THYROID GLAND

Thyroid Gland

The thyroid gland is a vital endocrine gland located in the neck, playing a crucial role in regulating metabolism, growth, and development. It is a butterfly-shaped gland, situated anterior to the trachea, and is composed of two lobes connected by an isthmus. The thyroid gland produces several hormones, including thyroxine (T4) and triiodothyronine (T3), which are essential for maintaining a stable metabolic rate.

Key Points

• The thyroid gland is located in the neck, anterior to the trachea.
• It is composed of two lobes connected by an isthmus.
• The gland is divided into two parts: the isthmus and the pyramidal lobe.
• The thyroid gland produces thyroxine (T4) and triiodothyronine (T3) hormones.
• T4 and T3 hormones regulate metabolism, growth, and development.
• The thyroid gland receives its blood supply from the inferior and superior thyroid arteries.
• The gland is innervated by the thyroid branches of the vagus nerve and the sympathetic nerves.
• The lymphatic drainage of the thyroid gland is through the deep cervical lymph nodes.
• The thyroid gland is surrounded by the pretracheal fascia and the deep cervical fascia.

Developmental Process

• The thyroid gland develops from the thyroid diverticulum, which forms from the floor of the pharynx during the 3rd week of embryonic development.
• The diverticulum grows downward and eventually forms the thyroid gland.
• The thyroid gland migrates upward to its final position in the neck.

Location and External Features

• The thyroid gland is situated in the anterior (front) part of the neck, below the larynx (voice box) and in front of the trachea (windpipe).
• It is encased in a fibrous capsule and is divided into two lobes: the right lobe and the left lobe.
• The lobes are connected by an isthmus, a narrow band of thyroid tissue.

Relations

• The thyroid gland is related to the following structures:
  • Anteriorly: Trachea
  • Posteriorly: Larynx
  • Inferiorly: Oesophagus
  • Superiorly: Trachea and larynx

Blood Supply

• The thyroid gland receives its blood supply from the following arteries:
  • Superior thyroid artery (branch of the external carotid artery)
  • Middle thyroid vein (drains into the internal jugular vein)
  • Inferior thyroid arteries (branches of the thyrocervical trunk)

Nerve Supply

• The thyroid gland receives its nerve supply from the following nerves:
  • External laryngeal nerve (a branch of the vagus nerve)
  • Inferior thyroid plexus (formed by branches of the sympathetic trunk)

Lymph Drainage

• The lymphatic drainage of the thyroid gland is through the deep cervical lymph nodes.
• The lymphatic vessels from the gland drain into the lymph nodes, which eventually drain into the jugulosubclavian trunk.

Muscle Action Sequence

• The thyroid gland is not directly associated with any muscles.
• However, the muscles of the neck, such as the sternocleidomastoid and the infrahyoid muscles, can affect the gland's position and function.

Thyroid Gland

The thyroid gland is a vital endocrine organ located in the neck, playing a crucial role in regulating metabolism, growth, and development. It secretes thyroid hormones, which are essential for maintaining a stable metabolic rate.

Development

• The thyroid gland develops from the endodermal thyroid diverticulum, which appears on either side of the pharyngeal floor.
• The diverticulum descends towards the larynx and eventually fuses to form a single gland.
• The thyroid gland is influenced by the hypothalamus and pituitary gland, which regulate its function through the release of thyroid-stimulating hormone (TSH).

Applied Anatomy

• The thyroid gland is a common site for thyroid nodules and malignancies.
• Thyroid surgery is a delicate procedure that requires knowledge of the gland's anatomy and relations to surrounding structures.
• The thyroid gland's blood supply and nerve supply are critical to consider during surgical procedures.