Topics / Anatomy / Thorax / Organs

Summary The thymus gland is a primary lymphoide organ which is located in the thoracic cavity. It is made of a cortex and a medulla. The blood supply is from the anterior intercostal, branches from the internal thoracic artery as well as the inferior thyroid artery. Venous drainage is from the left brachiocephalic, internal thoracic veins as well as the inferior thyroid veins.

Introduction

The thyroid gland is a primary lymphoid organ located in the thoracic cavity and neck. In children, it is lobulated and pink. At birth, it may be around 5 x 5 x 1cm in size, but it continues to grow in size until puberty. After puberty it decreases in size in a process known as involution.

Location

Superior and anterior mediastinum. May be found between the thyroid gland and the fourth costal cartilage. Lying behind the sternum and occasionally resting on the pericardium. The left brachiocephalic vein may be embedded within it.

Structure

Made up of two lobes which meet in the midline. It is surrounded by a capsule. Each lobe contains a cortex and a medulla. The cortex is divided into lobules by septa arising from the capsule.

The cortex is made of thymocytes (immature T cells) and epithelial cells. These thymocytes are supported by the epithelial reticular cells. The epithelial reticular cells form a network that is continuous with a similar network in the medulla.

The medulla is made of a network of epithelial cells. The lymphoid cells are fewer than in the cortex. In the medulla, you will find Hassall’s corpuscles which are formed by aggregations of the medullary epithelial cells.

Blood Supply

Arterial supply is via the anteiror intercostal arteries, small branches of the internal thoraxcic arteries, as well as the inferior thyroid branches.

Venous drainage is into the left brachiocephalic, internal thoracic veins as well as the inferior thyroid veins.

Lymphatic Drainage

Drain into the brachiocephalic, tracheobronchial and parasternal lymph nodes.

Innervation

Branches arising from the vagus nerve and the sympathetic chain. Some branches arise from the phrenic nerves to reach the capsule but they do not enter the thyroid gland.

References and Further Reading 1. Thymus. (2023, April 7). In Wikipedia. https://en.wikipedia.org/wiki/Thymus

Published on August 1, 2023

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Thymus Gland

Introduction

Location

Structure

Blood Supply

Lymphatic Drainage

Innervation

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