Thyroid Gland Anatomy – Dimensions, Arteries veins and Nerve Supply

The thyroid gland (glandula thyreoidea) is located in the anterior region of the neck and consists of two lobes and an isthmus. The lateral lobes are located at the level of the thyroid and cricoid cartilage, and the lower pole reaches the 5-6th cartilage of the trachea. In 30-50% of observations, there is an additional pyramidal lobe located above the isthmus. The thyroid gland is the largest gland of the endocrine system, its mass reaches 15-25 g. Additional (aberrant) lobes of the thyroid gland can be located at the level from the root of the tongue to the aortic arch.

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The right lobe of the gland is normally somewhat larger than the left and more abundantly vascularized, and in pathological conditions it increases to a greater extent. The gland is enclosed in a connective tissue sheath (capsule), consisting of inner and outer sheets, between which there is a slit-like space, made by loose fatty tissue, in which there are extraorgan arterial, venous and lymphatic vessels of the thyroid gland, parathyroid glands and the recurrent laryngeal nerve.

Connective tissue layers that divide the gland into lobules depart from the inner leaf of the gland capsule. The lobules consist of 20-40 follicles, their walls are lined with glandular follicular epithelium of a cubic shape. The follicles are filled with a homogeneous viscous mass (colloid) – a product produced by epithelial cells, and are enveloped outside by a network of capillaries. The colloid consists mainly of thyroglobulin, an iodine-containing glycoprotein. The colloid also includes RNA, DNA, cytochrome oxidase and other enzymes.

From the inner leaf of the capsule of the gland, connective tissue layers depart, which divide the gland into lobules. The lobules consist of 20-40 follicles, their walls are lined with glandular follicular epithelium of a cubic shape. The follicles are filled with a homogeneous viscous mass (colloid) – a product produced by epithelial cells, and are enveloped outside by a network of capillaries. The colloid consists mainly of thyroglobulin, an iodine-containing glycoprotein. The colloid also contains RNA, DNA, cytochrome oxidase and other enzymes. Connective tissue layers that divide the gland into lobules depart from the inner leaf of the gland capsule.

The lobules consist of 20-40 follicles, their walls are lined with glandular follicular epithelium of a cubic shape. The follicles are filled with a homogeneous viscous mass (colloid) – a product produced by epithelial cells, and are enveloped outside by a network of capillaries. The colloid consists mainly of thyroglobulin, an iodine-containing glycoprotein. The colloid also includes RNA, DNA, cytochrome oxidase and other enzymes. and are enveloped on the outside by a network of capillaries. The colloid consists mainly of thyroglobulin, an iodine-containing glycoprotein.

The colloid also contains RNA, DNA, cytochrome oxidase and other enzymes. and are enveloped on the outside by a network of capillaries. The colloid consists mainly of thyroglobulin, an iodine-containing glycoprotein. The colloid also includes RNA, DNA, cytochrome oxidase and other enzymes.

There are three types of thyroid cells:

  • type A – active follicular cells lining the follicle and involved in the metabolism of iodine and the synthesis of thyroid hormones;
  • type B – poorly differentiated (cambial) cells, which serve as precursors for the formation of A-cells;
  • type C – parafollicular cells located between follicular cells, not reaching the follicle lumen, are involved in the synthesis of the calcium-lowering hormone calcitonin.

It is these cells that are the source of various organ-specific benign and malignant tumors of the thyroid gland.

DIMENSIONS OF THYROID GLAND

  • Transverse size of the gland: 50-60 mm;
  • Longitudinal lobe size: 50-80 mm;
  • In the anteroposterior direction of the lateral lobes 18-20 mm;
  • The vertical dimension of the isthmus: 2.5-5 mm;
  • Isthmus thickness: 2-8 mm;

WEIGHT OF THYROID GLAND

The mass of the thyroid gland of an adult at the age of 20 – 60 is 16.3 – 18.5 g.

Women have more thyroid mass and volume than men.

AGE FEATURES

Newborns are characterized by a large size of the thyroid gland, which tends to decrease during the first year of life and reaches 1.0-2.5 g. Further, the size and mass of the thyroid gland gradually increase until the age of puberty – up to 10-14 g. In adult age, from 20 to 50 years, remains almost constant and averages 18 g. Subsequently, in connection with the phenomena of age-related atrophy, there is a decrease in the mass and volume of the thyroid gland practically without changing the function.

ANATOMICAL FEATURES OF THYROID

The gland is covered with a double capsule or shell:

  • External (fibrous capsule, capsula fibrosa);
  • Internal (own membrane of the gland).

The outer and inner capsules are loosely interconnected by means of fiber, in which vessels and nerves pass. The gland is fixed by ligaments from the outer capsule to the larynx and trachea, which explains its movement when the larynx moves during swallowing. Connective tissue bridges – trabeculae , dividing it into lobules, extend from the thin inner capsule into the gland tissue . Nerves, arteries, veins and lymphatic vessels pass through the thickness of the trabeculae. Trabeculae branch out and form the stroma of the gland – a connective tissue frame formed by collagen and elastic fibers. Lobules, in turn, consist of follicles – vesicles containing a colloid.

ARTERIES OF THE GLAND

  • Upper poles of the right and left lobes: the upper thyroid arteries (right and left, respectively) – branches of the external carotid arteries.
  • Lower poles of the right and left lobes: lower thyroid arteries (right and left) – branches of the thyroid trunks of the subclavian arteries. Sometimes the inferior thyroid artery can approach the lower pole, which can branch off from the brachiocephalic trunk, the subclavian artery, or directly from the aortic arch.

The branches of the thyroid arteries form multiple anastomoses in the capsule and in the tissue of the gland.

VEINS OF THE GLAND

The veins of the thyroid gland form plexuses located under the outer capsule, from which blood flows into the veins:

  • The upper and middle thyroid veins – into the internal jugular vein.
  • The lower thyroid veins – into the brachiocephalic vein.

LYMPHATIC VESSELS

Lymphatic vessels form a dense plexus, through which the colloid is removed. The lymphatic vessels of the thyroid gland accompany the course of the arteries and flow into the lymph nodes:

  • Thyroid;
  • Prelaryngeal
  • Pretracheal;
  • Paratracheal;
  • Mediastinal.

NERVES

The thyroid nerves extend from the cervical nodes of the right and left sympathetic trunks and from the vagus nerve and accompany the course of the vessels.

  • Afferent and parasympathetic innervation – from the superior laryngeal and recurrent laryngeal nerves – branches of the vagus nerve, are responsible for suppressing the function of the gland.
  • Sympathetic – from the cervical nodes, nerve impulses of sympathetic fibers are responsible for increasing the functional activity of the gland.

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Thyroid Gland Anatomy – 6 || Nerves Supply || Nerve vessels of Thyroid Gland
Thyroid Gland Anatomy – 6 || Lymphatic Drainage || Lymph vessels of Thyroid Gland

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