Topographic anatomy and localization
The anatomical location of the parathyroid glands (glandulae parathyroideae) is closely associated with the thyroid gland. As a rule, they are fixed to the posterior surface of its lateral lobes. In the classical anatomical norm, two symmetrical pairs are distinguished:
- Superior parathyroid glands (glandulae parathyroideae superiores). Their typical site of location is the boundary between the upper and middle thirds of the posteromedial surface of the lateral lobes of the thyroid gland. The topographical landmark for locating them is the lower border of the cricoid cartilage.
- Inferior parathyroid glands (glandulae parathyroideae inferiores). Traditionally, they are found in the lower part of the lateral lobes of the thyroid gland. Most often, they lie adjacent to the posterolateral surface, rising approximately 0.5–1 cm above the lower border of the lobes themselves.
It is worth noting a crucial anatomical variation: the inferior glands are not always rigidly fixed to the thyroid gland. Sometimes they can shift and be located in the surrounding loose adipose tissue significantly lower than the main organ. Furthermore, the total number of glands is an exceptionally variable parameter. In clinical practice, cases of a single gland are encountered, as well as multiple variants reaching seven or even eight endocrine bodies in a single person.
Macroscopic structure and physical parameters
Upon visual inspection of a specimen or during surgical intervention, the shape of the glands is defined as oval, and in some cases, slightly flattened. On palpation, their consistency is determined to be denser compared to the soft tissue of the thyroid gland itself.
The color of the organ is extremely important for identification. In children, the parenchyma has a delicate pale pink hue. However, with age, a color change occurs: the tissue acquires a brownish-yellow color. This age-related metamorphosis makes the parathyroid glands visually barely distinguishable from the nearby regional lymph nodes, which requires special attentiveness from the surgeon and anatomist.
The physical parameters of a single average gland are small:
- Longitudinal size: from 4 to 8 mm.
- Transverse size: from 3 to 4 mm.
- Thickness: varies within 1.5–3 mm.
- Average mass: is only 0.05–0.09 g.
Microscopic anatomy and functions
From the perspective of histological organization, each glandula parathyroidea is separated from surrounding tissues. Externally, it is securely covered by its own connective tissue capsule. From this outer shell, the finest connective tissue partitions (trabeculae) extend deep into the organ, providing a structural framework.
The parenchyma of the gland is formed by clusters of specialized epithelial cells. These cells are organized into characteristic structures — they form distinctive cords and dense groups. The space between the epithelial cords is filled with stroma — loose connective tissue. This connective tissue foundation is abundantly vascularized, meaning it is exceptionally rich in blood vessels, which is a typical sign of an actively secreting endocrine gland.
The sole yet critically important function of the parathyroid glands is endocrine. They synthesize and secrete parathyroid hormone into the bloodstream (in international nomenclature — parathormon or parathyrinum). The biological role of this hormone lies in the strict regulation of calcium and phosphorus metabolism in the human body, maintaining their constant level in the blood and tissues.
Briefly: answers to topical questions
Which specific cell types form the parenchyma of the parathyroid gland?
The parenchyma of the parathyroid gland is formed by epithelial cells — parathyrocytes, among which chief cells are distinguished (divided into active dark chief cells with pronounced basophilia and inactive light chief cells) and oxyphil cells with large mitochondria.
- Parathyrocytes (parathyrocytes) — the main functional cells of the gland.
- Chief cells (chief cells) — producers of parathyroid hormone, subdivided into dark and light.
- Oxyphil cells (oxyphil cells) — large elements with oxyphilic cytoplasm.
From which arteries is the blood supply to the parathyroid glands carried out?
The blood supply to the parathyroid glands is provided by arteries that branch into an abundant capillary network surrounding the parathyrocytes. Sources also indicate that the inferior thyroid artery approaches the posterior surface of the thyroid gland and anastomoses with the superior thyroid artery.
By which nerves is the innervation of the parathyroid glands carried out?
Innervation of the parathyroid glands is carried out by sympathetic and parasympathetic nerve fibers. Unmyelinated fibers end in terminals between parathyrocytes; sympathetic stimulation is carried out via α-adrenergic receptors.
From which embryonic primordia do the parathyroid glands develop?
The parathyroid glands develop from the epithelium of the pharyngeal pouches during embryogenesis.
- III and IV pharyngeal pouches (III and IV pharyngeal pouches) — the embryonic source of the endocrine cells of the gland.
To which anatomical regions can the inferior parathyroid glands ectopically locate in case of an atypical position?
In ectopic positioning, the parathyroid glands can be located in the superior mediastinum or along the thyrothymic ligament.
To memorize the function: "PARAs shields preserve CALCIUM and PHOSPHORUS" (Parathyroid hormone regulates the metabolism of these two elements).
Class and exam questions
Where should one look for the superior pair of parathyroid glands?
The superior glands (glandulae parathyroideae superiores) should be sought at the level of the lower margin of the cricoid cartilage, at the border of the upper and middle thirds of the posteromedial surface of the lateral lobes of the thyroid gland.
What number of parathyroid glands is considered normal?
Most commonly, two pairs (superior and inferior) are encountered, yet their number is extremely variable and can range from one to seven or eight.
What can the parathyroid gland be confused with in an adult?
With age, the glands acquire a brownish-yellow color, making them outwardly very similar to surrounding lymph nodes.
What does the parenchyma of the parathyroid gland consist of?
The parenchyma is formed by epithelial cells grouped into cords. Between them lies loose connective tissue permeated by a dense network of blood vessels.
What else to study on this topic
- Topography of the inferior parathyroid glands and their displacement into the adipose tissue
- Organization of the connective tissue framework and capsule of the gland
- Cellular structure of the epithelial cords of the parenchyma
- Vascularization of the parathyroid gland stroma
- Mechanism of action of parathyroid hormone on phosphorus-calcium metabolism
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