Anatomy of the Thymus and Tonsils

Dr Rania Gabr

• Roughly a bi-lobed structure• DEVELOPMENT- bilateral 3rd

pharyngeal pouches• EVOLUTION- largest at birth or

during infancy• Increases slightly during 1st

decade of life and decreases thereafter.

Thymus

Introduction It is a flattened lymphoid organ located in the

upper anterior mediastinum & lower part of the neck

Thymus

Thymus

It consists of two lateral lobes placed in close contact along the middle line, situated partly in the thorax, partly in the neck.

Con. . It is covered by the sternum, Below, it rests upon the pericardium, being separated from the aortic arch and great vessels by a layer of fascia

In the neck it lies on the front and sides of the trachea.

The two lobes generally differ in size; they are occasionally united, so as to form a single mass; and sometimes separated by an intermediate lobe.

The thymus is of a pinkish-gray color, soft, and lobulated on its surfaces. It is about 5 cm. in length, 4 cm. in breadth below, and about 6 mm. in thickness.

At birth it weighs about 15 grams, at puberty it weighs about 35 grams; after this it gradually decreases to 25 grams at twenty five years, less than 15 grams at sixty, and about 6 grams at seventy years.

Vasculature A rich arterial supply to the thymus is derived mainly from the:1.Anterior intercostal & 2.A.mediastinal branches of the internal thoracic arteries

Veins of the thymus end in the left brachiocephalic, internal thoracic & inferior thyroid veins.

The lymphatic vessels of the thymus end in the parasternal, brachiocephalic & tracheobrochial lymphnodes.

Blood Supply

Definition: - Ovoid lymphoid tissue with fibrous capsule laterally over the superior constrictor muscles. Its surface is covered with stratified squamous epithiluim & crypts. It has a medulla & cortex like all other lymphoid tissues. It is part of the Walderyers

ring .

The Tonsils

• Waldeyer's ring is a continuous band of lymphoid tissue that surrounds the upper pharynx.

• The superior portion of the ring is located in the nasopharynx and is composed of the adenoids, Laterally the palatine tonsils and, Anteriorly the lingual tonsils to complete the ring.

The Tonsils

Tonsillar crypts extend deeply into the body of the tonsil and are surrounded by lymphoid nodules. Debris and foreign particles collect within the crypts.

• The primary follicles are formed during embryonic development and differentiate into secondary follicles after birth.

• The secondary follicles mainly contain B lymphocytes at various stages of differentiation, along with scattered T lymphocytes.

• Tonsillar tumors or infections may result in ear pain due to referred pain conducted by cranial nerve IX: Glossopharyngeal nerve.

• Function:• Concerned with immune mechanism.• - 1st line of defense. The

lymphoid tissues produce lymphocytes.

• - T-cells produce plasma cells & help in antibody formation.

• Active phase lasts until 8-10 years of age.

• This function should not alter the decision to remove the tonsils if a valid indication for tonsillectomy exists.

Blood Supply: Arterial supply:

- Tonsilar branch of facial artery from the ext. carotid.- Descending palatine -------- > internal maxillary artery.- Ascending palatine -------- facial artery - Ascending pharyngeal ---- external carotid. - Dorsalis linguae ------- lingual artery

Venous drainage :occurs through the Para tonsillar vein, and the vessels also pass through to the pharyngeal plexus or facial vein after piercing the superior constrictor. Nerve supply :to the tonsil is from the glossopharyngeal nerve.

“The End ”

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