for release such as hormones, often into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).
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For other uses, see Thyroid cartilage.